KR102594032B1 - Method and apparatus for operating buffer state report in wireless communication system supporting device to device communication - Google Patents

Abstract

Provides a buffer status reporting operation method and device in a wireless communication system supporting terminal-to-device communication. In a wireless communication system supporting device-to-device (D2D) communication, a buffer status reporting operation method by a terminal includes the steps of changing the D2D transmission mode set in the terminal from a first transmission mode to a second transmission mode and the D2D When a buffer state report for data to be transmitted through communication is triggered, canceling the triggered buffer state report, wherein the first transmission mode is assigned from the base station. This is a mode in which the D2D communication is performed using resources, and the second transmission mode may be a mode in which the D2D communication is performed using resource pool information for the D2D communication.

Description

Method and device for operating buffer status report in a wireless communication system supporting communication between devices {METHOD AND APPARATUS FOR OPERATING BUFFER STATE REPORT IN WIRELESS COMMUNICATION SYSTEM SUPPORTING DEVICE TO DEVICE COMMUNICATION}

The present invention relates to wireless communication. In particular, in a wireless communication system supporting device-to-device communication, when a terminal performs device-to-device communication using resources allocated from a base station, a buffer state report is provided. ) relates to a method and device for operating.

Device-to-Device (D2D) 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 differentiated from existing D2D communication.

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

For terminal-to-device communication in this wireless communication system, the base station can schedule resources necessary for terminals existing in-coverage to transmit data through D2D communication. To this end, the terminal can inform the base station of the amount of data to be transmitted through D2D communication in the buffer within the terminal through a buffer state report.

Meanwhile, in exceptional cases, the terminal may transmit D2D data through self-selected resources without being allocated the resources required to transmit data through the D2D communication from the base station. However, in this case, if there is already a triggered buffer status report in the terminal, it has not yet been decided how the terminal will operate the triggered buffer status report, and specific operations and definitions for this are required. This is the situation.

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

Another technical object of the present invention is to provide a method and device by which terminals can efficiently allocate resources for terminal-to-device communication in a wireless communication system supporting terminal-to-device communication.

According to one aspect of the present invention, a method of operating a buffer status report by a terminal in a wireless communication system supporting device-to-device (D2D) communication includes transmitting the D2D transmission mode set in the terminal to the second transmission mode in the first transmission mode. A step of changing to a 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 in which the D2D communication is performed using resources allocated from the 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. You can.

According to another aspect of the present invention, a method of 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 that performs the D2D communication using resources allocated from a base station. Operating in a second transmission mode to perform the D2D communication using resource pool information for communication, and if there is no data to be transmitted through the D2D communication, canceling the triggered buffer status report. there is.

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

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

Hereinafter, in this specification, contents related to the present invention will be described in detail through exemplary drawings and examples along with the contents of the present invention. When adding reference signs to components in each drawing, it should be noted that the same components are given the same reference numerals as much as possible even if they are shown in different drawings. Additionally, when describing 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 will be omitted.

In addition, this specification describes a wireless communication network, and 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) in charge of the wireless communication network, or in the process of controlling the network and transmitting data. Work can be performed on 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, the wireless communication system 10 can provide communication services between a base station and a terminal. In a wireless communication system, a terminal and a base station can transmit and receive data wirelessly. Additionally, 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 can provide communication services to terminals within the transmission coverage of the base station through a specific frequency band. Coverage served by a base station can also be expressed in terms of site. A site may include a number of areas 15a, 15b, and 15c, which may be referred to as sectors. Each sector included in the site can be identified based on a different identifier. Each sector 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, and a femto base station ( It may be called by other terms such as Femto eNodeB), home base station (HeNodeB), relay, and remote radio head (RRH).

The terminal 12 may be fixed or mobile, and may be a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, or 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. Cell may be used as a term to indicate the frequency band provided by the base station, the coverage of the base station, or the base station.

Hereinafter, downlink refers to communication or a communication path from the base station 11 to the terminal 12, and uplink refers to communication or a 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 are no restrictions on the 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), and OFDM-FDMA. , various multiple access techniques such as OFDM-TDMA and OFDM-CDMA can be used. These modulation techniques increase the capacity of a communication system by demodulating signals received from multiple users of the communication system. Additionally, a Time Division Duplex (TDD) method transmitted using different times or a Frequency Division Duplex (FDD) method transmitted 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, as Layer 1 (L1) and Layer 1 (L1). It can be divided into layer 2 (L2) and layer 3 (L3).

