KR20160018309A - Method and apparatus for operating buffer state report in wireless communication system supporting device to device communication - Google Patents

Abstract

Provided are a method and an apparatus for operating buffer state report in a wireless communications system supporting device to device (D2D) communications. The method for operating the buffer state report by a terminal in the wireless communications system supporting the D2D communications comprises the following steps of: switching a D2D transmission mode set in the terminal from a first transmission mode to a second transmission mode; and when buffer state report for data to be transmitted is triggered via the D2D communications, canceling the triggered buffer state report. The first transmission mode is a mode which performs the D2D communications using resources assigned from a base station, and the second transmission mode may be a mode which performs the D2D communications using resource pool information for the D2D communications.

Description

TECHNICAL FIELD [0001] The present invention relates to a buffer status reporting method and apparatus in a wireless communication system supporting inter-

The present invention relates to wireless communication, and more particularly, to a wireless communication system supporting device-to-device communication, when a terminal performs communication between terminals using resources allocated from a base station, The present invention relates to a method and an apparatus for operating a mobile terminal.

D2D (Device to Device) communication is a communication method that has been available since the time of analog radio, and has a very long history. However, D2D communication in a wireless communication system is different from existing D2D communication.

D2D communication in a wireless communication system is a communication method in which terminals close to each other in geographical proximity use transmission and reception techniques of the wireless communication system in the frequency band of the wireless communication system or other bands but communicate directly with each other without going through an infrastructure such as a base station . This provides the advantage that the terminal can use the wireless communication in an area other than the area where the wireless communication infrastructure is constructed and reduce the network load of the wireless communication system.

For inter-terminal communication in such a wireless communication system, a base station can schedule resources required for in-coverage terminals to transmit data through D2D communication. In order to do this, the UE can inform the base station of the amount of data to be transmitted through the D2D communication in the intra-UE buffer through a buffer state report.

Meanwhile, in exceptional cases, the terminal may transmit D2D data through a resource selected by itself without being allocated resources required for data transmission in the D2D communication from the base station. However, in this case, when there is a buffer status report already triggered in the terminal, it has not yet been decided how the terminal should operate the triggered buffer status report, and specific operation and definition are required It is true.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for operating a buffer status report for data to be transmitted in inter-terminal communication in a wireless communication system supporting inter-terminal communication.

Another aspect of the present invention is to provide a method and an apparatus for efficiently allocating resources for communication between terminals in a wireless communication system supporting inter-terminal communication.

According to an aspect of the present invention, there is provided a method for reporting a buffer state by a terminal in a wireless communication system supporting D2D (Device to Device) communication, comprising: transmitting a D2D transmission mode set in the terminal to a second transmission And canceling the triggered buffer status report when a buffer status report for data to be transmitted in the D2D communication is triggered, 1 transmission mode is a mode in which the D2D communication is performed using resources allocated from a base station and the second transmission mode is a mode in which the D2D communication is performed using resource pool information for the D2D communication .

According to another aspect of the present invention, in a wireless communication system supporting D2D communication, a buffer state reporting method by a terminal includes the steps of: determining whether a terminal set in a first transmission mode for performing the D2D communication using a resource allocated from a base station, Operating in a second transmission mode for performing the D2D communication using resource pool information for communication, and canceling the triggered buffer status report if there is no data to be transmitted in the D2D communication have.

According to the present invention, in a wireless communication system, a terminal that allocates resources for inter-terminal communication in a terminal-to-terminal communication or a terminal in a service range of the base station can efficiently receive resources for inter-terminal communication.

1 is a diagram illustrating a wireless communication system to which the present invention is applied.
2 is a diagram for explaining the concept of a cellular network-based D2D communication applied to the present invention.
FIG. 3 is a diagram illustrating a process of transmitting a ProSe-BSR to which the present invention is applied.
4 to 8 are flowcharts illustrating a buffer status reporting method for inter-terminal communication by a terminal according to an embodiment of the present invention.
9 is a flowchart illustrating a buffer status reporting method for inter-terminal communication by a base station in an embodiment of the present invention.
10 is a block diagram illustrating a wireless communication system according to an embodiment of the present invention.

Hereinafter, the contents related to the present invention will be described in detail with reference to exemplary drawings and embodiments, together with the contents of the present invention. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

In addition, the present invention will be described with respect to a wireless communication network. The work performed in the wireless communication network may be performed in a process of controlling a network and transmitting data by a system (e.g., a base station) Work can be done at a terminal included in the network.

1 is a diagram illustrating a wireless communication system to which the present invention is applied.

Referring to FIG. 1, a wireless communication system 10 may provide a communication service between a base station and a terminal. In a wireless communication system, a terminal and a base station can transmit and receive data wirelessly. In addition, the wireless communication system may support device to device (D2D) communication between the terminal and the terminal. A wireless communication system supporting D2D communication will be described later.

In a wireless communication system 10, a base station (BS) 11 can provide a communication service through a specific frequency band to a terminal existing within the transmission coverage of the base station. The coverage served by the base station may also be expressed in terms of a site. A site may include a plurality of areas 15a, 15b, 15c, which may be referred to as sectors. Each of the sectors included in the site can be identified based on different identifiers. Each of the sectors 15a, 15b, and 15c can be interpreted as a partial area covered by the base station 11.

The base station 11 generally refers to a station that communicates with a user equipment (UE) 12 and includes an evolved NodeB (eNodeB), a Base Transceiver System (BTS), an access point, a femto base station Femto eNodeB, Home eNodeB (HeNodeB), Relay, Remote Radio Head (RRH), and the like.

The terminal 12 may be fixed or mobile and may be a mobile station, a mobile terminal, a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA) , A wireless modem, a handheld device, and the like.

The base station 11 may be referred to as various terms such as a megacell, a macrocell, a microcell, a picocell, a femtocell or the like depending on the size of the coverage provided by the corresponding base station. The cell may be used in terms of the frequency band provided by the base station, the coverage of the base station, or the term indicating the base station.

Hereinafter, a downlink refers to a communication or communication path from the base station 11 to the terminal 12, and an uplink refers to a communication or communication path from the terminal 12 to the base station 11 do. In the downlink, the transmitter may be part of the base station 11, and the receiver may be part of the terminal 12. In the uplink, the transmitter may be part of the terminal 12, and the receiver may be part of the base station 11.

