WO2016163745A1 - Method for selecting relay and transmitting/receiving signal through relay in wireless communication system and method therefor - Google Patents

Abstract

An embodiment of the present invention relates to a method for transmitting/receiving a signal through a relay by a UE in a wireless communication system, the method comprising the steps of: receiving discovery signals, which include ranking information, from a plurality of relays, respectively; selecting a first relay on the basis of the ranking information; and transmitting/receiving a signal with a network through the fist relay, wherein the ranking information is determined from at least one of the first relay's battery state information, the first relay's network connectivity information, Uu interface RSRP (reference signal received power) information, Uu interface RSRQ (reference signal received quality) information, Uu interface RSSI (received signal strength indicator) information, the relay's Tx power information, the relay's PHR (power headroom) information, the relay's load information, and information regarding the data rate or bandwidth that can be provided for the UE; when a broadcast message regarding a relay is received from the selected first relay, a relay reselecting operation is performed; and the broadcast message is transmitted either when it is determined that the relay can no longer provide the relay service on the basis of the ranking information value or when it is determined that the relay service can be provided but the quality is low.

Description

Selection method of relay and signal transmission and reception method through relay in wireless communication system and apparatus therefor

The following description relates to a wireless communication system, and more particularly, to a method and apparatus for selecting and relaying a signal through a relay.

Wireless communication systems are widely deployed to provide various kinds of communication services such as voice and data. In general, a wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Examples of multiple access systems include code division multiple access (CDMA) systems, frequency division multiple access (FDMA) systems, time division multiple access (TDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and single carrier frequency (SC-FDMA). division multiple access (MCD) systems and multi-carrier frequency division multiple access (MC-FDMA) systems.

In the present invention, the selection, reselection of a relay, a method of transmitting and receiving a signal through the selected relay, and service continuity, etc. are technical problems.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

According to an embodiment of the present invention, a method for transmitting and receiving a signal through a relay in a wireless communication system, the method comprising: receiving each discovery signal including ranking information from a plurality of relays; Selecting a first relay based on the ranking information; And transmitting and receiving a signal to and from a network through the first relay, wherein the ranking information is battery state information of the first relay. Connectivity information of the first relay to the network, Uu interface RSRP (Reference Signal Received Power) information, Uu interface RSRQ (Reference Signal Received Quality) information, Uu interface RSSI (Received Signal Strength Indicator) information, Tx Power information of the relay, It is determined from at least one of power headroom (PHR) information of a relay, load information of the relay, data rate or bandwidth information that can be provided for the terminal, and the broadcast associated with the relay from the selected first relay. When receiving a cast message, a relay reselection operation is performed, and the broadcast message may provide a relay service when the relay determines that the relay service can no longer be performed based on the ranking information value or may provide the relay service. Signal transmission and reception, which is transmitted in any one of the cases judged to be low It is the law.

An embodiment of the present invention, a terminal device for transmitting and receiving a signal through a relay in a wireless communication system, the transmission and reception device; And a processor, wherein the processor receives each discovery signal including ranking information from a plurality of relays, selects a first relay based on the ranking information, and transmits and receives a signal with a network through the first relay. And the ranking information is battery state information of the first relay. Connectivity information of the first relay to the network, Uu interface RSRP (Reference Signal Received Power) information, Uu interface RSRQ (Reference Signal Received Quality) information, Uu interface RSSI (Received Signal Strength Indicator) information, Tx Power information of the relay, It is determined from at least one of power headroom (PHR) information of a relay, load information of the relay, data rate or bandwidth information that can be provided for the terminal, and the broadcast associated with the relay from the selected first relay. In case of receiving a cast message, a relay reselection operation is performed. The broadcast message may be a case in which the relay determines that the relay service can no longer be performed based on the ranking information value or may provide the relay service, but the quality is low. It is a terminal device that is transmitted in any one of the cases determined. .

The selecting of the first relay based on the ranking information may include: checking a PC5 interface signal quality included in a discovery signal; Checking ranking information of relays whose PC5 interface signal quality is equal to or greater than a preset value; And selecting a relay according to the ranking information.

The ranking information may be generated by each of the plurality of relays specifically for the terminal.

The one or more pieces of information used to determine the ranking information may be indexed according to a mapping rule.

The mapping rule may be received from a ProSe function.

The relay reselection operation may include: receiving a discovery signal including ranking information from a plurality of relays; And selecting a second relay based on the ranking information.

The selecting of the second relay based on the ranking information may include: checking the PC5 interface signal quality included in the discovery signal; Checking ranking information of relays whose PC5 interface signal quality is equal to or greater than a preset value; And selecting a relay according to the ranking information.

After the terminal selects the second relay, the terminal can transmit information related to the new IP address to the GCS AS.

The information related to the new IP address may include an IP address, information indicating that the IP address has been changed, information indicating that the network coverage is out of service, information indicating that the network connection service is received through the relay, information indicating that the service continuity is requested, It may include one of the information indicating that the relay has been changed.

The terminal may receive a TMGI from the GCS AS in response to the new IP address.

When the terminal receives TMGI availability from the second relay, the terminal may transmit a release request of a unicast distribution leg to the GCS AS.

According to the present invention, the terminal can select the relay most efficiently, and the service can be continuously provided in the processor.

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

BRIEF DESCRIPTION OF THE DRAWINGS The drawings appended hereto are for the purpose of providing an understanding of the present invention and for illustrating various embodiments of the present invention and for describing the principles of the present invention together with the description of the specification.

1 is a diagram illustrating a schematic structure of an EPS (Evolved Packet System) including an Evolved Packet Core (EPC).

2 is an exemplary view showing the architecture of a general E-UTRAN and EPC.

3 is an exemplary view showing the structure of a radio interface protocol in a control plane.

4 is an exemplary view showing the structure of a radio interface protocol in a user plane.

5 is a flowchart illustrating a random access procedure.

6 is a diagram illustrating a connection process in a radio resource control (RRC) layer.

7 shows a data path through EPS.

8-9 show data paths in direct mode.

10 to 11 are diagrams for describing relay discovery models A and B. FIG.

12 and 14 illustrate a service continuity procedure.

15 is a diagram illustrating a configuration of a node device according to an embodiment of the present invention.

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

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

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

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

The following techniques can be used in various wireless communication systems. For clarity, the following description focuses on 3GPP LTE and 3GPP LTE-A systems, but the technical spirit of the present invention is not limited thereto.

Terms used in this document are defined as follows.

UMTS (Universal Mobile Telecommunications System): A third generation mobile communication technology based on Global System for Mobile Communication (GSM) developed by 3GPP.

Evolved Packet System (EPS): A network system composed of an Evolved Packet Core (EPC), which is a packet switched (PS) core network based on Internet Protocol (IP), and an access network such as LTE / UTRAN. UMTS is an evolutionary network.

NodeB: base station of GERAN / UTRAN. It is installed outdoors and its coverage is macro cell size.

eNodeB: base station of E-UTRAN. It is installed outdoors and its coverage is macro cell size.

