Patent Description:
The subject matter disclosed herein relates generally to wireless communications and more particularly relates to conveying unicast sessions over a direct communication link.

The following abbreviations are herewith defined, at least some of which are referred to within the following description: Third Generation Partnership Project ("<NUM> GPP"), Fifth Generation Core Network ("5CG"), Fifth Generation System ("5GS"), Absolute Radio Frequency Channel Number ("ARFCN"), Authentication, Authorization and Accounting ("AAA"), Access and Mobility Management Function ("AMF"), Access to Restricted Local Operator Services ("ARLOS"), Positive-Acknowledgment ("ACK"), Application Programming Interface ("API"), Authentication Center ("AuC"), Access Stratum ("AS"), Autonomous Uplink ("AUL"), AUL Downlink Feedback Information ("AUL-DFI"), Base Station ("BS"), Binary Phase Shift Keying ("BPSK"), Bandwidth Part ("BWP"), Cipher Key ("CK"), Clear Channel Assessment ("CCA"), Control Element ("CE"), Cyclic Prefix ("CP"), Cyclical Redundancy Check ("CRC"), Channel State Information ("CSI"), Common Search Space ("CSS"), Connection Mode ("CM", this is a NAS state in 5GS), Core Network ("CN"), Control Plane ("CP"), Data Radio Bearer ("DRB"), Dedicated Short Range Communication ("DSRC"), Discrete Fourier Transform Spread ("DFTS"), Downlink Control Information ("DCI"), Downlink ("DL"), Downlink Pilot Time Slot ("DwPTS"), Dual Connectivity ("DC"), Dual Registration mode ("DR mode"), Discontinuous Transmission ("DTX"), Enhanced Clear Channel Assessment ("eCCA"), Enhanced Licensed Assisted Access ("eLAA"), Enhanced Mobile Broadband ("eMBB"), Evolved Node-B ("eNB"), Evolved Packet Core ("EPC"), Evolved Packet System ("EPS"), EPS Mobility Management ("EMM", this is a NAS state in EPS), Evolved UMTS Terrestrial Radio Access ("E-UTRA"), E-UTRA Absolute Radio Frequency Channel Number ("EARFCN"), Evolved UMTS Terrestrial Radio Access Network ("E-UTRAN"), European Telecommunications Standards Institute ("ETSI"), Frame Based Equipment ("FBE"), Frequency Division Duplex ("FDD"), Frequency Division Multiple Access ("FDMA"), Frequency Division Orthogonal Cover Code ("FD-OCC"), General Packet Radio Service ("GPRS"), Generic Public Service Identifier ("GPSI"), Guard Period ("GP"), Global System for Mobile Communications ("GSM"), Globally Unique Temporary UE Identifier ("GUTI"), Hybrid Automatic Repeat Request ("HARQ"), Home Subscriber Server ("HSS"), Home Public Land Mobile Network ("HPLMN"), Information Element ("IE"), Integrity Key ("IK"), Internet-of Things ("IoT"), International Mobile Subscriber Identity ("IMSI"), Key Derivation Function ("KDF"), Licensed Assisted Access ("LAA"), Load Based Equipment ("LBE"), Listen-Before-Talk ("LBT"), Long Term Evolution ("LTE"), Multiple Access ("MA"), Mobility Management ("MM"), Mobility Management Entity ("MME"), Modulation Coding Scheme ("MCS"), Machine Type Communication ("MTC"), Multiple Input Multiple Output ("MIMO"), Mobile Station International Subscriber Directory Number ("MSISDN"), Multi User Shared Access ("MUSA"), Narrowband ("NB"), Negative-Acknowledgment ("NACK") or ("NAK"), New Generation (<NUM>) Node-B ("gNB"), New Generation Radio Access Network ("NG-RAN", a RAN used for 5GS networks), New Radio ("NR", a <NUM> radio access technology; also referred to as "<NUM> NR"), Next Hop (NH"), Next Hop Chaining Counter ("NCC"), Non-Access Stratum ("NAS"), Network Exposure Function ("NEF"), Non-Orthogonal Multiple Access ("NOMA"), Network Slice Selection Assistance Information ("NSSAI"), Operation and Maintenance System ("OAM"), Orthogonal Frequency Division Multiplexing ("OFDM"), Packet Data Unit ("PDU", used in connection with 'PDU Session'), Packet Switched ("PS", e.g., Packet Switched domain or Packet Switched service), Primary Cell ("PCell"), Physical Broadcast Channel ("PBCH"), Physical Cell Identity ("PCI"), Physical Downlink Control Channel ("PDCCH"), Physical Downlink Shared Channel ("PDSCH"), Pattern Division Multiple Access ("PDMA"), Physical Hybrid ARQ Indicator Channel ("PHICH"), Physical Random Access Channel ("PRACH"), Physical Resource Block ("PRB"), Physical Uplink Control Channel ("PUCCH"), Physical Uplink Shared Channel ("PUSCH"), Public Land Mobile Network ("PLMN"), Quality of Service ("QoS"), Quadrature Phase Shift Keying ("QPSK"), Radio Access Network ("RAN"), Radio Access Technology ("RAT"), Radio Resource Control ("RRC"), Random-Access Channel ("RACH"), Random Access Response ("RAR"), Radio Network Temporary Identifier ("RNTI"), Reference Signal ("RS"), Registration Area ("RA", similar to tacking area list used in LTE/EPC), Registration Management ("RM", refers to NAS layer procedures and states), Remaining Minimum System Information ("RMSI"), Resource Spread Multiple Access ("RSMA"), Round Trip Time ("RTT"), Receive ("RX"), Radio Link Control ("RLC"), Sparse Code Multiple Access ("SCMA"), Scheduling Request ("SR"), Single Carrier Frequency Division Multiple Access ("SC-FDMA"), Secondary Cell ("SCell"), Shared Channel ("SCH"), Session Management ("SM"), Session Management Function ("SMF"), Service Provider ("SP"), Signal-to-Interference-Plus-Noise Ratio ("SINR"), Single Network Slice Selection Assistance Information ("S-NSSAI"), Single Registration mode ("SR mode"), Sounding Reference Signal ("SRS"), System Information Block ("SIB"), Synchronization Signal ("SS"), Supplementary Uplink ("SUL"), Subscriber Identification Module ("SIM"), Tracking Area ("TA"), Transport Block ("TB"), Transport Block Size ("TBS"), Time-Division Duplex ("TDD"), Time Division Multiplex ("TDM"), Time Division Orthogonal Cover Code ("TD-OCC"), Transmission Time Interval ("TTI"), Transmit ("TX"), Unified Access Control ("UAC"), Unified Data Management ("UDM"), User Data Repository ("UDR"), Uplink Control Information ("UCI"), User Entity/Equipment (Mobile Terminal) ("UE"), UE Configuration Update ("UCU"), UE Route Selection Policy ("URSP"), Uplink ("UL"), User Plane ("UP"), Universal Mobile Telecommunications System ("UMTS"), UMTS Subscriber Identification Module ("USIM"), UMTS Terrestrial Radio Access ("UTRA"), UMTS Terrestrial Radio Access Network ("UTRAN"), Uplink Pilot Time Slot ("UpPTS"), Ultra-reliability and Low-latency Communications ("URLLC"), Visited Public Land Mobile Network ("VPLMN"), and Worldwide Interoperability for Microwave Access ("WiMAX"). As used herein, "HARQ-ACK" may represent collectively the Positive Acknowledge ("ACK") and the Negative Acknowledge ("NACK") and Discontinuous Transmission ("DTX"). ACK means that a TB is correctly received while NACK (or NAK) means a TB is erroneously received. DTX means that no TB was detected.