There is no limit to the multiple access scheme applied to the wireless communication system 10. [ For example, a CDMA (Code Division Multiple Access), a TDMA (Time Division Multiple Access), an FDMA (Frequency Division Multiple Access), an OFDMA (Orthogonal Frequency Division Multiple Access), an SC- , OFDM-TDMA, and OFDM-CDMA may be used. These modulation techniques increase the capacity of the communication system by demodulating signals received from multiple users of the communication system. Also, a time division duplex (TDD) scheme or a frequency division duplex scheme (FDD) scheme using different frequencies may be used for uplink and downlink transmission.

The layers of the radio interface protocol between the terminal and the base station are divided into a first layer (L1), a second layer (L1), and a second layer (L2) based on the lower three layers of an open system interconnection A second layer (L2), and a third layer (L3).

The physical layer belonging to the first layer provides an information transfer service using a physical channel. The physical layer is connected to a MAC layer (Media Access Control) layer through a transport channel. The data is transmitted between the MAC layer and the physical layer through a transmission channel. The transport channel is classified according to how the data is transmitted over the air interface. Further, data is transmitted through physical channels between different physical layers (i.e., between the physical layer of the terminal and the base station). The physical channel can be modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and uses time, frequency, and space generated by a plurality of antennas as radio resources.

For example, a physical downlink control channel (PDCCH) of a physical channel notifies a UE of resource allocation of a paging CHannel (DLH), a downlink shared channel (DL-SCH), and Hybrid Automatic Repeat Request (HARQ) And an uplink scheduling grant informing the UE of the resource allocation of the uplink transmission. The Physical Control Format Indicator CHannel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. Also, the PHICH (Physical Hybrid ARQ Indicator CHannel) carries HARQ ACK / NAK signals in response to the uplink transmission. Also, the Physical Uplink Control CHannel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request and CQI for downlink transmission. Also, the Physical Uplink Shared CHannel (PUSCH) carries UL-SCH (Uplink Shared CHannel). If necessary, the PUSCH may include CSI (Channel State Information) information such as HARQ ACK / NACK and CQI according to the setup and request of the base station.

The data link layer corresponding to the second layer of the OSI model includes a MAC layer, a Radio Link Control (RLC) layer, and a Packet Data Convergence Protocol (PDCP) layer.

The MAC layer performs multiplexing or demultiplexing into a transport block provided on a physical channel on a transport channel of a MAC SDU (Service Data Unit) belonging to a logical channel and a mapping between a logical channel and a transport channel can do. The MAC layer provides a service to the RLC layer through a logical channel. The logical channel can be divided into a control channel for transferring control area information and a traffic channel for transferring user area information. For example, there are data transmission or radio resource allocation as services provided from the MAC layer to the upper layer.

The RLC layer may perform concatenation, segmentation and reassembly of the RLC SDUs. In order to guarantee various QoS (Quality of Service) required by a radio bearer (RB), the RLC layer has three modes of Transparent Mode, Unacknowledged Mode and Acknowledged Mode And provides an operation mode.

The PDCP layer can perform transmission of user data, header compression and ciphering, transmission of control plane data, and encryption / integrity protection.

The Radio Resource Control (RRC) layer, which belongs to the third layer of the OSI model, is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of RBs . RB means a logical path provided by a first layer (PHY layer) and a second layer (MAC layer, RLC layer, PDCP layer) for data transmission between a UE and a network. The configuration of the RB means a process of defining characteristics of a radio protocol layer and a channel to provide a specific service, and setting each specific parameter and an operation method. RB may be classified into SRB (Signaling RB) and DRB (Data RB). The SRB is used as a path for transmitting the RRC message and the NAS (Non-Access Stratum) message in the control plane, and the DRB is used as a path for transmitting the user data in the user plane. In the following, DRB is simply expressed as RB without distinction between SRB and DRB.

2 is a diagram for explaining the concept of a cellular network-based D2D communication applied to the present invention.

D2D communication may mean a technique of directly transmitting and receiving data between terminals. Hereinafter, it is assumed that the terminal supports D2D communication in the embodiment of the present invention. Also, D2D can be replaced by Proximity based Service (ProSe) or ProSe-D2D. The use of the term ProSe for D2D means that the meaning of an access-based service can be added instead of changing the meaning of a technique for directly transmitting and receiving data between terminals.

Recently, there have been attempts to perform discovery and direct communication between devices in network coverage (out-coverage) or out-of-coverage for the purpose of public safety Research. A terminal transmitting a signal based on inter-terminal communication may be referred to as a transmission terminal (Tx UE), and a terminal receiving a signal based on inter-terminal communication may be defined as a reception terminal (Rx UE). The transmitting terminal may transmit a discovery signal, and the receiving terminal may receive a discovery signal. The roles of the transmitting terminal and the receiving terminal may be changed. On the other hand, the signal transmitted by the transmitting terminal may be received by two or more receiving terminals.

When terminals in close proximity in a cellular system perform D2D communication, the load of the base station can be dispersed. Also, when neighboring terminals perform D2D communication, terminals transmit data at a relatively short distance, so that transmission power consumption and latency of the terminal can be reduced. In addition, since the existing cellular-based communication and D2D communication use the same resources, the frequency utilization efficiency can be improved.

D2D communication can be classified into a communication method of a terminal located in an in-coverage of a network coverage (base station coverage) and a communication method of a terminal located out-of-coverage of a network.

2, communication between the first terminal 210 located in the first cell and the second terminal 220 located in the second cell, communication between the third terminal 230 located in the first cell and the third terminal located in the first cluster 210, 4 terminal 240 may be a D2D communication within the network coverage. The communication between the fourth terminal 240 located in the first cluster and the fifth terminal 250 located in the first cluster may be D2D communication outside the network coverage. Here, the fifth terminal 250 may operate as a cluster head (CH) of the first cluster. Here, the cluster head means a terminal that is responsible for allocating resources. The cluster header may include an ISS (Independent Synchronization Source) for synchronization of Out-of-coverage terminals.

D2D communication can be divided into a search procedure for performing discovery for communication between terminals and a direct communication procedure for transmitting and receiving control data and / or traffic data between terminals. D2D communication can be used for various purposes. For example, D2D communications within network coverage can be used for public safety, ultra-low latency services, and commercial-grade services. D2D communications outside network coverage can be used only for public safety.

As one embodiment of performing D2D communication, the base station 200 may transmit D2D resource allocation information to the first terminal 210. [ The first terminal 210 is a terminal located within the coverage of the base station 200. The D2D resource allocation information may include allocation information for transmission resources and / or reception resources that can be used for D2D communication between the first terminal 210 and another terminal (e.g., the second terminal 220).

