KR102394218B1 - Method and apparatus for synchronization procedure and resource management in device to device communication system - Google Patents

Abstract

The present disclosure relates to a 5G or pre-5G communication system to be provided to support a higher data rate after a 4G communication system such as LTE.
A method according to an embodiment of the present disclosure is a method for a terminal to synchronize with another terminal in a network performing direct communication (D2D) between devices. When data to be transmitted in the idle mode occurs, at least one scanning whether a synchronization signal is received from a base station; performing synchronization according to the received synchronization signal when the synchronization signal is received from the base station; measuring the signal strength of the synchronization signal received from the base station; And when data to be transmitted is generated in the idle mode, when the measured signal strength of the synchronization signal is lower than a preset first reception power, setting the synchronization relay terminal to transmit the synchronization signal; may include.

Description

Synchronization procedure and resource control method and apparatus for communication in a communication system between terminals

The present disclosure relates to a synchronization resource structure for inter-terminal discovery and communication, a synchronization support method such as a synchronization procedure, an apparatus, and a transmission resource structure used by a UE in inter-terminal discovery and communication, and resource control.

Efforts are being made to develop an improved 5G communication system or pre-5G communication system in order to meet the increasing demand for wireless data traffic after commercialization of the 4G communication system. For this reason, the 5G communication system or the pre-5G communication system is called a system after the 4G network (Beyond 4G Network) communication system or the LTE system after (Post LTE).

In order to achieve a high data rate, the 5G communication system is being considered for implementation in a very high frequency (mmWave) band (eg, such as a 60 gigabyte (60 GHz) band). In order to alleviate the path loss of radio waves and increase the propagation distance of radio waves in the ultra-high frequency band, in the 5G communication system, beamforming, massive MIMO, and Full Dimensional MIMO (FD-MIMO) are used. ), array antenna, analog beam-forming, and large scale antenna technologies are being discussed.

In addition, for network improvement of the system, in the 5G communication system, an evolved small cell, an advanced small cell, a cloud radio access network (cloud radio access network: cloud RAN), an ultra-dense network (ultra-dense network) , Device to Device communication (D2D), wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and reception interference cancellation Technology development is underway.

In addition, in the 5G system, the advanced coding modulation (ACM) methods FQAM (Hybrid FSK and QAM Modulation) and SWSC (Sliding Window Superposition Coding), and advanced access technologies FBMC (Filter Bank Multi Carrier), NOMA (non orthogonal multiple access), and sparse code multiple access (SCMA) are being developed.

Due to the recent spread of smartphones, data traffic is rapidly increasing. In the future, the number of smartphone users will further increase, and application services such as social network service (SNS) and games using it are expected to become more active. Accordingly, data traffic in wireless communication systems is expected to increase even more than now. In particular, the recent trend of communication goes beyond human-to-human communication, and if the new mobile market, human-to-object communication, and object-to-object intelligent communication using things, etc., is activated, the traffic transmitted to the base station will increase to an unbearable level. it is expected

Therefore, a technology capable of solving such an increase in traffic is required, and as one of them, a direct communication technology between devices is attracting attention. This technology, called Device to Device (hereinafter referred to as "D2D"), is attracting attention both in licensed bands of mobile communication and in unlicensed bands such as wireless LANs.

In mobile communication, D2D communication is particularly noteworthy in that it can increase the traffic capacity of the base station and reduce overload. That is, in D2D communication, user equipments (UEs) in the same cell or cells adjacent to each other establish a D2D link with each other and directly exchange data through the D2D link without going through an evolved NodeB (eNB). Therefore, the existing method uses link number two, such as the link between UE #1 and the eNB and the link between the eNB and UE #2, but in the D2D method, only one link can be used because direct communication between UE #1 and UE #2 This has the advantage of reducing the number of links.

LTE-based D2D communication technology may be classified into discovery between terminals and communication between terminals. Inter-terminal discovery is a sequence in which one terminal identifies the identities or interests of other terminals existing in its proximity, or informs other terminals located in close proximity of its identity or interest. means the process of In this case, the identity and interest may be an identifier (ID) of the terminal, an application identifier, or a service identifier, and may be variously configured according to a D2D service and an operation scenario.

In addition, one of the biggest characteristics of LTE-based D2D communication is not for the purpose of unicast communication as in cellular communication, but for the purpose of a public safety scenario. (communication) is supported. Therefore, feedback such as channel measurement report, hybrid ARQ, HARQ, and response signal (ACK/NACK) is not supported. It is the biggest task of D2D broadcast communication to support seamless communication between terminals even in the absence of a base station and to provide reliable link quality. In particular, in a scenario in which terminals must operate in a distributed manner without the aid of a base station, a resource conflict problem caused by occupying the same resource between different terminals needs to be resolved.

In addition, the main purpose of D2D communication is to prevent unnecessary radio resource waste by recognizing the demands for communication between people, communication between people and things, and communication between things, and to appropriately determine and service locally generated traffic. Therefore, current research on D2D communication is focusing on a method for efficiently operating a D2D discovery process in which multiple devices broadcast and receive information on services and content to the surroundings.

Recently, 3GPP standards organization is working on D2D communication for public safety net in LTE Release 12 standard.

LTE Release 12 intends to provide a broadcast service to basically support the Push-To-Talk (PTT) function in D2D communication for public safety nets. In addition, since D2D communication for the public safety net must be able to operate even in the absence of a base station, procedures such as synchronization and resource allocation must be performed between terminals. In the presence of a base station, the base station may control the base station to perform broadcasting within the resources allocated for the base station for D2D. The situation in which there is no base station in part should also be discussed in D2D communication for public safety net.

In addition, in order to perform D2D communication, a process of setting synchronization between devices is required. The device may establish synchronization between the devices by using time information received through a synchronous base station or a global positioning system (GPS) reception module. In this way, in a method in which the device sets synchronization using time information received through the synchronous base station or the GPS receiving module, the device is essentially required to connect to the synchronous base station or the GPS receiving module.

However, since a synchronous base station may not be supported depending on a communication method provided by a communication service provider, synchronization may not be established using time information received through the synchronous base station. In addition, if the device is located in a GPS shadow area (eg, between high-rise buildings, a tunnel, inside a building, etc.), the device may not be able to receive time information from the GPS and may not be able to set synchronization of the device. As a result, when the connection with the synchronous base station or the GPS receiving module is not smooth, there is a problem in that the device cannot even start D2D communication.

Accordingly, the present disclosure intends to provide a method and an apparatus for supporting synchronization between terminals necessary for D2D discovery and communication.

In addition, in the present disclosure, in-network coverage, partial network coverage, synchronization resource structure, synchronization required for D2D discovery and communication in the terminal out-of-network coverage It is intended to provide a procedure for setting up a synchronization signal, a condition for measurement of a synchronization signal and becoming a synchronization terminal, information related to synchronization and resource area transmitted through a synchronization signal, and a synchronization procedure.

In addition, the present disclosure intends to provide a transmission resource selection method for inter-terminal discovery and communication.

A method according to an embodiment of the present disclosure is a method for a terminal to synchronize with another terminal in a network performing direct communication between devices (D2D), the method comprising: scanning whether a synchronization signal is received from at least one base station ; performing synchronization according to the received synchronization signal when the synchronization signal is received from the base station; measuring the signal strength of the synchronization signal received from the base station; And when data to be transmitted is generated in the idle mode, when the measured signal strength of the synchronization signal is lower than a preset first reception power, setting the synchronization relay terminal to transmit the synchronization signal; may include.

An apparatus according to an embodiment of the present disclosure is a terminal device for performing direct communication (D2D) between devices, comprising: a radio processing unit for transmitting and receiving wireless signals with a base station or another terminal; a memory for storing control data; and a control unit for controlling the wireless processing unit,

The control unit is

Controls scanning whether a synchronization signal is received from at least one base station, performs synchronization according to the received synchronization signal when a synchronization signal is received from the base station, measures the signal strength of the synchronization signal received from the base station, and stops When data to be transmitted is generated in the mode state, when the measured signal strength of the synchronization signal is lower than a preset first reception power, the synchronization relay terminal may be set to transmit the synchronization signal.

A method according to another embodiment of the present disclosure is a method for a terminal to synchronize with another terminal in a network performing direct communication (D2D) between devices, the step of scanning whether a synchronization signal is received from the base station and the terminal ; scanning whether a signal is received from at least one adjacent synchronization relay terminal when no synchronization signal is received from any base station; when a synchronization signal is received from at least one synchronization relay terminal, selecting one synchronization signal based on the strength of received power among the received synchronization signals, and synchronizing the synchronization signal according to the selected synchronization signal; and transmitting the synchronization signal by setting the synchronization relay terminal to the synchronization relay terminal when the strength of the selected synchronization signal is lower than a preset second reception power when data to be transmitted are generated.

An apparatus according to another embodiment of the present disclosure is a terminal device for performing direct communication (D2D) between devices, comprising: a wireless processing unit configured to transmit and receive radio signals to and from a base station or another terminal; a memory for storing control data; and a control unit for controlling the wireless processing unit,

The control unit is

It scans whether a synchronization signal is received from a base station and a terminal, and when a synchronization signal is not received from any base station, it scans whether a signal is received from at least one adjacent synchronization relay terminal, and a synchronization signal is received from at least one synchronization relay terminal When received, one synchronization signal is selected from among the received synchronization signals on the basis of the received power strength, the synchronization signal is synchronized according to the selected synchronization signal, and when data to be transmitted occurs, the second reception signal strength of the selected synchronization signal is preset in advance. If it is lower than the power, it can be controlled to transmit a synchronization signal by setting it as a synchronization relay terminal.

When the D2D network according to the present disclosure is used, efficient and stable synchronization can be provided, and inter-terminal interference can be avoided and communication performance improvement can be expected in inter-terminal search and one-to-one and one-to-many communication.

1 is a conceptual diagram for explaining the overall D2D synchronization operation area, procedure, signal and message;
2 is a functional internal block diagram of a terminal to which the present invention can be applied;
3A and 3B are diagrams illustrating a structure for allocating D2D synchronization resources according to the present invention;
4A is a timing diagram illustrating a position at which a base station broadcasts main system information in a downlink (DL) band and a position at which a terminal broadcasts system information for D2D in an uplink (UL) band;
4B and 4C are exemplary diagrams for explaining a method of transmitting an offset of an OOC terminal when an IC terminal transmits a synchronization sequence and a synchronization channel to an OOC terminal;
5A to 5D are exemplary diagrams of a method for allocating transmission and reception resource regions according to the present invention;
6A to 6D are diagrams illustrating the structure of a resource region for performing D2D discovery or communication and the location and structure of synchronization resources;
7A to 7C are exemplary diagrams for explaining methods for using a periodic companion resource;
8A and 8B are network conceptual diagrams for explaining a scenario for selecting a synchronization sequence between an IC terminal and an OOC terminal;
9 is a flowchart for aligning transmission synchronization according to an embodiment of the present invention;
10A to 10C are flowcharts for explaining various embodiments of scanning for reception according to the present invention;
11 is a control flowchart for determining a condition for becoming a synchronous relay terminal according to the present invention;
12A and 12B are control flowcharts when a synchronization transmitting terminal stops transmitting a synchronization signal according to an embodiment of the present invention;
13A to 13D are conceptual diagrams for explaining a method in which a frame number and MIB or synchronization resource are transmitted in an LTE system;
14 is an exemplary diagram for explaining a D2D frame number determination scenario in a network area and in a partial network according to the present invention;
15 is a conceptual diagram for explaining a scenario for determining a D2D frame number outside a network area;
16 is a control flow chart for sorting and selecting synchronization information in consideration of absolute time according to the present invention;
17 is a flowchart for aligning and selecting synchronization information without considering absolute time according to the present invention;
18 is a diagram illustrating the structure of a synchronization resource according to the present invention;
19A to 19D are exemplary diagrams for explaining the structure of a resource region structure and a synchronization resource for performing D2D communication or D2D discovery according to the present invention;
20A and 20B are flowcharts of a synchronization procedure for transmission synchronization according to the present invention;
21a to 21c are diagrams illustrating a scanning procedure for reception according to the present invention;
22 is a flowchart illustrating a procedure for becoming a synchronous relay terminal according to the present invention;
23 is a flowchart for explaining a method of supplementing the problem of the existing hierarchical synchronization procedure outside the network area.

Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. In this case, it should be noted that in the accompanying drawings, the same components are denoted by the same reference numerals as much as possible. In addition, it should be noted that the drawings of the present invention attached below are provided to help the understanding of the present invention, and the present invention is not limited to the form or arrangement illustrated in the drawings of the present invention. In addition, detailed descriptions of well-known functions and configurations that may obscure the gist of the present invention will be omitted. In the following description, only parts necessary for understanding the operation according to various embodiments of the present invention will be described, and it should be noted that descriptions of other parts will be omitted so as not to obscure the gist of the present invention.

First, let's take a look at the D2D communication technology that is the basis of the present invention.

It is assumed that the hierarchical structure of a terminal using D2D communication technology consists of a D2D application layer, a D2D management layer, and a D2D transport layer. The D2D application layer refers to a D2D service application running on the terminal OS (Operating System), and the D2D management layer is responsible for converting the discovery information generated in the D2D application into a format suitable for the transport layer. It refers to the PHY/MAC layer of the LTE or WiFi wireless communication standard.

In D2D communication technology, inter-terminal discovery may have the following procedure. When a user executes a D2D application program, information for discovery is generated in the application layer and transmitted to the D2D management layer. The management layer converts the discovery information received from the application layer into a management layer message. These management layer messages are transmitted through the transport layer of the terminal. The terminals receiving the D2D data or the D2D signal through this process perform a reception operation in the reverse order of the transmission process.

Meanwhile, the communication between terminals is a communication method in which traffic is directly transferred between terminals without going through an infrastructure such as a base station or an access point (AP). In this case, the terminal-to-terminal communication performs the terminal-to-device discovery process, and then, based on the result, that is, the terminal-to-device communication may be performed without performing communication with the discovered terminals or without going through the terminal-to-device discovery process. Whether or not a discovery process between terminals is required prior to communication between terminals may vary depending on the D2D service and operation scenario.

The D2D service scenario can be broadly classified into a commercial service (commercial service or non public safety service) and a service related to public safety (public safety service). Each service may include a myriad of use cases, but representative examples include advertisement, SNS, game, public safety and public safety service.

Then, let's take a brief look at the form in which each of the above-described services is provided.

First, let's look at the case where the D2D service is applied to advertisements.

A network operator that supports D2D can advertise their identity to D2D users located in close proximity using pre-registered shops, cafes, movie theaters, restaurants, etc. using device-to-device navigation or device-to-device communication. In this case, the interests may be advertisements' promotions, event information, discount coupons, and the like. If the identity matches the user's interests, the user can visit the store and obtain more information using the existing cellular communication network or terminal-to-device communication. As another example, the individual user may search for a taxi located in the vicinity of the user through inter-terminal search, and may exchange data on his/her destination or fare information through existing cellular communication or inter-terminal communication.

Second, let's take a look at the case where D2D service is applied in SNS.

The user may transmit his/her application and interest in the corresponding application to other users located in a nearby area. In this case, the identity or interest used for inter-terminal search may be a friend list of an application or an application identifier. After the user searches between terminals, the user can share the contents such as photos and videos he owns with nearby users through terminal-to-device communication.

Third, let's take a look at the case where the D2D service is applied to the game.

The user searches for users and game applications with terminals capable of D2D service through the terminal-to-device search process to enjoy mobile games with other users in close proximity, and communicates between terminals to transmit data necessary for the game. can be done

Finally, let's look at the case where the D2D service is applied to public safety and disaster network services.

Police officers and firefighters can use D2D communication technology for public safety purposes. In other words, when cellular communication is not possible due to partial damage to the existing cellular network due to an emergency such as a fire or landslide or a natural disaster such as an earthquake, volcanic eruption, or tsunami, police officers and firefighters can use D2D communication technology to discover or Each emergency situation information can be shared among adjacent users.

Meanwhile, 3GPP LTE D2D standardization is currently in progress for both terminal-to-device discovery and communication, but the standardization range is different. Inter-terminal search is for commercial use and should be designed to operate only within the coverage of the base station (in network coverage). That is, inter-terminal search is not supported in a situation in which a base station does not exist or outside the coverage of the base station.

On the other hand, terminal-to-device communication is for public safety and disaster network services, not for commercial purposes. Therefore, communication between terminals is in the coverage of the base station (in network coverage), out of the coverage of the base station (out of network coverage), and the partial network coverage of the base station (partial network coverage: some terminals exist in the coverage of the base station and some terminals are in the coverage of the base station Communication in a situation that exists outside of coverage) must be supported. Therefore, in the public safety and disaster network service, communication between terminals must be performed without support for search between terminals.

In LTE D2D, where standardization is currently in progress, both terminal-to-device discovery and terminal-to-device communication are performed in an uplink subframe of LTE. That is, the D2D transmitter transmits a D2D discovery signal and data for D2D communication in the uplink subframe, and the D2D receiver receives it in the uplink subframe. In the current LTE system, since the terminal receives data and control information from the base station through downlink, and the terminal transmits data and control information through uplink to the base station, the operation of the D2D transmitter/receiver may be different from that of existing LTE. .

For example, a terminal that does not support the D2D function is equipped with an orthogonal frequency division multiplexing (OFDM)-based receiver to receive downlink data and control information from the base station, and the terminal sends uplink data and control information to the base station. In order to transmit , a single carrier-frequency division multiplexing (SC-FDM)-based transmitter is required. However, the D2D terminal must support both the cellular mode and the D2D mode. Therefore, the D2D terminal transmits D2D data and control information through an uplink together with an OFDM-based receiver for receiving downlink from the base station and an SC-FDM-based transmitter for transmitting data or control information through uplink to the base station. A separate SC-FDM receiver must be installed for reception.

Currently, LTE D2D defines two types of inter-terminal discovery methods according to resource allocation methods.

(1) Type 1 discovery: The base station provides the D2D terminals with an uplink resource pool usable for D2D discovery through a system information block (SIB) to all D2D terminals in the cell it manages. broadcast to In this case, the size of a resource available for D2D (eg, x consecutive subframes) and a resource period (eg, repeat every y seconds) may be informed. The D2D transmitting terminals that have received this select a resource to be used in a distributed manner and transmit a D2D discovery signal.

(2) Type 2 discovery: The base station informs the pool of discovery signal resources that D2D receiving terminals should receive through SIB. Meanwhile, a transmission discovery signal resource for D2D transmitting terminals is scheduled by the base station. That is, the base station instructs D2D transmitting terminals to transmit in a specific time-frequency resource. In this case, the scheduling of the base station may be performed through a semi-persistent method or a dynamic method.

The communication method between terminals can also be classified into the following two types according to resource allocation as in the terminal-to-device discovery method.

(1) Mode 1: When using the mode 1 method, the base station or the Release 10 relay directly informs the resource for transmitting data and control information for D2D communication used by the D2D transmitter.

(2) Mode 2: In the case of using the mode 2 method, the D2D transmitter performs itself in the corresponding resource pool based on the resource pool information for data and control information transmission acquired by the D2D transmitter. It selects and transmits resources distributedly.

Prior to the detailed description of the present invention, examples of interpretable meanings of some terms used in this specification are provided. However, it should be noted that the interpretation examples presented below are not limited.

A base station (Base Station) is one entity that communicates with the terminal, and may be referred to as a BS, a base transceiver station (BTS), a NodeB (NB), an eNodB (eNB), an access point (AP), or the like.

A user equipment (UE) is a subject that communicates with a base station, and may also be referred to as a UE, a device, a mobile station (MS), a mobile equipment (ME), a terminal, and the like.

Also, a terminal performing D2D communication may be divided into a synchronous transmitting terminal and a synchronous receiving terminal according to its role. The synchronization transmitting terminal (which may be referred to as a synchronization source) is a D2D synchronization signal (D2D Synchronization Signal, D2DSS) or a D2D synchronization channel (D2D Synchronization Channel (D2DSCH)) or a D2D broadcast channel (D2D Broadcast Channel, D2DBCH) Alternatively, as a terminal for transmitting a D2D System Information Channel (D2D SICH), it may include a Synchronization Reference UE and a Synchronization Relaying UE. In some cases, a 'base station' that transmits a D2D synchronization signal may be treated as one 'synchronization reference terminal'. A synchronization receiving terminal (which may be referred to as a D2DUE) is a terminal that receives (without transmitting) a synchronization signal or a synchronization channel.

The synchronization signal means a signal including a synchronization sequence that can be used to distinguish a cluster or a synchronization transmitting terminal, and the synchronization signal resource means a resource used to transmit the synchronization signal. The synchronization channel means a channel including a synchronization-related message or a system-related message, and the synchronization channel resource means a resource for transmitting the synchronization channel. The synchronization transmitting terminal may transmit a synchronization signal or a synchronization channel. Hereinafter, it should be noted that, for convenience, the synchronization signal can be described as a concept including both the synchronization signal and the synchronization channel, except for cases where they are strictly classified.

A synchronization reference terminal (or may be referred to as a Synchronization Reference UE, or an Independent Synchronization Source (I-SS)) is a synchronization transmitting terminal that serves as a synchronization representative for generating a cluster, and except when it exists in the base station area, The timing can be determined independently.

A synchronization relay terminal (or Synchronization Relaying UE, which may be referred to as a Dependent Synchronization Source (D-SS)) synchronizes timing with a synchronization reference terminal and relays (ie, receives a synchronization signal or a synchronization channel from the synchronization reference terminal) and transmission) is a synchronous transmission terminal. For example, when a synchronization relay terminal transmits a synchronization signal from a base station, the synchronization relay terminal serves as a synchronization head (SH) providing a reference time for one cluster in communication between terminals. may be A special type of synchronization relay terminal is a synchronization support terminal (Volunteering Synchronization UE), and may serve to transmit synchronization standards between a plurality of synchronization reference terminals.

In-Coverage UE is in RRC IDLE state or RRC CONNECTED state with the base station.

- RRC IDLE: A state in which a base station (or cell) is selected, a paging channel is monitored, and system information (SI) is acquired, but data is not exchanged with the base station am.

- RRC CONNECTED: It is a state in which data is exchanged with the base station through the data channel while watching the control channel. It is a state in which various measurement results of the base station and neighboring base stations are reported to assist the base station in scheduling.

1 is a conceptual diagram for explaining the overall D2D synchronization operation area, procedure, signal, and message.

First, let's take a look at the configuration of FIG. 1 . Referring to FIG. 1 , a first base station 101 has a first base station communication area 11 , and a first terminal 121 and a second terminal are located within the communication area of the first base station 101 (In-network coverage). A form in which the terminal 122 is located has been exemplified. In addition, the second base station 102 has a second base station communication area 12, exemplifying a form in which the third terminal 123 is located in the communication area of the second base station 102 . The fourth terminal 124 , the fifth terminal 125 , and the sixth terminal 126 located outside the first base station communication area 11 are in the first base station communication area 11 and the second base station communication area 12 . Although not included, a synchronization signal for D2D communication may be directly or indirectly received from the first terminal 121 located within the first base station communication area 11 . As such, the shapes of the fourth terminal 124 , the fifth terminal 125 , and the sixth terminal 126 will be referred to as partial network coverage.

In addition, in FIG. 1 , from a terminal not included in the first base station communication area 11 and the second base station communication area 12 , but also included in the first base station communication area 11 and the second base station communication area 12 . The seventh terminal 127 , the eighth terminal 128 , and the ninth terminal 129 are exemplified in an out-of-network coverage that does not receive a synchronization signal.

In the in-network coverage of the first base station area 11 or the second base station area 12, a synchronization signal is generally received from the base station and a reference time for transmission and reception is determined. In the 3GPP LTE standard, the terminal receives a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) from the base station to determine a symbol and a frame boundary. can In addition, the frame number of the currently received frame may be determined by receiving a broadcast channel (BCH) from the base station. In the LTE standard, a currently received frame may be informed by a system frame number (SFN), and a total of 1024 SFNs from SFN0 to SFN1023 may be informed. SFN0 is generally regarded as a reference frame number of one base station.