The physical layer belonging to the first layer provides information transfer service using a physical channel. The physical layer is connected to the upper layer, the Media Access Control (MAC) 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 wireless interface. Additionally, data is transmitted through physical channels between different physical layers (i.e., between the physical layers of the terminal and the base station). The physical channel can be modulated using OFDM (Orthogonal Frequency Division Multiplexing), and time, frequency, and space created by multiple antennas are utilized as radio resources.

For example, among physical channels, PDCCH (Physical Downlink Control CHannel) informs the terminal of resource allocation of PCH (Paging CHannel) and DL-SCH (DownLink Shared CHannel) and HARQ (Hybrid Automatic Repeat Request) information related to DL-SCH, It can carry an uplink scheduling grant that informs the terminal of resource allocation for uplink transmission. In addition, PCFICH (Physical Control Format Indicator CHannel) informs the UE of the number of OFDM symbols used in PDCCHs and is transmitted every subframe. Additionally, PHICH (Physical Hybrid ARQ Indicator CHannel) carries HARQ ACK/NAK signals in response to uplink transmission. Additionally, PUCCH (Physical Uplink Control CHannel) carries uplink control information such as HARQ ACK/NAK, scheduling request, and CQI for downlink transmission. Additionally, PUSCH (Physical Uplink Shared CHannel) carries UL-SCH (UpLink Shared CHannel). If necessary, depending on the settings and requests of the base station, PUSCH may include CSI (Channel State Information) information such as HARQ ACK/NACK and CQI.

The data link layer, which corresponds 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 multiplexes or demultiplexes MAC SDUs (Service Data Units) belonging to logical channels onto transport blocks provided through physical channels. can do. The MAC layer provides services to the RLC layer through logical channels. Logical channels can be divided into a control channel for transmitting control area information and a traffic channel for transmitting user area information. For example, services provided from the MAC layer to higher layers include data transfer or radio resource allocation.

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

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

The RRC (Radio Resource Control) layer, which belongs to the third layer of the OSI model, is responsible for controlling logical channels, transport channels, and physical channels in relation to the configuration, re-configuration, and release of RBs. . RB refers to the 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 the process of defining the characteristics of the wireless protocol layer and channel and setting each specific parameter and operation method to provide a specific service. RB can be divided into SRB (Signaling RB) and DRB (Data RB). SRB is used as a path to transmit RRC messages and NAS (Non-Access Stratum) messages in the control plane, and DRB is used as a path to transmit user data in the user plane. Hereinafter, simply referred to as RB without distinction between SRB and DRB means DRB.

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

D2D communication may refer to a technology that directly transmits and receives data between terminals. Hereinafter, in an embodiment of the present invention, it is assumed that the terminal supports D2D communication. Additionally, D2D can be replaced by the expression Proximity based Service (ProSe) or ProSe-D2D. The use of the term ProSe for D2D does not mean that the meaning of a technology for directly transmitting and receiving data between terminals is changed, but that the meaning of an access-based service can be added.

Recently, for purposes such as public safety, methods to perform discovery and direct communication between devices within or out of network coverage have been developed. It is being studied. A terminal that transmits a signal based on terminal-to-device communication can be defined as a transmitting terminal (Tx UE), and a terminal that receives a signal based on terminal-to-device communication can 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 roles of the transmitting terminal and the receiving terminal may change. Meanwhile, a signal transmitted by a transmitting terminal may be received by two or more receiving terminals.

In a cellular system, when terminals in close proximity perform D2D communication, the load on the base station can be distributed. Additionally, when adjacent terminals perform D2D communication, the terminals transmit data over a relatively short distance, so the consumption of the terminal's transmission power and transmission latency can be reduced. In addition, from the overall system perspective, frequency use efficiency can be improved because existing cellular-based communication and D2D communication use the same resources.

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

Referring to FIG. 2, communication between the first terminal 210 located in the first cell and the second terminal 220 located in the second cell, the third terminal 230 located in the first cell and the first terminal 230 located in the first cluster Communication between 4 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 of network coverage. Here, the fifth terminal 250 may operate as a cluster head (CH) of the first cluster. Here, the cluster head refers to 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 that performs discovery for communication between terminals and a direct communication procedure that transmits and receives control data and/or traffic data between terminals. D2D communication can be used for various purposes. For example, D2D communication within network coverage can be used for public safety, ultra-low latency services, commercial purposes, etc. D2D communication outside of network coverage can only be used for public safety.

As an example 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 about transmission resources and/or reception resources that can be used for D2D communication between the first terminal 210 and another terminal (for example, the second terminal 220).

