Transmitting user equipment, method thereof, and integrated circuit

Abstract

The present invention relates to a transmitting user equipment, comprising: a receiving unit, which receives multiple SL grants for a subsequent SC period in multiple subframes before the start of the subsequent SC period, wherein: the transmitting user equipment is configured with a maximum number of SL processes, and each of the SL grants is associated with one of the SL processes in a one-to-one manner based on the subframe in which the SL grant is received, and for one of the SL processes, a second SL grant for the subsequent SC period received in subframe n covers the first SL grant for the same subsequent SC period previously received in subframe n‑X, where X is an integer value equal to or greater than the maximum number of SL processes; a circuit, which associates the SL processes with the SL grants, respectively, and allocates radio resources within the subsequent SC period for each of the SL processes according to the associated SL grants; a transmitting unit, which uses the allocated radio resources to perform SL transmission including at least one side link control information SCI transmission and at least one data transmission.

Description

[0001] This application is a divisional application of the invention patent application with the application date of November 6, 2015, application number: 201580083985.1, and invention name: "Multiple side link control transmissions during the side link control period". Technical Field

[0002] The present disclosure relates to a mechanism for allocating radio resources to a transmitting user equipment (UE) for performing multiple direct sidelink transmissions over a sidelink interface to one or more receiving user equipment (UEs) during a sidelink period. In this regard, the present disclosure defines a method for the allocation mechanism and a UE applying the allocation mechanism described herein. Background Art

[0003] Long Term Evolution (LTE)

[0004] Third-generation mobile systems (3G), based on WCDMA radio access technology, are being widely deployed around the world. The first step in enhancing or evolving this technology is the introduction of High-Speed ​​Downlink Packet Access (HSDPA) and an enhanced uplink, also known as High-Speed ​​Uplink Packet Access (HUSPA), making the radio access technology highly competitive.

[0005] To prepare for further growth in user demand and to make it competitive with new radio access technologies, 3GPP introduced a new mobile communication system called Long Term Evolution (LTE). LTE is designed to meet the carrier needs for high-speed data and media transmission and large-capacity voice support for the next decade. The ability to provide high bit rates is a key feature of LTE.

[0006] The work item (WI) specification for Long Term Evolution (LTE), known as Evolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN), was finalized as Release 8 (LTE Release 8). The LTE system represents an efficient packet-based radio access and radio access network that provides all-IP-based functionality with low latency and low cost. In LTE, multiple adjustable transmission bandwidths, such as 1.4 MHz, 3.0 MHz, 5.0 MHz, 10.0 MHz, 15.0 MHz, and 20.0 MHz, are specified to achieve flexible system deployment using a given spectrum. In the downlink, radio access based on Orthogonal Frequency Division Multiplexing (OFDM) is adopted because of its inherent immunity to multipath interference (MPI), which is due to the low symbol rate, the use of a cyclic prefix (CP), and its association with different transmission bandwidth arrangements.

[0007] Single-carrier frequency division multiple access (SC-FDMA)-based radio access is adopted in the uplink because, given the limited transmission power of user equipment (UE), providing wide-area coverage takes precedence over increasing peak data rates. Many key packet radio access technologies, including multiple-input multiple-output (MIMO) channel transmission technology, are adopted, and an efficient control signaling structure is implemented in LTE Release 8 / 9.

[0008] LTE Architecture

[0009] Figure 1 The overall architecture is shown in Figure 1. The E-UTRAN consists of eNodeBs, which provide the E-UTRA user plane (PDCP / RLC / MAC / PHY) and control plane (RRC) protocol terminations towards the user equipment (UE). The eNodeB (eNB) is responsible for the physical (PHY), medium access control (MAC), radio link control (RLC) and packet data control protocol (PDCP) layers, which include functionality for user plane header compression and encryption. The eNodeB also provides radio resource control (RRC) functionality for the control plane. The eNodeB performs many functions, including radio resource management, admission control, scheduling, imposing negotiated uplink quality of service (QoS), cell information broadcast, encryption / decryption of user and control plane data, and compression / decompression of downlink / uplink user plane packet headers. The eNodeBs are interconnected via the X2 interface.

[0010] The eNodeB is also connected to the EPC (Evolved Packet Core) via the S1 interface, more specifically to the MME (Mobility Management Entity) via the S1-MME and to the Serving Gateway (SGW) via the S1-U. The S1 interface supports a many-to-many relationship between the MME / Serving Gateway and the eNodeB. The SGW routes and forwards user data packets, and also acts as a mobility anchor for the user plane during handover between eNodeBs and as an anchor for mobility between LTE and other 3GPP technologies (terminating the S4 interface and relaying traffic between the 2G / 3G system and the PDN GW). For user equipment in idle state, when downlink data for the user equipment arrives, the SGW terminates the downlink data path and triggers paging. The SGW manages and stores user equipment context, such as parameters for IP bearer services and network internal routing information. In the case of lawful interception, the SGW also performs replication of user traffic.

[0011] The MME is the key control node for the LTE access network. The MME is responsible for idle mode user equipment tracking and paging procedures, including retransmissions. The MME participates in bearer activation / deactivation processing and is also responsible for selecting the SGW for the user equipment at the time of initial attach and in the case of intra-LTE handover involving core network (CN) node relocation. The MME is responsible for authenticating the user (by interacting with the HSS). Non-access stratum (NAS) signaling terminates at the MME, and the MME is also responsible for generating and assigning temporary identities to user equipment. The MME checks the authorization of the user equipment to reside on the service provider's public land mobile network (PLMN) and imposes roaming restrictions on the user equipment. The MME is the endpoint in the network for ciphering / integrity protection of NAS signaling and handles security key management. The MME also supports lawful interception of signaling. The MME also provides control plane functions for mobility between LTE and 2G / 3G access networks, using the S3 interface terminating at the MME from the SGSN. The MME also terminates the S6a interface towards the home HSS for roaming user equipment.

[0012] Component Carrier Structure in LTE

[0013] The downlink component carriers of a 3GPP LTE system are subdivided in the time-frequency domain into so-called subframes. Figure 2 The two downlink time slots shown in FIG, the first downlink time slot includes a control channel region (PDCCH region) within the first OFDM symbol. Each subframe includes a given number of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), each OFDM symbol spanning the entire bandwidth of the component carrier. Therefore, each OFDM symbol includes a number of modulation symbols transmitted on the corresponding subcarriers. In LTE, the information transmitted in each time slot is composed of subcarriers and The resource grid description of OFDM symbols. is the number of resource blocks within the bandwidth. Depends on the downlink transmission bandwidth configured in the cell and should satisfy in and These are the minimum and maximum downlink bandwidths supported by the current version of the specification. The number of subcarriers in a resource block. For a conventional cyclic prefix subframe structure, and

[0014] Assuming a multi-carrier communication system employing OFDM (such as used in 3GPP Long Term Evolution (LTE)), the smallest unit of resources that can be allocated by the scheduling unit is a "resource block". A physical resource block (PRB) is defined as a contiguous OFDM symbol in the time domain (e.g., 7 OFDM symbols) and Figure 2 8) , which is available at http: / / www.3gpp.org and incorporated herein by reference.

[0015] A subframe consists of two time slots, so that there are 14 OFDM symbols in the subframe when a so-called "normal" CP (cyclic prefix) is used, and there are 12 OFDM symbols in the subframe when a so-called "extended" CP is used. For the sake of terminology, the time-frequency resources equivalent to the same consecutive subcarriers spanning a complete subframe are hereinafter referred to as a "resource block pair" or equivalently an "RB pair" or "PRB pair".

[0016] The term "component carrier" refers to a combination of several resource blocks in the frequency domain. In LTE, the term "component carrier" is no longer used; instead, the term has been changed to "cell," which refers to the combination of downlink and optional uplink resources. The association between the carrier frequencies of downlink resources and uplink resources is indicated in system information transmitted on the downlink resources.

[0017] Similar assumptions about component carrier structure will also apply to later releases.

[0018] Carrier aggregation in LTE-A to support wider bandwidth

[0019] The spectrum for IMT-Advanced was determined at the World Radiocommunication Conference 2007 (WRC-07). While the overall spectrum for IMT-Advanced was determined, the actual frequency bandwidth available varies by region or country. However, after determining the outline of the available spectrum, the Third Generation Partnership Project (3GPP) began standardizing the radio interface. At the 3GPP TSG RAN#39 meeting, a study item description for "Further development of E-UTRA (LTE-Advanced)" was approved. This study item covers, for example, the technical aspects to be considered in the evolution of E-UTRA to meet the requirements of IMT-Advanced.

[0020] LTE-Advanced systems support a bandwidth of 100 MHz, while LTE systems only support 20 MHz. The lack of radio spectrum has become a bottleneck for wireless network development, making it difficult to find spectrum bands wide enough for LTE-Advanced systems. Consequently, there is an urgent need to find ways to access wider radio spectrum bands, and a potential answer lies in carrier aggregation functionality.

[0021] In carrier aggregation, two or more component carriers are aggregated to support a wider transmission bandwidth of up to 100 MHz. Several cells in an LTE system are aggregated into one wider channel in an LTE-Advanced system (which is wide enough for 100 MHz), even though the cells in LTE may be in different frequency bands.

[0022] All component carriers can be configured to be compatible with LTE Release 8 / 9, at least when the bandwidth of the component carrier does not exceed the bandwidth supported by the LTE Release 8 / 9 cell. Not all component carriers aggregated by a user equipment will necessarily be compatible with Release 8 / 9. Existing mechanisms (e.g., barring) can be used to prevent Release 8 / 9 user equipment from camping on a component carrier.

[0023] A user equipment can simultaneously receive or transmit on one or more component carriers (corresponding to multiple serving cells) depending on its capabilities. An LTE-A Release 10 user equipment with the receiving and / or transmitting capabilities for carrier aggregation can simultaneously receive and / or transmit on multiple serving cells, whereas an LTE Release 8 / 9 user equipment can only receive and transmit on a single serving cell if the component carrier structure follows the Release 8 / 9 specifications.

[0024] Carrier aggregation is supported for both contiguous and non-contiguous component carriers, with each component carrier limited to a maximum of 110 resource blocks in the frequency domain (using 3GPP LTE (Release 8 / 9) numerology).

[0025] A user equipment compatible with 3GPP LTE-A (Release 10) can be configured to aggregate different numbers of component carriers, which originate from the same eNodeB (base station) and may have different bandwidths in the uplink and downlink. The number of configurable downlink component carriers depends on the downlink aggregation capability of the UE. Conversely, the number of configurable uplink component carriers depends on the uplink aggregation capability of the UE. Currently it may not be possible to configure a mobile terminal with more uplink component carriers than downlink component carriers. In a typical TDD deployment, the number of component carriers and the bandwidth of each component carrier are the same in the uplink and downlink. Component carriers originating from the same eNodeB do not need to provide the same coverage.

[0026] The spacing between the center frequencies of consecutively aggregated component carriers should be a multiple of 300kHz. This is to be compatible with the 100kHz frequency raster of 3GPP LTE (Release 8 / 9) while maintaining orthogonality with subcarriers having 15kHz spacing. Depending on the aggregation scenario, a small number of unused subcarriers can be inserted between consecutive component carriers to help achieve n×300kHz spacing.

[0027] The nature of the aggregation of multiple carriers is only exposed upwards to the MAC layer. For both uplink and downlink, a HARQ entity is required in the MAC for each aggregated component carrier. (In the absence of SU-MIMO for uplink), there is at most one transport block per component carrier. A transport block and its potential HARQ retransmissions need to be mapped to the same component carrier.

[0028] When carrier aggregation (CC) is configured, the mobile terminal has only one RRC connection with the network. When the RRC connection is established / reestablished, one cell provides security inputs (one ECGI, one PCI and one ARFCN) and non-access stratum mobility information (e.g., TAI), similar to LTE release 8 / 9. After the RRC connection is established / reestablished, the component carrier corresponding to the cell is called the downlink primary cell (PCell). In the connected state, each user equipment is always configured with one and only one downlink PCell (DL PCell) and one uplink PCell (UL PCell). Within the set of configured component carriers, other cells are called secondary cells (SCells); the carriers of the SCells are the downlink secondary component carrier (DL SCC) and the uplink secondary component carrier (UL SCC). Up to five serving cells including the PCell can be configured for a UE.

[0029] The characteristics of downlink and uplink PCell are:

[0030] For each SCell, in addition to downlink resources, the UE's use of uplink resources is also configurable (so the number of configured DL SCCs is always greater than or equal to the number of UL SCCs, and no SCell can be configured to use only uplink resources)

[0031] ● Unlike SCell, downlink PCell cannot be disabled

[0032] ● Reestablishment is triggered when the downlink PCell experiences Rayleigh fade (RLF), not when the SCell experiences RLF

[0033] ● Get non-access stratum information from downlink PCell

[0034] The PCell can only change with the handover process (i.e., with the security key change and RACH process)

[0035] PCell is used to transmit PUCCH

[0036] ● Uplink PCell is used to transmit Layer 1 uplink control information

[0037] ●From the UE's perspective, each uplink resource belongs to only one serving cell

[0038] Configuration and reconfiguration of component carriers, as well as addition and removal, can be performed by RRC. Activation and deactivation are accomplished via the MAC control unit. During intra-LTE handover, RRC can also add, remove, or reconfigure SCells for use in the target cell. When adding a new SCell, dedicated RRC signaling is used to send the SCell's system information required for transmission / reception (similar to how it is used for handover in Release 8 / 9). As each SCell is added to a UE, it is configured with a serving cell index; PCells always have a serving cell index of 0.

[0039] When a user equipment is configured with carrier aggregation, there is at least one pair of uplink and downlink component carriers that is always active. The downlink component carrier of the pair may also be referred to as a "DL anchor carrier." The same applies to the uplink.

[0040] When carrier aggregation is configured, user equipment can be scheduled on multiple component carriers simultaneously, but at most one random access procedure should be in progress at any time. Cross-carrier scheduling allows the PDCCH of a component carrier to schedule resources on another component carrier. For this purpose, a component carrier identification field, called CIF, is introduced in the corresponding DCI format.

[0041] When there is no cross-carrier scheduling, the association between uplink and downlink component carriers, established via RRC signaling, allows identification of the uplink component carrier to which a grant applies. The association of downlink component carriers to uplink component carriers does not necessarily need to be one-to-one. In other words, more than one downlink component carrier can be associated with the same uplink component carrier. Also, a downlink component carrier can be associated with only one uplink component carrier.

[0042] LTE uplink access solution

[0043] For uplink transmission, efficient user terminal transmission is required to maximize coverage. Single-carrier transmission combined with FDMA with dynamic bandwidth allocation has been selected as the evolved UTRA uplink transmission scheme. The main reasons for preferring single-carrier transmission are the lower peak-to-average power ratio (PAPR) compared to multi-carrier signals (OFDMA), and the corresponding improved power amplifier efficiency and improved coverage (higher data rates for a given terminal peak power). During each time interval, the Node B allocates a unique time / frequency resource to the user for transmitting user data, thereby ensuring intra-cell orthogonality. Orthogonal access in the uplink ensures improved spectral efficiency by eliminating intra-cell interference. The insertion of a cyclic prefix into the transmitted signal helps the base station (Node B) handle interference caused by multipath propagation.

[0044] The basic physical resource for data transmission consists of a frequency resource of size BWgrant during a time interval (e.g., a 0.5ms subframe), to which the coded information bits are mapped. It should be noted that a subframe (also called a transmission time interval (TTI)) is the minimum time interval for user data transmission. However, a frequency resource BWgrant over a period longer than one TTI can be allocated to a user by concatenating subframes.