Meanwhile, an operation within the network area includes an inter-cell operation. In the present invention, even if the terminal performs a transmission/reception operation according to a reference time for one synchronization device (base station or terminal), discovery according to a resource structure that can be configured by receiving a reference time from another synchronization device for an additional reception operation ) and communication. These assumptions may be applied to cell-to-cell operation, operation in partial network coverage, and operation in out-of-network coverage, respectively.

Among the terminals illustrated in FIG. 1 , the first terminal 121 , the fourth terminal 124 , the sixth terminal 126 , the seventh terminal 127 , and the eighth terminal 128 are for D2D discovery or D2D communication. It is a terminal that transmits a D2D signal. To illustrate this, in FIG. 1 , a D2D signal is transmitted. In addition, all terminals may receive a D2D signal for D2D discovery or D2D communication. The first terminal 121 may transmit a D2D signal. The terminals receiving the D2D signal transmitted from the first terminal 121 may be various cases. In FIG. 1, each case is exemplified in order to explain these various cases. First, in the example of FIG. 1 , the D2D signal transmitted by the first terminal 121 is received by the second terminal 122 belonging to the same serving base station (eNB 1) 101 as the first terminal 121. case is exemplified. Second, in the example of FIG. 1 , the D2D signal transmitted by the first terminal 121 is received by the third terminal 123 belonging to the adjacent second base station (eNB 2). Third, in the example of FIG. 1 , the case where the fourth terminal 124 located in the partial network area receives the D2D signal transmitted by the first terminal 121 is exemplified. At this time, in order to provide a reference time for reception to the third terminal 123 and the fourth terminal 124 except for the second terminal 122 receiving the reference time from the same first base station 101, the second terminal Terminal 1 121 transmits a synchronization signal and a synchronization channel.

If the terminal transmitting the synchronization signal and channel is different from the terminal transmitting the D2D signal, a mismatch phenomenon may occur in which the synchronization signal and channel are received but the D2D signal is not received from the viewpoint of the terminal that wants to receive the D2D signal. there is. Therefore, whether to transmit a D2D signal may be considered as a condition for a terminal to transmit a synchronization signal and a channel. These conditions will be described in more detail below.

The fourth terminal 124, the fifth terminal 125, and the sixth terminal 126 belonging to the partial network area are terminals outside the original network area, but the reference time of the first base station 101 is set to the first terminal 121. It is a terminal that has obtained the same reference time as that of the first base station 101 by receiving relaying through it. When such a reference time is relayed and passes through a large number of terminals, the reference time may be shifted. Therefore, hops for relaying should be considered. In FIG. 1 , the first terminal 121 is the first hop, the fourth terminal 124 and the fifth terminal 125 are the second hops, and the sixth terminal 126 is the third hop. Since there is a problem in that an error generated when a synchronization signal is received is amplified through multiple hops, the number of hops that can be relayed may be limited. A terminal corresponding to the limited last hop may transmit a synchronization signal and a channel according to a specific condition. Upon receiving the synchronization signal and channel transmitted from the terminal corresponding to the limited last hop, the terminal no longer performs relaying of the synchronization signal and channel.

Next, since the seventh terminal 127, the eighth terminal 128 and the ninth terminal 129 located outside the network did not receive the reference time relayed from any base station, they became directly synchronized terminals with an independent reference time. In the case of operation or when a synchronization signal from an independent synchronization source (hereinafter, referred to as I-SS) is detected to exceed a predetermined reception power, the reference time for transmission to the synchronization terminal may be matched. Terminals belonging to an area outside the network may operate according to a synchronous relay method or a flat method. In addition, when there is a D2D signal to be transmitted, the seventh terminal 127 , the eighth terminal 128 , and the ninth terminal 129 located in an area outside the network have a D2D signal to be transmitted in order to prevent mismatch of areas in which the synchronization signal is transmitted between the terminals. It may be considered to transmit the synchronization signal and channel only to . However, it is also necessary to transmit a synchronization signal and a channel even if there is no D2D signal to be transmitted according to the synchronization procedure method. The details thereof will be described in more detail below.

Timing information required for UE synchronization is three types of symbol timing, frame timing, and system frame number. Among them, the symbol timing and the frame timing can be matched by receiving the synchronization sequence among the synchronization signals. The system frame number (System Frame Number) is a number for distinguishing a frame called by the base station, and is called differently as a D2D frame number, a direct frame number, etc. in search or communication between terminals, and may be abbreviated as DFN. The DFN may be transmitted from the synchronization transmitting terminal to a synchronization channel or a broadcast channel among D2D synchronization signals.

2 is a functional internal block diagram of a terminal to which the present invention can be applied.

The terminal illustrated in FIG. 2 may be a functional internal block diagram of the first terminal 121 to the ninth terminal 129 illustrated in FIG. 1 , and if necessary, additional configurations other than the configuration illustrated in FIG. 2 may be added. Note that it may have, or may be configured not to include a part of the configuration of FIG. 2 . The terminal illustrated in FIG. 2 may be one of various types such as a smart phone, a mobile phone, a notebook computer, a tablet computer, and a node for relaying D2D communication.

The wireless communication unit 201 transmits the signal to be transmitted through the antenna ANT by performing band up-conversion and power amplification of the signal to be transmitted into a set band. Also, the wireless communication unit 201 may convert a signal received from the antenna ANT into a baseband signal by low-noise amplification and down-band conversion, and then output the signal to the modem 203 . In addition, the wireless communication unit 201 may additionally have a circuit configuration for operating according to a circuit configuration for LTE communication and other wireless communication methods together with a circuit configuration for D2D communication. For example, a circuit configuration for operation according to the WiFi scheme or a circuit configuration for GPS reception may be further included.

The modem 203 may encode and modulate a signal to be transmitted, and if necessary, convert a digital signal into an analog signal and output it to the wireless communication unit 201 . In addition, the modem 203 may demodulate and decode data received from the wireless communication unit 201 and output it to the control unit 205 . In addition, in some cases, the modem 203 may receive an analog signal from the wireless communication unit 201 . This can be converted into a digital signal.

The wireless communication unit 201 and the modem 203 may be collectively referred to as a “wireless processing unit”.

The control unit 205 performs overall control of operations performed in the terminal. In addition, the control unit 205 may perform all control of operations to be described later according to the present invention. If the modem 203 is implemented in the form of a communication processor, some of the operations of the controller 205 may be configured to be performed by the modem 203 . Also, in a specific case, the modem 203 and the controller 205 may be implemented as one processor. In addition, in a specific case, the wireless communication unit 201 , the modem 203 , the control unit 205 , and the memory 207 may be implemented in the form of a single chip. In the present invention, there is no particular restriction on the implementation examples of various types as described above, and it is sufficient that the operations described below can be performed. Also, in the following description, it is assumed that all operations are controlled by the controller 205 for convenience of explanation.

The memory 207 may store data according to a user's need, and may have an area for storing data required for control by the controller 205 and data generated during control by the controller 205 . The memory 207 may be configured in various forms, such as a ROM and/or a RAM or/and a hard disk or/and a CD-ROM or/and a DVD.

The input unit 209 is an input means for a user to input a command or data to the terminal, and may be various types of input means such as a plurality of keys or/and a touch screen or/and voice recognition or/and character recognition.

The display unit 211 is an output means for displaying the current state or operation state of the terminal, and may be configured as various output means such as LCD or/and LED or/and a speaker or/and a vibration motor.

Hereinafter, two embodiments to be described in the present invention will be described in detail based on the above-described contents and drawings. In the first embodiment of the present invention, a description will be given of a case belonging to an in-network coverage and an operation in an out-of-network coverage for D2D communication. Also, in the second embodiment of the present invention, discovery and communication in the D2D method will be described.

[Ⅰ] Operation in In-Network Coverage and Out-of-Network Coverage

[Structure of Synchronous Resources]

The synchronization resource may be composed of a synchronization resource unit (SRU) capable of transmitting and receiving a synchronization signal and a synchronization channel. One SRU is a set of resources for a synchronization signal (D2DSS) and a synchronization channel (PD2DSCH) transmitted by one synchronization terminal. The length of the synchronization resource unit may be, for example, in LTE, in subframe units (1 ms). At least one physical symbol unit is required to transmit a synchronization signal, and at least one physical symbol unit is required to transmit a synchronization channel. Since the synchronization channel is a message, a pilot pattern for evaluating the quality of the physical channel at the receiving end may be inserted in the middle of the synchronization channel resource.

The structure of the synchronization resource can be divided into various scenarios depending on how the timing and transmission resource areas between the terminals in the network area (In-Coverage network, IC) and the terminals outside the network area (Out-Of-Coverage network, OOC) are matched. can

The IC terminal may be instructed to transmit the synchronization signal from the base station, or may operate to transmit the synchronization signal by itself according to a condition determined or predetermined by the base station. These conditions will be described in detail below. When an IC terminal transmits a synchronization signal, an IC terminal located in an adjacent base station may receive it or an OOC terminal may receive it. If the OOC terminal receives the synchronization signal from the IC terminal and then follows the reference timing of the base station, it is called a type 1 OOC terminal (OOC_UE_cat1). Otherwise, it is called a type 2 OOC terminal (OOC_UE_cat2).

According to the synchronization operation setting, if the OOC terminal receives the synchronization signal from the IC terminal and then follows the reference time of the base station to which the IC terminal belongs, there are three types of terminals: IC terminal, type 1 OOC terminal, and type 2 OOC terminal. this will exist On the other hand, if the OOC terminal receives the synchronization signal from the IC terminal according to the synchronization operation setting and then maintains the reference time used for out-of-coverage without following the reference time of the base station, the IC terminal and the two types of OOC terminal There are only two types of terminals. A method in which a type 1 OOC terminal matches its transmission resource region with the transmission resource region indicated by the IC terminal is only possible in a scenario in which all three types of terminals exist.

When the location of each resource is fixed, for example, when the location of the DFN is fixed, the DFN of the IC (same as SFN) and the DFN of the OOC may be different. ) may or may not exist. When there is a predetermined offset, the synchronization source transmitted from the IC synchronization resource uses the synchronization signal for IC (identified by ID in the sequence or message), so it is distinguished from the synchronization signal transmitted by the OOC synchronization transmission terminal. When the OOC terminal detects a synchronization signal for IC, it selects one of a plurality of synchronization signals for ICs, and when the condition of becoming a synchronization transmitting terminal is satisfied, a plurality of OOC synchronizations having a predetermined offset with respect to the position of the selected IC synchronization signal A synchronization signal is transmitted by selecting one synchronization resource from among the resources. In this way, the IC terminal can detect the existence of the OOC terminal with low power by receiving the synchronization signal of the OOC terminal only for the OOC synchronization resource that is located in advance.

If the IC terminal is not performing synchronization signal transmission first, for example, when there is no data to transmit, it is difficult for the IC terminal to receive the signal of the OOC synchronization transmission terminal. It is possible to instruct the IC terminal to transmit the synchronization signal, or to transmit the synchronization signal to all IC terminals using a common control signal. At this time, the base station may control the synchronization signal to be transmitted for a specific time period, or the synchronization signal may be transmitted for a predetermined time period. may ignore the command of the base station when data transmission is being performed), and may instruct the terminals that do not perform data transmission among all IC terminals to stop the synchronization signal transmission.

When the IC terminal transmits a synchronization signal under the control of the base station and the OOC terminal receives and selects the synchronization signal of the IC terminal, the OOC terminal immediately synchronizes the previous synchronization signal transmission timing, or immediately after data transmission is completed, or newly synchronized The timing of the transmission terminal is changed to a new synchronization signal timing or a predetermined timing. The synchronization signal timing includes all symbols, subframes, and subframe numbers. By changing the synchronization signal transmission timing of the OOC terminal, the synchronization signal coincides with the OOC synchronization resource within the base station area, and the IC terminal can receive the synchronization signal of the OOC synchronization transmission terminal.

3A and 3B are diagrams illustrating a structure for allocating D2D synchronization resources according to the present invention.

Before referring to FIGS. 3A and 3B , a case and method of transmitting a synchronization signal will be briefly described. As for the synchronization resource, the terminal transmits the synchronization signal before the terminal having the discovery signal or communication control/data signal to transmit basically transmits the discovery signal or the communication control/data signal. To explain this in more detail, the terminal transmitting the synchronization signal within the synchronization resource and the resource region between the resource region start position from at least one synchronization period before the start of the resource region to transmit the discovery signal or communication control / data signal. Transmits a synchronization signal from a synchronization resource. In this case, the condition for transmitting the synchronization signal may be one of the following two conditions.

a) When the base station orders transmission

b) when a condition set by the base station or a predetermined condition is met;

The synchronization resource structure shown in FIG. 3A is a structure in which the IC terminal and the OOC terminal do not transmit synchronization signals at the same time.

Referring to FIG. 3A , the synchronization period 310 exemplifies a case of 40 ms. It exemplifies that the synchronization signal can be transmitted at different times depending on the terminal transmitting the synchronization signal in the D2D bandwidth (BW) during the synchronization period 310 . For example, the IC terminal may transmit SRU#0 as indicated by reference numeral 311 using six synchronization resource blocks (PRBs) for a preset time at the start of the synchronization period. Thereafter, D2D control and data 312 may be transmitted. The frame 301 exemplified above in FIG. 3A is exemplified by assuming a frame of 40 ms.

On the other hand, in the case of an OOC terminal, SRU#1 (321a) as shown in reference numeral 321 by using 6 synchronization resource blocks (PRBs) for a preset time at a location spaced apart by a preset time from the start time of the synchronization period and/or SRU#2 321b may be transmitted. D2D control and data 322 may be transmitted in a section in which SRU#1 321a or/and SRU#2 321b is not transmitted. When the OOC terminal transmits synchronization resource blocks (PRBs), positions spaced apart by a preset time from the start time of the synchronization period may be set such as 10 ms or 30 ms from the start time. At this time, the SRU#0 (311) and the SRU#1 (321a) must be spaced apart from each other at the start point of the synchronization period so that they do not overlap each other. Accordingly, in the case of an IC terminal, the frame 301 shown above in FIG. 3A may be transmitted, and in the case of an OOC terminal, the frame 302 of 40 ms shown below in FIG. 3A may be transmitted.

As illustrated in FIG. 3A , one synchronization resource for an IC terminal or an OOC terminal is periodically allocated every 40 ms, and the starting points may be different from each other. For example, when transmitting a synchronization signal, the IC terminal uses SRU#0 311 located at the beginning of the synchronization period allocated for the IC terminal or the start point of the system frame. On the other hand, when the OOC terminal transmits a synchronization signal, SRU#1 (321a) having an offset of 10 ms from the start of the system frame or the beginning of a synchronization period allocated for the OOC terminal or SRU#2 (321b) having an offset of 30 ms ) is used. According to this structure, the SRU#0 311 for the IC terminal transmits the synchronization signal to be received by the OOC terminal or the IC terminal belonging to the neighboring base station, and there is no need to receive the synchronization signal between the IC terminals in the affiliated base station. Therefore, synchronization signals from terminals overlap in one SRU#0 (311) resource, and it is helpful to improve reception performance for synchronization transmitting terminals to use the same sequence.

On the other hand, the OOC terminal uses two resources, SRU#1 (321a) and SRU#2 (321b), since neighboring synchronization transmitting terminals must be able to receive each other to help maintain timing without drifting. There may be several methods for the OOC terminal to select a synchronization resource so that it does not collide with a synchronization resource selected by an adjacent synchronization transmitting terminal. After acquiring the transmission timing, there is a resource selection method as follows for a synchronization resource specified or predetermined by the base station.

a) Monitor synchronous resources and use any of the empty resources. If the monitoring cycle is set, repeat the above operation in the next cycle.

b) Monitor resources allocated for I-SS among synchronization resources (eg SRU#1) and use any of the empty resources. When a terminal other than the I-SS performs synchronous transmission (for example, when the timing of another adjacent synchronization transmitting terminal does not match its own timing, or if the priority is determined, the synchronization signal of the synchronization transmitting terminal having a lower priority is If heard), monitor a resource other than the I-SS resource (eg SRU#2) and use any of the empty resources.

c) Randomly change the synchronization resource every certain period based on the probability p.

When determining an empty resource in the above methods, the criterion is obtained by comparing the reception power of the received synchronization signal with a predetermined reception power threshold or determined by the base station. In the above methods, the synchronization resource that has successfully received the synchronization signal is not determined as an empty resource.

3B is a diagram illustrating a case in which an IC terminal and an OOC terminal transmit a synchronization resource at the same time in one periodic resource.

Note that the same reference numerals as in FIG. 3A are also used in FIG. 3B. The frame 301 transmitted by the IC terminal during one synchronization period 310 is illustrated in the upper part of FIG. 3B. This exemplifies the case where the synchronization period 310 is 40 ms as described above, and in the case of the IC terminal in the D2D bandwidth (BW) during the synchronization period 310 for a preset time at the start of the synchronization period 6 SRU#0 may be transmitted as shown in reference numeral 311 by using synchronization resource blocks (PRBs). Thereafter, D2D control and data 312 may be transmitted.

On the other hand, in the case of an OOC terminal, SRU#1 as shown in reference numeral 321 using six synchronization resource blocks (PRBs) for a preset time at a location spaced apart by a preset time from the start of the synchronization period and the start of the synchronization period. 321a or/and SRU#2 321b. D2D control and data 322 may be transmitted in a section in which SRU#1 321a or/and SRU#2 321b is not transmitted. When the OOC terminal transmits synchronization resource blocks (PRBs), positions spaced apart by a preset time from the start time of the synchronization period may be set such as 20 ms from the start time.

Considering the condition that the terminal transmitting data in OOC becomes I-SS first and performs synchronous transmission, SRU#2 (321b) is allocated for I-SS, and SRU#1 (321a) is I-SS Assume that it is allocated for a terminal that is not. In this case, the IC terminal only needs to receive the I-SS synchronization signal. Therefore, SRU#0 (311), a synchronization resource for IC, and SRU#1 (321a), a synchronization resource for a synchronization transmitting terminal other than I-SS among OOC terminals, allow simultaneous transmission in the same subframe, compared to FIG. It is possible to reduce the number of resources of the OCC terminal that the terminal must receive. In the example of FIG. 3b, when the OOC terminal receiving the synchronization signal of the IC terminal becomes the synchronization transmitting terminal, it is self-evident to select SRU#2 (321b) in order to avoid collision with the SRU#0 (311), which is the transmission resource of the IC terminal. Do. In addition, another OOC terminal receiving the synchronization signal of the OOC terminal transmitted from SRU#2 321b may select SRU#1 321a to avoid collision.

[Synchronous resource offset]

If the location of the synchronization resource is the same in all base stations or all clusters, there is no need to transmit and receive an offset indicating the location of the synchronization resource between devices. However, when the base station wants to control the location of the synchronization resource or when the synchronization transmitting terminal considers the half-duplex and interference problem for the synchronization resource, the synchronization resource is set to a certain offset within one synchronization period, for example, 40 ms. , can be set to have 0~39ms. To this end, the base station may use a system information block (SIB) in the broadcast channel (BCH), or the synchronization transmitting terminal may broadcast the offset information using the synchronization channel or the D2D broadcast channel.

In a certain base station, the synchronization resource may start from SFN#0, or may start with an offset having a value smaller than one synchronization period by the control of the base station. Assuming that the synchronization resource starts from SFN#0 in the serving/camped base station, the offset for the location of the synchronization resource of the neighboring base station corresponds to the difference between SFN#0 of the belonging base station and SFN#0 of the neighboring base station.

To explain this more, if the synchronization resource starts transmission with a certain offset in the affiliated base station, the offset to the synchronization resource position of the neighboring base station corresponds to the difference between the SFN#0 of the affiliated base station and the synchronization resource start position of the neighboring base station. . Expressing this as a formula, it is equal to (difference between the belonging base station SFN#0 and the neighboring base station SFN#0) + (difference between the neighboring base station SFN#0 and the neighboring base station synchronization resource start positions). Since an offset in units of at least one subframe (1 ms) may occur between asynchronous base stations, assuming that the synchronization period is 40 ms, the range of the offset is 0 to 39 ms.

In the affiliated base station, a different operation may be required depending on whether the synchronization resource starts from SFN#0 or starts with an offset. If an offset smaller than the synchronization period is required in the affiliated base station, this information must be reported in the PD2DSCH (synchronization channel). Upon receiving this, the OOC terminal determines the SFN of the base station by subtracting the offset from the D2D Frame Number (DFN) indicated by the PD2DSCH. If the affiliated base station always starts the synchronization resource from SFN#0, the synchronization resource offset with the neighboring base station is equal to the difference between the affiliated base station's SFN#0 and the neighboring base station's SFN#0. Therefore, when expressing the resource region of the neighboring base station, it is possible to reduce the overhead by expressing [synchronization resource offset] + [offset between the neighboring base station SFN0 and the resource region starting point]. The resource region of the adjacent base station may be a synchronization resource, a discovery resource, a control resource for communication, a data resource for communication, and the like.

In addition, depending on whether or not offset information is used, there may be a method for indicating the location of the resource region as follows, and the following three cases may be exemplified.

a) SFN#0 position when using offset

b) When using an offset, the location of the resource area based on the starting point of the synchronization period

c) When the offset is not used, the DFN#0 reference resource area location

4A is a timing diagram illustrating a position at which a base station broadcasts main system information in a downlink (DL) band and a position at which a terminal broadcasts system information for D2D in an uplink (UL) band.

The base station broadcasts a new master information block (MIB) every 40 ms according to an existing general scheme. The same MIB is copied and sent with a period of 10ms between one new MIB period. At this time, 8 bits out of a total of 10 bits of the System Frame Number (SFN) are sent from the MIB, and since four identical MIBs are sent within a period of 40 ms, 2 bits to distinguish 10 ms In the Cyclic Redundancy Check (CRC) masking for MIB, the CRC is differentiated. The terminal determined to transmit the synchronization signal transmits the synchronization signal every 40 ms, and the base station to which the base station belongs is controlled by the base station at which position to transmit the SFN#0. For this operation, the base station transmits a system information block (SIB) through a broadcast channel and informs all terminals within the base station area of the offset between SFN#0 and the first synchronization resource. Since the period of the synchronization signal is 40ms, the range of the offset is 0~39ms. In this case, it is assumed that one subframe is 1 ms.

In addition, the base station informs the offset according to the SFN#0 criterion in the same way for information on the location of the resource pool. The base station may additionally provide information on synchronization resources and discovery/communication resource regions of adjacent base stations. Since the offset with respect to the synchronization resource of the neighboring base station can be commonly used to inform the location of the resource regions of a plurality of neighboring base stations, the offset of the synchronization resource may be indicated as a reference point when indicating each resource region.

When the UE transmits the synchronization channel together with the synchronization sequence, the synchronization channel includes a D2D Frame Number (DFN) #0 value in the synchronization resource located first with respect to SFN#0 and transmits it. Additionally, the UE may transmit an offset from SFN#0 to the first synchronization resource position through a synchronization channel. In FIG. 4A, it is assumed that the terminal additionally transmits an offset. The expression method of the DFN and the offset may be variously determined in order to inform the same timing. For example, "DFN#0 + 14ms" is equivalent to "DFN#1+4ms". This is because one unit of DFN represents 10 ms.

Then, with reference to FIG. 4A, the relationship between the time when the SFN and the DFN are transmitted and the offset will be described.

The upper timing diagram in FIG. 4A describes a case in which MIB is transmitted in downlink within a specific base station. That is, within the transmission period of the MIB transmitted in units of 40 ms, the first transmitted MIBs 401 , 411 , and 421 are MIBs including different information. In addition, the second and subsequent MIBs 402, 403, 404, 412, 413, 414, 422, 423, 424 transmitted within the same period are MIBs including the same information as the first transmitted MIB within the corresponding period.

Next, a timing diagram below in FIG. 4A is a timing diagram for explaining a case in which DFNs 405 , 415 , and 425 that can be used for D2D transmission are transmitted using uplink resources within a specific base station. As illustrated in FIG. 4A , in a specific base station, the MIB transmission period and the DFN transmission period may be the same 40 ms. In addition, as described above, the DFNs 405 , 415 , and 425 transmitted using the offset value transmitted through the MIB for each period have an offset value within one period of 40 ms from SFN#0. 4A exemplarily illustrates a case where the offset value is 14 ms.