The first terminal 210, which has received the D2D resource allocation information from the base station, 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 the D2D communication resources of the first terminal 210. The second terminal 220 may receive data transmitted from the first terminal 210 through resources indicated by information about D2D communication resources of the first terminal 210.

In D2D communication, a terminal can 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. If the physical layer control channel is not defined in D2D communication, the terminal can use various methods to transmit control data for D2D communication.

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

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

During 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 the terminal can perform D2D communication only when it is allocated resources for D2D communication from the base station, and the base station transmits a D2D grant to the transmitting terminal. The D2D grant includes parameter information to be determined by the base station among SA (Scheduling Assignment) information, which is control information that must be secured for D2D data reception at the receiving terminal during D2D communication, resource allocation information for the SA, and information determined by the SA. Resource allocation information for the indicated data is instructed to the transmitting terminal. Parameter information that must 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 identifies it as 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 instructions from the base station. The terminal can internally select a resource to use among available radio resources during D2D communication and transmit D2D data. The terminal has information indicating that a specific cell within the base station can support D2D through SIB (System Information Block)/dedicated signaling and D2D resource pool information for the second transmission mode provided by the base station. It can operate in the second transmission mode only for the specific cell if it exists.

However, if the base station does not allow operation in the second transmission mode, that is, there is information indicating that a specific cell within the base station can support D2D, 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. Additionally, if D2D resource pool information for the second transmission mode is valid only in RRC connected mode, the RRC IDLE mode terminal operates in the second transmission mode even if there is D2D resource pool information for the second transmission mode. Can not.

However, if the terminal is located outside the network service area, that is, in 'Any Cell Selection' mode, which is an RRC idle mode terminal but fails to select a serviceable cell, the terminal's UICC (USIM (Universal Subscriber Identity) Second transmission mode using D2D resource pool information for the second transmission mode stored in the module (Integrated Circuit Card), etc. or using D2D resource pool information for the second transmission mode received through the base station in the previous network service area. It can operate as .

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

Therefore, when a wireless communication system supports D2D communication, the base station needs to schedule the resources necessary for terminals existing in-coverage to transmit data through D2D communication, and for this, the base station needs to schedule the terminal's buffer. It is necessary to know how much data (hereinafter referred to as D2D data) exists to be transmitted through D2D communication. The terminal can inform the base station of the amount of data to be transmitted through D2D communication in the buffer within the terminal through the following procedure.

Figure 3 is a diagram showing a process in which a terminal transmits a ProSe-BSR to a base station to transmit D2D data in the first transmission mode in a wireless communication system according to the present invention.

In a wireless communication system, when there is data to be transmitted through a D2D link 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 refers to a BSR for D2D communication that is distinct from the BSR defined and used in the current wireless communication system.

When ProSe-BSR is triggered, the terminal transmits a scheduling request (SR) to the base station to induce allocation of resources for transmission of D2D data and ProSe-BSR (S320), and sends an uplink request to the SR from the base station. Receive a grant (UL grant) (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 the base station may use resources additionally allocated for the SR for D2D purposes separately from the SR. When defining an SR for D2D purposes separately from the existing SR, the SR may be defined separately as ProSe-SR. For convenience of explanation below, SR and ProSe-SR are collectively referred to as SR without distinction.

When an SR is triggered, the SR is pending until canceled. On the other hand, the terminal may not be able to accept all data pending for transmission in the uplink grant, or a MAC PDU (Media Access Control Protocol Data Unit) is configured and the MAC PDU is configured in a buffer state including even the last event that occurred. If it includes a ProSe-BSR, all pending SRs are canceled and the timer (sr-ProhibitTimer) to prevent SRs from being transmitted is stopped.

Specifically, if an SR is triggered and there is currently no pending SR, the terminal 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 transmission number of SR, the SR count value is increased by 1, the physical layer is instructed to transmit the SR signal through PUCCH, and sr-ProhibitTimer is started. However, if the SR_COUNTER value is greater than or equal to the maximum number of transmissions, the RRC is notified of the release of PUCCH and SRS, and all configured downlink allocations and uplink grants are cleared. Then, the random access procedure is initialized and all pending SRs are canceled.

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

When the UE receives the uplink grant for the SR, it transmits ProSe-BSR to the base station (S340). And when a D2D grant for ProSe-BSR is received from the base station (S350), data is transmitted to the target terminal using resources allocated for transmission of D2D data (S360). In this way, ProSe-BSR is for the terminal to inform the serving base station of information about the amount of data that can be transmitted in the D2D link buffer. In the present invention, as an example, the ProSe-BSR procedure is shown 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 the periodic BSR timer (periodicBSR-Timer) and retransmission BSR timer (retxBSR-Timer) for ProSe-BSR through signaling defined in the RRC layer, thereby establishing the ProSe-BSR procedure for the logical channel within each terminal. control. A logical channel group (LCG) can be configured in each terminal through optional signaling (optionally configured by RRC signal by eNB), and ProSe-BSR is performed targeting the LCG.