In certain wireless communication systems, V2X communication is supported using unicast communication over PC5. However, as of 3GPP Release <NUM>, no link layer mechanism exists for unicast communications over PC5.

<NPL>
discloses the proposal of using PFI as additional information for distinguishing the different PC5 unicast links (or Link Identifiers or Session Links) that may exist within the same UE.

The invention is defined by the appended independent claims and corresponds to <FIG> and to the related text in the description. The remaining figures and the text of the description are intended to better explain the invention. Disclosed are procedures for determining whether an active unicast session can be re-used. One method of a UE, e.g., for determining whether an active unicast session can be re-used, includes receiving, from an internal application (e.g., a V2X application or OS running on the source UE), a first request to establish a unicast session over a direct communication link to a target UE (i.e., a second UE). Here, the first request indicates a source application-layer identifier of the source UE and a target application-layer identifier of the target UE. The first method includes determining whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists. If an active unicast session between the source application-layer identifier and the target application-layer identifier already exists, then the first method includes re-using the already-existing active unicast session between the source UE and the target UE. Otherwise, if an active unicast session between the source application-layer identifier and the target application-layer identifier does not already exist, then the first method includes establishing a new unicast session between the source UE and target UE.

Code for carrying out operations for embodiments may be any number of lines and may be written in any combination of one or more programming languages including an object-oriented programming language such as Python, Ruby, Java, Smalltalk, C++, or the like, and conventional procedural programming languages, such as the "C" programming language, or the like, and/or machine languages such as assembly languages.

The code may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the code which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart diagrams and/or block diagrams.

The flowchart diagrams and/or block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of apparatuses, systems, methods, and program products.

Generally, the present disclosure describes systems, methods, and apparatus for determining whether an active unicast session can be re-used for UEs engaged in V2X communication. It is currently unclear how the Source UE determines that a unicast session is sent to the same Target UE. For example, a Source UE may support different V2X services, each V2X service requiring the Source UE to initiate a unicast session. In 3GPP Rel-<NUM>, the Source and Target UEs uses different Layer-<NUM> IDs for each V2X service. Therefore, it is not possible in 3GPP Rel-<NUM> to identify from the Layer-<NUM> IDs if the message is sent to the same Target UE.

If the Source UE knows a unicast message is sent to the same Target UE, then the Source UE may: <NUM>) Send the unicast session over the same RRC connection and <NUM>) Send the V2X message over the same unicast link. The present disclosure describes solutions on how UEs operating multiple V2X services can discover that a V2X message over unicast direct communication is sent to the Target UE.

<FIG> depicts a wireless communication system <NUM> for conveying unicast sessions over a direct communication link via V2X communication signals <NUM>. The wireless communication system <NUM> includes at least one remote unit <NUM>, a radio access network ("RAN") <NUM>, and a mobile core network <NUM>. The RAN <NUM> and the mobile core network <NUM> form a mobile communication network. The RAN <NUM> may be composed of a base unit <NUM> with which the remote unit <NUM> communicates using wireless communication links <NUM>. Even though a specific number of remote units <NUM>, base units <NUM>, wireless communication links <NUM>, RANs <NUM>, and mobile core networks <NUM> are depicted in <FIG>, one of skill in the art will recognize that any number of remote units <NUM>, base units <NUM>, wireless communication links <NUM>, RANs <NUM>, and mobile core networks <NUM> may be included in the wireless communication system <NUM>.

In one implementation, the RAN <NUM> is compliant with the <NUM> system specified in the 3GPP specifications. In another implementation, the RAN <NUM> is compliant with the LTE system specified in the 3GPP specifications. More generally, however, the wireless communication system <NUM> may implement some other open or proprietary communication network, for example WiMAX, among other networks.

The remote units <NUM> may include computing devices, such as desktop computers, laptop computers, personal digital assistants ("PDAs"), tablet computers, smart phones, smart televisions (e.g., televisions connected to the Internet), smart appliances (e.g., appliances connected to the Internet), set-top boxes, game consoles, security systems (including security cameras), vehicle on-board computers, network devices (e.g., routers, switches, modems), or the like. In some examples, the remote units <NUM> include wearable devices, such as smart watches, fitness bands, optical head-mounted displays, or the like. Moreover, the remote units <NUM> may be referred to as the UEs, subscriber units, mobiles, mobile stations, users, terminals, mobile terminals, fixed terminals, subscriber stations, user terminals, wireless transmit/receive unit ("WTRU"), a device, or by other terminology used in the art.

