Patent Publication Number: US-2017374674-A1

Title: Method for priority handling for buffer status reporting in a d2d communication system and device therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is a Continuation of co-pending U.S. patent application Ser. No. 14/793,231 filed on Jul. 7, 2015, which claims the benefit under 35 U.S.C. §119(e) to U.S. Provisional Application No. 62/054,362 filed on Sep. 23, 2014, all of which are hereby expressly incorporated by reference into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a wireless communication system and, more particularly, to a method for priority handling for buffer status reporting in a D2D (Device to Device) communication system and a device therefor. 
     Discussion of the Related Art 
     As an example of a mobile communication system to which the present invention is applicable, a 3rd Generation Partnership Project Long Term Evolution (hereinafter, referred to as LTE) communication system is described in brief 
       FIG. 1  is a view schematically illustrating a network structure of an E-UMTS as an exemplary radio communication system. An Evolved Universal Mobile Telecommunications System (E-UMTS) is an advanced version of a conventional Universal Mobile Telecommunications System (UMTS) and basic standardization thereof is currently underway in the 3GPP. E-UMTS may be generally referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, reference can be made to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”. 
     Referring to  FIG. 1 , the E-UMTS includes a User Equipment (UE), eNode Bs (eNBs), and an Access Gateway (AG) which is located at an end of the network (E-UTRAN) and connected to an external network. The eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service. 
     One or more cells may exist per eNB. The cell is set to operate in one of bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides a downlink (DL) or uplink (UL) transmission service to a plurality of UEs in the bandwidth. Different cells may be set to provide different bandwidths. The eNB controls data transmission or reception to and from a plurality of UEs. The eNB transmits DL scheduling information of DL data to a corresponding UE so as to inform the UE of a time/frequency domain in which the DL data is supposed to be transmitted, coding, a data size, and hybrid automatic repeat and request (HARQ)-related information. In addition, the eNB transmits UL scheduling information of UL data to a corresponding UE so as to inform the UE of a time/frequency domain which may be used by the UE, coding, a data size, and HARQ-related information. An interface for transmitting user traffic or control traffic may be used between eNBs. A core network (CN) may include the AG and a network node or the like for user registration of UEs. The AG manages the mobility of a UE on a tracking area (TA) basis. One TA includes a plurality of cells. 
     Device to device (D2D) communication refers to the distributed communication technology that directly transfers traffic between adjacent nodes without using infrastructure such as a base station. In a D2D communication environment, each node such as a portable terminal discovers user equipment physically adjacent thereto and transmits traffic after setting communication session. In this way, since D2D communication may solve traffic overload by distributing traffic concentrated into the base station, the D2D communication may have received attention as the element technology of the next generation mobile communication technology after 4G. For this reason, the standard institute such as 3GPP or IEEE has proceeded to establish the D2D communication standard on the basis of LTE-A or Wi-Fi, and Qualcomm has developed their own D2D communication technology. 
     It is expected that the D2D communication contributes to increase throughput of a mobile communication system and create new communication services. Also, the D2D communication may support proximity based social network services or network game services. The problem of link of a user equipment located at a shade zone may be solved by using a D2D link as a relay. In this way, it is expected that the D2D technology will provide new services in various fields. 
     The D2D communication technologies such as infrared communication, ZigBee, radio frequency identification (RFID) and near field communications (NFC) based on the RFID have been already used. However, since these technologies support communication only of a specific object within a limited distance (about 1 m), it is difficult for the technologies to be regarded as the D2D communication technologies strictly. 
     Although the D2D communication has been described as above, details of a method for transmitting data from a plurality of D2D user equipments with the same resource have not been suggested. 
     SUMMARY OF THE INVENTION 
     The object of the present invention can be achieved by providing a method for operating by an apparatus in wireless communication system, the method comprising; generating a MAC PDU (Medium Access Control Protocol Data Unit) if both of a PHR (Power Headroom Reporting) and a sidelink BSR (Buffer Status Reporting) are generated while the UE communicates with other UEs directly using a sidelink; and transmitting the MAC PDU, wherein the PHR is prioritized over the sidelink BSR when the UE prioritizes between the PHR and the sidelink BSR in the generated MAC PDU. 
     In another aspect of the present invention provided herein is an apparatus in the wireless communication system, the apparatus comprising: an RF (radio frequency) module; and a processor configured to control the RF module, wherein the processor is configured to generate a MAC PDU (Medium Access Control Protocol Data Unit) if both of a PHR (Power Headroom Reporting) and a sidelink BSR (Buffer Status Reporting) are generated while the UE communicates with other UEs directly using a sidelink, and to transmit the MAC PDU, wherein the PHR is prioritized over the sidelink BSR when the UE prioritizes between the PHR and the sidelink BSR in the generated MAC PDU. 
     Preferably, the method further comprising: after the UE allocates an uplink resource to a PHR MAC CE (Control Element) and a corresponding MAC sub-header in the MAC PDU, checking whether a remaining uplink resource in the MAC PDU can accommodate a sidelink BSR MAC CE and a corresponding MAC sub-header; if the remaining uplink resource can accommodate the sidelink BSR MAC CE and the corresponding MAC sub-header, allocating an uplink resource to the sidelink BSR MAC CE and the corresponding MAC sub-header. 
     Preferably, the method further comprising: after the UE allocates the uplink resource to the sidelink BSR MAC CE and the corresponding MAC sub-header in the MAC PDU, allocating a remaining uplink resource in MAC PDU to uplink data except data from UL-CCCH (Uplink-Common Control Channel), or padding BSR. 
     Preferably, the PHR is related to scheduling assistant information for uplink data transmission via Uu interface. 
     Preferably, the PHR is transmitted using a PHR MAC CE, an extended PHR MAC CE, or a dual connectivity PHR MAC CE. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. 
         FIG. 1  is a diagram showing a network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as an example of a wireless communication system; 
         FIG. 2A  is a block diagram illustrating network structure of an evolved universal mobile telecommunication system (E-UMTS), and  FIG. 2B  is a block diagram depicting architecture of a typical E-UTRAN and a typical EPC; 
         FIG. 3  is a diagram showing a control plane and a user plane of a radio interface protocol between a UE and an E-UTRAN based on a 3rd generation partnership project (3GPP) radio access network standard; 
         FIG. 4  is a diagram of an example physical channel structure used in an E-UMTS system; 
         FIG. 5  is a block diagram of a communication apparatus according to an embodiment of the present invention 
         FIG. 6  is a diagram for prioritization of two logical channels for three different uplink grants; 
         FIG. 7  is a diagram for signaling of buffer status and power-headroom reports; 
         FIG. 8A  is a diagram for a Short BSR and Truncated BSR MAC control element,  FIG. 8B  is for a Long BSR MAC control element; 
         FIG. 9  is an example of default data path for a normal communication; 
         FIGS. 10 and 11  are examples of data path scenarios for a proximity communication; 
         FIG. 12  is a conceptual diagram illustrating for a non-roaming reference architecture; 
         FIG. 13A  is a conceptual diagram illustrating for User-Plane protocol stack for ProSe Direct Communication, and  FIG. 13B  is Control-Plane protocol stack for ProSe Direct Communication; 
         FIG. 14  is a conceptual diagram illustrating for a PC5 interface for device to device direct discovery; 
         FIG. 15  is a conceptual diagram for priority handling buffer status reporting according to embodiments of the present invention; and 
         FIG. 16  is an example for priority handling buffer status reporting according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Universal mobile telecommunications system (UMTS) is a 3rd Generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). The long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS. 
     The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3G LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement. 
     Hereinafter, structures, operations, and other features of the present invention will be readily understood from the embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Embodiments described later are examples in which technical features of the present invention are applied to a 3GPP system. 
     Although the embodiments of the present invention are described using a long term evolution (LTE) system and a LTE-advanced (LTE-A) system in the present specification, they are purely exemplary. Therefore, the embodiments of the present invention are applicable to any other communication system corresponding to the above definition. In addition, although the embodiments of the present invention are described based on a frequency division duplex (FDD) scheme in the present specification, the embodiments of the present invention may be easily modified and applied to a half-duplex FDD (H-FDD) scheme or a time division duplex (TDD) scheme. 
       FIG. 2A  is a block diagram illustrating network structure of an evolved universal mobile telecommunication system (E-UMTS). The E-UMTS may be also referred to as an LTE system. The communication network is widely deployed to provide a variety of communication services such as voice (VoIP) through IMS and packet data. 
     As illustrated in  FIG. 2A , the E-UMTS network includes an evolved UMTS terrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC) and one or more user equipment. The E-UTRAN may include one or more evolved NodeB (eNodeB)  20 , and a plurality of user equipment (UE)  10  may be located in one cell. One or more E-UTRAN mobility management entity (MME)/system architecture evolution (SAE) gateways  30  may be positioned at the end of the network and connected to an external network. 
     As used herein, “downlink” refers to communication from eNodeB  20  to UE  10 , and “uplink” refers to communication from the UE to an eNodeB. UE  10  refers to communication equipment carried by a user and may be also referred to as a mobile station (MS), a user terminal (UT), a subscriber station (SS) or a wireless device. 
       FIG. 2B  is a block diagram depicting architecture of a typical E-UTRAN and a typical EPC. 
     As illustrated in  FIG. 2B , an eNodeB  20  provides end points of a user plane and a control plane to the UE  10 . MME/SAE gateway  30  provides an end point of a session and mobility management function for UE  10 . The eNodeB and MME/SAE gateway may be connected via an Si interface. 
     The eNodeB  20  is generally a fixed station that communicates with a UE  10 , and may also be referred to as a base station (BS) or an access point. One eNodeB  20  may be deployed per cell. An interface for transmitting user traffic or control traffic may be used between eNodeBs  20 . 
     The MME provides various functions including NAS signaling to eNodeBs  20 , NAS signaling security, AS Security control, Inter CN node signaling for mobility between 3GPP access networks, Idle mode UE Reachability (including control and execution of paging retransmission), Tracking Area list management (for UE in idle and active mode), PDN GW and Serving GW selection, MME selection for handovers with MME change, SGSN selection for handovers to 2G or 3G 3GPP access networks, Roaming, Authentication, Bearer management functions including dedicated bearer establishment, Support for PWS (which includes ETWS and CMAS) message transmission. The SAE gateway host provides assorted functions including Per-user based packet filtering (by e.g. deep packet inspection), Lawful Interception, UE IP address allocation, Transport level packet marking in the downlink, UL and DL service level charging, gating and rate enforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAE gateway  30  will be referred to herein simply as a “gateway,” but it is understood that this entity includes both an MME and an SAE gateway. 
     A plurality of nodes may be connected between eNodeB  20  and gateway  30  via the Si interface. The eNodeBs  20  may be connected to each other via an X2 interface and neighboring eNodeBs may have a meshed network structure that has the X2 interface. 
     As illustrated, eNodeB  20  may perform functions of selection for gateway  30 , routing toward the gateway during a Radio Resource Control (RRC) activation, scheduling and transmitting of paging messages, scheduling and transmitting of Broadcast Channel (BCCH) information, dynamic allocation of resources to UEs  10  in both uplink and downlink, configuration and provisioning of eNodeB measurements, radio bearer control, radio admission control (RAC), and connection mobility control in LTE ACTIVE state. In the EPC, and as noted above, gateway  30  may perform functions of paging origination, LTE-IDLE state management, ciphering of the user plane, System Architecture Evolution (SAE) bearer control, and ciphering and integrity protection of Non-Access Stratum (NAS) signaling. 
