WO2017171326A1 - Reference signal reception method in v2x communication and device for same - Google Patents

Abstract

Disclosed is a reference signal reception method in vehicle-to-something (V2X) communication. A terminal can receive a first reference signal which is mapped to a first symbol of a subframe and can receive a second reference signal in the subframe on the basis of a reference signal sequence applied to the first reference signal. The reference signal sequence of the first reference signal can indicate a mapping pattern of the second reference signal. Moreover, the symbol to which the first reference signal is mapped can have a cyclic prefix (CP) which is long in comparison with other symbols.

Description

Method for receiving reference signal in V2X communication and apparatus therefor

The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for receiving a reference signal in vehicle-to-something (V2X) communication.

As a discussion of fifth generation mobile communication, there is a discussion about new radio access technology (new RAT). The new radio access technology may support Enhanced Mobile Broadband (eMBB), Massive Machine Type Communication (mMTC), and Ultra Reliable and Low Latency Communications (URLLC). In addition, the new radio access technology can support vehicle-to-something (V2X) communication.

With the development of Intelligent Transportation Systems (ITS), various information such as real-time traffic information and / or safety warnings are being studied for the exchange of vehicles between vehicles. For example, vehicle communications for Proximity Service (ProSe) and Public Warning System are being studied. The communication interface to the vehicle may be collectively referred to as vehicle-to-something (V2X). V2X communication may be classified into vehicle-to-vehicle (V2V) communication, vehicle-to-pedestrian (V2P), and vehicle-to-infrastructure entity (V2I) communication. V2V communication may refer to communication between a vehicle and a vehicle. V2P may refer to communication between a vehicle and a device possessed by an individual (eg, a handheld terminal of a pedestrian or cyclist). In addition, V2I communication may refer to communication between a vehicle and a roadside unit (RSU). An RSU may refer to a traffic infrastructure entity. For example, the RSU may be an entity that sends a speed announcement. The vehicle, RSU, and handheld device may have a transceiver for V2X communication.

As described above, V2X communication may be used to notify a warning about various events such as safety. For example, information about an event that occurred in a vehicle or a road may be known to other vehicles or pedestrians through V2X communication. For example, information about a traffic accident, a change in road conditions, or a warning about an accident's risk may be communicated to other vehicles or pedestrians. For example, pedestrians adjacent to or crossing the road may be informed of the vehicle's access.

However, since it has a higher moving speed than pedestrians, the reliability of V2X communication may be relatively low. For example, due to the Doppler effect, the phase may change significantly. Also, for example, the channel state may change rapidly due to the movement of the vehicle. Accordingly, there is a demand for a method capable of performing highly stable communication in response to a rapidly changing channel condition.

The present invention was devised to solve the above problems, and provides a method for more stable communication in a new wireless access technology including V2X communication.

An object of the present invention is to provide a method for receiving a reference signal in V2X communication and an apparatus therefor.

As an embodiment for achieving the above technical problem, a method of receiving a reference signal of a terminal in vehicle-to-something (V2X) communication, the method comprising: receiving a first reference signal mapped to a first symbol of a subframe; And receiving a second reference signal mapped to the subframe based on the reference signal sequence applied to the first reference signal, wherein the reference signal sequence may indicate a mapping pattern of the second reference signal. .

Also, within the subframe, a symbol to which the first reference signal or the second reference signal is mapped may have a cyclic prefix (CP) of a length longer than the remaining symbols of the subframe.

In addition, a phase offset may be estimated using the CP of the first reference signal.

Also, the reference signal sequence may indicate a symbol or resource element to which the second reference signal is mapped.

In addition, the subframe may include a first slot and a second slot, and the first reference signal may be mapped to a first symbol of the first slot and the second slot.

In addition, the first reference signal may be used for data decoding in the subframe.

Further, the first reference signal and the second reference signal may be mapped onto different symbols of the subframe, and the first reference signal and the second reference signal may be mapped to different subcarriers.

According to embodiments of the present invention, channel estimation performance may be improved in V2X communication.

Dynamic channel estimation for varying channel estimation may be performed in embodiments of the present invention.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description in order to provide a thorough understanding of the present invention, provide an embodiment of the present invention and together with the description, illustrate the technical idea of the present invention.

1 illustrates a system structure of an LTE system that is an example of a wireless communication system.

2 shows a control plane of a wireless protocol.

3 shows a user plane of a wireless protocol.

4 is a diagram illustrating a structure of a type 1 radio frame.

5 is a diagram illustrating a structure of a type 2 radio frame.

6 is a diagram illustrating a resource grid in a downlink slot.

7 illustrates a structure of a downlink subframe.

8 is a diagram illustrating a structure of an uplink subframe.

9 shows a simplified D2D communication network.

10 illustrates a configuration of a resource unit according to an example.

11 shows a simplified V2X communication network.

12 is a diagram illustrating a pattern of a conventional CRS and DRS.

13 is a diagram illustrating an example of a DM RS pattern.

14 is a diagram illustrating examples of a CSI-RS pattern.

FIG. 15A shows the mapping of DMRS in normal cyclic prefix.

FIG. 15B shows the mapping of DMRS in extended cyclic prefix.

16 is a diagram for explaining intersymbol interference.

17 shows the structure of a symbol in one embodiment.

18 illustrates reference signal mapping according to an embodiment.

19 illustrates reference signal mapping according to another embodiment.

20 is a flowchart of a method of receiving a reference signal according to an embodiment.

21 is a schematic diagram of devices according to an embodiment of the present invention.

The following embodiments combine the components and features of the present invention in a predetermined form. Each component or feature may be considered to be optional unless otherwise stated. Each component or feature may be embodied in a form that is not combined with other components or features. In addition, some components and / or features may be combined to form an embodiment of the present invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment.

In the present specification, embodiments of the present invention will be described based on the relationship between data transmission and reception between vehicles. In the following description, the vehicle may mean, for example, a vehicle including a terminal, and may be referred to as a terminal. In the following description, a road side unit (RSU) may mean an infrastructure connectable to a base station, a relay, or a network. Here, the base station has a meaning as a terminal node of the network that directly communicates with the terminal. The specific operation described as performed by the base station in this document may be performed by an upper node of the base station in some cases. In addition, in the following description, a pedestrian includes a pedestrian moving on a bicycle and may mean a pedestrian carrying a terminal.

That is, it is obvious that various operations performed for communication with a terminal in a network composed of a plurality of network nodes including a base station may be performed by the base station or other network nodes other than the base station. A 'base station (BS)' may be replaced by terms such as a fixed station, a Node B, an eNode B (eNB), an access point (AP), and the like. The repeater may be replaced by terms such as relay node (RN) and relay station (RS). In addition, the term “terminal” may be replaced with terms such as a user equipment (UE), a mobile station (MS), a mobile subscriber station (MSS), a subscriber station (SS), and the like.

Specific terms used in the following description are provided to help the understanding of the present invention, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present invention.

In some instances, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

Embodiments of the present invention may be supported by standard documents disclosed in at least one of the wireless access systems IEEE 802 system, 3GPP system, 3GPP LTE and LTE-Advanced (LTE-A) system and 3GPP2 system. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all terms disclosed in the present document can be described by the above standard document.

