Method and apparatus for transmitting a synchronization signal for device-to-device communication in a wireless communication system

Abstract

The exemplary embodiments herein provide a method and apparatus for transmitting a synchronization signal for device-to-device (D2D) communication in a wireless communication system. The method includes: generating a D2D synchronization signal (D2DSS) from a D2D synchronization source that transmits the synchronization signal for D2D communication; and transmitting the D2DSS from the synchronization source to a UE performing D2D reception (Rx), wherein the D2DSS includes a primary D2D synchronization signal (PD2DSS) generated based on information associated with the synchronization source.

Description

[0001] This case is a divisional application of Chinese invention patent application 201480079714.4, entitled “Method and apparatus for transmitting synchronization signals for device-to-device communication in a wireless communication system,” filed on August 8, 2014.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to and the benefit of U.S. Provisional Application No. 61 / 979,003, filed on April 14, 2014, and Korean Patent Application No. 10-2014-0103977, filed on August 11, 2014, the disclosures of each of which are incorporated herein by reference in their entirety. Technical Field

[0004] The exemplary embodiments described herein relate to wireless communications, and more particularly, to a method and apparatus for transmitting a synchronization signal for device-to-device (D2D) communication in a wireless communication system. Background Art

[0005] Device-to-device (D2D) communication refers to a communication scheme that performs direct data transmission and reception between two adjacent user equipments (UEs) without an evolved Node B (eNode B). In other words, the two UEs act as the source and destination of data and perform communication.

[0006] D2D communication can be performed using a communication scheme that uses unlicensed frequency bands, such as wireless local area networks (LANs) and Bluetooth. However, communication schemes using unlicensed frequency bands struggle to provide planned and controlled services. In particular, their performance can be significantly degraded due to interference.

[0007] In contrast, D2D communications operated or provided in licensed frequency bands or in an environment with controlled inter-system interference can support Quality of Service (QoS), improve frequency usage efficiency through frequency reuse, and increase communication distance.

[0008] In D2D communication in a licensed frequency band, that is, in D2D communication based on cellular communication, the eNode B allocates UE resources, and the allocated resources may use cellular uplink channels.

[0009] D2D communication may include intra-cell D2D communication and inter-cell D2D communication. Inter-cell D2D communication may be implemented based on cooperative communication between two eNodeBs.

[0010] Therefore, what is needed is a method for efficiently utilizing resources for D2D communication services and allocating synchronization signals therefor in a recent wireless communication system. Summary of the Invention

[0011] One or more exemplary embodiments herein provide a method and apparatus for transmitting a synchronization signal for device-to-device (D2D) communication in a wireless communication system.

[0012] One or more exemplary embodiments herein provide a method and apparatus for configuring a synchronization signal in a wireless communication system supporting D2D communication.

[0013] One or more exemplary embodiments herein provide a method and apparatus for configuring a synchronization signal sequence with good correlation.

[0014] One or more embodiments herein provide a method for transmitting and receiving synchronization signals using device-to-device (D2D) communication between supporting UEs, the method comprising: receiving a synchronization signal transmitted from a synchronization source on a first UE; determining a root index based on the received synchronization signal; determining a synchronization timing reference based on the root index; and transmitting a synchronization signal for D2D communication based on the determined synchronization timing reference. Determining the synchronization timing reference comprises: determining a category of the synchronization source based on the root index; prioritizing the synchronization sources based on a determination of whether the synchronization source is an evolved Node B (eNode B), a UE synchronized with an eNode B, or a UE having a synchronization timing reference independent of the eNode B; and determining the synchronization timing reference based on the prioritization. One or more illustrative embodiments herein provide a method for transmitting and receiving synchronization signals using a user equipment (UE) supporting device-to-device (D2D) communication between supporting UEs. The method includes: receiving synchronization signals transmitted from different synchronization sources respectively on a UE; prioritizing the different synchronization sources based on categories of the different synchronization sources, the categories including evolved Node B (eNode B), UE synchronized with the eNode B, and UE having a synchronization timing reference independent of the eNode B; determining a reference synchronization source for the UE among the different synchronization sources; synchronizing with the reference synchronization source based on a synchronization timing reference associated with the reference synchronization source; and transmitting a signal from the UE based on the synchronization.

[0015] One or more illustrative embodiments herein provide a method for transmitting and receiving synchronization signals using a user equipment (UE) that supports device-to-device (D2D) communication between UEs. The method includes: receiving synchronization signals transmitted from different synchronization sources on the UE; prioritizing the different synchronization sources based on the received synchronization signals; determining a reference synchronization source for the UE among the different synchronization sources; synchronizing with the reference synchronization source based on a synchronization timing reference associated with the reference synchronization source; and transmitting a signal from the UE to the reference synchronization source based on the synchronization. Determining the reference synchronization source includes: determining a root index based on each synchronization signal received from the corresponding synchronization source; determining a category of the corresponding synchronization source based on the root index; prioritizing the different synchronization sources based on the corresponding category; and determining the reference synchronization source based on the prioritization.

[0016] According to one or more exemplary embodiments, D2D synchronization information can be efficiently indicated based on the device transmitting or receiving D2D signals. This allows for efficient transmission of D2D scheduling assignments (SAs) and data information by ensuring efficient synchronization between user equipments (UEs) within or outside of network coverage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram illustrating the concept of device-to-device (D2D) communication based on a cellular network.

[0018] Figure 2 is a conceptual diagram of a system to which a method for transmitting a synchronization signal is applied, according to one or more exemplary embodiments.

[0019] Figure 3 is a conceptual diagram of a system to which a method for transmitting a synchronization signal is applied, according to one or more exemplary embodiments.

[0020] Figure 4 is a conceptual diagram of a system to which a method for transmitting a synchronization signal is applied, according to one or more exemplary embodiments.

[0021] Figure 5 is a block diagram illustrating a wireless communication system according to one or more example embodiments.

[0022] Figure 6 FIG. 1 is a diagram illustrating a method for a D2D receiving (Rx) UE to receive a PD2DSS based on a received PD2DSS according to one or more exemplary embodiments.

[0023] Flowchart of an example method for selecting a D2D transmission mode based on a root index value. DETAILED DESCRIPTION

[0024] Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, even if the same components are shown in different figures, they will be represented by the same reference numerals. Furthermore, in the following description, if the detailed description of known functions and configurations introduced herein may make the subject matter of the present invention unclear, such description will be omitted.

[0025] This specification provides a description associated with a communication network, and tasks performed in the communication network can be performed in the process of controlling the network and transmitting data in a system that manages the corresponding communication network (e.g., an evolved Node B (eNode B)), or in a user equipment (UE) associated with the corresponding network.

[0026] Figure 1 is a diagram illustrating the concept of device-to-device (D2D) communication based on a cellular network according to one or more exemplary embodiments.

[0027] refer to Figure 1 The communication network between a first UE 110 located in the first cell and a second UE 120 located in the second cell may be D2D communication between two UEs within the network coverage area. Furthermore, the communication between a third UE 130 located in the first cell and a fourth UE 140 located in the first cluster may be D2D communication between a UE within the network coverage area and a UE outside the network coverage area. The communication between a fourth UE 140 located in the first cluster and a fifth UE 150 located in the first cluster may be D2D communication between two UEs outside the network coverage area.

[0028] D2D communication refers to a technology that can directly transmit and receive data between UEs. In the following, it is assumed that the UE described in the exemplary embodiment supports D2D communication. When a UE located close to a cellular system performs D2D communication, the load on the evolved Node B (eNode B) can be dispersed. In addition, when the UE performs D2D communication, the UE performs data transmission relative to a relatively short distance, thereby reducing the transmission power loss and transmission delay of the UE. In addition, from the perspective of the entire system, existing cellular-based communication and D2D communication use the same resources, thereby improving frequency utilization efficiency.

[0029] D2D communication can be divided into a communication method for UEs located within the network coverage (base station coverage) and a communication method for UEs located outside the network coverage (base station coverage). D2D communication may include an exploration process for performing exploration of communication between UEs, and a direct communication process for UEs to transmit and receive control data and / or traffic data. D2D communication can be used for a variety of purposes. For example, D2D within the network coverage can be used for public safety and non-public safety, such as commercial purposes, etc. D2D communication performed outside the network coverage can be used only for public safety.

[0030] A D2D synchronization source may indicate a node that transmits at least a D2D synchronization signal (D2DSS). The D2D synchronization source may transmit at least one D2DSS. The transmitted D2DSS may be used by the UE to acquire time-frequency synchronization. When the D2D synchronization source is an eNodeB, the D2DSS transmitted by the D2D synchronization source may include a synchronization signal (SS) equivalent to a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). The D2DSS transmitted by a D2D synchronization source different from the eNodeB may include the signals described in the present invention. For example, if the D2D synchronization source is a UE, a broadcast UE, a cluster head, a synchronization head, etc., then a D2DSS modified from a PSS (hereinafter referred to as a PD2DSS) or a D2DSS modified from an SSS (hereinafter referred to as a SD2DSS) may include the signals described in the present invention. The cluster head may include an independent synchronization source (ISS) for synchronizing UEs outside of coverage, or may also function as an ISS.

[0031] The D2DSS transmitted by the D2D synchronization source may include an identifier (ID) of the D2D synchronization source and / or the type of the D2D synchronization source. Furthermore, the D2DSS may include at least a primary device-to-device synchronization signal (PD2DSS) and a secondary device-to-device synchronization signal (SD2DSS). The PD2DSS is based on a Zadoff Chu sequence.

[0032] The sequence d(n) for PSS can be generated from the frequency domain Zadoff Chu sequence based on Equation 1.

[0033] [Formula 1]

[0034]

[0035] In Formula 1, u represents the root sequence index defined in Table 1.

[0036]

Table 1

[0037]

[0038] The sequence d(n) can be mapped to resource elements (REs) based on Formula 2.

[0039] [Formula 2]

[0040] a k,l =d(n),n=0,...,61

[0041]

[0042] Here, ak,l represents RE, k represents a subcarrier number, and l represents an OFDM symbol number.

[0043] The mapping of sequences for PSS to REs is determined based on the frame structure.

[0044] In case of frame structure type 1 for frequency division duplex (FDD), the PSS is mapped to the last OFDM symbol in slots 1 and 10 of a single radio frame.

[0045] In case of frame structure type 2 for time division duplex (TDD), the PSS is mapped to the third OFDM symbol in subframes 1 and 6 of a single radio frame.

[0046] Here, a single radio frame includes 10 subframes (subframes 0 to 9), and when a single subframe is formed of two slots, it corresponds to 20 slots (slots 0 to 19). In addition, a single slot includes a plurality of OFDM symbols.

[0047] Among REs (k, l) of an OFDM symbol, REs corresponding to Formula 3 may not be used but may be reserved to transmit a PSS.

[0048] Formula 3:

[0049]

[0050] n=-5,-4,...,-1,62,63,...66

[0051] The sequence d(0),...,d(61) for SSS can be generated by interleaving two binary sequences of length 31.

[0052] For a combination of two binary sequences defining the SSS and having a length of 31, the combination may have different values ​​between subframe 0 and subframe 5 according to Formula 4.

[0053] [Formula 4]

[0054]

[0055]

[0056] In Formula 4, the value of n satisfies 0≤n≤30, and m0 and m1 can be acquired from a physical layer cell identification (ID) group based on Formula 5.

[0057] [Formula 5]

[0058] m0=m′mod31

[0059]

[0060]

[0061] The result values ​​of Formula 5 can be expressed as listed in Tables 2 and 3.

[0062]

Table 2

[0063]

[0064]

Table 3

[0065]

[0066] Based on formula 6, the two sequences can be and Defined as an m-sequence Two different cyclic shifts of .

[0067] [Formula 6]

[0068]

[0069]

[0070] Formula 6 satisfies And 0≤i≤30, and x(i) can be defined by Formula 7.

[0071] [Formula 7]

[0072]

[0073] In Formula 7, the initial values ​​of x(i) may be set to x(0)=0, x(1)=0, x(2)=0, x(3)=0, and x(4)=1.

[0074] c0(n) and c1(n) are two scrambling sequences. These sequences can be determined based on the PSS and can be obtained based on formula 8 and the m sequence is defined by two different cyclic shifts of .

[0075] [Formula 8]

[0076]

[0077]

[0078] In formula 8, Physical layer cell ID group The physical layer ID in formula 8 satisfies And 0≤i≤30, and x(i) is defined by Formula 9.

[0079] [Formula 9]

[0080]

[0081] In Formula 9, the initial values ​​of x(i) may be set to x(0)=0, x(1)=0, x(2)=0, x(3)=0, and x(4)=1.

[0082] Scrambling sequence and Based on formula 10, the m sequence It is defined by the cyclic shift of .

[0083] [Formula 10]

[0084]

[0085]

[0086] In formula 10, m0 and m1 can be obtained from Table 2, and they satisfy and 0≤i≤30, and x(i) can be defined by Formula 11.

[0087] [Formula 11]

[0088]

[0089] In Formula 11, the initial value of x(i) may be set to x(0)=0, x(1)=0, x(2)=0, x(3)=0, x(4)=1.

[0090] The mapping of sequences for SSS to REs is determined based on the frame structure.

[0091] The sequence d(n) can be mapped to RE based on Formula 12.

[0092] [Formula 12]

[0093] a k,l =d(n),n=0,...,61

[0094]

[0095]

[0096] In formula 12, a k,l represents RE, k represents a subcarrier number, and l represents an OFDM symbol number.

[0097] REs (k, l) from the OFDM symbol and corresponding to Formula 13 may not be used and may be reserved for transmitting SSS.

[0098] [Formula 13]

[0099]

[0100]

[0101] n=-5,-4,...,-1,62,63,...66

[0102] The D2DSS transmitted by the D2D synchronization source may include a physical synchronization source identifier (PSSID) and / or a D2D synchronization source type and a PD2DSS. The PD2DSS is based on a Zadoff Chu sequence.