The remote units <NUM> may communicate directly with one or more of the base units <NUM> in the RAN <NUM> via uplink ("UL") and downlink ("DL") communication signals. Furthermore, the UL and DL communication signals may be carried over the wireless communication links <NUM>. Here, the RAN <NUM> is an intermediate network that provides the remote units <NUM> with access to the mobile core network <NUM>.

The remote units <NUM> may communicate with an application server <NUM> via a network connection with the mobile core network <NUM>. For example, an application <NUM> (e.g., web browser, media client, telephone/VoIP application) in a remote unit <NUM> may trigger the remote unit <NUM> to establish a PDU session (or other data connection) with the mobile core network <NUM> via the RAN <NUM>. The mobile core network <NUM> then relays traffic between the remote unit <NUM> and the application server <NUM> in the packet data network <NUM> using the PDU session. Note that the remote unit <NUM> may establish one or more PDU sessions (or other data connections) with the mobile core network <NUM>. As such, the remote unit <NUM> may concurrently have at least one PDU session for communicating with the packet data network <NUM> and at least one PDU session for communicating with another data network (not shown).

The base units <NUM> may be distributed over a geographic region. The base unit <NUM> may also be referred to as an access terminal, an access point, a base, a base station, a Node-B, an eNB, a gNB, a Home Node-B, a relay node, or by any other terminology used in the art. The base units <NUM> are generally part of a radio access network ("RAN"), such as the RAN <NUM>, that may include one or more controllers communicably coupled to one or more corresponding base units <NUM>. These and other elements of radio access network are not illustrated but are well known generally by those having ordinary skill in the art. The base units <NUM> connect to the mobile core network <NUM> via the RAN <NUM>.

The base units <NUM> may serve a number of remote units <NUM> within a serving area, for example, a cell or a cell sector, via a wireless communication link <NUM>. The base units <NUM> may communicate directly with one or more of the remote units <NUM> via communication signals. Generally, the base units <NUM> transmit DL communication signals to serve the remote units <NUM> in the time, frequency, and/or spatial domain. Furthermore, the DL communication signals may be carried over the wireless communication links <NUM>. The wireless communication links <NUM> may be any suitable carrier in licensed or unlicensed radio spectrum. The wireless communication links <NUM> facilitate communication between one or more of the remote units <NUM> and/or one or more of the base units <NUM>.

In one example, the mobile core network <NUM> is a <NUM> core ("5GC") or the evolved packet core ("EPC"), which may be coupled to a packet data network <NUM>, like the Internet and private data networks, among other data networks. A remote unit <NUM> may have a subscription or other account with the mobile core network <NUM>. Each mobile core network <NUM> belongs to a single public land mobile network ("PLMN").

The mobile core network <NUM> includes several network functions ("NFs"). As depicted, the mobile core network <NUM> includes multiple user plane functions ("UPFs") <NUM>. The mobile core network <NUM> also includes multiple control plane functions including, but not limited to, an Access and Mobility Management Function ("AMF") <NUM> that serves the RAN <NUM>, a Session Management Function ("SMF") <NUM>, a Policy Control Function ("PCF") <NUM>, and a Unified Data Management function ("UDM") <NUM>. The mobile core network <NUM> may also include an Authentication Server Function ("AUSF"), a Network Repository Function ("NRF") (used by the various NFs to discover and communicate with each other over APIs), or other NFs defined for the 5GC.

In various examples, the mobile core network <NUM> supports different types of mobile data connections and different types of network slices, wherein each mobile data connection utilizes a specific network slice. Here, a "network slice" refers to a portion of the mobile core network <NUM> optimized for a certain traffic type or communication service. A network instance may be identified by a S-NSSAI, while a set of network slices for which the remote unit <NUM> is authorized to use is identified by NSSAI. The various network slices may include separate instances of network functions, such as the SMF <NUM> and UPF <NUM>. The different network slices may share some common network functions, such as the AMF <NUM>. The different network slices are not shown in <FIG> for ease of illustration, but their support is assumed.

Although specific numbers and types of network functions are depicted in <FIG>, one of skill in the art will recognize that any number and type of network functions may be included in the mobile core network <NUM>. Moreover, where the mobile core network <NUM> is an EPC, the depicted network functions may be replaced with appropriate EPC entities, such as an MME, S-GW, P-GW, HSS, and the like. The mobile core network <NUM> may include a AAA server.

While <FIG> depicts components of a <NUM> RAN and a <NUM> core network, the described sidelink HARQ operation in NR V2X communication may apply to other types of communication networks and RATs, including IEEE <NUM> variants, GSM, GPRS, UMTS, LTE variants, CDMA <NUM>, Bluetooth, ZigBee, Sigfoxx, and the like. For example, in an LTE variant involving an EPC, the AMF <NUM> may be mapped to an MME, the SMF mapped to a control plane portion of a PGW and/or to an MME, the UPF map to an SGW and a user plane portion of the PGW, the UDM/UDR maps to an HSS, etc..

The remote units <NUM> may communicate directly with each other (e.g., device-to-device communication) using V2X communication signals <NUM>. Here, V2X transmissions may occur on V2X resources. As discussed above, a remote unit <NUM> may be provided with different V2X communication resources for different V2X modes. Mode-<NUM> corresponds to a NR network-scheduled V2X communication mode. Mode-<NUM> corresponds to a NR UE-scheduled V2X communication mode. Mode-<NUM> corresponds to an LTE network-scheduled V2X communication mode. Mode-<NUM> corresponds to an LTE UE-scheduled V2X communication mode.

Unicast mode of communication is currently supported only over NR based PC5 reference point. When Application layer (in a first UE, "UE-A") initiates a V2X service which requires PC5 unicast communication, the UE-A establishes a PC5 unicast link with the corresponding UE ("UE-B").