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used in various radio access systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of an Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is the evolution of 3GPP LTE. WiMAX can be described by the IEEE 802.16e standard (WirelessMAN-OFDMA Reference System) and the advanced IEEE 802.16m standard (WirelessMAN-OFDMA Advanced system). For clarity, the following description focuses on 3GPP LTE and 3GPP LTE-A systems, but the technical spirit of the present invention is not limited thereto.

LTE system structure

A system structure of an LTE system, which is an example of a wireless communication system to which the present invention can be applied, will be described with reference to FIG. 1. The LTE system is a mobile communication system evolved from the UMTS system. As shown in FIG. 1, the LTE system structure can be broadly classified into an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) and an Evolved Packet Core (EPC). The E-UTRAN is composed of a UE (User Equipment, UE) and an eNB (Evolved NodeB, eNB), and is called a Uu interface between the UE and the eNB, and an X2 interface between the eNB and the eNB. The EPC consists of a Mobility Management Entity (MME) that handles the control plane and a Serving Gateway (S-GW) that handles the user plane. The S1-MME interface is used between the eNB and the MME. The eNB and the S-GW are called S1-U interfaces, and they are collectively called S1 interfaces.

The radio interface protocol (Radio Interface Protocol) is defined in the Uu interface, which is a radio section, and consists of a physical layer, a data link layer, and a network layer horizontally. Is divided into a user plane for user data transmission and a control plane for signaling (control signal) transmission. This air interface protocol is based on the lower three layers of the Open System Interconnection (OSI) reference model, which is widely known in communication systems. Layer 1), Layer 2 (L2) including Medium Access Control (MAC) / Radio Link Control (RLC) / Packet Data Convergence Protocol (PDCP) layer, and Layer 3 (L3) including Radio Resource Control (RRC) layer. Third layer). They exist in pairs at the UE and the E-UTRAN, and are responsible for data transmission of the Uu interface.

Description of each layer of the wireless protocol shown in FIG. 2 and FIG. 3 is as follows. 2 is a diagram illustrating a control plane of a radio protocol, and FIG. 3 is a diagram illustrating a user plane of a radio protocol.

A physical layer (PHY) layer, which is a first layer, provides an information transfer service to a higher layer by using a physical channel. The PHY layer is connected to the upper Medium Access Control (MAC) layer through a transport channel, and data between the MAC layer and the PHY layer moves through this transport channel. At this time, the transport channel is largely divided into a dedicated transport channel and a common transport channel according to whether the channel is shared. Then, data is transferred between different PHY layers, that is, between PHY layers of a transmitting side and a receiving side through a physical channel using radio resources.

There are several layers in the second layer. First, the media access control (MAC) layer serves to map various logical channels to various transport channels, and also plays a role of logical channel multiplexing to map multiple logical channels to one transport channel. . The MAC layer is connected to a Radio Link Control (RLC) layer, which is a higher layer, by a logical channel, and the logical channel is a control channel that transmits information on the control plane according to the type of information to be transmitted. It is divided into (Control Channel) and Traffic Channel that transmits user plane information.

The RLC layer of the second layer performs segmentation and concatenation of data received from the upper layer to adjust the data size so that the lower layer is suitable for transmitting data in a wireless section. In addition, in order to guarantee various QoS required by each radio bearer (RB), TM (Transparent Mode), UM (Un-acknowledged Mode), and AM (Acknowledged Mode, Response mode). In particular, the AM RLC performs a retransmission function through an Automatic Repeat and Request (ARQ) function for reliable data transmission.

The Packet Data Convergence Protocol (PDCP) layer of the second layer is an IP containing relatively large and unnecessary control information for efficient transmission in a low bandwidth wireless section when transmitting IP packets such as IPv4 or IPv6. Performs Header Compression which reduces the packet header size. This transmits only the necessary information in the header portion of the data, thereby increasing the transmission efficiency of the radio section. In addition, in the LTE system, the PDCP layer also performs a security function, which is composed of encryption (Ciphering) to prevent third-party data interception and integrity protection (Integrity protection) to prevent third-party data manipulation.

The radio resource control (RRC) layer located at the top of the third layer is defined only in the control plane, and the configuration, re-configuration, and release of radio bearers (RBs) are performed. It is responsible for controlling logical channels, transport channels and physical channels. Here, the radio bearer (RB) refers to a logical path provided by the first and second layers of the radio protocol for data transmission between the terminal and the UTRAN, and in general, the establishment of the RB means a radio protocol required to provide a specific service. The process of defining the characteristics of the layer and the channel and setting each specific parameter and operation method. RB is divided into SRB (Signaling RB) and DRB (Data RB). SRB is used as a channel for transmitting RRC messages in the control plane, and DRB is used as a channel for transmitting user data in the user plane.

LTE / LTE-A Resource Structure / Channel

A structure of a downlink radio frame will be described with reference to FIGS. 4 and 5.

In a cellular OFDM wireless packet communication system, uplink / downlink data packet transmission is performed in subframe units, and one subframe is defined as a predetermined time interval including a plurality of OFDM symbols. The 3GPP LTE standard supports a type 1 radio frame structure applicable to frequency division duplex (FDD) and a type 2 radio frame structure applicable to time division duplex (TDD).

4 is a diagram illustrating a structure of a type 1 radio frame. The downlink radio frame consists of 10 subframes, and one subframe consists of two slots in the time domain. The time taken for one subframe to be transmitted is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms and one slot may have a length of 0.5 ms. One slot includes a plurality of OFDM symbols in the time domain and includes a plurality of resource blocks (RBs) in the frequency domain. In the 3GPP LTE system, since OFDMA is used in downlink, an OFDM symbol represents one symbol period. An OFDM symbol may also be referred to as an SC-FDMA symbol or symbol period. The resource block (RB) is a resource allocation unit and may include a plurality of consecutive subcarriers in one slot.

5 is a diagram illustrating a structure of a type 2 radio frame. Type 2 radio frames consist of two half frames, each of which has five subframes, a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS). One subframe consists of two slots. DwPTS is used for initial cell search, synchronization or channel estimation at the terminal. UpPTS is used for channel estimation at the base station and synchronization of uplink transmission of the terminal. The guard period is a period for removing interference generated in the uplink due to the multipath delay of the downlink signal between the uplink and the downlink. On the other hand, one subframe consists of two slots regardless of the radio frame type.

The structure of the radio frame is only an example, and the number of subframes included in the radio frame or the number of slots included in the subframe and the number of symbols included in the slot may be variously changed.

6 is a diagram illustrating a resource grid in a downlink slot. One downlink slot includes seven OFDM symbols in the time domain, and one resource block (RB) is shown to include twelve subcarriers in the frequency domain, but the present invention is not limited thereto. For example, one slot includes seven OFDM symbols in the case of a general cyclic prefix (CP), but one slot may include six OFDM symbols in the case of an extended-CP (CP). Each element on the resource grid is called a resource element. One resource block includes 12x7 resource elements. The number of NDLs of resource blocks included in a downlink slot depends on a downlink transmission bandwidth. The structure of the uplink slot may be the same as the structure of the downlink slot.

