Patent Publication Number: US-10334554-B2

Title: Reference signal reception method in wireless communication system, and device for same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage filing under 35 U.S.C. 371 of International Application No. PCT/KR2016/001936, filed on Feb. 26, 2016, which claims the benefit of U.S. Provisional Application Nos. 62/129,043, filed on Mar. 6, 2015, 62/135,688, filed on Mar. 19, 2015, and 62/140,406, filed on Mar. 30, 2015, the contents of which are all hereby incorporated by reference herein in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a wireless communication system, and more particularly, to a method of receiving a reference signal in a wireless communication system and an apparatus therefor. 
     BACKGROUND ART 
     Recently, various devices requiring machine-to-machine (M2M) communication and high data transfer rate, such as smartphones or tablet personal computers (PCs), have appeared and come into widespread use. This has rapidly increased the quantity of data which needs to be processed in a cellular network. In order to satisfy such rapidly increasing data throughput, recently, carrier aggregation (CA) technology which efficiently uses more frequency bands, cognitive ratio technology, multiple antenna (MIMO) technology for increasing data capacity in a restricted frequency, multiple-base-station cooperative technology, etc. have been highlighted. In addition, communication environments have evolved such that the density of accessible nodes is increased in the vicinity of a user equipment (UE). Here, the node includes one or more antennas and refers to a fixed point capable of transmitting/receiving radio frequency (RF) signals to/from the user equipment (UE). A communication system including high-density nodes may provide a communication service of higher performance to the UE by cooperation between nodes. 
     A multi-node coordinated communication scheme in which a plurality of nodes communicates with a user equipment (UE) using the same time-frequency resources has much higher data throughput than legacy communication scheme in which each node operates as an independent base station (BS) to communicate with the UE without cooperation. 
     A multi-node system performs coordinated communication using a plurality of nodes, each of which operates as a base station or an access point, an antenna, an antenna group, a remote radio head (RRH), and a remote radio unit (RRU). Unlike the conventional centralized antenna system in which antennas are concentrated at a base station (BS), nodes are spaced apart from each other by a predetermined distance or more in the multi-node system. The nodes can be managed by one or more base stations or base station controllers which control operations of the nodes or schedule data transmitted/received through the nodes. Each node is connected to a base station or a base station controller which manages the node through a cable or a dedicated line. 
     The multi-node system can be considered as a kind of Multiple Input Multiple Output (MIMO) system since dispersed nodes can communicate with a single UE or multiple UEs by simultaneously transmitting/receiving different data streams. However, since the multi-node system transmits signals using the dispersed nodes, a transmission area covered by each antenna is reduced compared to antennas included in the conventional centralized antenna system. Accordingly, transmit power required for each antenna to transmit a signal in the multi-node system can be reduced compared to the conventional centralized antenna system using MIMO. In addition, a transmission distance between an antenna and a UE is reduced to decrease in pathloss and enable rapid data transmission in the multi-node system. This can improve transmission capacity and power efficiency of a cellular system and meet communication performance having relatively uniform quality regardless of UE locations in a cell. Further, the multi-node system reduces signal loss generated during transmission since base station(s) or base station controller(s) connected to a plurality of nodes transmit/receive data in cooperation with each other. When nodes spaced apart by over a predetermined distance perform coordinated communication with a UE, correlation and interference between antennas are reduced. Therefore, a high signal to interference-plus-noise ratio (SINR) can be obtained according to the multi-node coordinated communication scheme. 
     Owing to the above-mentioned advantages of the multi-node system, the multi-node system is used with or replaces the conventional centralized antenna system to become a new foundation of cellular communication in order to reduce base station cost and backhaul network maintenance cost while extending service coverage and improving channel capacity and SINR in next-generation mobile communication systems. 
     DISCLOSURE OF THE INVENTION 
     Technical Task 
     A technical task of the present invention is to provide a method of receiving a reference signal in a wireless communication system and an operation related to the method. 
     Technical tasks obtainable from the present invention are non-limited the above-mentioned technical task. And, other unmentioned technical tasks can be clearly understood from the following description by those having ordinary skill in the technical field to which the present invention pertains. 
     Technical Solution 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, according to one embodiment, a method of receiving a reference signal for positioning in an unlicensed band, which is received by a terminal in a wireless communication system, includes receiving positioning reference signal (PRS)-related configuration information transmitted through the coordination of one or more unlicensed band cells, wherein the PRS-related configuration information includes information on a plurality of subbands within the unlicensed band on which the PRS is transmitted and information on a PRS transmission period for each of the plurality of the subbands, receiving and measuring a PRS using the PRS-related configuration information, and reporting a measurement result of the PRS to a serving cell. 
     Additionally or alternatively, the receiving and measuring the PRS may include performing PRS blind detection using the PRS-related configuration information. 
     Additionally or alternatively, the method may further include receiving information on the number of subbands on which the PRS blind detection is to be performed. 
     Additionally or alternatively, the method may further include receiving information on priority of a subband on which the PRS blind detection is to be performed. 
     Additionally or alternatively, the information on the PRS transmission period may be common to unlicensed band cells belonging to the same cell group. 
     Additionally or alternatively, the information on the PRS transmission period may include a transmission period, offset, or a burst length of the PRS. 
     Additionally or alternatively, the PRS-related configuration information may include information on whether or not the PRS transmission period belongs to channel occupation time for the one or more unlicensed band cells. 
     Additionally or alternatively, the receiving and measuring the PRS may include performing PRS blind detection during the channel occupation time. 
     Additionally or alternatively, the PRS-related configuration information may include information on the channel occupation time and information on the PRS transmission period. 
     Additionally or alternatively, the PRS-related configuration information may be received through downlink control information via a licensed band cell or an unlicensed band cell. 
     Additionally or alternatively, the method may further include determining that a PRS transmission subframe belongs to channel occupation time for the one or more unlicensed band cells if a reservation signal is received in a specific time period. 
     Additionally or alternatively, a PRS transmitted through the one or more unlicensed band cells may be transmitted on a resource element where a different unlicensed band cell does not transmit a PRS. 
     Additionally or alternatively, the measurement result of the PRS may be independent of a PRS measurement result on a licensed band. 
     To further achieve these and other advantages and in accordance with the purpose of the present invention, according to a different embodiment, a terminal configured to receive a reference signal for positioning through one or more unlicensed band cells in a wireless communication system includes an radio frequency (RF) unit and a processor controls the RF unit, wherein the processor receives positioning reference signal (PRS)-related configuration information transmitted through the coordination of one or more unlicensed band cells, wherein the PRS-related configuration information includes information on a plurality of subbands within the unlicensed band on which the PRS is transmitted and information on a PRS transmission period for each of the plurality of the subbands, receives and measures a PRS using the PRS-related configuration information, reports a measurement result of the PRS to a serving cell. 
     Technical solutions obtainable from the present invention are non-limited the above-mentioned technical solutions. And, other unmentioned technical solutions can be clearly understood from the following description by those having ordinary skill in the technical field to which the present invention pertains. 
     Advantageous Effects 
     According to one embodiment of the present invention, it is able to efficiently receive and measure a reference signal in a wireless communication system. 
     Effects obtainable from the present invention may be non-limited by the above mentioned effect. 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. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a diagram for an example of a radio frame structure used in a wireless communication system; 
         FIG. 2  is a diagram for an example of a downlink (DL)/uplink (UL) slot structure in a wireless communication system; 
         FIG. 3  is a diagram for an example of a downlink (DL) subframe structure used in 3GPP LTE/LTE-A system; 
         FIG. 4  is a diagram for an example of an uplink (UL) subframe structure used in 3GPP LTE/LTE-A system; 
         FIG. 5  is a diagram for a structure of transmitting a PRS; 
         FIGS. 6 and 7  are diagrams for RE mapping of a PRS (positioning reference signal); 
         FIG. 8  is a diagram for an example of an LBT (listen before talk)-based channel access operation according to a FBE (frame based equipment); 
         FIG. 9  is a diagram for an example of an LBT (listen before talk)-based channel access operation according to an LBE (load based equipment); 
         FIG. 10  is a diagram for an example of configuring a subframe (or positioning occasion) in which a PRS is transmitted according to one embodiment of the present invention; 
         FIG. 11  is a diagram for a plurality of subbands constructing an unlicensed band and CCA performed in a plurality of the subbands according to one embodiment of the present invention; 
         FIG. 12  is a diagram for a configuration of a subframe in which a PRS is transmitted according to one embodiment of the present invention; 
         FIG. 13  is a flowchart for an operation according to one embodiment of the present invention; 
         FIG. 14  is a block diagram for a device for implementing embodiment(s) of the present invention. 
     
    
    