After successful PC5 unicast link establishment, UE-A and UE-B use a same pair of Layer-<NUM> IDs for subsequent PC5-S signaling message exchange and V2X service data transmission, e.g., as specified in 3GPP TS <NUM>, clause <NUM>. The V2X layer of the transmitting UE indicates to the AS layer whether the message is for PC5-S signaling message (e.g., Direct Communication Accept, Link Layer Identifier Update Request/Response, Disconnect Request/Response) or service data transmission when it sends message over the established PC5 link. The V2X layer of receiving UE handles message if it is PC5-S signaling message while the V2X layer of receiving UE forwards the message to the upper layer if it is application data message.

Note that unicast mode supports per-flow QoS model. During the unicast link establishment, each UE self-assigns a PC5 Link Identifier and associates the PC5 Link Identifier with the Unicast Link Profile for the established unicast link. The PC5 Link Identifier is a unique value within the UE. The Unicast Link Profile identified by PC5 Link Identifier includes the application layer identifier and Layer-<NUM> ID of UE A, the application layer identifier and Layer-<NUM> ID of UE B and a set of PC5 QoS Flow Identifier(s) ("PFI(s)"). Each PFI is associated with QoS parameters (e.g., PQI and optionally Range).

The PC5 Link Identifier and PFI(s) are unchanged values for the established unicast link regardless of the change of application layer identifier and Layer-<NUM> ID. A UE uses PFI to indicate the PC5 QoS flow to AS layer, therefore AS layer identifies the corresponding PC5 QoS flow even if the source and/or destination Layer-<NUM> IDs are changed, e.g., due to privacy support. The UE uses PC5 Link Identifier to indicate the PC5 unicast link to V2X Application layer, therefore V2X Application layer identifies the corresponding PC5 unicast link even if there are more than one unicast link associated with one service type (e.g., the UE establishes multiple unicast links with multiple UEs for a same service type).

In some examples, a remote unit <NUM> re-uses an existing unicast session for multiple V2X services between the same pair of UEs, as described below in further detail with reference to <FIG>. In some examples, a remote unit <NUM> re-uses the same RRC connection to convey multiple unicast sessions over the same pair of UEs, as described below in further detail with reference to <FIG>.

In the following descriptions, the term eNB/ gNB is used for the base station but it is replaceable by any other radio access node, e.g., BS, eNB, gNB, AP, NR, etc. Further the operations are described mainly in the context of <NUM> NR. However, the proposed solutions/methods are also equally applicable to other mobile communication systems supporting serving cells/carriers being configured for Sidelink Communication over PC5 interface.

<FIG> depicts a procedure <NUM> for unicast link establishment over the PC5 reference point. Note that the PC5 reference point may be referred to herein as the "PC5 interface. " The procedure <NUM> involves a first UE ("UE-A") <NUM> and a second UE ("UE-B") <NUM> that communicate over the PC5 reference point. Each UE is one example of the remote unit <NUM> described above. Each UE includes an application layer <NUM> with one or more Applications, a V2X layer <NUM> and an access-stratum ("AS") layer <NUM>.

Unicast mode of communication is currently supported only over NR-based PC5 reference point. When Application layer <NUM> in the UE-A <NUM> initiates a V2X service which requires PC5 unicast communication, the source UE-A <NUM> establishes a PC5 unicast link with the corresponding target UE-B <NUM>.

After successful PC5 unicast link establishment, UE-A <NUM> and UE-B <NUM> use a same pair of Layer-<NUM> IDs for subsequent PC5-S signaling message exchange and V2X service data transmission, e.g., as specified in 3GPP TS <NUM>, clause <NUM>. The V2X layer <NUM> of the source/transmitting UE <NUM> indicates to the AS layer <NUM> whether the message is for PC5-S signaling message (e.g., Direct Communication Accept, Link Layer Identifier Update Request/Response, Disconnect Request/Response) or service data transmission when it sends message over the established PC5 link. The V2X layer <NUM> of the target/receiving UE-B <NUM> handles message if it is PC5-S signaling message while the V2X layer <NUM> of the UE-B <NUM> forwards the message to the upper layer (i.e., application layer <NUM>) if it is an application data message.

Note that unicast mode supports per-flow QoS model. During the unicast link establishment, each UE <NUM>-<NUM> self-assigns a PC5 Link Identifier and associates the PC5 Link Identifier with the Unicast Link Profile for the established unicast link. The PC5 Link Identifier is a unique value within the UE. The Unicast Link Profile identified by PC5 Link Identifier includes the application layer identifier and Layer-<NUM> ID of UE-A <NUM>, the application layer identifier and Layer-<NUM> ID of UE B and a set of PC5 QoS Flow Identifier(s) ("PFI(s)"). Each PFI is associated with QoS parameters (e.g., PQI and optionally Range).

Per 3GPP Rel-<NUM>, the PC5 Link Identifier and PFI(s) are unchanged values for the established unicast link regardless of the change of application layer identifier and Layer-<NUM> ID. A UE <NUM>-<NUM> uses PFI to indicate the PC5 QoS flow to the AS layer <NUM>, therefore the AS layer <NUM> identifies the corresponding PC5 QoS flow even if the source and/or destination Layer-<NUM> IDs are changed, e.g., due to privacy support. The UE <NUM>, <NUM> uses the PC5 Link Identifier to indicate the PC5 unicast link to the V2X Application layer <NUM>, therefore the V2X Application layer <NUM> identifies the corresponding PC5 unicast link even if there are more than one unicast link associated with one service type (e.g., a UE may establish multiple unicast links with multiple UEs for a same service type).