7 illustrates a structure of a downlink subframe. Up to three OFDM symbols in front of the first slot in one subframe correspond to a control region to which a control channel is allocated. The remaining OFDM symbols correspond to data regions to which a physical downlink shared channel (PDSCH) is allocated. The downlink control channels used in the 3GPP LTE system include, for example, a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), and a physical HARQ indicator channel. (PHICH: Physical Hybrid automatic repeat request Indicator CHannel). The PCFICH is transmitted in the first OFDM symbol of a subframe and includes information on the number of OFDM symbols used for control channel transmission in the subframe. The PHICH includes a HARQ Acknowledgment (ACK) / NACK (Negative ACK) signal as a response to uplink transmission. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). DCI includes uplink or downlink scheduling information or an uplink transmit power control command for a certain terminal group. The PDCCH includes a resource allocation and transmission format of a DL shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information of a paging channel (PCH), system information on a DL-SCH, and PD- Resource allocation of upper layer control messages, such as random access responses transmitted on the SCH, sets of transmit power control commands for individual terminals in any terminal group, transmit power control information, Voice over IP (VoIP) Activation may be included. A plurality of PDCCHs may be transmitted in the control region. The terminal may monitor the plurality of PDCCHs. The PDCCH is transmitted in an aggregation of one or more consecutive control channel elements (CCEs). CCE is a logical allocation unit used to provide a PDCCH with a coding rate based on the state of a radio channel. The CCE corresponds to a plurality of resource element groups. The PDCCH format and the number of available bits are determined according to the correlation between the number of CCEs and the coding rate provided by the CCEs. The base station determines the PDCCH format according to the DCI transmitted to the terminal, and adds a cyclic redundancy check (CRC) to the control information. The CRC is masked with an identifier called Radio Network Temporary Identifier (RNTI) according to the owner or purpose of the PDCCH. If the PDCCH is for a specific terminal, the cell-RNTI (C-RNTI) identifier of the terminal may be masked to the CRC. Or, if the PDCCH is for a paging message, a paging indicator identifier, eg, Paging-RNTI (P-RNTI), may be masked in the CRC. If the PDCCH is for system information (more specifically, System Information Block (SIB)), the system information identifier and system information RNTI (SI-RNTI) may be masked to the CRC. Random Access-RNTI (RA-RNTI) may be masked to the CRC to indicate a random access response that is a response to transmission of a random access preamble of the terminal.

8 is a diagram illustrating a structure of an uplink subframe. The uplink subframe may be divided into a control region and a data region in the frequency domain. A physical uplink control channel (PUCCH) including uplink control information is allocated to the control region. A physical uplink shared channel (PUSCH) including user data is allocated to the data area. In order to maintain a single carrier characteristic, one UE does not simultaneously transmit a PUCCH and a PUSCH. PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to a resource block pair occupy different subcarriers for two slots. This is called a resource block pair allocated to the PUCCH is frequency-hopped at the slot boundary. For example, in a D2D communication system, terminals may transmit and receive data to each other using an uplink data resource or a data resource corresponding thereto.

Hereinafter, various embodiments in which a terminal performs device to device communication (hereinafter, may be referred to as D2D communication or D2D direct communication) will be described. Although 3GPP LTE / LTE-A is described as an example for description, D2D communication may be applied to and used in other communication systems (IEEE 802.16, WiMAX, etc.).

D2D communication type

The D2D communication may be classified into a network coordinated D2D communication type and an autonomous D2D communication type according to whether D2D communication is performed through control of a network. The network cooperative D2D communication type may be further classified into a type in which only D2D transmits data (data only in D2D) and a type in which a network performs connection control only (Connection control only in network) according to the degree of network involvement. For convenience of explanation, hereinafter, a type in which only D2D transmits data will be referred to as a 'network-intensive D2D communication type', and a type in which a network performs only connection control will be referred to as a 'distributed D2D communication type'.

In the network centralized D2D communication type, only data is exchanged between D2D terminals, and connection control and radio resource allocation between the D2D terminals are performed by a network. D2D terminals may transmit and receive data or specific control information by using a radio resource allocated by a network. For example, HARQ ACK / NACK feedback or channel state information (CSI) for data reception between D2D terminals may be transmitted to other D2D terminals through a network rather than directly exchanged between the D2D terminals. Specifically, when the network establishes a D2D link between the D2D terminals and allocates radio resources to the established D2D link, the transmitting D2D terminal and the receiving D2D terminal may perform D2D communication using the allocated radio resources. That is, in the network centralized D2D communication type, D2D communication between D2D terminals is controlled by a network, and the D2D terminals may perform D2D communication using radio resources allocated by the network.

The network in the distributed D2D communication type plays a more limited role than the network in the network centralized D2D communication type. In the distributed D2D communication type, the network performs access control between the D2D terminals, but the radio resource allocation (grant message) between the D2D terminals may be occupied by the D2D terminals by themselves without competition. For example, HARQ ACK / NACK feedback or channel state information for data reception between D2D terminals for data reception between D2D terminals may be directly exchanged between D2D terminals without passing through a network.

As in the above-described example, D2D communication may be classified into a network-intensive D2D communication type and a distributed D2D communication type according to the degree of D2D communication intervention of the network. At this time, a common feature of the network-centralized D2D communication type and the distributed D2D communication type is that D2D access control can be performed by a network.

Specifically, a network in a network cooperative D2D communication type may establish a connection between D2D terminals by establishing a D2D link between D2D terminals to perform D2D communication. In setting the D2D link between the D2D terminals, the network may assign a physical D2D link identifier (LID) to the configured D2D link. The physical D2D link ID may be used as an identifier for identifying each of a plurality of D2D links between the plurality of D2D terminals.

In the autonomous D2D communication type, unlike the network centralized and distributed D2D communication types, D2D terminals can freely perform D2D communication without the help of a network. That is, in the autonomous D2D communication type, the D2D UE performs access control and occupation of radio resources by itself, unlike in the network-intensive and distributed D2D communication. If necessary, the network may provide the D2D user equipment with D2D channel information that can be used in the corresponding cell.

Setting up a D2D communication link

For convenience of description herein, a terminal capable of performing or performing D2D communication, which is direct communication between terminals, will be referred to as a D2D terminal. In addition, in the following description, “UE” may refer to a D2D user equipment. When it is necessary to distinguish between a transmitting end and a receiving end, a D2D terminal that transmits or intends to transmit data to another D2D terminal using a radio resource assigned to a D2D link during D2D communication is called a transmitting D2D terminal (D2D TX UE) A terminal that receives or intends to receive data from a transmitting D2D terminal will be referred to as a receiving D2D terminal (D2D RX UE). When there are a plurality of receiving D2D terminals to receive or intend to receive data from the transmitting D2D terminal, the plurality of receiving D2D terminals may be distinguished through a first to N prefix. Furthermore, for convenience of explanation, hereinafter, arbitrary nodes of the network end such as a base station, a D2D server, and an access / session management server for access control between D2D terminals or allocating radio resources to the D2D link will be referred to as 'networks'. Let's do it.

In order to transmit data to other D2D devices via D2D communication, the D2D device needs to check the existence of D2D devices located in the vicinity where data can be transmitted and received. For this purpose, D2D peer discovery ). The D2D UE performs D2D discovery within a discovery interval, and all D2D UEs may share the discovery interval. The D2D UE may receive D2D discovery signals transmitted by other D2D UEs by monitoring logical channels of the discovery area within the discovery period. The D2D terminals receiving the transmission signal of another D2D terminal prepare a list of adjacent D2D terminals using the received signal. In addition, it broadcasts its own information (ie, identifier) within the search interval, and other D2D UEs can receive the broadcast D2D discovery signal to know that the D2D UE exists within a range capable of performing D2D communication. .