     The EPC includes a mobility management entity (MME), a serving-gateway (S-GW), and a packet data network-gateway (PDN-GW). The MME has information about connections and capabilities of UEs, mainly for use in managing the mobility of the UEs. The S-GW is a gateway having the E-UTRAN as an end point, and the PDN-GW is a gateway having a packet data network (PDN) as an end point. 
       FIG. 3  is a diagram showing a control plane and a user plane of a radio interface protocol between a UE and an E-UTRAN based on a 3GPP radio access network standard. The control plane refers to a path used for transmitting control messages used for managing a call between the UE and the E-UTRAN. The user plane refers to a path used for transmitting data generated in an application layer, e.g., voice data or Internet packet data. 
     A physical (PHY) layer of a first layer provides an information transfer service to a higher layer using a physical channel. The PHY layer is connected to a medium access control (MAC) layer located on the higher layer via a transport channel. Data is transported between the MAC layer and the PHY layer via the transport channel. Data is transported between a physical layer of a transmitting side and a physical layer of a receiving side via physical channels. The physical channels use time and frequency as radio resources. In detail, the physical channel is modulated using an orthogonal frequency division multiple access (OFDMA) scheme in downlink and is modulated using a single carrier frequency division multiple access (SC-FDMA) scheme in uplink. 
     The MAC layer of a second layer provides a service to a radio link control (RLC) layer of a higher layer via a logical channel. The RLC layer of the second layer supports reliable data transmission. A function of the RLC layer may be implemented by a functional block of the MAC layer. A packet data convergence protocol (PDCP) layer of the second layer performs a header compression function to reduce unnecessary control information for efficient transmission of an Internet protocol (IP) packet such as an IP version 4 (IPv4) packet or an IP version 6 (IPv6) packet in a radio interface having a relatively small bandwidth. 
     A radio resource control (RRC) layer located at the bottom of a third layer is defined only in the control plane. The RRC layer controls logical channels, transport channels, and physical channels in relation to configuration, re-configuration, and release of radio bearers (RBs). An RB refers to a service that the second layer provides for data transmission between the UE and the E-UTRAN. To this end, the RRC layer of the UE and the RRC layer of the E-UTRAN exchange RRC messages with each other. 
     One cell of the eNB is set to operate in one of bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplink transmission service to a plurality of UEs in the bandwidth. Different cells may be set to provide different bandwidths. 
     Downlink transport channels for transmission of data from the E-UTRAN to the UE include a broadcast channel (BCH) for transmission of system information, a paging channel (PCH) for transmission of paging messages, and a downlink shared channel (SCH) for transmission of user traffic or control messages. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through the downlink SCH and may also be transmitted through a separate downlink multicast channel (MCH). 
     Uplink transport channels for transmission of data from the UE to the E-UTRAN include a random access channel (RACH) for transmission of initial control messages and an uplink SCH for transmission of user traffic or control messages. Logical channels that are defined above the transport channels and mapped to the transport channels include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a multicast traffic channel (MTCH). 
       FIG. 4  is a view showing an example of a physical channel structure used in an E-UMTS system. A physical channel includes several subframes on a time axis and several subcarriers on a frequency axis. Here, one subframe includes a plurality of symbols on the time axis. One subframe includes a plurality of resource blocks and one resource block includes a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use certain subcarriers of certain symbols (e.g., a first symbol) of a subframe for a physical downlink control channel (PDCCH), that is, an L1/L2 control channel. In  FIG. 4 , an L1/L2 control information transmission area (PDCCH) and a data area (PDSCH) are shown. In one embodiment, a radio frame of 10 ms is used and one radio frame includes 10 subframes. In addition, one subframe includes two consecutive slots. The length of one slot may be 0.5 ms. In addition, one subframe includes a plurality of OFDM symbols and a portion (e.g., a first symbol) of the plurality of OFDM symbols may be used for transmitting the L1/L2 control information. A transmission time interval (TTI) which is a unit time for transmitting data is 1 ms. 
     A base station and a UE mostly transmit/receive data via a PDSCH, which is a physical channel, using a DL-SCH which is a transmission channel, except a certain control signal or certain service data. Information indicating to which UE (one or a plurality of UEs) PDSCH data is transmitted and how the UE receive and decode PDSCH data is transmitted in a state of being included in the PDCCH. 
     For example, in one embodiment, a certain PDCCH is CRC-masked with a radio network temporary identity (RNTI) “A” and information about data is transmitted using a radio resource “B” (e.g., a frequency location) and transmission format information “C” (e.g., a transmission block size, modulation, coding information or the like) via a certain subframe. Then, one or more UEs located in a cell monitor the PDCCH using its RNTI information. And, a specific UE with RNTI “A” reads the PDCCH and then receive the PDSCH indicated by B and C in the PDCCH information. 
       FIG. 5  is a block diagram of a communication apparatus according to an embodiment of the present invention. 
     The apparatus shown in  FIG. 5  can be a user equipment (UE) and/or eNB adapted to perform the above mechanism, but it can be any apparatus for performing the same operation. 
     As shown in  FIG. 5 , the apparatus may comprises a DSP/microprocessor ( 110 ) and RF module (transceiver;  135 ). The DSP/microprocessor ( 110 ) is electrically connected with the transceiver ( 135 ) and controls it. The apparatus may further include power management module ( 105 ), battery ( 155 ), display ( 115 ), keypad ( 120 ), SIM card ( 125 ), memory device ( 130 ), speaker ( 145 ) and input device ( 150 ), based on its implementation and designer&#39;s choice. 
     Specifically,  FIG. 5  may represent a UE comprising a receiver ( 135 ) configured to receive a request message from a network, and a transmitter ( 135 ) configured to transmit the transmission or reception timing information to the network. These receiver and the transmitter can constitute the transceiver ( 135 ). The UE further comprises a processor ( 110 ) connected to the transceiver ( 135 : receiver and transmitter). 
     Also,  FIG. 5  may represent a network apparatus comprising a transmitter ( 135 ) configured to transmit a request message to a UE and a receiver ( 135 ) configured to receive the transmission or reception timing information from the UE. These transmitter and receiver may constitute the transceiver ( 135 ). The network further comprises a processor ( 110 ) connected to the transmitter and the receiver. This processor ( 110 ) may be configured to calculate latency based on the transmission or reception timing information. 
       FIG. 6  is a diagram for prioritization of two logical channels for three different uplink grants. 
     Multiple logical channels of different priorities can be multiplexed into the same transport block using the same MAC multiplexing functionality as in the downlink. However, unlike the downlink case, where the prioritization is under control of the scheduler and up to the implementation, the uplink multiplexing is done according to a set of well-defined rules in the terminal as a scheduling grant applies to a specific uplink carrier of a terminal, not to a specific radio bearer within the terminal. Using radio-bearer-specific scheduling grants would increase the control signaling overhead in the downlink and hence per-terminal scheduling is used in LTE. 
     The simplest multiplexing rule would be to serve logical channels in strict priority order. However, this may result in starvation of lower-priority channels; all resources would be given to the high-priority channel until its transmission buffer is empty. Typically, an operator would instead like to provide at least some throughput for low-priority services as well. Therefore, for each logical channel in an LTE terminal, a prioritized data rate is configured in addition to the priority value. The logical channels are then served in decreasing priority order up to their prioritized data rate, which avoids starvation as long as the scheduled data rate is at least as large as the sum of the prioritized data rates. Beyond the prioritized data rates, channels are served in strict priority order until the grant is fully exploited or the buffer is empty. This is illustrated in  FIG. 6 . 
     Regarding  FIG. 6 , it may be assumed that a priority of the logical channel  1  (LCH  1 ) is higher than a priority of the logical channel  2  (LCH  2 ). In case of (A), all prioritized data of the LCH  1  can be transmitted and a portion of prioritized data of the LCH  2  can be transmitted until amount of the scheduled data rate. In case of (B), all prioritized data of the LCH  1  and all prioritized data of the LCH  2  can be transmitted. In case of (C) all prioritized data of the LCH  1  and all prioritized data of the LCH  2  can be transmitted and a portion of data of the LCH  1  can be further transmitted. 
       FIG. 7  is a diagram for signaling of buffer status and power-headroom reports. 
     The scheduler needs knowledge about the amount of data awaiting transmission from the terminals to assign the proper amount of uplink resources. Obviously, there is no need to provide uplink resources to a terminal with no data to transmit as this would only result in the terminal performing padding to fill up the granted resources. Hence, as a minimum, the scheduler needs to know whether the terminal has data to transmit and should be given a grant. This is known as a scheduling request. 
     The use of a single bit for the scheduling request is motivated by the desire to keep the uplink overhead small, as a multi-bit scheduling request would come at a higher cost. A consequence of the single bit scheduling request is the limited knowledge at the eNodeB about the buffer situation at the terminal when receiving such a request. Different scheduler implementations handle this differently. One possibility is to assign a small amount of resources to ensure that the terminal can exploit them efficiently without becoming power limited. Once the terminal has started to transmit on the UL-SCH, more detailed information about the buffer status and power headroom can be provided through the inband MAC control message, as discussed below. 
     Terminals that already have a valid grant obviously do not need to request uplink resources. However, to allow the scheduler to determine the amount of resources to grant to each terminal in future subframes, information about the buffer situation and the power availability is useful, as discussed above. This information is provided to the scheduler as part of the uplink transmission through MAC control element. The LCID field in one of the MAC subheaders is set to a reserved value indicating the presence of a buffer status report, as illustrated in  FIG. 7 . 
     From a scheduling perspective, buffer information for each logical channel is beneficial, although this could result in a significant overhead. Logical channels are therefore grouped into logical-channel groups and the reporting is done per group. The buffer-size field in a buffer-status report indicates the amount of data awaiting transmission across all logical channels in a logical-channel group. A buffer status report represents one or all four logical-channel groups and can be triggered for the following reasons: 
     i) Arrival of data with higher priority than currently in the transmission buffer—that is, data in a logical-channel group with higher priority than the one currently being transmitted—as this may impact the scheduling decision. 
     ii) Change of serving cell, in which case a buffer-status report is useful to provide the new serving cell with information about the situation in the terminal. 
     iii) Periodically as controlled by a timer. 
     iv) Instead of padding. If the amount of padding required to match the scheduled transport block size is larger than a buffer-status report, a buffer-status report is inserted. Clearly it is better to exploit the available payload for useful scheduling information instead of padding if possible. 
     The Buffer Status Reporting (BSR) procedure is used to provide a serving eNB with information about the amount of data available for transmission (DAT) in the UL buffers of the UE. RRC may control BSR reporting by configuring the two timers periodicBSR-Timer and retxBSR-Timer and by, for each logical channel, optionally signaling Logical Channel Group which allocates the logical channel to an LCG (Logical Channel Group). 
     For the Buffer Status reporting procedure, the UE may consider all radio bearers which are not suspended and may consider radio bearers which are suspended. A Buffer Status Report (BSR) may be triggered if any of the following events occur:
         UL data, for a logical channel which belongs to a LCG, becomes available for transmission in the RLC entity or in the PDCP entity and either the data belongs to a logical channel with higher priority than the priorities of the logical channels which belong to any LCG and for which data is already available for transmission, or there is no data available for transmission for any of the logical channels which belong to a LCG, in which case the BSR is referred below to as “Regular BSR”;   UL resources are allocated and number of padding bits is equal to or larger than the size of the Buffer Status Report MAC control element plus its subheader, in which case the BSR is referred below to as “Padding BSR”;   retxBSR-Timer expires and the UE has data available for transmission for any of the logical channels which belong to a LCG, in which case the BSR is referred below to as “Regular BSR”;   periodicBSR-Timer expires, in which case the BSR is referred below to as “Periodic BSR”.       