4B and 4C are exemplary diagrams for explaining a method of transmitting an offset of an OOC terminal when an IC terminal transmits a synchronization sequence and a synchronization channel to the OOC terminal.

First, FIG. 4b shows a method in which an IC terminal transmits an offset along with a DFN value through a synchronization channel. As illustrated in FIG. 4B , it is assumed that the IC terminal is allocated a synchronization resource with an offset of 14 ms in DFN#0 from the base station. Accordingly, when the IC terminal transmits a value corresponding to DFN#0 and 14 ms on the synchronization channel, the OOC terminal determines the location of its synchronization resource based on the value. When the OOC terminal arbitrarily determines the location of the synchronization resource, the IC terminal must frequently perform a scanning operation to receive the synchronization signal of the OOC terminal, which is a burden on the IC terminal. Accordingly, the aim of FIGS. 4B and 4C is to reduce unnecessary reception operations by transmitting a synchronization signal by the OOC terminal at a location expected by the IC terminal. This method can reduce the reception operation through two options.

Option 1: The OOC terminal may determine the location of the synchronization resource according to the offset_SRU from the time when the synchronization signal of the IC terminal is received to the predetermined synchronization resource.

Option 2: The OOC terminal calculates the DFN#0 time point based on the offset value sent by the IC terminal at the time when the IC terminal's synchronization signal is received, and the location of the synchronization resource according to the offset_SRU from DFN#0 to the predetermined synchronization resource may decide

The reason for notifying the offset as in FIG. 4b is that even the OOC terminal needs to operate to have a different offset between the synchronous transmission terminals (for example, to avoid half-duplex or interference problems), and to match the operation with the IC terminal it is for However, option 1 calculates the offset based on the location of the synchronization resource of the IC terminal, which is based on the assumption that the location of the synchronization resource of the IC terminal is the reference time of the synchronization period. The synchronization resource structure of FIG. 3A may be referred to. On the other hand, option 2 has a difference in calculating the offset based on DFN#0.

Referring to FIG. 4B , when the IC terminal transmits the synchronization sequence and the synchronization channel to the OOC terminal, the transmission is exemplified with an offset of 14 ms. That is, the DFNs 405 , 415 , and 425 having an offset of DFN0 + 14 ms are transmitted as in FIG. 4A , and the period is 40 ms as described above. In addition, when there is a type 1 OOC terminal receiving a reference signal from a terminal located in the base station, the operation according to the two options is exemplified.

According to FIG. 4B , DFNs 431a , 441a , 451a indicating an offset value of 12 ms based on DFN#0 transmitted by the IC terminal may be transmitted as in option 1, or transmitted by the IC terminal as in option 2 An offset value of DFN#0 transmitted by the IC terminal is calculated based on one offset value, and the positions of synchronization resources 431b, 441b, 451b may be calculated according to the offset_SRU from DFN#0 to a predetermined synchronization resource. .

Meanwhile, in order to avoid the half-duplex problem, OOC UEs need to distinguish at least two or more synchronization resources, even between UEs with identical timings, that is, synchronization between UEs. For this purpose, a synchronization resource index may be used, but synchronization resources can be distinguished using a DFN value. For example, when "DFN value + offset value" is received from the synchronization channel, the offset value may be removed and a modular operation may be performed on the DFN value. For example, according to the result obtained by performing modular 4 operation on the DFN value, DFN#0 may be an IC terminal synchronization resource, DFN#1 may be the first OOC terminal synchronization resource, and DFN#3 may be the second OOC terminal synchronization resource. . The modular 4 operation is also possible using a method of using MSB or LSB 8 bits (bits) of the DFN 10 bits (bits). As another method, the N bits of MSB or LSB among fields indicating the offset are used. That is, if the offset is [0 to 9] ms, the IC terminal synchronization resource may be indicated, if [10 to 19] ms, the first OOC terminal synchronization resource, and if [30 to 39] ms, the second OOC terminal synchronization resource may be indicated. For example, when the offset is 6 bits, 00**** indicates the IC terminal synchronization resource, 01**** indicates the first OOC terminal synchronization resource, and 10**** indicates the second OOC terminal synchronization resource can indicate

According to FIG. 4C, when considering a synchronization procedure between OOC terminals that cannot receive base station timing, the DFN#0 reference time is not controlled by the network, so the offset may not be meaningful. Therefore, it is considered that the location of the synchronization resource is determined for the DFN, and the relative offset between the synchronization resources is also predetermined. In such a scenario, even if the IC terminal sends an offset, it is ignored and only the relative offset between the synchronization resources is considered to determine the synchronization resource. In this case, the index corresponding to the location of the synchronization resource must be informed. By using CRC masking or a demodulation reference signal (DMRS) in the synchronization channel, a required amount of N bits (eg, 1 bit) is used to inform the synchronization resource index (for SRU1 and SRU2). If there is no separate index information, a synchronization resource index can be obtained by performing a modular operation on the DFN value.

Referring to FIG. 4C attached, the IC terminal transmits DFN#0(405), DFN#4(415), and DFN#8(425) according to the network reference time, and the offset value is set in any of the methods described above. You can send one of them. However, the OOC terminal may ignore the offset value and set it according to the received DFN value according to the preset offset_SRU value (set as 12 ms in FIG. 4C). In addition, index information of the DFN may be defined as described above.

Separately from the example of FIGS. 4A to 4C described above, the base station can broadcast by setting the synchronization resource offset for the OOC terminal. By using the additional offset information, the base station can arrange the synchronization resource of the OOC terminal to a desired location, thereby controlling interference, and the IC terminal can also receive only the corresponding location according to this information, thereby reducing power consumption.

Table 1 below is a table showing which resource pool should be indicated to the receiving terminal according to the transmission/reception relationship between terminals.

When the reception resource region is explicitly indicated, the terminal receiving the synchronization signal performs a reception operation at the location of the reception resource region transmitted through the D2D synchronization channel. When the reception resource region is not explicitly indicated, the terminal receiving the synchronization signal assumes that the transmission terminal will operate in a predetermined (pre-configured or fixed) transmission resource region and performs the reception operation at the corresponding location. When the transmission resource region is explicitly indicated, only a case in which an IC terminal belonging to a base station having a higher priority indicates an OOC terminal is considered. A terminal that has received the explicitly indicated transmission resource region may operate in various ways as follows according to a predetermined rule.

a) Transmission and reception operations are performed in the transmission resource region informed by the IC terminal, and reception operations are not performed in all available resources other than the transmission resource region.

b) Transmit and receive operations are performed in the transmission resource region informed by the IC terminal, and receive operations are performed in all available resources other than the corresponding transmission resource region.

c) Only the transmission operation is performed in the transmission resource area notified by the IC terminal, and the reception operation is performed in all available resources other than the corresponding transmission resource area.

d) Only the transmission operation is performed in the transmission resource area notified by the IC terminal, and the reception operation is performed on all available resources that do not interfere with the transmission operation.

In order to set various operations as described above, the base station may transmit 1-bit information for distinguishing between a case in which the transmission resource region and the reception resource region are the same and a case in which the transmission resource region and the reception resource region are different through a synchronization channel. In this case, if information on one resource region is shared, the transmission resource region may be set in advance without separately indicating.

Then, the cases of the configuration of the transmission resource region and the reception resource region of <Table 1> exemplified above will be described in more detail.

- Case 1 : When the IC terminal transmits a synchronization signal to the OOC terminal, the OOC terminal receives the D2D signal for the Tx Resource Pool notified by the IC terminal through the D2D synchronization channel (or D2D broadcast channel). perform the action On the other hand, if the transmission resource region is not notified, the transmission operation may be performed on a resource with a predetermined location (eg, a resource determined based on the D2D frame number).

In another method of Case 1, the base station may inform the OOC terminal of the reception resource area even though it does not inform the transmission resource area in order to protect the IC terminal. This corresponds to the transmission resource region of the IC terminal, and the OOC terminal prioritizes reception of the IC terminal signal in the reception resource region informed by the base station among the predetermined transmission resource regions, and transmits and receives OOC terminals in other resources perform the action

- Case 2 : When the IC terminal receives the synchronization signal of the OOC terminal, and it is assumed that the priority of the IC terminal is higher, the OOC terminal cannot set the transmission or reception resource of the IC terminal. Since the OOC terminal does not receive base station control, it often uses a preset resource area. When the IC terminal receives the synchronization signal of the OOC terminal, it is assumed that transmission is performed in the preset resource region as described above, and the reception operation is performed. On the other hand, in the case of an OOC terminal that has been indirectly controlled by a base station or an OOC terminal that can control to use a resource area determined for each D2D communication group, the IC terminal may perform a reception operation based on the reception resource area included in the received synchronization channel. may be

- Case 3 : The OOC terminal receives a synchronization signal from another OOC terminal. For the same reason as described in Case 2 above, the OOC terminal may set a reception resource region or may operate in a predetermined reception resource region.

- Case 4 : This corresponds to a synchronous operation between terminals belonging to a neighboring base station, and since it is not possible to control the transmission operation of a terminal belonging to a neighboring base station, it is possible to control only the reception resource region similarly. The terminal may obtain at least one information of a synchronization period or an offset through a base station or through a synchronization channel transmitted by a terminal belonging to a neighboring base station, and may perform a reception operation based thereon.

Considering Cases 1 to 4 described above, the most economical setting method applicable to various scenarios can be considered while using only one resource area information. Then, let's take a look at the two most economical setting methods. In the following two methods, either one of the two methods can be selectively used.

a) When the IC terminal informs the transmission resource region as a synchronization channel, the OOC terminal receiving it performs transmission/reception operation in the corresponding transmission resource region. Upon receiving the synchronization channel of the OOC terminal, the OOC terminal regards the transmission resource region as a reception resource region and does not transmit in the corresponding reception resource region, but only performs a reception operation.

b) When the IC terminal informs the reception resource region as a synchronization channel, the OOC terminal that has received it performs a reception operation without transmitting in the reception resource region. Of course, the OOC terminal may perform transmission/reception operation in its own transmission resource region.

5A to 5D are exemplary diagrams of a method of allocating transmission and reception resource regions according to the present invention.

5A to 5D described below are examples of applying the above-described principle when allocating D2D transmission and reception resource regions. In addition, in FIGS. 5A to 5D, the three types of terminals will be described separately.

First, an In-Coverage UE (IC) is a UE capable of accessing a network by receiving a synchronization signal from a base station. Out-of-network (OOC) terminals are divided into two types. First, a type 1 OOC terminal (Out-of-coverage UE Cat.1) is a terminal that receives a synchronization signal relayed by an IC terminal and follows the reference timing of the base station. Second, a type 2 OOC terminal (Out-of-coverage UE Cat. 2) is a terminal that does not follow the reference timing of the base station.

First, referring to FIG. 5A , the IC terminal performs transmission/reception operation in the transmission resource region indicated by the base station, and among the IC terminals, the synchronous transmission terminal relays information on the transmission resource region and delivers it to the OOC terminal. The type 1 OOC terminal should perform transmission/reception operation only in the transmission resource area indicated by the base station. Meanwhile, the type 2 OOC terminal may perform transmission/reception operation in all of the preset resource regions.

Referring to FIG. 5A , the IC terminal may perform transmission and reception operations in the D2D transmission resource regions 501 , 502 , and 503 allocated from the base station. In FIG. 5A , it is indicated that the resource areas 501 , 502 , and 503 in which the IC terminal performs D2D transmission and reception operations are resources allocated from the base station to the D2D transmission resource pool. In addition, in the case of a type 1 OOC terminal receiving information on the synchronization transmission resource region from the IC terminal, as described above, the transmission/reception operation is performed only in the transmission resource regions 501, 502, and 503 indicated by the IC terminal, that is, indicated by the base station. carry out However, the type 2 OOC terminal may perform transmission/reception operation in the entire preset resource region, that is, the entire band 500 . A portion denoted as WAN in FIG. 5A may mean a resource area used in the LTE system.

Next, referring to FIG. 5B , the IC terminal is performing transmission/reception operation in the transmission resource area indicated by the base station. Also, among the IC terminals, the synchronous transmission terminal sets the same area as the transmission resource area as the reception resource area, relays information on the transmission resource area for the OOC terminal indicated by the base station, and delivers it to the OOC terminal. The type 1 OOC terminal should only perform reception in the reception resource region indicated by the base station, and may perform transmission/reception operation in the transmission resource region indicated by the base station. The reason for this setting is that, in terms of protecting the transmission link within the network area, the WAN is uplink, so the interference from the OOC terminal is insufficient. . Meanwhile, the type 2 OOC terminal may perform transmission/reception operation in all of the preset resource regions.

Referring to FIG. 5B attached thereto, the resources of the IC terminal are divided into resource pools 501 , 502 , and 503 allocated as D2D transmission resource regions from the base station and WAN resource regions. At this time, the synchronous transmission terminal among the IC terminals sets the transmission resource regions 501 , 502 , and 503 as the reception resource region and informs the type 1 OOC terminal of the reception resource region. Accordingly, the type 1 OOC terminal may set the D2D reception resource regions 521 , 522 , and 523 to the same timing as the D2D transmission resource region of the IC terminal. In addition, the type 1 OOC terminal may set all regions 531 , 532 , and 533 other than the reception resource region as the D2D transmission resource region, and may set only some of the regions as the transmission resource. The D2D transmission resource regions 531 , 532 , and 533 may follow the configuration of the base station as described above. In addition, the two-type OOC terminal may perform transmission/reception operation in the entire preset resource region, that is, the entire band 500 as shown in FIG. 5A .

Referring to FIG. 5C , the IC terminal performs transmission/reception operation in the transmission resource region indicated by the base station, and among the IC terminals, the synchronous transmission terminal relays information on the transmission resource region and delivers it to the OOC terminal. The type 1 OOC terminal should perform transmission/reception operation only in the transmission resource area indicated by the base station. Meanwhile, the type 2 OOC terminal may perform only a reception operation in a transmission resource region indicated by the base station among preset resource regions, and may perform transmission/reception operations in the remaining resources. The reason for setting as shown in FIG. 5c is to protect the IC terminal and the type 1 OOC terminal according to the base station timing from interference.

Referring back to FIG. 5C, the resources of the IC terminal are divided into resource pools 501, 502, and 503 allocated as D2D transmission resource regions from the base station and WAN resource regions. In this case, the synchronous transmission terminal among the IC terminals sets the resource at the same time as the transmission resource regions 501 , 502 , and 503 of the IC terminal as the transmission resource region and informs the type 1 OOC terminal of the transmission resource region. Therefore, the type 1 OOC terminal may set the D2D transmission resource regions 501 , 502 , and 503 to the same timing as the D2D transmission resource region of the IC terminal. In addition, the type 1 OOC terminal may set the resources 501 , 502 , and 503 allocated to the transmission resource region to the type 2 OOC terminal as the reception resource region, and then notify the type 2 OOC terminal. Accordingly, the reception resource regions 541 , 542 , and 543 of the type 2 OOC terminal may be set at the same time as the transmission resource region of the type 1 OOC terminal. The reason for this is the same as discussed above. Finally, the type 1 OOC terminal may set all regions 551 , 552 , and 553 other than the reception resource region of the type 2 OOC terminal as the D2D transmission resource region, and may set only some of them as the transmission resource. The D2D transmission resource regions 531 , 532 , and 533 may follow the configuration of the base station as described above.

FIG. 5D is similar to FIG. 5B described above, but for the same reason as in FIG. 5C without using all of the resource regions set in advance by the Type 2 OOC UE, in order to eliminate interference with the transmission resource region of the Type 1 OOC UE. Only the reception operation may be performed in the reception resource area transmitted by the synchronous transmission terminal, and the transmission/reception operation may be performed in the remaining resources among the preset resource areas.

Referring back to FIG. 5D, the resources of the IC terminal are divided into resource pools 501, 502, and 503 allocated as D2D transmission resource regions from the base station and WAN resource regions. At this time, among the IC terminals, the synchronous transmission terminal sets the resources at the same time as the transmission resource regions 501 , 502 , and 503 of the IC terminal as the reception resource regions 521 , 522 , 523 of the type 1 OOC terminal to 1 Notifies the slave OOC terminal of the reception resource area. Accordingly, the type 1 OOC terminal may set the D2D transmission resource regions 501, 502, and 503 of the IC terminal as its reception resource region. Also, the IC terminal sets the WAN resource to the transmission resource areas 531 , 532 , and 533 of the type 1 OOC terminal and informs the type 1 OOC terminals. Accordingly, for the type 1 OOC terminal, both a transmission resource region and a reception resource region may be configured.

The type 1 OOC terminal may also set the type 2 OOC terminal to set the transmission resource region and the reception resource region to the opposite of their assigned assignments. That is, the viewpoint of the reception resource regions 521 , 522 , 523 of the type 1 OOC terminal is set to the transmission resource regions 541 , 542 , 543 of the type 2 OOC terminal and instructs the type 2 OOC terminal, By setting the transmission resource regions 531 , 532 , 533 of the OOC terminal to the reception resource regions 551 , 552 , 553 of the type 2 OOC terminal, the type 2 OOC terminal may be notified.

In the example of FIGS. 5A to 5D described above, it is assumed that the synchronization timing of the IC terminal and the type 1 OOC terminal coincides with each other. However, in some systems, the OOC terminal may not follow the timing of the IC terminal. In order to reduce interference to the IC terminal in such an environment, the following method may be considered when the OOC terminal transmits a synchronization signal.

a) Sync resource hopping : The location of a synchronization resource that transmits a synchronization signal is changed according to a time variable. For example, the output of a function that takes a DFN value as an input becomes the changed resource location information for the resource location in DFN#0. Alternatively, the change position of the resource position as the DFN value increases by one may be determined. When there are a plurality of synchronization resources, the same change formula may be applied, or a different change formula may be applied to each resource.

b) Offset randomization : Although the period of the synchronization resource is fixed, the start position of the synchronization resource can be controlled by the offset value within one synchronization period. In such an environment, for example, a new offset value may be applied from the scanning period to a predetermined period longer than the synchronization period, for example, every scanning period. Terminals other than the synchronization transmitting terminal operate in the reception state during the scanning period to listen to the offset value newly set by the synchronization transmitting terminal. In detail, when the OOC terminal becomes a synchronization source, an arbitrary synchronization resource offset may be used without using a predetermined synchronization resource offset. Once the synchronous transmitting terminal becomes a synchronous transmitting terminal, it scans the surrounding conditions and decides whether to continue to play the role or to quit. It is changed to an arbitrary value in units of 1 subframe of LTE. In this case, if the offset set by the neighboring base station is known, it may be changed to an arbitrary value among the offsets in which synchronization resources do not collide in order to prevent interference.

As in the synchronization resource structure illustrated in FIGS. 3A and 3B , a plurality of synchronization resource units (SRUs) may be configured within one synchronization period. In the example of FIGS. 3A and 3B , each SRU is connected to a different type of synchronization transmitting terminal. For example, the location of the SRU may be determined according to the number of relay hops or the role (independent/support) of the synchronization transmitting terminal.

In the synchronization resource unit, the synchronization signal is transmitted in every SRU, but the synchronization channel may not be transmitted according to a specific condition. Looking at the condition in which the synchronization channel is not transmitted, the following conditions may exist.

a) When the period of the synchronization channel is set longer than the period of the synchronization signal

b) When the specific resource area designated by the base station and the SRU location overlap (for example, set to use only the synchronization signal (D2DSS) in the discovery resource area that is not controlled by the base station.)

c) As a result of monitoring the synchronization channel, if the synchronization channel reception performance is reduced due to the large number of participating terminals, the terminal may directly change the period or offset of the synchronization channel according to the monitoring result, and report the monitoring result to the base station and determine by the base station The period or offset of the synchronization channel may be changed. Alternatively, the UE may directly change the transmission probability of the synchronization channel according to the monitoring result of the synchronization channel, or report the monitoring result of the synchronization channel to the base station and determine the transmission probability of the synchronization channel by the base station.

6A to 6D are diagrams illustrating the structure of a resource region for performing D2D discovery or communication and the location and structure of a synchronization resource.

The structures illustrated in FIGS. 6A to 6D are arranged in a logical temporal order, and in reality, other resources may be added in addition to each indicated area. For example, in the case of a base station operating in TDD (Time Division Duplex), since the D2D resource region will be configured in the uplink, the downlink resource may be temporally located. However, from the standpoint of the D2D terminal, it can be logically configured as if continuous D2D resources exist.

6A is a diagram illustrating a structure of a resource region and a structure of a synchronization resource for performing D2D communication.

Referring to FIG. 6A , a resource area notified by the base station to perform D2D communication, that is, a scheduling assignment (SA) area (Pool) 611 and 612 and a data resource area for communication (Data Pool) 621, 622) and the structure of the synchronization resources 601a, 601b, and 601c for informing the reference time for the resource area. In the SA areas 611 and 612 , the UE transmits an SA signal including information on an allocated or selected data resource to an adjacent UE prior to data transmission. The terminal receiving the SA signal in the SA areas 611 and 612 receives the data signal from the interested transmitting terminal in the subsequent data areas 621 and 622 . The terminal located in the network area receives the broadcast channel (BCH) from the base station to confirm the absolute time of the reference frame (SFN0), and receives the SIB to obtain relative position information for the resource area indicated with respect to the reference frame.

On the other hand, a terminal located in an adjacent base station or located in a partial network area or outside the network first receives a synchronization signal and a synchronization channel from the terminal transmitted from the SRUs 601a, 601b, 601c, and receives the reference frame SFN0. ), and obtains relative position information for the resource region indicated with reference to the reference frame.

The D2D terminal may select one synchronization terminal according to a predetermined priority in order to synchronize the reference time for transmission. If there is a synchronization terminal having a different reference time from the selected synchronization terminal, it is used to synchronize the reference time for receiving a synchronization signal from another synchronization terminal while synchronizing the transmission reference time to the selected synchronization terminal for a certain period of time. During one synchronization signal period, one or more synchronization resources, that is, SRUs may be deployed. At this time, when the reference time for transmission is synchronized, in examining certain conditions for synchronization signal transmission such as reception power for a base station signal or a synchronization signal from another synchronization terminal, signal detection, etc., if there is no idle SRU, the synchronization signal It can operate to not transmit. That is, the terminal selects one of the idle SRUs and transmits the synchronization signal only when there is an idle SRU, even when the condition for operating the synchronization signal transmission is satisfied. A condition for determining an idle SRU may be applied relatively non-strictly. For example, if the number of synchronization signals received with more than a certain received power in one synchronization resource (SRU) does not exceed N, it may be determined as an idle SRU.

6B is a structure of a resource region and a synchronization resource for performing D2D discovery.

Referring to FIG. 6B , synchronization resources ( 601a, 601b, 601c, and 602a) are shown. As in FIG. 6A , for the discovery resource region 1 631, the BCH is received from the base station to confirm the absolute time of the reference frame SFN0, and the SIB is received and the relative position to the discovery resource region indicated based on the reference frame. get information

On the other hand, a terminal located in a neighboring base station or located in a partial network area or outside the network area first receives the synchronization signal and the synchronization channel from the terminal transmitted from the SRUs (601a, 601b, 601c) from the current frame number obtained from the The absolute time of the reference frame SFN0 is calculated, and relative position information for the resource region indicated with respect to the reference frame is obtained. For example, if the synchronization channel received from the terminal located in the neighboring base station indicates SFN10, the reference frame SFN#0 will be located 10 frames before.

On the other hand, with respect to the discovery resource region 2 (632), the terminal located in the neighboring base station receives the BCH and SIB from the affiliated base station, and the reference of the affiliated base station with respect to the starting point of the discovery resource region 2 (632) of one or more other base stations. Obtain relative position information with respect to time (SFN#0). Thus, when the starting point of the resource zone of another base station is reached, if the terminal performs transmission/reception operation with the WAN or the terminal is not transmitting a synchronization signal or other D2D signal, the synchronization signal and channel expected at the starting point of the resource zone receive

Although the synchronization signal is transmitted according to a specific condition, the synchronization channel may not be transmitted. By receiving the synchronization signal, the terminal located in the neighboring base station can match the accurate reception synchronization reference time for when the corresponding discovery resource region starts. This operation is not limited to this example and may also be applied to the D2D communication resource region.