The first terminal 210 receiving the D2D resource allocation information from the base station can transmit the D2D resource allocation information to the second terminal 220. [ The second terminal 220 may be a terminal located outside the coverage of the base station 200. The first terminal 210 and the second terminal 220 can perform D2D communication based on the D2D resource allocation information. Specifically, the second terminal 220 can acquire information on the D2D communication resources of the first terminal 210. [ The second terminal 220 can receive data transmitted from the first terminal 210 through the resource indicated by the information on the D2D communication resource of the first terminal 210. [

In D2D communication, a terminal can transmit physical layer control data to another terminal. However, a separate channel (for example, a physical uplink control channel (PUCCH)) for transmitting physical layer control data in D2D communication may not be defined. If the physical layer control channel is not defined in the D2D communication, the terminal can use various methods to transmit control data for D2D communication.

Here, the physical layer control data for synchronization in the D2D communication includes information transmitted through the synchronization channel, and may be provided through a PD2 DSCH (Physical D2D Synchronization CHannel) channel, for example. The physical layer control data for the data communication includes Scheduling Assignment (SA) information and may be provided through a channel similar to or similar to the PUSCH format for D2D communication. The actual traffic data distinguished from the physical layer control data in the D2D communication can be expressed by the term " D2D data ".

In addition, a scheme for transmitting upper layer control data in addition to the physical layer in D2D communication can be defined.

In the D2D communication, the terminal can operate in the first transmission mode and the second transmission mode. The first transmission mode is a mode in which a terminal can perform D2D communication only when resources are allocated for D2D communication from the base station, and the base station transmits the D2D grant to the transmitting side terminal. The D2D grant includes parameter information to be determined by the base station among SA (Scheduling Assignment) information, which is control information to be secured for D2D data reception at the receiving terminal in D2D communication, resource allocation information for the SA, And instructs the transmitting-side terminal about the resource allocation information on the indicated data. The parameter information to be determined by the base station includes resource allocation information on data indicated by the SA. The D2D grant may be delivered to a transmitting terminal through downlink control information (DCI), and may be delivered via a PDCCH or an EPDCCH. The D2D grant is control information distinguished from the D2D through the D2D-RNTI allocated to the UL grant or each UE. The D2D grant may be referred to as an SA / data grant. The D2D-RNTI is an identifier for performing D2D communication, which may be referred to as a Side Link (SL) -RNTI. The Sidelink refers to a UE to UE interface that performs D2D communication (ProSe direct communication and ProSe Direct Discovery) (Sidelink is defined as UE to UE interface for ProSe direct communication and ProSe Direct Discovery).

Meanwhile, the second transmission mode is a mode in which the terminal can perform D2D communication regardless of the indication of the base station. The terminal can internally select a resource to use among the available radio resources in D2D communication, and transmit the D2D data. The UE transmits information indicating that the particular cell in the base station can support D2D through the SIB (System Information Block) / dedicated signaling and D2D resource pool information for the second transmission mode provided from the base station Only the specific cell can operate in the second transmission mode only when it exists.

However, if there is information indicating that the base station does not allow operation in the second transmission mode, i.e., that the base specific cell can support D2D, D2D resource pool information for the second transmission mode is provided from the base station , It can not operate in the second transmission mode. Also, if the D2D resource pool information for the second transmission mode is valid only in the RRC connected mode, the RRC idle mode terminal can operate in the second transmission mode even though the D2D resource pool information for the second transmission mode exists Can not.

In the 'Any Cell Selection' mode, which is a case where the UE is located in a non-network service area, that is, when the RRC idle mode UE fails to select a serviceable cell, the UICC (Universal Subscriber Identity Module) Integrated Circuit Card) or the D2D resource pool information for the second transmission mode received through the base station in the previous network service area is used for the second transmission mode .

In a wireless communication system, a terminal reports its buffer status to a base station in order to allocate resources required for transmitting uplink data (data to be transmitted to a base station) existing in a buffer in a terminal, And scheduling resources to be allocated to each mobile station based on information.

Therefore, when a wireless communication system supports D2D communication, a base station needs to schedule resources required for in-coverage terminals to transmit data through D2D communication. To this end, (Hereinafter referred to as " D2D data ") to be transmitted in the D2D communication. The UE can inform the BS of the amount of data to be transmitted through the D2D communication in the intra-UE buffer through the following procedure.

3 is a diagram illustrating a process of transmitting a ProSe-BSR to a base station in order to transmit D2D data in a first transmission mode in a wireless communication system according to the present invention.

If there is data to be transmitted through the D2D link in the DRB configured for D2D in the terminal capable of D2D communication in the wireless communication system, a buffer status report (BSR) is triggered (S310). Hereinafter, in the present invention, BSR for D2D data is referred to as ProSe-BSR. The ProSe-BSR means a BSR for D2D communication that is different from the BSR defined and used in the current wireless communication system.

When the ProSe-BSR is triggered, the UE transmits a Scheduling Request (SR) to the BS to induce allocation of resources for transmission of D2D data and ProSe-BSR (S320) Grant (UL grant) is received (S330). Here, the SR is transmitted to the base station via the PUCCH. The SR may share the SR used in the existing wireless communication system or may use the resource allocated for the SR for the D2D by distinguishing it from the SR. When the SR for the D2D application is defined by distinguishing from the existing SR, the SR can be defined as being divided into ProSe-SR. For convenience of explanation, SR and ProSe-SR are collectively referred to as SR.

If an SR is triggered, the SR is pended until canceled. On the other hand, if the UE does not accept all the data pending for transmission by the UL grant, or if the MAC PDU is configured and the MAC PDU is included in the buffer state including the last event (SR-ProhibitTimer) to cancel all pending SRs and prevent the SRs from being transmitted.

More specifically, if the SR is triggered and the currently pending SR is not available, the terminal sets the SR count (SR_COUNTER) value to zero. However, if SR is pending and there is a valid PUCCH resource to send an SR at this Transmission Time Interval (TTI) and this TTI is not part of a measurement gap and sr-ProhibitTimer is not in progress If the value of SR_COUNTER is less than the maximum number of transmissions of the SR, increase the SR count value by 1 and instruct the physical layer to transmit the SR signal through the PUCCH and then start the sr-ProhibitTimer. However, if the SR_COUNTER value is greater than or equal to the maximum number of transmissions, the RRC is informed of the release of the PUCCH and SRS and clears all configured downlink allocations and uplink grants. Then, it initializes the random access procedure and cancels all pending SRs.

On the other hand, if the SR is pending but there is no available UL-SCH resource for transmission in any TTI, the UE initializes the random access procedure and cancels all pending SRs. Therefore, the ProSe-BSR can be delivered to the base station through the random access procedure.