UE (User Equipment): a user device. The UE may be referred to in terms of terminal, mobile equipment (ME), mobile station (MS), and the like. In addition, the UE may be a portable device such as a laptop, a mobile phone, a personal digital assistant (PDA), a smart phone, a multimedia device, or the like, or may be a non-portable device such as a personal computer (PC) or a vehicle-mounted device. In the context of MTC, the term UE or UE may refer to an MTC device.

Home NodeB (HNB): A base station of a UMTS network, which is installed indoors and has a coverage of a micro cell.

HeNB (Home eNodeB): A base station of an EPS network, which is installed indoors and its coverage is micro cell size.

Mobility Management Entity (MME): A network node of an EPS network that performs mobility management (MM) and session management (SM) functions.

Packet Data Network-Gateway (PDN-GW) / PGW: A network node of an EPS network that performs UE IP address assignment, packet screening and filtering, charging data collection, and the like.

Serving Gateway (SGW): A network node of an EPS network that performs mobility anchor, packet routing, idle mode packet buffering, and triggers the MME to page the UE.

Non-Access Stratum (NAS): Upper stratum of the control plane between the UE and the MME. A functional layer for exchanging signaling and traffic messages between a UE and a core network in an LTE / UMTS protocol stack, which supports session mobility and establishes and maintains an IP connection between the UE and the PDN GW. Supporting is the main function.

Packet Data Network (PDN): A network in which a server supporting a specific service (eg, a Multimedia Messaging Service (MMS) server, a Wireless Application Protocol (WAP) server, etc.) is located.

PDN connection: A logical connection between the UE and the PDN, represented by one IP address (one IPv4 address and / or one IPv6 prefix).

RAN (Radio Access Network): a unit including a NodeB, an eNodeB and a Radio Network Controller (RNC) controlling them in a 3GPP network. It exists between UEs and provides a connection to the core network.

Home Location Register (HLR) / Home Subscriber Server (HSS): A database containing subscriber information in the 3GPP network. The HSS may perform functions such as configuration storage, identity management, and user state storage.

Public Land Mobile Network (PLMN): A network composed for the purpose of providing mobile communication services to individuals. It may be configured separately for each operator.

Proximity Service (or ProSe Service or Proximity based Service): A service that enables discovery and direct communication between physically close devices or communication through a base station or through a third party device. In this case, user plane data is exchanged through a direct data path without passing through a 3GPP core network (eg, EPC).

ProSe communication: Means communication through a ProSe communication path between two or more ProSe capable terminals. Unless specifically stated otherwise, ProSe communication may mean one of ProSe E-UTRA communication, ProSe-assisted WLAN direct communication between two terminals, ProSe group communication, or ProSe broadcast communication.

-ProSe E-UTRA communication: ProSe communication using ProSe E-UTRA communication path

ProSe-assisted WLAN direct communication: ProSe communication using a direct communication path

ProSe communication path: As a communication path supporting ProSe communication, a ProSe E-UTRA communication path may be established between ProSe-enabled UEs or through a local eNB using E-UTRA. ProSe-assisted WLAN direct communication path can be established directly between ProSe-enabled UEs using WLAN.

EPC path (or infrastructure data path): user plane communication path through EPC

ProSe Discovery: A process of identifying / verifying a nearby ProSe-enabled terminal using E-UTRA

ProSe Group Communication: One-to-many ProSe communication using a common communication path between two or more ProSe-enabled terminals in close proximity.

ProSe UE-to-Network Relay: ProSe-enabled public safety terminal acting as a communication relay between ProSe-enabled network using E-UTRA and ProSe-enabled public safety terminal

ProSe UE-to-UE Relay: A ProSe-enabled public safety terminal operating as a ProSe communication relay between two or more ProSe-enabled public safety terminals.

-Remote UE: In the UE-to-Network Relay operation, a ProSe-enabled public safety terminal that is connected to the EPC network through ProSe UE-to-Network Relay without receiving service by E-UTRAN, that is, provides a PDN connection, and is a UE. In -to-UE Relay operation, a ProSe-enabled public safety terminal that communicates with other ProSe-enabled public safety terminals through a ProSe UE-to-UE Relay.

ProSe-enabled Network: A network that supports ProSe Discovery, ProSe Communication, and / or ProSe-assisted WLAN direct communication. Hereinafter, the ProSe-enabled Network may be referred to simply as a network.

ProSe-enabled UE: a terminal supporting ProSe discovery, ProSe communication and / or ProSe-assisted WLAN direct communication. Hereinafter, the ProSe-enabled UE and the ProSe-enabled Public Safety UE may be called terminals.

Proximity: Satisfying proximity criteria defined in discovery and communication, respectively.

SULP Location Platform (SLP): An entity that manages Location Service Management and Position Determination. SLP includes a SPL (SUPL Location Center) function and a SPC (SUPL Positioning Center) function. For details, refer to the Open Mobile Alliance (OMA) standard document OMA AD SUPL: "Secure User Plane Location Architecture".

User Service Description (USD): The application / service layer includes Temporary Mobile Group Identity (TMGI) for each MBMS service, session start and end time, frequencies, MBMS service area identities (MBMS SAIs) information belonging to the MBMS service area. To put in USD to the terminal. See 3GPP TS 23.246 for details.

ISR (Idle mode Signaling Reduction): When a terminal frequently moves between E-UTRAN and UTRAN / GERAN, waste of network resources occurs by repeated location registration procedure. As a way to reduce this, when the terminal is in idle mode, two RATs (Radio Access Technology) already registered after the location registration with MME and SGSN (hereinafter referred to as mobility management node) via E-UTRAN and UTRAN / GERAN, respectively. This is a technology that does not register a separate location when moving between cells or performing cell reselection. Therefore, when DL (downlink) data arrives to the terminal, paging is simultaneously sent to the E-UTRAN and UTRAN / GERAN, thereby successfully finding the terminal and delivering the DL data. [See 3GPP TS 23.401 and 3GPP TS 23.060]

MBMS Single Frequency Network (MBSFN): A simulcast transmission technique implemented by simultaneously transmitting the same waveform to multiple grouped cells covering a certain area.

Evolved Packet Core (EPC)

1 is a diagram illustrating a schematic structure of an EPS (Evolved Packet System) including an Evolved Packet Core (EPC).

EPC is a key element of System Architecture Evolution (SAE) to improve the performance of 3GPP technologies. SAE is a research project to determine network structure supporting mobility between various kinds of networks. SAE aims to provide an optimized packet-based system, for example, supporting various radio access technologies on an IP basis and providing enhanced data transfer capabilities.

Specifically, the EPC is a core network of an IP mobile communication system for a 3GPP LTE system and may support packet-based real-time and non-real-time services. In a conventional mobile communication system (i.e., a second generation or third generation mobile communication system), the core network is divided into two distinct sub-domains of circuit-switched (CS) for voice and packet-switched (PS) for data. The function has been implemented. However, in the 3GPP LTE system, an evolution of the third generation mobile communication system, the sub-domains of CS and PS have been unified into one IP domain. That is, in the 3GPP LTE system, the connection between the terminal and the terminal having the IP capability (capability), IP-based base station (for example, eNodeB (evolved Node B)), EPC, application domain (for example, IMS ( IP Multimedia Subsystem)). That is, EPC is an essential structure for implementing end-to-end IP service.

