KR20230024942A - 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 apparatus for operating a buffer state report in a wireless communication system supporting device to device communication. The method for operating a buffer state report by a device in a wireless communication system supporting device to device (D2D) communication comprises: changing a D2D transmission mode set in the device from a first transmission mode to a second transmission mode; and canceling, when a buffer state report for data to be transmitted through the D2D communication is triggered, the triggered buffer state report. In addition, the first transmission mode may be a mode in which the D2D communication is performed using resources allocated from a base station, and the second transmission mode may be a mode in which the D2D communication is performed using resource pool information for the D2D communication. Accordingly, resources for device to device communication can be efficiently allocated.

Description

Method and apparatus for reporting buffer status in a wireless communication system supporting terminal-to-device communication

The present invention relates to wireless communication, and more particularly, in a wireless communication system supporting device to device communication, when a terminal performs communication between terminals using resources allocated from a base station, a buffer state report (buffer state report) ) It relates to a method and device for operating.

D2D (Device to Device) communication is a communication method that has been possible since the days of analog radios and has a very long history. However, D2D communication in a wireless communication system is different from conventional D2D communication.

D2D communication in a wireless communication system is a communication in which terminals that are geographically close to each other directly exchange data without going through an infrastructure such as a base station using the transmission and reception technology of the wireless communication system in the frequency band of the wireless communication system or other bands. means This allows the terminal to use wireless communication outside of the area where the wireless communication infrastructure is built, and provides advantages of reducing the network load of the wireless communication system.

For communication between terminals in such a wireless communication system, a base station may schedule resources required for terminals existing in coverage to transmit data through D2D communication. To this end, the terminal may inform the base station of how much data to be transmitted through D2D communication exists in the buffer in the terminal through a buffer state report.

Meanwhile, in an exceptional case, the terminal may transmit D2D data through resources selected by itself without being allocated resources necessary for transmitting data through the D2D communication from the base station. However, in this case, when there is already a triggered buffer status report in the terminal, it has not yet been determined how the terminal will operate the triggered buffer status report, and specific operations and definitions for this are required. The situation is.

A technical problem of the present invention is to provide a method and apparatus for operating a buffer status report for data to be transmitted through terminal-to-device communication in a wireless communication system supporting terminal-to-device communication.

Another technical problem of the present invention is to provide a method and apparatus for efficiently allocating resources for communication between terminals to terminals in a wireless communication system supporting communication between terminals.

According to an aspect of the present invention, a method for operating a buffer status report by a terminal in a wireless communication system supporting device to device (D2D) communication includes a second transmission of a D2D transmission mode set in the terminal in a first transmission mode and, when a buffer state report for data to be transmitted through the D2D communication is triggered, canceling the triggered buffer state report. 1 transmission mode is a mode for performing the D2D communication using resources allocated from a base station, and the second transmission mode is a mode for performing the D2D communication using resource pool information for the D2D communication. can

According to another aspect of the present invention, a method for operating a buffer status report by a terminal in a wireless communication system supporting D2D communication includes a terminal set to a first transmission mode performing the D2D communication using a resource allocated from a base station, the D2D Operating in a second transmission mode for performing the D2D communication using resource pool information for communication, and canceling a triggered buffer status report when data to be transmitted through the D2D communication does not exist. there is.

According to the present invention, when communicating between devices in a wireless communication system, a terminal that allocates resources for communication between devices or a terminal existing within a service range of a base station can be efficiently allocated resources for communication between devices.

1 is a diagram showing a wireless communication system to which the present invention is applied.
2 is a diagram for explaining the concept of D2D communication based on a cellular network applied to the present invention.
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 method of operating a buffer status report for inter-device communication by a terminal according to an embodiment of the present invention.
9 is a flowchart illustrating a method of operating a buffer status report for communication between terminals by a base station according to 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, in the present specification, the content related to the present invention will be described in detail through exemplary drawings and embodiments along with the content of the present invention. In adding reference numerals to components of each drawing, it should be noted that the same components have the same numerals as much as possible, even if they are displayed on different drawings. In addition, in describing the embodiments of the present specification, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

In addition, this specification describes a wireless communication network, and the work performed in the wireless communication network is performed in the process of controlling the network and transmitting data in a system (for example, a base station) that manages the wireless communication network, or Work may be performed in a terminal included in the network.

1 is a diagram showing 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 may transmit and receive data wirelessly. In addition, the wireless communication system may support device to device (D2D) communication between terminals. A wireless communication system supporting D2D communication will be described later.

In the wireless communication system 10, a base station (BS) 11 may provide a communication service to a terminal existing within transmission coverage of the base station through a specific frequency band. Coverage serviced by a base station may also be expressed in terms of a site. A site may include a plurality of areas 15a, 15b, and 15c that may be referred to as sectors. Each sector included in the site may be identified based on a different identifier. Each of the sectors 15a, 15b, and 15c may 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, and a femto base station ( Femto eNodeB), Home eNodeB (HeNodeB), relay, and Remote Radio Head (RRH).

The terminal 12 may be fixed or mobile, and includes a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, and a personal digital assistant (PDA). , wireless modem, handheld device, etc.

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

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

There is no limitation on multiple access techniques applied to the wireless communication system 10. For example, code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), single carrier-FDMA (SC-FDMA), OFDM-FDMA Various multiple access schemes such as , OFDM-TDMA, and OFDM-CDMA may be used. These modulation techniques demodulate signals received from multiple users of the communication system to increase the capacity of the communication system. In addition, a time division duplex (TDD) method in which transmission is performed using different times or a frequency division duplex (FDD) method in which transmission is performed using different frequencies may be used for uplink transmission and downlink transmission.