     BEST MODE 
     Mode for Invention 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The accompanying drawings illustrate exemplary embodiments of the present invention and provide a more detailed description of the present invention. However, the scope of the present invention should not be limited thereto. 
     In some cases, to prevent the concept of the present invention 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. 
     In the present invention, a user equipment (UE) is fixed or mobile. The UE is a device that transmits and receives user data and/or control information by communicating with a base station (BS). The term ‘UE’ may be replaced with ‘terminal equipment’, ‘Mobile Station (MS)’, ‘Mobile Terminal (MT)’, ‘User Terminal (UT)’, ‘Subscriber Station (SS)’, ‘wireless device’, ‘Personal Digital Assistant (PDA)’, ‘wireless modem’, ‘handheld device’, etc. A BS is typically a fixed station that communicates with a UE and/or another BS. The BS exchanges data and control information with a UE and another BS. The term ‘BS’ may be replaced with ‘Advanced Base Station (ABS)’, ‘Node B’, ‘evolved-Node B (eNB)’, ‘Base Transceiver System (BTS)’, ‘Access Point (AP)’, ‘Processing Server (PS)’, etc. In the following description, BS is commonly called eNB. 
     In the present invention, a node refers to a fixed point capable of transmitting/receiving a radio signal to/from a UE by communication with the UE. Various eNBs can be used as nodes. For example, a node can be a BS, NB, eNB, pico-cell eNB (PeNB), home eNB (HeNB), relay, repeater, etc. Furthermore, a node may not be an eNB. For example, a node can be a radio remote head (RRH) or a radio remote unit (RRU). The RRH and RRU have power levels lower than that of the eNB. Since the RRH or RRU (referred to as RRH/RRU hereinafter) is connected to an eNB through a dedicated line such as an optical cable in general, cooperative communication according to RRH/RRU and eNB can be smoothly performed compared to cooperative communication according to eNBs connected through a wireless link. At least one antenna is installed per node. An antenna may refer to an antenna port, a virtual antenna or an antenna group. A node may also be called a point. Unlike a conventional centralized antenna system (CAS) (i.e. single node system) in which antennas are concentrated in an eNB and controlled an eNB controller, plural nodes are spaced apart at a predetermined distance or longer in a multi-node system. The plural nodes can be managed by one or more eNBs or eNB controllers that control operations of the nodes or schedule data to be transmitted/received through the nodes. Each node may be connected to an eNB or eNB controller managing the corresponding node via a cable or a dedicated line. In the multi-node system, the same cell identity (ID) or different cell IDs may be used for signal transmission/reception through plural nodes. When plural nodes have the same cell ID, each of the plural nodes operates as an antenna group of a cell. If nodes have different cell IDs in the multi-node system, the multi-node system can be regarded as a multi-cell (e.g., macro-cell/femto-cell/pico-cell) system. When multiple cells respectively configured by plural nodes are overlaid according to coverage, a network configured by multiple cells is called a multi-tier network. The cell ID of the RRH/RRU may be identical to or different from the cell ID of an eNB. When the RRH/RRU and eNB use different cell IDs, both the RRH/RRU and eNB operate as independent eNBs. 
     In a multi-node system according to the present invention, which will be described below, one or more eNBs or eNB controllers connected to plural nodes can control the plural nodes such that signals are simultaneously transmitted to or received from a UE through some or all nodes. While there is a difference between multi-node systems according to the nature of each node and implementation form of each node, multi-node systems are discriminated from single node systems (e.g. CAS, conventional MIMO systems, conventional relay systems, conventional repeater systems, etc.) since a plurality of nodes provides communication services to a UE in a predetermined time-frequency resource. Accordingly, embodiments of the present invention with respect to a method of performing coordinated data transmission using some or all nodes can be applied to various types of multi-node systems. For example, a node refers to an antenna group spaced apart from another node by a predetermined distance or more, in general. However, embodiments of the present invention, which will be described below, can even be applied to a case in which a node refers to an arbitrary antenna group irrespective of node interval. In the case of an eNB including an X-pole (cross polarized) antenna, for example, the embodiments of the preset invention are applicable on the assumption that the eNB controls a node composed of an H-pole antenna and a V-pole antenna. 
     A communication scheme through which signals are transmitted/received via plural transmit (Tx)/receive (Rx) nodes, signals are transmitted/received via at least one node selected from plural Tx/Rx nodes, or a node transmitting a downlink signal is discriminated from a node transmitting an uplink signal is called multi-eNB MIMO or CoMP (Coordinated Multi-Point Tx/Rx). Coordinated transmission schemes from among CoMP communication schemes can be categorized into JP (Joint Processing) and scheduling coordination. The former may be divided into JT (Joint Transmission)/JR (Joint Reception) and DPS (Dynamic Point Selection) and the latter may be divided into CS (Coordinated Scheduling) and CB (Coordinated Beamforming). DPS may be called DCS (Dynamic Cell Selection). When JP is performed, more various communication environments can be generated, compared to other CoMP schemes. JT refers to a communication scheme by which plural nodes transmit the same stream to a UE and JR refers to a communication scheme by which plural nodes receive the same stream from the UE. The UE/eNB combine signals received from the plural nodes to restore the stream. In the case of JT/JR, signal transmission reliability can be improved according to transmit diversity since the same stream is transmitted from/to plural nodes. DPS refers to a communication scheme by which a signal is transmitted/received through a node selected from plural nodes according to a specific rule. In the case of DPS, signal transmission reliability can be improved because a node having a good channel state between the node and a UE is selected as a communication node. 
     In the present invention, a cell refers to a specific geographical area in which one or more nodes provide communication services. Accordingly, communication with a specific cell may mean communication with an eNB or a node providing communication services to the specific cell. A downlink/uplink signal of a specific cell refers to a downlink/uplink signal from/to an eNB or a node providing communication services to the specific cell. A cell providing uplink/downlink communication services to a UE is called a serving cell. Furthermore, channel status/quality of a specific cell refers to channel status/quality of a channel or a communication link generated between an eNB or a node providing communication services to the specific cell and a UE. In 3GPP LTE-A systems, a UE can measure downlink channel state from a specific node using one or more CSI-RSs (Channel State Information Reference Signals) transmitted through antenna port(s) of the specific node on a CSI-RS resource allocated to the specific node. In general, neighboring nodes transmit CSI-RS resources on orthogonal CSI-RS resources. When CSI-RS resources are orthogonal, this means that the CSI-RS resources have different subframe configurations and/or CSI-RS sequences which specify subframes to which CSI-RSs are allocated according to CSI-RS resource configurations, subframe offsets and transmission periods, etc. which specify symbols and subcarriers carrying the CSI RSs. 
     In the present invention, PDCCH (Physical Downlink Control Channel)/PCFICH (Physical Control Format Indicator Channel)/PHICH (Physical Hybrid automatic repeat request Indicator Channel)/PDSCH (Physical Downlink Shared Channel) refer to a set of time-frequency resources or resource elements respectively carrying DCI (Downlink Control Information)/CFI (Control Format Indicator)/downlink ACK/NACK (Acknowledgement/Negative ACK)/downlink data. In addition, PUCCH (Physical Uplink Control Channel)/PUSCH (Physical Uplink Shared Channel)/PRACH (Physical Random Access Channel) refer to sets of time-frequency resources or resource elements respectively carrying UCI (Uplink Control Information)/uplink data/random access signals. In the present invention, a time-frequency resource or a resource element (RE), which is allocated to or belongs to PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH, is referred to as a PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE or PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH resource. In the following description, transmission of PUCCH/PUSCH/PRACH by a UE is equivalent to transmission of uplink control information/uplink data/random access signal through or on PUCCH/PUSCH/PRACH. Furthermore, transmission of PDCCH/PCFICH/PHICH/PDSCH by an eNB is equivalent to transmission of downlink data/control information through or on PDCCH/PCFICH/PHICH/PDSCH. 
       FIG. 1  illustrates an exemplary radio frame structure used in a wireless communication system.  FIG. 1( a )  illustrates a frame structure for frequency division duplex (FDD) used in 3GPP LTE/LTE-A and  FIG. 1( b )  illustrates a frame structure for time division duplex (TDD) used in 3GPP LTE/LTE-A. 
     Referring to  FIG. 1 , a radio frame used in 3GPP LTE/LTE-A has a length of 10 ms (307200Ts) and includes 10 subframes in equal size. The 10 subframes in the radio frame may be numbered. Here, Ts denotes sampling time and is represented as Ts=1/(2048*15 kHz). Each subframe has a length of 1 ms and includes two slots. 20 slots in the radio frame can be sequentially numbered from 0 to 19. Each slot has a length of 0.5 ms. A time for transmitting a subframe is defined as a transmission time interval (TTI). Time resources can be discriminated by a radio frame number (or radio frame index), subframe number (or subframe index) and a slot number (or slot index). 
     The radio frame can be configured differently according to duplex mode. Downlink transmission is discriminated from uplink transmission by frequency in FDD mode, and thus the radio frame includes only one of a downlink subframe and an uplink subframe in a specific frequency band. In TDD mode, downlink transmission is discriminated from uplink transmission by time, and thus the radio frame includes both a downlink subframe and an uplink subframe in a specific frequency band. 
     Table 1 shows DL-UL configurations of subframes in a radio frame in the TDD mode. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 Downlink- 
                   
               
               
                   
                 to-Uplink 
               
               
                   
                 Switch- 
               
               
                 DL-UL 
                 point 
                 Subframe number 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 configuration 
                 periodicity 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 0 
                 5 ms 
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 S 
                 U 
                 U 
                 U 
               
               
                 1 
                 5 ms 
                 D 
                 S 
                 U 
                 U 
                 D 
                 D 
                 S 
                 U 
                 U 
                 D 
               
               
                 2 
                 5 ms 
                 D 
                 S 
                 U 
                 D 
                 D 
                 D 
                 S 
                 U 
                 D 
                 D 
               
               
                 3 
                 10 ms  
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 4 
                 10 ms  
                 D 
                 S 
                 U 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 5 
                 10 ms  
                 D 
                 S 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 6 
                 5 ms 
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 S 
                 U 
                 U 
                 D 
               
               
                   
               
            
           
         
       
     
     In Table 1, D denotes a downlink subframe, U denotes an uplink subframe and S denotes a special subframe. The special subframe includes three fields of DwPTS (Downlink Pilot TimeSlot), GP (Guard Period), and UpPTS (Uplink Pilot TimeSlot). DwPTS is a period reserved for downlink transmission and UpPTS is a period reserved for uplink transmission. Table 2 shows special subframe configuration. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Normal cyclic prefix in downlink 
                 Extended cyclic prefix in downlink 
               
            
           
           
               
               
               
               
            
               
                   
                 UpPTS 
                   
                 UpPTS 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Special 
                   
                 Normal cyclic 
                 Extended 
                   
                 Normal 
                 Extended 
               
               
                 subframe 
                   
                 prefix in 
                 cyclic prefix 
                   
                 cyclic prefix 
                 cyclic prefix 
               
               
                 configuration 
                 DwPTS 
                 uplink 
                 in uplink 
                 DwPTS 
                 in uplink 
                 in uplink 
               
               
                   
               
               
                 0 
                  6592 · T s   
                 2192 · T s   
                 2560 · T s   
                  7680 · T s   
                 2192 · T s   
                 2560 · T s   
               
               
                 1 
                 19760 · T s   
                   
                   
                 20480 · T s   
               
               
                 2 
                 21952 · T s   
                   
                   
                 23040 · T s   
               
               
                 3 
                 24144 · T s   
                   
                   
                 25600 · T s   
               
               
                 4 
                 26336 · T s   
                   
                   
                  7680 · T s   
                 4384 · T s   
                 5120 · T s   
               
               
                 5 
                  6592 · T s   
                 4384 · T s   
                 5120 · T s   
                 20480 · T s   
               
               
                 6 
                 19760 · T s   
                   
                   
                 23040 · T s   
               
               
                 7 
                 21952 · T s   
                   
                   
                 12800 · T s   
               
               
                 8 
                 24144 · T s   
                   
                   
                 — 
                 — 
                 — 
               
               
                 9 
                 13168 · T s   
                   
                   
                 — 
                 — 
                 — 
               
               
                   
               
            
           
         
       
     