In order to allow a UE operating multiple V2X services (e.g., UE-A <NUM>, as depicted) to discover whether a V2X message over unicast direct communication is sent to the same target UE (e.g., UE-B <NUM>), the source UE <NUM> may re-use an existing unicast session for multiple V2X services between the same pair of UEs, as described below in further detail with reference to <FIG> and <FIG>. In certain examples, the source UE <NUM> may re-use the same RRC connection to convey multiple unicast sessions over the same pair of UEs, as described below in further detail with reference to <FIG>. In some examples, the source UE-A <NUM> may create a unicast link identifier ("ULI"), where the UE-A <NUM> and UE-B <NUM> use the unicast link identifier to discover whether a V2X message over unicast direct communication is sent to the same target UE. Here, the PC5-RNTI may be created based on the unicast link identifier. In certain examples, the unicast link identifier may be a combination of source Application-Layer ID and target Application-Layer ID.

<FIG> depicts a method <NUM> for determining whether an active unicast session can be re-used. In various examples, the method <NUM> is performed by a UE, such as the remote unit <NUM> described above, the UE-A <NUM> described above, the source UE <NUM> described below, and/or the user equipment apparatus <NUM>, described below. In some examples, the method <NUM> is performed by a processor, such as a microcontroller, a microprocessor, a central processing unit ("CPU"), a graphics processing unit ("GPU"), an auxiliary processing unit, a field programmable gate array ("FPGA"), or the like.

The method <NUM> begins and receives <NUM>, from an internal application (e.g., a V2X application or OS running on the source UE), a first request to establish a unicast session over a direct communication link to a target UE (i.e., a second UE). Here, the first request indicates a source application-layer identifier of the source UE and a target application-layer identifier of the target UE. Further details of the first request are described below.

The method <NUM> includes determining <NUM> whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists. Further details of determining whether an active unicast session exists are described below.

The method <NUM> includes re-using <NUM> an already-existing active unicast session between the source UE and the target UE in response to determining that an active unicast session between the source application-layer identifier and the target application-layer identifier already exists. Further details of re-using an existing unicast session are described below.

Otherwise, the method <NUM> includes establishing <NUM> a new unicast session between the source UE and target UE in response to determining that an active unicast session between the source application-layer identifier and the target application-layer identifier does not exist. Further details of establishing a new unicast session are described below. The method <NUM> ends.

Figured 4A-4B depict a procedure <NUM> for determining whether an active unicast session can be re-used. The procedure <NUM> shows a source UE <NUM> re-using an existing unicast session for multiple V2X services between the same pair of UEs (i.e., source UE <NUM> and target UE <NUM>). Here, the source UE <NUM> may be one example of the UE-A <NUM>, while target UE <NUM> may be one example of the UE-B <NUM>. <FIG> represent one example of a second solution for conveying unicast sessions over a direct communication link. The procedure <NUM> may extend the method <NUM> described above. In various examples, the source UE <NUM> may re-use an existing unicast session between the same pair of UEs when a V2X application requests to send a message over a unicast session of a different V2X service (e.g., different PSID).

In some examples, the source UE <NUM> initiating a new request for unicast session wherein the request includes existing active Unicast Link Identifiers as metadata. Here, the target UE <NUM> examines the Unicast Link Identifier(s) included in the request and determines whether an active unicast session already exists between the source UE <NUM> and the target UE <NUM>. If the target UE <NUM> identifies a match, the target UE <NUM> includes in the unicast link session response the existing Unicast Link Identifiers ("ULIs"). Note that the matched ULIs may be the matched source and target application layer IDs. The source UE <NUM> examines the response and determines whether an existing unicast link session can be re-used.

At <FIG>, the procedure <NUM> begins in step <NUM> as an application (e.g., V2X application) in the source UE <NUM> requests to establish a unicast session for a V2X service (see block <NUM>). The application includes in the request towards the V2X layer <NUM> of the source UE <NUM> the Application layer identifier of the source and target UEs (including the target UE <NUM>).

In step <NUM>, the source UE <NUM> retrieves the default destination Layer-<NUM> ID for the V2X service (PSID) for establishing a unicast session (existing procedure) (see block <NUM>).

In step <NUM>, the source UE <NUM> self-assigns a new ULI (as the source UE <NUM> does not know at this time whether an existing unicast link can be reused or whether a new unicast link is to be established to the same target UE), identifies all active unicast links, and includes them in a new unicast link request as metadata (see block <NUM>). In some examples, the metadata include target and source application layer identifiers.

In step <NUM>, the source UE <NUM> initiates a request for unicast session by broadcasting a Direct Communication Request (see messaging <NUM>). Here, the request includes: source Application-Layer identifier, target Application-Layer identifier, a source Layer-<NUM> identifier (of source UE <NUM>), a "default" destination Layer-<NUM> ID (i.e., from step <NUM>), the generated ULI and - as metadata - a set of unicast link identifiers identifying the active unicast session(s).

In step <NUM>, the target UE <NUM> receives the unicast request and identifies from the application layer identifiers that it is the target of the Direct Communication Request (see block <NUM>).

In step <NUM>, the target UE <NUM> identifies from the metadata that at least one active unicast session already exists with the source UE. The target UE <NUM> includes all matched ULIs of the existing active unicast session(s) in the response (see block <NUM>).

Continuing on <FIG>, at step <NUM> the target UE <NUM> responds to the unicast link request by sending a Direct Communication Accept message (see messaging <NUM>). Here, the Direct Communication Accept message includes: the Layer-<NUM> identifier for the target UE <NUM> as the message source layer-<NUM> ID, the source UE <NUM>'s layer-<NUM> ID as message target layer-<NUM> ID, the generated ULI (of the source UE <NUM>) and - as metadata - the matched ULI(s).

In step <NUM>, the source UE <NUM> determines from the matched ULI(s) of the metadata that the new unicast session can be conveyed over an existing unicast link (see block <NUM>).

In step <NUM>, the source UE <NUM> constructs a Unicast Link Profile that include the Source Application-Layer ID, the Target Application-Layer ID, the layer-<NUM> identifiers of the source UE <NUM> and target UE <NUM>, the ULI and PSID. The source UE <NUM> associates the unicast link to the Unicast Link Identifier (see block <NUM>).