[0045] LTE UL Scheduling Scheme

[0046] The uplink scheme in LTE supports both scheduled access (ie, controlled by the eNB), and contention-based access.

[0047] In the case of scheduled access, the UE is assigned specific frequency resources (i.e., time / frequency resources) by the eNB at specific times for uplink data transmission. Some time / frequency resources may be allocated for contention-based access, within which the UE can transmit without first being scheduled by the eNB. One scenario in which a UE performs contention-based access is, for example, random access, i.e., when the UE performs initial access to a cell or requests uplink resources.

[0048] For scheduled access, the Node B scheduler allocates unique time / frequency resources to the user for uplink data transmission. More specifically, the scheduler determines:

[0049] Which UE(s) are allowed to transmit,

[0050] ●Which physical channel resources,

[0051] • The transport format (Modulation and Coding Scheme MCS) used by the mobile terminal for transmission.

[0052] The assignment information is then signaled to the UE via a scheduling grant sent on the L1 / L2 control channel. For simplicity, this channel will be referred to as the "uplink grant channel" below. Therefore, the scheduling grant message contains information about which part of the frequency band the UE is allowed to use, the validity period of the grant, and the transport format that the UE must use for the upcoming uplink transmission. The shortest validity period is one subframe. Depending on the chosen scheme, additional information may also be included in the grant message. Only "per UE" grants are used to grant the right to transmit on the UL-SCH (i.e., there are no "per UE per RB" grants). Therefore, the UE needs to distribute the assigned resources among the radio bearers according to certain rules. Unlike in HSUPA, there is no UE-based transport format selection. The eNB decides the transport format based on some information (e.g., reported scheduling information and QoS information), and the UE must comply with the selected transport format. In HSUPA, the Node B allocates the maximum uplink resources, and the UE selects the transport format actually used for data transmission accordingly.

[0053] Since scheduling of radio resources is the most important function for determining quality of service in shared channel access networks, the UL scheduling scheme for LTE should meet multiple requirements in order to support efficient QoS management.

[0054] ● Starvation of low-priority services should be avoided

[0055] ● The scheduling scheme should support clear QoS differentiation for radio bearers / services

[0056] UL reporting should allow fine-grained buffer reporting (e.g. per radio bearer or per radio bearer group) to enable the eNB scheduler to identify for which radio bearer / service the data will be sent

[0057] ● It should be possible to clearly differentiate QoS between services for different users

[0058] ● Minimum bit rate per radio bearer should be available

[0059] As can be seen from the above list, a fundamental aspect of LTE scheduling is to provide a mechanism by which operators can control the division of their total cell capacity between radio bearers of different QoS classes. The QoS class of a radio bearer is identified by the QoS profile of the corresponding SAE bearer, which is signaled from the AGW to the eNB as described above. The operator can then allocate a specific amount of its total cell capacity to the total traffic associated with radio bearers of a particular QoS class. The primary purpose of this class-based approach is to be able to differentiate the treatment of packets based on the QoS class to which they belong.

[0060] Layer 1 / Layer 2 control signaling

[0061] In order to inform the scheduled users of their assignment status, transport format and other transmission-related information (e.g., HARQ information, transmit power control (TPC) commands), L1 / L2 control signaling is transmitted together with the data on the downlink. Assuming that the user assignment can change from subframe to subframe, L1 / L2 control signaling is multiplexed with the downlink data in the subframe. It should be noted that user assignment can also be performed based on TTI (Transmission Time Interval), and the TTI length can be a multiple of the subframe. The TTI length can be fixed for all users in the service area, can be different for different users, or can even be dynamic for each user. Generally, L1 / L2 control signaling only needs to be transmitted once per TTI. Without loss of generality, it is assumed below that TTI is equivalent to one subframe.

[0062] L1 / L2 control signaling is transmitted on the Physical Downlink Control Channel (PDCCH). The PDCCH carries messages known as Downlink Control Information (DCI), which in most cases includes resource allocations and other control information for a mobile terminal or group of UEs. Typically, several PDCCHs can be transmitted in one subframe.

[0063] It should be noted that in 3GPP LTE, allocations for uplink data transmission (also called uplink scheduling grants or uplink resource allocations) are also transmitted on the PDCCH. In addition, 3GPP Release 11 introduced the EPDCCH, which performs essentially the same function as the PDCCH (i.e., transmits L1 / L2 control signaling), even though the detailed transmission method differs from the PDCCH. Further details can be found in the current versions of 3GPP TS 36.211 and 36.213 (incorporated herein by reference). Therefore, unless otherwise specified, most of the items outlined in the background section and embodiments apply to the PDCCH as well as the EPDCCH or other means of transmitting L1 / L2 control signals.

[0064] Generally, information transmitted in L1 / L2 control signaling for allocating uplink or downlink radio resources (particularly LTE(-A) Release 10) can be categorized into the following items:

[0065] - User ID , indicating the assigned user. This is typically included in the checksum by masking the CRC with the user identification;

[0066] - Resource allocation information , indicating the resources (e.g., resource blocks, RBs) to which the user is assigned. Alternatively, this information is called a resource block allocation (RBA). Note that the number of RBs assigned to a user can be dynamic;

[0067] - Carrier indicator , which is used in the case where a control channel transmitted on a first carrier allocates resources on a second carrier (i.e., resources on or related to the second carrier) (cross-carrier scheduling);

[0068] - Modulation and coding schemes , which determines the modulation scheme and coding rate adopted;

[0069] - HARQ information , such as a New Data Indicator (NDI) and / or a Redundancy Version (RV), which are particularly useful in retransmissions of data packets or parts thereof;

[0070] - Power control commands , used to adjust the transmission power of the allocated uplink data or control information transmission;

[0071] - Reference signal information , such as an applied cyclic shift and / or orthogonal cover code index, for transmission or reception of a reference signal related to the allocation;

[0072] - Uplink or downlink allocation index , used to identify the allocation order, which is particularly useful in TDD systems;

[0073] - Hopping information , for example, an indication of whether and how to apply resource hopping to improve frequency diversity;

[0074] - CSI Request , which is used to trigger the transmission of channel state information in the allocated resources; and

[0075] - Multi-cluster information , which is a flag used to indicate and control whether transmission occurs in a single cluster (a contiguous set of RBs) or multiple clusters (at least two non-contiguous sets of contiguous RBs). Multi-cluster allocation has been introduced by 3GPP LTE-(A) Release 10.

[0076] It should be noted that the above list is non-exhaustive and, depending on the used DCI format, not all mentioned information items need to be present in every PDCCH transmission.

[0077] Downlink control information appears in several formats that differ in overall size and in the information contained in their fields, as described above. The different DCI formats currently defined for LTE are as follows and are described in detail in 3GPP TS 36.212, "Multiplexing and channel coding," Section 5.3.3.1 (current version v.12.4.0 available at http: / / www.3gpp.org and incorporated herein by reference). In addition, for further information on DCI formats and the specific information transmitted in DCI, please refer to the referenced technical standards or Chapter 9.3 of "LTE - The UMTS Long Term Evolution - From Theory to Practice," edited by Stefanie Sesia, Issam Toufik, and Matthew Baker (incorporated herein by reference).

[0078] - Format 0: DCI format 0 is used to transmit resource grant for PUSCH using single antenna port transmission in uplink transmission mode 1 or 2.

[0079] - Format 1: DCI format 1 is used to transmit resource allocation for single-codeword PDSCH transmission (downlink transmission modes 1, 2, and 7).

[0080] - Format 1A: DCI format 1A is used for compact signaling of resource allocation for single-codeword PDSCH transmissions and for dispatching dedicated preamble signatures to mobile terminals for contention-free random access (for all transmission modes).

[0081] - Format 1B: DCI format 1B is used for compact signaling of resource allocation for PDSCH transmission using closed-loop precoding with rank-1 transmission (downlink transmission mode 6). The information transmitted is the same as in format 1A, but with the addition of an indicator of the precoding vector applied to the PDSCH transmission.

[0082] -Format 1C: DCI format 1C is used for very compact transmission of PDSCH assignments. When using format 1C, PDSCH transmissions are restricted to using QPSK modulation. This is used, for example, to signal paging messages and broadcast system information messages.

[0083] Format 1D: DCI format 1D is used for compact signaling of resource allocations for PDSCH transmissions using multi-user MIMO. The information transmitted is the same as in format 1B, but instead of one of the bits for the precoding vector indicator, a single bit indicates whether a power offset is applied to the data symbol. This feature is required to indicate whether transmit power is shared between two UEs. Future releases of LTE may extend this to the case of power sharing between a larger number of UEs.

[0084] - Format 2: DCI format 2 is used to transmit resource allocation for PDSCH for closed-loop MIMO operation (transmission mode 4).

[0085] -Format 2A: DCI format 2A is used to transmit resource allocations for PDSCH for open-loop MIMO operation. The information transmitted is the same as format 2, except that if the eNodeB has two transmit antenna ports, there is no precoding information, and for four antenna ports, two bits are used to indicate the transmit rank (transmission mode 3).

[0086] - Format 2B: Introduced in Release-9 and used to transmit resource allocation for PDSCH for dual-layer beamforming (transmission mode 8).

[0087] - Format 2C: Introduced in Release 10 and used to transmit resource allocations for PDSCH for closed-loop single-user or multi-user MIMO operation with up to 8 layers (transmission mode 9).

[0088] - Format 2D: Introduced in Release 11 and used for transmission of up to 8 layers; mainly used for COMP (Coordinated Multipoint) (transmission mode 10).

[0089] - Formats 3 and 3A: DCI formats 3 and 3A are used to transmit power control commands for PUCCH and PUSCH with 2-bit or 1-bit power adjustment, respectively. These DCI formats contain individual power control commands for a group of UEs.

[0090] - Format 4: DCI format 4 is used to schedule PUSCH using closed-loop spatial multiplexing transmission in uplink transmission mode 2.

[0091] - Format 5: DCI format 5 is used for scheduling of the PSCCH (Physical Sidelink Control Channel) and also contains several SCI format 0 fields for scheduling of the PSSCH (Physical Sidelink Shared Control Channel). If the number of information bits in DCI format 5 mapped onto a given search space is less than the payload size of format 0 used to schedule the same serving cell, zeros shall be appended to format 5 until the payload size equals the payload size of format 0 including any padding bits appended to format 0.

[0092] 3GPP technical standard TS 35.212 (current version 12.4.0) defines control information for the sidelink in section 5.4.3 (incorporated herein by reference); detailed information on the sidelink is provided below.

[0093] SCI can transmit sidelink scheduling information for a destination ID. SCI format 0 is defined for scheduling of PSSCH. The following information is transmitted via SCI format 0:

[0094] Frequency hopping flag - 1 bit

[0095] ● Resource block allocation and jump resource allocation

[0096] ●Time Resource Mode - 7 bits

[0097] ● Modulation and coding scheme - 5 bits

[0098] Timing Advance Indicator - 11 bits

[0099] Group Destination ID - 8 bits

[0100] Logical Channel Prioritization LCP Process

[0101] For the uplink, the process by which the UE creates MAC PDUs for transmission using the allocated radio resources is fully standardized; this is designed to ensure that the UE meets the QoS for each configured radio bearer in an optimal and consistent manner across different UE implementations. Based on the uplink transmission resource grant message signaled on the PDCCH, the UE must decide the amount of data for each logical channel to include in the new MAC and, if necessary, allocate space for a MAC control element.

[0102] When constructing a MAC PDU with data from multiple logical channels, the simplest and most intuitive approach is based on absolute priority, where MAC PDU space is allocated to logical channels in descending order of logical channel priority. That is, data from the highest-priority logical channel is served first in the MAC PDU, followed by data from the next-highest-priority logical channel, and so on until the MAC PDU space is exhausted. While the absolute priority approach is relatively simple in terms of UE implementation, it can sometimes result in insufficient resources for data from lower-priority logical channels; insufficient resources means that data from lower-priority logical channels cannot be transmitted because data from higher-priority logical channels occupies all the MAC PDU space.

[0103] In LTE, a Prioritized Bit Rate (PBR) is defined for each logical channel to transmit data in order of importance while also preventing resource starvation for lower-priority data. The PBR is the minimum data rate guaranteed for a logical channel. Even if a logical channel has low priority, at least a small amount of MAC PDU space is allocated to guarantee the PBR. Therefore, using PBR can avoid resource starvation issues.

[0104] Constructing a MAC PDU with PBR involves two rounds. In the first round, each logical channel is serviced in descending order of logical channel priority, but the amount of data from each logical channel included in the MAC PDU is initially limited to the amount corresponding to the logical channel's configured PBR. After all logical channels have been serviced up to their PBR values, a second round is performed if there is space left in the MAC PDU. In the second round, each logical channel is again serviced in descending order of priority. The main difference between the second round and the first round is that MAC PDU space is allocated to each logical channel of lower priority only when all logical channels of higher priority have no more data to transmit.

[0105] A MAC PDU can include not only the MAC SDU from each configured logical channel, but also the MAC CE. With the exception of the Padding BSR, the MAC CE has a higher priority than the MAC SDU from the logical channel because the MAC CE controls the operation of the MAC layer. Therefore, when constructing a MAC PDU, the MAC CE (if present) is included first, and the remaining space is used for the MAC SDU from the logical channel. Then, if there is additional space left and it is large enough to include the BSR, the Padding BSR is triggered and included in the MAC PDU. The Logical Channel Prioritization (LCP) process is applied every time a new transmission is performed.

[0106] Logical channel prioritization is standardized, for example, in section 5.4.3.1 of 3GPP TS 36.321 (current version v12.5.0), which is incorporated herein by reference.

[0107] RRC controls the scheduling of uplink data through signaling for each logical channel:

[0108] ●priority, increasing priority values ​​indicate lower priority levels,

[0109] prioritizedBitRate, which sets the prioritized bit rate (PBR),

[0110] = bucketSizeDuration, which sets the token bucket size duration (BSD).

[0111] The UE shall maintain a variable Bj for each logical channel j. Bj shall be initialized to 0 when the associated logical channel is established and incremented for each TTI by the product of PBR × TTI duration, where PBR is the prioritized bit rate for logical channel j. However, the value of Bj MUST NOT exceed the token bucket size, and if the value of Bj is greater than the token bucket size for logical channel j, it shall be set to the token bucket size. The token bucket size for a logical channel is equal to PBR × BSD, where PBR and BSD are configured by upper layers.

[0112] LTE Device-to-Device (D2D) Proximity Services (ProSe)

[0113] Proximity-based applications and services represent an emerging socio-technical trend. Areas identified include commercial services and public safety-related services that will be of interest to operators and users. The introduction of Proximity Services (ProSe) capabilities in LTE will enable the 3GPP industry to serve this developing market and, at the same time, will address the pressing needs of several public safety groups working together on LTE.

[0114] Device-to-device (D2D) communication is a technical component of LTE Release 12. D2D technology enables D2D as the underlying layer of cellular networks to increase spectral efficiency. For example, if the cellular network is LTE, all data-carrying physical channels use SC-FDMA for D2D signaling. In D2D communication, user devices transmit data signals to each other over direct links using cellular resources, rather than through a radio base station. In this disclosure, the terms "D2D," "ProSe," and "sidelink" are used interchangeably.

[0115] D2D Communication in LTE

[0116] D2D communication in LTE focuses on two areas: discovery and communication.

[0117] ProSe (Proximity-based Services) direct discovery is defined as a procedure used by a ProSe-enabled UE to discover other ProSe-enabled UEs in its vicinity using E-UTRA direct radio signals via the PC5 interface. Figure 3 Schematically illustrates the PC5 interface for device-to-device direct discovery. Figure 4 The radio protocol stack (AS) for ProSe direct discovery is schematically illustrated.