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

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

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

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

For the ProSe-BSR procedure, the UE must consider suspended radio bearers (RBs) and all non-suspended RBs. ProSe-BSR can be divided into Regular ProSe-BSR (Regular ProSe-BSR), Padding ProSe-BSR (Padding ProSe-BSR), and Periodic ProSe-BSR (Periodic ProSe-BSR).

The Regular ProSe-BSR is an uplink transmission capable of transmitting data on a logical channel included in the LCG that has a higher priority than other logical channels in which data that can be transmitted is present in the RLC entity or PDCP entity, or data that can be transmitted is already present. Triggered when data becomes present. Additionally, Regular ProSe-BSR is triggered even when the retransmission BSR timer for ProSe-BSR expires and the UE has data that can be transmitted on the logical channel in the LCG.

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

Alternatively, the padding ProSe-BSR is triggered when uplink resources and resources for BSR transmission for a 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 periodic ProSe-BSR are transmitted in long ProSe-BSR format if more than one LCG (at least two LCGs) have data to transmit in the TTI in which the corresponding ProSe-BSR is transmitted, otherwise (one (If only the LCG has data to transmit), it can be transmitted in a short BSR format.

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

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 combined size of the long ProSe-BSR and the subheader of the long ProSe-BSR. Alternatively, if only the 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 is not canceled. If uplink resources for new transmission are allocated to this TTI, the UE instructs multiplexing and assembly procedures for generating a ProSe-BSR MAC control element and starts a periodic BSR timer (periodicBSR-Timer) for ProSe-BSR. Restarts and starts or restarts the retransmission BSR timer (retxBSR-Timer) for 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 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. Additionally, if regular ProSe-BSR or periodic ProSe-BSR can be transmitted, this will always take precedence over padding ProSe-BSR. Additionally, upon confirming receipt of an indicator indicating transmission of new data for all UL-SCHs, the terminal restarts the retransmission BSR timer. All triggered BSRs must be canceled when a BSR is included in a MAC PDU.

The UE transmits one regular or periodic ProSe-BSR in one TTI. Additionally, according to the present invention, the ProSe-BSR can be transmitted within the same TTI as the BSR of a wireless communication system. For example, ProSe-BSR for D2D service and existing BRS for general data service may be transmitted simultaneously in the same subframe (TTI). At this time, information classification for the corresponding BSR can 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 contain a regular or periodic ProSe-BSR. Accordingly, one padding ProSe-BSR may be included in any MAC PDUs that contain a regular or periodic BSR for a wireless communication system. That is, the padding BSR has a higher priority than the padding ProSe-BSR, but the padding ProSe-BSR may be included first only in any MAC PDU containing a regular or periodic BSR. This may also include cases where transmission of a single MAC PDU is requested in one TTI. All ProSe-BSRs always reflect the buffer status after the MAC PDUs to be transmitted are configured based on the D2D grant previously received by the UE based on the TTI at 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 for each LCG in the same TTI, and the buffer status value for the LCG must be the same 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. The 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 are canceled when receiving an uplink grant that can transmit all pending data, but cannot additionally transmit a BSR MAC control element. Additionally, all triggered BSRs are canceled when the BSR is included in the MAC PDU. In other words, the existing wireless communication system can cancel a triggered BSR only in the following situations.

1. When the resources secured through the UL grant in the corresponding subframe can accommodate all data to be transmitted in the uplink, but cannot include the BSR MAC CE including the MAC subheader.

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

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

As described above, during D2D communication, the base station needs to schedule the resources necessary for terminals existing in-coverage to transmit data through D2D communication, and for this, the terminal is instructed to send D2D communication to the base station in the terminal's buffer. It is possible to inform through BSR how much data (hereinafter referred to as D2D data) exists to be transmitted. However, in exceptional cases (for example, when the terminal cannot maintain an RRC connection with the base station), the terminal may perform D2D communication through resources selected by itself without being allocated from the base station the resources required to transmit data through D2D communication. Must 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 set or operates in the second transmission mode, resources for D2D transmission cannot be controlled by the base station. Therefore, the base station must reserve corresponding resources for D2D transmission. The reserved resources may 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 resources available for general wireless communication (for example, LTE communication) will decrease because the total resources are limited, which will affect the overall system transmission rate. You can. Therefore, the base station can reduce the number of terminals that can operate 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 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, the buffer that has already been triggered in the terminal If a status report exists, it has not yet been decided how to operate the triggered buffer status report.