In step <NUM>, the source UE <NUM> indicates to the target UE <NUM> that the unicast session is sent over an existing link (see messaging <NUM>). As depicted, this indication may be a Direct Communication Request that includes the ULI of the matched, existing unicast link.

In step <NUM>, the target UE <NUM> constructs a unicast link profile and associate it to the existing ULI (see block <NUM>). Here, the Unicast Link Profile may include the Source Application-Layer ID, the Target Application-Layer ID, the Layer-<NUM> identifiers for the source UE <NUM> and target UE <NUM>, ULI and PSID.

In steps 12a and 12b, both applications associate the unicast link to the Unicast link identifier (see blocks <NUM> and <NUM>).

In one example when a V2X application requests to initiate unicast session to convey a message of a specific V2X service (e.g., specific PSID), the source UE initiates a request for unicast communication over PC5, the UE includes in the request for a unicast session a PC5 link identifier. The PC5 link identifier may be self-generated by the transmitting UE and is signaled to the Target UE in the DCR message. When the target UE receive the request for unicast session over PC5, the UE identify if they are the target UEs by examining the application layer identifier included in the request.

If the UE identifies it is the target UE the UE self-assigns a PC5 link identifier and map it to the PC5 link identifier of the source UE. The target UE constructs a Unicast Link Profile including the source and target PC5 link identifiers, layer-<NUM> addresses and application layer identifiers and maps the Unicast link profile to the source and target PC5 link identifiers. The target UE then responds to the source UE by including in the unicast link response over PC5 the source and target PC5 link identifiers. The source UE also creates a Unicast Link Profile that contain the source and target PC5 link identifiers, layer-<NUM> addresses and application layer identifiers. The target UE maps the source and target PC5 link identifier to the unicast link profile. In one example the source and target PC5 link identifier may identify the Unicast Link Identifier. Both source and target UEs also advertise such unicast link identifier to the application layer.

<FIG> depicts a procedure <NUM> for determining whether an active unicast session can be re-used. The procedure <NUM> shows a source UE <NUM> re-using the same RRC connection to convey multiple unicast sessions of multiple V2X services to a target UE <NUM>. <FIG> represent one example of a third solution for conveying multiple unicast sessions over a direct communication link. The procedure <NUM> may extend the method <NUM> described above.

At <FIG>, the procedure <NUM> begins in step <NUM> as an application (e.g., V2X application) in the source UE <NUM> requests to establish a unicast session for a V2X service (see block <NUM>). Included in the request towards the V2X layer <NUM> of the UE are application layer identifiers of the source and target UEs and a PSID.

In step <NUM>, the source UE <NUM> retrieves the default destination layer-<NUM> ID for the V2X service (PSID) for establishing a unicast session (see block <NUM>).

In step <NUM>, the source UE <NUM> may self-assign a new ULI (as the source UE <NUM> may be unaware whether the unicast link is to be established to the same target UE <NUM>). Additionally, the source UE <NUM> may identify all active unicast links and include an identifier for each active unicast link as metadata in a new unicast link request (see block <NUM>).

In step <NUM>, the source UE <NUM> initiates a request for unicast session by broadcasting a Direct Communication Request (see messaging <NUM>). Here, the request includes: source and target Application-Layer identifiers, a source Layer-<NUM> identifier, a "default" destination Layer-<NUM> ID (i.e., from step <NUM>), the generated ULI and - as metadata - a set of unicast link identifiers identifying the active unicast session(s).

In step <NUM>, the target UE <NUM> constructs a Unicast Link Profile that include the Source Application-Layer ID, the Target Application-Layer ID, the Layer-<NUM> identifier for the source UE <NUM>, the "actual" Layer-<NUM> identifier for the target UE <NUM>, ULI and PSID. The target UE <NUM> associates the unicast link ULI provided by the source UE <NUM> (see block <NUM>).

Continuing at <FIG>, at step <NUM> the target UE <NUM> also identifies from the Direct Communication Request whether the target UE <NUM> has existing active unicast session(s) with the source UE <NUM> and includes all matched ULIs in the response (see block <NUM>).

In step <NUM>, the target UE <NUM> responds to the unicast link request by sending a Direct Communication Accept message (see messaging <NUM>). Here, the Direct Communication Accept message includes: the "actual" Layer-<NUM> identifier for the target UE <NUM> as the message source layer-<NUM> ID, the source UE <NUM>'s layer-<NUM> ID as message target layer-<NUM> ID, the generated ULI (of the source UE <NUM>) and - as metadata - the matched ULI(s).

In step <NUM>, the source UE <NUM> also constructs a Unicast Link Profile that include the Source Application-Layer ID, the Target Application-Layer ID, the layer-<NUM> identifiers of the source UE <NUM> and target UE <NUM>, the ULI and PSID. The source UE <NUM> associates the unicast link to the Unicast Link Identifier (see block <NUM>).

In steps 10a and 10b, both applications associate the unicast link to the Unicast link identifier (see blocks <NUM> and <NUM>).

In steps 11a and 11b, the source UE <NUM> and target UE <NUM> determine from the matched ULIs that the matched unicast session(s) can be provided over the same RRC connection between the two UEs (see blocks <NUM> and <NUM>).

In step <NUM>, the AS layer <NUM> sends data from the unicast sessions that have matched ULIs over an RRC connection using the same PC5 RNTI. This is applicable for the source-UE-to-target-UE direction as well as the target-UE-to-source-UE direction.

In one example the V2X layer <NUM> associates the unicast sessions of matched ULIs to one link profile (i.e., link is related to the same pair of source and target UE). The V2X layer <NUM> informs the AS layer <NUM> of the unicast sessions that are associated to the same target UE <NUM>. The AS layer <NUM> sends data from the unicast sessions that have matched ULIs over an RRC connection using the same PC5 RNTI. This is applicable for the source-UE-to-target-UE direction as well as the target-UE-to-source-UE direction.