[0118] In D2D communication, users transmit data signals to each other via direct links using cellular resources, rather than through a base station (BS). D2D users communicate directly while remaining under the control of the BS, at least while within the coverage of an eNB. Therefore, D2D can improve system performance by reusing cellular resources.

[0119] D2D is assumed to operate in the uplink LTE spectrum (in the case of FDD) or in the uplink subframes of the cell with coverage (in the case of TDD, except when outside of coverage). In addition, D2D transmission / reception does not use full-duplex on a given carrier. From the perspective of an individual UE, D2D signal reception and LTE uplink transmission on a given carrier do not use full-duplex, that is, simultaneous D2D signal reception and LTE UL transmission are not possible.

[0120] In D2D communication, when a specific UE1 has a transmitting role (transmitting user equipment or transmitting terminal), UE1 sends data and UE2 (receiving user equipment) receives the data. UE1 and UE2 can change their transmitting and receiving roles. Transmissions from UE1 can be received by one or more UEs, such as UE2.

[0121] Regarding the user plane protocol, a part of the agreement from the perspective of D2D communication is given below (see also 3GPP TS 36.843 current version 12.0.1 section 9.2.2, which is incorporated herein by reference):

[0122] PDCP:

[0123] -1:M D2D broadcast communication data (ie IP packets) should be handled as regular user plane data.

[0124] -Header-compression / decompression in PDCP is applicable to 1:M D2D broadcast communication.

[0125] ■U-mode header compression in PDCP for D2D broadcast operations for public safety;

[0126] ●RLC:

[0127] -RLC UM is used for 1:M D2D broadcast communication.

[0128] -RLC UM supports segmentation and reassembly at L2.

[0129] - A receiving UE needs to maintain at least one RLC UM entity for each transmitting peer UE.

[0130] - There is no need to configure the RLC UM receiver entity before receiving the first RLC UM data unit.

[0131] - So far, the need for RLC AM or RLC TM for D2D communication for user plane data transmission has not been identified.

[0132] MAC:

[0133] - No HARQ feedback is assumed for 1:M D2D broadcast communication.

[0134] - The receiving UE needs to know the source ID in order to identify the receiving RLC UM entity.

[0135] - The MAC header includes a L2 target ID, which enables filtering of packets at the MAC layer.

[0136] - L2 destination ID can be a broadcast, multicast or unicast address.

[0137] ■ L2 multicast / unicast: The L2 destination ID carried in the MAC header will enable the received RLC UM PDU to be discarded even before it is delivered to the RLC receiving entity.

[0138] ■ L2 broadcast: The receiving UE shall process all RLC PDUs received from all transmitting units and aim to assemble and pass IP packets to upper layers.

[0139] -The MAC subheader contains the LCID (to distinguish multiple logical channels).

[0140] - At least multiplexing / demultiplexing, priority handling and padding are useful for D2D.

[0141] ProSe direct communication related flags

[0142] 3GPP TS 36.300, current version 12.5.0, defines the following identifiers in section 8.3 for ProSe direct communication:

[0143] ● SL-RNTI (Sidelink Radio Network Temporary Identifier): a unique identifier used for ProSe direct communication scheduling;

[0144] ● Source Layer-2 ID : Identifies the sender of data in sidelink ProSe direct communication. The Source Layer-2 ID is 24 bits long and is used together with the ProSe Layer-2 Destination ID and LCID used to identify the RLC UM entity and PDCP entity in the receiver.

[0145] ● Destination Layer-2 ID : Identifies the destination of data in sidelink ProSe direct communication. The destination layer-2 ID is 24 bits long and is divided into two bit strings in the MAC layer:

[0146] ■ One bit string is the LSB portion (8 bits) of the destination layer-2 ID and is forwarded to the physical layer as the sidelink sidelink control layer-1 ID. This identifies the destination of the intended data in the sidelink control and is used to filter packets at the physical layer.

[0147] ■ The second bit string is the MSB part (16 bits) of the destination layer-2 ID and is carried within the MAC header. This is used to filter packets at the MAC layer.

[0148] No access layer signaling is required for group formation, and no access layer signaling is required to configure the source Layer-2 ID, destination Layer-2 ID, and sidelink control L1 ID in the UE. These identities are provided by higher layers or derived from identities provided by higher layers. In the case of multicast and broadcast, the ProSe UE ID provided by higher layers is directly used as the source Layer-2 ID, and the ProSe Layer-2 group ID provided by higher layers is directly used as the destination Layer-2 ID in the MAC layer.

[0149] Radio resource allocation for proximity based services

[0150] From the transmitting UE's perspective, a Proximity Services-enabled UE (ProSe-enabled UE) can operate in two modes for resource allocation:

[0151] On the one hand, Mode 1 refers to eNB-scheduled resource allocation, in which the UE requests transmission resources from the eNB (or Release 10 relay node), and in response, the eNodeB (or Release 10 relay node) schedules resources for the UE to use to transmit direct data and direct control information DCI (e.g., scheduling assignments). The UE needs to be RRC_CONNECTED in order to transmit data. Specifically, the UE sends a D2D Scheduling Request (D-SR or Random Access) to the eNB in ​​the usual way, followed by a Buffer Status Report (BSR) (see also the following section "Transmission Procedure for D2D Communication"). Based on the BSR, the eNB can determine that the UE has data for ProSe direct communication transmission and can estimate the resources required for the transmission.

[0152] Mode 2, on the other hand, refers to UE autonomous resource selection, in which the UE selects resources (time and frequency) from a resource pool by itself to transmit direct data and direct control information (i.e., SA). One resource pool is defined, for example, by the content of SIB18, i.e., by the field commTxPoolNormalCommon, and this specific resource pool is broadcast in the cell and then commonly available to all UEs in the cell that are still in the RRC_Idle state. In practice, the eNB can define up to four different instances of the pool, one for each of the four resource pools used to transmit SA messages and direct data. However, the UE should always use the first resource pool defined in the list, even if the UE is configured with multiple resource pools.

[0153] As an alternative, another resource pool may be defined by the eNB and signaled in SIB18, ie by using the field commTxPoolExceptional, which may be used by the UE in exceptional cases.

[0154] The resource allocation mode that the UE will use can be configured by the eNB. In addition, the resource allocation mode that the UE will use for D2D data transmission can also depend on the RRC state (i.e., RRC_IDLE and RRC_CONNECTED) and the coverage state of the UE (i.e., in coverage, out of coverage). If the UE has a serving cell (i.e., the UE is RRC_CONNECTED or camped on a cell in RRC_IDLE), the UE is considered to be in coverage.

[0155] The following rules regarding resource allocation mode apply to UE:

[0156] ● If the UE is out of coverage, the UE can only use Mode 2;

[0157] ● If the UE is in coverage, the UE may use Mode 1 if the eNB configures it accordingly;

[0158] ● If the UE is in coverage, the UE may use Mode 2 if the eNB configures it accordingly;

[0159] ● In the absence of exceptional circumstances, the UE shall only change from Mode 1 to Mode 2, or vice versa, if the eNB has configured it to do so. If the UE is in coverage, the UE shall only use the mode indicated by the eNB configuration unless one of the exceptional circumstances occurs;

[0160] ■The UE considers itself to be in an exceptional situation, for example, while T311 or T301 is running;

[0161] ● When an exceptional situation occurs, the UE is enabled to temporarily use Mode 2 even if it is configured to use Mode 1.

[0162] When in the coverage area of ​​an E-UTRA cell, the UE shall perform ProSe direct communication transmissions only on the UL carrier on the resources allocated by the cell, even if the resources of this carrier have been pre-configured, for example, in a UICC (Universal Integrated Circuit Card).

[0163] For a UE in RRC_IDLE, the eNB may choose one of the following options:

[0164] The eNB may provide a Mode 2 transmit resource pool in the SIB. UEs authorized for ProSe direct communication may use these resources for ProSe direct communication in RRC_IDLE.

[0165] ● The eNB may indicate in the SIB that the eNB supports D2D but does not provide resources for ProSe direct communication. The UE needs to enter RRC_CONNECTED to perform ProSe direct communication transmission.

[0166] For UE in RRC_CONNECTED:

[0167] ● When ProSe direct communication transmission needs to be performed, the UE authorized to perform ProSe direct communication transmission in RRC_CONNECTED indicates to the eNB that the UE wants to perform ProSe direct communication transmission;

[0168] The eNB verifies that the UE in RRC_CONNECTED is authorized for ProSe direct communication transmission using the UE context received from the MME.

[0169] ● The eNB may configure, through dedicated signaling, a Mode 2 resource allocation transmission resource pool for a UE in RRC_CONNECTED that can be used without restriction when the UE is in RRC_CONNECTED. Alternatively, the eNB may configure, through dedicated signaling, a Mode 2 resource allocation transmission resource pool for a UE in RRC_CONNECTED that the UE is allowed to use only in exceptional cases (otherwise relying on Mode 1).

[0170] When the UE is out of coverage, the resource pool used for scheduling allocation can be configured as follows:

[0171] • The resource pool for reception is pre-configured.

[0172] ● The resource pool used for sending is pre-configured.

[0173] When the UE is in coverage, the resource pool used for scheduling allocation can be configured as follows:

[0174] • The resource pool used for reception is configured by the eNB via RRC in dedicated or broadcast signaling.

[0175] • If Mode 2 resource allocation is used, the resource pool used for transmission is configured by the eNB via RRC.

[0176] • If Mode 1 resource allocation is used, the SCI (Sidelink Control Information) resource pool (also called Scheduling Assignment SA resource pool) used for transmission is unknown to the UE.

[0177] • If Mode 1 resource allocation is used, the eNB schedules specific resources for sidelink control information transmission (scheduling assignment).The specific resources allocated by the eNB are within the resource pool used to receive the SCI provided to the UE.

[0178] Figure 5 The usage of transmit / receive resources for overlay (LTE) and underlay (D2D) systems is illustrated.

[0179] Basically, the eNodeB controls whether the UE can apply Mode 1 or Mode 2 transmission. Once the UE knows its resources where it can send (or receive) D2D communication, in the current state-of-the-art technology, it uses the corresponding resources only for the corresponding transmission / reception. For example, in Figure 5 In the D2D subframe, the D2D subframe will only be used to receive or send D2D signals. Because the UE as a D2D device will operate in half-duplex mode, the UE can receive or send D2D signals at any time point. Similarly, Figure 5 Other subframes shown in may be used for LTE (coverage) transmission and / or reception.

[0180] The transmission process of D2D communication

[0181] The D2D data transmission process differs depending on the resource allocation mode. As described above for Mode 1, the eNB explicitly schedules resources for scheduling allocation and D2D data communication following a corresponding request from the UE. Specifically, the UE may be informed by the eNB that D2D communication is generally allowed, but that Mode 2 resources (i.e., resource pools) are not provided; this may be done, for example, by an exchange of a D2D communication interest indication by the UE and a corresponding response (D2D Communication Response), wherein the corresponding exemplary ProseCommConfig information element described above will not include commTxPoolNormalCommon, meaning that a UE that wants to start direct communication involving transmissions must request the E-UTRAN to allocate resources for each individual transmission. Therefore, in this case, the UE must request resources for each individual transmission, and the different steps of the request / grant process are exemplarily listed below for this Mode 1 resource allocation:

[0182] ● Step 1: UE sends SR (scheduling request) to eNB via PUCCH;

[0183] ● Step 2: The eNB grants UL resources (for the UE to send BSR) via PDCCH scrambled by C-RNTI;

[0184] ● Step 3: The UE sends a D2D BSR indicating the buffer status via PUSCH;

[0185] ● Step 4: The eNB grants D2D resources (for the UE to send data) via the PDCCH scrambled by the SL-RNTI;

[0186] ● Step 5: The D2D Tx UE transmits SA / D2D data according to the grant received in step 4.

[0187] The Scheduling Assignment (SA), also known as SCI (Sidelink Control Information), is a compact (low payload) message containing control information, such as pointers to the time-frequency resources, modulation and coding scheme, and group destination ID for the corresponding D2D data transmission. The SCI transmits sidelink scheduling information for one (ProSE) destination ID. The content of the SA (SCI) is essentially based on the grant received in step 4 above. The D2D grant and the SA content (i.e., the SCI content) are defined in 3GPP technical standard TS 36.212 current version 12.4.0, section 5.4.3, which is incorporated herein by reference and specifically defines SCI format 0 as previously mentioned in this "Technical Background" section.

[0188] On the other hand, for Mode 2 resource allocation, the above steps 1-4 are basically not required, and the UE autonomously selects resources for SA and D2D data transmission from the transmission resource pool configured and provided by the eNB.

[0189] Figure 6 Scheduling assignments for two UEs (UE-A and UE-B) and transmission of D2D data are exemplarily illustrated, resources used for transmission of the scheduling assignments are periodic, and resources used for D2D data transmission are indicated by the corresponding scheduling assignments.

[0190] Figure 7 The D2D communication timing for Mode 2 (autonomous scheduling) during one SA / data period (also called SC period, sidelink control period) is illustrated. Figure 8 The diagram illustrates D2D communication timing for Mode 1 (eNB scheduled assignments) during one SA / data period. An SC period is a time period that includes transmission of scheduled assignments and their corresponding data.

[0191] As from Figure 7 As can be seen, the UE sends a scheduling allocation using the transmit pool resources SA_Mode2_Tx_pool for Mode 2 scheduling allocations after the SA offset time. The first SA transmission is followed by three retransmissions of the same SA message. Then, after the first subframe of the SA resource pool (given by SA_offset), the UE begins D2D data transmission at a configured offset (Mode2data_offset), i.e., more specifically, using the transmit time resource mode (i.e., the T-RPT bitmap / pattern).

[0192] A D2D data transmission of a MAC PDU includes its first transmission and several retransmissions. Figure 8 ), assuming three retransmissions (i.e., the second, third, and fourth transmissions of the same MAC PDU). The Mode 2 T-RPT bitmap (Transmission Time Resource Mode (T-RPT)) essentially defines the timing of a MAC PDU transmission (the first transmission) and its retransmissions (the second, third, and fourth transmissions).

[0193] During one SA / data period, the UE can send multiple transport blocks (only one per subframe (TTI), i.e., one after another), but only to one ProSe destination group. In addition, the retransmission of one transport block must be completed before the first transmission of the next transport block begins, i.e., only one HARQ process is used to send multiple transport blocks.

[0194] As from Figure 8Obviously, for the resource allocation mode scheduled by the eNB (Mode 1), the D2D data transmission (ie, more specifically the T-RPT mode / bitmap) starts in the next UL subframe after the last SA transmission repetition in the SA resource pool. Figure 7 As described, the Mode 1 T-RPT bitmap (Time Resource Pattern for Transmission (T-RPT)) basically defines the timing of a MAC PDU transmission (first transmission) and its retransmissions (second, third and fourth transmissions).

[0195] ProSe network architecture and ProSe entities

[0196] Figure 9 A high-level exemplary architecture for a non-roaming case is illustrated, including different ProSe applications in respective UEs A and B, as well as a ProSe application server and ProSe functions in the network. Figure 9 The example architecture is taken from TS 23.303 v.12.4.0, Chapter 4.2, "Architectural Reference Model," which is incorporated herein by reference.

[0197] The functional entities are presented and described in detail in Section 4.4 of TS 23.303, which is incorporated herein by reference, entitled "Functional Entities." The ProSe function is a logical function used for network-related actions required by ProSe and plays a different role for each ProSe function. The ProSe function is part of the 3GPP Evolved Packet Core (EPC) and provides all relevant network services related to proximity services, such as authorization, authentication, and data handling.