     For Regular and Periodic BSR, if more than one LCG has data available for transmission in the TTI where the BSR is transmitted, the UE may report Long BSR. If else, the UE may report Short BSR. 
     If the Buffer Status reporting procedure determines that at least one BSR has been triggered and not cancelled, if the UE has UL resources allocated for new transmission for this TTI, the UE may instruct the Multiplexing and Assembly procedure to generate the BSR MAC control element(s), start or restart periodicBSR-Timer except when all the generated BSRs are Truncated BSRs, and start or restart retxBSR-Timer. 
     A MAC PDU may contain at most one MAC BSR control element, even when multiple events trigger a BSR by the time a BSR can be transmitted in which case the Regular BSR and the Periodic BSR shall have precedence over the padding BSR. 
     The UE may restart retxBSR-Timer upon indication of a grant for transmission of new data on any UL-SCH. 
     All triggered BSRs may be cancelled in case UL grants in this subframe can accommodate all pending data available for transmission but is not sufficient to additionally accommodate the BSR MAC control element plus its subheader. All triggered BSRs shall be cancelled when a BSR is included in a MAC PDU for transmission. 
     The UE shall transmit at most one Regular/Periodic BSR in a TTI. If the UE is requested to transmit multiple MAC PDUs in a TTI, it may include a padding BSR in any of the MAC PDUs which do not contain a Regular/Periodic BSR. 
     All BSRs transmitted in a TTI always reflect the buffer status after all MAC PDUs have been built for this TTI. Each LCG shall report at the most one buffer status value per TTI and this value shall be reported in all BSRs reporting buffer status for this LCG. 
     In summary, the BSR is triggered in any of the following situation: 
     i) when data arrive for a logical channel which has higher priority than the logical channels whose buffers are not empty; 
     ii) when data become available for the UE&#39;s buffer, which is empty; 
     iii) when the retxBSR-Timer expires and there is still data in the UE&#39;s buffer; 
     iv) when a periodicBSR-Timer expires; or 
     v) when the remaining space in a MAC PDU can accommodate a BSR. 
       FIG. 8A  is a diagram for a Short BSR and Truncated BSR MAC control element,  FIG. 8B  is for a Long BSR MAC control element. 
     Buffer Status Report (BSR) MAC control elements consist of either: i) Short BSR and Truncated BSR format: one LCG ID field and one corresponding Buffer Size field or ii) Long BSR format: four Buffer Size fields, corresponding to LCG IDs #0 through #3. 
     The BSR formats are identified by MAC PDU subheaders with LCIDs as specified in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Index 
                 LCID values 
               