When the MS receives the uplink grant for the SR, it transmits the ProSe-BSR to the BS (S340). When the D2D grant for the ProSe-BSR is received from the base station (S350), the data is transmitted to the target terminal using the resources allocated for the transmission of the D2D data (S360). Thus, the ProSe-BSR informs the serving BS of information on the amount of data that can be transmitted in the D2D link buffer. In the present invention, for example, the ProSe-BSR procedure is shown to be performed after the SR transmission. However, if the UE has received an uplink grant sufficient to transmit the ProSe-BSR before the SR transmission, the ProSe-BSR transmission may be performed before the SR transmission.

The base station constructs a periodic BSR timer (periodic BSR-Timer) and a retransmission BSR timer (retxBSR-Timer) for the ProSe-BSR through signaling defined in the RRC layer to generate a ProSe-BSR procedure . A logical channel group (LCG: Logical Channel Group) may be configured for each terminal by means of selective signaling (RRC signal by eNB), and the ProSe-BSR is performed on the LCG.

The LCG is set separately from the LCG that is the subject of the BSR for the wireless communication system. For example, LCG for ProSe-BSR and LCG for existing BSR are set differently.

Here, the LCG that is the object of the BSR for the wireless communication system has only the logical channels (DCCH, DTCH) set for data transmission of the wireless communication system, and the index of the LC may be 0 to 11 have. On the other hand, the LCG that is the object of the BSR for D2D communication has only the logical channels (PTCH) set for data transmission of the D2D as a component, and the index of the LC for this is the index of the LC for the wireless communication system 11), it can have indices 0 to 11 of the LC for D2D communication.

In addition, the base station can set a periodic timer / retransmission timer for ProSe-BSR and the like separately from the BSR for the wireless communication system for each terminal through the RRC.

The UE configures the ProSe-BSR based on the data buffered in each LCG in the UE. A maximum of four LCGs can be configured in a terminal. The format of ProSe-BSR is short BSR to report buffer status corresponding to one LCG or long BSR or truncated BSR to report buffer status corresponding to four LCGs. And so on.

For the ProSe-BSR procedure, the UE shall consider a suspended radio bearer (RB) and all RBs not reserved. The ProSe-BSR can be divided into a regular ProSe-BSR, a padding ProSe-BSR, and a periodic ProSe-BSR.

The regular ProSe-BSR is configured such that the data that can be transmitted in the logical channel included in the LCG exists in the RLC entity or the PDCP entity, or the uplink that can be transmitted to the logical channel having the higher priority than the other logical channels Triggered when data is present. Also, the regular ProSe-BSR is triggered even when the retransmission BSR timer for ProSe-BSR has expired and the terminal has data that can be transmitted to the logical channel in the LCG.

The padding BSR is triggered when resources for padding BSR transmission for an uplink resource and a wireless communication system are allocated and the number of remaining padding bits is equal to or greater than a size for ProSe-BSR transmission.

Alternatively, the padding ProSe-BSR is triggered when resources for BSR transmission for an uplink resource and a wireless communication system are allocated and the number of remaining padding bits is equal to or larger than a size for ProSe-BSR transmission.

And the periodic ProSe-BSR is triggered when the periodic BSR timer for ProSe-BSR expires.

The regular ProSe-BSR and the periodic ProSe-BSR are transmitted in a long ProSe-BSR format when more than one LCG (at least two LCGs) has data to be transmitted in the TTI in which the corresponding ProSe-BSR is transmitted, Only the LCG of the BSG has the data to be transmitted) can be configured and transmitted in the short BSR format.

The padding ProSe-BSR includes a ProSe-BSR having a length equal to or larger than a sum of the sub-headers of the short ProSe-BSR and the short ProSe-BSR having a small number of padding bits included in the MAC PDU, If the ProSe-BSR has less than a combined size and more than one LCG has data to transmit in the TTI to which the ProSe-BSR is transmitted, the truncated ProSe-BSR for the LCG including the logical channel with the highest priority in data transmission Format and transmitted. Otherwise, it is transmitted in short ProSe-BSR format. Or ProSe-BSR format is always available in the short ProSe-BSR format if only the short ProSe-BSR format is available.

The padding ProSe-BSR is transmitted in a long ProSe-BSR format when the padding bit number is equal to or larger than the sum of the long ProSe-BSR and the long ProSe-BSR subheader. Or only the ProSe-BSR format with a short ProSe-BSR format is available, it is always transmitted in the short ProSe-BSR format.

Meanwhile, the UE performs the ProSe-BSR procedure when at least one ProSe-BSR is triggered and not canceled. The UE instructs the multiplexing and assembly procedure for generation of the ProSe-BSR MAC control element if the uplink resource for the new transmission is assigned to this TTI and starts a periodic BSR timer (periodicBSR-Timer) for ProSe-BSR And restarts or restarts the retransmission BSR timer (retxBSR-Timer) for the ProSe-BSR. Here, the procedure for starting or restarting the periodic BSR timer for the ProSe-BSR is excluded when a truncated ProSe-BSR is generated. If the uplink resources for the new transmission are not allocated to this TTI, the regular ProSe-BSR is triggered.

 At this time, even if a plurality of ProSe-BSRs are triggered in one MAC PDU, only one ProSe-BSR MAC control element is included. In addition, when it is possible to transmit regular ProSe-BSR or periodic ProSe-BSR, this always takes precedence over padding ProSe-BSR. In addition, when confirming reception of an indicator for instructing transmission of new data to all UL-SCHs, the UE restarts the retransmission BSR timer. All triggered BSRs should be canceled when the BSR is included in the MAC PDU.

The terminal transmits one regular or periodic ProSe-BSR in one TTI. Also, according to the present invention, the ProSe-BSR can be transmitted in the same TTI as the BSR of the wireless communication system. For example, the ProSe-BSR for the D2D service and the existing BRS for the general data service may be simultaneously transmitted in the same subframe (TTI). At this time, the information classification for the corresponding BSR can be identified through the LCID.