[0198] For ProSe direct discovery and communication, the UE can obtain a specific ProSe UE identity, other configuration information, and authorization from the ProSe function over the PC3 reference point. Although a single ProSe function is presented for ease of illustration, multiple ProSe functions can be deployed in the network. The ProSe function includes three main sub-functions that perform different roles depending on the ProSe characteristics: the Direct Provisioning Function (DPF), the Direct Discovery Name Management Function, and the EPC-level Discovery Function. The DPF is used to provide the UE with the necessary parameters to use ProSe direct discovery and ProSe direct communication.

[0199] The term “UE” used in this connection refers to a ProSe-enabled UE that supports ProSe functionality such as:

[0200] ● ProSe control information is exchanged between the ProSe-enabled UE and the ProSe function over the PC3 reference point.

[0201] ● Procedures for opening ProSe direct discovery of other ProSe-enabled UEs over the PC5 reference point.

[0202] ● Procedures for one-to-many ProSe direct communication over the PC5 reference point.

[0203] ● Procedure for acting as a ProSe UE to Network Relay. The remote UE communicates with the ProSe UE to Network Relay over the PC5 reference point. The ProSe UE to Network Relay uses Layer-3 packet forwarding.

[0204] ● Control information is exchanged between ProSe UEs over the PC5 reference point, e.g. for UE to network relay detection and ProSe direct discovery.

[0205] ProSe control information is exchanged between another ProSe-enabled UE and the ProSe function over the PC3 reference point. In the case of a ProSe UE to a network relay element, the remote UE will send this control information over the PC5 user plane so that it is relayed towards the ProSe function over the LTE-Uu interface.

[0206] Configuration of parameters (e.g., including IP address, ProSe Layer-2 group ID, group security material, and radio resource parameters). These parameters can be pre-configured in the UE or, if in coverage, provided to the ProSe function in the network via signaling over the PC3 reference point.

[0207] The ProSe application server supports the storage of EPC ProSe user IDs and ProSe function IDs, as well as the mapping of application layer user IDs and EPC ProSe user IDs. The ProSe application server (AS) is an entity outside the scope of 3GPP. The ProSe application in the UE communicates with the ProSe AS via the application layer reference point PC1. The ProSe AS is connected to the 3GPP network via the PC2 reference point.

[0208] D2D UE coverage status

[0209] As previously mentioned, the resource allocation method for D2D communication depends on the RRC state (i.e., RRC_IDLE and RRC_CONNECTED) as well as the UE's coverage state (i.e., in coverage, out of coverage). If the UE has a serving cell (i.e., the UE is RRC_CONNECTED or is camped on a cell in RRC_IDLE), the UE is considered to be in coverage.

[0210] The two coverage states mentioned so far, namely, in coverage (IC) and out of coverage (OOC), are further distinguished into sub-states for D2D. Figure 10 Four different states are shown that a D2D UE can be associated with, which can be summarized as follows:

[0211] ● State 1: UE1 has uplink and downlink coverage. In this state, the network controls each D2D communication session. In addition, the network configures whether UE1 should use resource allocation mode 1 or mode 2.

[0212] State 2: UE2 has downlink coverage but no uplink coverage, i.e., only DL coverage. The network broadcasts a (contention-based) resource pool. In this state, the transmitting UE selects resources for SA and data from the resource pool configured by the network; in this state, resource allocation can only be made according to Mode 2 for D2D communication.

[0213] ● State 3: Since UE3 has no uplink and downlink coverage, UE3 is considered to be out of coverage (OOC). However, UE3 is in the coverage of some UEs (such as UE1) that are in the coverage of the cell, i.e., those UEs can also be called CP-relay UEs. Therefore, Figure 10 The area of ​​State-3 UEs in this state can be represented as the CP UE-Relay coverage area. A UE in this State-3 is also referred to as an OOC-State-3 UE. In this state, the UE receives some cell-specific information (SIB) sent by the eNB and forwarded to the OOC-State-3 UE by the CP UE-Relay UE in the cell's coverage area via the PD2DSCH. The (contention-based) network-controlled resource pool is signaled via the PD2DSCH.

[0214] • State 4: UE 4 is out of coverage and does not receive PD2DSCH from other UEs in the coverage of the cell. In this state, also known as State-4 OOC, the transmitting UE selects resources for data transmission from a (contention-based) pre-configured resource pool.

[0215] The reason for distinguishing between State-3OOC and State-4OOC is primarily to avoid potential interference between D2D transmissions from out-of-coverage devices and legacy E-UTRA transmissions. Typically, D2D-capable UEs will have pre-configured resource pools for transmitting D2D SAs and data for use when out of coverage. If these out-of-coverage UEs transmit on these pre-configured resource pools at the cell boundary, the interference between the D2D transmissions and the legacy transmissions in coverage could negatively impact communications within the cell.

[0216] If an in-coverage D2D-enabled UE forwards the D2D resource pool configuration to out-of-coverage devices near the cell boundary, the out-of-coverage UE can restrict its transmission to the resources specified by the eNode B, thereby minimizing interference with in-coverage conventional transmissions. Therefore, RAN1 has introduced a mechanism where in-coverage UEs are forwarding resource pool information and other D2D-related configurations to those devices just out of coverage (State-3 UE).

[0217] The Physical D2D Synchronization Channel (PD2DSCH) is used to carry this information about the D2D resource pools in coverage to network-neighboring UEs so that the network-neighboring resource pools are aligned.

[0218] D2D LCP process, sidelink logical channel

[0219] The LCP procedure for D2D will be different from the LCP procedure described above for "regular" LTE data. The following information is taken from TS 36.321 version 12.5.0, section 5.14.1.3.1, which describes LCP for ProSe; which is incorporated herein by reference in its entirety.

[0220] When performing a new transmission, the UE shall perform the following logical channel prioritization procedure:

[0221] The UE (e.g., MAC entity) shall allocate resources to the sidelink logical channels according to the following rules:

[0222] - The UE shall not segment the RLC SDU (or partially transmitted SDU) if the entire SDU (or partially transmitted SDU) fits into the remaining resources;

[0223] If the UE segments an RLC SDU from a sidelink logical channel, it shall maximize the size of the segments to fit the grant as closely as possible;

[0224] -UE should maximize data transmission;

[0225] - If the UE is given a sidelink grant size equal to or greater than 10 bytes while having data available to send, the UE shall not send only padding.

[0226] NOTE: The above rules imply that the order in which the sidelink logical channels are served is left to the UE implementation.

[0227] Typically, for a PDU, the MAC entity should only consider logical channels with the same source Layer-2 ID and destination Layer-2 ID pair. That is, for a PDU, the MAC entity in the UE should only consider logical channels of the same ProSe destination group (i.e., with the same destination group ID). The UE selects the ProSe destination group during the LCP procedure. Furthermore, in Release 12, a D2D transmitting UE can only send data to one ProSe destination group during one SA / data period.

[0228] All D2D (sidelink) logical channels (e.g., STCH, i.e., sidelink traffic channel) are assigned to the same logical channel group (LCG), i.e., have an LCG ID set to '11' (see TS 36.321, version 12.5.0, section 5.14.1.4, "Buffer Status Reporting"). In Release 12, there is no prioritization mechanism for D2D (sidelink) logical channels / groups. Essentially, from the UE's perspective, all sidelink logical channels have the same priority, i.e., the order in which the sidelink logical channels are served is left to the UE implementation.

[0229] For Release 13, a more advanced prioritization mechanism is considered, where each sidelink logical channel is associated with a logical channel priority, also known as PPPP (ProSe Per Packet Priority). Based on this logical channel priority, the UE selects a ProSe destination group for a given sidelink grant, i.e., the highest priority logical channel determines the ProSe destination group, and further resources are allocated to the logical channels belonging to the selected ProSe destination group (in order of decreasing priority).

[0230] For illustration purposes only, consider the following exemplary scenario, in which three ProSe logical channels LCH #1, LCH #2, and LCH #3 are established in the user equipment, and all three are associated with the same ProSe LCG (e.g., "11"). Exemplarily, it is assumed that LCH #1 and LCH #2 are allocated to ProSe destination group 1, and LCH #3 is allocated to ProSe destination group 2. Figure 12 Shown in.

[0231] ProSe buffer unit status report

[0232] Buffer status reporting is also adapted to ProSe and is currently defined in TS 36.321 Release 12 in section 5.14.1.4 “Buffer Status Reporting” in version 12.5.0 (incorporated herein by reference).

[0233] The (D2D) Sidelink Buffer Status Reporting procedure is used to provide the serving eNB with information about the amount of sidelink data available for transmission in the UE's sidelink buffer. The RRC controls sidelink BSR reporting by configuring two timers: Periodic-ProseBSR-Timer and RetxProseBSR-Timer. Each sidelink logical channel (STCH) is assigned to an LCG with an LCGID set to "11" and belongs to a ProSe destination group.

[0234] As detailed in TS36.321 section 5.14.1.4, a sidelink buffer status report (BSR) shall be triggered if certain specific events occur.

[0235] In addition, TS 36.321, Section 6.1.3.1a in its version 12.5.0 (incorporated herein by reference), defines the ProSe BSR MAC control element and its corresponding contents as follows. The ProSe Buffer Status Report (BSR) MAC control element includes a group index field, an LCG ID field, and a corresponding buffer size field for each reported D2D destination group. In more detail, for each included ProSe destination group, the following fields are defined:

[0236] ● Group Index: The Group Index field identifies the ProSe destination group. The length of this field is 4 bits. The value is set to the index of the destination identifier reported in the destinationInfoList;

[0237] ●LCG ID: The Logical Channel Group ID field identifies the group of logical channels for which the buffer status is being reported. The length of the field is 2 bits and it is set to "11";

[0238] • Buffer Size: The Buffer Size field identifies the total amount of data available in all logical channels of the ProSe destination group after all MAC PDUs for a TTI have been built. The amount of data is indicated in number of bytes.

[0239] ●R: Reserved bit, set to "0".

[0240] Figure 11A ProSe BSR MAC control element for an even number N (the number of ProSe destination groups) taken from TS 36.321 section 6.1.3.1a is shown.

[0241] As mentioned above, the transmission scheme for device-to-device communication differs from conventional LTE schemes, including the use of ProSe destination groups to identify the possible content of the data.Some currently defined mechanisms are quite inefficient. Summary of the Invention

[0242] Non-limiting and exemplary embodiments provide an improved method for allocating radio resources for a transmitting user equipment to perform a direct communication transmission via a direct sidelink connection to one or more receiving user equipments. The independent claims provide non-limiting and exemplary embodiments. Advantageous embodiments are subject to the dependent claims.

[0243] According to several aspects, direct communication transmissions performed by a transmitting user equipment are improved for scenarios where data is available for transmissions in the transmitting user equipment to more than one sidelink destination group, not only but particularly.

[0244] In a general first aspect, the technology disclosed herein is characterized in that a transmitting user equipment allocates radio resources to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface. For an SC period, the allocation of radio resources within a sidelink control (SC) period is limited by a maximum number of SL processes configured for the transmitting user equipment. A processor of the transmitting user equipment is adapted to obtain a plurality of SL licenses for a subsequent SC period and, from among the obtained SL licenses, select a number of SL licenses that were most recently obtained before the start of the subsequent SC period, the number of selected SL licenses not exceeding the maximum number of SL processes configured for the one SC period. In addition, the processor is adapted to associate a plurality of SL processes for the subsequent SC period such that each of the plurality of SL processes is associated with a different SL license from the selected plurality of SL licenses used to allocate radio resources within the subsequent SC period. Even further, for each of the plurality of SL processes, the radio resources are allocated within the subsequent SC period according to the selected SL license associated with the corresponding SL process for performing one of the plurality of SL transmissions to one of the one or more receiving user equipment. Each of the plurality of SL transmissions includes at least one sidelink control information SCI transmission and at least one data transmission over the SL interface.

[0245] In a general second aspect, the technology disclosed herein is characterized by a transmitting user equipment for allocating radio resources to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface. For a sidelink control SC period, the allocation of radio resources within the SC period is limited by a maximum number of SL processes configured for the transmitting user equipment. A processor is adapted to acquire a plurality of sidelink SL grants for a subsequent SC period in different subframes before the start of the subsequent SC period: each of the acquired SL grants is associated with one of the maximum number of SL processes based on the subframe in which the SL grant is acquired by applying an association scheme: each of the maximum number of SL processes is associated with an SL grant from a set of different subframes, and each of the subframes in the set is offset from each other by a predefined number of subframes. In addition, the processor is adapted to associate each of the plurality of the maximum number of SL processes with the one SL grant acquired in the corresponding set of different subframes and most recently acquired before the start of the subsequent SC period. Furthermore, for each of the plurality of SL processes, radio resources are allocated during the subsequent SC period according to the SL grant associated with the corresponding SL process for performing one of the plurality of SL transmissions to one or more receiving user equipments. Each of the plurality of SL transmissions includes at least one sidelink control information (SCI) transmission and at least one data transmission over the SL interface.

[0246] In a general third aspect, the technology disclosed herein is characterized by a transmitting user equipment for allocating radio resources to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink (SL) interface. A processor of the transmitting user equipment is adapted to autonomously select SL grants for the multiple SL transmissions from different resource pools, each SL grant being configured and made available for SL transmission within the communication system. The processor is adapted to associate, for each of the multiple SL transmissions, the SL grant to a different SL process selected from a differently configured resource pool. In addition, the processor is adapted to perform, for each of the multiple SL processes having an associated SL grant, a separate logical channel prioritization (LCP) procedure, the LCP procedure only taking into account logical channels of different destination group IDs. Furthermore, for each of the multiple SL processes, the radio resources are allocated within the same SC period for performing the multiple SL transmissions according to the autonomously selected SL grant associated with the corresponding SL process. Each of the multiple SL transmissions includes at least one sidelink control information (SCI) transmission and at least one data transmission via the SL interface.

[0247] In a general fourth aspect, the technology disclosed herein is characterized by a method for allocating radio resources for a transmitting user equipment to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink (SL) interface. For a sidelink control (SC) period, allocation of radio resources within the SC period is limited by a maximum number of SL processes configured for the transmitting user equipment. A plurality of SL grants for a subsequent SC period is acquired, and from among the acquired SL grants, a number of SL grants most recently acquired before the start of the subsequent SC period is selected, where the number of selected SL grants does not exceed the maximum number of SL processes configured for the one SC period. The plurality of SL processes for the subsequent SC period are then associated such that each of the plurality of SL processes is associated with a different one of the plurality of selected SL grants for allocating radio resources within the subsequent SC period. Thereafter, for each of the plurality of SL processes, radio resources are allocated within the subsequent SC period for performing one of the plurality of SL transmissions to one of the one or more receiving user equipment according to the selected SL grant associated with the corresponding SL process. Each of the plurality of SL transmissions comprises at least one sidelink control information (SCI) transmission and at least one data transmission via the SL interface.