On the other hand, when the discovery resource region 1 (631) and the discovery resource region 2 (632) are simultaneously operated, a field indicating whether or not the first section (eg, a subframe) of the resource region is used for the SRU is provided from the base station. It should be included in the BCH and SIB of In the case of a synchronization transmitting terminal, the existence of a resource for transmitting a synchronization signal must be determined according to a field indicating whether the SRU is used. In addition, in the case of a receiving terminal located in a neighboring base station, whether to receive a synchronization signal and a channel or a discovery signal in a corresponding resource region may be determined in advance according to a field indicating whether the SRU is used. This field is referred to as a periodic synchronization transmission field in the present invention. When the base station uses the periodic SRUs 601a, 601b, and 601c, the BCH or SIB informs the base station by turning on the periodic synchronization transmission field. On the other hand, in the case of using the aperiodic and one-shot SRU 602a, the periodic synchronization transmission field is turned OFF to inform the BCH or the SIB.

A terminal located in a partial network area or an area outside the network, when a separate SRU 602a is not used in the resource area 2 632, is transmitted from SRUs 601a, 601b, 601c that are transmitted periodically. By receiving the synchronization signal and the synchronization channel from the terminal, the absolute time of the reference frame (SFN0#) is confirmed, and the relative position information for both the resource area 1 631 and the resource area 2 632 shown with respect to the reference frame is obtained. acquire Such relative location information acquisition is also possible in the case of information relayed not only from a base station to which it belongs but also from an adjacent base station. After obtaining the relative position information for the resource region, it is in a dormant state and wakes up earlier than at least one synchronization period than the starting point of the resource region and receives synchronization signals from the periodic SRUs (601a, 601b, 601c) to correct synchronization can be performed.

On the other hand, when a separate SRU 602a is additionally used in the resource zone 2 632 , the terminal receives the periodic SRUs 601a , 601b , and 601c , and the reference of the affiliated base station for the resource zone of the adjacent base station It is possible to obtain relative position information from time (SFN#0), and after being in a dormant state, it wakes up just before reaching the starting point of the resource area 2 (632) and receives a synchronization signal from a separate SRU (602a) to synchronize Calibration can be performed. When only a separate SRU 602a is used in the resource region 2 632 without the periodic SRUs 601a, 601b, and 601c, the base station does not provide information on the start point of the resource region in advance, or If the terminal is located, an inefficient operation of performing a long time synchronization procedure in order for the terminal to receive the SRU 602a without periodicity may occur.

6C is an exemplary diagram of a resource domain structure and a synchronization resource structure for performing D2D discovery and communication, and FIG. 6D is another exemplary diagram of a resource domain structure and a synchronization resource structure for performing D2D discovery and communication. The difference between FIGS. 6C and 6D is whether the aperiodic SRU 602a is used for discovery resources. The contents of the periodic SRUs 601a, 601b, and 601c and the aperiodic SRU 602a can be used as in FIGS. 6A and 6B described above.

The periodic synchronization resources 601a, 601b, and 601c are suitable synchronization transmission schemes for D2D communication. In order to provide a reference timing for receiving a control channel (SA, Scheduling Assignment) area 610 and a data channel (Data) resource area 620 for D2D communication, a terminal satisfying a condition among D2D terminals transmits a synchronization signal. It can be a synchronous transmission terminal. When a terminal that does not transmit data becomes a synchronous transmission terminal, a situation may occur in which the receiving terminal cannot receive any data even after synchronizing. Therefore, having data to transmit is a basic condition for becoming a synchronous transmitting terminal. There are several ways to specify the condition that you have data to send. Let's take a look at this with reference to the accompanying Figures 7a to 7c.

7A to 7C are exemplary diagrams for explaining methods for using a periodic synchronization resource.

First, briefly describing the resource allocation situation of FIG. 7A , resources 701 and 702 not used for D2D communication, SA resources 711 and 712 , and resources 721 and 722 for D2D communication are mixed. may have been Since the situation in which these resources are mixed has already been described above, additional description is omitted. The locations of the SRU for transmitting the synchronization signal in these resources may be established. In this case, FIG. 7A shows synchronization resources 721a, 721b, 721c, 722a, 722b, in which a terminal having SA signals 711 and 712 or data to be transmitted is included in the SA or data areas 721 and 722, 722c) only indicates the method of transmission. That is, the SRUs 701a, 701b, 702a, 702b, and 702c of the resource areas 701 and 702 that are not allocated for D2D communication are not used. However, this method has a problem in that, for example, the immediately preceding synchronization resource of the SA resource areas 711 and 712 cannot be used. Since the synchronization signal is not transmitted before the SA resource region, the terminal to receive the SA and the data resource region receives the synchronization signal only after the SA starts.

Therefore, in order to solve the problem in FIG. 7A, as in FIG. 7B, a terminal having an SA signal or data to transmit, determines whether to use an SA between a synchronization resource and a synchronization resource following one synchronization period. Alternatively, if the data resource region exists, the synchronization signal may be transmitted. That is, it is possible to transmit the SRUs 701b1 and 702c1 not used in FIG. 7A before the SA areas 711 and 712 . In this case, the SRUs 701b1 and 702c1 transmitted before the SA regions 711 and 712 may be SRUs at a different time point than the SRUs 701b and 702c of FIG. 7A described above. That is, the SRUs 701b1 and 702c1 used in front of the SA areas 711 and 712 of FIG. 7B are shown in FIG. 7A described above, because they must have positions set as much as the preceding synchronization period according to the synchronization period existing in the data area. The SRUs 701b and 702c may be SRUs of different time points. Also, in some cases, the SRUs 701b1 and 702c1 used in front of the SA areas 711 and 712 of FIG. 7B may be SRUs at the same time as the SRUs 701b and 702c of FIG. 7A described above.

Although FIG. 7B described above enables a minimum synchronization operation, in actual implementation, it is necessary to receive a synchronization signal for a predetermined period in order to obtain performance above a predetermined level. For example, the reception performance in the physical layer may be improved by periodically receiving the synchronization signal. Alternatively, reception may be attempted prior to a known period in order to correct an error of an oscillator that controls timing. Alternatively, when a resource region of a neighboring cell is to be received, reception may be attempted in advance in consideration of an interval corresponding to a timing error between base stations.

In order to guarantee performance for these various scenarios, the base station may control the terminal to perform reception by w ahead of the expected synchronization signal transmission time by setting a reception window period. This is possible not only for the belonging base station but also for the resource area of the neighboring base station. The value of w may be reported by the base station as common information through a broadcast channel (BCH) or a system information block (SIB), or may be informed by an individual control signal for each terminal. In consideration of the terminal performing the reception operation based on the value of w, the terminal having a value of w and operating as a synchronization transmitting terminal is a synchronization signal in a synchronization resource between the time points ahead of the start point t of the expected resource region by w time units. to send

The reception window operation illustrated in FIG. 7C may additionally be considered in the operation in the discovery and OOC areas. In an asynchronous cell environment, a synchronization signal for a corresponding resource region may be distinguished in consideration of an error equal to a reception window size w (750) before and after a starting point of a D2D resource pool of a neighboring base station. The same window value or a different window value for each terminal may be used for a specific cell. The synchronization signal for D2D can be distinguished by using a window value for the starting point of the D2D resource region in the same way with respect to the synchronization resource of the belonging base station. The window value may separately inform values for the belonging base station and the neighboring base station by the base station.

That is, as shown in FIG. 7C , if the synchronization signal is distinguished by preceding the size of the window w 750 , the synchronization signals 701a , 701b , 702b transmitted from the preceding positions of the SA areas 711 and 712 are performed. , 702c) may be received. Therefore, at least one synchronization signal transmitted from the areas 701 and 702 before the synchronization signals 721a, 721b, 721c, 722a, 722b, 722c transmitted from the data areas 721 and 722 can be received, It is possible to obtain an accurate start time of the SA areas 711 and 712 .

Meanwhile, since the base station cannot inform the starting point of the D2D resource, the terminal outside the network uses a predetermined D2D resource area. The synchronization signal of the synchronization transmitting terminal includes a synchronization sequence and a synchronization channel, and the D2D frame number is transmitted in the synchronization channel. The location of the D2D resource region may be predetermined based on the D2D frame number. In out-of-coverage, a synchronous reception operation may be performed according to a predetermined window value for the starting point of the D2D resource region. The window value for each resource region of the IC terminal and the window value of the type 1 OOC terminal and the type 2 OOC terminal may be different from each other.

7A to 7C described above, the case where the synchronization resource and the SA resource region overlap is not illustrated, but the SA resource region and the synchronization resource may overlap in the same subframe according to the control of the base station. Since the SA resource region is relatively small compared to the data resource region (eg, the data resource region is 64 subframes, the SA resource region may be 2 subframes). SA resource efficiency can be greatly reduced. Therefore, as an exception, the synchronization signal is not transmitted in the synchronization resource overlapping the SA resource area. Instead, as shown in FIGS. 7B and 7C above, a method capable of synchronous transmission before the SA resource area should be applied.

[How to select a synchronous sequence]

The terminal that has received the synchronization signal determines its transmission timing based on the timing derived from the received synchronization signal, and then determines in advance which synchronization sequence to use when transmitting the synchronization signal when the condition of becoming a synchronization transmission terminal is satisfied. need to decide An operation to be considered is a problem of whether the synchronization sequence is used or a different sequence is used when the timing of a synchronization sequence is used as a transmission reference and when operating as a synchronization transmission terminal. First, it is assumed that the synchronization sequence transmitted by the IC terminal and the synchronization sequence transmitted by the OOC terminal are different.

8A and 8B are network conceptual diagrams for explaining a scenario for selecting a synchronization sequence between an IC terminal and an OOC terminal.

Referring to the configuration with reference to FIGS. 8A and 8B , the base station 801 has a predetermined communication area 810 , and an IC terminal 811 is included in the communication area 810 . Also illustrated are a type 1 OOC second terminal (UE2) 821 that receives a signal from the IC terminal 811 and a third terminal (UE3) 831 that cannot receive a signal from the network.

In FIG. 8A , when a type 1 OOC terminal (UE2) 821 receives a synchronization signal transmitted by an IC terminal (UE1) 811, since the priority of the terminal belonging to the base station is high, the UE2 821 has its own The transmission timing is changed to the timing received from the UE1 811 . And when the condition that the UE2 821 becomes a synchronous transmission terminal, for example, data to be transmitted occurs, the UE2 821 selects one resource from among the synchronization resources for OOC based on the timing received from the UE1 811 and uses it for OOC A synchronization sequence (D2DSSue_oon) is transmitted. In this case, the timing of the base station is limited to the range for receiving the synchronization sequence for IC (D2DSSue_net). The terminal UE3 831 receiving the synchronization sequence for OOC from the UE2 821 determines whether to follow the timing of the UE2 821 according to the determination condition it has. Such determination conditions may be based on, for example, synchronization signal reception power, variables included in the synchronization channel (D2D frame number, remaining time until scanning period, age of synchronization signal, validity period of synchronization transmitting terminal, number of relay hops, etc.). can

In FIG. 8B , when the OOC terminal (UE2) 821 receives the synchronization signal transmitted by the IC terminal (UE1) 811, since the priority of the terminal belonging to the base station is high, the UE2 821 transmits its transmission timing is changed to the timing received from UE1 (811). And when the condition that the UE2 821 becomes a synchronous transmission terminal, that is, when data to be transmitted occurs, the UE2 821 selects one resource from among the synchronization resources for OOC based on the timing received from the UE1 811 and uses it for IC Transmit a synchronous sequence. In this case, the timing of the base station may be extended to an infinite range for receiving the synchronization sequence for IC (D2DSSue_net). Therefore, it is possible to determine whether the synchronization sequence for IC is relayed based on variables (variables such as the number of relay hops, ID of the synchronization transmitting terminal, or synchronization signal accuracy) included in the synchronization channel to be relayed only to a certain range.

On the other hand, in the case of transmitting and receiving a synchronization signal between OOC terminals, there are advantages and disadvantages depending on whether the synchronization sequence of the synchronization signal to be followed coincides with or not. First, consider a case in which the same sequence as the sequence of the synchronization signal to be followed as the reference timing is used to transmit the synchronization signal. Since the same sequence is used between synchronized terminals and a different sequence is used by the out-of-synchronization terminals, when a different sequence is detected during the scanning process, it is immediately known that the synchronization is out of sync. However, there is a disadvantage in that a timing error caused by clock drift cannot be corrected when synchronized terminals move and meet again.

In another method, each synchronization transmitting terminal may use a different synchronization sequence. At this time, even if the synchronization terminal uses different synchronization sequences, it is difficult to detect an asynchronous situation due to the difference in the synchronization sequences. Therefore, in this case, it is advantageous to match all the synchronization resource locations. That is, since they cannot hear each other on the same resource due to a half-duplex problem, if there is a synchronization signal received at a time point other than synchronization transmission, it can be inferred that it is a signal from an out-of-synchronization terminal. Therefore, in this method, all the offsets for the starting point of the synchronization resource must be identically fixed.

In order to solve the above shortcomings, the following method can be considered.

When the OOC terminal receives the synchronization sequence transmitted by the IC terminal, the OOC terminal selects one of the synchronization sequences for OOC and transmits it or transmits it as a sequence in use. If the OOC terminal receives the synchronization signal of another OOC terminal and synchronizes the Tx timing, it is changed to the same sequence as the received synchronization sequence and transmitted. However, in a dynamic environment, a synchronization sequence may be periodically changed because a synchronization error may occur between terminals already synchronized. For example, an existing synchronization sequence may be changed to perform scanning in the scanning period. The scanning period is the same between terminals with the same synchronization (for example, a scanning period is set based on the DFN). If different sequences are used between terminals with the same synchronization in the scanning period, the synchronization is performed only by the difference in the sequence without calculating the timing error. errors can be distinguished. The operation may be replaced with an identifier (ID) of a synchronization transmitting terminal rather than a synchronization sequence.

Similar to the scheme of changing the sequence or synchronization transmitting terminal ID for each scanning period, the timing of the D2DSS in the case of a new I-SS after scanning (because there is no one around), that is, a symbol and a frame boundary While the timing is maintained, the following operations may be performed.

1) When the scanning time is determined by the D2D frame number, the DFN is changed.

2) If there is a control signal (Time-to-Scan, TTS) notifying a separate scanning time, the DFN is maintained and the TTS value is changed.

[Synchronous signal measurement method]

When a certain D2D terminal receives a synchronization signal, it measures another synchronization signal to determine whether to become a synchronization source UE or to report to the base station according to the connection state of the terminal with the base station ( can be measured). Meanwhile, in a situation in which a resource region requiring a periodic synchronization signal and a resource region sufficient for a one-shot synchronization signal are separated, a method of measuring the synchronization signal may vary depending on the case. In the case of a temporary synchronization signal, all synchronization terminals determined by the control of the base station or according to a predetermined condition must use the same single synchronization resource (SRU) to transmit. Therefore, in this case, the synchronization signal transmission is limited to a method of transmitting the same signal in the same resource using a single frequency network method.

In this case, since one or more synchronization signals are overlapped and received, the reception power may be higher than when one synchronization terminal transmits the synchronization signal to one resource, and the synchronization signal may be transmitted over a distance greater than the data transmission distance. When the resource for the periodic synchronization signal is allocated from the base station, the synchronization terminals determined by the control of the base station or according to a predetermined condition may select the idle synchronization resource and transmit the synchronization signal. In this case, since synchronization signals from as few synchronization terminals as possible overlap in the same resource, the reception power of the receiving terminal is relatively small compared to the case of temporary synchronization signal transmission, and there is not much difference from the data transmission distance.

Due to such an environmental difference, there may be a problem in making temporary synchronization signal transmission a measurement target for selecting a synchronization relay terminal for an OOC terminal. Therefore, it is natural to measure only the periodic synchronization signal for the selection of the synchronization relay terminal. To this end, first, the synchronization terminal located in the base station area should inform the synchronization resource location, that is, the period and offset information of the SRU through the synchronization signal and the synchronization channel. In addition, the synchronization terminal may relay information (offset, bitmap, etc.) about a resource region that does not use periodic synchronization resources.

Upon receiving the synchronization signal and the synchronization channel from the synchronization terminal, the terminal first measures the synchronization signal from the adjacent synchronization terminal in order to become a synchronization relay terminal. Based on the information on the resource region that does not use the periodic synchronization resource, the synchronization signal from the terminal belonging to the same base station received in the corresponding resource region may be ignored. (From the synchronization signal transmitted by the synchronization terminal and the ID included in the synchronization channel, it can be known whether the terminal belongs to the synchronization base station, that is, whether it transmits the same synchronization ID as the synchronization terminal that I decided to follow.) That is, in this example, the terminal Only the synchronization signal from the IC belonging to the base station and the type 1 OOC terminal or the type 2 OOC terminal not belonging to any base station is used for measurement.

As another example, the synchronization terminal may relay information (offset, bitmap, etc.) on a resource region using periodic synchronization resources. Upon receiving the synchronization signal and the synchronization channel from the synchronization terminal, the terminal first measures the synchronization signal from the adjacent synchronization terminal in order to become a synchronization relay terminal. Only the synchronization signal from the UE belonging to the same base station received in the resource region using the periodic synchronization resource is used for measurement. (This can be known from the sync sequence and ID included in the sync channel.)

On the other hand, in a resource region that does not use the periodic synchronization resource based on information on the resource region using the periodic synchronization resource or vice versa and the number of relay hops from the base station, a synchronization signal is nevertheless transmitted. You can decide whether to transmit periodically. For example, if the number of relay hops is 2, that is, when the base station (0 hop) -> terminal 1 (1 hop) -> terminal 2 (2 hops) is configured, terminal 2 is configured such that other terminals in the base station area periodically When operating in a resource region that does not use synchronization resources, synchronization transmission may be restricted so as not to be affected by signal transmission such as interference. However, when the number of relay hops corresponds to 3, that is, when the base station (0 hop) -> terminal 1 (1 hop) -> terminal 2 (2 hop) -> terminal 3 (3 hop) is configured, the signal of terminal 3 is the base station. Since the terminal does not reach within the region, synchronous transmission can be performed in a resource region that does not use the periodic synchronization resource.

Meanwhile, in the operation in the area outside the network, when the synchronization resource is divided into I-SS resources and V-SS resources, or when divided into a resource for a terminal with data and a resource for a terminal without data, measurement of a synchronization signal is limited to I-SS resources or resources for terminals with data. Therefore, when a certain terminal tries to measure the reception power by receiving a synchronization signal to check the condition for becoming a synchronization transmitting terminal, if the reception power of the synchronization signal from the terminal having the synchronization signal or data from the I-SS is greater than a predetermined X dBm, the synchronization It cannot be a transmitting terminal. According to this method, even if a terminal receives a synchronization signal from a terminal without V-SS or data at a nearby location, no synchronization signal is received (over X dBm) because there is no terminal with I-SS or data in a nearby location. If not, the terminal may be a synchronous transmission terminal.

[Sync for Tx]

From now on, we will look at the synchronization procedure for the overall inter-terminal discovery and communication. The overall synchronization procedure consists of a transmission synchronization procedure that sets the reference time for transmission and a reception synchronization procedure that matches the reference time for reception. This is to enable D2D discovery or communication signal reception according to the received synchronization signal when another synchronization signal is received even if the basic transmission time is set on the assumption that perfect synchronization is impossible outside the network area. Therefore, the whole procedure consists of a procedure of acquiring transmission synchronization after scanning to acquire periodic transmission synchronization and a procedure of determining a role, and a procedure of acquiring synchronization of reception after scanning to acquire synchronization of reception at the same time. Let's take a look at this operation with reference to FIG. 9 .

9 is a flowchart for aligning transmission synchronization according to an embodiment of the present invention.

Referring to FIG. 9 , when the terminal is turned on in step 900, that is, when the D2D operation is turned on, the step of first finding a base station (scan) starts. Such a scan operation may be performed through the wireless communication unit 201 and the modem 203 of FIG. 2 described above, and is performed under the control of the control unit 205 . If the terminal has been previously turned on, step 900 may be omitted. Note that in the description of FIG. 9 , the terminal may be a control operation performed by the controller 205 .

Thereafter, in step 902 , the terminal checks whether the current timing is a time for scanning for transmission. In scanning, the timing of finding the base station and the terminal and the timing of finding only the terminal may be different. Therefore, the terminal first performs an operation to find a base station in step 904. However, in the case of scanning to find only the terminal, the operation of step 904 for finding the base station is not performed, and the operation of step 920 for searching for the terminal may be proceeded directly. If at least one base station synchronization signal (PSS/SSS) is detected as a result of the scan in step 904, the control unit 205 proceeds to step 908 to select one of the base station synchronization signals to follow the reference time, and additionally to the synchronization relay terminal in step 910 It is decided whether to operate as (Relaying Synchronization Source R-SS). The process of selecting one of a plurality of base station synchronization signals may be generally based on received power strength like the existing LTE standard. The synchronization relay terminal determination procedure will be described in detail in the drawings to be described later. After determining the synchronization relay terminal, the control unit 205 proceeds to step 902 and returns to the step of periodically scanning the base station again.

On the other hand, if it is determined in step 906 that the base station synchronization signal is not detected, the terminal proceeds to step 920 to find a terminal synchronization signal from another synchronization transmitting terminal. After finding the synchronization terminal signal, the controller 205 proceeds to step 922 and checks whether at least one terminal synchronization signal (D2DSS) or a terminal broadcast/synchronization channel (D2DBCH/D2DSCH) is detected. If at least one terminal synchronization signal (D2DSS) or terminal broadcast/synchronization channel (D2DBCH/D2DSCH) is detected as a result of the check in step 922, the control unit 205 proceeds to step 924 and selects one of the terminal synchronization signals and selects a reference time In step 926, it is determined whether to additionally operate as a synchronous relay terminal. The process of selecting one of the plurality of terminal synchronization signals may be determined based on at least one of received power strength, D2D frame number, number of relay hops, synchronization terminal validity period, synchronization terminal age, and device synchronization phase information. there is. At this time, if the terminal having the search signal, communication control signal, and communication data signal to be transmitted does not detect the base station synchronization signal or the terminal synchronization signal as a result of the inspection in steps 906 and 922, the terminal itself is an independent synchronization transmitting terminal (Independent Synchronization). Source, I-SS).

On the other hand, unlike the terminal synchronized with the base station, the terminal synchronized with the synchronization transmitting terminal must periodically perform scanning. This is because the mobile station is more mobile than the base station, so the network volatility is high. The synchronization transmitting terminal should always check the condition for stopping the synchronization signal transmission. A detailed synchronization signal transmission stop procedure will be described with reference to the drawings to be described later.

In step 940, the terminal checks whether it is a time to scan for transmission, and if applicable, returns to step 902 to scan the base station or the terminal again. If it is not the scan time for transmission, it is checked whether it is a scan time for reception (Time to Scan for Reception) as in step 930. A detailed reception scanning procedure will be described in more detail in the drawings to be described later.

During the scan for transmission and the scan for reception, there may be a difference in the transmission method from the standpoint of the synchronous transmission terminal. The scan for transmission operates in anticipation of a synchronization change in the future, but maintains the existing transmission timing after the scan for reception. Therefore, in the scanning process for transmission, the synchronization transmitting terminal stops transmitting the synchronization signal during the scan period, but in the scanning process for reception, the synchronization transmitting terminal continues to transmit the transmitted synchronization signal during the scan period.

[Sync for Rx]

10A to 10C are flowcharts illustrating various embodiments of scanning for reception according to the present invention.

First, a scanning procedure for reception according to an embodiment of the present invention will be described with reference to FIG. 10A. In explaining FIG. 10, it should be noted that the terminal may be the control unit 205 as exemplified above, and are used interchangeably. In addition, if necessary, the operation will be described using the block diagram of FIG. 2 .

First, in step 1000, the UE checks whether D2D transmission or reception is in progress. For example, if the terminal is transmitting or receiving a control signal or data signal for discovery or communication, it may be difficult to receive another synchronization signal before the transmission/reception operation is completed. If the current signal is not being transmitted/received, the control unit 205 proceeds to step 1002 and checks whether it is a scanning time for reception (Time to Scan for Reception). In the case of always scanning for reception, this process may be omitted. If it corresponds to the scanning time, the control unit 205 proceeds to step 1004 to scan the base station synchronization signal, and in step 1006 checks whether the base station synchronization signal is heard, that is, whether the base station synchronization signal is received. If the synchronization signal of the base station is received as a result of the check in step 1006, the process proceeds to step 1010 to set a reception time reference, and to the step of checking a mode for receiving a D2D signal in step 1014.