[0103] For D2DSS, it is necessary to define PD2DSS. When the D2D synchronization source is an eNodeB, D2DSS can be equivalent to PSS / SSS. However, when the D2D synchronization source is different from the eNodeB, a new type of PD2DSS needs to be defined.

[0104] The UE should avoid misinterpreting a D2DSS transmitted by a D2D synchronization source other than the eNodeB as a typical DL synchronization signal, such as the PSS or SSS. If the UE misinterprets the received D2DSS as a DL synchronization signal typically transmitted from the eNodeB, the UE may mistakenly identify the D2D synchronization source transmitting the D2DSS as the eNodeB, or the UE may misidentify the synchronization information. Therefore, the sequence used for the D2DSS should be different from the sequence used in cellular communication (or the sequence used for the PSS or SSS). To this end, a sequence with a different root index than the sequence used for cellular communication can be defined and used.

[0105] When the D2D synchronization source is an eNodeB, the PD2DSS transmitted by the synchronization source is a PSS (Primary Synchronization Signal). When the D2D synchronization source is different from the eNodeB, the PD2DSS transmitted by the synchronization source can be defined based on the characteristics described herein. The PD2DSS can embody one or more characteristics of the PSS. For example, if the D2D synchronization source is a UE, a broadcast UE, a cluster head, a synchronization head, etc., then a D2DSS modified from the PSS (hereinafter referred to as the PD2DSS) can be configured.

[0106] When the D2D synchronization source is different from the eNodeB, in addition to the three general root indexes defined for the PSS, one or more embodiments herein may use one of the additional three root indexes, thereby providing a method for generating a PD2DSS sequence transmitted by the D2D synchronization source.

[0107] As an example, the root index of Table 4 may be used.

[0108] Example No. Root Index Example 1 38,26,37 Example 2 38,23,40 Example 3 38,19,44 Example 4 38,16,47 Example 5 38,5,58 Example 6 38,2,61

[0109] According to one or more exemplary embodiments, a transmission D2D synchronization source may be defined as a node that transmits a D2D direct synchronization signal to a UE, and may also be referred to as a transmission (Tx) synchronization source. Figure 1 , the transmission synchronization source for the first UE 110 may be the first eNodeB 100 , and the transmission synchronization source for the second UE 120 may be the first UE 110 or the second eNodeB 160 .

[0110] According to one or more exemplary embodiments, an initial D2D synchronization source may be defined as a node that initially sends a D2D synchronization signal, and may also be referred to as an initial synchronization source. Figure 1 In the example embodiment, the initial synchronization source for the second UE 120 may be the first eNodeB 100 or the second eNodeB 160.

[0111] According to one or more exemplary embodiments, an independent synchronization source (ISS) may be defined as a D2D synchronization source that is not an eNodeB but generates a D2D synchronization signal independently. Figure 1 In the example, the fifth UE 150 may be an ISS.

[0112] According to one or more exemplary embodiments, the hop count indicates the number of stages used to transmit the synchronization signal from the synchronization source to the UE, and is incremented by 1 for each stage. Figure 1 , when the eNodeB 110 transmits a synchronization signal to the second UE 120 through the first UE 110, the number of hops for the first UE 110 is 1, and the number of hops for the second UE 120 is 2.

[0113] The tier indicates the number of stages used to transmit a synchronization signal from a synchronization source identified by the system to a UE. The tier may be equivalent to the number of hops, and when there are hops not identified by the system, the tier may be smaller than the number of hops.

[0114] PD2DSCH indicates a physical D2D synchronization channel, and according to one or more exemplary embodiments, PD2DSCH may be used to indicate information such as a synchronization source type, a physical synchronization source identifier (PSSID), or a layer.

[0115] The cell ID may include multiple specific physical layer cell IDs, such as 504 physical layer cell IDs. can be divided into 168 specific physical layer cell ID groups, and each group includes three specific IDs. as well as Defined specific values, where is an integer ranging from 0 to 167 and represents the physical layer cell ID group, and As shown in is an integer ranging from 0 to 2, and represents the physical layer ID in the physical layer cell ID group.

[0116] The embodiment provided below describes a method of transmitting synchronization information such as synchronization source type, physical synchronization source identifier (PSSID), layer, etc. by using the position of PD2DSS, SD2DSS, D2DSS in a subframe and PD2DSCH.

[0117] Figure 2 is a conceptual diagram of a system to which a method for transmitting a synchronization signal is applied, according to one or more exemplary embodiments. Figure 2 The upper half of FIG. 2 shows synchronization signal transmissions performed from the eNodeB 200 to the first UE, from the first UE 210 to the second UE 220, and from the second UE 220 to the third UE 230, respectively. The eNodeB 200 may be an initial synchronization source (initial SS) for the first UE 210, the second UE 220, and the third UE 230. The eNodeB 200 may be a transmission synchronization source (Tx SS) for the first UE 210, the first UE 210 may be a Tx SS for the second UE 220, and the second UE 220 may be a Tx SS for the third UE 230.

[0118] refer to Figure 2In the lower half of FIG, the fourth UE 240 may not receive a synchronization signal from an eNodeB or other UEs, but may independently generate a synchronization signal and transmit the synchronization signal to other UEs. Thus, the fourth UE 240 corresponds to an ISS. Specifically, the fourth UE 240 may transmit a synchronization signal to the fifth UE 250, the fifth UE 250 may transmit a synchronization signal to the sixth UE 260, and the sixth UE 260 may transmit a synchronization signal to the seventh UE 270. The fourth UE 240 may be the initial synchronization source (initial SS) for the fifth UE 250, the sixth UE 260, and the seventh UE 270. The fourth UE 240 may be the transmission synchronization source (Tx SS) for the fifth UE 250, the fifth UE 250 may be the Tx SS for the sixth UE 260, and the sixth UE 260 may be the Tx SS for the seventh UE 270.

[0119] refer to Figure 2 , the layer when the synchronization signal transmitted from the eNodeB 200 is transmitted to the first UE 210 is referred to as the first layer, and the layer when the synchronization signal is transmitted to the second UE 220 via the first UE 210 is referred to as the second layer. Similarly, the layer when the synchronization signal is transmitted to the third UE 230 via the first UE 210 and the second UE 220 is referred to as the third layer.

[0120] One or more of the exemplary embodiments presented herein may be modified or altered by incorporating one or more features from other exemplary embodiments or configurations not specifically described herein.

[0121] Embodiments 1-1 to 1-5 describe a method for indicating D2D synchronization information when the initial synchronization source is an eNodeB and the maximum stratum is the third layer, and when the initial synchronization source is an ISS and the maximum stratum is the third layer.

[0122] [Example 1-1]

[0123]

Table 5

[0124]

[0125] In this embodiment, when the type of synchronization source (SS) is eNodeB or SS obtained from eNodeB (SS of relay eNodeB), the PCID of eNodeB can be used as the physical synchronization source identifier (PSSID), and 504 specific PSSIDs can exist.

[0126] When the type of synchronization source (SS) is an ISS or an SS obtained from an ISS (an SS relaying an ISS), a PSSID based on a UE ID of the ISS may be used as the PSSID, and 504 specific PSSIDs may exist.

[0127] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the examples in Table 5 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other cases corresponding to Examples 2-6 in which the transmission synchronization source is a UE, and each example can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used may be that of Table 4.

[0128] When the transmission synchronization source is a UE, the type of the initial synchronization source may be indicated by a physical D2D synchronization source channel (PD2DSCH). For example, the examples in Table 5 may be indicated based on such a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2 and 3 in which the type of the initial synchronization source is an eNodeB, and cases corresponding to cases 4-6 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH may have a one-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source may be determined to be an eNodeB through the root index value of the PD2DSS, and thus there is no need to indicate this separately.

[0129] In addition, when the transmission synchronization source is a UE, the tier can be indicated by the position used to transmit the D2DSS in the frequency resource domain or the PD2DSCH. For example, the example in Table 5 can be indicated based on such a classification, wherein the classification is divided into three cases, namely, a case corresponding to case 4 with a tier of 1, a case corresponding to cases 2 and 5 with a tier of 2, and another case corresponding to cases 3 and 6 with a tier of 3. Therefore, in this case, the indication value of the PD2DSCH can have a two-bit value. When the transmission synchronization source is an eNodeB, the tier can be identified by the root index value of the PD2DSS, and thus there is no need to indicate this separately.

[0130] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index has 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0131] Even if the type of synchronization source is a synchronization source derived from an eNodeB, a physical synchronization source identifier (PSSID) may have a value equivalent to the PCID of the eNodeB, and there may be 504 specific PSSIDs. The PSSID may be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence manner, where the root index can have three values ​​and can have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS can be used as the root index of the PD2DSS, and as an example, the root index in Table 4 is available. For example, the value used may be a SD2DSS value mapped to an SSS having 168 sequences in a one-to-one correspondence. Thus, the SD2DSS may have an integer ranging from 0 to 167, and the PSSID may be mapped to 504 (=3*168) IDs.

[0132] When the type of synchronization source is an ISS or a synchronization source derived from an ISS, the proximity-based service (ProSe) UE ID of the UE corresponding to the ISS may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 504 IDs based on a predetermined mapping rule. The PSSID may be expressed as and The root index of the PD2DSS may be mapped in a one-to-one manner, wherein the root index may have three values ​​and may have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS may be used as the root index of the PD2DSS, and as an example, the root index of Table 4 may be used. It can be mapped to an SSS having 168 sequences in a one-to-one correspondence manner and can have an integer ranging from 0 to 167. Thus, the PSSID can be mapped to 504 (=3*168) IDs.

[0133] [Example 1-2]

[0134]

Table 6

[0135]

[0136] In this embodiment, when the synchronization source (SS) type is an eNodeB, the PCID of the eNodeB can be used as the PSSID, and 504 specific PSSIDs can be used. When the synchronization source type is an SS derived from an eNodeB (an SS for relaying an eNodeB), a value modified based on the PCID of the eNodeB can be used as the PSSID, and there can be 168 or K specific PCIDs, where K is an integer less than 168.

[0137] When the synchronization source (SS) type is an ISS or an SS derived from an ISS (SS for relaying an ISS), the PSSID may be determined based on the UE ID of the ISS, and there may be 168 or K specific PSSIDs, where K is a value less than 168.

[0138] In this embodiment, the transmission synchronization source is indicated by the root index value of the PD2DSS, and the stratum when the transmission synchronization source is the eNodeB is 1, so the stratum does not need to be indicated separately.

[0139] When the transmission synchronization source is the UE, the level can be indicated by the root index of the PD2DSS. For example, the example in Table 6 can be indicated based on a classification that is divided into three cases, namely, a case corresponding to Example 4 where the level is 1, cases corresponding to Examples 2 and 5 where the level is 2, and cases corresponding to Examples 3 and 6 where the level is 3. Thus, for example, when the three root indexes of the newly defined PD2DSS are X, Y, and Z, respectively, the root index X can be set to indicate level 1, the root index Y can be set to indicate level 2, and the root index 3 can be set to indicate level 3. The root indexes of Table 4 can be used as the root indexes of the newly defined PD2DSS.

[0140] When the synchronization source type is eNodeB (Case 1), the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical layer synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and The root index of the PD2DSS may be included in a one-to-one correspondence, wherein the root index has three values ​​and may have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS may have one of 25, 29, and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equal to the SSS may be used as a value of the SD2DSS.

[0141] When the type of synchronization source is a synchronization source derived from an eNodeB (SS relaying an eNodeB) (cases 2 and 3), a physical synchronization source identifier (PSSID) may be mapped to 168 or K IDs based on the PCID of the eNodeB using a predetermined rule, where K is an integer less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or a value ranging from 0 to K-1. The PSSID may be expressed as and is associated with SD2DSS can be mapped to SSS in a one-to-one correspondence, wherein the SSS can have 168 values ​​and can have an integer ranging from 0 to 167, or the It can also be mapped to K values ​​in a one-to-one manner based on a sequence derived from SSS modification or local selection, where the SS has 168 sequences and can have an integer ranging from 0 to K-1, where K is a value less than 168. In this case, the exact PCID that the eNodeB has can be transmitted through the PD2DSCH.

[0142] When the type of synchronization source is an ISS or a synchronization source derived from an ISS (Examples 4, 5, and 6), the proximity-based service (ProSe) UE ID of the UE corresponding to the ISS may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 168 or K IDs according to a predetermined mapping rule, where K is an integer less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or from 0 to K-1. The PSSID may be expressed as and is associated with SD2DSS can be mapped to the SSS in a one-to-one correspondence, wherein the SSS can have 168 values ​​and can have integers ranging from 0 to 167, or the It may also be mapped to K values ​​in a one-to-one correspondence based on a sequence modified or partially selected from the SSS, wherein the SSS has 168 sequences and may have an integer ranging from 0 to K-1, where K is a value less than 168. In this case, the precise UE ID possessed by the ISS may be transmitted through the PD2DSCH.

[0143] [Examples 1-3]

[0144]

Table 7

[0145]

[0146] In this embodiment, when the type of synchronization source (SS) is eNodeB or SS derived from eNodeB (SS of relay eNodeB), the PCID of eNodeB can be used as the physical synchronization source identifier (PSSID), and there can be 504 specific PSSIDs.

[0147] When the type of synchronization source (SS) is ISS or SS derived from ISS (SS relaying ISS), PSSID based on UE ID of ISS may be used as PSSID, and there may be 168 or K specific PSSIDs, where K is a value less than 168.

[0148] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example of Table 7 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the cases corresponding to Examples 2-6 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used can be that of Table 4.

[0149] When the transmission synchronization source is a UE, the type of the initial synchronization source may be indicated by a physical D2D synchronization channel (PD2DSCH). For example, the example of Table 7 may be indicated based on a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2 and 3 in which the type of the initial synchronization source is an eNodeB, and cases corresponding to cases 4-6 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH may have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source may be determined to be an eNodeB through the root index value of the PD2DSS, and thus there is no need to indicate this separately.