Figures 4 to 8 are flowcharts showing a buffer status reporting operation method for terminal-to-terminal communication in one embodiment of the present invention. Hereinafter, with reference to FIGS. 4 to 8, the 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 that supports D2D communication can perform D2D communication when the user of the terminal configures the terminal to enable D2D communication through a user interface (UI). Alternatively, a network (e.g., a D2D server that manages the ProSe (Proximity Services) ID and ProSe Application ID of a terminal using D2D communication, a serving base station of the terminal, etc.) allows the user of the terminal to perform D2D communication. It may be finally determined whether the terminal configured to enable D2D communication is possible. That is, even if D2D communication is enabled by the user of the terminal, the terminal may perform D2D communication only when D2D communication is permitted by the network. Information about 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 cluster head) or a base station that is responsible for allocating resources for D2D communication during D2D communication. In this case, when performing D2D communication, the terminal must transmit a BSR for D2D data to the base station or the cluster head. Hereinafter, for convenience of explanation, the base station and the cluster head are collectively referred to as base stations. Additionally, BSR for D2D data is called ProSe-BSR.

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

When ProSe-BSR is triggered, the UE can determine whether the current D2D transmission mode of the UE is set to the second transmission mode (S420). As a result of confirmation, 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 is based on the ProSe-BSR triggered by the base station. ProSe-BSR MAC CE can be included in the MAC PDU and transmitted to the base station (S440).

For example, in exceptional cases as described above (when the timer related to the RRC reset procedure and/or the timer related to the handover is in progress or started, etc.) or when the D2D transmission mode of the terminal is changed to the second transmission mode by the base station. When the terminal changes the D2D transmission mode set in the terminal from the first transmission mode to the second transmission mode due to a case where permission is allowed, etc., the terminal switches all ProSe-BSRs that were 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 resources allocated from the base station, and the second transmission mode refers to a second transmission mode resource pool information for the D2D communication. This may refer to a mode in which the D2D communication is performed. In other words, all triggered ProSe-BSRs may be canceled if 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 terminal itself or the base station may transmit the D2D communication set in the terminal. It may be canceled when changing the mode from the first transmission mode to the second transmission mode.

The terminal operating in the first transmission mode and the terminal operating in the second transmission mode have the following D2D resource pool information included in the reception resource pool (commRxPool) and the general common transmission resource pool (commTxPoolNormalCommon) information in order to receive D2D data. must be checked. Here, the reception resource pool is information indicating resources allowed for reception by D2D terminals operating in RRC IDLE and Connected mode, and the common transmission resource pool is information allowed for transmission by D2D terminals operating in RRC IDLE mode. This is information that points to resources.

- SA resource pool information

- Data resource pool information (included if it is a general transmission resource pool, but not included if it is a resource pool for the first transmission mode among the reception resource pool configuration information)

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

Here, transmission resource pool information for exceptional cases (commTxPoolExceptional), which is defined separately from the resource pool information for the exceptional cases, may be defined.

All of the above resource pool information can be transmitted to all terminals in the cell through a broadcast channel, and a terminal wishing to perform D2D communication can receive D2D data that the terminal wishes to receive from radio resources based on all of the resource pool information. Monitoring operations must be performed to receive. The reception resource pool information includes transmission resource pool information dedicated by the base station for transmission operations in the first transmission mode or the second transmission mode only for terminals operating in RRC connected mode in the corresponding cell. may be included. The exclusively provided first or second transmission mode transmission resource pool information must be set so that no physical resources collide with each other in each cell to avoid mutual interference. In addition, when the amount of resources allocated for ProSe communication is insufficient and conflicting resources occur, the range of mutual interference is limited to the same resource range by ensuring that the characteristics of the transmission signals set for each cell, such as the cyclic prefix length, are the same. Cooperation between base stations must be achieved to enable this.