On the other hand, if it is determined in step 1006 that the base station synchronization signal is not heard, the control unit 205 proceeds to step 1008 and checks whether the terminal synchronization signal is heard. When the synchronization signal is not heard as a result of the check in step 1008, the control unit 205 ends the routine of FIG. 10A. However, if the terminal synchronization signal is heard as a result of the check in step 1008, the control unit 205 proceeds to step 1012 to set a reception time reference and proceeds to the step of checking the mode for receiving the D2D signal in step 1014.

As illustrated in FIG. 10A , in the step of receiving the D2D signal, there may be two synchronization modes: a first reception synchronization mode (Rx sync mode 1) and a second reception synchronization mode (Rx sync mode 2) of operation 1020 . In the Rx mode, the reception operation in the resource region of the cell to which it belongs is excluded because it is sufficient to use the transmission timing.

Then, let's look at the difference between Rx sync mode 1 and Rx sync mode 2.

- Rx sync mode 1 : It is assumed that a serving base station informs resource region information such as an offset with a neighboring base station as a difference from a reference frame timing (eg, SFN0). Therefore, D2D reception is performed only in the informed resource area, and when a synchronization signal from a terminal belonging to a received neighboring base station is detected, a symbol and a frame boundary are obtained from it, and a predetermined D2D operation is performed.

In the case of an OOC terminal in which the base station reference time is obtained through the relay of the synchronization signal by the terminal, the same as when the synchronization terminal is in the base station by receiving the offset with the neighboring base station and the resource area information of the neighboring base station transmitted through the synchronization channel receive operation can be performed. In this case, the receiving terminal should be able to confirm the ID of the base station to which the synchronization terminal is associated or camped through the synchronization signal of the synchronization terminal.

In the case of an OOC terminal that has acquired an independent reference time not derived from the receiving network, it is not easy to use Rx sync mode 1. That is, there is no synchronization relay terminal belonging to the base station, so a synchronization terminal is independently created. If complexity is not important, the following method is also possible. When the terminal belonging to the base station receives the reference time of the independent OOC terminal and reports it to the base station, the base station can inform the belonging terminals of the offset from the reference time of the independent OOC terminal based on the report from at least one terminal there is. However, if complexity is an issue, a method such as Rx sync mode 2 may be more efficient.

- Rx sync mode 2 : It is assumed that a neighboring base station or a synchronization terminal belonging to the neighboring base station informs the resource region information such as an offset with a neighboring base station from the reference timing (eg, SFN0) of the neighboring base station. The resource region information may include information on a search resource, a communication control resource, and a communication data resource as well as a synchronization resource. Therefore, it is necessary to receive every synchronization signal and channel, obtain a symbol and frame boundary from the synchronization signal, and check the current SFN and the location of the resource region from the synchronization channel. If the current timing corresponds to the confirmed D2D resource region, the D2D operation is performed in that resource region. If the current timing is not the confirmed D2D resource region, if there is no other operation with the WAN other than D2D, Idle until the D2D resource region arrives. You might as well wait.

In Rx sync mode 2, if the OOC terminal obtained the base station reference time through the relay of the synchronization signal by the terminal, or otherwise, the synchronization terminal receives the SFN and the resource area information of the neighboring base station delivered through the synchronization channel to D2D A receive operation may be performed.

10B is a flowchart for explaining in detail operations corresponding to Rx sync mode 1 and Rx sync mode 2 when compared with FIG. 10A. In the case of Rx sync mode 1, that is, in step 1030, information on the resource region start point of the neighboring base station is obtained based on the SIB received from the base station, and based on this, it is determined from which point to start scanning for reception. This is the step of updating the information list. In the case of Rx sync mode 2, that is, step 1032 acquires information on the resource region start point of the synchronization transmitting terminal as well as the adjacent base station through the terminal broadcast channel (D2DBCH) or the terminal synchronization channel (D2DSCH), and based on this, at a certain point in time It is a step of updating the information list on whether to start scanning for reception.

10C is a method of separately operating a scanning period for reception for a base station and a terminal compared to FIG. 10B.

Referring to FIG. 10C , in step 1000 , the controller 205 checks whether D2D transmission or reception is in progress. If it is determined in step 1000 that the signal is not currently being transmitted/received, the control unit 205 proceeds to step 1040 and checks whether it is a time to scan for reception from the base station. In the case of always scanning for reception, this process may be omitted. If it corresponds to the scanning time, the control unit 205 proceeds to step 1042 to scan the base station synchronization signal, and in step 1044 checks whether the base station synchronization signal is heard, that is, whether the base station synchronization signal is received. As a result of the check in step 1044, if the synchronization signal of the base station is received, the process proceeds to step 1046 to set a reception time reference from the base station, and proceeds to the step of checking the mode for receiving the D2D signal in step 1048.

On the other hand, if it is not the scanning time for reception from the base station as a result of the check in step 1040, the control unit 205 proceeds to step 1050 and checks whether the terminal is scanning time. If it is the scanning time of the terminal for receiving the result of the check in step 1050, scanning is performed for reception from the terminal in step 1052, and it is checked whether a synchronization signal is received from at least one terminal in step 1054. If a synchronization signal is detected in step 1054, the control unit 205 performs reception synchronization on one of the corresponding signals in step 1056. Thereafter, the control unit 205 checks whether the first reception synchronization mode or the second reception synchronization mode is in step 1048, and proceeds to step 1060 in the case of the first reception synchronization mode, and proceeds to step 1062 in the case of the second reception synchronization mode do.

In step 1060, in the second reception synchronization mode, the scanning time list for reception from the D2D channel is updated, and in step 1062, in the first reception synchronization mode, the base station scanning time list for reception is updated from the SIB.

As shown in FIG. 10C , the terminal manages a plurality of reception timings as a single list, as in step 1060 or step 1062, but managing all received timings is impossible due to limitations in the performance and memory of the communication chip. Therefore, it is necessary to perform a reception operation only for a certain number of reception timings. For example, if 5 reception timings need to be selected among the reception timings obtained from all 30 received synchronization signals, a problem of selection arises. For example, while tracking N Rx syncs, priority is considered in selecting N Rx syncs.

The exemplified priority puts the receiving operation of the base station or synchronous transmission terminal to which it belongs, that is, its own transmission timing as its top priority, and thereafter, the transmission timing of the base station, the transmission timing of the IC terminal, and the transmission timing of the OOC terminal in the order do. In this case, when N is 1, as an exception, the transmission timing of the base station is adjusted to have the highest priority. As another example, the base station's transmission timing is given the highest priority, and after that, its own transmission timing, the IC terminal's transmission timing, and the OOC terminal's transmission timing are set in the order of priority. In a system that considers absolute time, such as GPS, the transmission timing of the terminal using absolute time using GPS may be inserted between the transmission timing of the IC terminal and the transmission timing of the OOC terminal. In the above example, if the priorities are the same, it is determined that the received power of the synchronization signal is greater or the priority of the D2D Frame Number is higher.

On the other hand, the synchronization resource used by the terminal to transmit the discovery signal, the communication control signal, and the communication data signal and the synchronization resource used by the terminal transmitting the synchronization signal for support in the synchronization procedure even when there is no signal to be transmitted are separated in advance. In this case, the synchronization resource of the synchronization transmitting terminal supported by the receiving synchronization target to be tracked may be excluded. Alternatively, even if the synchronization resource is not separated, if the synchronization signal of the discovery/communication signal transmitting terminal and the non-supporting terminal can be distinguished in a sequence or message, the synchronization signal of the support terminal may be excluded from the tracking reception synchronization target.

If an appropriate synchronization procedure is not provided in the OOC environment, a cluster formed by a plurality of synchronization transmitting terminals may exist. In such an environment, it is difficult to match the transmission/reception areas between neighboring clusters, so it is necessary to perform simultaneous transmission/reception operations for multiple clusters. Since it is difficult to transmit according to the timing of a neighboring cluster in a situation where synchronization between clusters is not matched, transmission is performed according to the timing of the following synchronous transmitting terminal, and as described above, a plurality of timings of neighboring synchronous transmitting terminals are stored, It can operate accordingly. If D2D discovery and communication are to be performed with respect to a plurality of reception timings between OOC terminals having the same priority in reception timing, for example, the list may be organized in consideration of resource region collisions as follows.

a) The terminal determines the location of the resource region obtained from the reception timing located higher in the reception timing list.

b) The received timing list that temporally collides with the identified location of the resource area is marked as unused or deleted.

The above procedure may be applied differently depending on the type of resource region, and in more detail, for example, a collision may be allowed for a data resource region for communication without using conflicting reception timing for a control resource region for communication.

In addition to the synchronization timing and the collision problem with the resource domain, the collision problem with different resource domains should be considered. When a plurality of timings are tracked and resource region information is obtained from a synchronization channel accordingly, conflict between operations in one or more resource regions may occur. For example, the communication control resource region received from the IC terminal and the data resource region received from the OOC terminal may be set at the same time. As another example, the data resource region received from the IC terminal and the data resource region received from the OOC terminal may be set at the same time. In this case, in order to avoid confusion, the terminal may operate according to the following principle.

If the control resource region and the data resource region for D2D communication are in the same subframe, the control resource region has priority. Next, if the resource region received from the IC terminal and the resource region received from the OOC terminal are in the same subframe, the resource region received from the IC terminal has priority. In a situation that cannot be solved by the above two principles, a resource region received from a terminal having a high reception power of a synchronization signal is prioritized.

11 is a control flowchart for determining a condition for becoming a synchronous relay terminal according to the present invention.

The flowchart of FIG. 11 may actually correspond to the detailed operation of step 910 of FIG. 9 . Referring to FIG. 11 , in step 1100, the terminal first checks whether it has a search/control/data signal to be transmitted. In some examples, when the terminal is in the connected mode, it may not be checked whether the terminal has the search/control/data signal. If the inspection result of step 1100 has a search/control/data signal, the control unit 205 may check whether it is in a connected mode in the base station or a scanning time for transmission through steps 1102 and 1104 .

As a result of the check in step 1102, if in the connected mode within the base station area, the controller 205 may operate as a synchronous relay terminal under the control of the base station by one of the following four methods.

The first method is by Command-Report in step 1110. As in step 1112, the terminal checks whether a command for measurement of a synchronization signal is received from the base station, and when the command to measure a synchronization signal is received, in step 1114, After the UE performs the measurement, the measurement result may be reported to the base station in step 1116 . The base station then controls the terminal to operate as a synchronization relay terminal (based on the measurement result or other information).

The second method is based on the Request-Response in step 1120. As in step 1122, when the terminal makes a request to the base station with the intention to become a synchronous transmission (relay) terminal, the base station determines and then responds in step 1124. ) message is sent to the terminal. The terminal may additionally transmit the measurement result to the base station in step 1126 . If there is information to immediately operate as a synchronization relay terminal in the response message, the terminal operates as a synchronization relay terminal in step 1128 . When the measurement result is transmitted, the base station controls the terminal to operate as a synchronization relay terminal with a separate control signal.

The third method is by the BSR-Grant of step 1130. As in step 1132, the terminal can perform a buffer status report (BSR) for receiving the original data transmission resource, and in step 1134 and When performing buffer status report together, additional request information can be sent together. After determining, the base station may transmit whether the synchronization relay terminal is operating or not when transmitting the existing grant control signal to the terminal. The terminal may additionally transmit the measurement result to the base station in step 1136 . In some cases, the base station may request an additional measurement from the terminal. In addition, when an instruction from the base station to operate as a synchronization relay terminal is performed, the terminal may be configured as a synchronization relay terminal in step 1138 .

The fourth method is by blind configuration in step 1140, and the base station controls the terminal to operate as a synchronization relay terminal without any information. However, if the terminal unconditionally operates as a synchronization relay terminal, synchronous transmission is performed unnecessarily. Therefore, when the terminal is controlled by the base station to operate according to an additional method as in step 1142, conditions for becoming a synchronous relay terminal, for example, receive power for a base station signal, receive power for a terminal signal, etc. are measured or , it is possible to determine whether there is a search/control/data signal to be transmitted, and to become a synchronous relay terminal or to be suspended.

In measuring the terminal signal, a synchronization signal of a terminal belonging to the same base station may be measured or a synchronization signal of an OOC terminal may be measured. When a synchronization signal of a terminal belonging to the same base station is measured with a reception power lower than a specific value, it is determined that there is no synchronization transmitting terminal nearby and the synchronization signal is transmitted. Alternatively, if the synchronization signal of the I-SS terminal among the OOC terminals is measured with a received power higher than a specific value, the timing of the base station must be transmitted for interference mitigation due to the subsequent search/control/data signal transmission, so the IC terminal wants to transmit Even if the terminal does not have /control/data signal, it requests synchronization signal transmission from the base station or transmits it by itself.

If it is an idle mode rather than a connected mode, as in step 1104, in order to determine whether the terminal can become a synchronized wintering terminal by itself, first check whether it is a scanning period for transmission (if a scanning period is not set, it may be omitted there is). If it corresponds to the scanning section, in step 1152, a synchronization signal transmitted from a resident base station and a neighboring synchronization transmitting terminal is measured. If a predetermined condition is satisfied, it operates as a synchronous relay terminal in step 1154 . That is, the signal reception power from the base station is lower than a certain value X dBm, the synchronization signal reception power from the adjacent synchronization relay terminal is lower than the certain value Y dBm, and the signal reception power from the independent synchronization transmitting terminal among the adjacent OOC terminals. At least one of whether there is a search/control/data signal to be transmitted is higher than a certain value Z dBm, and the synchronous relay terminal may become or be suspended. When a synchronization signal of a terminal belonging to the same base station is measured with a reception power lower than a specific value, it is determined that there is no synchronization transmitting terminal nearby and the synchronization signal is transmitted. When the synchronization signal of the I-SS terminal among the OOC terminals is measured with a reception power higher than a specific value, the timing of the base station must be transmitted for interference mitigation by subsequent search/control/data signal transmission, so that the IC terminal intends to transmit the search/ Even if the terminal does not have a control/data signal, it is possible to transmit a synchronization signal.

[Conditions for becoming a synchronous relay or support terminal in OOC]

According to the procedure for becoming a synchronous relay terminal in an IC or OOC, when a search signal, a control signal for sending a communication, and a data signal are to be transmitted, it becomes a synchronous transmission terminal. This is to match the transmission area of the synchronization signal with the transmission area of the control and data signals as much as possible. However, in order to transmit a synchronization signal to a terminal outside the network area or to transmit a synchronization signal to a synchronization transmission terminal that is out of synchronization, there is a condition that the terminal becomes a synchronization transmission terminal even if it does not send a search/control/data signal except for a synchronization signal. For the receiving terminal, it is advantageous because it is not necessary to perform a reception operation that does not require a distinction between a terminal having a search/control/data signal and a terminal not having a search/control/data signal. For ease of explanation, a synchronization reference terminal (I-SS) is a terminal that transmits synchronization with a search/control/data signal, and a terminal that does not have a search/control/data signal but transmits synchronization if necessary It is called a support (R-SS, V-SS) terminal. Based on this classification, the following detailed operation can be configured for the I-SS setting condition in step 928 and the condition to become the R-SS in step 926 in FIG. 9 described above.

a) Conditions for becoming I-SS : When a search/control/data signal to be sent occurs, and before the receiving terminal transmits a synchronization signal from a point in time earlier than the start point of the resource area by a specific window size, Whether to transmit the synchronization signal may be determined based on at least one of the reception power of the synchronization signal transmitted by the neighboring I-SS and the priority value of the synchronization channel. That is, if the neighboring I-SS is nearby and the synchronization signal reception power is greater than a specific value, it does not become a synchronization transmission terminal. Alternatively, if the neighboring I-SS has a high priority value (for example, DFN) and must follow the timing, it does not become a synchronous transmitting terminal (that is, if the neighboring I-SS has a low priority value, it operates as a synchronous transmitting terminal) ). As another example, if the neighboring I-SS has a high priority value and is close to it at the same time, the synchronization signal reception power is large, it does not become a synchronization transmitting terminal. That is, if the neighboring I-SS has a low priority value or is far away, so that the synchronization signal reception power is low, it operates as a synchronization transmitting terminal.

b) Conditions to become R-SS/V-SS : The UE sends the I-SS (including the I-SS to which it belongs) in the scanning process even though there is no discovery/control/data signal to be sent. If multiple are found, and additionally, if there is no neighboring I-SS that is higher than or equal to the I-SS to which it belongs (that is, if there is only an I-SS having a lower priority than the I-SS to which it belongs), synchronization It can be a synchronous transmission terminal by transmitting a signal.

In order to support the procedure of becoming a synchronous transmitting terminal as described above, it is advantageous because the receiving terminal does not need to perform a reception operation that does not require the distinction between a synchronization reference terminal having a search/control/data signal and a synchronization relay/support terminal not having a search/control/data signal. The terminal can distinguish the synchronization reference terminal from the synchronization relay/support terminal in various ways as follows.

a) The synchronization reference terminal and the synchronization relay/support terminal set separate synchronization sequences or synchronization transmission terminal IDs. For example, a specific sequence or sequence set may be allocated for a synchronous relay/support terminal. Alternatively, a part of the ID range of the synchronous transmission terminal may be allocated for the synchronous relay/support terminal.

b) It is set so that the synchronization reference terminal and the synchronization relay/support terminal use separate synchronization resources. For example, in one synchronization period, the synchronization resource located in the first position is used by the synchronization reference terminal, and the synchronization resource located in the second position is used by the synchronization relay/support terminal. In order to distinguish them, it is necessary to inform the synchronization resource index used in the synchronization channel.

c) The synchronization reference terminal and the synchronization relay/support terminal are located at a different D2D Frame Number (DFN). For example, the synchronization reference terminal is DFN#0, DFN#4, DFN#8, ... Located in , the synchronization relay / support terminal is DFN#2, DFN#6, DFN#10, ... is located in Therefore, modular 4 operation is applied to the received DFN, and if 0, it is recognized as a synchronous reference terminal, and if 2, it can be recognized as a synchronous relay/support terminal.

A receiving terminal distinguishes a synchronization reference terminal from a synchronization relay/support terminal based on at least one of methods a), b), and c), and if the terminal is not a synchronization reference terminal, only the synchronization signal from the synchronization reference terminal It is accepted as the receiving target synchronous transmitting terminal. When the terminal is a synchronization reference terminal, all synchronization transmission terminals are accepted as reception target synchronization transmission terminals without distinguishing between the synchronization reference terminal and the synchronization relay/support terminal.

A more detailed classification method is as follows. For example, the synchronization reference terminal uses one selected synchronization sequence among the sequences for OOC, and various methods are possible for the synchronization relay/support terminal to be distinguished from the synchronization reference terminal. In the first method, the synchronization relay/support terminal may use a separate common synchronization sequence (or sequence set). The second method uses the same synchronization sequence as the synchronization reference terminal to which the synchronization relay/support terminal belongs, but information indicating that the synchronization relay/support terminal is a synchronization relay/support terminal may be transmitted through the synchronization channel. The information indicating that the terminal is a synchronization support terminal is the role bit (1 bit) of the synchronization transmitting terminal indicating the type of the synchronization terminal, information indicating the index/position of the synchronization resource (1 ~ 2 bits), or the D2D frame number (8 ~ 14 bits) can

In the case of information indicating the index/location of the synchronization resource, the role (synchronization standard and relay/support) according to the location of the synchronization resource must be determined in advance. For example, the synchronization resource located first in one synchronization period may be used by the synchronization reference terminal, and the synchronization resource located in the second position may be used by the synchronization relay/support terminal. In the case of a D2D frame number, the role (synchronization standard and relay/support) according to the D2D frame number must be determined in advance. For example, an odd-numbered D2D frame number may be used by a synchronization reference terminal, and an even-numbered D2D frame number may be used by a synchronization relay/support terminal. When the synchronization reference terminal and the synchronization relay/support terminal are divided as described above, various effects can be obtained. For example, in order to control the reception timing, only the synchronization signal transmitted by the neighboring synchronization reference terminal may be considered. In addition, in order for the synchronization reference terminal to determine the transmission timing, only the synchronization signal transmitted by the synchronization relay/support terminal may be considered. For example, when two synchronization reference terminals enter within a specific reception power of each other, the synchronization reference terminal of the lower priority belongs to the synchronization reference terminal of the higher priority.

In order to control the reception timing, the operation of detecting the synchronization signal transmitted by the neighboring synchronization reference terminal may always be performed, but after performing at a predetermined period or after determining and storing the reception timing up to a certain number of synchronization signals Detection may not be performed. When counting the number of the reception timing, it may further include a synchronization transmitting terminal belonging to the base station and relaying the base station timing. In order for the synchronization reference terminal to determine the transmission timing, the operation of detecting a synchronization signal transmitted by a neighboring synchronization relay/support terminal may always be performed, but the synchronization reference terminal may arbitrarily set a period or perform it at a predetermined period. The terminal may set the period for detecting the synchronization signal transmitted from the neighboring synchronization relay/support terminal to be larger than the period for detecting the synchronization signal transmitted from the neighboring synchronization reference terminal, or this relationship may be predetermined.

[Procedure to stop sending sync signal]

12A and 12B are control flowcharts when a synchronization transmitting terminal stops transmitting a synchronization signal according to an embodiment of the present invention.

First, referring to FIG. 12A, if there is no existing value measured for the synchronization signal in step 1200, the synchronization transmitting terminal measures the synchronization signal of the base station to which it belongs or/and the neighboring terminal. Thereafter, in step 1202, the synchronization transmitting terminal checks whether a command to stop the synchronization signal transmission from the base station is received. Upon receiving a command to stop transmission of the synchronization signal from the base station as a result of the check in step 1202, the terminal may immediately or as in step 1206 check whether the timer has expired and give up the role of the synchronization transmitting terminal.

As a result of the check in step 1202, if the terminal does not issue a transmission stop command from the base station (for example, an idle mode terminal), the synchronous transmitting terminal proceeds to step 1204 and finally the condition that succeeded when a determination to become a synchronous transmitting terminal is continued. make sure it is maintained. As a result of the check in step 1204, if the condition is still maintained, the synchronous transmission is continued, but if the condition is no longer satisfied, the synchronous transmission may be stopped immediately or proceeding to step 1208 if the condition is satisfied. In addition, even if the condition is no longer satisfied, in order to alleviate the problem from abrupt synchronous transmission interruption, if the operating time as a synchronous transmission terminal by the control of the base station or according to the timer value of the terminal is greater than the timer value, synchronous transmission can be stopped

As in the example of FIG. 12A , if the condition for becoming the latest synchronous transmitting terminal is not used, it is possible to determine whether to continue the synchronous transmitting terminal by sequentially considering detailed conditions as shown in FIG. 12Bd .

Referring to FIG. 12B, if there is no existing value measured for the synchronization signal in step 1200, the synchronization transmitting terminal measures the synchronization signal of the base station to which it belongs or/and the neighboring terminal. Thereafter, the synchronization transmitting terminal determines whether it is in a connection state with the base station in step 1220 . If it is in the connected state, the synchronization transmitting terminal may proceed to step 1222 and check whether a synchronization transmission stop command has been received from the base station. As a result of the check in step 1222, if a synchronization transmission stop command is received from the base station, the process proceeds to step 1250 to immediately stop transmission of the synchronization signal. On the other hand, if the synchronization transmission stop command is not received from the base station as a result of the check in step 1222, the synchronization transmission terminal proceeds to step 1224 and checks whether there is data to be transmitted. If there is data to be transmitted as a result of the check in step 1224, the process proceeds to step 1226 and compares the signal quality received from the base station with a preset threshold. In this case, when the quality of the signal received from the base station is less than the preset threshold, the synchronization transmitting terminal may stop transmitting the synchronization signal immediately or based on the timer expiration check in step 1230 in step 1250 . On the other hand, when the quality of the signal received from the base station is greater than or equal to the preset threshold, the synchronous transmission terminal maintains the synchronous transmission.