Information broadcasting for D2D discovery may be performed periodically. In addition, such broadcast timing may be predetermined by the protocol and known to the D2D terminals. In addition, the D2D UE may transmit / broadcast a signal during a portion of the discovery period, and each D2D UE may monitor signals that are potentially transmitted by other D2D UEs in the remainder of the D2D discovery period.

For example, the D2D discovery signal may be a beacon signal. In addition, the D2D search periods may include a plurality of symbols (eg, OFDM symbols). The D2D UE may transmit / broadcast the D2D discovery signal by selecting at least one symbol within the D2D discovery period. In addition, the D2D user equipment may transmit a signal corresponding to one tone in a symbol selected by the D2D user equipment.

After the D2D UEs discover each other through a D2D discovery process, the D2D UEs may perform a connection establishment process and transmit traffic to another D2D UE.

9 shows a simplified D2D communication network.

In FIG. 9, D2D communication between UEs UE1 and UE2 supporting D2D communication is performed. In general, a user equipment (UE) refers to a terminal of a user, but when a network equipment such as an evolved Node B (eNB) transmits and receives a signal according to a communication scheme between the terminals (UE 1 and UE 2), the eNB may also be a kind of user equipment. May be considered a UE.

UE1 may operate to select a resource unit corresponding to a specific resource in a resource pool, which means a set of resources, and transmit a D2D signal using the resource unit. UE2, which is a reception terminal, may configure a resource pool through which UE1 can transmit a signal, and detect a signal of UE1 in the corresponding pool. For example, when UE1 is in the connection range of the base station, the resource pool may inform the base station. Also, for example, when UE1 is outside the connection range of the base station, another terminal may inform UE1 of the resource pool or UE1 may determine the resource pool based on the predetermined resource. In general, a resource pool is composed of a plurality of resource units, and each terminal may select one or a plurality of resource units and use it for transmitting its own D2D signal.

10 illustrates a configuration of a resource unit according to an example.

In FIG. 10, the vertical axis represents frequency resources and the horizontal axis represents time resources. In addition, the radio resource is divided into N _T pieces on the time axis to configure N _T subframes. In addition, the frequency resource is divided into NF pieces on one subframe, and one subframe may include N _T symbols. Thus, a total of N _F * N _T resource units may be configured as a resource pool.

Since the D2D transmission resource (unit # 0) allocated to unit number 0 is repeated every N _T subframes, in the embodiment of FIG. 10, the resource poll may be repeated every N _T subframes. As shown in FIG. 10, certain resource units may appear periodically and repeatedly. In addition, in order to obtain a diversity effect in a time dimension or a frequency dimension, an index of a physical resource unit to which one logical resource unit is mapped may be changed according to a predetermined pattern. For example, the logical resource unit may be hopped on the time and / or frequency axis according to a predetermined pattern on the actual physical resource unit. In FIG. 10, a resource pool may mean a set of resource units that can be used for transmitting a signal by a terminal to which a D2D signal is to be transmitted.

The above-described resource pool may be subdivided into several types. For example, resource pools may be classified according to content of D2D signals transmitted from each resource pool. For example, the contents of the D2D signal may be classified as described below, and a separate resource pool may be set for each.

Scheduling Assignment (SA): SA (or SA information) is a location of resources used for transmission of a subsequent D2D data channel and a modulation and coding method necessary for demodulation of other data channels (Modulation). and Coding Scheme (MCS) and / or MIMO (Multiple Input Multiple Output) transmission scheme. In addition, the SA information may include an identifier (User Equipment Identifier) of the target terminal to which each transmitting terminal to transmit data. The signal including SA information may be multiplexed with D2D data on the same resource unit and transmitted. In this case, the SA resource pool may mean a resource pool in which scheduling allocation is multiplexed with D2D data and transmitted. .

-D2D data channel: The D2D data channel may mean a pool of resources used by a transmitting terminal to transmit user data by using resources designated through scheduling allocation. If the scheduling allocation can be multiplexed and transmitted together with the D2D resource data on the same resource unit, only a D2D data channel having a form other than the scheduling allocation information may be transmitted in the resource pool for the D2D data channel. That is, on an individual resource unit in the SA resource pool, a resource element for transmitting scheduling allocation information may be used for transmitting D2D data on the resource pool of the D2D data channel.

Discovery message: The discovery message resource pool means a resource pool for transmitting a discovery message that allows a transmitting terminal to transmit information such as its identifier (ID) so that neighboring terminals can discover itself. can do.

As described above, the D2D resource pool may be classified according to the content of the D2D signal. However, even if the contents of the D2D signal are the same, different support pools may be used depending on the transmission / reception attributes of the D2D signal. For example, even when the same D2D data channel or discovery message is transmitted, the transmission timing determination method of the D2D signal (for example, is transmitted at the time of reception of a synchronization reference signal or is applied by applying a certain timing advance at the time of reception). Resource allocation scheme (e.g., whether the eNB assigns a transmission resource of an individual signal to an individual transmission terminal or whether an individual transmission terminal selects its own transmission resource of an individual signal within a resource pool), or a signal format ( For example, each D2D signal may be divided into different resource pools according to the number of symbols occupied by one subframe or the number of subframes used to transmit one D2D signal.

As described above, the UE that wants to transmit data using D2D communication may first select an appropriate resource from the SA resource pool and transmit its own scheduling allocation (SA) information. In addition, for example, as the selection criteria of the SA resource pool, it is expected that there will be no data transmission in a resource not used for transmission of SA information of another terminal and / or a subframe following transmission of SA information of another terminal. The SA resource associated with the resource may be selected as the SA resource pool. In addition, the UE may select an SA resource linked to a data resource that is expected to have a low interference level. In addition, SA information may be broadcasted. Accordingly, terminals in the D2D communication system may receive broadcasted SA information. In the following description, "send" or "send" may be replaced with "broadcasting".

In the above-described D2D communication, the term D2D may be replaced with sidelinks.

11 shows a simplified V2X communication network.

V2X communication may be classified into vehicle-to-vehicle (V2V) communication, vehicle-to-pedestrian (V2P), and vehicle-to-infrastructure entity (V2I) communication. V2V communication may refer to communication between the vehicle 1101 and the vehicle 1102. Traffic information and the like may be shared between the vehicle 1101 and the vehicle 1102 through V2V communication. V2P may refer to communication between the vehicle 1101 and a device carried by the pedestrian 1103 (eg, a handheld terminal of a pedestrian or bicyclist). Since the pedestrian 1103 may also move along sidewalks adjacent to the road, information on dangers on the road may be shared through V2P communication. Also, V2I communication may refer to communication between the vehicle 1101 and a roadside unit (RSU) 1104. The RSU 1104 may refer to a traffic infrastructure entity. For example, the RSU 1104 may be an entity that sends a speed announcement. The handheld devices of the vehicles 1101, 1102, the RSU 1104, and the pedestrian 1103 may have a transceiver for V2X communication. V2X communication may be implemented using a technology similar to device-to-device (D2D) communication of the communication standard of the 3rd generation partnership project (3GPP). In addition, V2X communication may be implemented using a dedicated short-range communications (DSRC) technology of the Institute of Electrical and Electronics Engineers (IEEE).