[0150] In addition, when the initial synchronization source is an eNodeB and the transmission synchronization source is a UE, the position used to transmit the D2DSS in the frequency resource or PD2DSCH can be used to indicate the hierarchy. For example, the example in Table 7 can be indicated based on such a classification, wherein the classification is divided into two cases, namely, the case corresponding to Example 2 where the hierarchy is 2, and the case corresponding to Example 3 where the hierarchy is 3. Thus, the indication value of the PD2DSCH can have a 1-bit value. Here, the 1-bit information of the PD2DSCH can be designed to be different information from each other based on the coverage range, and can be designed not to be included in the coverage range. Thus, in Examples 4 to 6 where the initial synchronization source is an ISS, the hierarchy can be indicated by the root index value of the PD2DSS instead of by the PD2DSH. When the transmission synchronization source is an eNodeB, the hierarchy can be identified by the root index value of the PD2DSS, and thus there is no need to indicate it separately.

[0151] When the initial synchronization source is the ISS, the hierarchy level may be indicated by the root index of the PD2DSS. Examples 4-6 of Table 7 may be indicated based on a classification into three cases based on the hierarchy level. Thus, for example, when the root indexes of the newly defined PD2DSS are X, Y, and Z, respectively, the root index X may be set to indicate hierarchy level 1, the root index Y may be set to indicate hierarchy level 2, and the root index Z may be set to indicate hierarchy level 3. The root index of Table 4 is used as the root index of the newly defined PD2DSS.

[0152] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB can be used as a physical synchronization source identifier (PSSID), the physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence manner, where the root index of the PD2DSS can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. A one-to-one mapping to a root index of the SD2DSS may be used, wherein the root index has 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0153] Even if the type of synchronization source is a synchronization source derived from an eNodeB, a physical synchronization source identifier (PSSID) may have a value equivalent to the PCID of the eNodeB, and there may be 504 specific PSSIDs. The PSSID may be expressed as and It may be mapped to the root index of the PD2DSS in a one-to-one correspondence, wherein the root index may have three values ​​and may have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PDSS may be used as the root index of the PD2DSS, and as an example, the root index of Table 4 may be used. For example, the value used may be a SD2DSS value mapped to an SSS having 168 sequences in a one-to-one correspondence. Thus, the SD2DSS may have an integer ranging from 0 to 167, and the PSSID may be mapped to 504 (=3*168) IDs.

[0154] When the type of synchronization source is an ISS or a synchronization source derived from an ISS (Examples 4, 5, and 6), the proximity-based service (ProSe) UE ID of the UE corresponding to the ISS may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 168 or K IDs based on a predetermined mapping rule, where K is an integer less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or from 0 to K-1. The PSSID may be expressed as and is associated with SD2DSS can be mapped to SSS in a one-to-one correspondence, wherein the SSS can have 168 values ​​and can have an integer ranging from 0 to 167, or the It may also be based on a sequence modified or partially selected from the SSS and mapped to K values ​​in a one-to-one correspondence, wherein the SSS has 168 sequences and may have an integer ranging from 0 to K-1, where K is a value less than 168. In this case, the precise UEID of the ISS may be transmitted through the PD2DSCH.

[0155] [Examples 1-4]

[0156]

Table 8

[0157]

[0158] In this embodiment, when the type of synchronization source (SS) is eNodeB, the PCID of the eNodeB may be used as a physical synchronization source identifier (PSSID), and there may be 504 specific PSSIDs.

[0159] When the type of synchronization source (SS) is an SS derived from an eNodeB (SS of a relay eNodeB), a PSSID of the transmission synchronization source based on a UE ID may be used, and 504 specific PSSIDs may exist.

[0160] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example of Table 8 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-6 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index of Table 4 can be used.

[0161] When the transmission synchronization source is a UE, the type of the initial synchronization source may be indicated by a physical D2D synchronization channel (PD2DSCH). For example, the example of Table 8 may be indicated based on a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2 and 3 in which the type of the initial synchronization source is an eNodeB, and cases corresponding to cases 4-6 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH may have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source may be determined to be an eNodeB through the root index value of the PD2DSS, and thus there is no need to indicate this separately.

[0162] In addition, when the transmission synchronization source is a UE, the position used to transmit the D2DSS in the frequency resource domain or PD2DSCH can be used to indicate the hierarchy. For example, the examples in Table 8 can be indicated based on such a classification, wherein the classification is divided into three cases, namely, a case corresponding to case 4 with a hierarchy of 1, cases corresponding to cases 2 and 5 with a hierarchy of 2, and other cases corresponding to cases 3 and 6 with a hierarchy of 3. Therefore, the indication value of the PD2DSCH can have a 2-bit value. When the transmission synchronization source is an eNodeB, the hierarchy can be identified by the root index value of the PD2DSS, and thus there is no need to indicate it separately.

[0163] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index of the PD2DSS can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is the same as the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index has 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0164] When the type of synchronization source is a synchronization source derived from an eNodeB (SS relaying an eNodeB) or a synchronization source derived from an ISS (SS relaying an ISS), a proximity-based service (ProSe) UE ID possessed by a transmitting (Tx) UE may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 504 IDs based on a predetermined mapping rule. The PSSID may be expressed as and The PD2DSS root index can be mapped in a one-to-one correspondence to the root index of the PD2DSS, where the root index can have two values ​​and can have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS can be used as the root index of the PD2DSS, and as an example, the root index of Table 4 is available. The PD2DSS associated with the SD2DSS can be mapped in a one-to-one correspondence to the SSS having 168 sequences and integers ranging from 0 to 167. Thus, the PSSID can be mapped to 504 (=3*168) IDs.

[0165] [Examples 1-5]

[0166]

Table 9

[0167]

[0168] In this embodiment, when the type of the synchronization source (SS) is an eNodeB, the PCID of the eNodeB may be used as a physical synchronization source identifier (PSSID), and there may be 504 specific PSSIDs.

[0169] When the type of synchronization source (SS) is an SS derived from an eNodeB (SS relaying an eNode), an ISS, or an SS derived from an ISS (SS relaying an ISS), the PSSID used may be the transmission synchronization source based on the UE ID, and there may be 168 or K PSSIDs, where K is a value less than 168.

[0170] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example of Table 9 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-6 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root index of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used may be that of Table 4.

[0171] When the transmission synchronization source is a UE, the type of the initial synchronization source may be indicated using a physical D2D synchronization channel (PD2DSCH). For example, the examples in Table 9 may be indicated based on a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2 and 3 in which the type of the initial synchronization source is an eNodeB, and cases corresponding to cases 4-6 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH may have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source may be identified as an eNodeB through the root index value of the PD2DSS, and thus there is no need to indicate this separately.

[0172] When the transmission synchronization source is the UE, the root index of the PD2DSS may be used to indicate the level. For example, the example in Table 9 may be indicated based on a classification system, wherein the classification system is divided into three cases: a case corresponding to case 4 with a level of 1, cases corresponding to cases 2 and 5 with a level of 2, and other cases corresponding to cases 3 and 6 with a level of 3.

[0173] Thus, for example, when the root indexes of the newly defined PD2DSS are X, Y, and Z, respectively, root index X may be set to indicate level 1, root index Y may be set to indicate level 2, and root index Z may be set to indicate level 3. The root indexes of Table 4 may be used as the root indexes of the newly defined PD2DSS.

[0174] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index of the PD2DSS can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is the same as the root index of the PSS. The root index may be mapped to the SD2DSS in a one-to-one correspondence, wherein the root index has 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0175] When the type of synchronization source is a synchronization source derived from an eNodeB (SS relaying an eNodeB), an ISS, or a synchronization source derived from an ISS (SS relaying an ISS), the proximity-based service (ProSe) UE ID of the transmitting (Tx) UE may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 168 or K IDs based on a predetermined mapping rule, where K is a value less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or from 0 to K-1. The PSSID may be expressed as and is associated with SD2DSS can be mapped to an SSS having 168 sequences in a one-to-one correspondence, or can be mapped to K sequences based on sequences modified or partially selected from an SSS having 168 sequences, where K is a value less than 168. When mapped to 168 sequences, it can have an integer ranging from 0 to 167, and when mapped to K sequences in a one-to-one correspondence, it can have an integer ranging from 0 to K - 1. In this case, the precise UE ID of the transmission synchronization source can be transmitted through PD2DSCH.

[0176] Figure 3 is a conceptual diagram of a system to which a method for transmitting a synchronization signal is applied, according to one or more exemplary embodiments.

[0177] Figure 3 The upper half of the figure shows synchronization signal transmissions performed from the eNodeB 300 to the first UE 310, from the first UE 310 to the second UE 320, from the second UE 320 to the third UE 330, and from the third UE 330 to the fourth UE 340, respectively. The base station 300 may be an initial synchronization source (initial SS) for the first UE 310, the second UE 320, the third UE 330, and the fourth UE 340. The base station 300 may be a transmission synchronization source (Tx SS) for the first UE 310, the first UE 310 may be a Tx SS for the second UE 320, the second UE 320 may be a Tx SS for the third UE 330, and the third UE 330 may be a Tx SS for the fourth UE 340.

[0178] refer to Figure 3In the lower half of FIG, the fifth UE 350 may not receive a synchronization signal from an eNodeB or other UE, but may instead independently generate and transmit a synchronization signal. Thus, the fifth UE 350 corresponds to an ISS. Specifically, the fifth UE 350 may transmit a synchronization signal to the sixth UE 360, the sixth UE 360 may transmit a synchronization signal to the seventh UE 370, and the seventh UE 370 may transmit a synchronization signal to the eighth UE 380. The fifth UE 350 may be the initial synchronization source (initial SS) for the sixth UE 360, the seventh UE 370, and the eighth UE 380. The fifth UE 350 may be the transmission synchronization source (Tx SS) for the sixth UE 360, the sixth UE 360 may be the Tx SS for the seventh UE 370, and the seventh UE 370 may be the Tx SS for the eighth UE 380.

[0179] Embodiments 2-1 to 2-5 describe a method for indicating D2D synchronization information when the initial synchronization source is eNodeB and the maximum layer is the fourth layer (if eNodeB is excluded, the maximum layer is the third layer) and when the initial synchronization source is ISS and the maximum layer is the third layer.

[0180] [Example 2-1]

[0181]

Table 10

[0182]

[0183] In this embodiment, when the type of synchronization source is eNodeB or an SS derived from eNodeB (SS relaying eNodeB), the PCID of the eNodeB may be used as a physical synchronization source identifier (PSSID), and there may be 504 specific PSSIDs.

[0184] When the type of synchronization source (SS) is an ISS or an SS derived from an ISS (an SS relaying an ISS), a PSSID based on the UE ID of the ISS may be used, and there may be 504 specific PSSIDs.

[0185] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example in Table 10 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-7 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used can be that of Table 4.

[0186] When the transmission synchronization source is a UE, the type of the initial synchronization source can be indicated by a physical D2D synchronization channel (PD2DSCH). For example, the examples in Table 10 can be indicated based on such a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2-4 in which the type of the initial synchronization source is an eNodeB, and cases corresponding to cases 5-7 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH can have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source can be determined to be an eNodeB through the root index value of the PD2DSS. Therefore, there is no need to indicate this separately.

[0187] In addition, when the transmission synchronization source is a UE, the tier can be indicated by the position used to transmit the D2DSS in the frequency resource domain or the PD2DSCH. For example, Examples 2-7 of Table 10 can be indicated based on a classification, wherein the classification is divided into three cases, namely, a case corresponding to Examples 2 and 5 with a tier index of 1, a case corresponding to Examples 3 and 6 with a tier index of 2, and another case corresponding to Examples 4 and 7 with a tier index of 3. Thus, the indication value of the PD2DSCH can have a 2-bit value. When the transmission synchronization source is an eNodeB, the tier can be determined to have a value of 0 through the PD2DSS, and thus there is no need to indicate this separately.

[0188] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index has three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0189] Even if the synchronization source type is a synchronization source derived from an eNodeB (cases 2, 3, and 4), the physical synchronization source identifier (PSSID) may have a value equivalent to the PCID of the eNodeB, and there may be 504 specific PSSIDs. The PSSID may be expressed as and It may be mapped to the root index of the PD2DSS in a one-to-one correspondence, wherein the root index has three values ​​and may have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS may be used as the root index of the PD2DSS, and as an example, the root index of Table 4 may be used. For example, the value used may be a SD2DSS value mapped to an SSS having 168 sequences in a one-to-one correspondence. Thus, the SD2DSS may have an integer ranging from 0 to 167, and the PSSID may be mapped to 504 (=3*168) IDs.

[0190] When the synchronization source type is ISS or a synchronization source derived from ISS (cases 5, 6, and 7), the proximity-based service (ProSe) UE ID of the UE corresponding to the ISS may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 504 IDs based on a predetermined rule. The PSSID may be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index can have three values ​​and can have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS can be used as the root index of the PD2DSS, and as an example, the root index used can be the root index of Table 4. It can be mapped in a one-to-one correspondence to an SSS having 168 sequences and an integer ranging from 0 to 167. Therefore, the PSSID can be mapped to 504 (=3*168) IDs.

[0191] [Example 2-2]

[0192]

Table 11

[0193]

[0194] In this embodiment, when the synchronization source type is an eNodeB, the PCID of the eNodeB can be used as a physical synchronization source identifier (PSSID), and 504 specific PSSIDs can be used. When the synchronization source type is a synchronization source (SS) derived from an eNodeB (SS of a relay eNodeB), a value modified based on the PCID of the eNodeB can be used as the PSSID, and there can be 168 or K PSSIDs, where K is an integer less than 168.

[0195] When the type of synchronization source (SS) is an ISS or an SS derived from an ISS (SS relaying an ISS), the PSSID may be determined based on the UE ID of the ISS, and there may be 168 or K specific PSSIDs, where K is an integer less than 168.

[0196] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example in Table 11 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-7 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used may be that of Table 4.