In addition, if there is no data to be transmitted as a result of the check in step 1224, the synchronization transmitting terminal proceeds to step 1228 and checks whether the R-SS condition is satisfied. If the synchronization relay terminal condition is satisfied, the synchronization transmitting terminal proceeds to step 1226, and if it does not satisfy the R-SS condition, it proceeds to step 1250 to immediately stop the synchronization transmission.

On the other hand, if the synchronization transmitting terminal is an idle terminal as a result of the check in step 1240, proceed to step 1224, and if it is not an idle terminal, proceed to step 1242 to determine whether it is a synchronization reference terminal (I-SS) and there is data to be transmitted check When both of the above two conditions are satisfied, the synchronous transmission terminal maintains the synchronous transmission. On the other hand, if either one of the conditions is not satisfied, the process proceeds to step 1244 and it is checked whether the synchronization transmitting terminal is the R-SS and the R-SS state is satisfied. As a result of the check in step 1244, the synchronization transmitting terminal maintains the transmission of the synchronization signal only when the current state is the R-SS state and satisfies the current R-SS condition, and if at least one condition is not satisfied, proceeds to step 1250 to synchronize Signal transmission can be stopped.

[Relationship between base station ID and terminal synchronization signal]

The receiving terminal should be able to confirm the ID of the base station to which the synchronization terminal belongs through the synchronization signal (including the synchronization channel in a broad sense) of the synchronization terminal. For this purpose, the ID of the base station is transmitted as a synchronization signal as it is, or an ID of a synchronization signal for a terminal or a set of synchronization signals for a terminal having a predetermined relationship with the base station ID is transmitted. The terminal receiving the synchronization signal can check the ID of the base station to which the terminal that sent the synchronization signal belongs or resides from the ID of the synchronization signal. In another example, an ID for a set of base stations may be transmitted in a synchronization signal sent by the terminal.

[D2D Frame Number Priority]

In performing the synchronization procedure for D2D frame number, even if synchronization on the frame boundary is completed based on the received synchronization signal, when the operation procedure between different frames needs to be defined differently, each device This value is given because it is necessary to know if it is located. Therefore, the communication system is designed to distinguish different frames by assigning (system or) frame numbers or indexes. For example, in the LTE system, as in the example of FIG. 13A , by transmitting MIB (Master Information Blocks) 1301, 1302, 1303, 1311, 1312, 1313 through a BCH (Broadcast Channel), which is a control broadcast channel, an SFN is provided to the device. can tell you A system frame number (SFN) may be referred to as a radio frame number.

13A to 13D are conceptual diagrams for explaining a method in which a frame number and MIB or synchronization resource are transmitted in an LTE system.

That is, FIG. 13A is a diagram showing an example of a frame structure in an LTE system, in which MIBs 1301, 1302, 1303, 1311, 1312, 1313 are updated and transmitted in the first subframe SFN0 of one frame, for example Four identical MIBs are repeatedly transmitted with a period of 10 ms. In the LTE system, SFN is, for example, 10 bits of information, and may indicate system frame numbers from 0 to 1023 using the 10 bits of information. The BCH is originally 2 bits of CRC (Cyclic Redundancy Check) masking, so that when the BCH is received, 2 bits of information can be known. In addition, the MIB is transmitted on the BCH, and the MIB includes some SFN information of 8 bits. The original SFN 10bits information can be accurately known by combining the 2bits information that can be known when receiving the BCH and the SFN 8bits of the MIB. And since one frame period is 10 ms, the SFN may represent a maximum time of about 10 seconds. For example, if it is assumed that a broadcast section for inter-device discovery is required about once every 10 seconds, the base station may transmit SIB (System Information Block) on the BCH, which is a control broadcast channel, to inform SFN 0 as an inter-device broadcast frame.

The D2D frame number is a frame number used in communication between terminals corresponding to the system frame number of the base station. When the D2D synchronization resource is allocated every 10 ms as shown in FIG. 13B, one synchronization transmitting terminal can transmit every 10 ms, as when the base station transmits the BCH. However, since the transmission distance of one synchronous transmitting terminal is shorter than that of the base station, it is not desirable for one synchronous transmitting terminal to use every synchronization resource in that a synchronous relay or distributed synchronization method must be considered as a synchronization procedure.

Therefore, as shown in FIG. 13C , it is better to increase the synchronization period from 10 ms to 40 ms, and instead utilize the remaining synchronization resources 1302, 1303, 1304, 1312, 1313, 1314 in terms of performance in inter-terminal search and communication operation. and various applications are possible. That is, the D2D synchronization signal may be configured to be transmitted only in the first frames 1301 and 1311 in units of 40 ms.

Since the terminal is a mobile device unlike the base station, the terminal transmitting the synchronization signal may be overlapped in a certain area. At this time, if there is only one synchronization resource, the signals from the synchronization transmitting terminal not only act as interference with each other, but also when the synchronization transmitting terminal tries to receive the synchronization signal, due to the half-duplex problem, it is impossible to receive while transmitting on the same resource. does not exist. Therefore, it is advantageous in terms of performance to allocate time-separated resources between adjacent synchronous transmitting terminals.

As shown in FIG. 13D , the four synchronization transmitting terminals may transmit synchronization signals with different time differences (offsets) from the reference time point DFN0. As illustrated in FIG. 13D , the synchronization transmitting terminal 1 transmits a synchronization signal at the first synchronization resources 1301 and 1311 of the reference point DFN0, and the synchronization transmitting terminal 2 is the second synchronization resource of the reference point DFN0. The synchronization signals are transmitted from the ones 1302 and 1312, the synchronization transmitting terminal 3 transmits the synchronization signal at the third synchronization resources 1303 and 1313 of the reference time DFN0, and the synchronization transmitting terminal 4 is the reference time DFN0. ) of the fourth synchronization resources 1304 and 1314 can be configured to transmit a synchronization signal.

Each synchronous transmitting terminal may be, for example, a synchronous relay terminal located at 1 hop, 2 hop, 3 hop, or 4 hop according to the number of relay hops from the base station (hop 0). As another example, each synchronization transmitting terminal may be a synchronization transmitting terminal that individually detects whether a synchronization resource is idle and selects and transmits the corresponding idle resource. As another example, the synchronization transmitting terminal 1 may be an IC terminal, and the synchronization transmitting terminals 2, 3 and 4 may be OOC terminals. As another example, synchronization transmitting terminals 1 and 2 may be IC terminals, and synchronization transmitting terminals 3 and 4 may be OOC terminals. As another example, synchronization transmitting terminal 1 is a synchronization reference source that is a cluster head, and synchronization transmitting terminals 2, 3, and 4 are synchronization support terminals that help synchronization between cluster heads (Volunteering Synchronization). source).

According to the allocation method assumed in each example, the DFN may provide information indicating the role of the synchronization transmitting terminal. For example, when selecting a synchronization resource according to the number of hops, modular 4 operation is performed on the DFN received from the synchronization channel, that is, if DFN|mod4 becomes 0, it can be seen that the signal is transmitted by the synchronization transmitting terminal of one hop. . In the same way, if DFN|mod4 becomes 2, it can be seen that the resource is used by the 3 hop synchronous transmission terminal. As another example, if DFN|mod4 is 0, it can be known that the terminal within the base station area is a synchronization signal, and when DFN|mod4 is 2, it is known that the signal is transmitted from the second resource among the resources for the terminal outside the base station area. can As another example, if DFN|mod4 is 1, it can be seen that the signal is transmitted from the second resource among the resources for the terminal within the base station area, and if DFN|mod4 is 2, it is the first resource among the resources for the terminal outside the base station area. It can be seen that the signal is transmitted from As another example, if DFN|mod4 is 0, it can be known that the cluster head is a synchronization signal, and when DFN|mod4 is 2, it can be known that it is a signal transmitted from the second resource among the resources for the synchronization support terminal. In the above example, modular 4 is a case of using four resources, and if the number of synchronization resources is different, another modular operation may be applied. In the case of non-periodic synchronization resource allocation, other types of operators may be applied.

14 is an exemplary diagram for explaining a D2D frame number determination scenario in a network area and in a partial network according to the present invention.

Referring to FIG. 14 , base station 1 1401 has its own communication area 1400 , and base station 2 1411 also has its own communication area 1410 . Also, the terminal 1 1431 exemplifies a case where the communication area 1400 of the base station 1 1401 and the communication area 1410 of the base station 2 1411 overlap each other. In addition, as synchronous transmission terminals, synchronous transmission terminal 1 (SSUE1) 1441 belonging only to the communication area 1400 of the base station 1 1401 and the synchronization transmission terminal 2 (SSUE2) belonging only to the communication area 1410 of the base station 2 1411 (1442), synchronous transmission terminal 3 (SSUE3) 1443, which generates and transmits its own synchronization signal, and synchronization transmission terminal 4 (SSUE4) 1444, which receives absolute time from a satellite and transmits a synchronization signal is illustrated . Finally, a UE2 (UE2) 1432, a UE3 (UE3) 1433, and a UE4 (UE4) 1434 that do not belong to any base station are exemplified.

As illustrated in FIG. 14 , the terminal 1 (UE1) 1431 transmits the base station synchronization signal (PSS/SSS) and the base station broadcast channel (BCH) from the base station 1 (eNB1) 1401 and the base station 2 (eNB2) 1411 . and is receiving a terminal synchronization signal (D2DSS) and a terminal broadcast channel (D2DBCH) (or a terminal synchronization channel (PD2DSCH)) from the synchronization transmitting terminal 2 (SSUE2) 1442 . In general, since the base station synchronization signal has a higher priority than the terminal synchronization signal, the D2DSS and D2DBCH from SSUE2 1442 are ignored. Terminal 1 1431 selects one of the base stations based on the received power for PSS/SSS from base station 1 1401 and base station 2 1411 . In a specific situation, for example, while terminal 1 1431 belongs to base station 2 1411, reception failure for PSS/SSS is confirmed, and at this time, synchronization transmission terminal 2 1442 belonging to base station 2 1411. When a terminal synchronization signal (D2DSS) is received from , exceptionally, it may follow the terminal synchronization signal from the synchronization transmission terminal 2 1442 rather than another base station signal.

In FIG. 14 , a terminal 3 1433 receives a terminal synchronization signal and a terminal broadcast channel from a synchronization transmission terminal 1 1441 and a synchronization transmission terminal 2 1442 . In general, except for exceptional conditions, terminal 3 1433 selects one of a plurality of terminal synchronization signals according to the priority rule for terminal synchronization signals, and receives a terminal broadcast channel at a location determined by the selected terminal synchronization signal. do. If reception of the terminal broadcast channel is successful, a D2D Frame Number (DFN) is acquired and followed. In the above example, the exception condition is when the base station informs the information that the base station matches the absolute time (eg, the time provided by GPS), and after receiving the terminal broadcast channel along with the terminal synchronization signal, if there is a base station using the absolute time, the reference time of the corresponding base station If there is no base station using the absolute time, the reference time of the terminal synchronization signal selected as a result of the priority rule for the terminal synchronization signal and the DFN of the terminal broadcast channel are followed.

In FIG. 14, terminal 2 (1432) receives a terminal synchronization signal and a terminal broadcast channel from synchronization transmission terminal 1 (1441) located in the base station area and synchronization transmission terminal 3 (1443) located outside the base station area. In order for the second terminal 1432 to distinguish, the synchronization signal or synchronization channel must include information indicating the inside/outside of the base station area. Terminal 2 1432 selects a synchronization transmitting terminal located within the base station area with a higher priority than a synchronization transmitting terminal located outside the base station area. If there are a plurality of synchronous transmission terminals located in the base station area, the same operation is performed when the terminal 2 1432 selects the synchronization transmission terminals located in the base station area. The case of terminal 4 1434 in FIG. 14 is similar to that of terminal 3 1433, but is a case in which the synchronization transmitting terminal located outside the base station area has absolute time. Basically, there can be two rules.

1) Absolute time has the highest priority.

2) The base station has the highest priority.

However, each of these two rules can be problematic. If absolute time is the highest priority, terminal 4 (1434) must always follow the reference time of synchronization transmitting terminal 4 (1444). However, a signal transmitted by the terminal 4 1434 that is not synchronized with the base station may interfere with the terminal in the base station. On the other hand, if the base station is given the highest priority, terminal 4 (1434) must always follow the reference time of the synchronization transmitting terminal 2 (1442). Therefore, the terminal 4 1434 may receive interference from the terminal following absolute time and may also give interference to the terminal following the absolute time. In order to freely operate these two rules, the base station may send separate priority rule information, but in order to utilize the existing signal, the absolute time indicated by the base station may be used to inform the two rules.

For example, when the base station uses the absolute time, it can be adjusted to use the absolute time as the top priority. On the other hand, if the base station does not use the absolute time, it can be adjusted so that the base station uses it with the highest priority. That is, when a terminal receives a synchronization signal and a synchronization channel from a terminal within a network area having an absolute time with a terminal outside of the network area, it is based on information on whether absolute time is used, which was received when accessing/residing in the base station before. It is determined whether or not to use the transmitting terminal as the transmission time reference of the terminal. If the absolute time use value is not received or the validity period has passed, the operation is performed according to a predetermined decision rule.

15 is a conceptual diagram for explaining a scenario for determining a D2D frame number outside of a network area.

In FIG. 15 , terminal 1 1501 receives a synchronization signal and a synchronization channel from synchronization transmission terminal 1 1511 , synchronization transmission terminal 2 1512 , and synchronization transmission terminal 3 1513 located outside the network area. Unlike the scenario in which the synchronous transmitting terminal located in the network area exists, in this scenario, priority to the synchronous transmitting terminal belonging to the base station is excluded. Therefore, the synchronous transmitting terminal with absolute time has the highest priority. Terminal 1 1501 follows the reference time and D2D Frame Number (DFN) from the synchronous transmission terminal 1 1511 having an absolute time. On the other hand, terminal 2 1502, which has received the terminal synchronization signal and the terminal broadcast channel from the synchronization transmission terminal 2 1512 and the synchronization transmission terminal 3 1513, can select one of the synchronization transmission terminals by comparing the values of various variables. there is. For example, a value of at least one of ID, effective time, age, and number of relay hops of the synchronization transmitting terminal may be selected by comparing it with a large value or a small value. Since the exemplified variable requires additional information, the simplest variable is the DFN value itself currently used by the terminal. That is, one synchronous transmission terminal can be selected by comparing the large or small D2D frame number. Since the UE has already used the value for DFN to check the location of the resource region, the synchronization transmitting terminal transmits the possessed DFN through the UE broadcasting channel. In FIG. 15, when a synchronization signal and a synchronization channel are exchanged with each other like the synchronization transmitting terminal 3 (1513) and the synchronization transmitting terminal 4 (1514) in FIG. It is determined whether or not the synchronization transmitting terminal that has transmitted has a high priority. If the DFN value is the same between a plurality of synchronization transmitting terminals (which may also include own terminals), there is no need to change the synchronization transmitting terminal.

As a result of examining the examples of FIGS. 14 and 15 described above, the operation can be configured by dividing the case where the absolute time is largely considered in the system and the case where the system does not. Once absolute time is considered in the system, information on whether absolute time is used should be transmitted through a base station broadcast channel (BCH) or a terminal broadcast channel (D2DBCH or PD2DSCH). Under this assumption, the terminal can know whether the absolute time is used only after receiving a plurality of base station/terminal synchronization signals and a base station/terminal broadcast channel.

16 is a control flowchart for aligning and selecting synchronization information in consideration of absolute time according to the present invention.

The terminal starts scanning in step 1600 and scans a synchronization signal in step 1602. Here, starting the scanning may be an operation of turning on the wireless communication unit 201 and the modem 203 to receive the synchronization signal, and the detection of the synchronization signal is detected by controlling the wireless communication unit 201 and the modem 203 A broadcast channel is received with respect to one or more synchronized signals. The terminal may scan the synchronization signal in step 1602 and check whether the synchronization signal is detected in step 1604 . If the synchronization signal is detected, the process proceeds to step 1606. If the synchronization signal is not detected, the process proceeds to step 1620 to check the scanning retry. If scanning retry is necessary, proceed to step 1602. If scanning retry is not necessary, proceed to step 1612.

If the terminal proceeds from step 1604 to step 1606, it attempts to receive a broadcast channel, and proceeds to step 1608 to check whether reception of the broadcast channel has been successful. As a result of the check in step 1608, if the broadcast channel reception is unsuccessful, the process proceeds to step 1620. If the broadcast channel reception is successful, the process proceeds to step 1610 to store the information obtained by receiving the synchronization signal and the broadcast channel. Thereafter, the terminal proceeds to step 1612 to end the synchronization signal scanning, and when the scanning period is over, then in step 1614 to align the acquired information. Priority information to be used when sorting the information obtained in step 1614 may be replaced with whether absolute time is used, whether base station reference time is used, and information within/out of the network area (however, when terminal relay is set, the number of relay hops may be used. ), DFN value, and received power strength in the order of . When the alignment is completed, it is determined to follow the reference time and DFN of the highest synchronous transmitting terminal.

17 is a flowchart for aligning and selecting synchronization information without considering absolute time according to the present invention.

The terminal starts scanning in step 1700 and scans for a synchronization signal in step 1607. Here, starting the scanning may be an operation of turning on the wireless communication unit 201 and the modem 203 to receive the synchronization signal, and detection of the synchronization signal is the operation of the wireless communication unit 201 and the modem 203 A broadcast channel is received with respect to one or more synchronization signals detected by control. The terminal may scan the synchronization signal in step 1702 and check whether the synchronization signal is detected in step 1704 . If the synchronization signal is detected, the process proceeds to step 1706. If the synchronization signal is not detected, the process proceeds to step 17300 to check the scanning retry. If scanning retry is necessary, proceed to step 1702. If scanning retry is not necessary, proceed to step 17082.

If the terminal proceeds from step 1704 to step 1706, the terminal stores the synchronization information, and proceeds to step 1708 to end the synchronization signal scanning. Thereafter, the synchronization signal information may be sorted in step 1710 . Priority information to be used when aligning synchronization signal information can be arranged in the order of whether the base station reference time is used, whether the base station is in/out of the network area (the number of relay hops), and the received power strength. The terminal may then select the highest-level synchronization transmitting terminal in step 1712, and then proceeding to step 1714 to check whether the selected highest-level synchronization transmitting terminal uses the base station reference time. As a result of the check in step 1714, if the base station reference time is not used, the process proceeds to step 1718. If the base station reference time is used, the process proceeds to step 1716 to determine the highest synchronous transmission terminal.

On the other hand, in the case of proceeding to step 1718, the terminal attempts to receive a broadcast channel for all of the detected synchronization signals or for some synchronization signals from a higher priority. Thereafter, the terminal stores information on a broadcast channel that has been successfully received in step 1720, and proceeds to step 1722 and ends broadcast channel reception when the scanning period ends. In addition, the terminal aligns the received synchronization signal and broadcast channel information in step 1724. Priority information to be used for sorting is, for example, in/out of the network area (the number of relay hops), DFN, and received power strength in the order. When the alignment is completed, the terminal proceeds to step 1726 and determines to follow the reference time and DFN of the highest synchronization transmitting terminal.

[Transmission period and resource selection control method for Type1 Discovery]

A basic procedure for a search operation between terminals is as follows. The terminal first checks the discovery resource region set by the base station and checks the discovery mode of the discovery resource region. In the Type1 discovery mode, the terminal directly selects a resource, and in the Type2 discovery mode, the terminal requests and receives a resource from the base station. Only the case where there is a resource area corresponding to the Type1 discovery mode will be described. The discovery resource area is periodically allocated, for example, every 10 seconds. It is assumed that one UE can select only one discovery resource block in one period.

After the UE selects and senses n random resources among all N discovery resource blocks in the discovery resource area, if there is no resource block in which energy of X dBm or less is detected, it is determined as a congestion situation, and the discovery signal transmission period in the current resource block increases (or decreases transmission probability). If there is a resource block in which energy of X dBm or less is detected, it is determined as an idle resource, a random resource block is selected from among the idle resource blocks and transmitted, and the discovery signal transmission period is decreased (or transmission probability is increased). The reference value X dBm for determining the amount of received energy is controllable by the base station, and if X dBm is a very large value (infinity), it is the same as the random resource selection method because it is a method of selecting a random resource block among all resource blocks. The search signal transmission period may increase from the initial minimum period value to only the maximum period value. The minimum period value is basically the same as the period to which the search resource area is allocated (10 seconds in the example). It is also possible to increase the minimum period value up to the maximum multiple value (eg, 10) by logically increasing from 1 to 2, 3, and 4, rather than the period to which the actual search resource area is allocated. If the transmission rate is adjusted based on the transmission probability, the maximum period value may be exceeded if the probability is small. can Since there may be a number of UEs that have not been able to transmit until the maximum period, in another example, when X % of the maximum period is reached, the transmission probability is increased to a (p <a < 1), and when Y % is reached, the transmission probability is b (p<a<b<1) can be made to increase further. In some examples, when the transmission fails up to the maximum period, the terminal may request the base station to adjust the transmission probability. The UE can transmit the discovery signal more frequently based on the increased transmission probability according to the readjustment of the transmission probability of the base station. Although the above example describes the discovery signal, it can also be applied to a communication control area or a data transmission/reception area. In this case, the maximum period may be the maximum latency constraint of the corresponding traffic.

Various examples of the determination condition in the above operation are possible.

1) When there is a resource block of X dBm or less

2) When there is a resource block of X dBm or less, except for a subframe having a resource block of Y dBm or more

3) In case the resource block with receive power lower than the minimum receive power + alpha x (maximum receive power ?? minimum receive power) is less than A %

It can be understood that the above-described operations in the terminal are performed under the control of the controller 2050. The controller 205, the wireless communication unit 201, and the modem 203 do not necessarily have to be implemented as separate devices, but are a single unit. Of course, it can be implemented as a single component in the form of a chip.

The operations of the base station or the terminal described above can be realized by providing a memory device storing the corresponding program code in an arbitrary component in the base station or the terminal device. That is, the control unit 205 of the base station or terminal device may execute the above-described operations by reading and executing the program code stored in the memory device by a processor or a central processing unit (CPU).

The various components and modules of the entity, base station or terminal device described in this specification include a hardware circuit, for example, a complementary metal oxide semiconductor-based logic circuit, and firmware. and software and/or hardware circuitry, such as a combination of hardware and firmware and/or software embedded in a machine-readable medium. As an example, various electrical structures and methods may be implemented using electrical circuits such as transistors, logic gates, and application-specific semiconductors.

[Ⅱ] Operation of discovery and communication in D2D method

In the second embodiment of the present invention, discovery and communication in the D2D method will be described.

[Synchronous resource structure]

The synchronization resource may be composed of a synchronization resource unit (SRU) capable of transmitting and receiving a synchronization signal and a synchronization channel. One SRU is a set of resources for a synchronization signal (D2DSS) and a synchronization channel (PD2DSCH) transmitted by one synchronization terminal. At least one physical symbol unit is required to transmit a synchronization signal, and at least one physical symbol unit is required to transmit a synchronization channel. Since the synchronization channel is a message, a pilot pattern for evaluating the quality of the physical channel at the receiving end may be inserted in the middle of the synchronization channel resource.

In 3GPP, a demodulation reference signal (DMRS) for data demodulation is standardized, and some or modified patterns of DMRS patterns defined in the existing LTE standard may be used. The pattern generation method may be used by adding a pattern of the sequence itself, shifting the basic sequence at the symbol level, or adding scramble to the basic sequence. In consideration of a case in which a plurality of synchronization terminals transmit the same message, terminals logically located at the same location may use the same DMRS pattern. For example, a synchronization terminal located n hops from the base station may use a DMRS pattern corresponding to n hops in advance. In this case, there is no need to transmit information on the number of separate hops in the synchronization signal or the synchronization channel. According to another example, in addition to the number of hops in the DMRS pattern, whether the terminal uses an absolute reference time providing device such as a global positioning system (GPS), whether TDD/FDD is used, the required transmission distance level, power level, retransmission number, battery level, etc. may be sent.

18 is a diagram illustrating the structure of a synchronization resource according to the present invention.