The layers of the radio interface protocol between the terminal and the base station are based on the lower three layers of the open system interconnection (OSI) model, which is widely known in communication systems. It can be divided into a second layer (L2) and a third layer (L3).

A physical layer belonging to the first layer provides an information transfer service using a physical channel. The physical layer is connected to a media access control (MAC) layer, which is an upper layer, through a transport channel. Data is transmitted through a transport channel between the MAC layer and the physical layer. Transmission channels are classified according to how data is transmitted through the air interface. In addition, data is transmitted through physical channels between different physical layers (ie, between physical layers of a terminal and a base station). The physical channel may be modulated using OFDM (Orthogonal Frequency Division Multiplexing), and utilizes time, frequency, and space created by a plurality of antennas as radio resources.

For example, among the physical channels, a physical downlink control channel (PDCCH) informs the terminal of resource allocation of a paging channel (PCH) and a downlink shared channel (DL-SCH) and hybrid automatic repeat request (HARQ) information related to the DL-SCH, It may carry an uplink scheduling grant that informs the terminal of resource allocation of uplink transmission. In addition, PCFICH (Physical Control Format Indicator CHannel) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted in every subframe. In addition, PHICH (Physical Hybrid ARQ Indicator CHannel) carries a HARQ ACK/NAK signal in response to uplink transmission. In addition, PUCCH (Physical Uplink Control CHannel) carries uplink control information such as HARQ ACK/NAK, scheduling request, and CQI for downlink transmission. In addition, Physical Uplink Shared CHannel (PUSCH) carries UpLink Shared CHannel (UL-SCH). PUSCH may include Channel State Information (CSI) information such as HARQ ACK/NACK and CQI when necessary according to configuration 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 mapping between logical channels and transport channels and multiplexing or demultiplexing of MAC SDUs (Service Data Units) belonging to the logical channels into transport blocks provided as physical channels on the transport channels. can do. The MAC layer provides services to the RLC layer through logical channels. A 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, services provided from the MAC layer to the upper layer include data transfer or radio resource allocation.

The RLC layer may perform concatenation, segmentation, and reassembly of RLC SDUs. The RLC layer has three modes: Transparent Mode, Unacknowledged Mode, and Acknowledged Mode, to guarantee various Quality of Service (QoS) required by the Radio Bearer (RB). operation mode is provided.

The PDCP layer may perform user data delivery, header compression and ciphering, and control plane data delivery and encryption/integrity protection.

The RRC (Radio Resource Control) layer belonging to the third layer of the OSI model is responsible for controlling logical channels, transport channels, and physical channels in relation to configuration, re-configuration, and release of RBs. . RB means a logical path provided by the first layer (PHY layer) and the second layer (MAC layer, RLC layer, PDCP layer) for data transfer between the terminal and the network. Configuring an RB means a process of specifying characteristics of a radio protocol layer and a channel and setting specific parameters and operation methods in order to provide a specific service. RBs may be divided into Signaling RBs (SRBs) and Data RBs (DRBs). The SRB is used as a passage for transmitting RRC messages and Non-Access Stratum (NAS) messages in the control plane, and the DRB is used as a passage for transmitting user data in the user plane. Hereinafter, simply expressing RB without distinction between SRB and DRB means DRB.

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

D2D communication may refer to a technology for directly transmitting and receiving data between terminals. Hereinafter, in an embodiment of the present invention, it is assumed that the terminal supports D2D communication. In addition, D2D may be replaced with an expression called proximity based service (ProSe) or ProSe-D2D. The use of the term ProSe for D2D means that the meaning of a technology for directly transmitting and receiving data between terminals is not changed, but the meaning of an access-based service can be added.

Recently, a method of performing discovery and direct communication between devices in-coverage or out-of-coverage of a network for purposes such as public safety has been proposed. being studied A terminal transmitting a signal based on communication between terminals may be referred to as a transmitting terminal (Tx UE), and a terminal receiving a signal based on communication between terminals may be defined as a receiving terminal (Rx UE). The transmitting terminal may transmit a discovery signal, and the receiving terminal may receive the discovery signal. The respective roles of the transmitting terminal and the receiving terminal may be changed. Meanwhile, a signal transmitted by a transmitting terminal may be received by two or more receiving terminals.

In a cellular system, if terminals in close proximity perform D2D communication, the load of the base station may be distributed. In addition, when adjacent terminals perform D2D communication, since the terminals transmit data over a relatively short distance, transmission power consumption and transmission latency of the terminals can be reduced. In addition, from the point of view of the entire system, frequency use efficiency can be improved because existing cellular communication and D2D communication use the same resources.

D2D communication can be divided into a communication method of a terminal located within network coverage (base station coverage) and a communication method of a terminal located outside network coverage (Out-of-coverage).

Referring to FIG. 2 , communication between a first terminal 210 located in a first cell and a second terminal 220 located in a second cell, a third terminal 230 located in the first cell and a terminal located in the first cluster Communication between the four terminals 240 may be D2D communication within network coverage. 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 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 in charge of allocating resources. The cluster header may include an Independent Synchronization Source (ISS) for synchronization of out-of-coverage terminals.

D2D communication can be divided into a discovery procedure for performing discovery for communication between UEs and a direct communication procedure for transmitting and receiving control data and/or traffic data between UEs. D2D communication can be used for various purposes. For example, D2D communication within network coverage may be used for public safety, ultra-low latency service, commercial purpose service, and the like. D2D communication 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 on transmission resources and/or reception resources usable for D2D communication between the first terminal 210 and another terminal (eg, the second terminal 220).