The EPC may include various components, and in FIG. 1, some of them correspond to a serving gateway (SGW), a packet data network gateway (PDN GW), a mobility management entity (MME), and a serving general packet (SGRS) Radio Service (Supporting Node) and Enhanced Packet Data Gateway (ePDG) are shown.

The SGW (or S-GW) acts as a boundary point between the radio access network (RAN) and the core network, and is an element that functions to maintain a data path between the eNodeB and the PDN GW. In addition, when the UE moves over the area served by the eNodeB, the SGW serves as a local mobility anchor point. That is, packets may be routed through the SGW for mobility in the E-UTRAN (Universal Mobile Telecommunications System (Evolved-UMTS) Terrestrial Radio Access Network defined in 3GPP Release-8 or later). SGW also provides mobility with other 3GPP networks (RANs defined before 3GPP Release-8, such as UTRAN or GERAN (Global System for Mobile Communication (GSM) / Enhanced Data rates for Global Evolution (EDGE) Radio Access Network). It can also function as an anchor point.

The PDN GW (or P-GW) corresponds to the termination point of the data interface towards the packet data network. The PDN GW may support policy enforcement features, packet filtering, charging support, and the like. In addition, mobility management between 3GPP networks and non-3GPP networks (for example, untrusted networks such as Interworking Wireless Local Area Networks (I-WLANs), code-division multiple access (CDMA) networks, or trusted networks such as WiMax) Can serve as an anchor point for.

Although the example of the network structure of FIG. 1 shows that the SGW and the PDN GW are configured as separate gateways, two gateways may be implemented according to a single gateway configuration option.

The MME is an element that performs signaling and control functions to support access to the network connection of the UE, allocation of network resources, tracking, paging, roaming and handover, and the like. The MME controls control plane functions related to subscriber and session management. The MME manages a number of eNodeBs and performs signaling for the selection of a conventional gateway for handover to other 2G / 3G networks. The MME also performs functions such as security procedures, terminal-to-network session handling, and idle terminal location management.

SGSN handles all packet data, such as user's mobility management and authentication to other 3GPP networks (eg GPRS networks).

The ePDG acts as a secure node for untrusted non-3GPP networks (eg, I-WLAN, WiFi hotspots, etc.).

As described with reference to FIG. 1, a terminal having IP capability is an IP service network provided by an operator (ie, an operator) via various elements in the EPC, based on 3GPP access as well as non-3GPP access. (Eg, IMS).

1 illustrates various reference points (eg, S1-U, S1-MME, etc.). In the 3GPP system, a conceptual link defining two functions existing in different functional entities of E-UTRAN and EPC is defined as a reference point. Table 1 below summarizes the reference points shown in FIG. 1. In addition to the examples of Table 1, there may be various reference points according to the network structure.

Table 1

Reference point	Explanation
S1-MME	Reference point for the control plane protocol between E-UTRAN and MME
S1-U	Reference point between E-UTRAN and Serving GW for the per bearer user plane tunneling and inter eNodeB path switching during handover
S3	Reference point between the MME and SGSN providing user and bearer information exchange for mobility between 3GPP access networks in idle and / or active state. This reference point can be used in PLMN-to-PLMN-to-for example (for PLMN-to-PLMN handovers) (It enables user and bearer information exchange for inter 3GPP access network mobility in idle and / or active state This reference point can be used intra-PLMN or inter-PLMN (eg in the case of Inter-PLMN HO).)
S4	(Reference point between SGW and SGSN that provides related control and mobility support between the GPRS core and SGW's 3GPP anchor functionality.It also provides user plane tunneling if no direct tunnel is established.) and the 3GPP Anchor function of Serving GW.In addition, if Direct Tunnel is not established, it provides the user plane tunnelling.)
S5	Reference point providing user plane tunneling and tunnel management between the SGW and the PDN GW. It provides user plane tunneling and tunnel management between Serving GW and PDN GW. for Serving GW relocation due to UE mobility and if the Serving GW needs to connect to a non-collocated PDN GW for the required PDN connectivity.)
S11	Reference point between MME and SGW
SGi	Reference point between the PDN GW and the PDN. The PDN may be an operator external public or private PDN or, for example, an in-operator PDN for the provision of IMS services. It is the reference point between the PDN GW and the packet data network.Packet data network may be an operator external public or private packet data network or an intra operator packet data network, eg for provision of IMS services.This reference point corresponds to Gi for 3GPP accesses.)

Among the reference points shown in FIG. 1, S2a and S2b correspond to non-3GPP interfaces. S2a is a reference point that provides the user plane with associated control and mobility support between trusted non-3GPP access and PDN GW. S2b is a reference point that provides the user plane with relevant control and mobility support between the ePDG and PDN GW.

2 is an exemplary view showing the architecture of a general E-UTRAN and EPC.

As shown, an eNodeB can route to a gateway, schedule and send paging messages, schedule and send broadcaster channels (BCHs), and resources in uplink and downlink while an RRC (Radio Resource Control) connection is active. Can perform functions for dynamic allocation to the UE, configuration and provision for measurement of the eNodeB, radio bearer control, radio admission control, and connection mobility control. Within the EPC, paging can occur, LTE_IDLE state management, user plane can perform encryption, SAE bearer control, NAS signaling encryption and integrity protection.

3 is an exemplary diagram illustrating a structure of a radio interface protocol in a control plane between a terminal and a base station, and FIG. 4 is an exemplary diagram illustrating a structure of a radio interface protocol in a user plane between a terminal and a base station. .

The air interface protocol is based on the 3GPP radio access network standard. The air interface protocol is composed of a physical layer, a data link layer, and a network layer horizontally, and a user plane and control for data information transmission vertically. It is divided into a control plane for signal transmission.

The protocol layers are based on the lower three layers of the Open System Interconnection (OSI) reference model, which is widely known in communication systems, and includes L1 (first layer), L2 (second layer), and L3 (third layer). ) Can be separated.

Hereinafter, each layer of the radio protocol of the control plane shown in FIG. 3 and the radio protocol in the user plane shown in FIG. 4 will be described.

The physical layer, which is the first layer, provides an information transfer service using a physical channel. The physical layer is connected to a medium access control layer on the upper side through a transport channel, and data between the medium access control layer and the physical layer is transmitted through the transport channel. In addition, data is transferred between different physical layers, that is, between physical layers of a transmitting side and a receiving side through a physical channel.

The physical channel is composed of several subframes on the time axis and several sub-carriers on the frequency axis. Here, one subframe includes a plurality of symbols and a plurality of subcarriers on the time axis. One subframe consists of a plurality of resource blocks, and one resource block consists of a plurality of symbols and a plurality of subcarriers. The transmission time interval (TTI), which is a unit time for transmitting data, is 1 ms corresponding to one subframe.

According to 3GPP LTE, the physical channels existing in the physical layer of the transmitting side and the receiving side are physical downlink shared channel (PDSCH), physical uplink shared channel (PUSCH) and physical downlink control channel (PDCCH), which are control channels, It may be divided into a Physical Control Format Indicator Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel (PHICH), and a Physical Uplink Control Channel (PUCCH).

There are several layers in the second layer.