Referring to FIG. 18B , synchronization resources 1821 , 1822 , 1823 , and 1824 are located at different positions within one synchronization period 1810 , and other resources are resources 1831 and 1832 for D2D control and data. , 1833, 1834) are arranged. That is, as illustrated in FIG. 18A , a plurality of synchronization resource units (SRUs) 1821 , 1822 , 1823 , and 1824 may be configured within one synchronization period 1810 . In the above example, each SRU is connected to a different type of synchronous transmission terminal. For example, as illustrated in FIG. 18A , the location of the SRU may be determined according to the number of relay hops.

In the synchronization resource unit, the synchronization signal is transmitted in every SRU, but the synchronization channel may not be transmitted according to a specific condition. The conditions under which the synchronization channel is not transmitted are as follows.

a) When the period of the synchronization channel is set longer than the period of the synchronization signal,

b) When the specific resource area designated by the base station and the SRU location overlap (for example, when only the synchronization signal (D2DSS) is set to be used in the discovery resource area that is not controlled by the base station.)

c) as a result of monitoring the synchronization channel, when the reception performance of the synchronization channel decreases due to the large number of participating terminals; Depending on the monitoring result, the UE may directly change the period and offset of the synchronization channel, or report the monitoring result to the base station, and the base station may determine the period and offset of the synchronization channel to change.

19A to 19D are exemplary diagrams for explaining a structure of a resource region and a synchronization resource for performing D2D communication or D2D discovery according to the present invention.

The structures of FIGS. 19A to 19D are arranged in a logical temporal order, and in reality, resources other than each indicated area may be added. For example, in the case of a base station operating in TDD (Time Division Duplex), when the D2D resource region is configured in the uplink, the downlink resources may be located in the same band by time division. However, from the standpoint of the D2D terminal, it can be logically configured as if continuous D2D resources exist.

Referring to FIG. 19A , a resource area notified by a base station to perform D2D communication, that is, scheduling assignment (hereinafter referred to as SA) areas (Pools) 1911 and 1912 and data resource areas for communication (Data Pools) ( 1921 and 1922), and the structures of synchronization resources 1901, 1902, and 1903 for informing the reference time for the resource area are shown. In the SA area, the UE transmits an SA signal including information on an allocated or selected data resource to the neighboring UE prior to data transmission. The terminal receiving the SA signal in the SA area receives the data signal from the interested transmitting terminal in the subsequent data area. The terminal located in the network area receives a broadcast channel (BCH) from the base station to confirm the absolute time of the reference frame (SFN0), and receives a System Information Block (SIB) to the resource area indicated based on the reference frame. to obtain relative location information. A neighboring base station, a partial network area, or a terminal located outside the network area first receives the synchronization signal and the synchronization channel from the terminal transmitted from the SRU, checks the absolute time of the reference frame (SFN0), and the resource indicated based on the reference frame Acquires relative location information for an area.

The D2D terminal may select one synchronization terminal according to a predetermined priority in order to synchronize the reference time for transmission. If there is a synchronization terminal having a different reference time from the selected synchronization terminal, the transmission reference time is synchronized with the selected synchronization terminal for a certain period of time, and a synchronization signal from another synchronization terminal is used to synchronize the reference time for reception. During one synchronization signal period, one or more synchronization resources, that is, SRU may be deployed. When the reference time for transmission is synchronized, synchronization signal transmission such as reception power and signal detection for a synchronization signal from a base station signal or another synchronization terminal is performed. In examining a certain condition for this, if there is no idle SRU, it is possible to operate so as not to transmit a synchronization signal. That is, the terminal selects one of the idle SRUs and transmits the synchronization signal only when there is an idle SRU, even when the condition for operating the synchronization signal transmission is satisfied. This is to reduce interference between the synchronization signal including the synchronization sequence and the synchronization channel, and if the same synchronization sequence and synchronization channel are transmitted on the same resource as the synchronization resource used by the adjacent synchronization transmission terminal, there is no interference problem. Even if there is no idle SRU, the synchronization signal can be transmitted.

19B is a diagram illustrating a resource region structure and a synchronization resource structure for performing D2D discovery according to the present invention.

19B shows the absolute time of the reference frame (SFN0) by receiving the BCH from the base station for the discovery resource area 1 (1941) as in FIG. 19A, and receiving the System Information Block (SIB) based on the reference frame. Acquires relative location information for the indicated search resource area. A neighboring base station, a partial network area, or a terminal located outside the network area first calculates the absolute time of the reference frame (SFN0) from the current frame number obtained by receiving the synchronization signal and the synchronization channel from the terminal transmitted from the SRU, and the reference frame Relative location information for the resource area indicated with reference to is obtained.

For example, if the synchronization channel received from the terminal located in the adjacent base station indicates SFN10, the reference frame SFN0 will be located before 10 SFN periods. On the other hand, with respect to the discovery resource region 2 (1942), the terminal located in the neighboring base station receives the BCH and SIB from the affiliated base station, and the reference of the affiliated base station with respect to the starting point of the discovery resource region 2 (1942) of one or more other base stations. Obtain relative position information with respect to time (SFN0). Thus, when the starting point of the resource zone of another base station is reached, if the terminal performs transmission/reception operation with the WAN or the terminal is not transmitting a synchronization signal or other D2D signal, the synchronization signal and channel expected at the starting point of the resource zone receive Although the synchronization signal is transmitted according to a specific condition, the synchronization channel may not be transmitted. By receiving a synchronization signal near the approximate starting point of the resource region, the terminal located in the neighboring base station can match the accurate reception synchronization reference time for when the corresponding discovery resource region starts. This operation is not limited to this example and may also be applied to the D2D communication resource region.

On the other hand, when discovery resource region 1 ( 1941 ) and discovery resource region 2 ( 1942 ) are simultaneously operated, a field indicating whether or not the first section (eg, subframe, subframe) of the resource region is used for SRU is a base station should be included in the BCH and SIB from In the case of a synchronization transmitting terminal, the existence of a resource for transmitting a synchronization signal must be determined according to the field indicating whether the SRU is used. In the case of a receiving terminal located in a neighboring base station, a synchronization signal and a channel are received in the corresponding resource area. It can be determined in advance according to a field indicating whether to use the SRU or whether to receive a discovery signal. This field is referred to as a periodic synchronization transmission field in the present invention.

When the base station uses the periodic SRUs 1931, 1932, and 1933, the BCH or SIB informs the base station by turning on the periodic synchronization transmission field. When the aperiodic and temporary (one-shot) SRU 1934 is used, the periodic synchronization transmission field is turned OFF to inform the BCH or SIB.

If the base station informs that a separate SRU 1934 is not used in the resource zone 2 for a terminal located in a partial network area or outside the network area, the terminal is transmitted from periodically transmitted SRUs 1931, 1932, 1933 Receives a synchronization signal and a synchronization channel from , confirms the absolute time of the reference frame (SFN0), and obtains relative position information for both the resource region 1 (1941) and the resource region 2 (1942) indicated with respect to the reference frame. . Such relative location information acquisition is also possible in the case of information relayed not only from the belonging base station but also from the adjacent base station. After obtaining the relative location information for the resource region, it is in a dormant state and wakes up earlier than at least one synchronization period than the starting point of the resource region to receive a synchronization signal from the periodic SRU to perform synchronization correction.

On the other hand, when a separate SRU is additionally used in the resource zone 2 1942, the terminal receives the periodic SRU and obtains relative position information from the reference time (SFN0) of the belonging base station for the resource zone of the adjacent base station. In the idle state, it wakes up just before reaching the starting point of the resource zone 2 (1942) and receives a synchronization signal from a separate SRU to perform synchronization correction. When only a separate SRU 1934 is used in the resource zone 2 1942 without the periodic SRUs 11931, 1932, and 1933, the base station does not provide information on the start point of the resource zone in advance, or If the terminal is located, an inefficient operation of the terminal performing a long time synchronization procedure to receive an SRU without periodicity may occur.

19C is an exemplary diagram of a resource region structure and a synchronization resource structure for performing D2D discovery and communication according to the present invention, and FIG. 19D is a resource region structure and synchronization resource structure for performing D2D discovery and communication according to the present invention is another example of

Referring to FIG. 19C , periodic SRUs 1931 , 1932 , and 1933 are transmitted, and an SA area 1941 for resource allocation and a communication area 1921 for communication are located. Also, an area 1941 for search is illustrated together. Also, referring to FIG. 19D, unlike FIG. 19C, the aperiodic SRU 1934 is included in the first transmission area of the search area.

The base station may explicitly or implicitly inform whether to listen to a periodic synchronization signal or a temporary synchronization signal in order to obtain a reference time for this resource for each resource region information. In general, the SA resource area 1911 and the data resource area 1921 are for communication, and synchronization must be performed using a periodic synchronization signal. However, the discovery resource area 1941 can use both a periodic synchronization signal and a temporary synchronization signal. .

Accordingly, the base station may inform the explicit 1-bit information for the two synchronization configuration modes together with the resource region information as a broadcast channel (BCH and SIB) or a control signal for each terminal.

On the other hand, the implicit method is: The base station informs the resource area with two pieces of offset information. The first offset information is a value indicating the interval between the reference frame (SFN0) of the present base station and the neighboring base station. This can be informed by 10ms (FDD) or 20ms (TDD), which is a frame unit in LTE. The second offset information is a value indicating the interval from the reference frame (SFN0) of the neighboring base station to the start position of the resource region used by the neighboring base station. This can be informed by 1 ms, which is a subframe unit in LTE. The base station receives information about which resource region of the neighboring base station operates using the temporary synchronization signal from the network, and does not include the first offset information (or transmits null information) if the temporary synchronization signal is used. Otherwise, if a periodic synchronization signal is used, both the first and second offset information are transmitted. The terminal performs a synchronization reception operation that should be used to find the starting point of the corresponding resource region through the number of offset information of the base station or null information of the first offset information or the offset information format identifier.

In FIGS. 19A to 19D described above, it is generally assumed that the base station informs the base station through a broadcast channel (BCH) and a system information block (SIB), but in some cases, it is assumed that resource pool information is provided. The region information may be informed by a control signal for each terminal (Dedicated Signaling). When the first frame of the resource region is allocated as an aperiodic temporary synchronization signal resource, all terminals within the base station region transmit a synchronization signal in the first frame of the resource region if the resource region is indicated with a broadcast channel and a system information block. there is a possibility that However, when a resource region is separately notified to each terminal with a control signal for each terminal, there is a possibility that only a terminal that has received a control signal for each terminal from the base station can transmit a synchronization signal in the synchronization resource region notified by the base station.

[Synchronous signal measurement method]

When a certain D2D terminal receives a synchronization signal, it measures another synchronization signal to determine whether to become a synchronization source UE or to report to the base station according to the connection state of the terminal with the base station ( can be measured). Meanwhile, in a situation in which a resource region requiring a periodic synchronization signal and a resource region sufficient for a one-shot synchronization signal are separated, a method of measuring the synchronization signal may vary depending on the case. In the case of a temporary synchronization signal, all synchronization terminals determined by the control of the base station or according to a predetermined condition must use the same single synchronization resource (SRU) to transmit. Accordingly, in this case, the synchronization signal transmission is limited to a method of transmitting the same signal in the same resource using a single frequency network method (composite transmission). In this case, since one or more synchronization signals are overlapped and received, the reception power may be higher than when one synchronization terminal transmits the synchronization signal to one resource, and the synchronization signal may be transmitted over a distance greater than the data transmission distance.

On the other hand, when a resource for a periodic synchronization signal is allocated from the base station, synchronization terminals determined by the control of the base station or according to a predetermined condition may select an idle synchronization resource and transmit the synchronization signal. In this case, since synchronization signals from as few synchronization terminals as possible overlap in the same resource, the reception power of the receiving terminal is relatively small compared to the case of temporary synchronization signal transmission, and there is not much difference from the data transmission distance. Due to such an environmental difference, there may be a problem in using the temporary synchronization signal transmission as a measurement target for selecting a synchronization relay terminal for a terminal outside the network area.

Therefore, it is natural to measure only the periodic synchronization signal for the selection of the synchronization relay terminal. To this end, first, the synchronization terminal located in the base station area should inform the synchronization resource location, that is, the period and offset information of the SRU through the synchronization signal and the synchronization channel. In addition, the synchronization terminal located in the base station area may relay information (offset, bitmap, etc.) on a resource area that does not use periodic synchronization resources. In order to become a synchronization relay terminal, the terminal receiving the synchronization signal and the synchronization channel from the synchronization terminal located in the base station area first measures the synchronization signal from the adjacent synchronization terminal. A synchronization signal from a terminal belonging to the same base station received in the resource region from the information on the resource region that does not use the periodic synchronization resource may be ignored. (This can be known from the sync signal and ID included in the sync channel.)

As another example, the synchronization terminal may relay information (offset, bitmap, etc.) on a resource region using periodic synchronization resources. In order to become a synchronization relay terminal, the terminal receiving the synchronization signal and the synchronization channel from the synchronization terminal located in the base station area first measures the synchronization signal from the adjacent synchronization terminal. Only the synchronization signal from the UE belonging to the same base station received in the resource region using the periodic synchronization resource is used for measurement. (This can be known from the synchronization signal and the ID included in the synchronization channel.) The synchronization signal period and offset, and information on the resource region using the periodic synchronization resource may be pre-configured in the terminal. . The terminal desiring to become the synchronization relay terminal determines to become the synchronization relay terminal based on at least one of the measured reception power, reception quality, priority value, and D2D frame number of synchronization signals from terminals belonging to the same base station.

On the other hand, in a resource region that does not use the periodic synchronization resource based on information on the resource region using the periodic synchronization resource or vice versa and the number of relay hops from the base station, a synchronization signal is nevertheless transmitted. You can decide whether to transmit periodically. For example, assume that the number of relay hops corresponds to 2, that is, a case in which the base station (0-hop) -> terminal 1 (1 hop) -> terminal 2 (2 hops) is configured. In this case, terminal 2 may limit synchronization transmission so that other terminals within the base station area do not have an effect due to signal transmission, such as interference, when operating in a resource area that does not use periodic synchronization resources. However, when the number of relay hops corresponds to 3, that is, when the base station (0 hop) -> terminal 1 (1 hop) -> terminal 2 (2 hop) -> terminal 3 (3 hop) is configured, the signal of terminal 3 is the base station. Since the terminal does not reach within the region, synchronous transmission can be performed in a resource region that does not use the periodic synchronization resource.

[Sync for Tx]

From now on, we will look at the synchronization procedure for the overall inter-terminal discovery and communication. The overall synchronization procedure consists of a transmission synchronization procedure that sets the reference time for transmission and a reception synchronization procedure that matches the reference time for reception. This is to enable D2D search or communication signal reception according to the received synchronization signal when another synchronization signal is received even if the basic transmission time is set on the assumption that perfect synchronization is impossible outside the network area. Therefore, the whole procedure consists of a procedure of acquiring transmission synchronization after scanning to acquire periodic transmission synchronization and a procedure of determining a role, and a procedure of acquiring synchronization of reception after scanning to acquire synchronization of reception at the same time.

20A and 20B are flowcharts of a synchronization procedure for transmission synchronization according to the present invention.

First, referring to FIG. 20A, when the terminal is turned on in step 2000, that is, when the wireless communication unit 201 and the modem 203 for D2D operation under the control of the controller 205 are turned on, in step 2002, the base station is found It starts with the (scan) step. When at least one base station synchronization signal (PSS/SSS) is detected in step 2004, the terminal selects one of the base station synchronization signals in step 2006 to follow the reference time, and in step 2008 additionally a relaying synchronization source (R-) SS) to determine whether to operate. The process of selecting one of the plurality of base station synchronization signals is generally based on the received power strength or quality like the existing LTE standard. The synchronization relay terminal determination procedure will be described in detail in the drawings to be described later. After determining the synchronization relay terminal, the terminal periodically returns to the base station scan step in step 2002 again.

If the base station synchronization signal is not detected in step 2004, the terminal proceeds to step 2010 to find a terminal synchronization signal from another synchronization transmitting terminal. In step 2012, when at least one terminal synchronization signal (D2DSS) (or terminal broadcast/synchronization channel (D2DBCH/D2DSCH)) is detected, the terminal proceeds to step 2014, selects one terminal synchronization signal among them, follows the reference time, and additionally Proceeding to step 2016, it is determined whether to operate as a synchronous relay terminal. The process of selecting one of the plurality of terminal synchronization signals is determined based on at least one of received power strength, D2D frame number, number of relay hops, synchronization terminal validity period, synchronization terminal age, and device synchronization phase information . If the base station synchronization signal or the terminal synchronization signal is not detected, that is, when proceeding from step 2012 to step 2018, the terminal itself operates as an independent synchronization transmitting terminal (Independent Synchronization Source, I-SS).

On the other hand, unlike the terminal synchronized with the base station, the terminal synchronized with the synchronization transmitting terminal must periodically perform scanning. This is because the mobile station is more mobile than the base station, so the network volatility is high. The terminal checks whether it is a time to scan for transmission in step 2020, and returns to step 2002 in which the base station is scanned again if it corresponds to the scan time for transmission. If it is not the scan time for transmission, it proceeds to step 2022 to check whether it is a scan time for reception (Time to Scan for Reception). In some cases, the scan time for reception is not separately set and may be operated in the remaining time in which the transmission operation is prioritized according to the implementation of the terminal. A detailed reception scanning procedure will be described in more detail in the drawings to be described later.

During the scan for transmission and the scan for reception, there may be a difference in the transmission method from the standpoint of the synchronous transmission terminal. The scan for transmission operates in anticipation of a synchronization change in the future, but maintains the existing transmission timing after the scan for reception. Accordingly, in the scanning process for transmission, the synchronization transmitting terminal may stop transmitting the synchronization signal during the scan period, but in the scanning process for reception, the synchronization transmitting terminal continues to transmit the transmitted synchronization signal during the scan period.

20B further includes step 2030 when compared with FIG. 20A. In step 2030, it is assumed that the time to scan for transmission has different scan times for the base station and the terminal. That is, after the reference time of the synchronous transmitting terminal is followed, the base station may be scanned in a short period. When it is not the base station scan time, the scan may be performed with respect to the terminal at a long period.

[Sync for Rx]

A scanning procedure for reception according to the present invention is illustrated in FIGS. 21A to 21C . First, let's take a look at Figure 21a. First, in step 2100, the UE checks whether D2D transmission or reception is in progress. For example, if the terminal is transmitting or receiving a control signal or data signal for discovery or communication, it may be difficult to receive another synchronization signal before the transmission/reception operation is completed. If the result of the inspection in step 2100 is not in transmission/reception, in step 2102, it is checked whether it is a time to scan for reception. If it corresponds to the scanning time, the terminal scans the base station synchronization signal in step 2104, and when the base station synchronization signal is heard in step 2106, proceeds to step 2110 to set a reception time reference and move on to the D2D signal reception step. On the other hand, if the base station synchronization signal is not heard, the terminal checks whether the terminal synchronization signal is heard in step 2108, and if the terminal synchronization signal is heard, sets a reception time reference in step 2112 and proceeds to the D2D signal reception step.

In the D2D signal receiving step, there may be two synchronization modes: Rx sync mode 1 and Rx sync mode 2. Therefore, the mode is checked in step 2114 for receiving the D2D signal. In this case, the reception operation in the resource area of the cell to which it belongs in the Rx mode is excluded. In the case of reception mode 1, the terminal proceeds to step 2118, and in the case of reception mode 2, the terminal proceeds to step 2116.

Difference between Rx sync mode 1 and Rx sync mode 2:

- Rx sync mode 1 : It is assumed that a serving base station informs resource region information such as an offset with a neighboring base station as a difference from a reference frame timing (eg, SFN0). Therefore, D2D reception is performed only in the informed resource area, and when a synchronization signal from a terminal belonging to a received neighboring base station is detected, a symbol and a frame boundary are obtained from it, and a predetermined D2D operation is performed.

In the case of an out-of-coverage terminal in which the base station reference time is obtained through the relay of the synchronization signal by the terminal, the offset with the neighboring base station and the resource area information of the neighboring base station transmitted by the synchronization terminal through the synchronization channel By receiving , the reception operation can be performed in the same way as when in the base station. In this case, the receiving terminal should be able to confirm the ID of the base station to which the synchronization terminal is associated or camped through the synchronization signal of the synchronization terminal. Alternatively, it should be possible to confirm that the synchronization signal is set by the base station. To this end, the base station allocates one of a series of synchronization sequences (eg, D2DSSue_net sequence set) that can be allocated by the base station to the synchronization terminal.

It is not easy to use Rx sync mode 1 in the case of an out-of-coverage terminal that has acquired an independent reference time that is not derived from the receiving network. That is, there is no synchronization relay terminal belonging to the base station, so a synchronization terminal is independently created. The independent synchronization transmitting terminal arbitrarily selects one of a series of separately configured synchronization sequences (eg, D2DSSue_oon sequence set).

- If complexity is not important, the following method is also possible. When the terminal belonging to the base station receives the reference time of the independent out-of-coverage terminal and reports it to the base station, the base station offsets the reference time of the independent out-of-coverage terminal based on the report from at least one terminal may be informed to terminals belonging to However, if complexity is an issue, a method such as Rx sync mode 2 may be more efficient.

- Rx sync mode 2 : In this mode, it is assumed that a neighboring base station or a synchronization terminal belonging to the neighboring base station informs the resource region information such as an offset with the neighboring base station based on the reference timing (eg SFN0) of the neighboring base station. . Therefore, it is necessary to receive every synchronization signal and channel, obtain a symbol and frame boundary from the synchronization signal, and check the current SFN and the location of the resource region from the synchronization channel. If the current timing corresponds to the D2D resource region confirmed by the reception operation, the D2D operation is performed in the resource region, and if the current timing is not the confirmed D2D resource region, the D2D resource region is returned if there is no operation with the WAN other than D2D. It can also wait in the idle state until

In Rx sync mode 2, the SFN of the neighboring base station transmitted by the synchronization channel through the synchronization channel if it is an out-of-coverage terminal in which the base station reference time is obtained through the relay of the synchronization signal by the terminal or otherwise A D2D reception operation may be performed by receiving the resource region information and the resource region information.

21B is a detailed view of operations corresponding to Rx sync mode 1 and Rx sync mode 2. The terminal proceeds to step 2124 in case of Rx sync mode 1, and proceeds to step 2122 in case of Rx sync mode 2. In the case of Rx sync mode 1, the step of acquiring information on the resource region start point of the neighboring base station based on the SIB received from the base station and updating the information list on which time point to start scanning for reception based on this information am. In the case of Rx sync mode 2, information on the resource region starting point of the synchronization transmitting terminal as well as the adjacent base station is acquired through the terminal broadcasting channel (D2DBCH) or the terminal synchronization channel (D2DSCH), and based on this, scanning for reception It is a step to update the information list on whether to start.

21C is a method of separately operating a scanning period for reception for a base station and a terminal when compared to FIG. 21B.

In step 2100, the UE checks whether D2D transmission or reception is in progress. For example, if the terminal is transmitting or receiving a control signal or data signal for discovery or communication, it may be difficult to receive another synchronization signal before the transmission/reception operation is completed. If the result of the check in step 2100 is not in transmission/reception, in step 2102, it is checked whether it is a scanning time for reception from the base station (Time to Scan for Reception). If it corresponds to the scanning time, the terminal scans the base station synchronization signal in step 2104, and when the base station synchronization signal is heard in step 2130, proceeds to step 2132 to set the reception time reference and proceed to the D2D signal reception step. On the other hand, if the base station synchronization signal is not heard, the terminal ends the routine of FIG. 21C.

Also, if it is not the scanning time for reception from the base station as a result of the check in step 2102, the process proceeds to step 2140 to check whether the scanning time is for reception from the terminal. In the case of scanning time for reception from the terminal, the terminal scans a synchronization signal from the terminal in step 2142, and when a synchronization signal from the terminal is heard in step 2144, proceeds to step 2146 to set a reception time reference and receive a D2D signal goes to If the synchronization signal from the terminal is not heard in step 2144, the routine of FIG. 21c is terminated.

Meanwhile, when proceeding to step 2150, the terminal checks whether it is Rx sync mode 1 or Rx sync mode 2, and performs step 2154 in case of Rx sync mode 1, and performs step 2152 in case of Rx sync mode 2.

[Procedure to become a synchronous relay terminal (Become R-SS)]

22 illustrates a procedure for becoming a synchronous relay terminal in FIGS. 20A and 20B described above.