               
                   
                   
               
             
            
               
                   
                 00000 
                 CCCH 
               
               
                   
                 00001-01010 
                 Identity of the logical channel 
               
               
                   
                 01011-10110 
                 Reserved 
               
               
                   
                 10111 
                 ProSe Truncated BSR 
               
               
                   
                 11000 
                 ProSe BSR 
               
               
                   
                 11001 
                 Extended Power Headroom Report 
               
               
                   
                 11010 
                 Power Headroom Report 
               
               
                   
                 11011 
                 C-RNTI 
               
               
                   
                 11100 
                 Truncated BSR 
               
               
                   
                 11101 
                 Short BSR 
               
               
                   
                 11110 
                 Long BSR 
               
               
                   
                 11111 
                 Padding 
               
               
                   
                   
               
            
           
         
       
     
     The fields LCG ID and Buffer Size are defined as follow:
         LCG ID: The Logical Channel Group ID field identifies the group of logical channel(s) which buffer status is being reported. The length of the field is 2 bits;   Buffer Size: The Buffer Size field identifies the total amount of data available across all logical channels of a logical channel group after all MAC PDUs for the TTI have been built. The amount of data is indicated in number of bytes. It shall include all data that is available for transmission in the RLC layer and in the PDCP layer; the definition of what data shall be considered as available for transmission. The size of the RLC and MAC headers are not considered in the buffer size computation. The length of this field is 6 bits. If extendedBSR-Sizes is not configured, the values taken by the Buffer Size field are shown in Table 2. If extendedBSR-Sizes is configured, the values taken by the Buffer Size field are shown in Table 3.       

     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Buffer Size 
               
               
                   
                 Index 
                 (BS) value [bytes] 
               
               
                   
                   
               
             
            
               
                   
                  0 
                 BS = 0 
               
               
                   
                  1 
                    0 &lt; BS &lt;= 10 
               
               
                   
                  2 
                   10 &lt; BS &lt;= 12 
               
               
                   
                  3 
                   12 &lt; BS &lt;= 14 
               
               
                   
                  4 
                   14 &lt; BS &lt;= 17 
               
               
                   
                  5 
                   17 &lt; BS &lt;= 19 
               
               
                   
                  6 
                   19 &lt; BS &lt;= 22 
               
               
                   
                  7 
                   22 &lt; BS &lt;= 26 
               
               
                   
                  8 
                   26 &lt; BS &lt;= 31 
               
               
                   
                  9 
                   31 &lt; BS &lt;= 36 
               
               
                   
                 10 
                   36 &lt; BS &lt;= 42 
               
               
                   
                 11 
                   42 &lt; BS &lt;= 49 
               
               
                   
                 12 
                   49 &lt; BS &lt;= 57 
               
               
                   
                 13 
                   57 &lt; BS &lt;= 67 
               
               
                   
                 14 
                   67 &lt; BS &lt;= 78 
               
               
                   