Hereinafter, a method of transmitting an alarm message through V2X communication according to an embodiment of the present application will be described. In the following description, the following description will focus on V2V communication, but the following embodiments may be applied to V2I and / or V2P communication. In addition, the following embodiments are described based on the communication standards of 3GPP, but may also be implemented by techniques corresponding to the communication standards of IEEE. In addition, in the following description, the terms transmission and broadcasting may be interchanged. In addition, in the following description, a vehicle or a pedestrian may mean a vehicle or a pedestrian carrying user equipment. In the following description, a vehicle or a pedestrian may be used as a term meaning the terminal itself.

Reference Signal (RS)

When transmitting a packet in a wireless communication system, since the transmitted packet is transmitted through a wireless channel, signal distortion may occur during the transmission process. In order to correctly receive the distorted signal at the receiving end, the distortion must be corrected in the received signal using the channel information. In order to find out the channel information, a method of transmitting the signal known to both the transmitting side and the receiving side and finding the channel information with the distortion degree when the signal is received through the channel is mainly used. The signal is called a pilot signal or a reference signal.

When transmitting and receiving data using multiple antennas, it is necessary to know the channel condition between each transmitting antenna and the receiving antenna to receive the correct signal. Therefore, a separate reference signal must exist for each transmit antenna.

In a mobile communication system, RSs can be classified into two types according to their purpose. One is an RS used for channel information acquisition, and the other is an RS used for data demodulation. Since the former is an RS for allowing the terminal to acquire downlink channel information, the former should be transmitted over a wide band, and even if the terminal does not receive downlink data in a specific subframe, it should be able to receive and measure the corresponding RS. Such RS is also used for measurement for handover and the like. The latter is an RS that is transmitted together with the corresponding resource when the base station transmits a downlink, and the terminal can estimate the channel by receiving the corresponding RS, thus demodulating data. This RS should be transmitted in the area where data is transmitted.

In the existing 3GPP LTE (eg, 3GPP LTE Release-8) system, two types of downlink RSs are defined for unicast services. One of them is a common reference signal (Common RS, CRS), the other is a dedicated reference signal (Dedicated RS, DRS). The CRS is used for measurement of channel state information, measurement for handover, and the like, and may be referred to as cell-specific RS. DRS is used for data demodulation and may be referred to as UE-specific RS. In the existing 3GPP LTE system, DRS is used only for data demodulation, and CRS can be used for both purposes of channel information acquisition and data demodulation.

The CRS is a cell-specific RS and is transmitted every subframe for a wideband. The CRS may be transmitted for up to four antenna ports according to the number of transmit antennas of the base station. For example, if the number of transmitting antennas of the base station is two, CRSs for antenna ports 0 and 1 are transmitted, and if four, CRSs for antenna ports 0 to 3 are transmitted.

FIG. 12 is a diagram illustrating patterns of CRSs and DRSs on one resource block (14 OFDM symbols in time x 12 subcarriers in frequency in case of a general CP) in a system in which a base station supports four transmit antennas. In FIG. 5, resource elements RE denoted as 'R0', 'R1', 'R2' and 'R3' indicate positions of CRSs for antenna port indexes 0, 1, 2, and 3, respectively. Meanwhile, the resource element denoted as 'D' in FIG. 5 indicates the position of the DRS defined in the LTE system.

LTE-A system of the advanced evolution of the LTE system, can support up to eight transmit antennas in the downlink. Therefore, RS for up to eight transmit antennas should also be supported. Since the downlink RS in the LTE system is defined for up to four antenna ports only, if the base station has four or more up to eight downlink transmission antennas in the LTE-A system, RSs for these antenna ports must be additionally defined. do. As RS for up to eight transmit antenna ports, both RS for channel measurement and RS for data demodulation should be considered.

One of the important considerations in designing an LTE-A system is backward compatibility. Backward compatibility means that the existing LTE terminal supports to operate correctly in the LTE-A system. From the point of view of RS transmission, if RS is added for up to eight transmit antenna ports in the time-frequency domain where CRS defined in the LTE standard is transmitted every subframe over the entire band, the RS overhead becomes excessively large. do. Therefore, in designing RS for up to 8 antenna ports, consideration should be given to reducing RS overhead.

RS newly introduced in LTE-A system can be classified into two types. One of them is an RS for channel measurement for selecting a transmission rank, a modulation and coding scheme (MCS), a precoding matrix index (PMI), and the like. Channel State Information RS (CSI-RS), and the other is a demodulation-reference signal (DM RS) which is an RS for demodulating data transmitted through up to eight transmit antennas.

CSI-RS for channel measurement purposes is characterized in that the CRS in the existing LTE system is designed for channel measurement-oriented purposes, unlike the CRS used for data demodulation at the same time as the channel measurement, handover, etc. have. Of course, the CSI-RS may also be used for the purpose of measuring handover. Since the CSI-RS is transmitted only for the purpose of obtaining channel state information, unlike the CRS in the existing LTE system, the CSI-RS does not need to be transmitted every subframe. Thus, to reduce the overhead of the CSI-RS, the CSI-RS may be designed to be transmitted intermittently (eg, periodically) on the time axis.

If data is transmitted on a downlink subframe, a DM RS is transmitted to a terminal scheduled for data transmission. The DM RS dedicated to a specific terminal may be designed to be transmitted only in a resource region in which the terminal is scheduled, that is, in a time-frequency region in which data for the terminal is transmitted.

13 is a diagram illustrating an example of a DM RS pattern defined in an LTE-A system. In FIG. 6, a position of a resource element in which a DM RS is transmitted is transmitted on one resource block in which downlink data is transmitted (14 OFDM symbols in time and 12 subcarriers in frequency). The DM RS may be transmitted for four antenna ports ( antenna port indexes 7, 8, 9 and 10) which are additionally defined in the LTE-A system. DM RSs for different antenna ports may be divided into being located in different frequency resources (subcarriers) and / or different time resources (OFDM symbols) (ie, may be multiplexed in FDM and / or TDM schemes). In addition, DM RSs for different antenna ports located on the same time-frequency resource may be distinguished from each other by orthogonal codes (ie, multiplexed in the CDM manner). In the example of FIG. 13, DM RSs for antenna ports 7 and 8 may be located in resource elements REs indicated as DM RS CDM group 1, which may be multiplexed by an orthogonal code. Likewise, DM RSs for antenna ports 9 and 10 may be located in resource elements indicated as DM RS group 2 in the example of FIG. 13, which may be multiplexed by an orthogonal code.