In step 2200, the terminal checks whether it is in the connected mode within the base station area. As a result of the check in step 2200, if the terminal is in a connected mode within the base station area, it can operate as a synchronous relay terminal under the control of the base station by one of the following three methods.

The first method is by Command-Report as in step 2210. In step 2212, when the terminal receives a command for measurement of a synchronization signal from the base station, it proceeds to step 2214. After the terminal performs measurement, the measurement result is transmitted to the base station. report to

The second method is by Request-Reponse as in step 2220. In step 2222, when the terminal makes a request to the base station with the intention to become a synchronous transmission (relay) terminal, the base station determines and sends a response message. send to the terminal. Accordingly, the terminal receives a response message in step 2224, and the terminal may additionally transmit the measurement result to the base station in step 2226. If there is information to operate as a synchronization relay terminal directly in the response message, the terminal operates as a synchronization relay terminal. When the measurement result is transmitted, the base station controls the terminal to operate as a synchronization relay terminal with a separate control signal.

The third method is by the BSR-Grant as in step 2230. In step 2232, the terminal transmits additional request information together when performing a buffer status report (BSR) for receiving the original data transmission resource. After determining, the base station may transmit whether the synchronization relay terminal is operating or not when transmitting the existing grant control signal to the terminal. Accordingly, in step 2224, the terminal may receive a resource allocation message including whether the synchronization relay terminal is operating. In some cases, the base station may request an additional measurement from the terminal. Accordingly, the terminal may perform an additional measurement report in step 2236 .

Through one of the three methods described above, the terminal may proceed to step 2250 to become a synchronization relay terminal.

If the result of the check in step 2200 is an idle mode instead of the connected mode, the terminal may proceed to step 2202 and check whether there is data to be transmitted first (b). If there is no data to be transmitted, it does not necessarily operate as a synchronous relay terminal.

In another example, it may operate as a synchronous relay terminal regardless of data to be transmitted (a). In step 2240, in order to determine whether the terminal can become a self-synchronous terminal by itself, it is checked whether it is a scanning period for transmission. If it corresponds to the scanning period, the terminal proceeds to step 2242 and measures a synchronization signal transmitted from a resident base station or a neighboring synchronization transmitting terminal. If a predetermined condition is satisfied, the terminal operates as a synchronization relay terminal in step 2244 . This condition determines whether the signal reception power from the base station is lower than a certain value X dBm, the synchronization signal reception power from the adjacent synchronization relay terminal is lower than a certain value Y dBm, and the signal reception power from the adjacent independent synchronization transmission terminal is It may be determined whether the condition is satisfied by evaluating at least one of whether the value Z is higher than dBm. The operation may be performed by replacing the reception power of the synchronization signal with the reception quality.

[Relationship between base station ID and terminal synchronization signal]

The receiving terminal should be able to confirm the ID of the base station to which the synchronization terminal belongs through the synchronization signal (including the synchronization channel in a broad sense) of the synchronization terminal. For this purpose, the ID of the base station is transmitted as a synchronization signal as it is, or an ID of a synchronization signal for a terminal or a set of synchronization signals for a terminal having a predetermined relationship with the base station ID is transmitted. The terminal receiving the synchronization signal can check the ID of the base station to which the terminal that sent the synchronization signal belongs or resides from the ID of the synchronization signal. In another example, a zone identifier (Zone ID) indicating a set of a plurality of base stations may be transmitted in a synchronization signal transmitted by the terminal. Specifically, the ID of the synchronization signal may be connected to one of the synchronization sequence sets.

[Zone ID]

- Zone may consist of at least one or more base stations. Instead of Zone, it can be replaced with terms such as Clustering, Grouping, and Common Configuration.

- When the zone information is received from the upper layer through the BCH or SIB transmitted by the base station, it is not necessary to distinguish serving cell information. (It is assumed that the base station already informs the base station's synchronization signal resource location and synchronization signal ID.)

- Zone means that all or part of RRC (Radio Resource Control) parameter information for D2D communication between base stations is commonly used by a plurality of base stations. For example, even if the allocation bitmap information of the resource region is shared, the starting point of the resource region for each base station may be expressed by different offsets. Alternatively, even if the allocated bitmap information and the offset are the same, the location of the D2D frequency resource for each base station may be different. To this end, zone-specific information and cell-specific information may be divided and informed by the SIB. The information for each zone is known together with the Zone ID, and it can be seen that the information for each base station is information of the belonging base station implicitly by receiving the SIB. On the other hand, when the base station transmits resource zone information through the SIB, it must be explicitly informed which zone the base station belongs to. That is, the base station should inform the resource zone information of the zone to which it belongs and the resource zone information of the zone to which it does not belong separately.

- If it is difficult in terms of additional signaling and support for idle mode terminals to distinguish between the belonging zone and the non-affiliated zone resource zone information, a method of not specifying the belonging zone may be considered. In this method, a list of synchronization signal IDs that can be used in the corresponding zone are sent together with the resource zone information of a specific zone. The type of synchronization signal may include PSS/SSS from the base station or D2DSS from the terminal. When the terminal receives the synchronization signal and confirms the synchronization signal ID, the Zone ID associated with the synchronization signal ID can be determined by reviewing the Zone list stored in the terminal.

- In a scenario where Zone IDs are managed independently for each PLMN, PLMN IDs in addition to Zone IDs must be additionally transmitted from SIB or PD2DSCH.

- There may be cases where the network informs the offset information between zones. In this case, there is no need to transmit SFN information in the PD2DSCH for operation between base stations. However, for outside the network area, SFN (or D2D Frame Number) must always be transmitted in the PD2DSCH. To this end, the base station may indicate whether to transmit SFN (DFN) information in the PD2DSCH to all terminals through a broadcast channel or to a certain terminal through a control channel for each terminal.

- Zone ID can be configured separately, but it is an existing paging area ID or TAG (Timing Advance Group) that binds multiple cells used for CoMP (Coordinated Multi Point) operation to have the same Timing Advance (TA). It can also be configured by reusing IDs. Otherwise, the common parameter may be applied to all base stations within one PLMN (Public Land Mobile Network, operator network identification number) area without Zone ID.

- Zone ID and Zone-specific information about a specific Zone ID may be received in advance from a D2D server (or a proximity service server) or an MME (Mobility Management Entity) upon initial access of the terminal. If it is not provided to the UE at the time of initial access, all or part of Zones must be informed from the base station to the BCH and SIB when belonging to/residing in the base station. If Zone ID is not configured separately, the D2D server or MME informs the common parameters for all base stations during initial access.

[Hierarchical Improvement Plan]

23 is a flowchart for explaining a method of supplementing the problems of the existing hierarchical synchronization procedure outside the network area.

The terminal turns on the D2D function in step 2300, and scans a signal received from the base station in step 2302. Thereafter, the terminal checks whether a synchronization signal is detected from the base station in step 2304 . When a synchronization signal is detected from the base station, the terminal may synchronize with the base station in step 2306 and become a synchronization relay terminal (R-SS).

Meanwhile, if a synchronization signal is not received from the base station in step 2034, the terminal scans a signal received from the terminal in step 2310, and checks whether a synchronization signal synchronized with the base station is detected from at least one specific terminal in step 2312. When a synchronization signal synchronized with the base station is received from at least one specific terminal in step 2312, the terminal proceeds to step 2314 to perform synchronization with the terminal having the highest priority, and proceeds to step 2316 to the synchronization relay terminal (R- If the condition of SS) is satisfied, it may be a synchronous relay terminal (R-SS).

On the other hand, when proceeding from step 2312 to step 2320, the terminal checks whether a terminal having the highest priority is detected. If the terminal having the highest priority is detected as a result of the check in step 2320, the process proceeds to step 2322, synchronizes with the terminal having the highest priority, and in step 2324, when the condition of the synchronization relay terminal (R-SS) is satisfied, the synchronization relay terminal (R-SS) can be On the other hand, if the terminal having the highest priority is not detected in step 2320, it becomes an independent synchronous transmission terminal (I-SS) in step 2326.

In addition, the terminal may check whether it is time for transmission in step 2330, and if it is the time for transmission, proceed to step 2302 and if not, proceed to step 2332 and scan for reception.

The existing hierarchical synchronization procedure is performed by performing synchronization relay up to a predetermined maximum number of hops from an independent synchronization transmitting terminal (I-SS). However, since synchronization between clusters configured by different independent synchronous transmission terminals is out of sync, interference between terminals belonging to the cluster or timing of operations is not matched. Therefore, in FIG. 23, high synchronization performance is achieved by integrating the process of periodically changing independent synchronous transmitting terminals and gradual convergence based on the received reference time when each independent synchronous transmitting terminal determines the reference time accordingly. The I-SS determination method in step 2326 is based on a priority value that each terminal transmits through a terminal broadcast channel or a terminal synchronization channel. A terminal desiring to become an I-SS transmits the generated priority value to an adjacent terminal, and the adjacent terminals find a terminal with the highest priority value among them and set the transmission synchronization. Additionally, for stable performance, one synchronization transmitting terminal may be selected by comparing priorities only for synchronization signals having received power strength or quality equal to or greater than a predetermined threshold. After setting the transmission synchronization, the terminal determines whether to operate as a synchronization relay terminal.

Conditions for operating as a synchronous relay terminal include the reception power strength of the terminal synchronization signal received from the selected synchronization transmitting terminal, the reception power strength of the synchronization signal from the synchronization relay terminal having the same number of hops belonging to the same adjacent cluster, and the D2D search/communication signal. based on at least one of whether or not to transmit. When the terminal receives synchronization signals from multiple synchronization transmitting terminals in the scanning period for transmission and the scanning period for reception, the terminal updates the reference time to be used when operating as an I-SS next. Based on the timing obtained by receiving different synchronization signals according to a predetermined rule, the reference time to be used during I-SS operation is determined. there is. Examples of such a rule may include an average timing determination method, a priority timing determination method, a pulse-coupled oscillator method, a D2D frame number-based determination method, a timer value-based determination method, and the like. A terminal that has started operation with I-SS transmits a synchronization signal with I-SS and performs a scanning process during the operation time of the synchronization transmitting terminal determined in advance, arbitrarily determined by the terminal, controlled by the base station, or determined according to a predetermined rule. . When the I-SS condition is met again according to the scanning result, the above operation is repeated to determine the transmission timing based on the synchronization signal reception timing received during the time period previously operated as the I-SS.

[D2D Frame Number Priority]

In performing the synchronization procedure for communication, even if synchronization on the frame boundary is completed based on the received synchronization signal, if the operation procedure between different frames needs to be defined differently, it is necessary to know in which frame each device is located. It is a value given because it is necessary. Therefore, the communication system is designed so that different frames can be distinguished from each other by assigning a (system) frame number or index. For example, in the LTE system, as in the example of FIG. 24A , the SFN may be informed to the device by transmitting a Master Information Block (MIB) through a Broadcast Channel (BCH), which is a control broadcast channel. A system frame number (SFN) may be referred to as a radio frame number (Radio Frame Number).

Since the configuration of such a frame number has been described with reference to FIGS. 13A to 13D of the first embodiment described above, a further description thereof will be omitted herein.

Next, a scenario for determining a D2D frame number in a network area and in a partial network will be described with reference to FIG. 14 described in the first embodiment.

As illustrated in FIG. 14 , the terminal 1 (UE1) 1431 transmits the base station synchronization signal (PSS/SSS) and the base station broadcast channel (BCH) from the base station 1 (eNB1) 1401 and the base station 2 (eNB2) 1411 . and is receiving a terminal synchronization signal (D2DSS) and a terminal broadcast channel (D2DBCH) (or a terminal synchronization channel (PD2DSCH)) from the synchronization transmitting terminal 2 (SSUE2) 1442 . In general, since the base station synchronization signal has a higher priority than the terminal synchronization signal, the D2DSS and D2DBCH from SSUE2 1442 are ignored. Terminal 1 1431 selects one of the base stations based on the received power for PSS/SSS from base station 1 1401 and base station 2 1411 . In a specific situation, for example, while terminal 1 1431 belongs to base station 2 1411, reception failure for PSS/SSS is confirmed, and at this time, synchronization transmission terminal 2 1442 belonging to base station 2 1411. When a terminal synchronization signal (D2DSS) is received from , exceptionally, it may follow the terminal synchronization signal from the synchronization transmission terminal 2 1442 rather than another base station signal.

In FIG. 14 , a terminal 3 1433 receives a terminal synchronization signal and a terminal broadcast channel from a synchronization transmission terminal 1 1441 and a synchronization transmission terminal 2 1442 . In general, except for exceptional conditions, terminal 3 1433 selects one of a plurality of terminal synchronization signals according to the priority rule for terminal synchronization signals, and receives a terminal broadcast channel at a location determined by the selected terminal synchronization signal. do. The priority rule is determined based on at least one of the received power strength or quality of the terminal synchronization signal, the base station ID or the synchronization transmission terminal ID indicated by the synchronization signal, or the SFN or the DFN indicated by the synchronization signal or the broadcast channel. If reception of the terminal broadcast channel is successful, a D2D Frame Number (DFN) is acquired and followed. If the terminal conforming to the DFN becomes a synchronization relay terminal, it calculates a subframe for transmitting a synchronization signal and the DFN based on the obtained DFN standard, and transmits the calculated subframe and the DFN on the synchronization signal or the terminal broadcasting channel. In the above example, the exception condition is when the base station informs you of the information that the base station matches the absolute time (eg, the time provided by GPS), if there is a base station that receives the terminal broadcasting channel and uses the absolute time according to the information included, the reference time of the base station is followed. , if there is no base station using the absolute time, the reference time of the terminal synchronization signal selected as a result of the priority rule for the terminal synchronization signal and the DFN of the terminal broadcasting channel are followed.

In FIG. 14, terminal 2 (1432) receives a terminal synchronization signal and a terminal broadcast channel from synchronization transmission terminal 1 (1441) located in the base station area and synchronization transmission terminal 3 (1443) located outside the base station area. In order for the second terminal 1432 to distinguish, the synchronization signal or synchronization channel/broadcast channel should include information indicating the inside/outside of the base station area. Terminal 2 (1432) selects the synchronization transmitting terminal 1 (1441) located in the base station area with a higher priority than the synchronization transmitting terminal 3 (1443) located outside the base station area. If there are a plurality of synchronous transmission terminals located in the base station area, it operates according to the same priority rule as when the terminal 2 1432 selects the synchronization transmission terminals located in the base station area. The case of terminal 4 1434 in FIG. 14 is similar to that of terminal 3 1433, but is a case in which the synchronization transmitting terminal located outside the base station area has absolute time. There may be basically two rules, and since these rules have already been described in the previous description of FIG. 14 , a further description will be omitted here.

In addition, the scenario of determining the D2D frame number outside the network area has already been described in 15 of the first embodiment described above, and the same can be applied to the second embodiment as well. Therefore, in the second embodiment, an additional description of the scenario of determining the D2D frame number outside the network area will be omitted.

Similarly, the procedure for sorting and selecting synchronization information in consideration of absolute time has been described with reference to FIG. 16 of the first embodiment. That is, the operation 2022 of FIG. 20A or 20B that describes the entire operation of the second embodiment may be applied mutatis mutandis to the operation of FIG. 16 or FIG. 17 described in the first embodiment. Therefore, an additional description will be omitted here.

[Inter-PLMN support method]

There may be two methods to support D2D discovery and communication between terminals belonging to different PLMNs. For example, assuming that there are UE 1 and UE 2 belonging to PLMN 1 and PLMN 2, respectively, according to the first method, each UE transmits in its own PLMN and receives in another PLMN. According to the second method, each terminal moves to another PLMN to transmit, and to receive in the PLMN to which it belongs.

The first method can be applied as it is based on the resource area information of the belonging base station and the neighboring base station notified by the network within the same PLMN. However, when the resource area information between the base stations is dynamically switched, it It may not be easy to inform you. In addition, since the terminal 2 has a high priority for the belonging PLMN2, it may not perform the reception operation for the other PLMN during transmission/reception operation in the belonging PLMN. Therefore, even if terminal 1 transmits in PLMN1, it is difficult to guarantee whether a signal can be received by terminal 2 belonging to PLMN2.

In the second method, even if terminal 1 belongs to PLMN1, it receives information from the base station that D2D support is possible in PLMN2, detects a base station synchronization signal in the frequency band used by PLMN2, and if access is possible, D2D communication from the corresponding base station , and, if necessary, can perform D2D discovery and communication by belonging to a corresponding base station of PLMN2. The second method may be particularly useful when two-way discovery or communication between two terminals is desired.

Considering both of these two methods, it may be useful to know whether the terminal belonging to another PLMN is controlled to receive the PLMN belonging to the terminal 1 from the perspective of the terminal to transmit (Terminal 1). To this end, it is not realistic to inform each terminal whether the corresponding PLMN has been received because a lot of overhead occurs. Instead, it is possible to control the D2D terminal to which the base station belongs to receive the D2D signal in the operating frequency band of a specific PLMN through a broadcast channel, a system information block (SIB), or a control signal for each terminal.

The base station may additionally inform the belonging terminal of information on the frequency band of the specific PLMN and the temporal resource region in which time period it is to be received. A terminal belonging to PLMN1 (terminal 1) that wants to transmit a D2D signal to a terminal belonging to PLMN2 (terminal 2) first switches to the frequency band of PLMN2 and detects a base station synchronization signal. Receives system information (SIB) (or control signal for each terminal), and if the corresponding base station acquires information indicating that the corresponding base station has controlled to receive PLMN1 from the belonging terminals, the D2D signal by the base station control or terminal determination in the originally belonging PLMN1 to send If not, that is, if there is no information indicating that the corresponding base station has controlled to receive PLMN1 from the belonging terminals, or if information is obtained, it switches to PLMN2 and accesses the corresponding base station, and transmits a D2D signal by base station control or terminal determination. send According to another example, the information on whether to control reception of a specific PLMN transmitted from the SIB may be relayed by the UE receiving the SIB of the base station and transmitted through the synchronization channel (PD2DSCH).

[Transmission period and resource selection control method for Type1 Discovery]

A basic procedure for a search operation between terminals is also the same as in the first embodiment described above. In addition, if the performance according to the three determination conditions is not guaranteed, the base station can determine the period value, the transmission probability, etc. and instruct the terminal, but in the condition that the base station area is wide, accurate control according to the situation of the terminal is difficult. In fact, it is impossible. Therefore, in the above example, the initial transmission period value or the transmission probability value may be determined by the control of the base station, and the value may be changed by the terminal according to the determination of the surrounding conditions. In another example, the base station may indicate to the terminal the minimum and maximum values of the transmission period value or the probability value, and the terminal may change the values according to the determination of surrounding conditions within a range of values determined by the base station.

[Fallback operation]

If a certain terminal operates the T310 timer because the reception quality of the base station reference signal is reduced, and the base station synchronization signal is not caught while the T310 is running, it receives a synchronization signal (D2DSS) from the terminal belonging to the belonging base station and receives the reference signal Set the time. If synchronization signals from both the base station and the belonging terminal are not received for longer than time T310, a handover or base station reconfiguration procedure may be performed. After setting the reference time based on the base station synchronization signal or the terminal synchronization signal, it is switched to Mode 2 and communicates with the fallback resource specified in advance. In order to reduce the overhead of notifying the fallback resource to a separate resource area, the base station converts some of the resource allocation patterns in Mode 1 or 2 through a broadcast channel or a control channel for each terminal as a fallback resource in advance to the broadcast channel and system information. can tell you

The embodiments disclosed in the present specification and drawings described above are merely provided as specific examples to easily explain the contents of the present invention and help understanding, and are not intended to limit the scope of the present invention. Therefore, the scope of the present invention should be construed as including all changes or modifications derived based on the technical idea of the present invention in addition to the embodiments disclosed herein are included in the scope of the present invention.

11, 12, 810, 1400, 1410: base station area
101, 102, 801, 1401, 1411: base station
121, 122, 123, 124, 125, 126, 127, 128, 129, 811, 821. 831, 1431, 1432, 1433, 1434. 1441, 1442., 1443, 1444, 1501, 1502, 1511, 1512, 1513 , 1514: terminal
201: wireless communication unit 203: modem
205: control unit 207: memory
209: input unit 211: display unit

Claims (28)

In a method for synchronization between terminals in a network supporting device-to-device direct communication (D2D),
identifying whether the terminal exists in the area of the base station in the terminal;
Measuring signal power received from the base station in the terminal when the terminal in a radio resource control (RRC) idle state requires D2D communication;
transmitting, by the terminal, a synchronization signal in at least one subframe for D2D synchronization signal transmission when the received signal power is lower than a first threshold value; and
Transmitting D2D data from the terminal to the second terminal through a subframe for D2D communication; A method for synchronizing terminals between terminals in a network supporting device-to-device direct communication (D2D), comprising: a. According to claim 1,
identifying whether a synchronization signal is received from at least one other terminal when the terminal is out of coverage of the base station; and
Transmitting a synchronization signal in at least one subframe for D2D synchronization signal transmission when the terminal is outside the area of the base station and a synchronization signal is not received from the other terminal ) synchronization method between terminals in a network that supports. According to claim 1,
measuring signal power received from a third terminal when the terminal is outside the area of the base station; and
Transmitting a synchronization signal in at least one subframe for D2D synchronization signal transmission when the power received from the third terminal is lower than a predetermined threshold value; further comprising, supporting direct communication (D2D) between devices Synchronization method between terminals in a network. 4. The method of claim 3,
Synchronization method between terminals in a network supporting device-to-device direct communication (D2D) further comprising; selecting a terminal having the highest priority when synchronization signals are received from two or more terminals. 5. The method of claim 4,
Synchronization method between terminals in a network supporting device-to-device direct communication (D2D), wherein each of the synchronization signals received from the two or more terminals includes information identifying within the base station area or outside the base station area. The method of claim 1,
selecting a subframe for D2D synchronization based on the synchronization offset when a system information block (SIB) received from the base station includes synchronization offset information; and
Transmitting a D2D synchronization signal to the second terminal through the selected subframe; The method for synchronization between terminals in a network supporting device-to-device direct communication (D2D) further comprising a. In a terminal device supporting device-to-device direct communication (D2D),
a radio processing device configured to transmit and receive to a base station and other terminals;
a memory configured to store control data; and
at least one processor configured to control the radio processing device;
The processor is:
Identifies whether the terminal exists within the area of the base station (in coverage),
When the terminal is in a radio resource control (RRC) idle state and D2D communication is required, the radio processing device controls to measure the signal power received from the base station,
controlling the radio processing device to transmit a synchronization signal in at least one subframe for D2D synchronization signal transmission when the received signal power is lower than a first threshold, and
A terminal device that controls the radio processing device to transmit D2D data through a subframe for D2D communication to a second terminal, and supports direct communication (D2D) between devices. 8. The method of claim 7, wherein the at least one processor comprises:
Identifies whether a synchronization signal is received from at least one other terminal when the terminal is out of coverage of the base station, and
Direct communication between devices, further controlling the radio processing device to transmit a synchronization signal in at least one subframe for D2D synchronization signal transmission when the terminal is outside the area of the base station and a synchronization signal is not received from the other terminal A terminal device supporting (D2D). 8. The method of claim 7, wherein the at least one processor comprises:
When the terminal is outside the area of the base station, controlling the radio processing device to measure the signal power received from the third terminal, and
When the power received from the third terminal is lower than a predetermined threshold, controlling the radio processing device to transmit a synchronization signal in at least one subframe for D2D synchronization signal transmission, device-to-device direct communication (D2D) support terminal device. The method of claim 9, wherein the at least one processor comprises:
A terminal device supporting device-to-device direct communication (D2D) that selects a terminal having the highest priority when synchronization signals are received from two or more terminals. 11. The method of claim 10,
A terminal device supporting device-to-device direct communication (D2D), wherein each of the synchronization signals received from the two or more terminals includes information identifying within the base station area or outside the base station area. 12. The method of claim 11, wherein the at least one processor comprises:
When a system information block (SIB) received from the base station includes synchronization offset information, selecting a subframe for D2D synchronization based on the synchronization offset, and
A terminal device supporting device-to-device direct communication (D2D) for controlling the radio processing device to transmit a D2D synchronization signal to the second terminal through the selected subframe.
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