According to a fourth solution for conveying unicast sessions over a direct communication link, a source UE may create a random number of bits - e.g., <NUM> bits - (referred to as 'ULI-x') and send the ULI-x to the target UE along with metadata. Recall that both the procedure <NUM> and the procedure <NUM> include exchanging metadata, e.g., in the direct communication request and direct communication response. According to this fourth solution, the metadata includes all the ULIs (e.g., ULI-a, ULI-b, etc.) and the target verifies if it identifies one of the received ULIs.

If yes, then the same ULI (e.g., ULI-a) is used for the second session as well. If not, then the identifier 'ULI-x' is adopted by the target and indicates acceptance back to the source. Both source and target UEs update their metadata accordingly. In one example, a UE updates its metadata by adding the new session ID related Layer-<NUM> source and destination IDs to the exiting profile for ULI-a. In another example, a UE updates its metadata by creating a new context with ULI-x for the newly created session and adding Layer-<NUM> source and destination IDs. Where an already-existing unicast session cannot be re-used, the ULI-x is passed on to Access Stratum - and Access Stratum creates a PC5-RNTI based on this. This may be done by either adopting the entire ULI (ULI-x in current example), adopting part of it (say <NUM> MSB bits) and appending <NUM> randomly generated bits or even by only generating the PC5-RNTI with <NUM> randomly generated bits.

In the above examples, <NUM> bits are just taken as an example but any other bit length for the concerned IDs is also possible. The length of the identities must be sufficient to minimize the probability of any two UEs (from a large set of UEs in a dense traffic situation) generating the same random identity. If collision happens (e.g., more than one transmitter UE concurrently use the same randomly generated identity towards the same destination UE), then the Upper layers of any of the involved UEs (the transmitter UE(s) and/ or receiver UE) may detect that the received V2X message is not intended for them, e.g., based on Station ID, temporary UE identity, application ID or something similar.

In this case, the UE that detects the collision may send a Unicast PC5-S and/ or PC5-RRC message including the colliding identity in question (ULI and/ or PC5-RNTI) indicating the recipient to discard the identity (or identities) in question and start afresh by generating a new random number. As one optimization, only the sender of the previous message where collision was detected, is informed of the collision and this sender is then responsible for starting afresh by generating a new random number towards the (default) destination ID for the corresponding PC5-S link.

The PC5-RNTI is carried in each of the PC5-RRC message and the target responds back with PC5-RRC message including the same PC5-RNTI. Part of (or entire) PC5-RNTI can also be used at the physical layer (e.g., in SCI) for enabling filtering at the target UEs.

Note that the PC5 RNTI (RRC connection on PC5) can be explicitly released by either of the UEs when all V2X applications terminate and upper layer identities (Application identities, L2-identities, PLIs and/ or ULIs) need to be released or, implicitly upon expiry of a timer used to monitor inactivity.

In any of the above solutions, instead of transmitting the ULI of the active unicast sessions as metadata in cleartext, the source UE transmits a hashed version of such identifiers. Here, both source and target UEs must use the same hashing function.

In any of the above solutions, the source or target UE determines if the existing unicast session can be re-used if both V2X services operate on the same mode of operation (e.g., both in-coverage or both out of-coverage).

In any of the above solutions, if one unicast session is lost, then both UEs may recover the unicast session by advertising the unicast link identifier of all active unicast sessions. The UEs transmit the unicast link identifiers based on a pre-configured timer. If the timer expires, then the UEs delete the unicast link identifier and the associated Unicast Link Profile.

In any of the above solutions, instead of the source UE transmitting the active ULIs as metadata (e.g., step <NUM> in procedures <NUM>, <NUM>), the target UE may include in the DCR response all active ULIs (the advantage is that such approach does not require to transmit all active ULIs in broadcast). Here, the source UE determines from the active ULI if there are any existing active ULIs and informs the AS layer that the same RRC connection can be used and/or informs the target UE that the same unicast session can be used.

In any of the above solutions, the ULI identifier corresponds to the source and target Layer-<NUM> IDs of the source and target UE.

According to a fifth solution for conveying unicast sessions over a direct communication link, the transmitter and received UEs solicit and provide PC5 HARQ feedback for the PSSCH transmissions made by the transmitter UE (i.e., source UE) to one or more receiver UE(s). In various examples, the transmitter UE gets to know the total number of member UEs in the group based on Upper layer information, e.g., the upper layer(s) provide the total number of UEs in the group to the lower layer(s). Here, this knowledge at the Physical layer is accurate to the extent required for physical layer functioning at any given point in time; even if the group members are updated, the Physical layer is informed in a reasonably quick time frame.

For SL unicast and groupcast, HARQ feedback and HARQ combining in the physical layer may be supported. In various examples, HARQ-ACK feedback for a PSSCH is carried in SFCI format(s) via PSFCH in resource allocation Modes <NUM> and <NUM>.

When SL HARQ feedback is enabled for unicast, in the case of non-CBG operation the receiver UE generates HARQ-ACK if it successfully decodes the corresponding TB. It generates HARQ-NACK if it does not successfully decode the corresponding TB after decoding the associated PSCCH targeted to the receiver UE.

When SL HARQ feedback is enabled for groupcast, it is supported to use TX-RX distance and/or RSRP in deciding whether to send HARQ feedback. In the case of non-CBG operation, two options are supported:.

According to SL HARQ feedback Option <NUM>, the Receiver UE (i.e., target UE) transmits HARQ-NACK on PSFCH if it fails to decode the corresponding TB after decoding the associated PSCCH and transmits no signal on PSFCH otherwise (i.e., the Rx UE does not transmit HARQ-ACK on PSFCH if it successfully decodes the corresponding TB).

According to SL HARQ feedback Option <NUM>, the Receiver UE ("Rx UE") transmits HARQ-ACK on PSFCH if it successfully decodes the corresponding TB. Additionally, the Rx UE transmits HARQ-NACK on PSFCH if it does not successfully decode the corresponding TB after decoding the associated PSCCH which targets the receiver UE.