Upon receiving the D2D resource allocation information from the base station, the first terminal 210 may 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 may perform D2D communication based on D2D resource allocation information. Specifically, the second terminal 220 may obtain information about D2D communication resources of the first terminal 210 . The second terminal 220 may receive data transmitted from the first terminal 210 through a resource indicated by the information on the D2D communication resource of the first terminal 210 .

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

Here, the physical layer control data for synchronization in D2D communication includes information transmitted through a synchronization channel, and may be provided through, for example, a Physical D2D Synchronization CHannel (PD2DSCH) channel. The physical layer control data for the data communication includes Scheduling Assignment (SA) information, and may be provided through a channel similar to or identical to a PUSCH format for D2D communication. In D2D communication, actual traffic data that is distinguished from physical layer control data may be expressed as D2D data.

Additionally, a scheme for transmitting higher layer control data in addition to the physical layer in D2D communication may be defined.

During D2D communication, the terminal may operate in the first transmission mode and the second transmission mode. The first transmission mode is a mode in which the UE can perform D2D communication only when resources for D2D communication are allocated from the base station, and the base station transmits the D2D grant to the transmitting UE. The D2D grant is based on parameter information to be determined by the base station, resource allocation information for the SA, and SA (Scheduling Assignment) information, which is control information to be secured for D2D data reception by the receiving terminal during D2D communication. The resource allocation information for the indicated data is instructed to the transmitting terminal. Parameter information to be determined by the base station includes resource allocation information for data indicated by the SA. The D2D grant is delivered to the transmitting terminal through downlink control information (DCI), and may be delivered through PDCCH or EPDCCH. The D2D grant is control information that is distinguished for D2D use through an uplink grant or a D2D-RNTI allocated to each terminal. The D2D grant may also be expressed as an SA/data grant. The D2D-RNTI is an identifier for performing D2D communication, and may be called 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 that 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 instructions of the base station, and the terminal can transmit D2D data by internally selecting a resource to be used among available radio resources during D2D communication. The UE receives information indicating that a specific cell in the base station can support D2D through System Information Block (SIB)/dedicated signaling and D2D resource pool information for the second transmission mode provided from the base station. Only when it exists, it can operate in the second transmission mode only for the specific cell.

However, if the base station does not allow operation in the second transmission mode, that is, information indicating that a specific cell within the base station can support D2D exists, but D2D resource pool information for the second transmission mode is provided from the base station. If not, it cannot operate in the second transmission mode. In addition, when the D2D resource pool information for the second transmission mode is valid only in the RRC connected mode, the RRC idle (IDLE) mode terminal operates in the second transmission mode even if there is the D2D resource pool information for the second transmission mode. Can not.

However, when the terminal is located outside the network service area, that is, in case of the 'Any Cell Selection' mode, which is a case where the terminal is in RRC idle mode but fails to select a serviceable cell, the UICC (Universal Subscriber Identity (USIM) of the terminal Module (Integrated Circuit Card) or the like, or D2D resource pool information for the second transmission mode received through the base station in the previous network service area. can work as

In a wireless communication system, a terminal reports its buffer status to the base station in order to be allocated resources necessary for transmitting uplink data (data to be transmitted to the base station) existing in a buffer in the terminal, and the base station reports the buffer status reported by the terminal. Based on the information, resources to be allocated to each terminal are scheduled.

Therefore, when the wireless communication system supports D2D communication, the base station needs to schedule resources required for terminals existing in coverage to transmit data through D2D communication. To this end, the base station needs to schedule the terminal's buffer It is necessary to know how much data (hereinafter referred to as D2D data) to be transmitted through D2D communication exists. The terminal may notify the base station how much data to be transmitted through D2D communication exists in the buffer in the terminal through the following procedure.

3 is a diagram illustrating a process in which a terminal transmits 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.

In a wireless communication system, when data to be transmitted through a D2D link exists in a DRB configured for D2D in a terminal capable of D2D communication, 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 ProSe-BSR is triggered, the terminal transmits a scheduling request (SR: Scheduling Request) to the base station to induce allocation of resources for transmission of D2D data and ProSe-BSR (S320), and uplink for SR from the base station A grant (UL grant) is received (S330). Here, the SR is transmitted to the base station through PUCCH. The SR may be used by sharing the SR used in the existing wireless communication system, or a resource additionally allocated for the SR for D2D by distinguishing it from the SR may be used. When the SR for D2D is defined differently from the existing SR, the SR may be defined by being classified as ProSe-SR. For convenience of description below, SR and ProSe-SR are collectively referred to as SR without distinction.

When an SR is triggered, the SR is pending until cancelled. On the other hand, the terminal does not accept all the data pending transmission of the uplink grant, or the MAC PDU (Media Access Control Protocol Data Unit) is configured and the MAC PDU is configured in a buffer state including the last event. In the case of including the ProSe-BSR, all pending SRs are canceled and a timer (sr-ProhibitTimer) for preventing SRs from being transmitted is stopped.

Specifically, when the SR is triggered and there is no currently pending SR, the UE sets the SR count (SR_COUNTER) value to 0. However, if the SR is pending and there are valid PUCCH resources to send the SR in this Transmission Time Interval (TTI), this TTI is not part of the measurement gap and the sr-ProhibitTimer is not in progress , If the SR_COUNTER value is less than the maximum number of SR transmissions, the SR count value is increased by 1, and the SR-ProhibitTimer is started after instructing the physical layer to transmit the SR signal through the PUCCH. However, if the value of SR_COUNTER is greater than or equal to the maximum number of transmissions, release of PUCCH and SRS is notified to RRC, and all configured downlink allocations and uplink grants are cleared. Then, the random access procedure is initialized and all pending SRs are canceled.