       FIG. 2  illustrates an exemplary downlink/uplink slot structure in a wireless communication system. Particularly,  FIG. 2  illustrates a resource grid structure in 3GPP LTE/LTE-A. A resource grid is present per antenna port. 
     Referring to  FIG. 2 , a slot includes a plurality of OFDM (Orthogonal Frequency Division Multiplexing) symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. An OFDM symbol may refer to a symbol period. A signal transmitted in each slot may be represented by a resource grid composed of N RB   DL/UL *N SC   RB  subcarriers and N symb   DL/UL  OFDM symbols. Here, N RD   DL  denotes the number of RBs in a downlink slot and N RB   UL  denotes the number of RBs in an uplink slot. N RB   DL  and N RB   UL  respectively depend on a DL transmission bandwidth and a UL transmission bandwidth. N symb   DL  denotes the number of OFDM symbols in the downlink slot and N symb   UL  denotes the number of OFDM symbols in the uplink slot. In addition, N SC   RB  denotes the number of subcarriers constructing one RB. 
     An OFDM symbol may be called an SC-FDM (Single Carrier Frequency Division Multiplexing) symbol according to multiple access scheme. The number of OFDM symbols included in a slot may depend on a channel bandwidth and the length of a cyclic prefix (CP). For example, a slot includes 7 OFDM symbols in the case of normal CP and 6 OFDM symbols in the case of extended CP. While  FIG. 2  illustrates a subframe in which a slot includes 7 OFDM symbols for convenience, embodiments of the present invention can be equally applied to subframes having different numbers of OFDM symbols. Referring to  FIG. 2 , each OFDM symbol includes N RB   DL/UL *N SC   RB  subcarriers in the frequency domain. Subcarrier types can be classified into a data subcarrier for data transmission, a reference signal subcarrier for reference signal transmission, and null subcarriers for a guard band and a direct current (DC) component. The null subcarrier for a DC component is a subcarrier remaining unused and is mapped to a carrier frequency (f0) during OFDM signal generation or frequency up-conversion. The carrier frequency is also called a center frequency. 
     An RB is defined by N symb   DL/UL  (e.g., 7) consecutive OFDM symbols in the time domain and N SC   RB  (e.g., 12) consecutive subcarriers in the frequency domain. For reference, a resource composed by an OFDM symbol and a subcarrier is called a resource element (RE) or a tone. Accordingly, an RB is composed of N symb   DL/UL *N SC   RB REs. Each RE in a resource grid can be uniquely defined by an index pair (k, 1) in a slot. Here, k is an index in the range of 0 to N symb   DL/UL *N SC   RB −1 in the frequency domain and 1 is an index in the range of 0 to N symb   DL/UL −1. 
     Two RBs that occupy N SC   RB  consecutive subcarriers in a subframe and respectively disposed in two slots of the subframe are called a physical resource block (PRB) pair. Two RBs constituting a PRB pair have the same PRB number (or PRB index). A virtual resource block (VRB) is a logical resource allocation unit for resource allocation. The VRB has the same size as that of the PRB. The VRB may be divided into a localized VRB and a distributed VRB depending on a mapping scheme of VRB into PRB. The localized VRBs are mapped into the PRBs, whereby VRB number (VRB index) corresponds to PRB number. That is, nPRB=nVRB is obtained. Numbers are given to the localized VRBs from 0 to N VRB   DL −1, and N VRB   DL =N RB   DL  is obtained. Accordingly, according to the localized mapping scheme, the VRBs having the same VRB number are mapped into the PRBs having the same PRB number at the first slot and the second slot. On the other hand, the distributed VRBs are mapped into the PRBs through interleaving. Accordingly, the VRBs having the same VRB number may be mapped into the PRBs having different PRB numbers at the first slot and the second slot. Two PRBs, which are respectively located at two slots of the subframe and have the same VRB number, will be referred to as a pair of VRBs. 
       FIG. 3  illustrates a downlink (DL) subframe structure used in 3GPP LTE/LTE-A. 
     Referring to  FIG. 3 , a DL subframe is divided into a control region and a data region. A maximum of three (four) OFDM symbols located in a front portion of a first slot within a subframe correspond to the control region to which a control channel is allocated. A resource region available for PDCCH transmission in the DL subframe is referred to as a PDCCH region hereinafter. The remaining OFDM symbols correspond to the data region to which a physical downlink shared chancel (PDSCH) is allocated. A resource region available for PDSCH transmission in the DL subframe is referred to as a PDSCH region hereinafter. Examples of downlink control channels used in 3GPP LTE include a physical control format indicator channel (PCFCH), a physical downlink control channel (PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of a subframe and carries information regarding the number of OFDM symbols used for transmission of control channels within the subframe. The PHICH is a response of uplink transmission and carries an HARQ acknowledgment (ACK)/negative acknowledgment (NACK) signal. 
     Control information carried on the PDCCH is called downlink control information (DCI). The DCI contains resource allocation information and control information for a UE or a UE group. For example, the DCI includes a transport format and resource allocation information of a downlink shared channel (DL-SCH), a transport format and resource allocation information of an uplink shared channel (UL-SCH), paging information of a paging channel (PCH), system information on the DL-SCH, information about resource allocation of an upper layer control message such as a random access response transmitted on the PDSCH, a transmit control command set with respect to individual UEs in a UE group, a transmit power control command, information on activation of a voice over IP (VoIP), downlink assignment index (DAI), etc. The transport format and resource allocation information of the DL-SCH are also called DL scheduling information or a DL grant and the transport format and resource allocation information of the UL-SCH are also called UL scheduling information or a UL grant. The size and purpose of DCI carried on a PDCCH depend on DCI format and the size thereof may be varied according to coding rate. Various formats, for example, formats 0 and 4 for uplink and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3 and 3A for downlink, have been defined in 3GPP LTE. Control information such as a hopping flag, information on RB allocation, modulation coding scheme (MCS), redundancy version (RV), new data indicator (NDI), information on transmit power control (TPC), cyclic shift demodulation reference signal (DMRS), UL index, channel quality information (CQI) request, DL assignment index, HARQ process number, transmitted precoding matrix indicator (TPMI), precoding matrix indicator (PMI), etc. is selected and combined based on DCI format and transmitted to a UE as DCI. 
     In general, a DCI format for a UE depends on transmission mode (TM) set for the UE. In other words, only a DCI format corresponding to a specific TM can be used for a UE configured in the specific TM. 
     A PDCCH is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). The CCE is a logical allocation unit used to provide the PDCCH with a coding rate based on a state of a radio channel The CCE corresponds to a plurality of resource element groups (REGs). For example, a CCE corresponds to 9 REGs and an REG corresponds to 4 REs. 3GPP LTE defines a CCE set in which a PDCCH can be located for each UE. A CCE set from which a UE can detect a PDCCH thereof is called a PDCCH search space, simply, search space. An individual resource through which the PDCCH can be transmitted within the search space is called a PDCCH candidate. A set of PDCCH candidates to be monitored by the UE is defined as the search space. In 3GPP LTE/LTE-A, search spaces for DCI formats may have different sizes and include a dedicated search space and a common search space. The dedicated search space is a UE-specific search space and is configured for each UE. The common search space is configured for a plurality of UEs. Aggregation levels defining the search space is as follows. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                   
                   
                   
                 Number of 
               
            
           
           
               
               
               
            
               
                   
                 Search Space 
                 PDCCH 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Aggregation Level 
                   
                 candidates 
               
               
                   
                 Type 
                 L 
                 Size [in CCEs] 
                 M (L)   
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 UE-specific 
                 1 
                 6 
                 6 
               
               
                   
                   
                 2 
                 12 
                 6 
               
               
                   
                   
                 4 
                 8 
                 2 
               
               
                   
                   
                 8 
                 16 
                 2 
               
               
                   
                 Common 
                 4 
                 16 
                 4 
               
               
                   
                   
                 8 
                 16 
                 2 
               
               
                   
                   
               
            
           
         
       
     
     A PDCCH candidate corresponds to 1, 2, 4 or 8 CCEs according to CCE aggregation level. An eNB transmits a PDCCH (DCI) on an arbitrary PDCCH candidate with in a search space and a UE monitors the search space to detect the PDCCH (DCI). Here, monitoring refers to attempting to decode each PDCCH in the corresponding search space according to all monitored DCI formats. The UE can detect the PDCCH thereof by monitoring plural PDCCHs. Since the UE does not know the position in which the PDCCH thereof is transmitted, the UE attempts to decode all PDCCHs of the corresponding DCI format for each subframe until a PDCCH having the ID thereof is detected. This process is called blind detection (or blind decoding (BD)). 
     The eNB can transmit data for a UE or a UE group through the data region. Data transmitted through the data region may be called user data. For transmission of the user data, a physical downlink shared channel (PDSCH) may be allocated to the data region. A paging channel (PCH) and downlink-shared channel (DL-SCH) are transmitted through the PDSCH. The UE can read data transmitted through the PDSCH by decoding control information transmitted through a PDCCH. Information representing a UE or a UE group to which data on the PDSCH is transmitted, how the UE or UE group receives and decodes the PDSCH data, etc. is included in the PDCCH and transmitted. For example, if a specific PDCCH is CRC (cyclic redundancy check)-masked having radio network temporary identify (RNTI) of “A” and information about data transmitted using a radio resource (e.g., frequency position) of “B” and transmission format information (e.g., transport block size, modulation scheme, coding information, etc.) of “C” is transmitted through a specific DL subframe, the UE monitors PDCCHs using RNTI information and a UE having the RNTI of “A” detects a PDCCH and receives a PDSCH indicated by “B” and “C” using information about the PDCCH. 
     A reference signal (RS) to be compared with a data signal is necessary for the UE to demodulate a signal received from the eNB. A reference signal refers to a predetermined signal having a specific waveform, which is transmitted from the eNB to the UE or from the UE to the eNB and known to both the eNB and UE. The reference signal is also called a pilot. Reference signals are categorized into a cell-specific RS shared by all UEs in a cell and a modulation RS (DM RS) dedicated for a specific UE. A DM RS transmitted by the eNB for demodulation of downlink data for a specific UE is called a UE-specific RS. Both or one of DM RS and CRS may be transmitted on downlink. When only the DM RS is transmitted without CRS, an RS for channel measurement needs to be additionally provided because the DM RS transmitted using the same precoder as used for data can be used for demodulation only. For example, in 3GPP LTE(-A), CSI-RS corresponding to an additional RS for measurement is transmitted to the UE such that the UE can measure channel state information. CSI-RS is transmitted in each transmission period corresponding to a plurality of subframes based on the fact that channel state variation with time is not large, unlike CRS transmitted per subframe. 
       FIG. 4  illustrates an exemplary uplink subframe structure used in 3GPP LTE/LTE-A. 
     Referring to  FIG. 4 , a UL subframe can be divided into a control region and a data region in the frequency domain. One or more PUCCHs (physical uplink control channels) can be allocated to the control region to carry uplink control information (UCI). One or more PUSCHs (Physical uplink shared channels) may be allocated to the data region of the UL subframe to carry user data. 
     In the UL subframe, subcarriers spaced apart from a DC subcarrier are used as the control region. In other words, subcarriers corresponding to both ends of a UL transmission bandwidth are assigned to UCI transmission. The DC subcarrier is a component remaining unused for signal transmission and is mapped to the carrier frequency f 0  during frequency up-conversion. A PUCCH for a UE is allocated to an RB pair belonging to resources operating at a carrier frequency and RBs belonging to the RB pair occupy different subcarriers in two slots. Assignment of the PUCCH in this manner is represented as frequency hopping of an RB pair allocated to the PUCCH at a slot boundary. When frequency hopping is not applied, the RB pair occupies the same subcarrier. 
     The PUCCH can be used to transmit the following control information.
         Scheduling Request (SR): This is information used to request a UL-SCH resource and is transmitted using On-Off Keying (OOK) scheme.   HARQ ACK/NACK: This is a response signal to a downlink data packet on a PDSCH and indicates whether the downlink data packet has been successfully received. A 1-bit ACK/NACK signal is transmitted as a response to a single downlink codeword and a 2-bit ACK/NACK signal is transmitted as a response to two downlink codewords. HARQ-ACK responses include positive ACK (ACK), negative ACK (NACK), discontinuous transmission (DTX) and NACK/DTX. Here, the term HARQ-ACK is used interchangeably with the term HARQ ACK/NACK and ACK/NACK.   Channel State Indicator (CSI): This is feedback information about a downlink channel Feedback information regarding MIMO includes a rank indicator (RI) and a precoding matrix indicator (PMI).       