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 Table 1 and Table 2 below, 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 the RRC connection re-establishment procedure is initiated. And, it stops when a suitable Evolved UMTS Terrestrial Radio Access (E-UTRA) cell is selected or a cell using another radio access technology (RAT) is selected. Additionally, it expires when entering the RRC idle state. Also, referring to Table 2, the T304 timer sends an RRC connection reconfiguration message including mobility control information. It starts when receiving or receiving a message (MobilityFromEUTRACommand message) containing a cell change order. Here, the RRC connection reconfiguration message including the mobility control information may be called a handover command message. In other words, the T304 timer starts during handover within the LTE network or during inter-RAT handover to the LTE system, and stops when the handover is successfully completed. Meanwhile, when the UE cancels ProSe-BSR, the timer configured for ProSe-BSR The periodic BSR timer (periodic BSR-timer) and the retransmission BSR timer (retxBSR-timer) can be reset. The periodic BSR timer and retransmission BSR timer configured for the initialized ProSe-BSR may be set to a startable state when the D2D transmission mode of the terminal is changed from the second transmission mode to the first transmission mode.

In addition, when 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), it can determine whether resource pool information for the second transmission mode exists. There is (S520). Here, when the D2D transmission mode set in the terminal is changed due to an exceptional case, the first transmission mode may be changed 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 is transmission resource pool information for exceptional cases defined separately from the resource pool information for the exceptional cases ( commTxPoolExceptional). Therefore, when changing the D2D transmission mode set in the terminal from the first transmission mode to the fallback mode, it can be additionally determined whether resource pool information for the fallback mode exists (S520). Here, the resource pool information to be applied preferentially in the fallback mode may be general transmission resource pool information or transmission resource pool information for exceptional cases. If at least one of the two resource pool information exists, the terminal configures all logical channels (PTCH: ProSe Communication Traffic Channel) for D2D communication between the terminals to prevent ProSe-BSR from being triggered any longer. It can be excluded from the triggering target of ProSe-BSR (S530). However, if both of the above two types of resource pool information do not exist, the terminal cannot operate in the second communication mode and thus may suspend data transmission for the PTCH (S540).

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

In the case of handover, after the terminal completes handover to the target base station (immediately after the T304 timer stops), it immediately changes to the first transmission mode and operates in the handover preparation stage, that is, the source base station transfers the current terminal to the target base station. When delivering a handover request message containing terminal information including ProSe configuration information such as transmission mode, and when the target base station transmits a message allowing handover based on this to the source base station, it includes ProSe configuration information necessary for operation of the first transmission mode. and deliver it. The configuration information may include D2D-RNTI information to be used by the target base station, ProSe-BSR-related configuration information, and SA pool information.

Meanwhile, in another embodiment, as shown in FIG. 7, when the D2D transmission mode set in the terminal changes from the first transmission mode to the second transmission mode due to an exceptional case, etc. (S710), the terminal transmits data through D2D communication. Depending on the existence of data, it is possible to decide whether to cancel ProSe-BSR. For example, when the D2D transmission mode set for the terminal changes from the first transmission mode to the second transmission mode as the timer related to the RRC reset procedure and/or the timer related to the handover are in progress, the UE transmits data to be transmitted through D2D communication. ProSe-BSR can be canceled only if does not exist (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. And, if second transmission mode resource pool information exists, all PTCHs can be excluded from the triggering target of ProSe-BSR, and if second transmission mode resource pool information does not exist, data transmission for all PTCHs can be stopped.

Meanwhile, in another embodiment, as shown in FIG. 8, the terminal may operate in the second transmission mode with the first transmission mode set without changing the D2D transmission mode (S810). This may be performed when the base station does not propose a D2D transmission mode for the UE and/or when at least one of the timer for the RRC reset procedure and the timer for handover is in progress or started. In this case, even though the terminal can transmit D2D data in the second transmission mode, it transmits the D2D data in the first transmission mode when it receives the D2D grant from the base station. That is, the terminal can maintain the first transmission mode as the D2D transmission mode. In this case, even if the terminal starts operation in the second transmission mode, it may not cancel triggering of ProSe-BSR because it is set to the first transmission mode. However, the terminal may determine whether data to be transmitted through D2D communication exists and, if there is no data to be transmitted through D2D communication, cancel the triggered BSR (S820).

Meanwhile, if the exceptional case is resolved but the UE cannot maintain the RRC connection mode (i.e., when the timer for RLF or the timer for handover expires), the UE may change the D2D transmission mode to the second transmission mode. . And, D2D data can be transmitted based on the secured second transmission mode D2D resource pool information.

Meanwhile, as another embodiment, in the above exceptional case, the terminal cancels ProSe-BSR through a reset operation of the MAC entity. Reset of the MAC entity may be performed upon request from a higher layer. The MAC entity reset operation includes the following operations.

- Stop all running timers.

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

- Any triggered SR and/or ProSe-SR procedures are canceled.

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

- Flush soft buffers for all DL HARQ processes other than those related to PSCH.