Meanwhile, when the SR is pending but there is no UL-SCH resource available for transmission in any TTI, the UE initializes a random access procedure and cancels all pending SRs. Accordingly, the ProSe-BSR may be delivered to the base station through the random access procedure.

Upon receiving the uplink grant for the SR, the UE transmits the ProSe-BSR to the base station (S340). When receiving the D2D grant for ProSe-BSR from the base station (S350), data is transmitted to the target terminal using resources allocated for transmission of D2D data (S360). As such, the ProSe-BSR is for the UE to notify the serving base station of information about the amount of transmittable data present in the D2D link buffer. In the present invention, as an example, the ProSe-BSR procedure is illustrated as being performed after SR transmission. However, if the UE receives an uplink grant sufficient to transmit ProSe-BSR before SR transmission, ProSe-BSR transmission may be performed before SR transmission.

The base station configures a periodic BSR timer (periodicBSR-Timer) and a retransmission BSR timer (retxBSR-Timer) for ProSe-BSR through signaling defined in the RRC layer, and thus ProSe-BSR procedure for logical channels in each terminal. to control A logical channel group (LCG) may be configured in each terminal through optional signaling (optionally configured by RRC signal by eNB), and ProSe-BSR is performed for the LCG.

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

Here, the LCG, which is the target of the BSR for the wireless communication system, has only logical channels (DCCH, DTCH) set for data transmission of the wireless communication system as components, and the index of the LC for this can be 0 to 11 there is. On the other hand, the LCG that is the target of the BSR for D2D communication has only the logical channels (PTCH) configured for data transmission of the D2D as components, and the index of the LC for this is the index of the LC for the wireless communication system (0 ~ 11), may have LC indexes 0 to 11 for D2D communication.

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

The UE configures ProSe-BSR based on data buffered in each LCG in the UE. Up to 4 LCGs can be configured in the UE. The format of ProSe-BSR is a short BSR for reporting the buffer status corresponding to one LCG, or a long BSR or truncated BSR for reporting the buffer status corresponding to 4 LCGs. etc. may exist.

For the ProSe-BSR procedure, the UE must consider suspended radio bearers (RBs) and all non-reserved RBs. ProSe-BSR can be divided into regular ProSe-BSR, padding ProSe-BSR, and periodic ProSe-BSR.

The regular ProSe-BSR is capable of transmitting to a logical channel having a higher priority than other logical channels in which data transmittable in the logical channel included in the LCG exists in the RLC entity or PDCP entity, or in which transmittable data already exists. Uplink transmittable Triggered when data is present. In addition, the regular ProSe-BSR is triggered even when the retransmission BSR timer for the ProSe-BSR expires and the terminal has transmittable data on a logical channel within the LCG.

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

Alternatively, the padding ProSe-BSR is triggered when uplink resources and resources for BSR transmission for the wireless communication system are allocated and the number of remaining padding bits is equal to or greater than the 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 the long ProSe-BSR format when more than one LCG (at least two LCGs) have data to be transmitted in the TTI in which the corresponding ProSe-BSR is transmitted, and otherwise (one When only the LCG of has data to be transmitted), it may be configured in a short BSR format and transmitted.

The padding ProSe-BSR is equal to or larger than the sum of the short ProSe-BSR and the short ProSe-BSR subheaders in the number of padding bits included in the MAC PDU, but the long ProSe-BSR and the long ProSe-BSR subheaders are used. A truncated ProSe-BSR for the LCG containing the logical channel with the highest priority for data transmission if more than one LCG has data to be transmitted in the TTI in which the ProSe-BSR is transmitted that is smaller than the combined size It can be configured in a format and transmitted. In other cases, it is transmitted in a short ProSe-BSR format. Alternatively, when only the short ProSe-BSR format is available, the short ProSe-BSR format is always transmitted.

Meanwhile, the padding ProSe-BSR is transmitted in the long ProSe-BSR format when the number of padding bits is equal to or greater than the sum of the long ProSe-BSR and the long ProSe-BSR subheader. Alternatively, when only the short ProSe-BSR format is possible, the short ProSe-BSR format is always transmitted.

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

At this time, one MAC PDU includes only one ProSe-BSR MAC control element even if multiple ProSe-BSRs are triggered. In addition, if regular ProSe-BSR or periodic ProSe-BSR can be transmitted, it always takes precedence over padding ProSe-BSR. In addition, upon confirming reception of an indicator indicating transmission of new data for all UL-SCHs, the UE restarts the retransmission BSR timer. All triggered BSRs shall be canceled when the BSR is included in the MAC PDU.

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

If the UE is requested to transmit multiple MAC PDUs in one TTI, one padding ProSe-BSR may be included in any MAC PDUs that do not include regular or periodic ProSe-BSR. Accordingly, one padding ProSe-BSR may be included in any MAC PDUs containing a regular or periodic BSR for a wireless communication system. That is, although the padding BSR has a higher priority than the padding ProSe-BSR, the padding ProSe-BSR may be included first only for any MAC PDU including the regular or periodic BSR. This may include a case where transmission of a single MAC PDU is requested in one TTI. All ProSe-BSRs always reflect the buffer state after MAC PDUs to be transmitted are configured based on the D2D grant previously received by the UE based on the TTI in which the ProSe-BSR is transmitted. Each LCG reports one buffer status value per TTI, and the buffer status value is reported through the ProSe-BSR for the LCG in all ProSe-BSRs. That is, one ProSe-BSR value must be transmitted per LCG in the same TTI, and the buffer status value for the LCG must be the same value in all ProSe-BSRs transmitted in the same TTI. Meanwhile, it is not allowed for the padding ProSe-BSR to cancel the regular or periodic ProSe-BSR. Padding ProSe-BSR is triggered for a specific MAC PDU, and the triggering of the padding ProSe-BSR is canceled when a specific MAC PDU is generated.