First, the medium access control (MAC) layer of the second layer serves to map various logical channels to various transport channels, and also logical channel multiplexing to map several logical channels to one transport channel. (Multiplexing). The MAC layer is connected to the upper layer RLC layer by a logical channel, and the logical channel includes a control channel for transmitting information of a control plane according to the type of information to be transmitted. It is divided into a traffic channel that transmits user plane information.

The Radio Link Control (RLC) layer of the second layer adjusts the data size so that the lower layer is suitable for transmitting data to the radio section by segmenting and concatenating data received from the upper layer. It plays a role.

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

The radio resource control layer (hereinafter RRC) layer located at the top of the third layer is defined only in the control plane, and the configuration and resetting of radio bearers (abbreviated as RBs) are performed. It is responsible for the control of logical channels, transport channels and physical channels in relation to configuration and release. In this case, RB means a service provided by the second layer for data transmission between the terminal and the E-UTRAN.

If there is an RRC connection (RRC connection) between the RRC of the terminal and the RRC layer of the wireless network, the terminal is in the RRC connected mode (Connected Mode), otherwise it is in the RRC idle mode (Idle Mode).

Hereinafter, the RRC state and the RRC connection method of the UE will be described. The RRC state refers to whether or not the RRC of the UE is in a logical connection with the RRC of the E-UTRAN. If the RRC state is connected, the RRC_CONNECTED state is called, and the RRC_IDLE state is not connected. Since the UE in the RRC_CONNECTED state has an RRC connection, the E-UTRAN can grasp the existence of the UE in units of cells, and thus can effectively control the UE. On the other hand, the UE in the RRC_IDLE state cannot identify the existence of the UE by the E-UTRAN, and the core network manages the unit in a larger tracking area (TA) unit than the cell. That is, the terminal in the RRC_IDLE state is only detected whether the terminal exists in a larger area than the cell, and the terminal must transition to the RRC_CONNECTED state in order to receive a normal mobile communication service such as voice or data. Each TA is identified by a tracking area identity (TAI). The terminal may configure a TAI through a tracking area code (TAC), which is information broadcast in a cell.

When the user first turns on the power of the terminal, the terminal first searches for an appropriate cell, then establishes an RRC connection in the cell, and registers the terminal's information in the core network. Thereafter, the terminal stays in the RRC_IDLE state. The terminal staying in the RRC_IDLE state (re) selects a cell as needed and looks at system information or paging information. This is called camping on the cell. When it is necessary to establish an RRC connection, the UE staying in the RRC_IDLE state makes an RRC connection with the RRC of the E-UTRAN through an RRC connection procedure and transitions to the RRC_CONNECTED state. There are several cases in which a UE in RRC_IDLE state needs to establish an RRC connection. For example, a user's call attempt, a data transmission attempt, etc. are required or a paging message is received from E-UTRAN. Reply message transmission, and the like.

A non-access stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management.

The following describes the NAS layer shown in FIG. 3 in detail.

ESM (evolved Session Management) belonging to the NAS layer performs functions such as default bearer management and dedicated bearer management, and is responsible for controlling the terminal to use the PS service from the network. The default bearer resource is characterized in that it is allocated from the network when it is connected to the network when it first accesses a specific Packet Data Network (PDN). At this time, the network allocates an IP address usable by the terminal so that the terminal can use the data service, and also allocates QoS of the default bearer. LTE supports two types of bearer having a guaranteed bit rate (GBR) QoS characteristic that guarantees a specific bandwidth for data transmission and reception, and a non-GBR bearer having a best effort QoS characteristic without guaranteeing bandwidth. In case of Default bearer, Non-GBR bearer is assigned. In the case of a dedicated bearer, a bearer having a QoS characteristic of GBR or non-GBR may be allocated.

The bearer allocated to the terminal in the network is called an evolved packet service (EPS) bearer, and when the EPS bearer is allocated, the network allocates one ID. This is called EPS Bearer ID. One EPS bearer has a QoS characteristic of a maximum bit rate (MBR) or / and a guaranteed bit rate (GBR).

5 is a flowchart illustrating a random access procedure in 3GPP LTE.

The random access procedure is used for the UE to get UL synchronization with the base station or to be allocated UL radio resources.

The UE receives a root index and a physical random access channel (PRACH) configuration index from the eNodeB. Each cell has 64 candidate random access preambles defined by a Zadoff-Chu (ZC) sequence, and the root index is a logical index for the UE to generate 64 candidate random access preambles.

Transmission of the random access preamble is limited to a specific time and frequency resource for each cell. The PRACH configuration index indicates a specific subframe and a preamble format capable of transmitting the random access preamble.

The UE sends the randomly selected random access preamble to the eNodeB. The UE selects one of the 64 candidate random access preambles. Then, the corresponding subframe is selected by the PRACH configuration index. The UE transmits the selected random access preamble in the selected subframe.

Upon receiving the random access preamble, the eNodeB sends a random access response (RAR) to the UE. The random access response is detected in two steps. First, the UE detects a PDCCH masked with random access-RNTI (RA-RNTI). The UE receives a random access response in a medium access control (MAC) protocol data unit (PDU) on the PDSCH indicated by the detected PDCCH.

6 shows a connection process in a radio resource control (RRC) layer.

As shown in FIG. 6, the RRC state is shown depending on whether the RRC is connected. The RRC state refers to whether or not an entity of the RRC layer of the UE is in a logical connection with an entity of the RRC layer of the eNodeB. When the RRC state is connected, the RRC state is referred to as an RRC connected state. The non-state is called the RRC idle state.

Since the UE in the connected state has an RRC connection, the E-UTRAN may determine the existence of the corresponding UE in units of cells, and thus may effectively control the UE. On the other hand, the UE in the idle state (idle state) can not be identified by the eNodeB, the core network (core network) is managed by the tracking area (Tracking Area) unit that is larger than the cell unit. The tracking area is a collection unit of cells. That is, the idle state (UE) is determined only in the presence of the UE in a large area, and in order to receive a normal mobile communication service such as voice or data, the UE must transition to the connected state (connected state).

When a user first powers up a UE, the UE first searches for an appropriate cell and then stays in an idle state in that cell. When the UE staying in the idle state needs to establish an RRC connection, the UE establishes an RRC connection with the RRC layer of the eNodeB through an RRC connection procedure and transitions to an RRC connected state. .

There are several cases in which the UE in the idle state needs to establish an RRC connection. For example, a user's call attempt or uplink data transmission is required, or a paging message is received from EUTRAN. In this case, the response message may be transmitted.

In order to establish an RRC connection with the eNodeB, the UE in an idle state must proceed with an RRC connection procedure as described above. The RRC connection process is largely a process in which a UE sends an RRC connection request message to an eNodeB, an eNodeB sends an RRC connection setup message to the UE, and a UE completes RRC connection setup to the eNodeB. (RRC connection setup complete) message is sent. This process will be described in more detail with reference to FIG. 6 as follows.

1) When a UE in idle mode attempts to establish an RRC connection due to a call attempt, a data transmission attempt, or a response to an eNodeB's paging, the UE first sends an RRC connection request message. Send to eNodeB.

2) When the RRC connection request message is received from the UE, the eNB accepts the RRC connection request of the UE when the radio resources are sufficient, and transmits an RRC connection setup message, which is a response message, to the UE. .