If the UE is requested to transmit a plurality of MAC PDUs in one TTI, one padding ProSe-BSR may be included in any MAC PDUs that do not include a regular or periodic ProSe-BSR. Thus, one padding ProSe-BSR may be included in any MAC PDUs that include a regular or periodic BSR for a wireless communication system. That is, the padding BSR has higher priority than the padding ProSe-BSR, but the padding ProSe-BSR can be included first for any MAC PDU including the regular or periodic BSR. This may include a case where a single TTI is requested to transmit a single MAC PDU. All ProSe-BSRs always reflect the buffer status after the MAC PDUs to be transmitted based on the D2D grant received previously by the UE based on the TTI of the ProSe-BSR are transmitted. Each LCG reports one buffer status value per TTI, and the buffer status value is reported in all ProSe-BSRs via the ProSe-BSR for the LCG. That is, one ProSe-BSR value should be transmitted for each LCG in the same TTI, and the buffer status value for LCG in all ProSe-BSRs transmitted in the same TTI should be the same value. On the other hand, padding ProSe-BSR is not allowed to cancel regular or periodic ProSe-BSR. The padding ProSe-BSR is triggered for a specific MAC PDU, and the trigger of the padding ProSe-BSR is canceled when a specific MAC PDU is generated.

However, in the case of the existing wireless communication system, all triggered BSRs are canceled when they receive all the pending data but receive an uplink grant which can not be further transmitted the BSR MAC control element. Also, all triggered BSRs are canceled when the BSR is included in the MAC PDU. That is, the existing wireless communication system can cancel the triggered BSR only in the following situations.

1. When the resource secured through the UL grant in the corresponding subframe can accommodate all the data to be transmitted in the uplink but the BSR MAC CE including the MAC subheader can not be included.

In this case, the UE cancels the triggered BSR and transmits all data to be transmitted in the uplink on the uplink.

2. When BSR is included in MAC PDU for uplink transmission.

As described above, in the D2D communication, the base station needs to schedule resources required for in-coverage terminals to transmit data through D2D communication. To do so, the terminal transmits a D2D communication (Hereinafter referred to as " D2D data "). However, in exceptional cases (for example, when the UE can not maintain the RRC connection state with the base station), the UE does not allocate resources required for transmitting data through the D2D communication to the D2D Data must be transferable. For this purpose, a first transmission mode and a second transmission mode can be supported in D2D communication.

However, when the terminal is set or operated in the second transmission mode, the resources for D2D transmission can not be controlled by the base station. Therefore, the base station must prepare the resource for D2D transmission. The reserved resources can be determined by the number of terminals capable of operating in the second transmission mode and the expected resource consumption of each terminal.

If the resources reserved for the second transmission mode increase, the amount of available resources for general wireless communication (e.g., LTE communication) is reduced because the total resources are limited, which affects the overall system throughput . Therefore, the base station can reduce the number of terminals that can operate in the second transmission mode to reduce the resource amount reserved for the second transmission mode. To support this, the base station may allow the terminal to operate in the second transmission mode only in exceptional cases.

However, when the D2D transmission mode set in the terminal changes from the first transmission mode to the second transmission mode, or when the terminal set in the first transmission mode operates in the second transmission mode, If there is a status report, how to operate the triggered buffer status report has not yet been determined.

4 to 8 are flowcharts illustrating a buffer status reporting method for inter-terminal communication by a terminal according to an embodiment of the present invention. 4 to 8, when the D2D transmission mode set in the terminal changes from the first transmission mode to the second transmission mode, or when the terminal set in the first transmission mode operates in the second transmission mode, Describes how to operate the status report.

A terminal supporting D2D communication can perform D2D communication when a user of the terminal sets up the terminal to enable D2D communication through a user interface (UI). Or, a D2D server that manages a ProSe (Proximity Services) ID and a ProSe application ID of a terminal using D2D communication, a serving base station of the terminal, etc.) of a network (for example, It is possible to finally determine whether or not the D2D communication can be performed by the terminal set to be D2D communication. That is, even if the terminal is set to enable D2D communication by the user of the terminal, D2D communication may be performed only when D2D communication is permitted by the network. Information on whether or not D2D communication is possible can be displayed on the screen of the terminal.

The resources for D2D communication may be allocated by a terminal (hereinafter, cluster head) or a base station that is responsible for allocating resources for D2D communication in D2D communication. In this case, when the terminal performs D2D communication, the terminal must transmit the BSR for the D2D data to the base station or the cluster head. Hereinafter, the base station and the cluster head are collectively referred to as a base station for convenience of explanation. BSR for D2D data is also referred to as ProSe-BSR.

4, the ProSe-BSR may be triggered by the same triggering condition as the BSR for the existing uplink data (S410). At this time, a different LCID may be used for the ProSe-BSR than the BSR for the existing uplink data. As an example, the ProSe-BSR may be assigned a new LCID to distinguish the short ProSe-BSR, the truncated ProSe-BSR and the long ProSe-BSR. Alternatively, one ProSe-BSR format may be used as the BSR for D2D data, and a new LCID may be used to indicate this.

If the ProSe-BSR is triggered, the terminal can determine whether the D2D transmission mode of the current terminal is set to the second transmission mode (S420). As a result, if the UE is set to the second transmission mode, the triggered ProSe-BSR can be canceled (S430). If the UE is not set to the second transmission mode, the uplink resource allocation based on the ProSe- The BS may transmit the ProSe-BSR MAC CE to the BS in the MAC PDU (S440).

For example, in an exceptional case (such as when a RRC reset procedure timer and / or a handover related timer is in progress or starts), or the base station changes the D2D transmission mode of the terminal to the second transmission mode When the UE changes the D2D transmission mode set in the UE from the first transmission mode to the second transmission mode, the UE transmits all the ProSe-BSRs that have been triggered for operation in the first transmission mode You can cancel. Here, the first transmission mode refers to a mode in which the D2D communication is performed using a resource allocated from a base station, and the second transmission mode refers to a second transmission mode resource pool information for the D2D communication And the D2D communication may be performed using the D2D communication mode. In other words, all triggered ProSe-BSRs can be canceled when the D2D communication mode set in the UE changes from the first transmission mode to the second transmission mode due to an exceptional case, and the D2D transmission Mode can be canceled when changing from the first transmission mode to the second transmission mode.

In order to receive D2D data, the UE operating in the first transmission mode and the UE operating in the second transmission mode transmit the following D2D resource pool information (commRxPoolNormalCommon) included in the reception resource pool (commRxPool) and the common common transmission resource pool . Herein, the reception resource pool is information indicating resources that are allowed to be received by the D2D terminal operating in the RRC IDLE and Connected mode, and the general common transmission resource pool is allowed to be transmitted by the D2D terminal operating in the RRC IDLE mode It is information indicating the resources.

- SA resource pool information

- Data resource pool information (included in case of general common transmission resource pool but not in case of resource pool for first transmission mode among reception resource pool configuration information)

- TDD configuration information (included only when receiving resource pool information is neighboring cell and operates as TDD)

Herein, for exceptional cases, transmission resource pool information (commTxPoolExceptional) for an exceptional case defined separately from the resource pool information may be defined.