However, in the case of an existing wireless communication system, all triggered BSRs can send all pending data, but are canceled when receiving an uplink grant that cannot additionally send a 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 data to be transmitted in uplink, but cannot include the BSR MAC CE including the MAC subheader.

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

2. When MAC PDU for uplink transmission includes BSR.

As described above, during D2D communication, the base station needs to schedule resources required for terminals existing in coverage to transmit data through D2D communication. How much data (hereinafter referred to as D2D data) to be transmitted may be informed through BSR. However, in an exceptional case (for example, when the terminal cannot maintain an RRC connection state with the base station), the terminal does not allocate resources necessary for transmitting data through the D2D communication from the base station, and uses D2D resources selected by itself. You should be able to transmit data. To this end, the first transmission mode and the second transmission mode may be supported during D2D communication.

However, when the terminal is configured or operating in the second transmission mode, resources for D2D transmission cannot be controlled by the base station. Therefore, the base station must reserve the corresponding resource for D2D transmission. The reserved resources may be determined by the number of terminals capable of operating in the second transmission mode and expected resource consumption of each terminal.

If the number of resources reserved for the second transmission mode increases, since the total resources are limited, the amount of resources available for general wireless communication (eg, LTE communication) will decrease, which will affect the overall system transmission rate. can Therefore, the base station can reduce the number of terminals capable of operating in the second transmission mode in order to reduce the amount of resources 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 UE is changed from the first transmission mode to the second transmission mode, or the UE set in the first transmission mode operates in the second transmission mode, the buffer already triggered in the UE When a status report exists, it has not yet been determined how to operate the triggered buffer status report.

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

A terminal supporting D2D communication may perform D2D communication when a user of the terminal configures the terminal to enable D2D communication through a user interface (UI). Alternatively, a network (eg, a D2D server that manages ProSe (Proximity Services) ID and ProSe Application ID of a terminal using D2D communication, a serving base station of the corresponding terminal, etc.) allows the user of the terminal to perform D2D communication. It is also possible to finally determine whether D2D communication is possible for a terminal set to do so. That is, the terminal may perform D2D communication only when D2D communication is permitted by the network even if the user of the terminal sets D2D communication to be possible. Information on whether D2D communication is possible may be displayed on the screen of the terminal.

Resources for D2D communication may be allocated by a terminal (hereinafter referred to as a cluster head) or a base station responsible for allocating resources for D2D communication during D2D communication. In this case, when performing D2D communication, the UE must transmit a BSR for D2D data to the base station or the cluster head. Hereinafter, for convenience of description, the base station and the cluster head are collectively referred to as a base station. In addition, BSR for D2D data is referred to as ProSe-BSR.

Referring to FIG. 4 as an embodiment, ProSe-BSR may be triggered by the same triggering condition as the existing BSR for uplink data (S410). In this case, an LCID different from that of the existing BSR for uplink data may be used for ProSe-BSR. For example, a new LCID for distinguishing a short ProSe-BSR, a truncated ProSe-BSR, and a long ProSe-BSR may be allocated to the ProSe-BSR. Alternatively, one ProSe-BSR format may be used as a BSR for D2D data, and one new LCID indicating this may be used.

When ProSe-BSR is triggered, the UE may determine whether the current D2D transmission mode of the UE is set to the second transmission mode (S420). As a result of the check, the terminal can cancel the triggered ProSe-BSR if it is set to the second transmission mode (S430), and if it is not set to the second transmission mode, uplink resource allocation based on the ProSe-BSR triggered by the base station At this time, the ProSe-BSR MAC CE may be included in the MAC PDU and transmitted to the base station (S440).

For example, in an exceptional case as described above (when an RRC reset procedure related timer and/or a handover related timer are in progress or started) or when the base station changes the D2D transmission mode of the UE to the second transmission mode. When the terminal changes the D2D transmission mode set in the terminal from the first transmission mode to the second transmission mode due to the case of permission, etc., the terminal transmits all ProSe-BSRs that have been triggered for operation in the first transmission mode. can be canceled Here, the first transmission mode refers to a mode for performing the D2D communication using resources allocated from a base station, and the second transmission mode includes second transmission mode resource pool information for the D2D communication. It may refer to a mode in which the D2D communication is performed using In other words, all triggered ProSe-BSRs may be canceled when the D2D communication mode set in the terminal changes from the first transmission mode to the second transmission mode due to an exceptional case, and the D2D transmission set in the terminal by the terminal itself or the base station When the mode is changed from the first transmission mode to the second transmission mode, it may be canceled.

The UE operating in the first transmission mode and the UE operating in the second transmission mode receive the following D2D resource pool information included in reception resource pool (commRxPool) and common transmission resource pool (commTxPoolNormalCommon) information in order to receive D2D data. should be checked. Here, the reception resource pool is information indicating resources that are allowed to be received by D2D terminals operating in RRC IDLE and Connected modes, and the common transmission resource pool is information in which transmission is allowed by D2D terminals operating in RRC IDLE mode. Information that points to resources.