     The quantity of control information (UCI) that a UE can transmit through a subframe depends on the number of SC-FDMA symbols available for control information transmission. The SC-FDMA symbols available for control information transmission correspond to SC-FDMA symbols other than SC-FDMA symbols of the subframe, which are used for reference signal transmission. In the case of a subframe in which a sounding reference signal (SRS) is configured, the last SC-FDMA symbol of the subframe is excluded from the SC-FDMA symbols available for control information transmission. A reference signal is used to detect coherence of the PUCCH. The PUCCH supports various formats according to information transmitted thereon. 
     Table 4 shows the mapping relationship between PUCCH formats and UCI in LTE/LTE-A. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                 Number 
                   
                   
               
               
                   
                   
                 of bits 
                   
                   
               
               
                   
                   
                 per 
                   
                   
               
               
                 PUCCH 
                 Modulation 
                 subframe, 
                   
                   
               
               
                 format 
                 scheme 
                 M bit   
                 Usage 
                 Etc. 
               
               
                   
               
             
            
               
                 1 
                 N/A 
                 N/A 
                 SR (Scheduling 
                   
               
               
                   
                   
                   
                 Request) 
                   
               
               
                 1a 
                 BPSK 
                 1 
                 ACK/NACK or 
                 One codeword 
               
               
                   
                   
                   
                 SR + ACK/NACK 
                   
               
               
                 1b 
                 QPSK 
                 2 
                 ACK/NACK or 
                 Two codeword 
               
               
                   
                   
                   
                 SR + ACK/NACK 
                   
               
               
                 2 
                 QPSK 
                 20 
                 CQI/PMI/RI 
                 Joint coding 
               
               
                   
                   
                   
                   
                 ACK/NACK 
               
               
                   
                   
                   
                   
                 (extended 
               
               
                   
                   
                   
                   
                 CP) 
               
               
                 2a 
                 QPSK + BPSK 
                 21 
                 CQI/PMI/RI + 
                 Normal CP 
               
               
                   
                   
                   
                 ACK/NACK 
                 only 
               
               
                 2b 
                 QPSK + QPSK 
                 22 
                 CQI/PMI/RI + 
                 Normal CP 
               
               
                   
                   
                   
                 ACK/NACK 
                 only 
               
               
                 3 
                 QPSK 
                 48 
                 ACK/NACK or 
                   
               
               
                   
                   
                   
                 SR + ACK/NACK or 
                   
               
               
                   
                   
                   
                 CQI/PMI/RI + 
                   
               
               
                   
                   
                   
                 ACK/NACK 
               
               
                   
               
            
           
         
       
     
     Referring to Table 4, PUCCH formats 1/1a/1b are used to transmit ACK/NACK information, PUCCH format 2/2a/2b are used to carry CSI such as CQI/PMI/RI and PUCCH format 3 is used to transmit ACK/NACK information. 
     Generally, in a cellular communication system, various methods for acquiring position information of a UE in a network are used. Representatively, a positioning scheme based on OTDOA (observed time difference of arrival) exists in the LTE system. According to the positioning scheme, the UE may be configured to receive PRS (positioning reference signal) transmission related information of eNBs from a higher layer signal, and may transmit a reference signal time difference (RSTD) which is a difference between a reception time of a PRS transmitted from a reference eNB and a reception time of a PRS transmitted from a neighboring eNB to a eNB or network by measuring PRS transmitted from cells in the periphery of the UE, and the network calculates a position of the UE by using RSTD and other information. In addition, other schemes such as an A-GNSS(Assisted Global Navigation Satellite System) positioning scheme, an E-CID(Enhanced Cell-ID) scheme, and a UTDOA(Uplink Time Difference of Arrival) exist, and various location-based services (for example, advertisements, position tracking, emergency communication means, etc.) may be used based on these positioning schemes. 
     [LTE Positioning Protocol] 
     In the LTE system, an LPP (LTE positioning protocol) has been defined to the OTDOA scheme, and notifies the UE of OTDOA-ProvideAssistanceData having the following configuration through IE (information element). 
     
       
         
           
               
             
               
                   
               
             
            
               
                   -- ASN1START 
               
               
                   OTDOA-ProvideAssistanceData ::= SEQUENCE { 
               
               
                   otdoa-ReferenceCellInfoOTDOA-ReferenceCellInfo OPTIONAL, 
               
               
                 -- Need ON 
               
               
                   otdoa-NeighbourCellInfo  OTDOA-NeighbourCellInfoList 
               
               
                 OPTIONAL, -- Need ON 
               
               
                   otdoa-Error OTDOA-Error OPTIONAL, -- Need ON 
               
               
                   ... 
               
               
                   } 
               
               
                 -- ASN1STOP 
               
               
                   
               
            
           
         
       
     
     In this case, OTDOA-ReferenceCellInfo means a cell which is a reference of RSTD measurement, and is configured as follows. 
     
       
         
           
               
             
               
                   
               
             
            
               
                   -- ASN1START 
               
               
                   OTDOA-ReferenceCellInfo ::= SEQUENCE { 
               
            
           
           
               
               
            
               
                   physCellId 
                 INTEGER (0..503), 
               
            
           
           
               
               
               
            
               
                   cellGlobalId 
                 ECGI OPTIONAL, 
                 -- Need ON 
               
               
                   earfcnRef 
                 ARFCN-ValueEUTRA 
                 OPTIONAL, --Cond 
               
               
                 NotSameAsServ0 
               
            
           
           
               
               
            
               
                   antennaPortConfig 
                 ENUMERATED {ports1-or-2, ports4, ... } 
               
            
           
           
               
               
            
               
                   OPTIONAL, 
                 -- Cond NotSameAsServ1 
               
            
           
           
               
            
               
                   cpLength ENUMERATED { normal, extended, ... }, 
               
            
           
           
               
               
            
               
                   prsInfo PRS-Info 
                 OPTIONAL, -- Cond PRS 
               
               
                   ..., 
               
               
                   [[ earfcnRef-v9a0 
                 ARFCN-ValueEUTRA-v9a0 OPTIONAL -- 
               
               
                 Cond NotSameAsServ2 
               
               
                   ]] 
               
               
                   } 
               
               
                   -- ASN1STOP 
               
               
                   
               
            
           
         
       
     
     Meanwhile, OTDOA-NeighbourCellInfo means cells (for example, eNB or TP) which is a target for RSTD measurement, and may include information on maximum 24 neighboring cells per frequency layer with respect to maximum three frequency layers. That is, OTDOA-NeighbourCellInfo may notify the UE of information on a total of 3*24=72 cells. 
     
       
         
           
               
             
               
                   
               
             
            
               
                   -- ASN1START 
               
               
                   OTDOA-NeighbourCellInfoList  ::=  SEQUENCE  (SIZE 
               
               
                 (1..maxFreqLayers)) OF OTDOA-NeighbourFreqInfo 
               
               
                   OTDOA-NeighbourFreqInfo ::= SEQUENCE (SIZE (1..24)) OF 
               
               
                 OTDOA-NeighbourCellInfoElement 
               
               
                   OTDOA-NeighbourCellInfoElement ::= SEQUENCE { 
               
            
           
           
               
               
            
               
                   physCellId 
                 INTEGER (0..503), 
               
               
                   cellGlobalId 
                 ECGI OPTIONAL, -- Need ON 
               
            
           
           
               
            
               
                   earfcn ARFCN-ValueEUTRA OPTIONAL,  --  Cond 
               
               
                 NotSameAsRef0 
               
            
           
           
               
               
            
               
                   cpLength 
                 ENUMERATED {normal, extended, ...} 
               
               
                   OPTIONAL, 
                 -- Cond NotSameAsRef1 
               
            
           
           
               
               
               
            
               
                   prsInfo PRS-Info 
                 OPTIONAL, 
                 -- Cond NotSameAsRef2 
               
            
           
           
               
               
            
               
                   antennaPortConfig 
                 ENUMERATED {ports-1-or-2, ports-4, ...} 
               
               
                   OPTIONAL, 
                 -- Cond NotsameAsRef3 
               
            
           
           
               
               
               
            
               
                   slotNumberOffset 
                 INTEGER (0..19) 
                 OPTIONAL, -- Cond 
               
               
                 NotSameAsRef4 
               
               
                   prs-SubframeOffset 
                 INTEGER (0..1279) 
                 OPTIONAL,  -- 
               
               
                 Cond InterFreq 
               
            
           
           
               
            
               
                   expectedRSTD INTEGER (0..16383), 
               
               
                   expectedRSTD-Uncertainty  INTEGER (0..1023), 
               
               
                   ..., 
               
            
           
           
               
               
            
               
                   [[ earfcn-v9a0 
                 ARFCN-ValueEUTRA-v9a0  OPTIONAL -- 
               
            
           
           
               
            
               
                 Cond NotSameAsRef5 
               
               
                   ]] 
               
               
                   } 
               
               
                   maxFreqLayers INTEGER ::= 3 
               
               
                   -- ASN1STOP 
               
               
                   
               
            
           
         
       
     
     In this case, PRS-Info which is IE included in OTDOA-ReferenceCellInfo and OTDOA-NeighbourCellInfo has PRS information, and is specifically configured, as follows, as PRS Bandwidth, PRS Configuration Index (IPRS), Number of Consecutive Downlink Subframes, and PRS Muting Information. 
     