                 15 
                   78 &lt; BS &lt;= 91 
               
               
                   
                 16 
                   91 &lt; BS &lt;= 107 
               
               
                   
                 17 
                   107 &lt; BS &lt;= 125 
               
               
                   
                 18 
                   125 &lt; BS &lt;= 146 
               
               
                   
                 19 
                   146 &lt; BS &lt;= 171 
               
               
                   
                 20 
                   171 &lt; BS &lt;= 200 
               
               
                   
                 21 
                   200 &lt; BS &lt;= 234 
               
               
                   
                 22 
                   234 &lt; BS &lt;= 274 
               
               
                   
                 23 
                   274 &lt; BS &lt;= 321 
               
               
                   
                 24 
                   321 &lt; BS &lt;= 376 
               
               
                   
                 25 
                   376 &lt; BS &lt;= 440 
               
               
                   
                 26 
                   440 &lt; BS &lt;= 515 
               
               
                   
                 27 
                   515 &lt; BS &lt;= 603 
               
               
                   
                 28 
                   603 &lt; BS &lt;= 706 
               
               
                   
                 29 
                   706 &lt; BS &lt;= 826 
               
               
                   
                 30 
                   826 &lt; BS &lt;= 967 
               
               
                   
                 31 
                   967 &lt; BS &lt;= 1132 
               
               
                   
                 32 
                  1132 &lt; BS &lt;= 1326 
               
               
                   
                 33 
                  1326 &lt; BS &lt;= 1552 
               
               
                   
                 34 
                  1552 &lt; BS &lt;= 1817 
               
               
                   
                 35 
                  1817 &lt; BS &lt;= 2127 
               
               
                   
                 36 
                  2127 &lt; BS &lt;= 2490 
               
               
                   
                 37 
                  2490 &lt; BS &lt;= 2915 
               
               
                   
                 38 
                  2915 &lt; BS &lt;= 3413 
               
               
                   
                 39 
                  3413 &lt; BS &lt;= 3995 
               
               
                   
                 40 
                  3995 &lt; BS &lt;= 4677 
               
               
                   
                 41 
                  4677 &lt; BS &lt;= 5476 
               
               
                   
                 42 
                  5476 &lt; BS &lt;= 6411 
               
               
                   
                 43 
                  6411 &lt; BS &lt;= 7505 
               
               
                   
                 44 
                  7505 &lt; BS &lt;= 8787 
               
               
                   
                 45 
                  8787 &lt; BS &lt;= 10287 
               
               
                   
                 46 
                  10287 &lt; BS &lt;= 12043 
               
               
                   
                 47 
                  12043 &lt; BS &lt;= 14099 
               
               
                   
                 48 
                  14099 &lt; BS &lt;= 16507 
               
               
                   
                 49 
                  16507 &lt; BS &lt;= 19325 
               
               
                   
                 50 
                  19325 &lt; BS &lt;= 22624 
               
               
                   
                 51 
                  22624 &lt; BS &lt;= 26487 
               
               
                   
                 52 
                  26487 &lt; BS &lt;= 31009 
               
               
                   
                 53 
                  31009 &lt; BS &lt;= 36304 
               
               
                   
                 54 
                  36304 &lt; BS &lt;= 42502 
               
               
                   
                 55 
                  42502 &lt; BS &lt;= 49759 
               
               
                   
                 56 
                  49759 &lt; BS &lt;= 58255 
               
               
                   
                 57 
                  58255 &lt; BS &lt;= 68201 
               
               
                   
                 58 
                  68201 &lt; BS &lt;= 79846 
               
               
                   
                 59 
                  79846 &lt; BS &lt;= 93479 
               
               
                   
                 60 
                  93479 &lt; BS &lt;= 109439 
               
               
                   
                 61 
                 109439 &lt; BS &lt;= 128125 
               
               
                   
                 62 
                 128125 &lt; BS &lt;= 150000 
               
               
                   
                 63 
                 BS &gt; 150000 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
            
               
                   
                  0 
                 BS = 0 
               
               
                   
                  1 
                    0 &lt; BS &lt;= 10 
               
               
                   
                  2 
                    10 &lt; BS &lt;= 13 
               
               
                   
                  3 
                    13 &lt; BS &lt;= 16 
               
               
                   
                  4 
                    16 &lt; BS &lt;= 19 
               
               
                   
                  5 
                    19 &lt; BS &lt;= 23 
               
               
                   
                  6 
                    23 &lt; BS &lt;= 29 
               
               
                   
                  7 
                    29 &lt; BS &lt;= 35 
               
               
                   
                  8 
                    35 &lt; BS &lt;= 43 
               
               
                   
                  9 
                    43 &lt; BS &lt;= 53 
               
               
                   
                 10 
                    53 &lt; BS &lt;= 65 
               
               
                   
                 11 
                    65 &lt; BS &lt;= 80 
               
               
                   
                 19 
                    80 &lt; BS &lt;= 98 
               
               
                   
                 13 
                    98 &lt; BS &lt;= 120 
               
               
                   
                 14 
                   120 &lt; BS &lt;= 147 
               
               
                   
                 15 
                   147 &lt; BS &lt;= 181 
               
               
                   
                 16 
                   181 &lt; BS &lt;= 223 
               
               
                   
                 17 
                   223 &lt; BS &lt;= 274 
               
               
                   
                 18 
                   274 &lt; BS &lt;= 337 
               
               
                   
                 19 
                   337 &lt; BS &lt;= 414 
               
               
                   
                 20 
                   414 &lt; BS &lt;= 509 
               
               
                   
                 21 
                   509 &lt; BS &lt;= 625 
               
               
                   
                 22 
                   625 &lt; BS &lt;= 769 
               
               
                   
                 23 
                   769 &lt; BS &lt;= 945 
               
               
                   
                 24 
                   945 &lt; BS &lt;= 1162 
               
               
                   
                 25 
                   1162 &lt; BS &lt;= 1429 
               
               
                   
                 26 
                   1429 &lt; BS &lt;= 1757 
               
               
                   
                 27 
                   1757 &lt; BS &lt;= 2161 
               
               
                   
                 28 
                   2161 &lt; BS &lt;= 2657 
               
               
                   
                 29 
                   2657 &lt; BS &lt;= 3267 
               
               
                   
                 30 
                   3267 &lt; BS &lt;= 4017 
               
               
                   
                 31 
                   4017 &lt; BS &lt;= 4940 
               
               
                   
                 32 
                   4940 &lt; BS &lt;= 6074 
               
               
                   
                 33 
                   6074 &lt; BS &lt;= 7469 
               
               
                   
                 34 
                   7469 &lt; BS &lt;= 9185 
               
               
                   
                 35 
                   9185 &lt; BS &lt;= 11294 
               
               
                   
                 36 
                  11294 &lt; BS &lt;= 13888 
               
               
                   
                 37 
                  13888 &lt; BS &lt;= 17077 
               
               
                   
                 38 
                  17077 &lt; BS &lt;= 20999 
               
               
                   
                 39 
                  20999 &lt; BS &lt;= 25822 
               
               
                   
                 40 
                  25822 &lt; BS &lt;= 31752 
               
               
                   
                 41 
                  31752 &lt; BS &lt;= 39045 
               
               
                   