[0197] When the transmission synchronization source is a UE, the type of the initial synchronization source may be indicated using a physical D2D synchronization channel (PD2DSCH). For example, the examples in Table 11 may be indicated based on such a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2-4 in which the type of the initial synchronization source is an eNodeB, and another case corresponding to cases 5-7 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH may have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source may be determined to be an eNodeB through the root index value of the PD2DSS. Thus, there is no need to indicate this separately.

[0198] When the transmission synchronization source is the UE, the level can be indicated by the root index of the PD2DSS. For example, the example of Table 11 can be indicated based on a classification, wherein the classification is divided into three cases, namely, a case corresponding to cases 2 and 5 where the level index is 1, a case corresponding to cases 3 and 6 where the level index is 2, and another case corresponding to cases 4 and 7 where the level index is 3. Thus, for example, when the root indexes of the newly defined PD2DSS are X, Y, and Z, respectively, the root index X can be set to indicate level 1, the root index Y can be set to indicate level 2, and the root index Z can be set to indicate level 3. The root index of Table 4 can be used as the root index of the newly defined PD2DSS.

[0199] When the type of synchronization source is eNodeB (Case 1), the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer value ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0200] When the synchronization source type is a synchronization source derived from an eNodeB (SS relaying an eNodeB) (cases 2, 3, and 4), the physical synchronization source identifier (PSSID) can be mapped to 168 or K IDs based on the PCID of the eNodeB using a predetermined rule, where K is an integer less than 168. Thus, the PSSID can have a value ranging from 0 to 167 or from 0 to K-1. The PSSID can be expressed as and associated with SD2DSS It may be mapped in a one-to-one manner to an SSS that may have 168 values ​​and may have an integer ranging from 0 to 167, or it may be mapped in a one-to-one manner to K values ​​based on a sequence modified or partially selected from an SSS having 168 sequences or an integer ranging from 0 to K-1, where K is an integer less than 168. In this case, the precise PCID of the eNodeB may be transmitted through the PD2DSCH.

[0201] When the synchronization source type is an ISS or a synchronization source derived from an ISS (SS relaying an ISS) (Cases 5, 6, and 7), the Proximity-Based Service (ProSe) UE ID of the UE corresponding to the ISS may be used as a Physical Synchronization Source Identifier (PSSID), and the PSSID may be mapped to 168 or K IDs based on a predetermined rule, where K is an integer less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or from 0 to K-1. The PSSID may be expressed as and is associated with SD2DSS It can be mapped in a one-to-one manner to an SSS that can have 168 values ​​and an integer ranging from 0 to 167, or it can be mapped in a one-to-one manner to K values ​​based on a sequence modified or partially selected from an SSS having 168 sequences or an integer ranging from 0 to K-1, where K is an integer less than 168. Thus, the PSSID can have a value ranging from 0 to 167 or ranging from 0 to K-1. In this case, the accurate PCID of the ISS can be transmitted through the PD2DSCH.

[0202] [Example 2-3]

[0203]

Table 12

[0204]

[0205] In this embodiment, when the type of synchronization source is eNodeB or an SS derived from eNodeB (SS relaying eNodeB), the PCID of the eNodeB may be used as a physical synchronization source identifier (PSSID), and there may be 504 specific PSSIDs.

[0206] When the type of synchronization source (SS) is an ISS or an SS derived from an ISS (an SS relaying an ISS), a PSSID may be determined based on the ISSID, and there may be 168 or K specific PSSIDs, where K is an integer less than 168.

[0207] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the examples in Table 12 can be divided into two cases, namely, the case corresponding to Case 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Cases 2-7 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used can be that of Table 4.

[0208] When the transmission synchronization source is a UE, the type of the initial synchronization source can be indicated by a physical D2D synchronization channel (PD2DSCH). For example, the examples in Table 12 can be indicated based on such a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2-4 in which the type of the initial synchronization source is an eNodeB, and cases corresponding to cases 5-7 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH can have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source can be determined to be an eNodeB through the root index value of the PD2DSS. Therefore, there is no need to indicate this separately.

[0209] Furthermore, when the initial synchronization source is an eNodeB and the transmission synchronization source is a UE, the tier can be indicated by the location used to transmit the D2DSS in the frequency resource domain or PD2DSCH. For example, Examples 2-7 of Table 12 can be indicated based on a classification, wherein the classification is divided into three cases: a case corresponding to Example 2 with a tier of 1, a case corresponding to Example 3 with a tier of 2, and a case corresponding to Example 4 with a tier of 3. Therefore, the PD2DSCH indication value can be a 2-bit value. Here, the 2-bit information of the PD2DSCH can be designed to differ based on the coverage situation, and this 2-bit information of the PD2DSCH is designed for situations where it is not included in the coverage area. Thus, in Examples 5 and 6 where the initial synchronization source is an ISS, the tier can be indicated by the root index value of the PD2DSS rather than the PD2DSCH. When the transmission synchronization source is an eNodeB, the tier can be identified by the root index value of the PD2DSS, and thus there is no need to indicate it separately.

[0210] When the initial synchronization source is the ISS, the tier can be indicated by the root index of the PD2DSS. Examples 5 and 6 in Table 12 can be divided into a total of three cases based on tier. Thus, for example, when the root indexes of the newly defined PD2DSS are X, Y, and Z, respectively, root index X can be set to indicate tier 1, root index Y can be set to indicate tier 2, and root index Z can be set to indicate tier 3. The root index of Table 4 can be used as the root index of the newly defined PD2DSS.

[0211] When the type of synchronization source is eNodeB (Case 1), the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index has three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0212] Even if the synchronization source type is a synchronization source derived from an eNodeB (cases 2, 3, and 4), the physical synchronization source identifier (PSSID) may have a value equivalent to the PCID of the eNodeB, and there may be 504 specific PSSIDs. The PSSID may be expressed as and It may be mapped to the root index of the PD2DSS in a one-to-one correspondence, wherein the root index has three values ​​and may have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS may be used as the root index of the PD2DSS, and as an example, the root index of Table 4 may be used. For example, the value used may be a SD2DSS value mapped to an SSS having 168 sequences in a one-to-one correspondence. Thus, the SD2DSS may have an integer ranging from 0 to 167, and the PSSID may be mapped to 504 (=3*168) IDs.

[0213] When the synchronization source type is an ISS or a synchronization source derived from an ISS (SS relaying an ISS) (Cases 5, 6, and 7), the Proximity-Based Service (ProSe) UE ID of the UE corresponding to the ISS may be used as a Physical Synchronization Source Identifier (PSSID), and the PSSID may be mapped to 168 or K IDs based on a predetermined rule, where K is an integer less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or from 0 to K-1. The PSSID may be expressed as and associated with SD2DSS It may be mapped in a one-to-one manner to an SSS that may have 168 values ​​and may have an integer ranging from 0 to 167, or it may be mapped in a one-to-one manner to K values ​​based on a sequence modified or partially selected from an SSS having 168 sequences or an integer ranging from 0 to K-1, where K is an integer less than 168. In this case, the precise UE ID of the ISS may be transmitted through the PD2DSCH.

[0214] [Example 2-4]

[0215]

Table 13

[0216]

[0217] In this embodiment, when the type of the synchronization source is an eNodeB, the PCID of the eNodeB may be used as the PSSID, and 504 specific PSSIDs may be used.

[0218] When the type of synchronization source (SS) is SS derived from eNodeB (SS relaying eNodeB), ISS, or SS derived from ISS (SS relaying ISS), the PSSID can be determined based on the UE ID of the transmission synchronization source, and there can be 504 specific PSSIDs.

[0219] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the examples in Table 13 can be divided into two cases, namely, the case corresponding to Case 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Cases 2-7 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used can be that of Table 4.

[0220] When the transmission synchronization source is a UE, the type of the initial synchronization source can be indicated by a physical D2D synchronization channel (PD2DSCH). For example, the examples in Table 13 can be indicated based on such a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2-4 in which the type of the initial synchronization source is an eNodeB, and cases corresponding to cases 5-7 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH can have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source can be determined to be an eNodeB through the root index value of the PD2DSS. Therefore, there is no need to indicate this separately.

[0221] In addition, when the transmission synchronization source is a UE, the level can be indicated by the location used to transmit the D2DSS in the frequency resource domain or the PD2DSCH. For example, the example in Table 13 can be indicated based on a classification, wherein the classification is divided into three cases, namely, cases corresponding to cases 2 and 5 with a level index of 1, cases corresponding to cases 3 and 6 with a level index of 2, and another case corresponding to cases 4 and 7 with a level index of 3. Therefore, the indication value of the PD2DSCH can have a 2-bit value.

[0222] When the type of synchronization source is eNodeB (Case 1), the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index has three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0223] When the synchronization source type is a synchronization source derived from an eNodeB (SS relaying an eNodeB), an ISS, or a synchronization source derived from an ISS (SS relaying an ISS) (Examples 2, 3, 4, 5, 6, and 7), the proximity-based service (ProSe) UE ID of the transmitting (Tx) UE may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 504 IDs based on a predetermined mapping rule. The PSSID may be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index has three values ​​and can have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS can be used as the root index of the PD2DSS, and as an example, the root index used can be the root index of Table 4. It can be mapped in a one-to-one correspondence to an SSS that can have 168 sequences and can have integers ranging from 0 to 167. Thus, the PSSID can be mapped to 504 (=3*168) IDs.

[0224] [Example 2-5]

[0225]

Table 14

[0226]

[0227] In this embodiment, when the type of the synchronization source is an eNodeB, the PCID of the eNodeB may be used as the PSSID, and there may be 504 specific PSSIDs.

[0228] When the type of synchronization source (SS) is SS derived from eNodeB (SS relaying eNodeB), ISS or SS derived from ISS (SS relaying ISS), the PSSID based on the UE ID of the transmission synchronization source can be used, and there can be 168 or K specific PSSIDs, where K is less than 168.

[0229] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example in Table 14 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-7 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used can be that of Table 4.

[0230] When the transmission synchronization source is a UE, the type of the initial synchronization source can be indicated by a physical D2D synchronization channel (PD2DSCH). For example, the examples in Table 14 can be indicated based on such a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2-4 in which the type of the initial synchronization source is an eNodeB, and cases corresponding to cases 5-7 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH can have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source can be determined to be an eNodeB through the root index value of the PD2DSS. Therefore, there is no need to indicate this separately.

[0231] When the transmission synchronization source is the eNode B, the stratum has only an index value of 0. And, the stratum may be indicated by any one of 25, 29, and 34 which are the root indexes of the PD2DSS.

[0232] When the transmission synchronization source is the UE, the level can be indicated by the root index of the PD2DSS. For example, the example of Table 14 can be indicated based on a classification, wherein the classification is divided into three cases, namely, cases corresponding to cases 2 and 5 where the level index is 1, cases corresponding to cases 3 and 6 where the level index is 2, and cases corresponding to cases 4 and 7 where the level index is 3. Thus, for example, when the root indexes of the newly defined PD2DSS are X, Y, and Z, respectively, the root index X can be set to indicate level 1, the root index Y can be set to indicate level 2, and the root index Z can be set to indicate level 3. The root index of Table 4 can be used as the root index of the newly defined PD2DSS.

[0233] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0234] When the synchronization source type is a synchronization source derived from an eNodeB (SS relaying an eNodeB), an ISS, or a synchronization source derived from an ISS (SS relaying an ISS), the proximity-based service (ProSe) UE ID of the transmitting (Tx) UE may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 168 or K IDs based on a predetermined mapping rule, where K is a value less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or a value ranging from 0 to K-1. The PSSID may be expressed as and is associated with SD2DSS It can be mapped to the SSS having 168 sequences in a one-to-one correspondence, or can be mapped to K sequences based on sequences modified or partially selected from the SSS having 168 sequences, where K is a value less than 168. When mapped to 168 sequences, it can have an integer ranging from 0 to 167, and when mapped to K sequences in a one-to-one correspondence, it can have an integer ranging from 0 to K - 1. In this case, the precise UE ID of the transmission synchronization source can be transmitted through PD2DSCH.

[0235] Figure 4 is a conceptual diagram of a system to which a method for transmitting a synchronization signal is applied, according to one or more exemplary embodiments.

[0236] Figure 4 The upper half of FIG. 4 shows synchronization signal transmissions performed from an eNodeB 400 to a first UE 410, from the first UE 410 to a second UE 420, and from the second UE 420 to a third UE 430, respectively. The eNodeB 400 may be an initial synchronization source (initial SS) for the first UE 410, the second UE 420, and the third UE 430. The eNodeB 400 may be a transmission synchronization source (Tx SS) for the first UE 410, the first UE 410 may be a Tx SS for the second UE 420, and the second UE 420 may be a Tx SS for the third UE 430.

[0237] refer to Figure 4 In the lower part of the UE 440, the fourth UE 440 may not receive a synchronization signal from an eNodeB or other UEs, but may generate and transmit a synchronization signal independently. Thus, the fourth UE 440 corresponds to the ISS. The fourth UE 440 may transmit a direct synchronization signal to the fifth UE 450. Thus, relative to the fifth UE 450, the fourth UE 440 may be both an initial synchronization source (initial SS) and a transmission synchronization source (Tx SS). Figure 4In this example, there may be multiple UEs between fourth UE 440 and fifth UE 450. Fourth UE 440 may transmit a direct synchronization signal to one of the UEs, and the UEs that use UE 440 as the initial synchronization source may transmit a direct synchronization signal to fifth UE 450. Even in this case, that is, even if the synchronization of fourth UE 440, which serves as the initial synchronization source, is transmitted to fifth UE 450 via multiple UEs, fifth UE 450 assumes the first stratum to be a single stratum. In other words, when the initial synchronization source is the ISS, the stratum may be assumed to be the same value, or the stratum may not be defined.

[0238] Embodiments 3-1 to 3-5 describe a method for indicating D2D synchronization information when the initial synchronization source is eNodeB and the maximum layer is the third layer (if eNodeB is excluded, the maximum layer is the second layer) and when the initial synchronization source is ISS and the maximum layer is the first layer.