3) When the UE receives the RRC connection setup message, it transmits an RRC connection setup complete message to the eNodeB. When the UE successfully transmits an RRC connection establishment message, the UE establishes an RRC connection with the eNodeB and transitions to the RRC connected mode.

ProSe (Proximity Service)

Prose service means a service capable of discovery and direct communication between physically adjacent devices, communication through a base station, or communication through a third device.

FIG. 7 illustrates a default data path through which two UEs communicate in EPS. This basic route goes through the operator's base station (eNodeB) and the core network (ie, EPC). In the present invention, such a path will be referred to as an infrastructure data path (or EPC path). In addition, communication through such an infrastructure data path will be referred to as infrastructure communication.

8 shows a direct mode communication path between two UEs based on Prose. This direct mode communication path does not go through an eNodeB and a core network (ie, EPC) operated by an operator. FIG. 8 (a) illustrates a case where UE-1 and UE-2 camp on different eNodeBs while transmitting and receiving data through a direct mode communication path. FIG. 8 (b) illustrates camping on the same eNodeB. FIG. 2 illustrates a case in which two UEs that are on exchange data via a direct mode communication path.

9 shows a communication path (locally-routed data path) through an eNodeB between two UEs based on Prose. The communication path through the eNodeB does not go through the core network (ie, EPC) operated by the operator.

Meanwhile, a remote UE (UE) that is out of network coverage (or not served or difficult to serve by E-UTRAN) may receive a connection service to a network through a ProSe UE-Network relay. That is, the remote UE can exchange signals with the network through a relay, where the signal means one or more of data traffic and control messages. The terminal may search for ProSe UE-Network relay through direct discovery. 10 illustrates a relay discovery model A relay procedure, and FIG. 11 illustrates a relay discovery model B procedure.

Referring to FIG. 10, the UE UE-1 includes Type = 'Announcement', announcer info, Discovery Type = 'UE-NW Relay Discovery', PLMN ID, Connectivity Info, prose Relay UE ID, Group Info, and the like. A direct discovery message can be transmitted. The monitoring terminals (UE-2, UE-3, UE-4, UE-5) looking for a relay in the proximity of the UE-1 may receive the message. Referring to FIG. 11, a discoverer UE (UE-1) for searching for a relay is Type = 'Solicitation', Discovery Type = 'UE-NW Relay Discovery', PLMN ID, Connectivity Info, prose UE ID, Group A direct discovery message including Info may be transmitted. Among the discovery terminals (UE-2, UE-3, UE-4, and UE-5) that have received the UE, UEs capable of providing UE-to-Network Relay services are Type = 'Response', announcer info, and Discovery Type. = A direct discovery message including 'UE-NW Relay Discovery', PLMN ID, Connectivity Info, prose Relay ID, status, etc. may be transmitted to the discoverer terminal. The following parameters may be used in such a direct discovery procedure. As a common parameter, the message type indicates whether it is Model A which is Announcement discovery or Model B which is Solicitation / Response discovery. The discovery type indicates whether the UE-to-Network relay discovery, Group Member discovery, or UE-to-UE relay discovery.

As a parameter for UE-to-Network relay discovery, ProSe relay UE ID is a link layer identifier for direct communication and is related to the PDN connection established by the UE-to-Network relay. Announcer / Discoverer info provides information about announcing or discoverer users. Discoveree info (Model B) provides information about the discovery. In the case of Model A, the Connectivity Info identifies connectivity provided by the UE-to-Network relay, and in the case of Model B, the information about the connection that the discoverer UE is interested in. Status / maintenance flags may indicate, for example, whether a relay is temporarily disconnected or if the battery is bad and a different relay should be selected. Group Info indicates information on a group (Model A) currently being relayed by a UE-to-Network relay or information on a group (Model B) that a remote UE is looking for. The ProSe UE ID is the link layer identifier of the discoverer, used in direct communication (Model B). Radio Layer Information includes information about radio layer information. For example, this may include radio conditions between the base station and the UE-to-Network relay, and information to help the remote UE select an appropriate UE-to-Network relay.

As a parameter for group member discovery, the ProSe UE ID is a link layer identifier used for direct communication. Announcer / Discoverer info provides information about announcing or discoverers. Discoveree info (Model B) is information about discovery. Target Info (Model B) provides information about targeted discoverees (single user or group).

As a parameter for UE-to-UE relay discovery, the ProSe UE ID is a link layer identifier for direct communication. Announcer / Discoverer info provides information about announcing or discoverers. Remote User Info provides information about the user of the remote UE. Discoveree info (Model B) is information about a discovery.

Among the above-described parameters, Status / maintenance flags and Radio Layer Information are dynamically changing information and are important information for the remote UE to select / reselect UE-to-Network relay. For example, if there are a large number of selectable UE-to-Network relays, the remote UE must select one of the UE-to-Network relays, which can utilize the above information and currently provide network connection services to itself. The above information may be utilized when selecting a UE-to-network relay other than the provided UE-to-Network relay.

In addition, since the direct discovery-related message is transmitted to the air, a small message is advantageous. This is because when one discovery related message is transmitted to the air, it is more efficient to be divided into a plurality of messages from the radio point of view and transmitted at once rather than being sent to the air several times. Accordingly, the announcing UE, the discoverer UE, and the discoveree UE are promised to transmit a direct discovery message having a size of 232 bits. In 3GPP TS 24.334 11.2.5, a 232 bit PC5 discovery message is defined as shown in Table 2, which is transmitted by the terminal through the PC5 interface. (In Table 2, 12.2.2.xx indicates that the contents are referred to as the contents of 3GPP TS 24.334.)

TABLE 2

Information Element	Type / Reference	Presence	Length (bits)
Message Type	Message Type12.2.2.10	M	8
ProSe Application Code	Binary12.2.2.6	M	184
MIC	Binary12.2.2.11	M	32
UTC-based Counter LSB	Binary12.2.2.22	M	8

Hereinafter, a description will be given of a relay selection method according to an embodiment of the present invention, a signal transmission and reception method through a relay, a service continuity procedure related to such an embodiment, or a service continuity procedure as an independent embodiment. In the following description, simply referred to as 'relay' means 'UE-to-Network relay', and there is a separate description accordingly. Hereinafter, the description will be focused on a UE-to-Network relay, but may be extended to a UE-to-UE relay. In this case, when the UE-to-UE relay provides a relay service between the first UE and the second UE, the radio related information on the Uu interface may be replaced with radio related information on the PC5 interface with the first UE. The converted ranking information can be provided to the second UE.

Relay (re) selection using ranking information and signal transmission and reception through relay

The terminal according to an embodiment of the present invention may receive each discovery signal including ranking information from a plurality of relays, and select a first relay based on the ranking information. In addition, the first relay may transmit and receive a signal with the network. Here, when receiving a broadcast message related to a relay from the selected first relay, a relay reselection operation may be performed.

In this regard, first, the ranking information will be described in detail. The ranking information may be terminal-specifically generated by each of the plurality of relays. The relay transmits a status / maintenance flags parameter and radio layer information when transmitting a discovery message for relay discovery (a message indicating that the relay indicates its existence in case of Model A and a response message for solicitation of a remote UE in case of Model B). For each of the parameters, or a combination of the two pieces of information, one parameter or a third parameter may be included in the form of ranking information.