14 is a diagram illustrating examples of a CSI-RS pattern defined in an LTE-A system. FIG. 14 shows the location of a resource element in which a CSI-RS is transmitted on one resource block in which downlink data is transmitted (14 OFDM symbols in time and 12 subcarriers in frequency). In some downlink subframes, the CSI-RS pattern of one of FIGS. 14 (a) to 14 (e) may be used. The CSI-RS may be transmitted for eight antenna ports ( antenna port indexes 15, 16, 17, 18, 19, 20, 21, and 22) which are additionally defined in the LTE-A system. CSI-RSs for different antenna ports may be divided into being located in different frequency resources (subcarriers) and / or different time resources (OFDM symbols) (ie, may be multiplexed in FDM and / or TDM schemes). In addition, CSI-RSs for different antenna ports located on the same time-frequency resource may be distinguished from each other by orthogonal codes (ie, multiplexed in a CDM manner). In the example of FIG. 14 (a), CSI-RSs for antenna ports 15 and 16 may be located in the resource elements RE denoted as CSI-RS CDM group 1, which may be multiplexed by an orthogonal code. In the example of FIG. 14A, CSI-RSs for antenna ports 17 and 18 may be located in resource elements indicated as CSI-RS CDM group 2, which may be multiplexed by an orthogonal code. In the example of FIG. 14A, CSI-RSs for antenna ports 19 and 20 may be located in resource elements indicated as CSI-RS CDM group 3, which may be multiplexed by an orthogonal code. In the example of FIG. 14 (a), CSI-RSs for antenna ports 21 and 22 may be located in resource elements indicated as CSI-RS CDM group 4, which may be multiplexed by an orthogonal code. The same principle described with reference to FIG. 14A may be applied to FIGS. 14B through 14E.

The RS patterns of FIGS. 12 to 14 are merely exemplary and are not limited to specific RS patterns in applying various embodiments of the present invention. That is, even when RS patterns different from those of FIGS. 12 to 14 are defined and used, various embodiments of the present invention may be equally applied.

The following descriptions are explained on the assumption of vehicle-to-something (V2X), for example V2V, communication, but may be applied to other communications such as D2D. As described above, in some scenarios in which the terminal moves (eg, V2X), a frequency offset error may occur. For example, due to the Doppler effect, when the received signal exceeds a certain range of frequency offset, the receiving terminal may not be able to decode the received signal.

FIG. 15A illustrates the mapping of the DeModulation Reference Signal (DMRS) to the normal cyclic prefix, and FIG. 15B illustrates the mapping of the DMRS to the extended cyclic prefix.

For example, in V2X communication, a subframe structure having a conventional LTE PUSCH (Physical Uplink Shared Channel) structure may be used. In the current LTE system, DMRS in a subframe of a normal cyclic prefix (CP) may be arranged as shown in FIG. 15A. As shown in FIG. 15A, for example, the DMRS may be disposed in 3rd and 10th Orthogonal Frequency Division Multiplexing (OFDM) symbols. In addition, in the current LTE system, the DMRS in the subframe of the extended CP may be arranged as shown in FIG. 15B. As shown in FIG. 15B, for example, the DMRS may be disposed in OFDM symbols 2 and 8.

The new radio access technology (new RAT), which is currently under discussion, can support a terminal with a moving speed of 500 km per hour. In addition, in a new radio access technology, a carrier frequency of 100 GHz may be supported. Therefore, due to an increase in the moving speed of the terminal and an increase in the carrier frequency, the phase offset due to the Doppler Effect and the frequency offset may change rapidly. Therefore, a reference signal can be newly designed for estimating such a phase offset.

The Doppler effect when the carrier frequency of 6 GHz is used is approximately 2.8 KHz, and the Doppler effect when the carrier frequency of 30 GHz is used is approximately 14 KHz. The frequency offset when the carrier frequency of 6 GHz is used is approximately 0.6 KHz, and the frequency offset when the carrier frequency of 30 GHz is used is approximately 3 KHz. When the carrier frequency of 6 GHz is used, the effect of the Doppler effect and the frequency offset is approximately 3.4 KHz. In addition, when a carrier frequency of 30 GHz is used, the effects of the Doppler effect and the frequency offset are approximately 17 KHz. Thus, when a carrier frequency of 6 GHz is used, the coherence time is about 0.147 ms. In addition, when a carrier frequency of 30 GHz is used, the coherence time is about 0.03 ms. It can be assumed that one transmission time interval (TTI) includes 14 symbols and has a length of 0.2 ms. Thus, about 10 symbols are interfered when a carrier frequency of 6 GHz is used. In addition, about two symbols are interfered when a carrier frequency of 30 GHz is used. In addition, as described above, when the carrier frequency is increased to 30GHz or more, or when the mobility of the terminal is high, such as V2X communication, the magnitude of the phase offset may be further increased.

Thus, for the correction of the phase offset, the density of the reference signal on the time axis can be increased. In addition, the phase offset changes over time. Therefore, a reference signal having a high density has an advantage in phase offset correction. As described above, in a new radio access technology including V2X communication, high carrier frequency and high terminal mobility may be required. Therefore, in the new radio access technology, a new type of reference signal may be used to correct the phase offset.

Referring back to FIG. 12, the downlink common reference signal (CRS) of the current LTE system is mapped to OFDM symbols 0, 4, 8, and 11 in the case of antenna ports 0 and 1. In a new radio access technology, reference signal mapping similar to that of FIG. 12 may be used. For example, the phase offset may be estimated through channel comparison between OFDM symbol 0 and OFDM symbol 4. In this case, however, it is difficult to estimate the phase offset of a channel having a coherence time of 2 symbols or less.

Referring back to FIG. 12, the downlink CRS of the LTE system is transmitted at intervals of six resource elements (REs) in one OFDM symbol. That is, the CRS is transmitted every six resource elements in the frequency domain. Such reference signal mapping may be referred to as reference signal mapping in the form of a six comb. In comb-shaped reference signal mapping, a reference signal is mapped to a plurality of symbols in a subframe, and a reference signal mapped to a previous symbol and a reference signal mapped to a subsequent symbol do not overlap on the frequency domain.

In comb-shaped reference signal mapping, the reference signal is repeated on the time axis. Therefore, the phase offset may be estimated by comparing the repeated reference signals. However, data may also be transmitted in the OFDM symbol to which the reference signal is transmitted. That is, some resource elements of one OFDM symbol may be used for the reference signal, and the remaining resource elements may be used for data transmission. In this case, in order to compare the reference signals on the time axis, it is necessary to puncture the data of the symbol to which the reference signals are mapped. Accordingly, resource elements mapped with data on the frequency axis must be punctured, and then the reference signals must be compared on the time axis. Thus, the complexity for phase offset estimation can be increased.

Hereinafter, a reference signal for solving the above-described problem will be described. The following reference signals may be used for estimation of phase offset or channel estimation. In addition, the following reference signal may be for a new radio access technology.

Referring to FIG. 16, due to delay spread, inter-symbol interference (ISI) occurs at the receiving end. Thus, to prevent intersymbol interference, each OFDM symbol has a guard interval called cyclic prefix. In the current LTE system, as shown in FIGS. 15A and 15B, two kinds of cyclic prefixes may be used according to channel conditions. Circular transposition is created by additionally mapping the rear part of the symbol to the front of the symbol.

For example, an OFDM symbol to which a reference signal is mapped may have a CP longer than a cyclic prefix (CP) of an OFDM symbol to which the reference signal is not mapped. As described above, the CP of an OFDM symbol is a repetition of a portion of the symbol. Therefore, except for a section in which inter-symbol interference occurs due to delay spread, a part of the OFDM symbols except for CP is repeated. Therefore, since a part of the OFDM symbol is repeated in a part of the CP and the back of the OFDM symbol, the estimation of the phase offset can be performed in one OFDM symbol by comparing the two signals.

17 shows the structure of a symbol in one embodiment.