[0239] [Example 3-1]

[0240]

Table 15

[0241]

[0242] In this embodiment, when the type of synchronization source (SS) is eNodeB or SS derived from eNodeB (SS of relay eNodeB), the PCID of eNodeB can be used as the physical synchronization source identifier (PSSID), and there can be 504 specific PSSIDs.

[0243] When the type of synchronization source is an ISS or an SS derived from an ISS (an SS relaying an ISS), a PSSID based on a UE ID of the ISS may be used as the PSSID, and 504 specific PSSIDs may exist.

[0244] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example in Table 15 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-4 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root index of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used can be that of Table 4.

[0245] When the transmission synchronization source is a UE, the type of the initial synchronization source may be indicated using a physical D2D synchronization channel (PD2DSCH). For example, the examples in Table 15 may be indicated based on such a classification, wherein the classification is divided into two cases, namely, cases corresponding to cases 2 and 3 in which the type of the initial synchronization source is an eNodeB, and a case corresponding to case 4 in which the type of the initial synchronization source is an independent synchronization source (ISS). Thus, the indication value of the PD2DSCH may have a 1-bit value. When the transmission synchronization source is an eNodeB, the initial synchronization source may be determined to be an eNodeB through the root index value of the PD2DSS. Thus, there is no need to indicate this separately.

[0246] Furthermore, when the transmission synchronization source is a UE and the initial synchronization source is an eNodeB, the tier can be indicated by the location used to transmit the D2DSS in the frequency resource domain or the PD2DSCH. For example, Cases 2 and 3 corresponding to the conditions derived from Table 15 can be indicated based on a classification in which the classification is divided into two cases: Case 2 where the tier is the second tier, and Case 3 where the tier is the third tier. Thus, the PD2DSCH indication value can have a single 1-bit value. When the transmission synchronization source is an eNodeB, the tier is an event, and thus the tier can be identified by information associated with the type of transmission synchronization source.

[0247] Furthermore, the case where the transmission synchronization source is the ISS also corresponds to Case 4, where the case is an event and can be identified by information associated with the initial synchronization source, thereby not needing to be indicated separately.

[0248] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index has three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0249] Even if the synchronization source type is a synchronization source derived from an eNodeB, the physical synchronization source identifier (PSSID) may have a value equivalent to the PCID of the eNodeB, and there may be 504 specific PSSIDs. The PSSID may be expressed as and It may be mapped to the root index of the PD2DSS in a one-to-one correspondence, wherein the root index has three values ​​and may have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS may be used as the root index of the PD2DSS, and as an example, the root index of Table 4 may be used. For example, the value used may be a SD2DSS value mapped to an SSS having 168 sequences in a one-to-one correspondence. Thus, the SD2DSS may have an integer ranging from 0 to 167, and the PSSID may be mapped to 504 (=3*168) IDs.

[0250] When the synchronization source type is an ISS or a synchronization source derived from an ISS, a proximity-based service (ProSe) UE ID of a UE corresponding to the ISS may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 504 IDs based on a predetermined rule. The PSSID may be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index can have three values ​​and can have an integer ranging from 0 to 2. As an example, the root index used can be the root index of Table 4. For example, the values ​​used may be the values ​​of the SD2DSS that are mapped to the SSS having 168 sequences in a one-to-one correspondence. It can be mapped in a one-to-one correspondence to an SSS that can have 168 sequences and integers ranging from 0 to 167. Thus, the PSSID can be mapped to 504 (=3*168) IDs.

[0251] [Example 3-2]

[0252] Table 16

[0253]

[0254] In this embodiment, when the synchronization source (SS) type is an eNodeB, the PCID of the eNodeB can be used as the PSSID, and there can be 504 specific PSSIDs. When the synchronization source type is a synchronization source (SS) derived from an eNodeB (SS of a relay eNodeB), a value modified based on the PCID of the eNodeB can be used as the PSSID, and there can be 168 or K PSSIDs, where K is an integer less than 168.

[0255] When the type of synchronization source (SS) is an ISS or an SS derived from an ISS (SS relaying an ISS), the PSSID may be determined based on the UE ID of the ISS, and there may be 168 or K specific PSSIDs, where K is an integer less than 168.

[0256] In this embodiment, the type of transmission synchronization source is indicated by the root index value of the PD2DSS. In Example 1 of Table 16, the transmission synchronization source is the eNodeB. Therefore, one of 25, 29, and 34, which are equivalent to the root index of the PSS, can be used as the root index of the PD2DSS. In contrast, in Examples 2-4, a newly defined root index different from the root index of the PSS can be used as the PD2DSS. As an example, the root index of Table 4 can be used.

[0257] For cases 2-4 where the transmission synchronization source is a UE, the cases can be divided into cases corresponding to cases 2 and 3 where the initial synchronization source is an eNodeB, and cases corresponding to case 4 where the initial synchronization source is an ISS. For example, when the three root indexes selected from Table 4 are X, Y, and Z, respectively, in case 2 or 3 where the initial synchronization source is an eNodeB, the transmission synchronization source can be indicated by root index X or Y, and in case 4 where the initial synchronization source is an ISS, the transmission synchronization source can be indicated by root index Z.

[0258] The hierarchy can be indicated by the root index of the PD2DSS. In Example 1 where the transmission synchronization source and the initial synchronization source are the eNodeB, the root index of the PD2DSS can be indicated by one of 25, 29, and 34.

[0259] For cases 2-4 where the transmission synchronization source is the UE, these cases can be indicated by the newly defined root index value of the PD2DSS. When the three root index values ​​of the newly defined PD2DSS are X, Y, and Z, each of cases 2-4 can be indicated by X, Y, and Z. For example, case 2 can be indicated by X, case 3 can be indicated by Y, and case 4 can be indicated by Z.

[0260] When the type of synchronization source is eNodeB (Case 1), the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0261] When the type of synchronization source is a synchronization source derived from an eNodeB (SS relaying an eNodeB) (cases 2 and 3), a physical synchronization source identifier (PSSID) may be mapped to 168 or K IDs based on the PCID of the eNodeB using a predetermined rule, where K is an integer less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or from 0 to K-1. The PSSID may be expressed as and associated with SD2DSS It may be mapped in a one-to-one manner to an SSS that may have 168 values ​​and may have an integer ranging from 0 to 167, or it may be mapped in a one-to-one manner to K values ​​based on a sequence modified or partially selected from an SSS having 168 sequences or an integer ranging from 0 to K-1, where K is an integer less than 168. In this case, the precise PCID of the eNodeB may be transmitted through the PD2DSCH.

[0262] When the type of synchronization source is an ISS or a synchronization source derived from an ISS (Case 4), the proximity-based service (ProSe) UE ID of the UE corresponding to the ISS may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 168 or K IDs based on a predetermined rule, where K is an integer less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or from 0 to K-1. The PSSID may be expressed as and is associated with SD2DSS It can be mapped in a one-to-one manner to an SSS that can have 168 values ​​and an integer ranging from 0 to 167, or it can be mapped in a one-to-one manner to K values ​​based on a sequence modified or partially selected from an SSS having 168 sequences or an integer ranging from 0 to K-1, where K is an integer less than 168. Thus, the PSSID can have a value ranging from 0 to 167 or ranging from 0 to K-1. In this case, the accurate PCID of the ISS can be transmitted through the PD2DSCH.

[0263] [Example 3-3]

[0264]

Table 17

[0265]

[0266] In this embodiment, when the type of synchronization source is eNodeB or an SS derived from eNodeB (SS relaying eNodeB), the PCID of the eNodeB may be used as a physical synchronization source identifier (PSSID), and there may be 504 specific PSSIDs.

[0267] When the synchronization source (SS) type is ISS or SS derived from ISS (SS relaying ISS), the PSSID used may be based on the UE ID of the ISS, and there may be 168 or K specific PSSIDs, where K is an integer less than 168.

[0268] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example in Table 17 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-4 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root index of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. As an example, the root index of Table 4 can be used.

[0269] When the transmission synchronization source is a UE, the type of the initial synchronization source can be indicated using a physical D2D synchronization channel (PD2DSCH). For example, the example in Table 17 can be indicated based on such a classification, where the classification is divided into two cases, namely, cases 2 and 3 corresponding to the initial synchronization source type being an eNodeB, and case 4 corresponding to the initial synchronization source type being an independent synchronization source (ISS). Therefore, the indication value of the PD2DSCH can have a 1-bit value.

[0270] When the transmission synchronization source is a UE and the initial synchronization source is an eNodeB, the tier can be indicated by the location used to transmit the D2DSS in the frequency resource domain or the PD2DSCH. For example, Cases 2 and 3 corresponding to the conditions derived from Table 15 can be indicated based on a classification in which the classification is divided into two cases, namely, Case 2 where the tier is the second tier and Case 3 where the tier is the third tier. Thus, the indication value of the PD2DSCH can have a single bit. When the transmission synchronization source is an eNodeB, the tier is a single event, and thus the tier can be identified by information associated with the type of transmission synchronization source.

[0271] Also, the case where the transmission synchronization source is the ISS corresponds to Case 4, where the cases are the same event, and thus can be identified by information associated with the initial synchronization source, and thus do not need to be indicated separately.

[0272] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0273] Even if the type of synchronization source is a synchronization source derived from an eNodeB, a physical synchronization source identifier (PSSID) may have a value equivalent to the PCID of the eNodeB, and there may be 504 specific PSSIDs. The PSSID may be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index has three values ​​and can have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS can be used as the root index of the PD2DSS, and as an example, the root index used can be the root index in Table 4. For example, the value used may be a SD2DSS value mapped to an SSS having 168 sequences in a one-to-one correspondence. Thus, the SD2DSS may have an integer ranging from 0 to 167, and the PSSID may be mapped to 504 (=3*168) IDs.

[0274] When the type of synchronization source is an ISS or a synchronization source derived from an ISS (Case 4), the proximity-based service (ProSe) UE ID of the UE corresponding to the ISS may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 168 or K IDs based on a predetermined rule, where K is an integer less than 168. Thus, the PSSID may have a value ranging from 0 to 167 or from 0 to K-1. The PSSID may be expressed as and associated with SD2DSS It may be mapped in a one-to-one manner to an SSS that may have 168 values ​​and may have an integer ranging from 0 to 167, or it may be mapped in a one-to-one manner to K values ​​based on a sequence modified or partially selected from an SSS having 168 sequences or an integer ranging from 0 to K-1, where K is an integer less than 168. In this case, the precise UEID of the ISS may be transmitted through the PD2DSCH.

[0275] [Example 3-4]

[0276] Table 18

[0277]

[0278] In this embodiment, when the type of the synchronization source is an eNodeB, the PCID of the eNodeB may be used as the PSSID, and there may be 504 specific PSSIDs.

[0279] When the type of synchronization source (SS) is SS derived from eNodeB (SS relaying eNodeB), ISS or SS derived from ISS (SS relaying ISS), the PSSID based on the UE ID of the transmission synchronization source can be used as the PSSID, and there can be 504 specific PSSIDs.

[0280] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example in Table 18 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-4 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root indexes of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used can be that of Table 4.

[0281] When the transmission synchronization source is a UE, the type of the initial synchronization source can be indicated using a physical D2D synchronization channel (PD2DSCH). For example, the example in Table 18 can be indicated based on such a classification, where the classification is divided into two cases, namely, cases 2 and 3 corresponding to the initial synchronization source type being an eNodeB, and case 4 corresponding to the initial synchronization source type being an independent synchronization source (ISS). Therefore, the indication value of the PD2DSCH can have a 1-bit value.

[0282] When the transmission synchronization source is an eNodeB, the hierarchy does not exist, thereby excluding Case 1, and this can be identified by information associated with the synchronization source. Therefore, this case does not need to be separately indicated.

[0283] When the transmission synchronization source is an SS derived from an eNodeB (SS of a relay eNodeB), the tier can be indicated by the location used to transmit the D2DSS in the frequency resource domain or PD2DSCH. For example, the example in Table 18 can be divided into two cases: case 2 corresponding to tier 2 and case 3 corresponding to tier 3. Therefore, the PD2DSCH indication value can have a 1-bit value.

[0284] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index has three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0285] When the type of synchronization source is a synchronization source derived from an eNodeB (SS relaying an eNodeB), an ISS, or a synchronization source derived from an ISS (SS relaying an ISS), the proximity-based service (ProSe) UE ID of the transmitting (Tx) UE may be used as a physical synchronization source identifier (PSSID), and the PSSID may be mapped to 504 IDs based on a predetermined mapping rule. The PSSID may be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index has three values ​​and can have an integer ranging from 0 to 2. In this case, a newly defined root index different from the root index of the PSS can be used as the root index of the PD2DSS, and as an example, the root index used can be the root index of Table 4. It can be mapped in a one-to-one correspondence to an SSS that can have 168 sequences and integers ranging from 0 to 167. Thus, the PSSID can be mapped to 504 (=3*168) IDs.

[0286] [Examples 3-5]

[0287] Table 19

[0288]

[0289] In this embodiment, when the type of the synchronization source is an eNodeB, the PCID of the eNodeB may be used as the PSSID, and there may be 504 specific PSSIDs.

[0290] When the type of synchronization source (SS) is SS derived from eNodeB (SS relaying eNodeB), ISS or SS derived from ISS (SS relaying ISS), the PSSID used can be based on the UE ID of the transmission synchronization source, and there can be 168 or K specific PSSIDs, where K is less than 168.

[0291] In this embodiment, the type of transmission synchronization source can be indicated by the root index value of the PD2DSS. For example, the example in Table 19 can be divided into two cases, namely, the case corresponding to Example 1 in which the transmission synchronization source is an eNodeB, and the other case corresponding to Examples 2-4 in which the transmission synchronization source is a UE, and each case can be indicated by the root index value of the PD2DSS. When the transmission synchronization source is an eNodeB, the PD2DSS can use 25, 29, and 34, which are equivalent to the root index of the PSS. When the transmission synchronization source is a UE, the PD2DSS can use a newly defined root index that is different from the root index of the PSS. For example, the root index used can be that of Table 4.