                 42 
                  39045 &lt; BS &lt;= 48012 
               
               
                   
                 43 
                  48012 &lt; BS &lt;= 59039 
               
               
                   
                 44 
                  59039 &lt; BS &lt;= 72598 
               
               
                   
                 45 
                  72598 &lt; BS &lt;= 89272 
               
               
                   
                 46 
                  89272 &lt; BS &lt;= 109774 
               
               
                   
                 47 
                  109774 &lt; BS &lt;= 134986 
               
               
                   
                 48 
                  134986 &lt; BS &lt;= 165989 
               
               
                   
                 49 
                  165989 &lt; BS &lt;= 204111 
               
               
                   
                 50 
                  204111 &lt; BS &lt;= 250990 
               
               
                   
                 51 
                  250990 &lt; BS &lt;= 308634 
               
               
                   
                 52 
                  308634 &lt; BS &lt;= 379519 
               
               
                   
                 53 
                  379519 &lt; BS &lt;= 466683 
               
               
                   
                 54 
                  466683 &lt; BS &lt;= 573866 
               
               
                   
                 55 
                  573866 &lt; BS &lt;= 705666 
               
               
                   
                 56 
                  705666 &lt; BS &lt;= 867737 
               
               
                   
                 57 
                  867737 &lt; BS &lt;= 1067031 
               
               
                   
                 58 
                 1067031 &lt; BS &lt;= 1312097 
               
               
                   
                 59 
                 1312097 &lt; BS &lt;= 1613447 
               
               
                   
                 60 
                 1613447 &lt; BS &lt;= 1984009 
               
               
                   
                 61 
                 1984009 &lt; BS &lt;= 2439678 
               
               
                   
                 62 
                 2439678 &lt; BS &lt;= 3000000 
               
               
                   
                 63 
                 BS &gt; 3000000 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 9  is an example of default data path for communication between two UEs. With reference to  FIG. 9 , even when two UEs (e.g., UE 1 , UE 2 ) in close proximity communicate with each other, their data path (user plane) goes via the operator network. Thus a typical data path for the communication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW). 
       FIGS. 10 and 11  are examples of data path scenarios for a proximity communication. If wireless devices (e.g., UE 1 , UE 2 ) are in proximity of each other, they may be able to use a direct mode data path ( FIG. 10 ) or a locally routed data path ( FIG. 11 ). In the direct mode data path, wireless devices are connected directly each other (after appropriate procedure(s), such as authentication), without eNB and SGW/PGW. In the locally routed data path, wireless devices are connected each other through eNB only. 
       FIG. 12  is a conceptual diagram illustrating for a non-roaming reference architecture. 
     PC 1  to PC 5  represent interfaces. PC 1  is a reference point between a ProSe application in a UE and a ProSe App server. It is used to define application level signaling requirements. PC 2  is a reference point between the ProSe App Server and the ProSe Function. It is used to define the interaction between ProSe App Server and ProSe functionality provided by the 3GPP EPS via ProSe Function. One example may be for application data updates for a ProSe database in the ProSe Function. Another example may be data for use by ProSe App Server in interworking between 3GPP functionality and application data, e.g. name translation. PC 3  is a reference point between the UE and ProSe Function. It is used to define the interaction between UE and ProSe Function. An example may be to use for configuration for ProSe discovery and communication. PC 4  is a reference point between the EPC and ProSe Function. It is used to define the interaction between EPC and ProSe Function. Possible use cases may be when setting up a one-to-one communication path between UEs or when validating ProSe services (authorization) for session management or mobility management in real time. 
     PC 5  is a reference point between UE to UE used for control and user plane for discovery and communication, for relay and one-to-one communication (between UEs directly and between UEs over LTE-Uu). Lastly, PC 6  is a reference point may be used for functions such as ProSe Discovery between users subscribed to different PLMNs. 
     Especially, the following identities are used for ProSe Direct Communication:
         Source Layer-2 ID identifies a sender of a D2D packet at PC 5  interface. The Source Layer-2 ID is used for identification of the receiver RLC UM entity;   Destination Layer-2 ID identifies a target of the D2D packet at PC 5  interface. The Destination Layer-2 ID is used for filtering of packets at the MAC layer. The Destination Layer-2 ID may be a broadcast, groupcast or unicast identifier; and   SA L1 ID identifier in Scheduling Assignment (SA) at PC 5  interface. SA L1 ID is used for filtering of packets at the physical layer. The SA L1 ID may be a broadcast, groupcast or unicast identifier.       

     No Access Stratum signaling is required for group formation and to configure Source Layer-2 ID and Destination Layer-2 ID in the UE. This information is provided by higher layers. 
     In case of groupcast and unicast, the MAC layer will convert the higher layer ProSe ID (i.e. ProSe Layer-2 Group ID and ProSe UE ID) identifying the target (Group, UE) into two bit strings of which one can be forwarded to the physical layer and used as SA L1 ID whereas the other is used as Destination Layer-2 ID. For broadcast, L2 indicates to L1 that it is a broadcast transmission using a pre-defined SA L1 ID in the same format as for group- and unicast. 
     In summary, for the PC 5  interface, there are several features as following: 
     i) The Source Layer-2 ID and the Destination Layer-2 ID in front of the MAC PDU without MAC subheader, ii) It is too early to exclude MAC CE for D2D, iii) One D2D group can be composed of UEs supporting different MAC PDU formats, iv) Include a MAC PDU format version number in the first field of D2D MAC PDU, v) Separate HARQ entity for D2D. 
     On the other hand, for the Uu interface, there are several features different from the PC 5  interface as following: 
     i) It might be beneficial for the network to know which buffer status information is mapped to which D2D communication groups of a UE, ii) Group Index is informed to the eNB by BSR (either explicit or implicit), iii) The eNB is aware of Group ID, and mapping relation between Group ID and Group Index, and iv) The UE reports Group ID, and mapping relation between Group ID and Group Index to the eNB. 
       FIG. 13A  is a conceptual diagram illustrating for User-Plane protocol stack for ProSe Direct Communication, and  FIG. 13B  is Control-Plane protocol stack for ProSe Direct Communication. 
       FIG. 13A  shows the protocol stack for the user plane, where PDCP, RLC and MAC sublayers (terminate at the other UE) perform the functions listed for the user plane (e.g. header compression, HARQ retransmissions). The PC 5  interface consists of PDCP, RLC, MAC and PHY as shown in  FIG. 13A . 
     User plane details of ProSe Direct Communication: i) There is no HARQ feedback for ProSe Direct Communication, ii) MAC sub header contains LCIDs (to differentiate multiple logical channels), iii) The MAC header comprises a Source Layer-2 ID and a Destination Layer-2 ID, iv) At MAC Multiplexing/demultiplexing, priority handling and padding are useful for ProSe Direct communication, v) RLC UM is used for ProSe Direct communication, vi) Segmentation and reassembly of RLC SDUs are performed, vii) A receiving UE needs to maintain at least one RLC UM entity per transmitting peer UE, viii) An RLC UM receiver entity does not need to be configured prior to reception of the first RLC UM data unit, and ix) U-Mode is used for header compression in PDCP for ProSe Direct Communication. 
     A UE may establish multiple logical channels. LCID included within the MAC subheader uniquely identifies a logical channel within the scope of one source Layer-2 ID and Destination Layer-2 ID combination. All logical channels are mapped to one specified logical channel group (e.g. LCGID 3). It is up to the UE implementation in which order to serve the logical channels. Parameters for Logical channel prioritization are not configured 
       FIG. 13B  shows the protocol stack for the control plane, where RRC, RLC, MAC, and PHY sublayers (terminate at the other UE) perform the functions listed for the control plane. A D2D UE does not establish and maintain a logical connection to receiving D2D UEs prior to a ProSe Direct communication. 
       FIG. 14  is a conceptual diagram illustrating for a PC 5  interface for device to device direct discovery. 
     ProSe Direct Discovery is defined as the procedure used by the ProSe-enabled UE to discover other ProSe-enabled UE(s) in its proximity using E-UTRA direct radio signals via PC 5 . ProSe Direct Discovery is supported only when the UE is served by E-UTRAN. 
     Upper layer handles authorization for announcement and monitoring of discovery information. Content of discovery information is transparent to Access Stratum (AS) and no distinction in AS is made for ProSe Direct Discovery models and types of ProSe Direct Discovery. 
     The UE can participate in announcing and monitoring of discovery information in both RRC IDLE and RRC CONNECTED state as per eNB configuration. The UE announces and monitors its discovery information subject to the half-duplex constraint. 
     Announcing and Monitoring UE maintains the current UTC time. Announcing UE transmits the discovery message which is generated by the ProSe protocol taking into account the UTC time upon transmission of the discovery message. In the monitoring UE the ProSe protocol provides the message to be verified together with the UTC time upon reception of the message to the ProSe function. 
     The Radio Protocol Stack (AS) for ProSe Direct Discovery consists of only MAC and PHY. 
     The AS layer performs the following functions:
         Interfaces with upper layer (ProSe Protocol): The MAC layer receives the discovery information from the upper layer (ProSe Protocol). The IP layer is not used for transmitting the discovery information.   Scheduling: The MAC layer determines the radio resource to be used for announcing the discovery information received from upper layer.   Discovery PDU generation: The MAC layer builds the MAC PDU carrying the discovery information and sends the MAC PDU to the physical layer for transmission in the determined radio resource. No MAC header is added.       