       
         
           
               
             
               
                   
               
             
            
               
                 PRS-Info ::= SEQUENCE { 
               
               
                 prs-Bandwidth ENUMERATED { n6, n15, n25, n50, n75, n100, ... }, 
               
               
                 prs-ConfigurationIndex INTEGER (0..4095), 
               
               
                 numDL-Frames ENUMERATED {sf-1, sf-2, sf-4, sf-6, ...}, 
               
               
                 ..., 
               
               
                 prs-MutingInfo-r9  CHOICE { 
               
               
                 po2-r9   BIT STRING (SIZE(2)), 
               
               
                 po4-r9   BIT STRING (SIZE(4)), 
               
               
                 po8-r9   BIT STRING (SIZE(8)), 
               
               
                 po16-r9 BIT STRING (SIZE(16)), 
               
               
                 ... 
               
               
                 } OPTIONAL    -- Need OP 
               
               
                 } 
               
               
                 -- ASN1STOP 
               
               
                   
               
            
           
         
       
     
       FIG. 5  illustrates a PRS transmission structure according to the above parameters. 
     At this time, PRS Periodicity and PRS Subframe Offset are determined in accordance with a value of PRS Configuration Index (IPRS), and their correlation is as follows. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 PRS Configuration Index 
                 PRS Periodicity 
                 PRS Subframe Offset 
               
               
                   
                 (I PRS ) 
                 (subframes) 
                 (subframes) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                  0-159 
                 160 
                 I PRS   
               
               
                   
                 160-479 
                 320 
                 I PRS -160 
               
               
                   
                  480-1119 
                 640 
                 I PRS -480 
               
               
                   
                  1120-23399 
                 1280 
                  I PRS -1120 
               
               
                   
                   
               
            
           
         
       
     
     [PRS(Positioning Reference Signal)] 
     The PRS has a transmission occasion, that is, a positioning occasion at a period of 160, 320, 640, or 1280 ms, and may be transmitted for N DL subframes consecutive for the positioning occasion. In this case, N may have a value of 1, 2, 4 or 6. Although the PRS may be transmitted substantially at the positioning occasion, the PRS may be muted for inter-cell interference control cooperation. Information on such PRS muting is signaled to the UE as prs-MutingInfo. A transmission bandwidth of the PRS may be configured independently unlike a system bandwidth of a serving eNB, and is transmitted to a frequency band of 6, 15, 25, 50, 75 or 100 resource blocks (RBs). Transmission sequences of the PRS are generated by initializing a pseudo-random sequence generator for every OFDM symbol using a function of a slot index, an OFDM symbol index, a cyclic prefix (CP) type, and a cell ID. The generated transmission sequences of the PRS are mapped to resource elements (REs) depending on a normal CP or an extended CP as shown in  FIG. 6  (normal CP) and  FIG. 7  (extended CP). A position of the mapped REs may be shifted on the frequency axis, and a shift value is determined by a cell ID. The positions of the REs for transmission of the PRS shown in  FIGS. 6 and 7  correspond to the case that the frequency shift is 0. 
     The UE receives designated configuration information on a list of PRSs to be searched from a position management server of a network to measure PRSs. The corresponding information includes PRS configuration information of a reference cell and PRS configuration information of neighboring cells. The configuration information of each PRS includes a generation cycle and offset of a positioning occasion, and the number of continuous DL subframes constituting one positioning occasion, cell ID used for generation of PRS sequences, a CP type, the number of CRS antenna ports considered at the time of PRS mapping, etc. In addition, the PRS configuration information of the neighboring cells includes a slot offset and a subframe offset of the neighboring cells and the reference cell, an expected RSTD, and a level of uncertainty of the expected RSTD to support determination of the UE when the UE determines a timing point and a level of time window used to search for the PRS to detect the PRS transmitted from the neighboring cell. 
     Meanwhile, the RSTD refers to a relative timing difference between an adjacent or neighboring cell j and a reference cell i. In other words, the RSTD may be expressed by T subframeRxj −T subframeRxi , wherein T subframeRxj  refers to a timing point at which a UE starts to receive a specific subframe from the neighboring cell j, and T subframeRxi  refers to a timing point at which a UE starts to receive a subframe, which is closest to the specific subframe received from the neighboring cell j in terms of time and corresponds to the specific subframe, from the reference cell i. A reference point for an observed subframe time difference is an antenna connector of the UE. 
     Although the aforementioned positioning schemes of the related art are already supported by the 3GPP UTRA and E-UTRAN standard (for example, (LTE Rel-9), higher accuracy is recently required for an in-building positioning scheme. That is, although the positioning schemes of the related art may commonly be applied to outdoor/indoor environments, in case of E-CID scheme, general positioning accuracy is known as 150 m in a non-LOS (NLOS) environment and as 50 m in a LOS environment. Also, the OTDOA scheme based on the PRS has a limit in a positioning error, which may exceed 100 m, due to an eNB synchronization error, a multipath propagation error, a quantization error in RSTD measurement of a UE, and a timing offset estimation error. Also, since a GNSS receiver is required in case of the A-GNSS scheme, the A-GNSS scheme has a limit in complexity and battery consumption, and has a restriction in using in-building positioning. 
     [LTE (LTE-U) in Unlicensed Band] 
     Recently, with the advent of a smart device, data traffic is considerably increasing. As a result, a next generation wireless communication system such as 3GPP LTE-A is trying to find ways to efficiently utilizing a limited frequency band. In particular, the next generation wireless communication system considers managing a cellular network on such an unlicensed band as 2.4 GHz or 5 GHz. The unlicensed band regulates each of communication nodes to perform wireless transmission and reception based on an LBT operation such as CCA (clear channel assessment) and the like. 
     For example, regulation of Europe illustrates two types of LBT-based channel access operation respectively referred to as FBE (frame based equipment) and LBE (load based equipment). The FBE configures a single frame using channel occupancy time (e.g., 1-10 ms) corresponding to time capable of maintaining transmission when a communication node succeeds in accessing a channel and idle time corresponding to the minimum 5% of the channel occupancy time. The CCA is defined as an operation of observing a channel for at least 20 μs of the last part of the idle time. In this case, a communication node periodically performs the CCA in a unit of the frame. If a channel is unoccupied, the communication node transmits data during the channel occupancy time. If a channel is occupied, the communication node waits until a CCA slot of a next period while postponing transmission.  FIG. 8  shows an example of the FBE operation. 
     Meanwhile, in case of the LBE, a communication node configures a value of q∈ {4, 5, . . . , 32} first and performs CCA on a single slot. If a channel is unoccupied in the first CCA slot, the communication node can transmit data by securing channel occupancy time as much as a length of (13/32)q ms. If a channel is occupied in the first CCA slot, the communication node randomly selects a value of N∈ {1, 2, . . . , q}, stores the selected value as an initial value of a counter, and senses a channel state in a unit of a CCA slot. If a channel is unoccupied in a specific CCA slot, the communication node reduces the value stored in the counter by 1. If the value stored in the counter becomes 0, a user equipment (UE) can transmit data with channel occupancy time as much as a length of (13/32)q ms.  FIG. 9  shows an example of the LBE operation. 
     In the example, an occupied state of a channel or an unoccupied state of the channel can be determined based on whether or not reception power exceeds a prescribed threshold in a CCA slot. For example, according to the Wi-Fi standard (e.g., 801.11ac), a CCA threshold is regulated by −62 dBm and −82 dBm for a non-Wi-Fi signal and a Wi-Fi signal, respectively. In particular, if a signal rather than a Wi-Fi signal is received with power equal to or greater than −62 dBm, an STA (station) or an AP (access point) does not perform signal transmission to avoid interference occurrence. Meanwhile, a wireless communication system such as 3GPP LTE-A, and the like, considers a method of combining a cell operating on a licensed band (hereinafter, L-cell) and a cell operating on an unlicensed band (hereinafter, U-cell) with each other using a CA (carrier aggregation) technique and a method of performing LBT-based DL/UL transmission in the U-cell. 
     Meanwhile, although the aforementioned legacy positioning schemes are already supported by 3GPP UTRA and E-UTRA standard (e.g., LTE Rel-9), it is necessary to have an enhanced positioning scheme to have a higher accuracy for in-building positioning. In particular, although the legacy positioning schemes correspond to techniques capable of being commonly applied to outdoor/indoor environment, in case of E-CID scheme, a general positioning accuracy is known as 150 m and 50 m in NLOS environment and LOS environment, respectively. Moreover, the OTDOA scheme based on a PRS has such a critical point as a positioning error capable of exceeding 100 m due to an eNB synchronization error, an error generated by multipath propagation, an RSTD measurement quantization error of a UE, timing offset estimation error, and the like. In case of A-GNSS scheme, since the A-GNSS scheme requires a GNSS receiver, this scheme has a critical point in complexity and battery consumption. This scheme has a restriction on in-building positioning. 
     The present invention basically considers a method for an eNB to calculate location information of a UE. In particular, if a cellular network transmits a specific pilot signal (e.g., a specific reference signal capable of being separately identified according to an eNB/TP (transmission point)) to a UE, the UE measures each pilot signal, calculates a positioning-related estimation value using a specific positioning scheme (e.g., OTDOA and RSTD estimation value report), and reports the estimation value to the eNB. And, the present invention considers a situation that L-Cell operating on a legacy licensed band is combined with U-cell operating on an unlicensed band. 
     In case of transmitting a PRS using a wider bandwidth, it may be able to increase RSTD measurement accuracy of a UE due to duality of frequency domain and time domain. This is because, since a resolution of the time domain is equivalent to inverse of the frequency domain, if a signal is transmitted on a wider frequency band, a unit of time capable of being measured by the UE becomes more detail. Hence, it may be able to aggregate an unlicensed band of a wider bandwidth together in the same cell using CA technique to transmit a PRS. If a UE is able to utilize the PRS, it is expected that it is able to estimate RSTD of higher resolution. Or, although a PRS is not transmitted using both a licensed band and an unlicensed band at the same time, if a PRS is opportunistically transmitted on an unlicensed band of a relatively wider frequency unit (wider bandwidth) and a UE is able to utilize the PRS, it is expected that it is able to increase measurement accuracy of the UE. 
     In case of considering environment that wireless transmission and reception are performed based on an LBT operation on an unlicensed band, when a PRS is transmitted, it may be difficult for a UE to measure the PRS. Since the UE is unable to precisely know channel occupancy time of each of neighboring eNBs, it is difficult for the UE to identify timing at which a PRS of a neighboring eNB is transmitted. Since it is unable to guarantee that channel occupancy time of each eNB is aligned, if an eNB transmits a signal such as data at the timing that a specific eNB transmits a PRS, the signal may work as big interference. When a UE intends to measure a value such as RSTD by utilizing PRSs transmitted from two eNBs, if one of the eNBs has no DL data to transmit and does not occupy channel occupancy time, the UE is unable to measure the value or the UE may obtain an outdated measurement value because the UE performs measurement after waiting for a channel occupancy time of the eNB. Due to the aforementioned various reasons, when eNBs transmit PRSs on an unlicensed band and a UE intends to utilize the PRSs, it may be necessary for the eNBs to transmit the PRSs via coordination. 
     And, it may be able to configure at least one or more subframes (or positioning occasions) in which a PRS is transmitted on an unlicensed band to be overlapped via a predefined coordination or coordination of eNBs via a signal between the eNBs. 
       FIG. 10  shows an example of configuring a subframe (or positioning occasion) in which the PRS is transmitted. A case 1 and a case 2 of  FIG. 10  illustrate a case that a PRS transmission subframe (or positioning occasion) has a period/offset for a subframe of absolute timing irrespective of a channel occupancy time configuration. A case 3 illustrates a case that a PRS transmission subframe (or positioning occasion) is indicated by a specific subframe period belonging to a channel occupancy time period. 
     Meanwhile, in case of the cases 2 and 3 of  FIG. 10 , an eNB  2  transmits a PRS in an SF #n, whereas eNBs  1  and  3  do not transmit a PRS. Hence, in a situation that a PRS is transmitted on an unlicensed band and a UE measure the PRS, the UE performs positioning-related measurement on a serving cell only when a PRS transmission subframe of the serving cell belongs to channel occupancy time. On the contrary, since the UE is unable to identify channel occupancy time for the remaining adjacent cell, the UE performs blind detection on a PRS of the adjacent cell within the channel occupancy time to which the PRS transmission subframe of the serving cell is set to perform the positioning-related measurement. 
     In case of the case 3, although the eNBs  1  and  3  transmit a PRS in an SF #n+4, data rather than a PRS can be transmitted in the eNB 2 . In this case, the data transmitted from the eNB 2  may work as an interference source for PRS measurement of a different eNB. 
     In order to avoid the interference, it may be able to configure not to transmit data in a subframe in which a PRS is not transmitted within channel occupation time including a PRS transmission subframe via a predefined coordination or a coordination of eNBs via a signal between the eNBs. In particular, it may be able to configure a muting operation to be performed in the subframe in which the PRS is not transmitted. 
     Or, it may be able to configure specific channel occupancy time to be used for transmitting a PRS only via a predefined coordination or a coordination of eNBs via a signal between the eNBs. And, it may be able to configure all subframes (or certain number of subframes) within the channel occupancy time to transmit a PRS. 
     Similarly, if at least one or more PRS transmission subframes are included in specific channel occupancy time, it may be able to configure all subframes (or certain number of subframes) within the channel occupancy time to transmit a PRS. 
     Whether to include a PRS transmission subframe in specific channel occupancy time can be commonly configured via a predefined coordination or a coordination of eNBs via a signal between the eNBs. And, information on whether or not a PRS transmission subframe is included in specific channel occupancy time can be indicated to a UE. In this case, a length of the channel occupancy time in which the PRS transmission subframe is included can be identically configured between eNBs. 
     Information on whether or not a PRS transmission subframe is included in specific channel occupancy time can be indicated using a method described in the following.
         Whether or not a PRS transmission subframe is included in channel occupancy timing corresponding to specific timing is indicated via a higher layer signal. For example, if an SF #n, an SF #n+40, and an SF #n+80 are indicated by a higher layer signal and channel occupancy time is configured by {SF #n+15˜SF #n+25} and {SF #n+35˜SF #n+45}, a UE may consider that channel occupancy time corresponding to {SF #n+35˜SF #n+45} includes a PRS transmission subframe only. As a different example, if a period/offset of a PRS is indicated and a subframe corresponding to the period/offset is included in channel occupancy time, a UE may consider that a PRS transmission subframe is included in the channel occupancy time.   Whether or not a PRS transmission subframe is included in channel occupancy timing corresponding to specific timing is indicated via DCI of L-Cell.   Whether or not a PRS transmission subframe is included in channel occupancy timing corresponding to specific timing is indicated via DCI of U-Cell.   If an eNB practically transmits data in accordance with a subframe or an OFDM symbol boundary of LTE-A system, a timing gap may exist between idle determination timing of U-Cell and actual transmission timing. In particular, since the eNB and a UE are unable to exclusively use the U-Cell and the U-Cell is used via CS-based contention, a different system may attempt to transmit information during the timing gap. Hence, for example, the U-Cell may transmit a reservation signal during the timing gap to prevent the different system from transmitting information during the timing gap. In this case, the reservation signal may correspond to “dummy information” or “copy for a part of PDSCH” which is transmitted to reserve the U-Cell as a resource of the UCell. The reservation signal can be transmitted during the timing gap (i.e., between idle determination timing of U-Cell and actual transmission timing). Whether or not a PRS transmission subframe is included in channel occupation time corresponding to specific timing is indicated through the reservation signal.       