[0248] In a general fifth aspect, the technical feature disclosed herein is a method for allocating radio resources for a transmitting user equipment to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface. For a sidelink control SC period, the allocation of radio resources within the SC period is limited by a maximum number of SL processes configured for the transmitting user equipment. A plurality of sidelink SL grants for a subsequent SC period are acquired in different subframes before the start of the subsequent SC period: each of the acquired SL grants is associated with one of the maximum number of SL processes based on the subframe in which the SL grant is acquired by applying an association scheme: each of the maximum number of SL processes is associated with an SL grant from a set of different subframes, and each of the subframes in the set is offset from each other by a predefined number of subframes. Each of the plurality of the maximum number of SL processes is then associated with the SL grant that was acquired in the corresponding set of different subframes and that was most recently acquired before the start of the subsequent SC period. Thereafter, for each of the plurality of SL processes, radio resources are allocated during the subsequent SC period according to the SL grant associated with the corresponding SL process for performing one of the plurality of SL transmissions to one or more receiving user equipments. Each of the plurality of SL transmissions includes at least one sidelink control information (SCI) transmission and at least one data transmission over the SL interface.

[0249] In a general sixth aspect, the technology disclosed herein is characterized by a method for allocating radio resources to a transmitting user equipment for performing multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface. SL grants for multiple SL transmissions are autonomously selected from different resource pools, each SL grant being configured and made available for SL transmission within the communication system. Then, for each of the multiple SL transmissions, the SL grant is associated with a different SL process selected from the differently configured resource pool. Thereafter, for each of the multiple SL processes with the associated SL grant, a separate logical channel prioritization LCP process is performed, the LCP process only taking into account logical channels of different destination group IDs. Finally, for each of the multiple SL processes, the radio resources are allocated within the same SC period according to the autonomously selected SL grant associated with the corresponding SL process for performing the multiple SL transmissions. Each of the multiple SL transmissions includes at least one sidelink control information SCI transmission and at least one data transmission via the SL interface.

[0250] In a general seventh aspect, the technology disclosed herein is characterized by a transmitting user equipment that allocates radio resources to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface, the transmitting user equipment comprising: a receiving unit that receives multiple SL grants for a subsequent sidelink control SC period in a plurality of subframes before the start of the subsequent SC period, wherein: the transmitting user equipment is configured with a maximum number of SL processes, and each of the multiple SL grants is associated with one of the maximum number of SL processes in a one-to-one manner based on the subframe in which the SL grant is received, and for one of the maximum number of SL processes, a second SL grant for the subsequent SC period received in subframe n overwrites a first SL grant for the same subsequent SC period previously received in subframe nX, where X is an integer value equal to or greater than the maximum number of SL processes; and a circuit that is coupled to the receiving unit to associate the maximum number of SL processes with the second SL grant. Processes are respectively associated with the multiple SL licenses, and radio resources within the subsequent SC period are allocated to each of the maximum number of SL processes based on the associated SL licenses; and a sending unit is coupled to the circuit and uses the allocated radio resources to perform multiple SL transmissions including at least one side link control information SCI transmission and at least one data transmission.

[0251] In a general eighth aspect, the technology disclosed herein is characterized by a method for allocating radio resources for a transmitting user equipment to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface, the method comprising the following steps performed by the transmitting user equipment: receiving multiple SL grants for a subsequent sidelink control SC period in multiple subframes before the start of the subsequent SC period, wherein: the transmitting user equipment is configured with a maximum number of SL processes, and each of the multiple SL grants is associated with one of the maximum number of SL processes in a one-to-one manner based on the subframe in which the SL grant is received, and for one of the maximum number of SL processes, the second SL grant for the subsequent SC period received in subframe n covers the first SL grant for the same subsequent SC period previously received in subframe nX, where X is an integer value equal to or greater than the maximum number of SL processes; associating the maximum number of SL processes with the multiple SL grants, respectively, and allocating radio resources within the subsequent SC period for each of the maximum number of SL processes based on the associated SL grants; and using the allocated radio resources, performing multiple SL transmissions including at least one sidelink control information SCI transmission and at least one data transmission.

[0252] In a general ninth aspect, the technology disclosed herein is characterized by an integrated circuit for controlling a process for allocating radio resources by a transmitting user equipment to perform a plurality of direct SL transmissions to one or more receiving user equipment in a communication system over a sidelink SL interface, the integrated circuit comprising circuitry for controlling the process, the process comprising: receiving a plurality of SL grants for a subsequent sidelink control SC period in a plurality of subframes preceding the start of the subsequent SC period, wherein: the transmitting user equipment is configured with a maximum number of SL processes, and each of the plurality of SL grants is associated with the maximum number of SL processes in a one-to-one manner based on the subframe in which the SL grant is received. one of the maximum number of SL processes, and for one of the maximum number of SL processes, a second SL grant received in subframe n for the subsequent SC period covers the first SL grant previously received in subframe nX for the same subsequent SC period, where X is an integer value equal to or greater than the maximum number of SL processes; associating the maximum number of SL processes with the multiple SL grants, respectively, and allocating radio resources within the subsequent SC period for each of the maximum number of SL processes according to the associated SL grants; and using the allocated radio resources, performing multiple SL transmissions including at least one side link control information SCI transmission and at least one data transmission.

[0253] Additional benefits and advantages of the disclosed embodiments will be apparent from the description and drawings. Benefits and / or advantages may be provided individually by the various embodiments and features disclosed in the description and drawings, and need not be provided in full to obtain one or more of them.

[0254] These general and specific aspects may be implemented using systems, methods and computer programs, and any combination of systems, methods and computer programs. BRIEF DESCRIPTION OF THE DRAWINGS

[0255] Exemplary embodiments are described in more detail below with reference to the accompanying drawings.

[0256] Figure 1 shows an exemplary architecture of a 3GPP LTE system,

[0257] Figure 2 shows an exemplary downlink resource grid for a downlink time slot of a subframe defined for 3GPP LTE (Release 8 / 9),

[0258] Figure 3 Schematically illustrates the PC 5 interface for device-to-device direct discovery,

[0259] Figure 4 Schematically illustrates the radio protocol stack for ProSe direct discovery,

[0260] Figure 5 illustrates the use of transmit / receive resources for overlay (LTE) and underlay (D2D) systems,

[0261] Figure 6 The diagram illustrates the scheduling allocation and D2D data transmission for two UEs.

[0262] Figure 7 illustrates D2D communication timing for UE autonomous scheduling mode 2,

[0263] Figure 8 The diagram shows the D2D communication timing for scheduling mode 1 for eNB scheduling,

[0264] Figure 9 illustrates an exemplary architecture model of ProSe for non-roaming scenarios,

[0265] Figure 10 The figure shows the cell coverage in four different states that a D2D UE can be associated with.

[0266] Figure 11 The figure shows the ProSe buffer status reporting MAC control unit defined in the standard.

[0267] Figure 12 illustrates the association between ProSe logical channels, ProSe LCGs, and ProSe destination groups for an exemplary scenario,

[0268] Figure 13 illustrates D2D communication timing for two eNB-scheduled D2D transmissions according to a first variation of the first embodiment, and

[0269] Figure 14 D2D communication timing for two eNB-scheduled D2D transmissions according to a second variation of the first embodiment is illustrated. DETAILED DESCRIPTION

[0270] A user equipment (UE), mobile station, mobile node, or user terminal is a physical entity within a communication system. A user equipment may have several functional components, including an interface that enables it to communicate via a medium within the communication system (e.g., with other user equipment). Similarly, an evolved Node B (eNB), base station, network node, or network terminal has several functional components, including an interface that enables it to communicate via the same medium within the communication system (e.g., with user equipment).

[0271] The term "radio resources" is used broadly in the context of this specification to refer to physical radio resources such as time-frequency resources (eg, resource elements RE or resource blocks, RBs) used by user equipment and / or by an eNodeB as a communication medium, as described above.

[0272] The term "(direct) sidelink (SL) transmission" is used broadly in the context of this specification to refer to direct transmission between two user equipments, i.e., not via an evolved Node B (eNB). Sidelink communication is established between two user equipments exchanging sidelink transmissions. Hereinafter, the term "(direct) sidelink communication" is used synonymously with device-to-device (D2D) communication or ProSe communication.

[0273] Additionally, direct sidelink transmissions are performed over a "sidelink (SL) interface," a term used broadly in the context of this specification to refer to the functionality of a user equipment that provides sidelink transmissions. In 3GPP LTE terminology, the sidelink interface is the PC5 interface described in the background section.

[0274] The term "sidelink (SL) process" is used broadly in the context of this specification to refer to a process configured within a user equipment that can be associated with a sidelink grant. Such a sidelink process is said to be configured to provide the corresponding user equipment with the ability to associate a SL grant with it on a per-SC period basis. In 3GPP LTE terminology, a sidelink process is maintained by a sidelink HARQ entity at the MAC entity for transmissions on the Sidelink Shared Channel (SL-SCH), as described in the Background section.

[0275] However, in the context of this specification, sidelink processing should not be limited in this respect. Rather, sidelink processing may simply involve storing and maintaining a memory area within the user equipment that stores and maintains associated sidelink grants or sidelink grant information. This memory area is managed by the user equipment, for example, by associating (or storing) the memory area with newly received sidelink grant information or (re)initializing (or erasing) the memory area to remove previously associated sidelink grant information.

[0276] The term "Sidelink Control (SC) period" is used broadly in the context of this specification to refer to the period of time during which a user equipment performs a sidelink transmission. Each sidelink transmission consists of at least one scheduling assignment (sidelink control information) transmission and at least one corresponding data transmission. In other words, the "Sidelink Control period" can also be thought of as the period during which a sidelink grant is valid. In 3GPP LTE terminology, the "Sidelink Control period" is either an SA / Data period or an SC (Sidelink Control) period.

[0277] The term “ProSe destination group” or “sidelink destination group” is used throughout the specification to refer to one source layer 2 ID-destination layer 2 ID pair, for example, as defined in 3GPP LTE terminology.

[0278] The expressions "obtaining a (sidelink) grant", "receiving a (sidelink) grant" and similar expressions broadly refer to a user equipment obtaining / receiving a (sidelink) grant from a responsible eNodeB (i.e., Mode 1 functionality). Conversely, the expression "autonomously selecting a (sidelink) grant" and similar expressions broadly refer to a UE identifying a (sidelink) grant on its own, i.e., by autonomously selecting resources for the grant from an appropriate transmission resource pool(s) (i.e., Mode 2 functionality) (i.e., the UE receives the grant internally).

[0279] The currently standardized transmission schemes for D2D communication related to Mode 1 (ie, eNB-scheduled) and Mode 2 (autonomous scheduling) have been explained in the background section.

[0280] Currently, a UE can have only one (valid) sidelink grant (SL grant) per sidelink control period (SC period). Consequently, a UE is currently configured with only one SL process associated with the same grant. Even if the eNB issues several grants to the UE in Mode 1, the UE considers only the most recently (i.e., last) received one as the valid SL grant for the SC period. Specifically, the SL process overwrites the previously received SL grant(s), so the SL process is only associated with the most recently received SL grant.

[0281] Accordingly, since only one SL grant is available per SC period, a UE can only send one scheduling assignment (SA) or sidelink control information (SCI) per SC period. Furthermore, a transmitting UE can only send data to one or more receiving UEs of one ProSe destination group in each scheduling assignment (SA) or scheduling control information (SCI), respectively.

[0282] More specifically, for MAC message data unit(s) (PDU(s)) associated with one SCI, the transmitting UE shall only consider logical channels with the same source layer 2 ID - destination layer 2 ID pair. This currently standardized D2D transmission scheme results in several disadvantages.

[0283] If a UE has data for more than one ProSe destination group in its buffer(s), the transmitting UE is restricted to transmitting data to only one ProSe destination group per SC period. Consequently, data for the remaining ProSe destination group(s) is delayed by at least one additional SC period. In other words, since a Scheduling Assignment (SA) or Sidelink Control Information (SCI) transmission can indicate only one ProSe destination group, the corresponding data transmission is restricted to the same ProSe destination group.

[0284] Depending on the configured SC periodicity and the number of SC periods required to send complete data to one ProSe target group, the delay can be significant, leading to unfavorable sidelink communication characteristics. This can even be the case when radio resources allow sending data for more than the first served ProSe destination group.

[0285] Furthermore, the transmitting UE can only inefficiently utilize the D2D transmission resources it has allocated for data transmission by the evolved Node B (eNB). The evolved Node B (eNB) can allocate more D2D transmission resources than the transmitting UE requires (via SL grants). However, due to being limited to one ProSe destination group, the transmitting UE cannot utilize all allocated radio resources, for example, if the UE does not have enough data in its buffer for one ProSe destination group. This can occur, for example, if the buffer status information signaled by the transmitting UE to the eNB is inaccurate or outdated. In this case, some of the allocated radio resources remain unused because they cannot be used to transmit data for another ProSe destination group within the same SC period.

[0286] The following exemplary embodiments are conceived by the inventors to alleviate the problems explained above.

[0287] Some of these exemplary embodiments will be implemented within the broad specifications given by the 3GPP standards and are explained in part in the technical background section, with the addition of certain key features as described below with respect to various embodiments. It should be noted that the embodiments may be advantageously used, for example, in mobile communication systems, such as the 3GPP LTE-A (Release 10 / 11 / 12 / 13) communication system described in the technical background section above, but the embodiments are not limited to their use only in this particular exemplary communication network.

[0288] The following explanations should not be construed as limiting the scope of the present disclosure, but rather as examples to better understand the embodiments of the present disclosure. Those skilled in the art will appreciate that the general principles of the present disclosure, as set forth in the claims, can be applied in different scenarios and in ways not explicitly described herein. For illustrative purposes, several assumptions are made, but these assumptions do not limit the scope of the following embodiments.

[0289] Accordingly, the following scenarios are assumed for the purpose of explaining various embodiments and should not limit the embodiments thereof.

[0290] First embodiment

[0291] The first embodiment for solving the above problems will be described in detail below. Figure 13To explain the implementation of the first embodiment. For the purpose of illustration, some assumptions are made, but they should not limit the scope of the embodiment.

[0292] First, assume that user equipment is capable of ProSe communication (ProSe-enabled UE), that is, D2D transmission is performed directly between UEs without detouring via the eNodeB. In addition, the UE should have data for multiple sidelink destination groups (i.e., ProSe destination groups) available for transmission, but the improved direct sidelink transmission mechanism according to this first embodiment is also applicable to the case where only data for a single sidelink destination group is available for transmission in the UE.

[0293] The first embodiment improves direct sidelink transmission by introducing the concept of sidelink processes in the UE to which sidelink grants can be assigned on a one-to-one basis. In other words, the UE can handle multiple sidelink grants by operating a corresponding sidelink process for each sidelink grant. The sidelink processes can be addressed using corresponding identifiers (hereinafter exemplarily referred to as sidelink process IDs).

[0294] Current standardized mobile communication systems only allow a UE to use a single valid sidelink grant in each sidelink control (SC) period (any previously received (one or more) sidelink grants except the most recent one are overwritten). In contrast, the first embodiment improves D2D communication by allowing a UE to have more than one valid sidelink grant in each same SC period.

[0295] In other words, according to the first embodiment, a transmitting UE is allowed to have one valid sidelink grant for each sidelink process, so that a transmitting UE configured with multiple sidelink processes for one SC period can have the same number of valid sidelink grants. Therefore, for a UE, the maximum number of sidelink processes limits its sidelink communication capability.

[0296] Secondly, assume that the user equipment of this embodiment is configured with a maximum number of sidelink processes. This maximum number of SL processes can be implementation-specific and therefore pre-configured within the user equipment. The maximum number can also be UE-specific, such that the UE is configured by the eNodeB in whose coverage the UE is located. Or the number can even be network-specific, such that every UE within the same network is configured with the same maximum number of sidelink processes. The mechanisms for UE-specific or network-specific configuration can involve RRC signaling.

[0297] It is worth noting that even if the sidelink transmission is a direct transmission from one (transmitting) UE to one or more (receiving) UEs, it is not necessary that all UEs involved in such sidelink transmission be configured with the same maximum number of sidelink processes.