     There are two types of resource allocation for discovery information announcement.
         Type 1: A resource allocation procedure where resources for announcing of discovery information are allocated on a non UE specific basis, further characterized by: i) The eNB provides the UE(s) with the resource pool configuration used for announcing of discovery information. The configuration may be signaled in SIB, ii) The UE autonomously selects radio resource(s) from the indicated resource pool and announce discovery information, iii) The UE can announce discovery information on a randomly selected discovery resource during each discovery period.   Type 2: A resource allocation procedure where resources for announcing of discovery information are allocated on a per UE specific basis, further characterized by: i) The UE in RRC CONNECTED may request resource(s) for announcing of discovery information from the eNB via RRC, ii) The eNB assigns resource(s) via RRC, iii) The resources are allocated within the resource pool that is configured in UEs for monitoring.       

     For UEs in RRC IDLE, the eNB may select one of the following options:
         The eNB may provide a Type 1 resource pool for discovery information announcement in SIB. UEs that are authorized for Prose Direct Discovery use these resources for announcing discovery information in RRC IDLE.   The eNB may indicate in SIB that it supports D2D but does not provide resources for discovery information announcement. UEs need to enter RRC Connected in order to request D2D resources for discovery information announcement.       

     For UEs in RRC_CONNECTED,
         A UE authorized to perform ProSe Direct Discovery announcement indicates to the eNB that it wants to perform D2D discovery announcement.   The eNB validates whether the UE is authorized for ProSe Direct Discovery announcement using the UE context received from MME.   The eNB may configure the UE to use a Type 1 resource pool or dedicated Type 2 resources for discovery information announcement via dedicated RRC signaling (or no resource).   The resources allocated by the eNB are valid until a) the eNB de-configures the resource(s) by RRC signaling or b) the UE enters IDLE. (FFS whether resources may remain valid even in IDLE).       

     Receiving UEs in RRC_IDLE and RRC_CONNECTED monitor both Type 1 and Type 2 discovery resource pools as authorized. The eNB provides the resource pool configuration used for discovery information monitoring in SIB. The SIB may contain discovery resources used for announcing in neighbor cells as well. 
     By supporting ProSe communication, the data are transmitted over either PC 5  interface or Uu interface. Although there is no explicit agreement on having a separate ProSe BSR for ProSe communication, it seems to be a common RAN2 understanding that the UE uses ProSe BSR for requesting resource for the data transmission over PC 5  interface. 
       FIG. 15  is a conceptual diagram for priority handling buffer status reporting according to embodiments of the present invention. 
     It was pointed out that priority handling rule is needed for ProSe BSR. In this application, we discuss how the UE handles ProSe BSR MAC CE in LCP procedure. 
     In MAC specification, for LCP procedure, the relative priority is defined as follows,
         MAC control element for C-RNT1 or data from UL-CCCH;   MAC control element for BSR, with exception of BSR included for padding;   MAC control element for PHR or Extended PHR;   data from any Logical Channel, except data from UL-CCCH;   MAC control element for BSR included for padding.       