     A UE performs PRS blind detection on a reference cell and a neighbor cell in a time period indicated (predetermined) as channel occupancy time in which a PRS transmission subframe is included to perform positioning-related measurement. 
     According to current LTE standard, a transmission sequence of a PRS is generated by initializing a pseudo-random sequence generator in every OFDM symbol with a function of a slot index, an OFDM symbol index, a cyclic prefix (CP) type, and a physical cell ID. As shown in  FIGS. 6 and 7 , the generated sequences are mapped to a resource element (RE) depending on a normal CP or an extended CP according to the reference. 
     REFERENCE 
     The reference signal sequence R L,N     S   (m) shall be mapped to complex-valued modulation symbols a k,l   (p)  used as reference signal for antenna port p=6 in slot n s . 
     
       
         
           
             
               
                 
                   
                     
                       a 
                       
                         k 
                         , 
                         l 
                       
                       
                         ( 
                         p 
                         ) 
                       
                     
                     = 
                     
                       
                         
                           r 
                           
                             l 
                             , 
                             
                               n 
                               s 
                             
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             m 
                             ′ 
                           
                           ) 
                         
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       where 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     Normal 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     cyclic 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     prefix 
                     ⁢ 
                     
                       : 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     k 
                     = 
                     
                       
                         6 
                         ⁢ 
                         
                           ( 
                           
                             m 
                             + 
                             
                               N 
                               RB 
                               DL 
                             
                             - 
                             
                               N 
                               
                                 R 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 B 
                               
                               PRS 
                             
                           
                           ) 
                         
                       
                       + 
                       
                         
                           ( 
                           
                             6 
                             - 
                             l 
                             + 
                             
                               v 
                               shift 
                             
                           
                           ) 
                         
                         ⁢ 
                         mod 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         6 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     l 
                     = 
                     
                       { 
                       
                         
                           
                             
                               
                                 
                                   
                                     3 
                                     , 
                                     5 
                                     , 
                                     6 
                                   
                                 
                                 
                                   
                                     
                                       if 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       
                                         n 
                                         s 
                                       
                                       ⁢ 
                                       mod 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       2 
                                     
                                     = 
                                     0 
                                   
                                 
                               
                               
                                 
                                   
                                     1 
                                     , 
                                     2 
                                     , 
                                     3 
                                     , 
                                     5 
                                     , 
                                     6 
                                   
                                 
                                 
                                   
                                     
                                       
                                         
                                           
                                             
                                               if 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               
                                                 n 
                                                 s 
                                               
                                               ⁢ 
                                               mod 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               2 
                                             
                                             = 
                                             
                                               1 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               and 
                                             
                                           
                                           ⁢ 
                                           
                                               
                                           
                                         
                                       
                                     
                                     
                                       
                                         
                                           ( 
                                           
                                             1 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             or 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             2 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             PBCH 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             antenna 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             ports 
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     2 
                                     , 
                                     3 
                                     , 
                                     5 
                                     , 
                                     6 
                                   
                                 
                                 
                                   
                                     
                                       
                                         
                                           
                                             
                                               if 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               
                                                 n 
                                                 s 
                                               
                                               ⁢ 
                                               mod 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               2 
                                             
                                             = 
                                             
                                               1 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               and 
                                             
                                           
                                           ⁢ 
                                           
                                               
                                           
                                         
                                       
                                     
                                     
                                       
                                         
                                           ( 
                                           
                                             4 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             PBCH 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             antenna 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             ports 
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                 
                               
                             
                             ⁢ 
                             
                               
 
                             
                             ⁢ 
                             m 
                           
                           = 
                           0 
                         
                         , 
                         1 
                         , 
                         … 
                         ⁢ 
                         
                             
                         
                         , 
                         
                           
                             
                               2 
                               · 
                               
                                 N 
                                 RB 
                                 PRS 
                               
                             
                             - 
                             
                               1 
                               ⁢ 
                               
                                 
 
                               
                               ⁢ 
                               
                                 m 
                                 ′ 
                               
                             
                           
                           = 
                           
                             
                               m 
                               + 
                               
                                 N 
                                 RB 
                                 
                                   max 
                                   , 
                                   DL 
                                 
                               
                               - 
                               
                                 
                                   N 
                                   RB 
                                   PRS 
                                 
                                 ⁢ 
                                 
                                   
 
                                 
                                 ⁢ 
                                 Extended 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 cyclic 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 prefix 
                                 ⁢ 
                                 
                                   : 
                                 
                                 ⁢ 
                                 
                                   
 
                                 
                                 ⁢ 
                                 k 
                               
                             
                             = 
                             
                               
                                 
                                   6 
                                   ⁢ 
                                   
                                     ( 
                                     
                                       m 
                                       + 
                                       
                                         N 
                                         RB 
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                                       - 
                                       
                                         N 
                                         
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                                           ⁢ 
                                           
                                               
                                           
                                           ⁢ 
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                                     ) 
                                   
                                 
                                 + 
                                 
                                   
                                     ( 
                                     
                                       5 
                                       - 
                                       l 
                                       + 
                                       
                                         v 
                                         shift 
                                       
                                     
                                     ) 
                                   