[0292] For cases 2-4 where the transmission synchronization source is a UE, the cases can be divided into cases corresponding to cases 2 and 3 where the initial synchronization source is an eNodeB, and cases corresponding to case 4 where the initial synchronization source is an ISS. For example, when the three root indexes selected from Table 4 are X, Y, and Z, respectively, in case 2 or 3 where the initial synchronization source is an eNodeB, the transmission synchronization source can be indicated by root index X or Y, while in case 4 where the initial synchronization source is an ISS, the transmission synchronization source can be indicated by root index Z.

[0293] The hierarchy can be indicated by the root index of the PD2DSS. In Example 1 where the transmission synchronization source and the initial synchronization source are the eNodeB, the root index of the PD2DSS can be indicated by one of 25, 29, and 34.

[0294] For cases 2-4 where the transmission synchronization source is the UE, these cases can be indicated by the newly defined root index value of the PD2DSS. When the three root index values ​​of the newly defined PD2DSS are X, Y, and Z, each of cases 2-4 can be indicated by X, Y, and Z. For example, case 2 can be indicated by X, case 3 can be indicated by Y, and case 4 can be indicated by Z.

[0295] When the synchronization source type is eNodeB, the physical layer cell ID corresponding to the PCID of the eNodeB It can be used as a physical synchronization source identifier (PSSID). The physical layer cell ID can be expressed as and It can be mapped to the root index of the PD2DSS in a one-to-one correspondence, where the root index can have three values ​​and can have an integer ranging from 0 to 2. In this case, the root index of the PD2DSS can have one of 25, 29 and 34, which is equivalent to the root index of the PSS. It may be mapped to a root index of the SD2DSS in a one-to-one correspondence, wherein the root index may have 168 values ​​and may have an integer ranging from 0 to 167. In this case, a value equivalent to the SSS may be used as a value of the SD2DSS.

[0296] When the type of synchronization source is a synchronization source derived from an eNodeB (SS relaying an eNodeB), an ISS, or a synchronization source derived from an ISS (SS relaying an ISS), a physical synchronization source identifier (PSSID) is based on the proximity-based service (ProSe) UE that the transmitting (Tx) UE has, and can be mapped to 168 or K IDs based on a predetermined mapping rule, where K is a value less than 168. Thus, the PSSID can have a value ranging from 0 to 167 or a value ranging from 0 to K-1. The PSSID can be expressed as and is associated with SD2DSS It can be mapped to the SSS having 168 sequences in a one-to-one correspondence, or can be mapped to K values ​​based on a sequence modified or partially selected from the SSS having 168 sequences, where K is an integer less than 168. When mapped to 168 sequences, it can have an integer ranging from 0 to 167, and when mapped to K sequences in a one-to-one correspondence, it can have an integer ranging from 0 to K - 1. In this case, the precise UE ID of the transmission synchronization source can be transmitted through PD2DSCH.

[0297] Figure 5 is a block diagram of a wireless communication system according to one or more exemplary embodiments.

[0298] refer to Figure 5 The D2D synchronization source 500 includes a radio frequency (RF) unit 505, a processor 510, and a memory 515. The memory 515 is connected to the processor 510 and stores various information for driving the processor 510. The RF unit 505 is connected to the processor 510 and transmits and / or receives wireless signals. For example, the RF unit 505 can send a D2DSS to a UE 550 performing D2D reception.

[0299] The processor 510 can implement the proposed functions, processes and / or methods. In particular, the processor 510 can execute Figure 2-4 For example, the processor 510 may include a synchronization information determining unit 511 and a D2DSS generating unit 513 .

[0300] The synchronization information determining unit 511 may determine synchronization information for generating the D2DSS. The synchronization information may include the type of synchronization source, a physical synchronization source identifier (PSSID), and a layer.

[0301] The D2DSS generation unit 513 generates a D2DSS based on the type, PSSID, and layer information of the synchronization source determined in the synchronization information determination unit 511. The D2DSS may include a PD2DSS, an SD2DSS, and a PD2DSCH. The type of synchronization source, the physical synchronization source identifier (PSSID), and layer information may be indicated by the D2DSS, and some information may be indicated by the position of the D2DSS in a subframe.

[0302] According to one or more exemplary embodiments, information associated with the synchronization source, such as synchronization source (SS) type, physical synchronization source identification (PSSID), tier, etc., may be estimated based on the received D2DSS. Operations of UE 500 may be implemented by processor 510.

[0303] The memory 515 is connected to the processor 510 and stores various information for driving the processor 510. For example, the memory 515 may store synchronization information and may store the PD2DSS, SD2DSS, PD2DSCH, and the location for receiving the D2DSS in the time-frequency resource. Furthermore, the memory 515 may provide the synchronization information to the processor 510 in response to a request from the processor 510.

[0304] The UE 550 performing D2D reception may include a processor 555, a memory 560, and a radio frequency (RF) unit 565. The RF unit 565 is connected to the processor 555 and transmits and / or receives wireless signals. The processor 555 may implement the proposed functions, processes, and / or methods. For example, the processor 555 may include a D2DSS determination unit 557 and a synchronization unit 559.

[0305] The D2D determination unit 557 can determine the D2DSS received from the D2D synchronization source 500, thereby estimating the synchronization information indicated by the received D2DSS. The synchronization information may include the type of synchronization source, the physical synchronization source identifier (PSSID), and the hierarchy. The D2DSS used to indicate synchronization information may include the PD2DSS, SD2DSS, and PD2DSCH. Some of the synchronization information may be indicated by the position of the D2DSS in a subframe.

[0306] The synchronization unit 512 may acquire synchronization with a synchronization source using information acquired through the D2DSS.

[0307] The processor 510 of the D2D synchronization source 500 or the processor 555 of the UE 550 performing D2D reception may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and / or data processing devices. The memory may include a read-only memory (ROM), a random access memory (RAM), flash memory, a memory card, a storage medium, and / or other storage devices. The RF unit may include baseband circuitry for processing wireless signals. When the embodiments are implemented as software, the described scheme may be implemented as a module (processing, function, etc.) that performs the described functions. The module may be stored in a memory and may be executed by a processor. The memory may be configured internally or externally to the processor and may be connected to the processor by various well-known means.

[0308] In the described exemplary system, although the method is described as a series of steps or blocks based on the flowchart, aspects of the present invention are not limited to the order of these steps, and the steps can be performed in a different order or in parallel with other steps. In addition, it is obvious to those skilled in the art that the steps in the flowchart are not exclusive, and other steps can also be included without affecting the scope of the present invention, or one or more steps in the flowchart can be omitted.

[0309] The following describes in detail the method for configuring the D2DSS based on synchronization information. First, the method for configuring the PD2DSS will be described with reference to different types of synchronization sources. Although the following description is based on the Figure 4 The illustrated case is based on the case where the initial synchronization source is the eNodeB and the maximum stratum is layer 3 (when the eNodeB is excluded, the maximum stratum is layer 2) and the case where the initial synchronization source is the ISS and the maximum stratum is layer 1 (or undefined), but the description is also applicable to the case where the initial synchronization source is the eNodeB and the maximum stratum is layer 3 (when the eNodeB is excluded, the maximum stratum is layer 2). Figure 2 and 3 The example described.

[0310] Configuration 1) When the synchronization source is an eNode B

[0311] In this case, the PD2DSS is a synchronization signal sent from an eNodeB to a UE, and the UE may be a UE within network coverage (an in-coverage UE). In this case, both the original synchronization source and the transmission synchronization source are the eNodeB, so the PD2DSS, which is identical to the PSS, may be transmitted. Therefore, the root index of the PD2DSS, which is equivalent to the PSS, may be one of 25, 29, and 34.

[0312] Reference again Figure 4 , this case may correspond to transmission from the eNodeB 400 to the first UE 410.

[0313] Configuration 2) When the synchronization source is an SS derived from an eNodeB (SS of a relay eNodeB), and the transmitting UE is a UE within the network coverage, for example, within the coverage of the eNodeB (in-coverage UE)

[0314] In this case, the transmitted PD2DSS is a synchronization signal modified from the PSS (e.g., root index, etc.), and the PD2DSS can be configured from the D2DSS sequence contained in D2DSSue_net. The D2DSSue_net indicates a set of D2DSS sequences transmitted from a UE whose transmission timing reference is the eNodeB. The transmission of the D2D synchronization signal is a UE-to-UE transmission, with the transmitting (Tx) UE being an in-coverage UE and the receiving (Rx) UE being a UE outside of network coverage (out-of-coverage UE).

[0315] Here, the Tx UE receives a synchronization signal generated from the PSS / SSS from the eNodeB, and transmits synchronization information obtained through the reception to the Rx UE through a synchronization signal generated from the first D2DSS sequence (first PD2DSS sequence+first SD2DSS) included in D2DSSue_net.

[0316] Reference again Figure 4 , the transmission may correspond to transmission from the first UE 410 to the second UE 420. In this case, a newly defined root index different from the root index of the PSS may be used as the root index of the PD2DSS, and the root index of the PD2DSS may be defined as shown in Table 4. When the three newly defined root indexes are X, Y, and Z, X may be used in this case. That is, X may be used as the root index of the first PD2DSS sequence.

[0317] Configuration 3) When the synchronization source is an SS derived from an eNodeB (SS of a relay eNodeB), and the transmitting UE is a UE outside the network coverage, for example, outside the coverage of the eNodeB (out-of-coverage UE)

[0318] In this case, the transmitted PD2DSS may be configured from the D2DSS sequence contained in D2DSSue_net in the same manner as the case where the transmitting UE is an in-coverage UE. In this case, both the Tx UE and the Rx UE may be out-of-coverage UEs.

[0319] Here, the Tx UE receives the synchronization signal generated from the first D2DSS sequence (first PD2DSS sequence + first SD2DSS sequence) included in the D2DSSue_net from the UE in coverage, and sends the synchronization information obtained through the reception to the Rx UE through the synchronization signal generated from the second D2DSS sequence (second PD2DSS sequence + second SD2DSS sequence) included in the D2DSSue_net.

[0320] Reference again Figure 4 , the transmission may correspond to a transmission from the second UE 420 to the third UE 430. In this case, a newly defined root index different from the root index of the PSS may be used as the root index of the PD2DSS, and the root index of the PD2DSS may be defined as shown in Table 4. When the three newly defined root indexes are X, Y, and Z, the root index used may be Y, which is different from the root index used when the transmitting UE is an in-coverage UE. That is, Y may be used as the root index of the second PD2DSS sequence.

[0321] Configuration 4) When the synchronization source is the ISS or an SS derived from the ISS (an SS relaying the ISS)

[0322] In this case, the transmitted PD2DSS can be a synchronization signal modified from the PSS (e.g., root index, etc.). The PD2DSS can be configured from the D2DSS sequence included in D2DSSue_oon and can be transmitted. D2DSSue_oon indicates a set of D2DSS sequences transmitted from a UE whose transmission timing reference is not the eNodeB. In this case, both the Tx UE and the Rx UE can be out-of-coverage UEs, and the Tx UE can be an ISS or an SS derived from the ISS (an SS that relays the ISS).

[0323] Here, when the Tx UE is an ISS, the Tx UE may transmit its own synchronization information to the Rx UE through a synchronization signal generated from the third D2DSS sequence (third PD2DSS sequence+third SD2DSS sequence) included in D2DSSue_oon.

[0324] Here, when the TxUE is an SS derived from the ISS, the TxUE will receive the synchronization signal generated from the third D2DSS sequence (third PD2DSS sequence + third SD2DSS sequence) contained in the D2DSSue_oon from the ISS or other SS derived from the ISS, and when the opportunity arises, it can transmit the synchronization information obtained through the reception to or not to the receiving (Rx) UE through the synchronization signal generated from the third D2DSS sequence (third PD2DSS sequence + third SD2DSS sequence) contained in the D2DSS ue_oon.

[0325] Reference again Figure 4 , which may correspond to transmission from the fourth UE 440 to the fifth UE 450. In this case, a newly defined root index different from the root index of the PSS may be used as the root index of the PD2DSS, and the root index of the PD2DSS may be defined as Table 4. When the three newly defined root indexes are X, Y, and Z, respectively, Z may be used as the root index, which is different from X and Y used when the synchronization source is an SS derived from an eNodeB (SS of a relay eNodeB). That is, Z may be used as the root index of the third PD2DSS sequence.

[0326] The following describes a method for configuring a PD2DSS when a UE performing D2D reception (Rx) is within or outside network coverage.

[0327] 1) The UE performing D2D reception (Rx) is within the network coverage

[0328] A D2D Rx UE within network coverage detects the PSS / SSS from the eNodeB and selects it as the timing reference. In this case, the PSS may correspond to the PSS of Configuration 1. A D2D Rx UE within network coverage may detect a D2DSS other than the PSS / SSS from the eNodeB, prioritize the PSS / SSS from the eNodeB, and select it as the timing reference. The D2D Rx UE may transmit the D2DSS to other UEs. In this case, the transmitted PD2DSS may correspond to the PD2DSS of Configuration 2.

[0329] 2) UE performing D2D reception (Rx) outside network coverage

[0330] A D2D Rx UE outside network coverage can detect one or more D2DSSs from one or more UEs and can select one of the signals as the timing reference. In this case, the D2D Tx UE can be one of the ISS, the SS derived from the eNodeB (the SS relaying the eNodeB), and the SS derived from the ISS (the SS relaying the ISS). If no D2DSS is detected, the D2D Rx UE itself can act as the ISS. In this case, the root index of the detected PD2DSS can be one of X, Y, and Z. The following describes the timing reference selection method for each case and the PD2DSS transmission method when the D2D Rx UE is the new synchronization source.