     As ProSe BSR is newly introduced for Prose communication, RAN2 need to define the relative priority for ‘MAC CE for ProSe BSR, with exception of ProSe BSR included for padding’ and ‘MAC CE for ProSe BSR included for padding’. 
     In general, the legacy operation shouldn&#39;t be impeded by the additional feature unless it is justified in terms of motivation/gain/complexity. In this sense, ‘MAC CE for ProSe BSR, with exception of ProSe BSR included for padding’ has to have lower priority than at least ‘MAC control element for BSR, with exception of BSR included for padding’. 
     Padding BSR is additional information which could be transmitted only when uplink resource is left to include Padding BSR. As ProSe communication is additional feature in Rel-12, it is straightforward that ‘MAC CE for ProSe BSR included for padding’ has the lowest priority in LCP procedure, i.e., lower priority than ‘MAC CE for BSR included for padding’. 
     Then, there are three options as follows: 
     1. Option 1 is to prioritize the MAC CE for ProSe BSR over the MAC CE for PHR. Although PHR MAC CE is deprioritized than BSR MAC CE in legacy operation, it doesn&#39;t mean that PHR MAC CE has lower priority than ProSe BSR MAC CE as well. Considering that PHR MAC CE carries important scheduling assistant information for data transmission over Uu interface, Option 1 seems not desirable as it possibly has a negative impact on scheduling for Uu interface as well as data transmission on Uu interface. 
     Regarding the option 1, the relative priority is defined as follows: 
     i) MAC control element for C-RNTI or data from UL-CCCH; 
     ii) MAC control element for BSR, with exception of BSR included for padding; 
     iii) MAC control element for ProSe BSR, with exception of ProSe BSR included for padding; 
     iv) MAC control element for PHR or Extended PHR; 
     v) Data from any Logical Channel, except data from UL-CCCH; 
     vi) MAC control element for BSR included for padding; and 
     vii) MAC CE for ProSe BSR included for padding. 
     2. Option 2 is to prioritize ‘scheduling assistant information for data transmission over Uu interface’ over ‘scheduling assistant information for data transmission over PC 5  interface’. In option 2, data transmission over Uu interface is deprioritized than the MAC CE for ProSe BSR, hence, it also has an impact on data transmission on Uu interface. However, Option 2 is acceptable because delayed data transmission might not be a critical problem. 
     Regarding the option  2 , the relative priority is defined as follows: 
     i) MAC control element for C-RNTI or data from UL-CCCH; 
     ii) MAC control element for BSR, with exception of BSR included for padding; 
     iii) MAC control element for PHR or Extended PHR; 
     iv) MAC control element for ProSe BSR, with exception of ProSe BSR included for padding; 
     v) Data from any Logical Channel, except data from UL-CCCH; 
     vi) MAC control element for BSR included for padding; and 
     vii) MAC CE for ProSe BSR included for padding. 
     3. Option 3 is to prioritize ‘data transmission over Uu interface and scheduling assistant information for Uu interface’ over ‘data transmission over PC 5  interface and scheduling assistant information for PC 5  interface’. In Option 3, if there is continuous on-going uplink data transmission over Uu interface, the ProSe BSR would be delayed for a long time. Considering that ProSe BSR MAC CE carries important scheduling assistant information for PC 5  interface, Option 3 is not acceptable. 
     Regarding the option 3, the relative priority is defined as follows: 
     i) MAC control element for C-RNTI or data from UL-CCCH; 
     ii) MAC control element for BSR, with exception of BSR included for padding; 
     iii) MAC control element for PHR or Extended PHR; 
     iv) Data from any Logical Channel, except data from UL-CCCH; 
     v) MAC control element for ProSe BSR, with exception of ProSe BSR included for padding; 
     vi) MAC control element for BSR included for padding; and 
     vii) MAC CE for ProSe BSR included for padding. 
     With above analysis, Option 2 is preferred because it has an acceptable impact on data transmission over Uu interface while enabling ProSe communication. Thus, our invention refers that ‘MAC CE for ProSe BSR, with exception of BSR included for padding’ has higher priority than Uu data but has lower priority than Uu scheduling assistant information, i.e., Option 2. 
     Regarding FIG. 15, when the UE generates a MAC PDU if both of a PHR (Power Headroom Reporting) and a sidelink BSR (Buffer Status Reporting) are generated while the UE communicates with other UEs directly using a sidelink, 
     the PHR is prioritized over the sidelink BSR when the UE prioritizes between the PHR and the sidelink BSR in the generated MAC PDU (S 1501 ). 
     Preferably, the PHR is related to scheduling assistant information for uplink data transmission via Uu interface. 
     Preferably, the PHR is transmitted using a PHR MAC CE, an extended PHR MAC CE, or a dual connectivity PHR MAC CE. 
     The UE allocates an uplink resource to a PHR MAC CE and a corresponding MAC sub-header in the MAC PDU (S 1503 ), and then checks whether a remaining uplink resource in the MAC PDU can accommodate a sidelink BSR MAC CE and a corresponding MAC sub-header (S 1505 ). 
     If the remaining uplink resource can accommodate the sidelink BSR MAC CE and the corresponding MAC sub-header, the UE can allocate an uplink resource to the sidelink BSR MAC CE and the corresponding MAC sub-header (S 1507 ). If there is no remaining uplink resource after the UE allocates an uplink resource to a PHR MAC CE and a corresponding MAC sub-header in the MAC PDU, the UE cannot allocate an uplink resource to the sidelink BSR MAC CE and the corresponding MAC sub-header (S 1509 ). 
     After the UE allocates the uplink resource to the sidelink BSR MAC CE and the corresponding MAC sub-header in the MAC PDU, the UE allocates a remaining uplink resource in MAC PDU to uplink data except data from UL-CCCH, or padding BSR (S 1511 ). 
     The UE transmits the MAC PDU after generating the MAC PDU (S 1513 ). 
       FIG. 16  is an example for priority handling buffer status reporting according to embodiments of the present invention. 
     The UE triggers a Regular BSR for Uu data and a Regular BSR for PC 5  data simultaneously. Regarding Uu BSR, the UE reports a long BSR because there are multiple LCG that has data available for transmission. The UE has total 100 bytes of Uu data available for transmission, which is not from UL-CCCH. 
     Regarding ProSe BSR, the UE report a BS for the Group of which the data becomes available for transmission. 
     The UE is allocated with 60 bytes of uplink resource. When the UE has uplink resource allocated for new transmission for this TTI, the UE generates the Uu BSR MAC CE, firstly. The size of Uu BSR MAC CE is 3 bytes. And then, the UE generates the ProSe BSR MAC CE. The size of ProSe BSR MAC CE is, e.g., 1 byte. 
     In the 60 bytes of MAC PDU, the UE allocates uplink resource to Uu BSR MAC CE and the corresponding MAC sub-header, which consumes 4 bytes. The remaining space in MAC PDU is 56 bytes. 
     The UE checks if the remaining space in MAC PDU can allocate uplink resource to the ProSe BSR MAC CE and the corresponding MAC sub-header. If yes, the UE allocate uplink resource to ProSe BSR MAC CE and the corresponding MAC sub-header, which consumes 2 bytes. The remaining space in MAC PDU is 54 bytes. 
     In the remaining 54 bytes of MAC PDU, the UE allocate uplink resource to MAC SDUs for Uu data and the corresponding MAC sub-headers, which consumes rest of the allocated uplink resource, i.e., 54 bytes. 
     As an example, the generated MAC PDU is shown in the  FIG. 16 . As long as the MAC CEs are placed before the MAC SDUs and after the MAC header, there is no specific placing order between MAC CEs. 
     The embodiments of the present invention described herein below are combinations of elements and features of the present invention. The elements or features may be considered selective unless otherwise mentioned. Each element or feature may be practiced without being combined with other elements or features. Further, an embodiment of the present invention may be constructed by combining parts of the elements and/or features. Operation orders described in embodiments of the present invention may be rearranged. Some constructions of any one embodiment may be included in another embodiment and may be replaced with corresponding constructions of another embodiment. It is obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an embodiment of the present invention or included as a new claim by subsequent amendment after the application is filed. 
     In the embodiments of the present invention, a specific operation described as performed by the BS may be performed by an upper node of the BS. Namely, it is apparent that, in a network comprised of a plurality of network nodes including a BS, various operations performed for communication with an MS may be performed by the BS, or network nodes other than the BS. The term ‘eNB’ may be replaced with the term ‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc. 
     The above-described embodiments may be implemented by various means, for example, by hardware, firmware, software, or a combination thereof 
     In a hardware configuration, the method according to the embodiments of the present invention may be implemented by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, microcontrollers, or microprocessors. 
     In a firmware or software configuration, the method according to the embodiments of the present invention may be implemented in the form of modules, procedures, functions, etc. performing the above-described functions or operations. Software code may be stored in a memory unit and executed by a processor. The memory unit may be located at the interior or exterior of the processor and may transmit and receive data to and from the processor via various known means. 
     Those skilled in the art will appreciate that the present invention may be carried out in other specific ways than those set forth herein without departing from the spirit and essential characteristics of the present invention. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. The scope of the invention should be determined by the appended claims and their legal equivalents, not by the above description, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.