                                   ⁢ 
                                   mod 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   6 
                                   ⁢ 
                                   
                                     
 
                                   
                                   ⁢ 
                                   l 
                                 
                               
                               = 
                               
                                 { 
                                 
                                   
                                     
                                       
                                         
                                           
                                             
                                               4 
                                               , 
                                               5 
                                             
                                           
                                           
                                             
                                               
                                                 if 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 
                                                   n 
                                                   s 
                                                 
                                                 ⁢ 
                                                 mod 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 2 
                                               
                                               = 
                                               0 
                                             
                                           
                                         
                                         
                                           
                                             
                                               1 
                                               , 
                                               2 
                                               , 
                                               4 
                                               , 
                                               5 
                                             
                                           
                                           
                                             
                                               
                                                 
                                                   
                                                     
                                                       
                                                         if 
                                                         ⁢ 
                                                         
                                                             
                                                         
                                                         ⁢ 
                                                         
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                                                           s 
                                                         
                                                         ⁢ 
                                                         mod 
                                                         ⁢ 
                                                         
                                                             
                                                         
                                                         ⁢ 
                                                         2 
                                                       
                                                       = 
                                                       
                                                         1 
                                                         ⁢ 
                                                         
                                                             
                                                         
                                                         ⁢ 
                                                         and 
                                                       
                                                     
                                                     ⁢ 
                                                     
                                                         
                                                     
                                                   
                                                 
                                               
                                               
                                                 
                                                   
                                                     ( 
                                                     
                                                       1 
                                                       ⁢ 
                                                       
                                                           
                                                       
                                                       ⁢ 
                                                       or 
                                                       ⁢ 
                                                       
                                                           
                                                       
                                                       ⁢ 
                                                       2 
                                                       ⁢ 
                                                       
                                                           
                                                       
                                                       ⁢ 
                                                       PBCH 
                                                       ⁢ 
                                                       
                                                           
                                                       
                                                       ⁢ 
                                                       antenna 
                                                       ⁢ 
                                                       
                                                           
                                                       
                                                       ⁢ 
                                                       ports 
                                                     
                                                     ) 
                                                   
                                                 
                                               
                                             
                                           
                                         
                                         
                                           
                                             
                                               2 
                                               , 
                                               4 
                                               , 
                                               5 
                                             
                                           
                                           
                                             
                                               
                                                 
                                                   
                                                     
                                                       
                                                         if 
                                                         ⁢ 
                                                         
                                                             
                                                         
                                                         ⁢ 
                                                         
                                                           n 
                                                           s 
                                                         
                                                         ⁢ 
                                                         mod 
                                                         ⁢ 
                                                         
                                                             
                                                         
                                                         ⁢ 
                                                         2 
                                                       
                                                       = 
                                                       
                                                         1 
                                                         ⁢ 
                                                         
                                                             
                                                         
                                                         ⁢ 
                                                         and 
                                                       
                                                     
                                                     ⁢ 
                                                     
                                                         
                                                     
                                                   
                                                 
                                               
                                               
                                                 
                                                   
                                                     ( 
                                                     
                                                       4 
                                                       ⁢ 
                                                       
                                                           
                                                       
                                                       ⁢ 
                                                       PBCH 
                                                       ⁢ 
                                                       
                                                           
                                                       
                                                       ⁢ 
                                                       antenna 
                                                       ⁢ 
                                                       
                                                           
                                                       
                                                       ⁢ 
                                                       ports 
                                                     
                                                     ) 
                                                   
                                                 
                                               
                                             
                                           
                                         
                                       
                                       ⁢ 
                                       
                                         
 
                                       
                                       ⁢ 
                                       m 
                                     
                                     = 
                                     0 
                                   
                                   , 
                                   1 
                                   , 
                                   … 
                                   ⁢ 
                                   
                                       
                                   
                                   , 
                                   
                                     
                                       
                                         2 
                                         · 
                                         
                                           N 
                                           RB 
                                           PRS 
                                         
                                       
                                       - 
                                       
                                         1 
                                         ⁢ 
                                         
                                           
 
                                         
                                         ⁢ 
                                         
                                           m 
                                           ′ 
                                         
                                       
                                     
                                     = 
                                     
                                       m 
                                       + 
                                       
                                         N 
                                         RB 
                                         
                                           max 
                                           , 
                                           DL 
                                         
                                       
                                       - 
                                       
                                         N 
                                         RB 
                                         PRS 
                                       
                                     
                                   
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     According to LTE standard, a PRS is not mapped to an RE to which PBCH, PSS, or SSS is assigned. And, the PRS is not mapped to an OFDM symbol in which a CRS is transmitted. In order to avoid a collision with a PDCCH region, the PRS is not mapped to first three OFDM symbols. 
     Due to the characteristic of an unlicensed band, when a signal is not transmitted during prescribed time, if a neighboring eNB performs CCA, a channels state can be determined as idle and it may attempt to perform communication on the unlicensed band via channel occupancy time period configuration. Hence, if a signal is not transmitted in a specific OFDM symbol of a subframe in which a PRS is transmitted, it may unintentionally recognize that the neighboring eNB is in an idle state. 
     Hence, PRS RE mapping of a subframe in which a PRS is transmitted on an unlicensed band can be configured according to rules described in the following.
         It may be able to configure a specific subframe not to transmit PDCCH on an unlicensed band. When a subframe in which a PRS is transmitted is configured not to transmit PDCCH on an unlicensed band, if the number of PBCH antenna port corresponds to 1 or 2, the PRS can be mapped to a specific RE of second and third OFDM symbols (l=1,2) of a first slot. In case of a subframe in which a PRS is transmitted on an unlicensed band, if the number of PBCH antenna port corresponds to 4, the PRS can be mapped to a specific RE of third OFDM symbol (l=2) of a first slot.   It may be able to configure a specific subframe not to transmit PDCCH and a CRS on an unlicensed band. In this case, a PRS RE can be mapped to a specific RE of an OFDM symbol including an RE to which a CRS is supposed to be transmitted. And, if a specific subframe is configured not to transmit a CRS on an unlicensed band, it may be able to configure a PRS to be mapped to a specific RE of a specific PFDM symbol I=1 for 1 or 2 CRS antenna port, I=2 for 2 or 4 CRS antenna ports).   It may be able to configure not to transmit PBCH, PSS, and/or SSS due to aperiodic/opportunistic transmission on an unlicensed band. In this case, a PRS RE can be mapped to a specific RE of an OFDM symbol including an RE to which PBCH, PSS, and/or SSS are supposed to be transmitted.       