[0298] More specifically, a transmitting UE can be configured with a maximum number of SL processes that is greater than the maximum number of SL processes for one or more receiving UEs to which the sidelink transmission is directed. Furthermore, it is only necessary to ensure that all SL transmissions from the transmitting UE can be received by one or more receiving UEs within the sidelink destination group. In this regard, both the transmitting UE and the receiving UE are configured with a sufficient number of sidelink processes.

[0299] Nevertheless, for a simplified configuration of transmitting and receiving UEs, it is assumed that the maximum number of sidelink processes is network-specific. For example, the maximum number of sidelink processes can be m = {2, 4, 8}, where the following examples refer to the case where each UE is configured with m = 2 (two) sidelink processes within the communication system. Thus, this exemplary UE is capable of processing two different sidelink grants simultaneously (thus, the UE has two valid sidelink grants, sometimes also referred to as configured sidelink grants available within the SC period).

[0300] In general, the UE performs D2D transmission operations for each sidelink process having a corresponding sidelink grant within the same SC period, for example, respectively according to the standardized concepts for performing D2D transmission as explained in the background section. Specifically, for each sidelink grant available to the UE (i.e., for each sidelink process), the UE determines a sidelink destination group and generates a corresponding transport block containing data destined for the determined sidelink destination group. Radio resources are allocated for D2D transmission according to the corresponding sidelink grant. For each sidelink grant available to the UE (i.e., for each sidelink process), the UE generates corresponding sidelink control information identifying the sidelink destination group for the corresponding D2D transmission and the allocated radio resources, and performs D2D transmission for the sidelink control information for each sidelink grant (process) and the corresponding data using the allocated radio resources of the corresponding sidelink grant.

[0301] The details of these steps for performing D2D transmission are omitted here, and reference is made to the corresponding paragraphs in the background section of this application instead.

[0302] The above-described principles based on the first embodiment bring various advantages. Already established procedures can be reused in the described aspects without modification. For example, since no additional information needs to be carried, the same SCI format 0 can be used to transmit sidelink control information. In addition, since the D2D transmission used for each sidelink process remains unchanged compared to the currently standardized D2D transmission, the receiving UE does not (and in fact does not need to) distinguish between the D2D transmission performed for one sidelink process according to the first embodiment and the D2D transmission performed according to the current standard. Therefore, the UE behavior on the receiving side does not need to be adapted.

[0303] Furthermore, the first embodiment allows more data to be sent within the SC period, thus increasing the data rate for D2D transmission.

[0304] Furthermore, the first embodiment allows data destined for some sidelink destination groups to be transmitted within the same SC period by, for example, selecting a different sidelink destination group for each of the sidelink processes. Therefore, resource shortage for a specific sidelink destination group can be avoided.

[0305] So far, it has been generally assumed that the UE has some side link grants available, without focusing on how the UE obtains them in the first place. This will be described in more detail below.

[0306] First variant

[0307] In a first variant, the transmitting UE acquires a plurality of sidelink grants for at least some of the maximum number of sidelink processes configured for the UE in this first embodiment. The plurality of sidelink grants is signaled by the eNodeB, and the UE receives the plurality of sidelink grants using a standardized signaling scheme (e.g., via the PDCCH).

[0308] From these multiple sidelink grants obtained, the transmitting UE selects several sidelink grants. For example, the number of sidelink grants selected by the UE can be n = {2, 4, 8}, and the illustrated example shows a case where the UE is configured to select n = 2 sidelink grants. In other words, the transmitting UE does not store or maintain all sidelink grants signaled by the eNodeB and subsequently obtained by the UE, but only several sidelink grants.

[0309] Specifically, the transmitting UE selects several sidelink grants acquired most recently before the start of the sidelink control period from the acquired multiple sidelink grants. Assuming that the sidelink control period starts at a specific subframe, the transmitting UE selects those sidelink grants acquired last before the specific subframe.

[0310] However, this does not mean that the transmitting UE can only perform the selection of the number of sidelink grants at the beginning of the sidelink control period. Rather, the UE can implement such selection of the sidelink grants by (re)associating each of the multiple sidelink processes with the most recently acquired sidelink grant in an alternating manner (e.g., by overwriting the memory area involved).

[0311] Thus, whenever a new, more recent sidelink grant is acquired, the UE may assign the newly acquired sidelink grant to the sidelink process having the oldest sidelink grant among the multiple sidelink processes, thereby also selecting several most recent sidelink grants at the beginning of the sidelink control period. In this regard, the UE may alternate the multiple sidelink processes while assigning the most recently acquired sidelink grant to the multiple sidelink processes.

[0312] Now refer to Figure 13 . In this example, it is assumed that the UE is configured with n=2 (two) sidelink grants to be selected and m=2 (two) maximum sidelink processes. The UE acquires a sidelink grant until the start of the sidelink control period at subframe N (more precisely, until 4 subframes before the start of the sidelink control period, i.e., at subframe N-4).

[0313] The first sidelink grant acquired (e.g., at subframe N-13) is associated with the first of m=2 (two) configured sidelink processes, and the subsequently acquired sidelink grant (e.g., at subframe N-11) is associated with the second of the two configured sidelink processes. In other words, the sidelink grants are cyclically associated with the configured sidelink processes.

[0314] When another sidelink grant is acquired, for example, at subframe N-8, the UE knows that it is configured to select only n=2 (two) sidelink grants and therefore continues (or loops) to (re)associate the newly acquired sidelink grant with the first of the m=2 (two) configured sidelink processes. In other words, the sidelink grant acquired at subframe N-13 and previously (also) associated with the first of the two configured sidelink processes is overwritten.

[0315] It is worth noting that this round-robin association with the configured sidelink processes depends on the number of sidelink grants to be selected (n=2), rather than on the maximum number of sidelink processes configured for the UE (m=2). Moreover, the number of selected sidelink grants (n=2) must not exceed the maximum number of configured sidelink processes (m=2) (n<=m).

[0316] Finally, when the UE obtains a further sidelink grant, for example, at subframe N-6, this sidelink grant is again associated with the second of the m=2 (two) configured sidelink processes. Thus, the sidelink grant obtained at subframe N-11 and previously (also) associated with the second of the two configured sidelink processes is overwritten.

[0317] In summary, by applying the behavior described above, the transmitting UE has acquired multiple sidelink grants and, at the start of the sidelink control period (more precisely, four subframes before the start), selects, from among the multiple sidelink grants, several sidelink grants that were most recently acquired before the start of the sidelink control period. Furthermore, each of the n=2 (two) selected sidelink grants is associated with a different one of the m=2 (two) configured sidelink processes.

[0318] In an advantageous implementation, before associating a new, recently acquired sidelink grant with a corresponding one of the configured sidelink processes, the transmitting UE determines whether this newly acquired sidelink grant corresponds to another sidelink grant that is already associated with a different one of the multiple configured sidelink processes. If this is the case, and if the two acquired sidelink grants indicate the same radio resources for multiple sidelink transmissions (i.e., resulting in a radio resource conflict), the identical newly received sidelink grant is discarded (i.e., the newly acquired sidelink grant is not associated with the corresponding sidelink process). Thus, a cyclic association with the configured sidelink processes is maintained.

[0319] While the above mechanisms are simple, they may advantageously exploit this behavior to mitigate interference or distortion on the medium (ie, the PDCCH) used by the eNodeB to signal sidelink grants to the transmitting UE.

[0320] Conventionally, an eNodeB handles interference or distortion by signaling the same sidelink grant multiple times to the transmitting UE (e.g., on the PDCCH). The UE only acquires sidelink grants that are not affected by the interference or distortion. Therefore, the probability of successfully acquiring a sidelink grant at the transmitting UE increases each time the same sidelink grant is repeatedly signaled by the eNodeB. A conventional transmitting UE overwrites the SL grant each time it successfully acquires it. This approach is simple and reliable as long as the same sidelink grant is involved.

[0321] Applying this approach to multiple sidelink grants indicating radio resources for different sidelink transmissions between a transmitting UE and one or more receiving UEs is not straightforward. Furthermore, the eNodeB does not know which of the multiple sidelink grants the transmitting UE successfully acquired and which it failed to acquire. In other words, the eNodeB cannot assess whether one or another of the multiple sidelink grants needs to be retransmitted before the start of the SC period.

[0322] In any case, the transmitting UE in the first variant assumes repeated signaling of different sidelink grants and, upon successfully acquiring multiple sidelink grants, selects from among the acquired sidelink grants several sidelink grants that were most recently acquired before the start of the sidelink period. Furthermore, the sidelink grants are thus acquired by the UE before the subsequent SC period.

[0323] This approach is advantageous for the following reasons: in the event that the UE successfully acquires all sidelink grants signaled by the evolved Node B, selecting multiple most recently acquired sidelink grants results in different sidelink grants being provided to the transmitting UE; therefore, the transmitting UE is able to perform multiple (different) sidelink transmissions to one or more receiving UEs.

[0324] Furthermore, in the event that the UE successfully acquires the last several sidelink grants signaled by the eNodeB, selection of the most recently acquired grant also results in a different grant being provided to the transmitting UE. Thus, all but the last several sidelink grants may not be successfully acquired, as long as the last signaled plurality of sidelink grants are successfully acquired by the transmitting UE.

[0325] However, if, for example, the last of the sidelink grants signaled by the eNodeB is not successfully acquired by the UE (better: not acquired at all), the UE selects several successfully acquired sidelink grants other than the last sidelink grant that was not successfully signaled. Moreover, this situation results in the transmitting UE acquiring multiple different sidelink grants, as will become apparent from the following considerations:

[0326] Assuming repeated signaling of different sidelink grants, even in this case, since the repeated signaling of the evolved Node B ensures that the selected several sidelink grants are also different, the sending UE successfully obtains different sidelink grants, which can therefore be used by the sending UE to perform multiple (different) sidelink transmissions to one or more receiving UEs.

[0327] Furthermore, even if one of the sidelink grants signaled by the eNodeB during a transmission is not successfully acquired by the UE (i.e., not acquired), selection of the most recently received plurality of sidelink grants may result in the acquisition of a different sidelink grant, provided that an excess of different sidelink grants signaled by the eNodeB (or "spare" sidelink grants) are provided within the most recently acquired sidelink grant successfully acquired by the transmitting UE. In other words, by increasing the periodicity with which the eNodeB repeatedly signals different sidelink grants relative to the number of sidelink grants acquired by the transmitting UE, it is possible to ensure that at least the most recently acquired sidelink grant is successfully acquired by the UE.

[0328] In summary, selection of multiple recently acquired sidelink grants by a transmitting UE provides a mechanism that allows the UE to perform multiple (different) sidelink transmissions to one or more receiving UEs without losing the advantages of better interference or distortion suppression as part of conventional practice.

[0329] In addition, this approach has the advantage that it does not require any identification information to be included in the sidelink grant to associate the acquired sidelink grant with one of the maximum number of sidelink processes configured for the transmitting UE. Therefore, by the UE individually associating the acquired sidelink grant with the corresponding sidelink grant in the maximum number of sidelink processes, the information and therefore the size of each sidelink grant signaled can be kept to a minimum.

[0330] The number of sidelink grants selected by the UE cannot exceed the maximum number of sidelink processes configured for the UE for the sidelink control period. This ensures that all of the sidelink grants selected by the UE can be associated with different sidelink grants from the selected number of sidelink grants used to allocate radio resources within the sidelink control period. For each sidelink process associated with a different one of the selected sidelink grants, the UE allocates radio resources within the sidelink control period for which the sidelink grant is received, according to the associated sidelink grant for performing a corresponding one of the plurality of sidelink transmissions to one of the one or more receiving UEs.

[0331] According to an exemplary implementation, the number of sidelink grants selected by the UE corresponds to a maximum number of sidelink processes configured for the UE during the sidelink control period. Thus, all of the configured maximum number of sidelink processes may be associated with different sidelink grants from the selected number of sidelink grants used to allocate radio resources within the sidelink control period.

[0332] An exemplary implementation of the above principles applying the first variant may involve the following changes to the relevant 3GPP technical standard in TS 36.321 from its current version V12.7.0. Only the relevant subsections are provided below for reasons of brevity, however, all other parts of this document TS 36.321 are also incorporated herein by reference only.

[0333] 5.14 SL-SCH Data Transmission

[0334] 5.14.1 SL-SCH Data Transmission

[0335] 5.14.1.1 SL License Receipt and SCI Transmission

[0336] In order to transmit on the SL-SCH, the MAC entity must have a sidelink grant. A MAC entity may have up to x Sidelink Permit The sidelink permission selections are as follows:

[0337] If the MAC entity is configured to dynamically receive sidelink grants on the PDCCH or EPDCCH and there is more data available in the STCH than can be transmitted in the current SC period, the MAC entity shall:

[0338] - determining a set of subframes in which transmission of the SCI and transmission of the first transport block occurs using the received sidelink grant according to section 14.2.1 of [2];

[0339] Will The last x subframes received up to and including the 4 subframes before the start subframe of the first available SC period The received sidelink grant is considered as a configured sidelink grant, overwriting the previously configured sidelink grant occurring in the same SC period (if applicable);

[0340] - Clearing the configured sidelink grant at the end of the corresponding SC period;

[0341] - Otherwise, if the MAC entity is configured by upper layers to use a resource pool for transmission, as indicated in section 5.10.4 of [8], and there is more data available in the STCH than can be transmitted in the current SC period, and if the MAC entity has no configured sidelink grant, then the MAC entity shall:

[0342] - Randomly select a sidelink grant from a resource pool configured by upper layers. The random function should be such that each allowed choice [2] can be selected with equal probability;

[0343] - determining a set of subframes in which transmission of the SCI and transmission of the first transport block occurs using the selected sidelink grant according to section 14.2.1 of [2];

[0344] - consider the selected sidelink grant to be the configured sidelink grant occurring in those subframes starting at the start of the first available SC period, which starts at least 4 subframes after the subframe in which the sidelink grant is selected;

[0345] - Clearing the configured sidelink grant at the end of the corresponding SC period;

[0346] NOTE: Retransmissions on the SL-SCH will not occur after the configured sidelink grant is cleared.

[0347] For each subframe, the MAC entity shall:

[0348] - If the MAC entity has a configured sidelink grant occurring in this subframe:

[0349] - If the configured sidelink grant corresponds to the transmission of an SCI:

[0350] -Instructs the physical layer to transmit the SCI corresponding to the configured sidelink grant.

[0351] Otherwise, if the configured sidelink grant corresponds to the transmission of the first transport block:

[0352] - Deliver the configured sidelink grant and associated HARQ information to the sidelink HARQ entity for that subframe.

[0353] 5.14.1.2 Sidelink HARQ Operation

[0354] 5.14.1.2.1 Sidelink HARQ Entity

[0355] There is a sidelink HARQ entity at the MAC entity for transmission on the SL-SCH, which maintains X Sidelink processing.

[0356] For each subframe of SL-SCH, the sidelink HARQ entity shall:

[0357] - If a sidelink grant has been indicated for this sidelink transaction and there is SL data available for transmission:

[0358] - Get MAC PDU from the "Multiplexing and Assembly" entity;

[0359] - Delivers MAC PDUs and sidelink grants and HARQ information to the sidelink process;

[0360] -Indicates that the sidelink process triggers a new transmission.

[0361] - Otherwise, if the subframe corresponds to a retransmission opportunity for sidelink processing:

[0362] - Indicates that the sidelink process triggered a retransmission.

[0363] NOTE: The resources for retransmission opportunities are specified in subclause 14.2.1 of [2].