- For each DL HARQ process other than those related to PSCH, transmission for any TB received next is considered the 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 those related to PTCH, 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 the handover procedure (when MCI (Mobility Control Information) is included in the RRC reconfiguration message), the terminal is connected to the logical channel related to the D2D data transmission at the start of the handover procedure. Re-establish RLC and PDCP in all DRBs except those related to PTCH.

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

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

Figure 9 is a flowchart showing a buffer status reporting operation method for communication between terminals by a base station in one embodiment of the present invention.

Referring to FIG. 9, the base station may transmit a second transmission mode permission message to the first terminal within coverage (S910). Here, the first terminal may be a terminal in which the D2D transmission mode is set to the first transmission mode. The first terminal that has received the second transmission mode permission message 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 can receive ProSe-BSR from a second terminal set to 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 second terminal that received this can perform D2D communication with the target terminal using the allocated resources. there is.

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

For the release operation, release information may be included and transmitted in configuration information about transmission resources in the RRC reconfiguration message. Alternatively, when the terminal receives an RRC reconfiguration message including mobility control information (MCI) from the base station, it can automatically release configuration information about transmission resources in the RRC reconfiguration message.

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

Alternatively, if the configuration for transmission resources for the first transmission mode or the second transmission mode is canceled as described above, the terminal switches to fallback mode when transmitting data using the transmission resource pool information for exceptional cases received through system information. It can work. As described above, the configuration information for the first or second transmission mode configured by the source base station is released due to the handover operation, but the RRC connected mode is maintained, so transmission resource pool information for exceptional cases that can be used in the RRC connected mode The 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 (base station that transmitted the RRC reconfiguration message including the MCI), and the RRC reconfiguration message including the MCI. It may be included and provided within the terminal, and the terminal may perform operations 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 can be used.

After handover is completed, the terminal may maintain the second transmission mode or fallback mode until it receives and reflects information for configuring transmission resources during configuration for ProSe communication operations from the target base station.

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 may maintain the reception operation but stop all transmission operations. In other words, it can operate in ProSe transmission stop mode. As described above, the configuration information for the first or second transmission mode configured by the source base station is released due to the handover operation, so ProSe transmission operation is impossible. This is limited to the terminal operating in RRC connected mode at the source base station and the physical resources in the transmission resource pool dedicated by the base station for transmission operation in the first or second transmission mode and the use of the target base station. (dedicated) If a collision may occur between physical resources within the transmission resource pool, the 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 within the target base station. Therefore, transmission operation is stopped to remove such interference factors.

After handover is completed, the terminal may maintain the transmission stop mode until it receives and reflects information for configuring transmission resources during configuration for ProSe communication operations from the target base station.

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 a handover operation, the base station determines that the RRC parameters between the base station and the terminal do not match, the base station determines that downlink or uplink synchronization is not properly performed, or security This is when you want to change the key value shared between the base station and the terminal used for this purpose.

Figure 10 is a block diagram showing 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 and transmits and/or receives wireless signals. For example, the RF unit 1010 may receive the second transmission mode permission message and D2D resource allocation information published in this specification from the base station 1050. Additionally, the RF unit 1010 may transmit an uplink signal such as the ProSe-BSR disclosed herein to the base station 1050.

Processor 1005 implements the functions, processes and/or methods proposed herein. Specifically, the processor 1005 ensures that all steps according to FIGS. 4 to 8 are 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 ProSe-BSR is triggered. If the current D2D transmission mode of the terminal is set to the second transmission mode, the tire determination unit 1007 determines whether the timer related to the RRC reset procedure and/or the timer related to handover are in progress. The cancellation unit 1008 cancels all triggered ProSe-BSRs when the RRC reset procedure-related timer and/or handover-related timer is in progress. At this time, the periodic BSR timer and 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 types of resource pool information exists, all PTCHs configured for the D2D communication between the terminals can be excluded from the triggering target of the ProSe-BSR in order to prevent ProSe-BSR from being triggered any more. there is. If the two types of resource pool information do not exist, the processor 1005 cannot operate in the second communication mode and thus may suspend data transmission for the PTCH.

Thereafter, when the timer determination unit 1007 determines that the RRC reset procedure-related timer and/or the handover-related timer has been stopped, the processor 1005 determines that the exceptional case has been resolved and the initialized periodic BSR timer and The retransmission BSR timer can be started and the normal ProSe-BSR procedure can be restarted.

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, etc., and transmits the second transmission to the processor 1005 according to the request of the processor 1005. Resource pool information for the mode can be provided.