- SA resource pool information

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

- TDD configuration information (included only when the reception resource pool information is a neighboring cell and operates in TDD)

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

All of the above resource pool information can be transmitted to all terminals within a corresponding cell through a broadcast channel, and a terminal wishing to perform D2D communication operates D2D data that the corresponding terminal wishes to receive in a radio resource based on all of the resource pool information. It is necessary to perform a monitoring operation to receive the In the reception resource pool information, transmission resource pool information provided as a dedicated service by the base station for a transmission operation in the first transmission mode or the second transmission mode only for the terminal operating in the RRC connected mode in the corresponding cell can be included The first transmission mode or second transmission mode transmission resource pool information provided exclusively should be set so that there are no physical resources colliding with each other in order to avoid mutual interference. In addition, if resources that collide with each other occur because the amount of resources allocated for ProSe communication is not sufficient, the range of mutual interference is limited to the same resource range by making the characteristics of the transmission signals set for each cell, such as the cyclic prefix length, the same. Cooperation between base stations must be made so that this can be done.

Here, the timer related to the RRC resetting procedure may be a T311 timer, and the timer related to handover may be a T304 timer, which may be defined as shown in Table 1 and Table 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 the RRC connection re-establishment procedure; In case of handover to E-UTRA, perform the actions defined in the specifications applicable for the source RAT.

Referring to Table 1, the T311 timer starts when an RRC connection re-establishment procedure is initiated. In addition, when an appropriate Evolved UMTS Terrestrial Radio Access (E-UTRA) cell is selected or a cell using another radio access technology (RAT) is selected, it is stopped. In addition, it expires when entering the RRC idle state. Referring to Table 2, the T304 timer sends an RRC connection reconfiguration message including mobility control information. or when a message (MobilityFromEUTRACommand message) including a cell change order is received. 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 is started during handover within the LTE network or during inter-RAT handover to the LTE system, and is stopped when the handover is successfully completed. A periodic BSR-timer and a retransmission BSR timer (retxBSR-timer) may be reset. The periodic BSR timer and the retransmission BSR timer configured for the initialized ProSe-BSR may be set to a startable state when the D2D transmission mode of the UE is changed from the second transmission mode to the first transmission mode.

In addition, as shown in FIG. 5, when the UE changes the D2D transmission mode set in the UE from the first transmission mode to the second transmission mode (S510), it can determine whether resource pool information for the second transmission mode exists. Yes (S520). Here, when the D2D transmission mode set in the UE is changed due to an exceptional case, the first transmission mode may be changed to a 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 is transmission resource pool information for an exceptional case defined separately from the resource pool information for the exceptional case ( commTxPoolExceptional). Therefore, when 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 resource pool information for the fallback mode exists (S520). Here, the resource pool information to be preferentially applied in the fallback mode may be general common transmission resource pool information or transmission resource pool information for an exceptional case. If at least one of the two pieces of resource pool information exists, the UE transmits all logical channels (PTCH: ProSe Communication Traffic Channel) configured for the D2D communication between the UEs in order to prevent ProSe-BSR from triggering any more. It can be excluded from the triggering target of ProSe-BSR (S530). However, since the terminal cannot operate in the second communication mode when neither of the two pieces of resource pool information exists, the terminal may suspend data transmission for the PTCH (S540).

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

In the case of handover, after the terminal completes handover to the target base station (immediately after the T304 timer is stopped), it is changed to the first transmission mode and is ready for handover to operate, that is, the source base station transfers the current terminal to the target base station. When a handover request message including terminal information including ProSe configuration information such as transmission mode is transmitted and the target base station transmits a message allowing handover to the source base station based on this, ProSe configuration information necessary for the first transmission mode operation is included. and deliver it The configuration information may include D2D-RNTI information to be used in the target base station, configuration information related to ProSe-BSR, and SA pool information.

Meanwhile, in another embodiment, as shown in FIG. 7, when the D2D transmission mode set in the terminal is changed from the first transmission mode to the second transmission mode due to an exceptional case (S710), D2D communication is performed. Whether or not to cancel ProSe-BSR may be determined according to whether data exists. For example, when the D2D transmission mode set in the UE is changed from the first transmission mode to the second transmission mode as the RRC reset procedure related timer and/or the handover related timer are in progress, the UE transmits data through D2D communication. ProSe-BSR can be canceled only when there is no (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. Even in this case, the terminal can determine whether resource pool information for the second transmission mode exists. In addition, when the second transmission mode resource pool information exists, all PTCHs may be excluded from triggering targets of ProSe-BSR, and data transmission for all PTCHs may be stopped when the second transmission mode resource pool information does not exist.

Meanwhile, as shown in FIG. 8 as another embodiment, the terminal may operate in the second transmission mode while the first transmission mode is set without changing the D2D transmission mode (S810). This may be performed when the base station does not propose the D2D transmission mode of the UE and/or when at least one of the timer related to the RRC reset procedure and the timer related to the handover is in progress or started. In this case, even though the terminal can transmit D2D data in the second transmission mode, upon receiving the D2D grant from the base station, the terminal transmits the D2D data in the first transmission mode. That is, the terminal may maintain the first transmission mode as the D2D transmission mode. In this case, even if the UE starts operating in the second transmission mode, it may not cancel ProSe-BSR triggering because it is set to the first transmission mode. However, the terminal determines whether data to be transmitted through D2D communication exists, and if data to be transmitted through D2D communication does not exist, the triggered BSR can be canceled (S820).

On the other hand, the terminal can change the D2D transmission mode to the second transmission mode when the exceptional case is resolved but the RRC connection mode cannot be maintained (ie, when the RLF timer or the handover timer expires). . In addition, D2D data may be transmitted based on the secured second transmission mode D2D resource pool information.

Meanwhile, as another embodiment, in the exceptional case, the UE cancels the ProSe-BSR through a reset operation of the MAC entity. Reset of the MAC entity may proceed according to a request of an upper layer. The MAC entity reset operation includes the following operations.