[0364] According to an alternative implementation, a sidelink grant reception window associated with an SC period is introduced, which represents the time period during which received sidelink grants are considered for the corresponding SC period. The sidelink grant reception window associated with SC period n starts at subframe y-3 and ends four subframes prior to the start subframe of SC period n, where subframe y represents the start subframe of SC period n-1 (the previous SC period). For the first variant, the UE uses the last x received sidelink grants (if available) received within the sidelink grant reception window as the configured sidelink grant for the corresponding SC period.

[0365] Second variant

[0366] In a second variation, the transmitting UE acquires a plurality of sidelink grants for at least some of the maximum number of sidelink processes configured for the UE in the first embodiment. The plurality of sidelink grants is signaled by the eNodeB, and the UE receives the plurality of sidelink grants using a standardized signaling scheme (e.g., via the PDCCH).

[0367] It is important to realize that for the second variant, the signaled grant is acquired in different subframes before the start of the sidelink control period (to be precise: up to 4 subframes before the start). In other words, depending on the subframe when the sidelink grant is acquired, the transmitting UE assumes (potentially) different behavior when allocating the sidelink grant to one of the configured maximum number (see above, e.g., m = {2, 4, 8}) of sidelink processes.

[0368] It is noteworthy that, like the previous variant, this second variant does not allow the UE to select (and thereby associate) n sidelink grants corresponding to a subset of the maximum number of m configured sidelink processes. Rather, the UE is adapted to associate the acquired maximum number m of sidelink grants from the plurality of sidelink grants with the sidelink processes configured within the transmitting UE. Obviously, for this behavior, it is necessary for the UE to actually acquire the maximum number m of sidelink grants.

[0369] As described above, when acquiring a sidelink, a subframe determines the sidelink process associated therewith within the transmitting UE. More specifically, since multiple sidelink grants are signaled and thus acquired in different subframes before the start of the sidelink control period (specifically, up to 4 subframes before the start), the subframe allows for unambiguous allocation for associating each acquired sidelink grant with one of the configured maximum number of sidelink grants.

[0370] The transmitting UE applies an association scheme for associating an acquired sidelink grant with one of a configured maximum number of sidelink processes. This association scheme is defined as follows: each of the maximum number of SL processes is associated with a sidelink grant from a different set of subframes, and each of the subframes in the corresponding set is offset from each other by a predefined number (e.g., o) of subframes.

[0371] In other words, each set of different subframes in which sidelink grants are acquired defines an association of these sidelink grants with one of the configured sidelink processes. Because each of these sets relates to a different subframe, each set of subframes is distinct from another. Furthermore, the subframes of each set are offset relative to one another. Thus, subsequent subframes can associate the acquired sidelink grants with different sidelink grants from the configured maximum number of sidelink processes. In other words, the sidelink grants associated with different sidelink processes are transmitted in an interleaved manner and with synchronized timing.

[0372] In summary, by applying the association scheme for each subframe when the transmitting UE acquires a sidelink grant, the transmitting UE can (re)associate one of the maximum number of sidelink processes with the most recently acquired sidelink grant (e.g., by overwriting the memory area involved). In this regard, each of the configured maximum number of sidelink processes is associated with a sidelink grant that was acquired in a corresponding set of different subframes and that was most recently acquired before the start of a subsequent sidelink control period.

[0373] Now refer to Figure 14 An example is shown in FIG. In this example, it is assumed that the UE is configured with a maximum number of m = 2 (two) sidelink processes, and that the offset between different subframes within a set corresponds to a predefined number o = 2 (two) subframes. This example should not be construed as limiting the basic concept, as offsets of, for example, o = {2, 4, 8} are also possible, as will become apparent from the following. The UE acquires a sidelink grant until the start of subframe N of the sidelink control period (more precisely: until 4 subframes N-4 before the start of the sidelink control period).

[0374] As is apparent from the above, the offset between different subframes within a set (e.g., o=2) can correspond to the maximum number of configured sidelink processes (e.g., m=2), or can be greater than this (thereby leaving intermediate subframes not allocated to one or another of the maximum number of sidelink processes).

[0375] Furthermore, the corresponding definition of an offset between different subframes within a set (e.g., o=2) and a maximum number of configured sidelink processings (e.g., m=2) enables the most efficient use of the medium (e.g., PDCCH) for signaling sidelink grants, while a larger offset in the maximum number allows for reduced monitoring of the same medium by the transmitting UE, thereby improving its battery efficiency.

[0376] In addition to the example shown, the association scheme defines, for the first of a maximum number m = 2 sidelink processes, an association based on a first set of different subframes (including subframes N-14, N-12, N-10, N-8, N-6, and N-4). For the second of the maximum number m = 2 sidelink processes, the association scheme defines an association based on a second set of different subframes (including subframes N-13, N-11, N-9, N-7, and N-5). For both sets, the different subframes are offset from each other by a predetermined number o = 2 (two) subframes.

[0377] The first sidelink grant obtained by the UE, for example at subframe N-13, is associated with the second of m=2 (two) configured sidelink processes, because, applying the above-mentioned association scheme, the UE determines that the sidelink grant is obtained in a subframe belonging to a second set of different subframes, and thus the UE assumes that this sidelink grant is associated with the second of the maximum number m=2 sidelink processes.

[0378] Subsequently, another sidelink grant obtained by the UE, for example, at subframe N-11, is also associated with the second of the two configured sidelink processes, again because this sidelink grant is obtained in a subframe belonging to the second set of subframes. Regardless of any previous sidelink grants, the UE (re)associates the newly obtained sidelink grant (e.g., at N-11) with the second of the m=2 (two) configured sidelink processes. In other words, the sidelink grant obtained at subframe N-13 and previously (also) associated with the second of the two configured sidelink processes is overwritten.

[0379] Thereafter, another sidelink grant obtained by the UE, for example at subframe N-8, is associated with the first of m=2 (two) configured sidelink processes, because, applying the above-mentioned association scheme, the UE determines that the sidelink grant is obtained in a subframe belonging to the first set of different subframes, and thus the UE assumes that this sidelink grant is associated with the first of the maximum number m=2 sidelink processes.

[0380] Finally, another sidelink grant obtained by the UE, for example at subframe N-6, is also associated with the first of the two configured sidelink processes, again because this sidelink grant is obtained in a subframe belonging to the first set of subframes. The sidelink grant obtained at subframe N-8 and previously (also) associated with the first of the two configured sidelink processes is overwritten.

[0381] In summary, by applying the above behavior, the transmitting UE has acquired multiple sidelink grants and at the start of the associated sidelink control period (more precisely, 4 subframes before the start), each of the multiple maximum number m=2 sidelink processes is associated with a sidelink grant that was acquired in a corresponding set of different subframes and that has been most recently acquired before the start of the subsequent sidelink control period.

[0382] For each of the multiple SL processes, the transmitting UE allocates radio resources within a subsequent sidelink control period according to the sidelink grant associated with the corresponding sidelink process for performing one of the multiple sidelink transmissions to one or more receiving user equipments.

[0383] According to an exemplary implementation of the first or second variant, the transmitting UE continues to acquire a sidelink grant for (i.e., subsequent) a sidelink control period until four subframes prior to the start of the sidelink control period. This provides the eNodeB with accurate information about when the most recent sidelink grant was available to the UE. In other words, the eNodeB can pre-plan its appropriate sidelink grant signaling.

[0384] In another exemplary implementation of the first or second variant, each of the multiple sidelink processes is reinitialized (or refreshed) before the start of a (i.e., subsequent) sidelink control period to allow its association with a later (i.e., further subsequent) sidelink control period. Assuming that a sidelink grant can be acquired until four subframes before the start of a sidelink control period, the multiple sidelink processes are reinitialized as early as possible, i.e., three subframes before the start of the sidelink control period. This ensures that sidelink grants acquired for a later (i.e., further subsequent) sidelink control period can be associated with the sidelink process as early as possible, which is particularly advantageous in the second variant, but is not limited thereto.

[0385] According to another exemplary implementation of the first and second variants, after associating each of the selected sidelink grants with a different one of the sidelink processes, the transmitting UE performs a Logical Channel Prioritization (LCP) procedure for each of the associated sidelink processes. Each of the LCP procedures identifies a different ProSe destination group, which can ensure that multiple sidelink transmissions are each performed to a different one or more receiving UEs.

[0386] An exemplary implementation of the above principles applying the second variant may involve the following changes to the current version V12.7.0 of the relevant 3GPP technical standard in TS 36.321. Only the relevant subsections are provided below for reasons of brevity, however, all other parts of this document TS 36.321 are also incorporated herein by reference.

[0387] 5.14SL-SCH Data Transmission

[0388] 5.14.1 SL-SCH Data Transmission

[0389] 5.14.1.1 SL License Receipt and SCI Transmission

[0390] In order to transmit on the SL-SCH, the MAC entity must have a sidelink grant. A MAC entity may have up to x Sidelink Permit The sidelink permission selections are as follows:

[0391] If the MAC entity is configured to dynamically receive sidelink grants on the PDCCH or EPDCCH and there is more data available in the STCH than can be transmitted in the current SC period, the MAC entity shall:

[0392] - determining a set of subframes in which transmission of the SCI and transmission of the first transport block occurs using the received sidelink grant according to section 14.2.1 of [2];

[0393] - consider the received sidelink grant to be the configured sidelink grant occurring in those subframes starting at the start of the first available SC period starting at least 4 subframes after the subframe in which the sidelink grant was received, On this side The line link grant is received X subframes before the subframe in which the line link grant is received, Overwrites a previously configured sidelink grant occurring in the same SC period (if applicable);

[0394] - Clearing the configured sidelink grant at the end of the corresponding SC period;

[0395] - Otherwise, if the MAC entity is configured by upper layers to use a resource pool for transmission, as indicated in section 5.10.4 of [8], and there is more data available in the STCH than can be transmitted in the current SC period, and if the MAC entity has no configured sidelink grant, then the MAC entity shall:

[0396] - Randomly select a sidelink grant from a resource pool configured by upper layers. The random function should be such that each allowed choice [2] can be selected with equal probability;

[0397] - determining a set of subframes in which transmission of the SCI and transmission of the first transport block occurs using the selected sidelink grant according to section 14.2.1 of [2];

[0398] - consider the selected sidelink grant to be the configured sidelink grant occurring in those subframes starting at the start of the first available SC period, which starts at least 4 subframes after the subframe in which the sidelink grant is selected;

[0399] - Clearing the configured sidelink grant at the end of the corresponding SC period;

[0400] NOTE: Retransmissions on the SL-SCH will not occur after the configured sidelink grant is cleared.

[0401] For each subframe, the MAC entity shall:

[0402] - If the MAC entity has a configured sidelink grant occurring in this subframe:

[0403] - If the configured sidelink grant corresponds to the transmission of an SCI:

[0404] -Instructs the physical layer to transmit the SCI corresponding to the configured sidelink grant.

[0405] Otherwise, if the configured sidelink grant corresponds to the transmission of the first transport block:

[0406] - Deliver the configured sidelink grant and associated HARQ information to the sidelink HARQ entity for that subframe.

[0407] 5.14.1.2 Sidelink HARQ Operation

[0408] 5.14.1.2.1 Sidelink HARQ Entity

[0409] There is a sidelink HARQ entity at the MAC entity for transmission on the SL-SCH, which maintains X Sidelink processing.

[0410] For each subframe of SL-SCH, the sidelink HARQ entity shall:

[0411] - If a sidelink grant has been indicated for this sidelink transaction and there is SL data available for transmission:

[0412] - Get MAC PDU from the "Multiplexing and Assembly" entity;

[0413] - Delivers MAC PDUs and sidelink grants and HARQ information to the sidelink process;

[0414] -Indicates that the sidelink process triggers a new transmission.

[0415] - Otherwise, if the subframe corresponds to a retransmission opportunity for sidelink processing:

[0416] - Indicates that the sidelink process triggered a retransmission.

[0417] NOTE: The resources for retransmission opportunities are specified in subclause 14.2.1 of [2].

[0418] According to another implementation, at a given TTI, if a sidelink grant is received in this TTI, the UE identifies the sidelink process with which the sidelink grant is associated. The sidelink grant received in subframe n overrides the sidelink grant received in subframe nX, where X represents a predefined integer value.

[0419] Second embodiment

[0420] A second embodiment for addressing the aforementioned issues will be described in detail below. Specifically, this embodiment focuses on, but is not limited to, multiple sidelink transmissions for Mode 2 resource allocation. Furthermore, a mechanism is designed that allows radio resources to be allocated to perform multiple direct sidelink (SL) transmissions over the SL interface to one or more receiving user equipment in a communication system during a Sidelink Control (SC) period.

[0421] In more detail, the transmitting UE autonomously selects SL grants from different resource pools for multiple SL transmissions, each SL grant being configured and usable for SL transmission within the communication system. In addition, for each of the multiple SL transmissions, the UE must associate the SL grant with a different SL process selected from a different configured resource pool.

[0422] For each of the multiple SL processes with associated SL grants, the transmitting UE performs a separate Logical Channel Prioritization (LCP) procedure that only considers logical channels with different destination group IDs. Thus, for each of the multiple SL processes, the UE allocates radio resources according to the autonomously selected SL grants associated with the corresponding SL process within the same or overlapping SC periods.

[0423] Thus, a transmitting UE can be configured to perform multiple SL transmissions within the same sidelink control period, each of which is directed to one or more receiving UEs. Furthermore, the restriction of only allowing SL transmissions to different ProSe destination groups within the same SC period or overlapping SC periods (for cases where the transmitting UE performs SL transmissions in different transmission resource pools) advantageously eliminates the need for any additional transport block, TB, or MAC layer reordering mechanisms. In other words, ProSe in-sequence delivery is thereby implemented.

[0424] According to an exemplary implementation, the transmitting UE further determines, for each subframe within the SC period, whether the allocated radio resources are used for multiple SL transmissions within the same subframe. Specifically, since ProSe communication is performed in the uplink frequency band using a single-carrier frequency division multiple access (SC-FDMA) scheme, multiple SL transmissions must meet the single-carrier characteristic, as will become apparent below.

[0425] As is apparent from the SC-FDMA scheme, a transmitting UE can perform only a single transport block (TB) transmission per transmission time interval (TTI). However, the radio resources autonomously selected for multiple SL transmissions within the same SC period may not satisfy this property. In other words, the radio resources may not be allocated for the same multiple SL transmissions.

[0426] If the transmitting UE determines that the allocated radio resources are not arranged correctly, i.e., the above-mentioned single carrier characteristic for each transmission time interval is not satisfied, then the UE may skip the corresponding SCI and / or data transmission for the SL processing with a lower ranking logical channel priority for SL transmission, or the UE may skip the corresponding SCI and / or data transmission for the SL processing with a lower ranking resource pool associated with the SL processing.

[0427] Logical channel priority refers to the data transmission portion of an SL transmission. Additionally, resource pool ranking establishes a priority for the data transmission portion of an SL transmission. Furthermore, since each resource pool provides multiple retransmissions as described above, skipping individual transmissions is generally negligible for system performance.

[0428] In summary, this advantageous implementation enforces compatibility of multiple SL transmissions with the SC-FDMA scheme by the transmitting UE when multiple SL transmissions are performed within the same SC period, each of which is directed to one or more receiving UEs. This avoids defining compatibility between SL grants autonomously selected from different resource pools.

[0429] It should be noted that in cases where the SL grant issued by the eNB may result in the radio resources allocated within the SC period being scheduled for multiple SL transmissions within the same subframe, skipping some corresponding SCI and / or data transmissions may also be necessary for the eNB-controlled resource allocation mode (mode 1).