The ranking information is i) battery status information of the relay (e.g., percentage of battery remaining). ii) the connectivity information of the relay to the network (for example, indicating that the connection is lost or about to be disconnected), iii) Uu interface reference signal received power (RSRP) information, iv) Uu interface RSRQ (Reference Signal Received Quality) information, v) Uu interface Received Signal Strength Indicator (RSSI) information, vi) Tx Power information used for direct discovery and / or direct communication of the relay, vii) Power headroom (PHR) information of the relay, viii) load information of the relay (e.g., information indicating the load state to be charged based on the number of remote UEs currently served by the relay), ix) data rate or bandwidth that can be provided for the terminal (bandwidth) may be determined from one or more of the information. If the Status / maintenance flags parameter and the Radio Layer Information parameter are included in the discovery message, respectively, some or all of the above information may be used to determine ranking information for each parameter. In addition, any information useful for relay selection / reselection may be used to determine ranking information. The information used to determine the ranking information is mainly radio related information (or radio layer information or AS layer information) between the relay and the network (for example, eNodeB). In addition, the relay is used to provide network connection service to the remote UE. It may include usable radio related information (or radio layer information or AS layer information).

One or more pieces of information used to determine ranking information may be indexed / numbered according to mapping rules. That is, the information of i) to ix) listed above may be mapped / modified into exponentialized / numeric values, respectively. Mapping / modification may be performed in one or more of an AS layer, NAS layer, and ProSe layer. If the above mapping / modification is performed in the AS layer, a mapping rule needs to be configured in the AS layer or provided to the AS layer. If the above mapping / modification is performed in the ProSe layer, information measured / inferred / obtained in the AS layer from the above-listed information should be provided to the ProSe layer.

At this time, the better the state may be mapped / transformed to a lower exponent / number, on the contrary, the better the state can be mapped / transformed to a higher index / number. Alternatively, a plurality of pieces of information may be mapped / modified into one index / number in a combined form. At this time, all indexes / numbers may be configured in the same range / range / category, or different indexes / numbers may be configured in different ranges / range / category. For example, all of the information used to determine the ranking information may be mapped to 1, 2, and 3. Specifically, for example, when the battery level is low, it may be mapped to 1, 2 to 3, 3 to high, and RSRP to 1, to 2 to 2, and to 3 to high. As another example, the remaining battery level is mapped to 1, low to 2, and high to 3, and the RSRP may be mapped to one of 0 to 99 according to a range of RSRP values as shown in Table 3 below.

TABLE 3

Reported value	Measured quantity value	Unit	Mapping value
RSRP_00	RSRP <-140	dBm	0
RSRP_01	-140 = <RSRP <-139	dBm	One
RSRP_02	-139 = <RSRP <-138	dBm	2
…	…	…	...
RSRP_95	-46 = <RSRP <-45	dBm	95
RSRP_96	-45 = <RSRP <-44	dBm	96
RSRP_97	-44 = <RSRP	dBm	97

Such a mapping rule may be preconfigured in a relay or may be provided from a network. Or it may be received from the ProSe Function. If the ProSe Function provides the mapping rule, whether the relay is roaming or non-roaming, it may always be provided from the ProSe Function in the Home PLMN. Alternatively, if the relay is roaming, it can be provided from the ProSe Function in the Visited PLMN. At this time, the relay may be provided by directly contacting the Visited ProSe Function, or the relay may receive the mapping rule by contacting the Home ProSe Function and the Home ProSe Function by contacting the ProSe Function of the Visited PLMN where the relay is located. It can also be provided in combination with. The mapping rule configured in the relay or provided from the ProSe function may be in the form of a MO (Management Object). The mapping rule may be updated by the network by information such as relay status information and the number of relays. In addition, the mapping rule may be one or more, and the relay may apply one of them according to appropriate criteria.

Alternatively, the ranking information may be index information, index information, priority information, weight information, numerated information, and the like. Each of these pieces of information is 1, 2,... , As the ranking information in the form of one of five values. The lowest rank may be considered good / excellent / more appropriate by the Remote UE in relay selection, while the lowest rank is bad / lower / less appropriate by the Remote UE in relay selection. May be considered.

Subsequently, the indexed / numerical value may be converted / converted / calculated into one ranking value through the mapping or the like as described above. At this time, a weight may be applied to each index / number. If different exponents / numbers are composed of different ranges / range / category, all the exponents / numbers represented by different ranges / range / category are scaled to the same scale (ie, by normalizing) You can also convert / calculate.

The relay may determine the ranking information in other ways besides exponentialization / numbering. For example, when each pieces of information required to determine the ranking information satisfy a certain condition or are in a range, the ranking information may be determined to be a specific value. Specifically, ranking information may be determined using a rule as shown in Table 4 below. Here, the detailed information related to the rule may be replaced with the description of the mapping rule.

Table 4

Battery level	Uu interface RSRP	ranking
Prize	Great		3
Prize	usually	3
medium	Great		2
medium	usually	2
Prize	Bad	One
Ha	Great	One
medium	Bad	0
Ha	usually	0
Ha	Bad	0

As such, when the ranking information is determined, the relay may transmit a discovery signal including the ranking information. If the ranking information is not good, the relay may transmit a broadcast message related to the relay. Here, the broadcast message related to the relay may be transmitted when it is determined that the relay service can no longer be performed or the service is provided based on the ranking information value but the quality is low. However, this may be an operation when the relay service is already provided, and if the relay has not started providing the relay service, the relay may not transmit / broadcast the relay discovery related message. That is, in the case of Model A or B relay discovery, the relay may determine that the relay service is no longer available or provide the service based on the ranking information value, but if it is determined that the quality is low, the relay discovery related message is transmitted / received. Do not broadcast. The information included in the message may be part of a ranking information value or may be a separate parameter. This causes the remote UE to select another relay.

As described above, when the terminal receives a broadcast message related to the relay, the terminal may reselect the relay.

The broadcast message related to the relay may be transmitted to each remote UE instead of being transmitted in a broadcast format.

Confirming the PC5 interface signal quality included in the discovery signal for both the selection of the relay and the reselection of the relay, checking the ranking information of the relays whose PC5 interface signal quality is equal to or greater than a preset value, and selecting the relay according to the ranking information. Can be performed according to. Check the information (Connectivity info, Group info, etc.) or the combination of layers above the Radio layer (ie, Access Stratum layer) for relays (ie, PC5 interface signal quality above a certain threshold) that the relay service is determined to be capable of. do. The information above the radio layer is information included in the discovery message transmitted by the relay and may be for providing a connectivity service to a network.

service continuity procedure

a) when the UE changes the UE-to-Network relay

Referring to FIG. 12, a procedure for service continuity when a UE changes a UE-to-Network relay will be described.

UE-1 has a direct connection with relay # 1. UE-1 discovers that it cannot have a network connection through UE-to-Network relay # 1. (E.g., when away from UE-to-Network relay # 1 or when receiving a broadcast message related to a relay from a pre-selected first relay, as described above), the UE is UE-to to minimize service interruption. You must attempt a connection with another UE-to-Network relay before losing the connection with the network relay.