All of the resource pool information can be transmitted to all terminals in a corresponding cell through a broadcast channel, and a terminal to perform a D2D communication operation can receive D2D data Lt; RTI ID = 0.0 > a < / RTI > In the reception resource pool information, transmission resource pool information provided in a dedicated manner by the base station for a transmission operation in the first transmission mode or the second transmission mode is transmitted to only the terminal operating in the RRC connected mode in the corresponding cell . The first transmission mode or the second transmission mode transmission resource pool information dedicated for the dedicated transmission should be set so that there is no physical resource colliding with each other in each cell in order to avoid mutual interference. In addition, when resources that are collided with each other due to insufficient resource amount allocated for ProSe communication are generated, transmission signal characteristics set for each cell are made equal to each other, such as a cyclic prefix length, so that the range of mutual interference is limited to the same resource range The cooperation between the base stations should be made.

Here, the RRC reset procedure related timer may be a T311 timer, and the handover related timer may be a T304 timer, and may be defined as shown in the following Tables 1 and 2, respectively.

Timer Start Stop At expiry T311 Upon initiating the RRC connection re-establishment procedure Selection of a suitable E-UTRA cell or a cell using another RAT. Enter RRC_IDLE

Timer Start Stop At expiry T304 Reception of RRCConnectionReconfiguration message including the MobilityControl Info or
reception of MobilityFromEUTRACommand message including CellChangeOrder Criterion for successful completion of handover within E-UTRA, handover to E-UTRA or cell change order is met (the criterion is specified in the target RAT in case of inter-RAT) In case of cell change order from E-UTRA or intra E-UTRA handover, initiate RRC connection re-establishment procedure; In case of handover to E-UTRA, perform the actions specified in RAT.

Referring to Table 1, the T311 timer starts when an RRC connection re-establishment procedure is started. Then, when an appropriate Evolved UMTS Terrestrial Radio Access (E-UTRA) cell is selected, or when a cell using another radio access technology (RAT) is selected, it is stopped. Also, when entering the RRC idle state, it expires.

Also, referring to Table 2, the T304 timer receives an RRC connection reconfiguration message including mobility control information or a message including a cell change order (MobilityFromEUTRACommand message. < / RTI > Here, the RRC connection reconfiguration message including the mobility control information may be referred to as a handover command message. That is, the T304 timer starts during an inter-RAT handover to an LTE network handover or an LTE system, and is stopped when the handover is successfully completed.

On the other hand, when canceling the ProSe-BSR, the UE can reset the periodic BSR-timer and the retransmission BSR timer (retxBSR-timer) configured for the ProSe-BSR. The periodic BSR timer and the retransmission BSR timer configured for the initialized ProSe-BSR may be set to a state ready for starting when the D2D transmission mode of the UE changes from the second transmission mode to the first transmission mode.

In addition, if the terminal changes the D2D transmission mode set in the terminal from the first transmission mode to the second transmission mode as shown in FIG. 5 (S510), the terminal can determine whether there is resource pool information for the second transmission mode (S520). Here, if the D2D transmission mode set in the terminal is changed by an exceptional case, the mode may be changed from the first transmission mode to the fallback mode (S510). The fallback mode is defined as the same D2D terminal operation as the second transmission mode, but the resource pool information for the fallback mode includes transmission resource pool information for an exceptional case defined separately from the resource pool information for the exceptional case commTxPoolExceptional). Therefore, if the D2D transmission mode set in the terminal is changed from the first transmission mode to the fallback mode, it may be additionally determined whether the resource pool information for the fallback mode exists (S520). Herein, the resource pool information to be preferentially applied in the fallback mode may be the general common transmission resource pool information or the transmission resource pool information for the exceptional case. If there is at least one of the two resource pool information, the UE transmits all of the ProSe Communication Traffic Channel (PTCH) configured for the D2D communication between the UEs so that the ProSe-BSR is no longer triggered. May be excluded from the triggering target of ProSe-BSR (S530). However, if the two resource pool information does not exist, the UE can not suspend data transmission to the PTCH because it can not operate in the second communication mode (S540).

Thereafter, as shown in FIG. 6, the exceptional case is resolved (for example, the RRC reset procedure related timer and / or the handover related timer is suspended) and the D2D transmission mode set in the terminal is set to the first transmission Mode (S610), the UE can start the initialized periodic BSR timer and the retransmission BSR timer, and can transmit a buffer status report for data to be transmitted in the D2D communication. That is, the normal ProSe-BSR procedure can be restarted (S620).

In the case of handover, in order to operate immediately after the terminal completes the handover to the target base station (immediately after the T304 timer is stopped), the handover preparation step, that is, the source base station transmits the current terminal And transmits the handover request message including the terminal information including the ProSe configuration information, such as the transmission mode, to the source base station based on the handover request message. The target base station includes the ProSe configuration information required for the first transmission mode operation . The configuration information may include D2D-RNTI information, ProSe-BSR configuration information, and SA pool information to be used by the target base station.

7, if the D2D transmission mode set in the terminal is changed from the first transmission mode to the second transmission mode due to an exceptional situation (S710), the terminal transmits the D2D communication You can decide whether to cancel the ProSe-BSR depending on the presence of data. For example, if the D2D transmission mode set in the UE changes from the first transmission mode to the second transmission mode due to the RRC reset procedure related timer and / or the handover related timer being in progress, the data to be transmitted in the D2D communication The ProSe-BSR can be canceled (S720). At this time, all ProSe-BSR timers (periodic BSR timer and retransmission BSR timer) are initialized and may not start until the UE changes the D2D transmission mode to the first transmission mode. In this case, the terminal can also determine whether there is resource pool information for the second transmission mode. If the second transmission mode resource pool information exists, all PTCHs are excluded from the triggering target of ProSe-BSR, and if there is no second transmission mode resource pool information, data transmission for all PTCHs can be stopped.

In another embodiment, as shown in FIG. 8, the terminal may operate in a second transmission mode with the first transmission mode set without changing the D2D transmission mode (S810). This may be done when the base station does not propose the D2D transmission mode of the terminal and / or when at least one of the timers for the RRC reset procedure and the handover related timer is in progress or is started. In this case, even though the terminal can transmit D2D data in the second transmission mode, when the terminal receives the D2D grant from the base station, it transmits D2D data in the first transmission mode. That is, the terminal can maintain the first transmission mode as the D2D transmission mode. In this case, even if the UE starts the operation in the second transmission mode, it can not cancel the triggering of the ProSe-BSR because it is set to the first transmission mode. However, if the UE does not have data to be transmitted in the D2D communication, it can cancel the triggered BSR (S820).