[0430] According to an embodiment of the present disclosure, at least the following sending user equipment and method thereof are disclosed.

[0431] According to a transmitting user equipment of the present disclosure, a transmitting user equipment is provided for allocating radio resources to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface. For a sidelink control SC period, the allocation of radio resources within the SC period is limited by the maximum number of SL processes configured for the transmitting user equipment. The transmitting user equipment comprises: a processor adapted to acquire multiple SL licenses for a subsequent SC period, and to select, from among the acquired SL licenses, several SL licenses most recently acquired before the start of the subsequent SC period, wherein the number of the selected SL licenses does not exceed the maximum number of SL processes configured for the one SC period; the processor is further adapted to associate the multiple SL processes for the subsequent SC period so that each of the multiple SL processes is associated with a different SL license among the selected several SL licenses for allocating radio resources within the subsequent SC period; and the processor is further adapted to, for each of the multiple SL processes, processing, allocating the radio resource within the subsequent SC period according to the selected SL grant associated with the corresponding SL processing for performing one of the multiple SL transmissions to one of the one or more receiving user equipments, each of the multiple SL transmissions including at least one sidelink control information SCI transmission and at least one data transmission through the SL interface.

[0432] According to the transmitting user equipment of the present disclosure, the number of SL grants selected corresponds to the maximum number of SL processes configured for the one SC period.

[0433] According to the transmitting user equipment of the present disclosure, only the SL grants until 4 subframes before the start of the SC period are acquired for the subsequent SC period.

[0434] According to the transmitting user equipment of the present disclosure, each of the plurality of SL processes is reinitialized before the start of an SC period so as to allow it to be associated with an SL grant for a further subsequent SC period thereafter.

[0435] According to the transmitting user equipment of the present disclosure, each of the multiple SL processes is reinitialized at 3 subframes before the start of the SC period.

[0436] According to the transmitting user equipment of the present disclosure, the processor is further adapted to perform a Logical Channel Prioritization (LCP) procedure for each of the plurality of SL processes associated with the SL grant.

[0437] According to the transmitting user equipment of the present disclosure, performing each of the plurality of LCP procedures includes identifying a different destination group ID for performing the plurality of SL transmissions to one or more receiving user equipments.

[0438] A transmitting user equipment according to the present disclosure is used to allocate radio resources to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface, and for a sidelink control SC period, the allocation of radio resources within the SC period is limited by a maximum number of SL processes configured for the transmitting user equipment, the transmitting user equipment comprising: a processor adapted to acquire multiple sidelink SL grants for a subsequent SC period in different subframes before the start of the subsequent SC period: ● by applying an association scheme, each of the acquired SL grants is associated with one of the maximum number of SL processes based on the subframe in which the SL grant is acquired: ● each SL process in the maximum number of SL processes is associated with SL grants from a set of different subframes, and each of the subframes in the set is offset from each other by a predefined number of subframes; the processor is further adapted to associate each of the maximum number of multiple SL processes with the SL license that was acquired in the corresponding set of different subframes and that was most recently acquired before the start of the subsequent SC period; and the processor is further adapted to allocate radio resources for each of the multiple SL processes within the subsequent SC period according to the SL license associated with the corresponding SL process for performing one of the multiple SL transmissions to one or more receiving user equipment, each of the multiple SL transmissions comprising at least one side link control information SCI transmission and at least one data transmission through the SL interface.

[0439] According to the transmitting user equipment of the present disclosure, the predefined number of subframes corresponds to the maximum number of SL processes configured for the transmitting user equipment.

[0440] According to the transmitting user equipment of the present disclosure, only the SL grants until 4 subframes before the start of the SC period are acquired for the subsequent SC period.

[0441] According to the transmitting user equipment of the present disclosure, each of the plurality of SL processes is reinitialized before the start of an SC period so as to allow it to be associated with an SL grant for a further subsequent SC period thereafter.

[0442] According to the transmitting user equipment of the present disclosure, each of the multiple SL processes is reinitialized at 3 subframes before the start of the SC period.

[0443] According to the transmitting user equipment of the present disclosure, the processor is further adapted to perform a Logical Channel Prioritization (LCP) procedure for each of the plurality of SL processes associated with the SL grant.

[0444] According to the transmitting user equipment of the present disclosure, performing each of the plurality of LCP procedures includes identifying a different destination group ID for performing the plurality of SL transmissions to one or more receiving user equipments.

[0445] According to the transmitting user equipment of the present disclosure, it is used to allocate radio resources to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a side link SL interface. The transmitting user equipment includes: a processor, adapted to autonomously select SL licenses for multiple SL transmissions from different resource pools, each SL license being configured and made available for SL transmission within the communication system; the processor is also adapted to, for each of the multiple SL transmissions, associate the SL license to a different SL processing selected from a differently configured resource pool; the processor is also adapted to, for each of the multiple SL processings having an associated SL license, perform a separate logical channel prioritization LCP process, the LCP process only taking into account logical channels with different destination group IDs; and the processor is also adapted to, for each of the multiple SL processings, allocate the radio resources according to the autonomously selected SL license associated with the corresponding SL processing within the same SC period for performing the multiple SL transmissions, each of the multiple SL transmissions including at least one side link control information SCI transmission and at least one data transmission via the SL interface.

[0446] According to the transmitting user equipment of the present disclosure, the processor is also suitable for determining, for each subframe within the SC period, whether the allocated radio resources are arranged for multiple SL transmissions within the same subframe, and in the case of determination: ● skipping the corresponding SCI and / or data transmission for the SL processing with a lower ranking logical channel priority for SL transmission, or ● skipping the corresponding SCI and / or data transmission for the SL processing with a lower ranking resource pool associated with the SL processing.

[0447] According to the present disclosure, a method for allocating radio resources for a transmitting user equipment to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface is provided. For a sidelink control SC period, the allocation of radio resources within the SC period is limited by the maximum number of SL processes configured for the transmitting user equipment. The method includes the following steps performed by the transmitting user equipment: obtaining multiple SL licenses for a subsequent SC period, and selecting from the obtained SL licenses several SL licenses that were most recently acquired before the start of the subsequent SC period, the number of selected SL licenses not exceeding the maximum number of SL processes configured for the one SC period; associating multiple SL processes for the subsequent SC period so that each of the multiple SL processes is associated with a different SL license among the selected several SL licenses for allocating radio resources within the subsequent SC period; and for each of the multiple SL processes, allocating the radio resources within the subsequent SC period according to the selected SL license associated with the corresponding SL process for performing one of the multiple SL transmissions to one of the one or more receiving user equipment, each of the multiple SL transmissions including at least one sidelink control information SCI transmission and at least one data transmission via the SL interface.

[0448] According to a method for allocating radio resources for a transmitting user equipment to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface according to the present disclosure, for a sidelink control SC period, the allocation of radio resources within the SC period is limited by the maximum number of SL processes configured for the transmitting user equipment, the method comprising the following steps performed by the transmitting user equipment: obtaining multiple sidelink SL grants for the subsequent SC period in different subframes before the start of the subsequent SC period: ● by applying an association scheme, each of the obtained SL grants is associated with one of the maximum number of SL processes based on the subframe in which the SL grant is obtained: ● each SL process in the maximum number of SL processes is associated with SL grants from a set of different subframes, and each of the subframes in the set is offset from each other by a predefined number of subframes; associating each of the multiple SL processes in the maximum number of SL processes with the SL grant that was obtained in the corresponding set of different subframes and that was most recently obtained before the start of the subsequent SC period; and for each of the multiple SL processes in the subsequent SC Radio resources are allocated within a time period according to an SL grant associated with a corresponding SL process for performing one of the multiple SL transmissions to one or more receiving user equipments, each of the multiple SL transmissions comprising at least one sidelink control information SCI transmission and at least one data transmission through the SL interface.

[0449] According to the present disclosure, a method for allocating radio resources for a transmitting user equipment to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system via a sidelink SL interface includes the following steps performed by the transmitting user equipment: autonomously selecting SL licenses for multiple SL transmissions from different resource pools, each SL license being configured and made available for SL transmission within the communication system; for each of the multiple SL transmissions, associating the SL license to a different SL processing selected from a differently configured resource pool; for each of the multiple SL processings with associated SL licenses, performing a separate logical channel prioritization LCP process, which LCP process only takes into account logical channels with different destination group IDs; and for each of the multiple SL processings, allocating the radio resources according to the autonomously selected SL license associated with the corresponding SL processing within the same SC period for performing the multiple SL transmissions, each of the multiple SL transmissions including at least one sidelink control information SCI transmission and at least one data transmission via the SL interface.

[0450] Hardware and software implementations of the present disclosure

[0451] Other exemplary embodiments involve implementing the various embodiments described above using hardware, software, or software in conjunction with hardware. In this regard, a user terminal (mobile terminal) and an eNodeB (base station) are provided. The user terminal and the base station are adapted to perform the methods described herein and include corresponding entities that appropriately participate in the methods, such as a receiving unit, a transmitting unit, and a processor.

[0452] It should also be recognized that the various embodiments can be implemented or executed using a computing device (processor). The computing device or processor can be, for example, a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, etc. Various embodiments can also be implemented or embodied by combining these devices. Specifically, each functional block used in the description of each of the above embodiments can be implemented as an integrated circuit by LSI. They can be formed into chips individually, or a chip can be formed to include part or all of the functional blocks. They can include data inputs and outputs coupled thereto. Depending on the difference in integration, the LSI here can be referred to as IC, system LSI, super LSI or ultra LSI. However, the technology for implementing integrated circuits is not limited to LSI and can be implemented by using a dedicated circuit or a general-purpose processor. In addition, an FPGA (field programmable gate array) that can be programmed after LSI manufacturing or a reconfigurable processor in which the connections and settings of the circuit units placed inside the LSI can be reconfigured can be used.

[0453] Furthermore, various embodiments may be implemented via software modules executed by a processor or directly in hardware. Combinations of software modules and hardware implementations are also possible. Software modules may be stored on any type of computer-readable storage medium, such as RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROMs, DVDs, and the like. It should also be noted that the various features of different embodiments may be used individually or in any combination with respect to the features of another embodiment.

[0454] Those skilled in the art will recognize that many changes and / or modifications may be made to the present disclosure as shown in the specific embodiments. Therefore, the present embodiments are to be considered in all aspects as illustrative and not restrictive.

Claims

1. A transmitting user equipment for allocating radio resources to perform multiple direct SL transmissions to one or more receiving user equipments in a communication system over a sidelink (SL) interface, the transmitting user equipment comprising: A receiving unit receives a plurality of SL grants for a subsequent sidelink control (SC) period in a plurality of subframes before the start of the subsequent SC period, wherein: The sending user equipment is configured with a maximum number of SL processes, Each of the plurality of SL grants is associated with one of the maximum number of SL processes based on the subframe in which the SL grant is acquired by applying an association scheme to each subframe in which the UE acquires the SL grant, wherein: o Each of the maximum number of SL processes is associated with a SL grant from a different set of subframes, o Each subframe in the corresponding set is offset from each other by a predetermined number X of subframes, and for one of said maximum number of SL processes, a second SL grant for said subsequent SC period received in subframe n overwrites a first SL grant for the same said subsequent SC period previously received in subframe nX, where X is an integer value equal to or greater than the maximum number of SL processes; circuit, which is coupled to the receiving unit, associating the maximum number of SL processes with the plurality of SL licenses, respectively, and allocating radio resources in the subsequent SC period for each of the maximum number of SL processes according to an associated SL grant; and The transmitting unit is coupled to the circuit and performs a plurality of SL transmissions including at least one sidelink control information SCI transmission and at least one data transmission using the allocated radio resources.

2. The sending user equipment according to claim 1, wherein: For the subsequent SC period, only multiple SL grants until 4 subframes before the start of the subsequent SC period are received.

3. The transmitting user equipment according to claim 1, wherein: Each of the maximum number of SL processes is reinitialized before the subsequent SC period begins.

4. The transmitting user equipment according to claim 3, wherein: Each of the maximum number of SL processes is reinitialized 3 subframes before the start of the subsequent SC period.

5. The sending user equipment according to claim 1, wherein: The circuitry performs a Logical Channel Prioritization (LCP) procedure for each of the maximum number of SL processes.

6. The transmitting user equipment according to claim 5, wherein: The LCP process includes identifying different destination group IDs used in the multiple SL transmissions.

7. A method for allocating radio resources for a transmitting user equipment to perform multiple direct SL transmissions to one or more receiving user equipments in a communication system over a sidelink (SL) interface, the method comprising the following steps performed by the transmitting user equipment: A plurality of SL grants for a subsequent sidelink control (SC) period is received in a plurality of subframes before a start of the subsequent SC period, wherein: The sending user equipment is configured with a maximum number of SL processes, and Each of the plurality of SL grants is associated with one of the maximum number of SL processes based on the subframe in which the SL grant is acquired by applying an association scheme to each subframe in which the UE acquires the SL grant, wherein: o Each of the maximum number of SL processes is associated with a SL grant from a different set of subframes, o Each subframe in the corresponding set is offset from each other by a predetermined number X of subframes, and for one of said maximum number of SL processes, a second SL grant for said subsequent SC period received in subframe n overwrites a first SL grant for the same said subsequent SC period previously received in subframe nX, where X is an integer value equal to or greater than the maximum number of SL processes; associating the maximum number of SL processes with the plurality of SL licenses, respectively, and allocating radio resources in the subsequent SC period for each of the maximum number of SL processes according to an associated SL grant; and Using the allocated radio resources, a plurality of SL transmissions including at least one sidelink control information SCI transmission and at least one data transmission are performed.

8. The method of claim 7, wherein: For the subsequent SC period, only multiple SL grants until 4 subframes before the start of the subsequent SC period are received.

9. The method of claim 7, wherein: Each of the maximum number of SL processes is reinitialized before the subsequent SC period begins.

10. The method of claim 9, wherein: Each of the maximum number of SL processes is reinitialized 3 subframes before the start of the subsequent SC period.

11. The method according to claim 7, wherein: The steps performed by the transmitting user equipment include performing a Logical Channel Prioritization (LCP) procedure for each of the maximum number of SL processes.

12. The method of claim 11, wherein: The LCP process includes identifying different destination group IDs used in the multiple SL transmissions.

13. An integrated circuit for controlling a process for allocating radio resources by a transmitting user equipment to perform multiple direct SL transmissions to one or more receiving user equipment in a communication system over a sidelink (SL) interface, the integrated circuit comprising circuitry for controlling the process, the process comprising: A plurality of SL grants for a subsequent sidelink control (SC) period is received in a plurality of subframes before a start of the subsequent SC period, wherein: The transmitting user equipment is configured with a maximum number of SL processes, and each of the plurality of SL grants is associated with one of the maximum number of SL processes based on the subframe in which the SL grant is obtained, by applying an association scheme to each subframe in which the transmitting UE obtains the SL grant, wherein: o Each of the maximum number of SL processes is associated with a SL grant from a different set of subframes, o Each subframe in the corresponding set is offset from each other by a predetermined number X of subframes, and for one of said maximum number of SL processes, a second SL grant for said subsequent SC period received in subframe n overwrites a first SL grant for the same said subsequent SC period previously received in subframe nX, where X is an integer value equal to or greater than the maximum number of SL processes; associating the maximum number of SL processes with the plurality of SL licenses, respectively; allocating radio resources in the subsequent SC period for each of the maximum number of SL processes according to an associated SL grant; and Using the allocated radio resources, a plurality of SL transmissions including at least one sidelink control information SCI transmission and at least one data transmission are performed.

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