In FIG. 17, symbols corresponding to one subcarrier in one slot are shown. In the embodiment of FIG. 17, the CP has the same signal as the CP corresponding section. As described above, the portion due to delay spread cannot be used due to the intersymbol interference. Therefore, a portion of the CP except for delay spread and a portion of the CP corresponding section have the same signal. Accordingly, the estimation of the phase offset in one OFDM symbol may be performed by comparing the portion a and the portion b of FIG. 17.

In addition, when phase offset estimation is performed in one OFDM symbol, the estimated phase offset may be applied to adjacent symbols. Thus, the phase offset can be estimated without using a reference signal mapped to another symbol on the time axis. Therefore, the reference signal density can be reduced by mapping the reference signal to only one symbol for each beam. In addition, a reference signal may be mapped to only one symbol for a plurality of beams transmitted for the same channel.

For example, part of the control channel may be transmitted in a different beam than the data channel for information intended for all terminals in the cell. In addition, part of the control channel may be transmitted using only OFDM symbols of a shorter length than one conventional subframe. In this case, estimation of phase offset using one OFDM symbol may be used. Therefore, as described above, a reference signal may be mapped to only one OFDM symbol.

In a new radio access technology, a reference signal may be mapped to the first OFDM symbol of a subframe. For example, a reference signal for the downlink control channel may be transmitted in the first OFDM symbol of the subframe. In addition, the downlink control channel may be decoded or received based on the reference signal of the first OFDM symbol. By transmitting a reference signal in the first OFDM of the subframe, the downlink control channel can be quickly decoded.

However, it may be difficult to estimate the phase offsets of all downlink channels using only the reference signal mapped to the first OFDM symbol. Thus, within a subframe, an additional reference signal can be transmitted. For example, for even mapping of the reference signals, additional reference signals may be mapped onto the first OFDM symbol of the second slot of the subframe. That is, the reference signal may be mapped to the first OFDM symbol of each slot. Hereinafter, the additional reference signal may refer to a reference signal other than the first reference signal of the subframe or slot on the time axis. In addition, hereinafter, the first reference signal may refer to a reference signal mapped to the first OFDM symbol of a subframe or slot on the time axis.

For example, additional reference signals may be mapped based on channel conditions, frame structure, and / or carrier frequency. For example, in the case of a specific carrier frequency, all channels of each slot may be estimated using the reference signal of the first symbol. On the other hand, for other carrier frequencies, all channels of each slot may not be estimated using the reference signal of the first symbol. For example, if a carrier frequency of 6 GHz is used, the coherence time is 0.147 ms, so that a channel of approximately one subframe (for example, 0.2 ms) can be estimated based on the first reference signal of each slot. It may be. However, when a carrier frequency of 30 GHz is used, in addition to the reference signal mapped to the first symbol of each slot, an additional reference signal may be required because the coherence time is very short. Thus, for example, additional reference signals may be mapped in a frame structure above a certain length, a channel state below a threshold (eg, CQI), and / or a carrier frequency above a predetermined value.

Information about the additional reference signal may be transmitted through Radio Resource Control (RRC) signaling. In addition, information about the additional reference signal may be transmitted through control information (eg, downlink control information). The information of the additional reference signal may indicate the DMRS pattern of the additional reference signal. For example, the information of the additional reference signal may directly or indirectly indicate the information of the additional reference signal included in one transmission time interval (TTI). Also, for example, the information of the additional reference signal may include information of OFDM symbols to which the additional reference signal is mapped.

In addition, the information of the additional reference signal may be indicated by the reference signal sequence of the first reference signal. For example, the information of the additional reference signal may correspond to the information of the additional reference signal included in the slot. Also, for example, the information of the additional reference signal may include information of at least one OFDM symbol to which the additional reference signal is mapped in the slot.

In addition, for example, the information of the additional reference signal may be preset according to the carrier frequency and / or frame structure. In addition, as described above, the information of the additional reference signal may be preset according to the situation of the channel. For example, the information of the additional reference signal may correspond to the information of the additional reference signal included in the slot or TTI. In addition, for example, the information of the additional reference signal may include information of at least one OFDM symbol to which the additional reference signal is mapped in a slot or TTI. For example, in the case of V2X communication, the roadside unit (RSU) may be preset with a DMRS pattern based on surrounding conditions. For example, when the roadside unit is located in the city or on the highway, the average speed of the vehicles around each time can be predicted. Accordingly, the DMRS pattern of the additional reference signal used by the roadside unit may be preset based on the position of the roadside unit. For example, as the average speed is higher, the reference signal density of the additional reference signal may increase.

As described above, an OFDM symbol in which a reference signal is located may have a longer length CP than other OFDM symbols in a slot or subframe. In addition, the reference signal density in a slot or subframe may vary. In this case, in order to align symbol boundaries, the CP lengths of all OFDM symbols to which the reference signals are mapped may be increased. In addition, the reference signal may be mapped in a comb form within a slot or subframe. For example, the reference signal may be mapped in a symbol at intervals of six resource elements. In this case, resource elements to which a reference signal is not mapped may be used for data transmission. Meanwhile, when the CP of OFDM symbols mapped with a reference signal is increased, the number of OFDM symbols in a subframe may be reduced or the length of the subframe may be increased. In addition, the CP length of the remaining OFDM symbols to which the reference signal is not mapped may be reduced. In addition, even if the CP of the OFDM symbol to which the reference signal is mapped is increased, the size of the OFDM symbol to which the reference signal is mapped may be maintained. That is, as the CP increases, the length of the remaining reference signals in the symbol may decrease.

18 illustrates reference signal mapping according to an embodiment.

In the embodiment of Fig. 18, the first reference signal is the first reference signal of the slot. In addition, the second reference signal may correspond to the additional reference signal of the above-described embodiments. As described above, the reference signal sequence of the first reference signal may indicate information about the second reference signal. For example, the reference signal sequence of the first reference signal may include information of a symbol to which the second reference signal is mapped, a reference signal sequence mapped to the second reference signal, and / or a symbol to which the second reference signal existing in the slot is mapped. It can indicate the number of.

In addition, as described above, a symbol to which the first reference signal and the second reference signal are mapped may have a CP having a longer length than other remaining symbols. In addition, channel estimation (eg, phase offset estimation) may be performed based on one OFDM symbol to which the first reference signal or the second reference signal is mapped.

19 illustrates reference signal mapping according to another embodiment.

The embodiment of FIG. 19 is similar to the embodiment of FIG. 18. Therefore, the above descriptions with respect to the embodiment of FIG. 18 may be equally applied to the embodiment of FIG. 19. However, in the embodiment of FIG. 19, the first reference signal and the second reference signal are mapped to a comb type. Accordingly, the reference signal sequence applied to the first reference signal may indicate a pattern to which the second reference signal is mapped. That is, the first reference signal and the second reference signal may be mapped on different symbols and different subcarriers.

The reference signal sequence of the first reference signal may directly or indirectly indicate a resource element to which the second reference signal is mapped. In the embodiment of FIG. 19, the first reference signal and the second reference signal are mapped at intervals of six resource elements on the frequency axis. That is, five resource elements exist between two resource elements to which each reference signal is mapped on the frequency axis. In addition, the interval between resource elements is not limited to FIG. 19. The first reference signal and the second reference signal may be mapped at intervals of resource elements different from those of FIG. 19.