The base station 1050 includes a radio frequency (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 and transmits and/or receives wireless signals. Processor 1060 implements the functions, processes and/or methods proposed herein. In the above-described embodiment, the operation of the base station 1050 may be implemented by the processor 1060. The processor 1060 generates the second transmission mode permission message published in this specification and schedules resources for D2D communication based on the ProSe-BSR received from the terminal.

As an example, the processor 1060 may include a timer value setting unit 1061, a ProSe-BSR confirmation 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 confirmation unit 1062 can confirm the ProSe-BSR received from the terminal 1000. The D2D resource allocation unit 1063 may allocate resources for D2D communication to the terminal 1000 operating in another first transmission mode based on the ProSe-BSR.

A processor may include an application-specific integrated circuit (ASIC), other chipset, logic circuitry, 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 wireless signals. When this embodiment is implemented in software, the above-described techniques can be implemented as modules (processes, functions, etc.) that perform the above-described functions. Modules are stored in memory and can be executed by a processor. Memory may be internal or external to the processor and may be connected to the processor by a variety of well-known means.

In the above-described exemplary system, the methods are described on a flowchart basis as a series of steps or blocks; however, the invention is not limited to the order of the steps, and some steps may occur simultaneously or in a different order than other steps as described above. You can. Additionally, those skilled in the art will understand that the steps shown in the flowchart are not exclusive and that other steps may be included or one or more steps in the flowchart may be deleted without affecting the scope of the present invention.

The above-described embodiments include examples of various aspects. Although it is not possible to describe all possible combinations for representing the various aspects, those skilled in the art will recognize that other combinations are possible. Accordingly, the present invention is intended to include all other substitutions, modifications and changes 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 in exceptional cases to the wireless device;
transmitting to the wireless device one or more messages containing information on a resource allocation mode for direct data transmission between the wireless device and another wireless device;
transmitting one or more scheduling messages to the wireless device for direct data transfer between the wireless device and the other wireless device;
The resource pool information for direct data transmission in exceptional cases is provided when the wireless device determines a radio link failure (RLF) associated with a problem in Radio Resource Control (RRC) connection with the base station. A method for causing a wireless device to cancel buffer status reports (BSRs) to the base station scheduled by the base station for the direct data transmission between the wireless device and the other wireless device and perform the direct data transmission. . The method of claim 1, wherein the CommTxPoolExceptional field is transmitted to the wireless device via a system information block. The method of claim 1, wherein the CommTxPoolExceptional field is transmitted to the wireless device over a broadcast channel. According to paragraph 1,
The method further comprising transmitting information about a resource selection mode to the wireless device, causing the wireless device to change from the resource allocation mode to the resource selection mode based on the determined RLF. As a base station,
transceiver; and
a processor operably coupled to the transceiver, the processor comprising:
send a CommTxPoolExceptional field to the wireless device indicating resource pool information for direct data transmission in exceptional cases;
transmit to the wireless device one or more messages containing information of a resource allocation mode for direct data transmission between the wireless device and another wireless device;
configured to transmit one or more scheduling messages to the wireless device for direct data transfer between the wireless device and the other wireless device;
The resource pool information for direct data transmission in exceptional cases is provided when the wireless device determines a radio link failure (RLF) associated with a problem in Radio Resource Control (RRC) connection with the base station. Causes the wireless device to cancel buffer status reports (BSRs) to the base station for the direct data transmission between the wireless device and the other wireless device scheduled by the base station, and to transmit the direct data. A base station that performs. 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:
The base station is further configured to transmit, to the wireless device, 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. A computer-readable recording medium containing instructions, comprising:
The instructions, when executed by a processor operably coupled to the transceiver, cause the base station to:
send a CommTxPoolExceptional field to the wireless device indicating resource pool information for direct data transmission in exceptional cases;
transmit to the wireless device one or more messages containing information of a resource allocation mode for direct data transmission between the wireless device and another wireless device;
transmit one or more scheduling messages to the wireless device for direct data transfer between the wireless device and the other wireless device;
The resource pool information for direct data transmission in exceptional cases is provided when the wireless device determines a radio link failure (RLF) associated with a problem in Radio Resource Control (RRC) connection with the base station. Causes the wireless device to cancel buffer status reports (BSRs) to the base station for the direct data transmission between the wireless device and the other wireless device scheduled by the base station, and to transmit the direct data. A computer-readable recording medium that allows performing. 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 via a broadcast channel. The method of claim 9, wherein the instructions, when executed by the processor, cause the base station to further:
A computer-readable recording medium that causes the wireless device to transmit, to the wireless device, information about a resource selection mode that causes the wireless device to change from the resource allocation mode to the resource selection mode, based on the determined RLF.