Meanwhile, if the exceptional case is resolved but the RRC connection mode can not be maintained (i.e., the timer for RLF or the timer for handover is expired), the terminal can change the D2D transmission mode to the second transmission mode . The D2D data can be transmitted based on the secured second transmission mode D2D resource pool information.

In another embodiment, the MS cancels the ProSe-BSR through the reset operation of the MAC entity in the exceptional case. The reset of the MAC entity can be performed by the request of the upper layer. The MAC entity reset operation includes the following operations.

- Stop all ongoing timers.

- The value of the NDI (new data indicator) for all the UL HARQ processes other than the uplink HARQ processes related to the PSCH is set to zero.

- If there is a triggered SR and / or ProSe-SR procedure, it is canceled.

- If there is a triggered BSR and / or ProSe-BSR procedure, it is canceled.

- And flushes the soft buffers for all DL HARQ processes other than the DL HARQ processes associated with the PSCH.

- For each DL HARQ process other than the DL HARQ processes associated with the PSCH, the transmission for any subsequently received TB is considered as a very first transmission.

Here, the PSCH (ProSe Communication Shared CHannel) is a transport channel for D2D data transmitted from the MAC layer to the physical layer.

If the exceptional case is caused by the start of the RRC re-establishment procedure, the UE suspends all DRBs except the DRBs associated with the PTCH, which is a logical channel related to the D2D data transmission, at the start of the RRC re-establishment procedure. If the exceptional case is caused by the start of the handover procedure (when the MCI (Mobility Control Information) is included in the RRC reconfiguration message), the UE generates a logical channel related to the D2D data transmission Re-establishment of RLC and PDCP in all DRBs except DRBs associated with PTCH.

When the MAC entity for D2D communication is separated from the MAC entity for wireless communication, in the exceptional case, the MAC entity for D2D communication is reset and the ProSe-BSR is canceled.

At this time, the UE in the exceptional case does not trigger the ProSe-BSR even if the RLC in the DRB associated with the PTCH and the transmittable data exist in the PDCP. That is, the ProSe-BSR triggering is not exceptional and is possible only when the UE is set to operate in the first transmission mode and is in the RRC connected mode.

9 is a flowchart illustrating a buffer status reporting method for inter-terminal communication by a base station in an embodiment of the present invention.

Referring to FIG. 9, the base station may transmit a second transmission mode grant message to the first terminal in the coverage (S910). Here, the first terminal may be a terminal whose D2D transmission mode is set to the first transmission mode. The first terminal receiving the second transmission mode grant message may change the D2D transmission mode to the second transmission mode in the exceptional case described above.

If the first terminal is changed to the second transmission mode, the base station may receive the ProSe-BSR from the second terminal set in the first transmission mode in addition to the first terminal (S920). Then, the base station can allocate resources for D2D communication in the second terminal based on the received ProSe-BSR (S930), and the receiving terminal can perform D2D communication with the target terminal using the allocated resources have.

As another example, if the UE receives an RRC reconfiguration message including mobility control information (MCI) from the base station, the UE releases the configuration of the transmission resource during the configuration for the ProSe communication operation. This is to indicate that the configuration information for the first transmission mode or the second transmission mode configured by the source base station is no longer valid since the corresponding terminal moves to the target base station through handover.

The release information may be included in the configuration information for the transmission resources in the RRC reconfiguration message for the release operation. Alternatively, if the UE receives an RRC reconfiguration message including mobility control information (MCI) from the base station, the UE may release the configuration information for the transmission resource in the RRC reconfiguration message.

When the configuration for the transmission resources for the first transmission mode or the second transmission mode is released as described above, the UE operates in the second transmission mode at the time of data transmission using the general common transmission resource pool information received through the system information do. The QoS of the ProSe communication can be maintained by using resources available to the ProSe communication transmission resources even in the RRC IDLE mode instead of the configuration information for the first transmission mode or the second transmission mode configured by the source base station released due to the handover operation as described above .

Alternatively, when the configuration for the transmission resource for the first transmission mode or the second transmission mode is released as described above, the UE uses the transmission resource pool information for the exceptional case received through the system information to perform a fallback mode Can operate. Since the configuration information for the first transmission mode or the second transmission mode configured by the source base station is released due to the handover operation as described above, but the RRC connected mode is maintained, the transmission resource pool information for the exceptional case available in the RRC connected mode The QoS of the ProSe communication can be maintained.

The transmission resource pool information used at this time may be the resource pool information for ProSe communication provided by the target base station to the source base station (the base station that has transmitted the RRC reconfiguration message including the MCI), and the RRC reconfiguration message And the UE can perform an operation related to the transmission based on the information provided by the target BS.

If there is no or no transmission resource pool information provided from the target base station, transmission resource pool information in system information previously received from the source base station can be used.

The UE can maintain the second transmission mode or the fallback mode until receiving the information for the configuration of the transmission resource in the configuration for the ProSe communication operation from the target base station after the handover is completed.

Alternatively, if the configuration for the transmission resource for the first transmission mode or the second transmission mode is released as described above, the terminal can suspend all transmission operations while maintaining the reception operation. That is, it can operate in the ProSe transmission stop mode. Since the configuration information for the first transmission mode or the second transmission mode configured by the source base station is released due to the handover operation as described above, ProSe transmission operation is impossible. This is because only the terminal operating in the RRC connected mode in the source base station transmits only the physical resources in the transmission resource pool and the target base station dedicatedly provided by the base station for the transmission operation in the first transmission mode or the second transmission mode a ProSe communication signal transmitted based on the transmission resource pool information of the source base station may act as an interference of other ProSe communication signals in the target base station when a collision can occur between physical resources in a dedicated transmission resource pool. Therefore, the transmission operation is stopped in order to eliminate such interference factors.

The UE can maintain the transmission stop mode until receiving the information for the configuration of the transmission resource in the configuration for the ProSe communication operation from the target base station after the handover is completed.

The source base station and the target base station may be different base stations or the same base station. In case of the same base station, the frequency band may be changed due to handover and may not be changed. If the base station or the frequency band is not changed despite performing the handover operation, the base station determines that the RRC parameters between the base station and the UE do not match with each other, or determines that the downlink or uplink synchronization is not properly performed. And to change the key value shared by the BS and the MS.

10 is a block diagram illustrating a wireless communication system according to an embodiment of the present invention.