In step S1201, UE-1 discovers ProSe UE-to-Network relay # 2 and establishes one-to-one direct communication. As such, UE-1 may obtain an IP address from the UE-to-Network relay, or may obtain an IP address in another manner. Alternatively, the UE may store in advance an IP address used by the UE out of network coverage.

After the terminal selects the second relay in step S1202, the terminal may transmit information related to the new IP address to the GCS AS (Group Communication Service Application Server). That is, UE-1 may provide the GCS AS with one or more of the information related to the new IP address listed in Table 5 below or including notifying the GCS AS that a new IP address has been obtained as described above. Such information may be explicit, implicit, or provided in a combined form. The above information may be provided by the UE-1, or may be provided by the UE-to-Network relay, and some information may be provided by the UE-1 and some information may be provided by the UE-to-Network relay.

Table 5

a) IP address: This is an IP address to be used for out of network coverage as described in step S1201 b) Information indicating that the IP address has changed c) Information indicating that the network coverage is out of service d) UE-to-Network Information indicating that a network connection service is received through a relay. E) Information indicating a request for service continuity. F) Information indicating that a UE-to-Network relay has been changed.

As described above, the GCS AS updates or establishes a unicast distribution leg (or a connection / configuration for transmitting downlink traffic to UE-1 in a unicast manner) according to one of the conditions listed in Table 6 below. It can be performed by satisfying the above conditions. Such a condition may be checked based on information provided by the UE, information possessed by the GCS AS, information obtained by the GCS AS from another network node, and the like.

Table 6

1) The GCS AS knows that the UE has acquired a new IP address or changed it. 2) The GCS AS knows that the UE is out of network coverage. 4) the GCS AS knows that the UE needs service continuity, and 5) the UE-to-Network relay has changed.

GCS AS may provide a TMGI that should be used to receive MBMS content. Alternatively, UE- 1 may already have TMGI information obtained from the GCS AS when it was in network coverage, or when receiving network connection service by a previous UE-to-Network relay. Alternatively, TMGI information may be set in the UE.

In operation S1203, the UE- 1 may request the ProSe UE-to-Network relay to start monitoring a specific TMGI availability. The ProSe UE-to-Network relay may broadcast the TMGI when a TMGI is detected on the MCCH of the serving cell. This step may not be performed if the UE-to-Network relay # 2 has already announce the possibility of receiving the TMGI.

In step S1204, if UE-1 receives the availability of TMGI from the ProSe UE-to-Network relay, UE-1 requests the GCS AS to release the unicast distribution leg. As such, UE-1 may know the availability by UE-to-Network relay # 2 announces the possibility of receiving TMGI, whereas cell and current relay where UE-to-Network relay # 1 was previously relayed Since the cell in which the UE-to-Network relay # 2 is located is the same cell, it may be known whether the MBMS reception possibility (ie, reception or not) for the TMGI is possible.

b) UE goes off network (UE goes off network)

Referring to FIG. 13, a procedure for service continuity when the terminal moves out of network coverage will be described.

UE-1 recognizes that it is disconnected or completely disconnected from the network. The UE should attempt to use a UE-to-Network relay to minimize service interruption before going off-network.

In step S1301, the UE- 1 may discover the UE-to-Network relay and establish 1: 1 direct communication.

 As such, UE-1 may obtain an IP address from the UE-to-Network relay, or may obtain an IP address in another manner. Alternatively, the UE may store in advance an IP address used by the UE out of network coverage.

After the terminal selects the relay in step S1302, it can transmit information related to the new IP address to the GCS AS. That is, UE-1 may provide the GCS AS with one or more of the information related to the new IP address listed in Table 7 below, including or informing the GCS AS that it has obtained a new IP address as described above. Such information may be explicit, implicit, or provided in a combined form. The above information may be provided by the UE-1, or may be provided by the UE-to-Network relay, and some information may be provided by the UE-1 and some information may be provided by the UE-to-Network relay.

TABLE 7

a) IP address: This is an IP address to be used for out of network coverage as described in step S1301 b) Information indicating that the IP address has changed c) Information indicating that the network coverage is out of service d) UE-to-Network Information indicating that a network connection service is received through a relay. E) Information indicating that a service continuity is requested.

As described above, the GCS AS updates or establishes a unicast distribution leg (or connection / configuration for transmitting downlink traffic to UE-1 in a unicast manner) according to one of the conditions listed in Table 8 below. It can be performed by satisfying the above conditions. Such a condition may be checked based on information provided by the UE, information possessed by the GCS AS, information obtained by the GCS AS from another network node, and the like.

Table 8

1) The GCS AS knows that the UE has acquired a new IP address or changed it. 2) The GCS AS knows that the UE is out of network coverage. 4) GCS AS recognizes that UE needs service continuity

GCS AS may provide a TMGI that should be used to receive MBMS content. Alternatively, UE- 1 may already have TMGI information obtained from the GCS AS when it was in network coverage, or when receiving network connection service by a previous UE-to-Network relay. Alternatively, TMGI information may be set in the UE.

In operation S1303, the UE- 1 may request the ProSe UE-to-Network relay to start monitoring a specific TMGI availability. The ProSe UE-to-Network relay may broadcast the TMGI when a TMGI is detected on the MCCH of the serving cell. This step may not be performed if the UE-to-Network relay has already announce the possibility of receiving the TMGI.

In step S1304, if UE-1 receives the availability of TMGI from the ProSe UE-to-Network relay, UE-1 requests the GCS AS to release the unicast distribution leg. As such, UE-1 may know the availability of the UE-to-Network relay by announce the possibility of receiving TMGI, whereas cell when UE-1 is in network coverage and cell where UE-to-Network relay is located Since this is the same cell, it may be known whether the MBMS reception possibility (ie, reception or not) for the TMGI is possible.

c) UE moves into network coverage (UE moves into network)

Referring to Figure 14, looks at the procedure for the service continuity when the terminal moves out of the network coverage into the network coverage.

UE-1 has a direct connection with the UE-to-Network relay. UE-1 recognizes that by moving into the network, it can have a direct connection with the network. In step S1401, UE-1 attaches to the network. You can also create additional PDN connections for group communication.

In step S1402, the UE may transmit information related to the new IP address to the GCS AS. That is, UE-1 may provide the GCS AS with one or more of the information related to the new IP address listed in the following Table 9, including or instead of notifying the GCS AS that it has obtained a new IP address as described above. Such information may be explicit, implicit, or provided in a combined form.

Table 9

A) IP address: This is the IP address obtained from the network through step S1401. B) Information indicating that the IP address has been changed. C) Information indicating that it has entered network coverage. D) Network connection via UE-to-Network relay. Information to inform you that you are not receiving services. E) Information to request that you request a service continuity.

As described above, the GCS AS updates or establishes a unicast distribution leg (or a connection / configuration for transmitting downlink traffic to UE-1 in a unicast manner) as described above. It can be performed by satisfying the above conditions. Such a condition may be checked based on information provided by the UE, information possessed by the GCS AS, information obtained by the GCS AS from another network node, and the like.