- Stop all running timers.

- Values of new data indicators (NDIs) for all uplink HARQ processes other than uplink HARQ processes related to PSCH are set to 0.

- 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.

- Soft buffers for all DL HARQ processes other than DL HARQ processes related to PSCH are flushed.

- For each DL HARQ process other than DL HARQ processes related to PSCH, transmission for any TB received next is considered as very first transmission.

Here, 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 occurs due to the start of the RRC reconfiguration procedure, the UE suspends all DRBs except for the DRBs related to PTCH, which is a logical channel related to the D2D data transmission, when the RRC reconfiguration procedure starts. If the exceptional case occurs due to the start of a handover procedure (when Mobility Control Information (MCI) is included in the RRC reconfiguration message), the terminal is a logical channel related to the D2D data transmission at the start of the handover procedure Re-establishment of RLC and PDCP in all DRBs except DRBs related to PTCH.

If 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 ProSe-BSR is canceled.

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

9 is a flowchart illustrating a method of operating a buffer status report for communication between terminals by a base station according to an embodiment of the present invention.

Referring to FIG. 9 , the base station may transmit a second transmission mode permission message to a first terminal within coverage (S910). Here, the first terminal may be a terminal for which the D2D transmission mode is set to the first transmission mode. Upon receiving the second transmission mode permission message, the first terminal may change the D2D transmission mode to the second transmission mode in the above-described exceptional case.

When the first terminal changes to the second transmission mode, the base station may receive ProSe-BSR from a second terminal set to the first transmission mode other than the first terminal (S920). Then, the base station may allocate resources for D2D communication in the second terminal based on the received ProSe-BSR (S930), and the second terminal receiving this may perform D2D communication with the target terminal using the allocated resources. there is.

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

For the release operation, release information may be included in configuration information about transmission resources in the RRC reconfiguration message and transmitted. Alternatively, when the terminal receives an RRC reconfiguration message including mobility control information (MCI) from the base station, the terminal may perform an operation of releasing configuration information on transmission resources in the RRC reconfiguration message by itself.

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

Alternatively, if the configuration for the transmission resources for the first transmission mode or the second transmission mode is released as described above, the terminal enters the fallback mode when transmitting data using the transmission resource pool information for exceptional cases received through the system information. It can work. Although the configuration information for the first transmission mode or the second transmission mode configured in the source base station is released due to the handover operation as described above, since the RRC connected mode is maintained, transmission resource pool information for an exceptional case that can be used in the RRC connected mode as well. QoS of ProSe communication can be maintained using

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

If there is no transmission resource pool information provided from the target base station or is not provided, transmission resource pool information in system information previously received from the source base station may be used.

After the handover is completed, the terminal may maintain the second transmission mode or the fallback mode until information for configuring a transmission resource among configurations for a ProSe communication operation is received from the target base station and reflected therein.

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 may maintain the reception operation but stop all transmission operations. That is, it may operate in ProSe transmission stop mode. As described above, since the configuration information for the first transmission mode or the second transmission mode configured in the source base station is released due to the handover operation, the ProSe transmission operation is impossible. This is the physical resource in the transmission resource pool dedicated by the base station for the transmission operation in the first transmission mode or the second transmission mode only for the terminal operating in the RRC connected mode in the source base station and dedicated to the target base station. (dedicated) This is because when a collision may occur between physical resources in a transmission resource pool, a ProSe communication signal transmitted based on the transmission resource pool information of the source base station may act as interference with other ProSe communication signals in the target base station. Accordingly, the transmission operation is stopped to remove such an interference factor.

After the handover is completed, the terminal may maintain the transmission stop mode until information for configuration of transmission resources among configurations for ProSe communication operation is received from the target base station and reflected therein.

Here, the source base station and the target base station may be different base stations or the same base station. In the case of the same base station, the frequency band may or may not change due to handover. If the base station or frequency band does not change despite performing the handover operation, the base station determines that the RRC parameters between the base station and the terminal do not match each other, or that the downlink or uplink synchronization is not properly performed, or the base station determines that security It is time to change the key value shared by the base station and the terminal used for

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 terminal-to-device 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, a radio frequency (RF) 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 radio signals. For example, the RF unit 1010 may receive the second transmission mode permission message and D2D resource allocation information posted in this specification from the base station 1050 . In addition, the RF unit 1010 may transmit an uplink signal such as ProSe-BSR disclosed in this specification to the base station 1050.

The processor 1005 implements the functions, processes and/or methods proposed herein. Specifically, the processor 1005 causes all steps according to FIGS. 4 to 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 determining unit 1006 determines whether 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 a timer related to an RRC reset procedure and/or a timer related to handover is in progress. The cancellation unit 1008 cancels all ProSe-BSRs that have been triggered when the timer related to the RRC resetting procedure and/or the timer related to handover are in progress. At this time, a periodic BSR-timer and a retransmission BSR timer (retxBSR-timer) configured for ProSe-BSR may be reset.

Meanwhile, the processor 1005 may check whether resource pool information for the second transmission mode or resource pool information for the fallback mode exists. If at least one of the two resource pool information exists, all PTCHs configured for the D2D communication between the terminals may be excluded from the triggering target of the ProSe-BSR so that the ProSe-BSR is no longer triggered. there is. The processor 1005 cannot operate in the second communication mode when the two pieces of resource pool information do not exist, and thus may suspend data transmission for the PTCH.