Referring to FIG. 10, a wireless communication system supporting inter-terminal communication according to the present invention includes a terminal 1000 and a base station (or cluster head) 1050.

The terminal 1000 includes a processor 1005, an RF unit (radio frequency unit) 1010, and a memory 1015. The memory 1015 is connected to the processor 1005 and stores various information for driving the processor 1005. [ The RF unit 1010 is connected to the processor 1005 to transmit and / or receive a radio signal. For example, the RF unit 1010 may receive the second transmission mode grant message and D2D resource allocation information published herein from the base station 1050. [ In addition, the RF unit 1010 may transmit an uplink signal, such as a ProSe-BSR, as disclosed herein, to the base station 1050.

Processor 1005 implements the functions, processes and / or methods suggested herein. Specifically, processor 1005 causes all steps according to FIGS. 4-8 to be performed.

  For example, the processor 1005 may include a ProSe-BSR triggering determination unit 1006, a timer determination unit 1007, and a cancellation unit 1008. The ProSe-BSR triggering determination unit 1006 determines whether the ProSe-BSR is triggered. When the D2D transmission mode of the current terminal is set to the second transmission mode, the tire determination unit 1007 determines whether the RRC reset procedure related timer and / or the handover related timer is in progress. The cancellation unit 1008 cancels all ProSe-BSRs that have been triggered when the RRC reset procedure related timer and / or handover related timer is in progress. At this time, the periodic BSR-timer configured for the ProSe-BSR and the retransmission BSR timer (retxBSR-timer) can be reset.

Meanwhile, the processor 1005 can check whether there is resource pool information for the second transmission mode or resource pool information for the fallback mode. If there is at least one of the two resource pool information, all the PTCHs configured for the D2D communication between the terminals can be excluded from the triggering target of the ProSe-BSR so that the ProSe-BSR is no longer triggered have. The processor 1005 can suspend the data transmission to the PTCH because it can not operate in the second communication mode if the two resource pool information does not exist.

Thereafter, if it is determined by the timer determining unit 1007 that the RRC reset procedure related timer and / or the handover related timer is stopped, the processor 1005 determines that the exceptional case is resolved and initializes the periodic BSR timer and / The retransmission BSR timer can be started and the normal ProSe-BSR procedure can be restarted.

The memory 1015 stores the resource pool information for the second transmission mode according to the present specification, information on whether or not the second transmission mode is allowed, and transmits the second transmission mode to the processor 1005 according to a request of the processor 1005. [ Resource pool information for the mode, and the like.

The base station 1050 includes a radio frequency (RF) unit 1055, a processor 1060, and a memory 1065. The memory 1065 is coupled to the processor 1060 and stores various information for driving the processor 1060. The RF unit 1055 is connected to the processor 1060 to transmit and / or receive wireless signals. Processor 1060 implements the functions, processes, and / or methods suggested herein. The operation of base station 1050 in the above-described embodiment may be implemented by processor 1060. [ Processor 1060 generates a second transmission mode grant message published herein and schedules resources for D2D communication based on the ProSe-BSR received from the terminal.

For example, the processor 1060 may include a timer value setting unit 1061, a ProSe-BSR verifying unit 1062, and a D2D resource assigning unit 1063. The timer value setting unit 1061 sets various timer values described in this specification. The timer value set by the timer value setting unit 1061 can be transmitted to the terminal through the RF unit 1055. [ The ProSe-BSR confirmation unit 1062 can confirm the ProSe-BSR received from the terminal 1000. [ The D2D resource allocation unit 1063 can allocate resources for D2D communication to the terminal 1000 operating in the first transmission mode based on the ProSe-BSR.

The processor may comprise an application-specific integrated circuit (ASIC), other chipset, logic circuitry and / or a data processing device. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The RF unit may include a baseband circuit for processing the radio signal. When the present embodiment is implemented in software, the above-described technique may be implemented by a module (process, function, etc.) that performs the above-described function. The module is stored in memory and can be executed by the processor. The memory may be internal or external to the processor and may be coupled to the processor by any of a variety of well known means.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (11)

A method for reporting a buffer status by a terminal in a wireless communication system supporting D2D (Device to Device) communication,
Changing a D2D transmission mode set in the terminal from a first transmission mode to a second transmission mode; And
Canceling the triggered buffer status report when a buffer status report for data to be transmitted through the D2D communication is triggered,
Lt; / RTI >
Wherein the first transmission mode is a mode for performing the D2D communication using a resource allocated from a base station and the second transmission mode performs the D2D communication using resource pool information for the D2D communication And a buffer status reporting operation mode. The method according to claim 1,
Wherein the modifying comprises:
Wherein at least one of a timer for a radio link failure or a timer for a handover is in progress or is started. The method according to claim 1,
Wherein the modifying comprises:
And when the change to the second transmission mode is permitted by the base station. The method according to claim 1,
If the resource pool information is present, excluding the logical channel configured for the D2D communication between the terminals from the triggering target of the buffer status report for the data to be transmitted through the D2D communication. The method according to claim 1,
And suspending data transfer for a logical channel configured for the D2D communication between the terminals if the resource pool information does not exist. The method according to claim 1,
Wherein the canceling comprises:
Resetting a periodic BSR-timer and a retransmission BSR-timer, and canceling the triggered buffer status report. The method according to claim 6,
After said canceling step,
If the D2D transmission mode is changed from the second transmission mode to the first transmission mode, initiating the periodic BSR timer and the retransmission BSR timer and transmitting a buffer status report for data to be transmitted in the D2D communication The buffer status reporting method comprising: The method according to claim 1,
Further comprising the step of determining whether there is data to be transmitted in the D2D communication,
Wherein the canceling comprises:
Wherein at least one of the timer related to the radio link failure and the timer related to the handover is in progress and the data to be transmitted through the D2D communication does not exist. A method for reporting a buffer status by a terminal in a wireless communication system supporting D2D (Device to Device) communication,
A terminal set in a first transmission mode for performing the D2D communication using a resource allocated by a base station operates in a second transmission mode for performing the D2D communication using resource pool information for the D2D communication step; And
Canceling a triggered buffer state report if there is no data to be transmitted in the D2D communication;
Wherein the buffer status reporting method comprises: 10. The method of claim 9,
Wherein the operating comprises:
Wherein at least one of a timer for a radio link failure or a timer for a handover is in progress or is started. 10. The method of claim 9,
The terminal,
And if the RRC (Radio Resource Control) connection mode can not be maintained, the D2D transmission mode is changed to the second transmission mode.

Images