Table 10

1) The GCS AS knows that the UE has acquired a new IP address or changed it. 2) The GCS AS knows that the UE is in network coverage. 4) the GCS AS knows that the UE needs service continuity, and 5) the GCS AS knows that the UE is directly connected to the network.

GCS AS may provide a TMGI that should be used to receive MBMS content. Or UE-1 may already have TMGI information obtained from the GCS AS when it was previously out of network coverage. Alternatively, TMGI information may be set in the UE.

In step S1403, UE-1 may check whether TMGI for MBMS is available. This step may not be performed if it is already known whether MBMS reception is possible for the TMGI in the cell where UE-1 is located. UE-1 may check whether the MBMS can be received from the network. Alternatively, when the UE-1 receives the network connection service from the UE-to-Network relay, the cell where the relay is present is the same as the cell where the UE-1 is currently located. As a cell, it may be known whether MBMS reception is possible (ie, reception or not) for the TMGI.

 In step S1404, if UE-1 knows the availability of the corresponding TMGI, UE-1 requests the GCS AS to release the unicast distribution leg.

In the above description, a GCS AS (Group Communication Service Application Server) is described as a network node operating for service continuity. However, various network nodes may play the same role. It is also possible for two or more nodes to perform an interaction. AS can also be called Application, Server, Function, etc. In addition to the GCS AS, a network node may be a group communication AS, an MCPTT AS, a ProSe function, a network node constituting an EPC, a network node constituting an IMS, or an eNode.

15 is a diagram showing the configuration of a preferred embodiment of a terminal device and a network node device according to an example of the present invention.

The terminal device 100 according to the present invention with reference to FIG. 15 may include a transceiver 110, a processor 120, and a memory 130. The transceiver 110 may be configured to transmit various signals, data and information to an external device, and to receive various signals, data and information to an external device. The terminal device 100 may be connected to an external device by wire and / or wirelessly. The processor 120 may control the overall operation of the terminal device 100, and may be configured to perform a function of the terminal device 100 to process and process information to be transmitted and received with an external device. In addition, the processor 120 may be configured to perform a terminal operation proposed in the present invention. The memory 130 may store the processed information for a predetermined time and may be replaced with a component such as a buffer (not shown).

Referring to FIG. 15, the network node apparatus 200 according to the present invention may include a transceiver 210, a processor 220, and a memory 230. The transceiver 210 may be configured to transmit various signals, data and information to an external device, and to receive various signals, data and information to an external device. The network node device 200 may be connected to an external device by wire and / or wirelessly. The processor 220 may control the overall operation of the network node device 200, and may be configured to perform a function of calculating and processing information to be transmitted / received with an external device. In addition, the processor 220 may be configured to perform the network node operation proposed in the present invention. The memory 230 may store the processed information for a predetermined time and may be replaced with a component such as a buffer (not shown).

In addition, the specific configuration of the terminal device 100 and the network device 200 as described above, may be implemented so that the above-described matters described in various embodiments of the present invention can be applied independently or two or more embodiments are applied at the same time, overlapping The description is omitted for clarity.

Embodiments of the present invention described above may be implemented through various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof.

For implementation in hardware, a method according to embodiments of the present invention may include one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), and Programmable Logic Devices (PLDs). It may be implemented by field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of an implementation by firmware or software, the method according to the embodiments of the present invention may be implemented in the form of an apparatus, procedure, or function for performing the above-described functions or operations. The software code may be stored in a memory unit and driven by a processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various known means.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Various embodiments of the present invention as described above have been described with reference to the 3GPP system, but may be applied to various mobile communication systems in the same manner.

Claims (12)

1. In a method for transmitting and receiving a signal through a relay in a wireless communication system,

   Receiving each discovery signal including ranking information from a plurality of relays;

   Selecting a first relay based on the ranking information; And

   Transmitting and receiving a signal to and from a network through the first relay;

   Including;

   The ranking information is battery state information of the first relay. Connectivity information of the first relay to the network, Uu interface RSRP (Reference Signal Received Power) information, Uu interface RSRQ (Reference Signal Received Quality) information, Uu interface RSSI (Received Signal Strength Indicator) information, Tx Power information of the relay, It is determined from one or more of PHR (Power headroom) information of the relay, load information of the relay, data rate or bandwidth information that can be provided for the terminal,

   When a broadcast message related to a relay is received from the selected first relay, a relay reselection operation is performed.

   The broadcast message is transmitted when the relay determines that the relay service can no longer be based on the ranking information value or when the relay service can be provided but the quality is determined to be low. How to send and receive signals.
2. The method of claim 1,

   Selecting a first relay based on the ranking information

   Checking the PC5 interface signal quality included in the discovery signal;

   Checking ranking information of relays whose PC5 interface signal quality is equal to or greater than a preset value; And

   Selecting a relay according to the ranking information;

   Signal transmission and reception method comprising a.
3. The method of claim 1,

   The ranking information is generated by each of the plurality of relays specifically for the terminal.
4. The method of claim 1,

   And the one or more information used to determine the ranking information is indexed according to a mapping rule.
5. The method of claim 5,

   The mapping rule is a signal received and received from the ProSe Function.
6. The method of claim 1,

   The relay reselection operation,

   Receiving a discovery signal including ranking information from the plurality of relays; And

   Selecting a second relay based on the ranking information;

   Signal transmission and reception method comprising a.
7. The method of claim 6,

   Selecting a second relay based on the ranking information

   Checking the PC5 interface signal quality included in the discovery signal;

   Checking ranking information of relays whose PC5 interface signal quality is equal to or greater than a preset value; And

   Selecting a relay according to the ranking information;

   Signal transmission and reception method comprising a.
8. The method of claim 6,

   The terminal selects the second relay, and then transmits information related to a new IP address to a GCS AS, signal transmission and reception method.
9. The method of claim 8,

   The information related to the new IP address may include an IP address, information indicating that the IP address has been changed, information indicating that the network coverage is out of service, information indicating that the network connection service is received through the relay, information indicating that the service continuity is requested, Signal transmission and reception method comprising one of the information indicating that the relay has changed.
10. The method of claim 8,

    And the terminal receives a TMGI from the GCS AS in response to the new IP address.
11. The method of claim 8,

    If the terminal receives the TMGI availability (availability) from the second relay, the terminal transmits a release request of the unicast distribution leg to the GCS AS, signal transmission and reception method.
12. A terminal device for transmitting and receiving a signal through a relay in a wireless communication system,

    A transceiver; And

    Includes a processor,

    The processor receives each discovery signal including ranking information from a plurality of relays, selects a first relay based on the ranking information, transmits and receives a signal with a network through the first relay,

    The ranking information is battery state information of the first relay. Connectivity information of the first relay to the network, Uu interface RSRP (Reference Signal Received Power) information, Uu interface RSRQ (Reference Signal Received Quality) information, Uu interface RSSI (Received Signal Strength Indicator) information, Tx Power information of the relay, It is determined from one or more of PHR (Power headroom) information of the relay, load information of the relay, data rate or bandwidth information that can be provided for the terminal,

    When a broadcast message related to a relay is received from the selected first relay, a relay reselection operation is performed.

    The broadcast message is transmitted when the relay determines that the relay service can no longer be based on the ranking information value or when the relay service can be provided but the quality is determined to be low. Terminal device.

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