20 is a flowchart of a method of receiving a reference signal according to an embodiment.

The UE may receive a subframe including the reference signal (S2001). As described above, the reference signal may include a first reference signal and a second reference signal. For example, the terminal may receive the first reference signal in the first symbol of the subframe and receive the second reference signal based on the reference signal sequence applied to the first reference signal. As described above, the first reference signal may be mapped to the first symbol of the slot. For example, the reference signal sequence of the first reference signal may indicate a pattern to which the second reference signal is mapped. Also, for example, the reference signal sequence may indicate a symbol or resource element to which the second reference signal is mapped. The above-described mapping of the reference signal can be applied to this embodiment.

In addition, as described above, the terminal may perform channel estimation (S2002) based on the reference signal. For example, the terminal may perform channel estimation using one symbol to which a reference signal is mapped. For example, the terminal may estimate the phase offset. In addition, the terminal may decode the data (S2003) based on the reference signal. As described above, the symbol to which the reference signal is mapped may have a cyclic prefix having a length longer than the remaining symbols in the subframe. In addition, the terminal may estimate the phase offset using the cyclic prefix.

Although omitted for convenience of description, the above-described embodiments may be combined with the reference signal receiving method of FIG. 20.

FIG. 21 is a diagram for schematically describing a configuration of devices to which the embodiments of the present invention described with reference to FIGS. 1 to 20 may be applied as an embodiment of the present invention.

In FIG. 21, the first device 2100 and the second device 2150 may include radio frequency units (RF units) 2110 and 2160, processors 2120 and 2170, and optionally memories 2130 and 2180. have. The first device 2100 and the second device 2150 may be terminals, vehicles, pedestrians, RSUs, base stations, and / or infrastructure constituting V2X communication.

Each radio frequency (RF) unit 2130, 2160 may include a transmitter 2111, 2161 and a receiver 2112, 2162, respectively. Each RF unit 2130, 2160 may be a transceiver. The transmitter 2111 and the receiver 2112 of the first device 2100 are configured to transmit and receive signals with the second device 2150 and other terminals, and the processor 2120 is configured to send the transmitter 2111 and the receiver 2112. May be functionally connected to the transmitter 2111 and the receiver 2112 to control a process of transmitting and receiving signals with other devices. Meanwhile, the first device 2100 and / or the second device 2150 may be a base station.

In addition, the processor 2120 may perform various processing on the signal to be transmitted, transmit the same to the transmitter 2111, and may perform processing on the signal received by the receiver 2112. If necessary, the processor 2120 may store information included in the exchanged message in the memory 2130.

With the above-described structure, the first device 2100 can perform the method of various embodiments of the present invention described above. For example, each signal and / or message may be transmitted and received using a transmitter and / or receiver of an RF unit, and each operation may be performed under the control of a processor.

Although not shown in FIG. 21, the first device 2100 may include various additional components according to the device application type. For example, when the first device 2100 is for intelligent metering, the first device 2100 may include an additional configuration for power measurement, and the like. The power measurement operation may be performed by the processor 2120. It may be controlled, or may be controlled by a separately configured processor (not shown).

For example, the second device 2150 may be a base station. In this case, the transmitter 2161 and the receiver 2162 of the base station are configured to transmit and receive signals with other base stations, servers, and devices, and the processor 2170 is functionally connected to the transmitter 2161 and the receiver 2162. The transmitter 2161 and the receiver 2162 may be configured to control a process of transmitting and receiving a signal with other devices. In addition, the processor 2170 may perform various processing on a signal to be transmitted, transmit the same to the transmitter 2161, and may perform processing on a signal received by the receiver 2162. If necessary, the processor 2170 may store information included in the exchanged message in the memory 2130. With this structure, the base station 2150 can perform the methods of the various embodiments described above.

In FIG. 21, the processors 2120 and 2170 of each of the first device 2110 and the second device 2150 instruct an operation (eg, control) in the first device 2110 and the second device 2150, respectively. , Coordination, management, etc.). Respective processors 2120 and 2170 may be connected to memories 2130 and 2180 that store program codes and data. The memories 2130 and 2180 are coupled to the processors 2120 and 2170 to store operating systems, applications, and general files.

The processors 2120 and 2170 of the present invention may also be referred to as a controller, a microcontroller, a microprocessor, a microcomputer, or the like. The processors 2120 and 2170 may be implemented by hardware or firmware, software, or a combination thereof. When implementing embodiments of the present invention using hardware, application specific integrated circuits (ASICs) or digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs) configured to perform the present invention. Field programmable gate arrays (FPGAs) may be provided in the processors 2120 and 2170.

Meanwhile, when implementing embodiments of the present invention using firmware or software, the firmware or software may be configured to include a module, a procedure, or a function for performing the functions or operations of the present invention, and to perform the present invention. Firmware or software configured to be may be provided in the processor or stored in a memory to be driven by the processor.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

It is apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit and essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

Embodiments of the present invention as described above may be applied to various mobile communication systems.

Claims (14)

1. A method of receiving a reference signal of a terminal in V2X (Vehicle-to-Something) communication,

   Receiving a first reference signal mapped to a first symbol of a subframe; And

   Receiving a second reference signal mapped to the subframe based on a reference signal sequence applied to the first reference signal,

   The reference signal sequence indicates a mapping pattern of the second reference signal.
2. The method of claim 1,

   In the subframe, the symbol to which the first reference signal or the second reference signal is mapped has a cyclic prefix (CP) of a longer length than the remaining symbols of the subframe.
3. The method of claim 2,

   And a phase offset is estimated using the CP of the first reference signal.
4. The method of claim 1,

   The reference signal sequence indicates a symbol or resource element to which the second reference signal is mapped.
5. The method of claim 1,

   The subframe consists of a first slot and a second slot,

   And the first reference signal is mapped to a first symbol of a first slot and a second slot.
6. The method of claim 1,

   The first reference signal is used for data decoding in the subframe.
7. The method of claim 1,

   The first reference signal and the second reference signal are mapped onto different symbols of the subframe,

   And the first reference signal and the second reference signal are mapped on different subcarriers.
8. A terminal for receiving a reference signal in V2X (Vehicle-to-Something) communication,

   Transceiver; And

   A processor configured to control the transceiver;

   The processor,

   Receive a first reference signal mapped to a first symbol of a subframe, and

   And receive a second reference signal mapped to the subframe based on the reference signal sequence applied to the first reference signal.

   The RS sequence indicates a mapping pattern of the second RS.
9. The method of claim 8,

   Within the subframe, the symbol to which the first reference signal or the second reference signal is mapped has a cyclic prefix (CP) of a length longer than the remaining symbols of the subframe.
10. The method of claim 9,

    And the processor is further configured to further estimate a phase offset using the CP of the first reference signal.
11. The method of claim 8,

    The RS sequence indicates a symbol or resource element to which the second RS is mapped.
12. The method of claim 8,

    The subframe consists of a first slot and a second slot,

    The first reference signal is mapped to a first symbol of a first slot and a second slot.
13. The method of claim 8,

    The first reference signal is used for data decoding in the subframe.
14. The method of claim 8,

    The first reference signal and the second reference signal are mapped onto different symbols of the subframe,

    The first reference signal and the second reference signal are mapped to different subcarriers.

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