     It may be able to configure not to transmit a CRS and PDCCH to a PRS transmission subframe belonging to specific channel occupation time of an unlicensed band. 
     If PBCH, PSS, and SSS are collided with PRS transmission in a specific subframe belonging to specific channel occupancy time of an unlicensed band, it may be able to configure the PRS transmission to be preferentially performed. Or, it may be able to configure the PBCH, PSS, and SSS transmission to be preferentially performed. The configuration can be configured in advance or can be signaled to a UE. 
     When an eNB performs CCA on an unlicensed band and identifies a channel state, if the eNB performs the CCA at a time on a wider frequency band, although a partial band is occupied by other devices, the eNB may determine that the whole band is busy. Due to the operation, an occupation probability is relatively reduced on the unlicensed band and data is inefficiently transmitted. In order to avoid the inefficient situation, the whole frequency band is divided into relatively narrow frequency bands and CCA can be independently performed on each of the frequency bands. In this case, CCA is performed on each of the frequency bands and it may be able to independently configure channel occupancy time.  FIG. 11  shows an example that an unlicensed band of 80 MHz is divided into four 20 MHz bands, CCA is performed on each of the four 20 MHz bands, and channel occupancy time is configured. 
     Whether or not an eNB commonly includes a PRS transmission subframe in specific channel occupancy time for prescribed time duration can be independently configured for each frequency band via a predefined coordination or a coordination of eNBs via a signal between the eNBs. 
     Or, it may be able to eNB-commonly configure a PRS transmission subframe to be always included in channel occupation time for a specific frequency band for a prescribed time period via a predefined coordination or a coordination of eNBs via a signal between the eNBs. 
     Or, it may be able to eNB-commonly configure a PRS transmission subframe to be included in a partial channel occupation time for a specific frequency band for a prescribed time period via a predefined coordination or a coordination of eNBs via a signal between the eNBs. 
     Meanwhile, according to current LTE standard, a position of an RE to which a PRS is mapped can be shifted on a frequency axis. In this case, a shift value is determined by a physical cell ID. Specifically, since a position of an RE to which a PRS is mapped is determined by a value of (PCID mod 6), if a plurality of eNBs transmit a PRS at the same time, the number of eNBs transmitting a PRS to the same RE increases in some cases and an interference problem may occur. As a result, an accuracy of positioning-related measurement can be reduced. In order to solve the problem, it may be able to configure channel occupancy time to which a PRS transmission subframe belongs to be overlapped between eNBs not transmitting a PRS to the same RE via a predefined coordination or a coordination of eNBs via a signal between the eNBs. Hence, a UE performs blind detection while expecting that a PRS is transmitted in channel occupancy time of eNBs not transmitting the PRS to the same RE on the unlicensed band and performs positioning-related measurement. 
     For example, when a neighboring eNB has PCID 0 to 11, it may be able to configure a PRS transmission subframe shown in  FIG. 12 . Specifically, it may be able to configure an eNB having PCID 0 to 5 to have channel occupancy time to which a PRS transmission subframe belongs during a common time period and configure an eNB having PCID 6 to 11 to have channel occupancy time to which a PRS transmission subframe belongs during a different common time period. 
     In the aforementioned proposals, an eNB becoming a target of coordination can be determined by a location server. Or, whether or not an individual eNB is coordinated can be determined using such a scheme as request and respond in a manner of being triggered by a request of a specific eNB. And, a coordination range can also be indicated by the location server (or, a specific eNB triggering coordination). For example, the location server (or, a specific eNB triggering coordination) may indicate that positioning-related coordination on the unlicensed band is valid for a specific frequency/time resource range only. 
     A UE can independently report a positioning-related measurement value on an unlicensed band and a positioning-related measurement value on a licensed band. For example, the UE can report RSTD and RSTD quality for an unlicensed band and a licensed band, respectively. 
     It may inform a UE of a time period in which a PRS is transmitted via higher layer signaling (or, dynamic signaling) in advance. Or, it may inform the UE of the time period in which the PRS is transmitted by providing a period/offset/burst length to the UE. If the time period in which the PRS is transmitted is included in secured channel occupancy time, an eNB can transmit the PRS. In this case, a burst corresponds to a time period consisting of one or more transmission units (e.g., subframe). 
     The UE performs blind detection on the PRS in a time period in which the PRS is indicated to be transmitted using the aforementioned method to perform positioning-related measurement. 
     As mentioned in the foregoing description, in consideration of a situation that the whole frequency band is divided into narrow frequency bands, CCA is performed on each of the frequency bands to identify a channel state, and channel occupancy time is independently configured, it may inform a UE of a time period in which a PRS is transmitted via higher layer signaling (or, dynamic signaling) in advance. Or, it may inform the UE of the time period in which the PRS is transmitted by providing a period/offset/burst length to the UE. 
     If a time period in which a PRS is transmitted is included in channel occupancy time which is secured according to a frequency band, an eNB can transmit the PRS. In other word, the eNB transmits the PRS during the time period configured to transmit the PRS for all of a part of frequency bands, which have secured channel occupancy time, among a plurality of frequency bands. A UE performs blind detection on the PRS in the time period configured to transmit the PRS according to each frequency band to perform positioning-related measurement. 
     The maximum number of frequency bands on which PRS blind detection is to be performed by a specific eNB at specific timing can be set to a UE. Or, the number of frequency bands capable of performing PRS blind detection from a specific eNB at specific timing can be set to the UE. And, priority of frequency bands to perform PRS blind detection at specific timing can be set to the UE. 
     If a specific eNB is able to configure channel occupancy time to be the same or to be overlapped on contiguous frequency bands, it may be able to transmit a single PRS on the contiguous frequency bands according to a contiguous CA scheme. A UE performs blind detection on the single PRS on the contiguous frequency bands in addition to the blind detection according to a frequency band, combines positioning-related measurement results, and individually or selectively reports the result. 
     In general, a wireless service provider divides a spatial region into cells of appropriate coverage and makes an eNB belonging to each of the cells perform wireless communication with UEs belonging to the cell to minimize inter-cell interference and permit simultaneous transmission between neighboring cells. By doing so, it may be able to enhance overall system performance. This operation may correspond to a preferable operation when LTE system is managed on an unlicensed band. Yet, since LTE nodes (e.g., eNB, UE) on the unlicensed band transmit a signal based on LBT, if a specific node occupies a channel to transmit a signal, a different node determines that the channel is busy according to a CCA result. Hence, it is highly probable that it is unable to reuse a frequency. Hence, in order to maximize frequency reuse of an LBT-based LTE system on an unlicensed band, it is preferable to define a (recommended) node group (e.g., an eNB managed by the same service provider) capable of performing simultaneous transmission. In this case, it is necessary for each node belonging to the node group to recognize a signal transmitted by a different node belonging to the node group in the course of performing CCA and exclude power (or energy) used for transmitting the signal from power (energy) used for performing the CCA. 
     In this case, when a specific frequency/time resource is indicated to transmit a PRS and the resource is included in channel occupancy time, if a neighboring eNB configures channel occupancy time and transmits data, it may work as interference. As a result, accuracy of positioning-related measurement can be degraded. 
     In order to prevent the interference, it may be able to configure a plurality of eNBs to have a common PRS transmission period/offset/burst length on a specific frequency band via a predefined coordination or a coordination of eNBs via a signal between the eNBs. 
     Or, it may be able to configure eNBs not to transmit a PRS or data on a specific frequency band and specific timing via a predefined coordination or a coordination of eNBs via a signal between the eNBs. 
     Hence, a UE may be able to expect that a data is not transmitted at the timing at which a PRS is configured to be transmitted. 
     The UE receives PRS transmission period/offset/burst length information on a plurality of eNBs and a muting pattern of the timing according to a frequency band (or the whole frequency band). The UE performs blind detection on a PRS in a time period configured to transmit the PRS to each eNB to perform positioning-related measurement. 
       FIG. 13  is a flowchart for an operation according to one embodiment of the present invention. 
       FIG. 13  shows a method of receiving a reference signal for determining a position in a wireless communication system. The method can be performed by a terminal. 
     The terminal may receive configuration information about a PRS that is to be transmitted through coordination of at least one or more unlicensed band cells [S 1310 ]. The configuration information may include information on a plurality of subbands in the unlicensed band on which the PRS is transmitted and information on a PRS transmission period according to a plurality of the subbands. The terminal may receive and measure a PRS using the configuration information [S 1320 ]. Subsequently, the terminal may report a measurement result of the PRS to a serving cell [S 1330 ]. 
     In order for the terminal to receive and measure the PRS, the terminal may perform PRS blind detection using the PRS-related configuration information. 
     The terminal may receive information on the number of subbands on which the PRS blind detection is to be performed from the serving cell. The terminal may receive information on priority of subbands on which the PRS blind detection is to be performed from the serving cell. 
     The PRS transmission period information may be common to unlicensed band cells belonging to the same cell group. 
     The PRS transmission period information may include a period, offset, and a burst length for which a PRS is transmitted. 
     The PRS-related configuration information may include information on whether or not a PRS transmission period is included in channel occupation time for the one or more unlicensed band cells. 
     In order for the terminal to receive and measure the PRS, the terminal may perform PRS blind detection in the channel occupation time. 
     The PRS-related configuration information may include information on the channel occupation time and information on the PRS transmission period. 
     The PRS-related configuration information may be received via downlink control information through a licensed band cell or an unlicensed band cell. 
     If a reservation signal is received in a specific time period, the terminal may determine that a PRS transmission subframe is included in channel occupation time for the at least one or more unlicensed band cells. 
     A PRS, which is transmitted via the at least one or more unlicensed band cells, may be transmitted in a resource element where a different unlicensed band cell does not transmit a PRS. 
     A measurement result of the PRS may be independent of a measurement result of a PRS transmitted on a licensed band. 
     So far, embodiments according to the present invention are briefly explained with reference to  FIG. 13 . Yet, the embodiments related to  FIG. 13  may alternatively or additionally include at least a part of the aforementioned embodiment(s). 
       FIG. 14  is a block diagram illustrating a transmitter  10  and a receiver  20  configured to implement embodiments of the present invention. Each of the transmitter  10  and receiver  20  includes a radio frequency (RF) unit  13 ,  23  capable of transmitting or receiving a radio signal that carries information and/or data, a signal, a message, etc., a memory  12 ,  22  configured to store various kinds of information related to communication with a wireless communication system, and a processor  11 ,  21  operatively connected to elements such as the RF unit  13 ,  23  and the memory  12 ,  22  to control the memory  12 ,  22  and/or the RF unit  13 ,  23  to allow the device to implement at least one of the embodiments of the present invention described above. 
     The memory  12 ,  22  may store a program for processing and controlling the processor  11 ,  21 , and temporarily store input/output information. The memory  12 ,  22  may also be utilized as a buffer. The processor  11 ,  21  controls overall operations of various modules in the transmitter or the receiver. Particularly, the processor  11 ,  21  may perform various control functions for implementation of the present invention. The processors  11  and  21  may be referred to as controllers, microcontrollers, microprocessors, microcomputers, or the like. The processors  11  and  21  may be achieved by hardware, firmware, software, or a combination thereof. In a hardware configuration for an embodiment of the present invention, the processor  11 ,  21  may be provided with application specific integrated circuits (ASICs) or digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), and field programmable gate arrays (FPGAs) that are configured to implement the present invention. In the case which the present invention is implemented using firmware or software, the firmware or software may be provided with a module, a procedure, a function, or the like which performs the functions or operations of the present invention. The firmware or software configured to implement the present invention may be provided in the processor  11 ,  21  or stored in the memory  12 ,  22  to be driven by the processor  11 ,  21 . 
     The processor  11  of the transmitter  10  performs predetermined coding and modulation of a signal and/or data scheduled by the processor  11  or a scheduler connected to the processor  11 , and then transmits a signal and/or data to the RF unit  13 . For example, the processor  11  converts a data sequence to be transmitted into K layers through demultiplexing and channel coding, scrambling, and modulation. The coded data sequence is referred to as a codeword, and is equivalent to a transport block which is a data block provided by the MAC layer. One transport block is coded as one codeword, and each codeword is transmitted to the receiver in the form of one or more layers. To perform frequency-up transformation, the RF unit  13  may include an oscillator. The RF unit  13  may include Nt transmit antennas (wherein Nt is a positive integer greater than or equal to 1). 
     The signal processing procedure in the receiver  20  is configured as a reverse procedure of the signal processing procedure in the transmitter  10 . The RF unit  23  of the receiver  20  receives a radio signal transmitted from the transmitter  10  under control of the processor  21 . The RF unit  23  may include Nr receive antennas, and retrieves baseband signals by frequency down-converting the signals received through the receive antennas. The RF unit  23  may include an oscillator to perform frequency down-converting. The processor  21  may perform decoding and demodulation on the radio signal received through the receive antennas, thereby retrieving data that the transmitter  10  has originally intended to transmit. 
     The RF unit  13 ,  23  includes one or more antennas. According to an embodiment of the present invention, the antennas function to transmit signals processed by the RF unit  13 ,  23  are to receive radio signals and deliver the same to the RF unit  13 ,  23 . The antennas are also called antenna ports. Each antenna may correspond to one physical antenna or be configured by a combination of two or more physical antenna elements. A signal transmitted through each antenna cannot be decomposed by the receiver  20  anymore. A reference signal (RS) transmitted in accordance with a corresponding antenna defines an antenna from the perspective of the receiver  20 , enables the receiver  20  to perform channel estimation on the antenna irrespective of whether the channel is a single radio channel from one physical antenna or a composite channel from a plurality of physical antenna elements including the antenna. That is, an antenna is defined such that a channel for delivering a symbol on the antenna is derived from a channel for delivering another symbol on the same antenna. An RF unit supporting the Multiple-Input Multiple-Output (MIMO) for transmitting and receiving data using a plurality of antennas may be connected to two or more antennas. 
     In embodiments of the present invention, the UE operates as the transmitter  10  on uplink, and operates as the receiver  20  on downlink. In embodiments of the present invention, the eNB operates as the receiver  20  on uplink, and operates as the transmitter  10  on downlink. 
     The transmitter and/or receiver may be implemented by one or more embodiments of the present invention among the embodiments described above. 
     Detailed descriptions of preferred embodiments of the present invention have been given to allow those skilled in the art to implement and practice the present invention. Although descriptions have been given of the preferred embodiments of the present invention, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention defined in the appended claims. Thus, the present invention is not intended to be limited to the embodiments described herein, but is intended to have the widest scope consistent with the principles and novel features disclosed herein. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to wireless communication devices such as a terminal, a relay, and a base station.