[0331] a) When a PD2DSS with a root index of X is received and selected as the timing reference

[0332] In this case, the D2D Rx UE detects a D2DSS including a PD2DSS corresponding to Configuration 2 and selects it as the timing reference. When the UE is the synchronization source of the D2DSS, the UE can transmit the D2DSS. In this case, the transmitted PD2DSS can be configured as a PD2DSS of Configuration 3.

[0333] a) When a PD2DSS with a root index of Y is received and selected as the timing reference

[0334] In this case, the D2D Rx UE detects a D2DSS including a PD2DSS corresponding to Configuration 3 and selects it as the timing reference. When the UE is the synchronization source of the D2DSS, the UE can transmit the D2DSS. In this case, the transmitted PD2DSS can be configured as a PD2DSS of Configuration 3.

[0335] a) When a PD2DSS with a root index of Z is received and selected as the timing reference

[0336] In this case, the D2D Rx UE detects a D2DSS including a PD2DSS corresponding to Configuration 4 and selects it as the timing reference. When the UE is the synchronization source of the D2DSS, the UE can transmit the D2DSS. In this case, the transmitted PD2DSS can be configured as a PD2DSS of Configuration 4.

[0337] d) When D2DSS is not detected

[0338] In this case, the D2D Rx UE may act as an ISS and transmit a D2DSS. In this case, the transmitted PD2DSS may be configured as a PD2DSS of Configuration 4.

[0339] When the D2D Rx UE receives all PD2DSSs with root indices X, Y, and Z, it may select the timing reference in the order of X>Y>Z or in different priority orders.

[0340] Hereinafter, a method for configuring PD2DSS of configurations 1-4 based on each hop number and level when the original synchronization source is an eNodeB or an ISS will be described.

[0341] First, described are the hierarchy and configuration of the D2DSS for each hop number when the initial synchronization source is the eNodeB. When the hop number is 1, the hierarchy is set to 0, and the transmitted D2DSS may include a PSS of configuration 1. When the hop number is 2, the hierarchy is set to 1, and the transmitted D2DSS may include a PD2DSS of configuration 2. When the hop number is 3, the hierarchy is set to 2, and the transmitted D2DSS may include a PD2DSS of configuration 3. When the hop number is 4 or more, the hierarchy is set to 2, and the transmitted D2DSS may include a PD2DSS of configuration 3. These configurations may be applied to reference Figure 2-4 The described embodiment. Figures 2 to 4 , and other configurations may be applied to other embodiments.

[0342] Described below is the hierarchy and configuration of the D2DSS for each hop number when the initial synchronization source is the ISS. When the hop number is 1, the hierarchy is set to 0, and the transmitted D2DSS may include a PD2DSS of configuration 4. When the hop number is 1 or greater, the hierarchy is set to 0, and the transmitted D2DSS may include a PD2DSS. These configurations may be applied to reference Figure 4 The embodiments described herein are intended to be construed as follows, and other configurations may apply to other embodiments.

[0343] The sequence of SD2DSS can be defined to use one of 168 sequences in the same manner as the sequence of SSS, where the 168 sequences are generated by interleaving two binary sequences of length 31, or it can also be defined to use only K sequences based on sequences modified or partially selected from SSS having 168 sequences.

[0344] In this case, K may be an integer smaller than 168.

[0345] Figure 6 is a flowchart illustrating an example method by which a D2D Rx UE may select a D2D transmission mode based on a received root index value of a PD2DSS according to one or more exemplary embodiments.

[0346] refer to Figure 6 A method for estimating a D2D transmission mode includes: receiving at least one D2DSS in step S605; and extracting a PD2DSS from the received D2DSS in step S615 to estimate a root index of the PD2DSS. Subsequently, in step S620, the D2D Rx UE determines whether a D2DSS exists whose root index value corresponds to one of 25, 29, and 34. If it is determined that a corresponding D2DSS exists, then in step S625, the D2D transmission mode selects the D2DSS of configuration 1 as a timing reference.

[0347] If it is determined in step S620 that the corresponding root index value does not exist, then in step S630, the D2D Rx UE determines whether there is a root index value of the PD2DSS corresponding to X among the previously defined values. If it is determined that the corresponding root index value exists, then in step 635, the D2D Rx UE selects the D2DSS of configuration 2 as the timing reference. The previously defined root index value may be one of the root indexes in Table 4, or the first value of the three root indexes may be set to X.

[0348] If it is determined in steps S620 and S630 that the corresponding root index value does not exist, then in step S640, the D2D Rx UE determines whether a root index value of the PD2DSS corresponding to Y exists among the previously defined values. If it is determined that the corresponding root index value exists, then in step 645, the D2D Rx UE selects the D2DSS of configuration 3 as the timing reference. The previously defined root index value may be one of the root indexes in Table 4, or the second value of the three root indexes may be set to Y.

[0349] If it is determined in steps S620, S630, and S640 that a corresponding root index value does not exist, then in step S650, the D2D Rx UE determines whether a root index value of the PD2DSS corresponding to Z exists among the previously defined values. If it is determined that a corresponding root index value exists, then in step S655, the D2D Rx UE selects the D2DSS of configuration 4 as the timing reference. The previously defined root index value may be one of the root indexes in Table 4, or the third value of the three root indexes may be set to Z.

[0350] In steps S620, 630, 640, and 650, if no root indexes corresponding to 25, 29, 34, X, Y, and Z are detected, then in step S660, the UE itself acts as an ISS and transmits a D2DSS. In this case, the transmitted D2DSS may be configured to include a PD2DSS of configuration 4.

[0351] The exemplary embodiments herein provide root indexes for the PD2DSS for each configuration type. For configuration 1 (PSS / SSS configuration when the synchronization source is an eNodeB), one of 25, 29, and 34, which are root indices of the PSS, will be used as the root index of the PD2DSS. For configuration 2 (D2DSS sequence configuration included in D2DSSue_net when the synchronization source is an SS derived from an eNodeB (SS for a relay eNodeB) and the Tx UE is an in-coverage UE), one of the three new root indices is used (e.g., X is the first value of the three new root indices in Table 4). For configuration 3 (D2DSS sequence configuration included in D2DSSue_net when the synchronization source is an SS derived from an eNodeB (SS for a relay eNodeB) and the Tx UE is an out-of-coverage UE), another root index of the three new root indices is used (e.g., Y, where Y is the second value of the three new root indices in Table 4). For configuration 4 (D2DSS sequence configuration included in D2DSSue_oon when the synchronization source is the ISS or the SS derived from the ISS (SS relaying the ISS)), another one of the three new root indexes is used (for example, Z, where Z is the third value of the three new root indexes in Table 4).

[0352] If three new root indexes are not defined and only the three existing root indexes 25, 29 and 34 are used, then one of 25, 29 and 34 can be configured as X (for example, X=25), another can be configured as Y (for example, Y=29), and another can be configured as Z (for example, Z=34).

[0353] As described above, the type of initial synchronization source, such as an eNodeB or an independent synchronization source (ISS), may be indicated by other information besides the root index, such as a PD2DSCH indication value that may have a 1-bit value. Furthermore, whether the transmission synchronization source is an in-coverage UE or an out-of-coverage UE may be determined based on other information besides the root index.

[0354] Furthermore, according to one or more exemplary embodiments, a UE supporting D2D communication may receive a synchronization signal transmitted from a synchronization source, determine a root index based on the received synchronization signal, determine a synchronization timing reference based on the root index, and transmit a synchronization signal for D2D communication based on the determined synchronization timing reference. The UE may receive more than one synchronization signal transmitted from different synchronization sources respectively. If the received synchronization signal meets certain requirements, such as received signal power, the UE may select one of the received synchronization signals and may select a corresponding reference synchronization source to synchronize the UE. By selecting a synchronization source, the UE may determine a synchronization timing reference based on the corresponding synchronization signal. The synchronization signal transmitted from the synchronization source may include a primary synchronization signal and a secondary synchronization signal. The secondary synchronization signal may be transmitted together with the primary synchronization signal or separately from the primary synchronization signal.

[0355] The UE may determine the type of synchronization source based on the root index associated with the primary synchronization signal transmitted from the synchronization source. Based on the root index associated with the received primary synchronization signal, it may be determined whether the primary synchronization signal is a PSS transmitted by the eNodeB or a PD2DSS transmitted by the UE.

[0356] The UE may then prioritize synchronization sources based on determining whether the synchronization source is an eNodeB, a UE synchronized with an eNodeB, or a UE having a synchronization timing reference independent of the eNodeB. The synchronization timing reference and / or reference synchronization source may be determined based on priority.

[0357] The UE may also determine whether the synchronization source is a UE within the coverage of the eNodeB or a UE outside the coverage of the eNodeB among the UEs synchronized with the eNodeB. In this configuration, the UE may further determine whether the synchronization source is a UE within the coverage of the eNodeB or a UE outside the coverage of the eNodeB, and prioritize the synchronization sources accordingly. Here, the UE synchronized with the eNodeB may be a UE that synchronizes directly with the eNodeB or a UE that uses the eNodeB as its initial synchronization source.

[0358] Once the UE selects a reference synchronization source for the UE to complete its own synchronization processing, the UE can generate synchronization signals for D2D communication with the target UE based on the category of the reference synchronization source. For example, if an eNodeB or a UE synchronized with an eNodeB is selected as the reference synchronization source, the UE can generate synchronization signals for D2D communication with the target UE based on the set for within coverage (D2DSSue_net). Furthermore, if a UE with a synchronization timing reference independent of the eNodeB is selected as the reference synchronization source, the UE can generate synchronization signals for D2D communication with the target UE based on the set for outside coverage (D2DSSue_oon). Since the UE is not an eNodeB, the synchronization signal used for D2D communication with the target UE is associated with a root index different from root indices 25, 29 and 34.

[0359] According to one or more exemplary embodiments, a synchronization signal used for D2D communication with a target UE may include a primary D2D synchronization signal and a secondary D2D synchronization signal, wherein the primary synchronization signal is associated with a root index corresponding to a number other than 25, 29, and 34. The primary D2D synchronization signal and the secondary D2D synchronization signal may be transmitted using different frequency-time resources. The secondary D2D synchronization signal may be generated based on one of 168 identifiers corresponding to a set for in-coverage (D2DSSue_net) or one of 168 identifiers corresponding to a set for out-of-coverage (D2DSSue_oon).

[0360] If no synchronization reference source is selected, the UE can independently determine the synchronization timing reference, thereby becoming an independent synchronization source that is not associated with the synchronization timing of the eNode B. When the UE acts as an independent synchronization source (ISS) or the UE selects a reference synchronization timing source derived from a UE acting as an ISS, the UE can transmit a synchronization signal determined based on the out-of-coverage set (D2DSSue_oon).

[0361] According to one or more exemplary embodiments, D2D synchronization information may be effectively indicated based on a device for transmitting or receiving a D2D signal.

[0362] The above description is intended to illustrate exemplary embodiments of the concepts of the present invention. It will be apparent to those skilled in the art that various modifications and variations are possible without departing from the spirit and scope of the concepts of the present invention. Therefore, the present invention intends to cover modifications and variations of the exemplary embodiments provided they fall within the scope of the appended claims and their equivalents.

Claims

1. A first wireless user equipment, comprising: a receiver for receiving a synchronization signal transmitted from a synchronization source; a processor configured to determine a root index value based on the received synchronization signal, and to determine a synchronization timing reference based on the root index value; as well as a transmitter, configured to transmit a synchronization signal for communication between the first wireless user equipment and the second wireless user equipment based on the determined synchronization timing reference, The processor is configured to determine the synchronization timing reference by performing the following operations: Determining a category of the synchronization source based on the root index value; prioritizing the synchronization sources among wireless user devices synchronized with one or more base stations based on determining whether the synchronization sources are wireless communication devices located within the coverage area of ​​the base station or wireless communication devices located outside the coverage area of ​​the base station; and The synchronization timing reference is determined based on the prioritization.

2. The first wireless user equipment according to claim 1, wherein The root index value is one of a plurality of values ​​including: a first value indicating that the synchronization source is a base station; a second value indicating that the synchronization source is a wireless user equipment synchronized with a base station; and A third value indicates that the synchronization source is a wireless user equipment having a synchronization timing reference independent of the base station.

3. The first wireless user equipment according to claim 2, wherein: The second value includes at least one of the following: a value indicating that the synchronization source is a wireless user equipment located within the coverage area of ​​a base station; or A value indicating that the synchronization source is a wireless user equipment located outside the coverage of a base station.

4. The first wireless user equipment according to claim 1, wherein The processor is configured to: generating said synchronization signal for communication based on the set for within coverage, and Therein, a base station or a wireless user equipment synchronized with the base station is selected as a transmission synchronization source for the determined synchronization timing reference.

5. The first wireless user equipment according to claim 1, wherein The processor is configured to: generating said synchronization signal for communication based on the set for out of coverage, and A wireless user equipment having a synchronization timing reference independent of the base station is selected as a transmission synchronization source for the determined synchronization timing reference.

6. The first wireless user equipment according to claim 1, wherein: The transmitter transmits the synchronization signal for communication by: generating a primary synchronization signal associated with the value; generating an auxiliary synchronization signal; and The primary synchronization signal is transmitted and the secondary synchronization signal is transmitted.

7. The first wireless user equipment according to claim 1, wherein: The processor is configured to: determining that the first wireless user equipment is an independent synchronization source, and The first wireless user equipment does not determine a synchronization timing reference based on one or more received synchronization signals.

8. A method for wireless communication, comprising: receiving, by the first wireless user equipment, a synchronization signal transmitted from a synchronization source; Determining a root index value based on the received synchronization signal; Determining a synchronization timing reference based on the root index value; as well as transmitting a synchronization signal for communication between the first wireless user equipment and the second wireless user equipment based on the determined synchronization timing reference, Wherein determining the synchronization timing reference comprises: Determining a category of the synchronization source based on the root index value; prioritizing the synchronization sources among wireless user devices synchronized with one or more base stations based on determining whether the synchronization sources are wireless user devices located within coverage of the base station or wireless user devices located outside coverage of the base station; and The synchronization timing reference is determined based on the prioritization.