Thereafter, when it is determined by the timer determination unit 1007 that the timer related to the RRC resetting procedure and/or the timer related to the handover are stopped, the processor 1005 determines that the exceptional case is resolved and initializes the periodic BSR timer and It can start the retransmission BSR timer and restart the normal ProSe-BSR procedure.

The memory 1015 stores resource pool information for the second transmission mode according to the present specification, information on whether the second transmission mode is allowed, and the like, and transmits the second transmission to the processor 1005 according to a request of the processor 1005. Resource pool information for the mode may be provided.

The base station 1050 includes a radio frequency (RF) unit (RF) unit 1055, a processor 1060, and a memory 1065. The memory 1065 is connected 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 radio signals. The processor 1060 implements the functions, processes and/or methods proposed herein. Operations of the base station 1050 in the above-described embodiment may be implemented by the processor 1060. The processor 1060 generates the second transmission mode permission message disclosed in this specification 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 checking unit 1062, and a D2D resource allocation 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 may be transmitted to the terminal through the RF unit 1055. The ProSe-BSR checker 1062 may check the ProSe-BSR received from the terminal 1000 . The D2D resource allocator 1063 may allocate resources for D2D communication to the terminal 1000 operating in a different first transmission mode based on the ProSe-BSR.

A processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and/or data processing devices. 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 radio signals. When this embodiment is implemented as software, the above-described technique may be implemented as a module (process, function, etc.) that performs the above-described functions. A module can be stored in memory and executed by a processor. The memory may be internal or external to the processor, and may be coupled with the processor in a variety of well-known means.

In the exemplary system described above, the methods are described on the basis of a flow chart as a series of steps or blocks, but the invention is not limited to the order of steps, some steps may occur in a different order or concurrently with other steps as described above. can Further, those skilled in the art will understand that the steps shown in the flowcharts are not exclusive, and that other steps may be included or one or more steps of the flowcharts may be deleted without affecting the scope of the present invention.

The foregoing embodiments include examples of various aspects. It is not possible to describe all possible combinations to represent the various aspects, but those skilled in the art will recognize that other combinations are possible. Accordingly, it is intended that the present invention cover all other substitutions, modifications and variations falling within the scope of the following claims.

Claims (12)

As a method of operating a base station,
Transmitting a CommTxPoolExceptional field indicating resource pool information for direct data transmission to a wireless device in an exceptional case;
Transmitting one or more messages including information of a resource allocation mode for direct data transmission between the wireless device and another wireless device to the wireless device;
sending one or more scheduling messages to the wireless device for direct data transmission between the wireless device and the other wireless device;
The resource pool information for direct data transmission in an exceptional case, when the wireless device determines a radio link failure (RLF) associated with a problem of a Radio Resource Control (RRC) connection with the base station, in the exceptional case causing a wireless device to cancel buffer status reports (BSRs) for the direct data transmission scheduled by the base station and perform the direct data transmission. 2. The method of claim 1, wherein the CommTxPoolExceptional field is transmitted to the wireless device via a system information block. 2. The method of claim 1, wherein the CommTxPoolExceptional field is transmitted to the wireless device over a broadcast channel. According to claim 1,
Transmitting information about a resource selection mode that causes the wireless device to change from the resource allocation mode to a resource selection mode based on the determined RLF to the wireless device. As a base station,
transceiver; and
a processor operably coupled to the transceiver, the processor comprising:
Sending a CommTxPoolExceptional field indicating resource pool information for direct data transmission to the wireless device in an exceptional case;
transmit one or more messages including information of a resource allocation mode for direct data transmission between the wireless device and another wireless device to the wireless device;
configured to transmit one or more scheduling messages to the wireless device for direct data transmission between the wireless device and the other wireless device;
The resource pool information for direct data transmission in an exceptional case, when the wireless device determines a radio link failure (RLF) associated with a problem of a Radio Resource Control (RRC) connection with the base station, in the exceptional case A base station that causes a wireless device to cancel buffer status reports (BSRs) for the direct data transmission scheduled by the base station and perform the direct data transmission. 6. The base station of claim 5, wherein the CommTxPoolExceptional field is transmitted to the wireless device via a system information block. 6. The base station of claim 5, wherein the CommTxPoolExceptional field is transmitted to the wireless device over a broadcast channel. The method of claim 5, wherein the processor,
and transmit information about a resource selection mode that causes the wireless device to change from the resource allocation mode to a resource selection mode based on the determined RLF, to the wireless device. A computer readable recording medium containing instructions,
The instructions, when executed by a processor operatively connected to the transceiver, cause the base station to:
sending a CommTxPoolExceptional field indicating resource pool information for direct data transmission to the wireless device in an exceptional case;
transmit one or more messages including information of a resource allocation mode for direct data transmission between the wireless device and another wireless device to the wireless device;
send one or more scheduling messages to the wireless device for direct data transmission between the wireless device and the other wireless device;
The resource pool information for direct data transmission in an exceptional case, when the wireless device determines a radio link failure (RLF) associated with a problem of a Radio Resource Control (RRC) connection with the base station, in the exceptional case A computer readable medium that causes a wireless device to cancel buffer status reports (BSRs) for the direct data transfer scheduled by the base station and perform the direct data transfer. 10. The computer readable medium of claim 9, wherein the CommTxPoolExceptional field is transmitted to the wireless device via a system information block. 10. The computer readable medium of claim 9, wherein the CommTxPoolExceptional field is transmitted to the wireless device over a broadcast channel. 10. The method of claim 9, wherein the instructions, when executed by the processor, cause the base station to further:
Causes the wireless device to transmit information about a resource selection mode that causes the wireless device to change from the resource allocation mode to a resource selection mode based on the determined RLF, to the wireless device.

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