9. The method according to claim 8, wherein The root index value is one of a plurality of values ​​including: a first value indicating that the synchronization source is a base station; a second value indicating that the synchronization source is a wireless user equipment synchronized with a base station; and A third value indicates that the synchronization source is a wireless user equipment having a synchronization timing reference independent of the base station.

10. The method of claim 9, wherein the second value comprises at least one of: a value indicating that the synchronization source is a wireless user equipment located within the coverage area of ​​a base station; or A value indicating that the synchronization source is a wireless user equipment located outside the coverage of a base station.

11. The method according to claim 8, further comprising: The synchronization signal for communication is generated based on the in-coverage set, wherein a base station or a wireless user equipment synchronized with a base station is selected as a transmission synchronization source for the determined synchronization timing reference.

12. The method according to claim 8, further comprising: Based on the set for out of coverage, said synchronization signal is generated for communication, wherein a wireless user equipment having a synchronization timing reference independent of the base station is selected as a transmission synchronization source for the determined synchronization timing reference.

13. The method of claim 8, wherein transmitting the synchronization signal for communication comprises: generating a primary synchronization signal associated with the value; generating an auxiliary synchronization signal; as well as The primary synchronization signal is transmitted and the secondary synchronization signal is transmitted.

14. The method according to claim 8, further comprising: It is determined that the first wireless user device is an independent synchronization source, wherein the first wireless user device does not determine a synchronization timing reference based on one or more received synchronization signals.

15. A first wireless communication device, comprising: a receiver for receiving a synchronization signal transmitted from a synchronization source; a processor configured to determine a root index value based on the received synchronization signal, and to determine a synchronization timing reference based on the root index value; as well as a transmitter for transmitting a synchronization signal for communication between the first wireless communication device and the second wireless communication device based on the determined synchronization timing reference, The determining, by the processor, the synchronization timing reference includes: Determining a category of the synchronization source based on the root index value; prioritizing the synchronization sources based on determining whether the synchronization source is a base station, a wireless communication device synchronized with a base station, or a wireless communication device having a synchronization timing reference independent of the base station; determining whether the synchronization source is a wireless communication device located within the coverage of the base station or a wireless communication device located outside the coverage of the base station among the wireless communication devices synchronized with the base station; Prioritizing the synchronization sources further based on determining whether the synchronization sources are wireless communication devices located within coverage of a base station or wireless communication devices located outside coverage of the base station; and The synchronization timing reference is determined based on the prioritization.

16. The first wireless communication device of claim 15, wherein the root index value is one of a plurality of values ​​comprising: a first value indicating that the synchronization source is a base station; a second value indicating that the synchronization source is a wireless communication device synchronized with a base station; and A third value indicates that the synchronization source is a wireless communication device having a synchronization timing reference independent of a base station.

17. The first wireless communication device of claim 16, wherein the second value comprises at least one of: a value indicating that the synchronization source is a wireless communication device located within the coverage area of ​​a base station; or A value indicating that the synchronization source is a wireless communication device located outside the coverage of a base station.

18. The first wireless communication device of claim 15, wherein the processor is configured to: generating said synchronization signal for communication based on the set for within coverage, and The base station or a wireless communication device synchronized with the base station is selected as a transmission synchronization source of the determined synchronization timing reference.

19. The first wireless communication device of claim 15, wherein the processor is configured to: generating said synchronization signal for communication based on the set for out of coverage, and Therein, a wireless communication device having a synchronization timing reference independent of the base station is selected as a transmission synchronization source for the determined synchronization timing reference.

20. The first wireless communication device of claim 15, wherein the synchronization signal transmitted by the transmitter for communication comprises: generating a primary synchronization signal associated with the value; generating an auxiliary synchronization signal; as well as The primary synchronization signal is transmitted and the secondary synchronization signal is transmitted.

21. The first wireless communication device of claim 15, wherein the processor is configured to: determining that the first wireless communication device is an independent synchronization source, and The first wireless communication device does not determine a synchronization timing reference based on the received synchronization signal.

22. A method for wireless communication, comprising: receiving a synchronization signal transmitted from a synchronization source; determining a root index value based on the received synchronization signal, and determining, by a processor, a synchronization timing reference based on the root index value; as well as transmitting a synchronization signal for communication between the first wireless communication device and the second wireless communication device based on the determined synchronization timing reference, Wherein determining the synchronization timing reference by the processor comprises: Determining a category of the synchronization source based on the root index value; prioritizing the synchronization sources based on determining whether the synchronization source is a base station, a wireless communication device synchronized with a base station, or a wireless communication device having a synchronization timing reference independent of the base station; determining whether the synchronization source is a wireless communication device located within the coverage of the base station or a wireless communication device located outside the coverage of the base station among the wireless communication devices synchronized with the base station; Prioritizing the synchronization sources further based on determining whether the synchronization sources are wireless communication devices located within coverage of a base station or wireless communication devices located outside coverage of the base station; and The synchronization timing reference is determined based on the prioritization.

23. The method of claim 22, wherein the root index value is one of a plurality of values ​​comprising: a first value indicating that the synchronization source is a base station; a second value indicating that the synchronization source is a wireless communication device synchronized with a base station; and A third value indicates that the synchronization source is a wireless communication device having a synchronization timing reference independent of a base station.

24. The method of claim 23, wherein the second value comprises at least one of: a value indicating that the synchronization source is a wireless communication device located within the coverage area of ​​a base station; or A value indicating that the synchronization source is a wireless communication device located outside the coverage of a base station.

25. The method of claim 22, further comprising: The synchronization signal is generated for communication based on the set for within coverage, wherein a base station or a wireless communication device synchronized with a base station is selected as a transmission synchronization source for the determined synchronization timing reference.

26. The method of claim 22, further comprising: Based on the set for out of coverage, the synchronization signal is generated for communication, wherein a wireless communication device having a synchronization timing reference independent of the base station is selected as a transmission synchronization source for the determined synchronization timing reference.

27. The method of claim 22, wherein transmitting the synchronization signal for communication comprises: generating a primary synchronization signal associated with the value; generating an auxiliary synchronization signal; as well as The primary synchronization signal is transmitted and the secondary synchronization signal is transmitted.

28. The method of claim 22, further comprising: A determination is made that the first wireless communication device is an independent synchronization source, wherein the first wireless communication device does not determine a synchronization timing reference based on a received synchronization signal.

29. A first user equipment (UE) supporting communication between UEs, the first UE comprising: a receiver for receiving a synchronization signal transmitted from a synchronization source; a processor configured to determine a root index based on the received synchronization signal, and to determine a synchronization timing reference based on the root index; as well as a transmitter for transmitting a synchronization signal for communication based on the determined synchronization timing reference, In order to determine the synchronization timing reference, the processor performs the following operations: According to the root index, the category of the synchronization source is determined, prioritizing the synchronization sources based on determining whether the synchronization source is an evolved Node B (eNode B), a UE synchronized with an eNode B, or a UE having a synchronization timing reference independent of the eNode B, and determining the synchronization timing reference based on the prioritization; and Wherein, with respect to the transmission of the synchronization signal for communication, the processor performs the following operations: generating said synchronization signal for communication based on the set for within-coverage use when an eNodeB or a UE synchronized with an eNodeB is selected as a reference synchronization source for the determined synchronization timing reference, and When a UE having a synchronization timing reference independent of an eNodeB is selected as the reference synchronization source, the synchronization signal for communication is generated based on a set for out of coverage. 30 . The first UE according to claim 29 , wherein for the determining the synchronization timing reference, when the root index corresponds to 25, 29, or 34, the processor determines that the synchronization source is an eNodeB. 31 . The first UE according to claim 29 , wherein for the determining the synchronization timing reference, when the root index corresponds to a number other than 25, 29, and 34, the processor determines that the synchronization source is a UE.

32. The first UE according to claim 31, wherein the processor determines whether the synchronization source is a UE located within the coverage of the eNodeB or a UE located outside the coverage of the eNodeB among the UEs synchronized with the eNodeB, and The processor may also prioritize the synchronization sources based on determining whether the synchronization source is a UE located within a coverage area of ​​an eNodeB or a UE located outside a coverage area of ​​the eNodeB.

33. The first UE of claim 29, wherein the set for in-coverage and the set for out-of-coverage correspond to different root indices, and the different root indices correspond to numbers different from 25, 29, and 34, respectively.

34. The first UE of claim 33 , wherein for the synchronization signal transmitted for D2D communication, the processor generates a primary synchronization signal associated with a root index corresponding to a number other than 25, 29, and 34, and generates a secondary synchronization signal based on one of 168 identifiers corresponding to the set for in-coverage or one of 168 identifiers corresponding to the set for out-of-coverage, and The transmitter transmits the primary synchronization signal and the secondary synchronization signal.

35. The first UE of claim 29, wherein the processor determines that the first UE is an independent synchronization source, and wherein the first UE does not determine a synchronization timing reference based on one or more received synchronization signals.

36. The first UE of claim 35, wherein when the first UE functions as an independent synchronization source, the transmitter transmits a synchronization signal determined based on a set for out of coverage.

37. A first user equipment, comprising: a radio frequency unit, configured to receive synchronization signals transmitted from different synchronization sources; as well as a processor, configured to determine categories of the different synchronization sources based on the received synchronization signal, determine a synchronization timing reference of a reference synchronization source for the first user equipment, synchronize with the reference synchronization source based on the synchronization timing reference, and generate a synchronization signal for communication between the first user equipment and a second user equipment, wherein the radio frequency unit transmits the synchronization signal for the communication based on the determined synchronization timing reference, The processor is configured to determine the synchronization timing reference by: Prioritizing the different synchronization sources based on the categories of the different synchronization sources, wherein the categories in order of priority include: base stations; A user equipment synchronized with a base station and located within the coverage area of ​​the base station; a user equipment synchronized with a base station but located outside the coverage area of ​​the base station; and User equipment with a synchronized timing reference independent of the base station; determining the reference synchronization source for the first user equipment among the different synchronization sources based on the priority ranking; and The synchronization timing reference is determined.

38. The first user equipment according to claim 37, wherein the processor is configured to generate the synchronization signal for the communication by: When a base station or a user equipment synchronized with a base station is selected as a transmission synchronization source for the determined synchronization timing reference, the synchronization signal for the communication is generated based on the set for within coverage.

39. The first user equipment according to claim 37, wherein the processor is configured to generate the synchronization signal for the communication by: The synchronization signal for device-to-device communication is generated based on the set for out of coverage when a user equipment having a synchronization timing reference independent of the base station is selected as a transmission synchronization source for the determined synchronization timing reference.

40. The first user equipment of claim 37, wherein the generated synchronization signal comprises: If the determined synchronization timing reference corresponds to a user equipment that is synchronized with a base station but is outside the coverage of the base station, determining a first value based on the determined synchronization timing reference, or If the determined synchronization timing reference corresponds to a user equipment having a synchronization timing reference independent of the base station, determining a second value based on the determined synchronization timing reference, and wherein the second value is different from the first value.

41. The first user equipment according to claim 37, wherein the processor is configured to generate the synchronization signal for the communication by: generating a primary synchronization signal based on a root index of the reference synchronization source; and Generate auxiliary synchronization signal, The synchronization signal used for the communication includes the primary synchronization signal and the secondary synchronization signal.

42. The first user equipment according to claim 37, wherein: A first root index associated with a user equipment located within the coverage area of ​​the base station and synchronized with the base station is different from a second root index associated with a user equipment having a synchronization timing reference independent of the base station.

43. The first user equipment according to claim 37, wherein both a user equipment synchronized with a base station and located within the coverage of the base station and a user equipment synchronized with a base station but located outside the coverage of the base station transmit the synchronization signal based on a synchronization signal sequence in the set for within coverage. The set used within the coverage area indicates a set of synchronization signal sequences transmitted from a user equipment, and a transmission timing reference of the user equipment is a base station.

44. The first user equipment according to claim 43, wherein the processor is configured to generate the synchronization signal for the communication by: If a user equipment synchronized with a base station and located within the coverage of the base station or a user equipment synchronized with a base station but located outside the coverage of the base station is selected as a reference synchronization source, generating a secondary synchronization signal for the communication based on the set for within the coverage area; or generating a secondary synchronization signal for said communication based on the set for out of coverage if a user equipment having a synchronization timing reference independent of the base station is selected as a reference synchronization source, The set used for out-of-coverage areas indicates a set of synchronization signal sequences transmitted from a user equipment, and a transmission timing reference of the user equipment is not a base station.

45. The first user equipment according to claim 44, wherein the set for in-coverage and the set for out-of-coverage correspond to different root indexes, respectively.

46. ​​The first user equipment according to claim 37, wherein the root index is determined based on a primary synchronization signal in the received synchronization signal, and Wherein at least one of the categories is determined based on the root index.

47. The first user equipment according to claim 37, wherein the processor is configured to determine the reference synchronization source for the first user equipment by: If the root index of a first synchronization source corresponds to 25, 29, or 34, and the root indexes of other synchronization sources correspond to values ​​other than 25, 29, or 34, the first synchronization source is determined as a reference synchronization source.

48. The first user equipment according to claim 37, wherein the processor is configured to determine the reference synchronization source of the first user equipment by: The first synchronization source is determined as the reference synchronization source based on the following operations: determining that the root index of the different synchronization source does not correspond to 25, 29, or 34; and The reference synchronization source is determined based on whether the root index of the first synchronization source corresponds to a first value different from a second value of a second synchronization source.

49. The first user equipment according to claim 37, further comprising: Memory, The processor comprises: a synchronization information confirmation unit; and Synchronization signal generation unit.

50. A system for wireless communication, comprising: The first user equipment according to any one of claims 37 to 49; as well as A base station is configured to transmit one or more signals to the first user equipment.

51. The system of claim 50, further comprising the second user device configured to receive the synchronization signal for device-to-device communication.

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