Based on the knowledge of total number of member UEs in the group, the Physical layer of a transmitter UE may determine the amount of feedback resources required. The determination of required feedback resources will be according to the Physical layer structure still to be finalized in 3GPP. The transmitter UE, having made this determination, will compare the number of group member UEs, amount of feedback resources available and the reliability required for a particular V2X message. The reliability is directly derivable from the VQI/ priority indicated by Upper layer for the corresponding Packet for transmission. As an example, if the reliability required is <NUM> '<NUM>' e.g., as for "Emergency trajectory alignment between UEs supporting V2X application" and "Sensor information sharing between UEs supporting V2X application scenarios" then only feedback Option <NUM> must be used. For lesser-required reliability, option <NUM> alone can be used if the total number of member UEs in the group is higher compared with available feedback resources; or, a mix of Option <NUM> and Option <NUM> can be used.

The actual utilized resources for HARQ feedback can be less compared to what has been determined by the transmitter, as indicated above. This is since only the receiver UE(s) that are inside the MCR (Minimum Communication Range) are required to provide the HARQ feedback. This may at first sound like a resource wastage but indeed avoids much complexity that would arise if the transmitter had to beforehand know the real-time distance of each of the receiver UE.

A detailed (transmitter) UE behavior is revealed for selecting between Option <NUM>, Option <NUM> (or a mix) considering the following three aspects: <NUM>) total number of member UEs in the group, <NUM>) amount of available HARQ feedback resources, and <NUM>) reliability required for corresponding V2X PSSCH packet transmission.

A different threshold for each of those items may lead to a combination that uses either option or uses a certain mix of these.

As a first example, if Reliability > Threshold_reliability, then use Option <NUM> for as many UEs as possible. In case of shortage of feedback resources use Option <NUM> for remaining UEs, closer to the transmitter - based on distance_threshold. The distance_threshold is calculated as a ratio of remaining UEs to the total receiver UEs in the group multiplied by MCR (Minimum Communication Range).

As a second example, if Reliability < Threshold_reliability and number of total receiver UEs in the group is more than threshold_max_option2, then use Option <NUM>.

In Mode <NUM> V2X communication (i.e., network-scheduled NR-based V2X), the transmitter UE needs to ask for the feedback resources from the gNB in addition to (re)transmission resources. For this reason, the transmitter UE needs to inform the gNB on the number of member UEs in the group destination where the transmitter would like to send intended V2X message(s). This information along with the size of the V2X message, periodicity etc. needs to be informed to the gNB for each of the group destination where the transmitter intends to make transmissions. This information can be carried in messages similar to Sidelink UE information and/or NR UE Assistance information as defined in LTE RRC (<NUM>) specification. These messages carry the number of member UEs in a group, corresponding size of the V2X message, periodicity, priority/ VQI etc. for each group where a transmitter is interested in transmitting data to the gNB.

Upon receiving the UE request, the gNB provides the transmission resources and PC5 HARQ feedback time-frequency and code resources accordingly in Mode <NUM> V2X communication. As a signaling optimization, the feedback resources can be linked with PSSCH transmission resources using certain time-frequency offset. All the codes can be used by the transmitter UE, or the same can be explicitly signaled by the gNB to the transmitter.

The amount of PC5 feedback resources for retransmission can be same as that for PC5 feedback resources for transmission, obtained in a similar way as for transmission, as described above. Therefore, in Mode <NUM> V2X communication, the time-frequency PC5 HARQ feedback resources for (re)-transmission are obtained either explicitly from gNB or using an offset with respect to the PSSCH resources. For PC5 HARQ feedback transmission, either all the codes can be used by the transmitter UE, or the same can be explicitly signaled by the gNB to the transmitter.

The transmitter UE needs to allocate the feedback resources to the group member UEs. This can be done using PC5 RRC where the transmitter semi statically configures the UEs with either/ both Option <NUM>, Option <NUM> resources. Actual usage of option (either/ both) and the corresponding condition (e.g., Tx-Rx distance less than certain Threshold_A use Option <NUM>, rest Option B) are controlled and indicated in SCI and depends among others on reliability/ priority of the transmission.

<FIG> depicts a user equipment apparatus <NUM> that may be used for determining whether an active unicast session can be re-used. The user equipment apparatus <NUM> is used to implement one or more of the solutions described above. The user equipment apparatus <NUM> may be one example of the remote unit <NUM>, the UE-A <NUM>, and/or the source UE <NUM>, described above. Furthermore, the user equipment apparatus <NUM> may include a processor <NUM>, a memory <NUM>, an input device <NUM>, an output device <NUM>, and a transceiver <NUM>. In some examples, the input device <NUM> and the output device <NUM> are combined into a single device, such as a touchscreen. In certain examples, the user equipment apparatus <NUM> may not include any input device <NUM> and/or output device <NUM>. In various examples, the user equipment apparatus <NUM> may include one or more of: the processor <NUM>, the memory <NUM>, and the transceiver <NUM>, and may not include the input device <NUM> and/or the output device <NUM>.

The processor <NUM> may include any known controller capable of executing computer-readable instructions and/or capable of performing logical operations. For example, the processor <NUM> may be a microcontroller, a microprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, or similar programmable controller. The processor <NUM> executes instructions stored in the memory <NUM> to perform the methods and routines described herein.

The processor <NUM> controls the user equipment apparatus <NUM> to implement the above described UE behaviors. The processor <NUM> receives, e.g., from an internal application or operating system, a first request to establish a unicast session over a direct communication link to a first UE (i.e., target UE). Here, the first request indicates a source application-layer identifier of the apparatus and a target application-layer identifier of the target UE. The processor <NUM> determines determining whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists.

If an active unicast session between the source application-layer identifier and the target application-layer identifier already exists, then the processor <NUM> re-uses the already-existing active unicast session between the apparatus <NUM> and the target UE. Otherwise, if an active unicast session between the source application-layer identifier and the target application-layer identifier does not already exist, then the processor <NUM> establishes a new unicast session between the apparatus <NUM> and the target UE.

In some examples, the first request is for a first V2X service and the already-existing active unicast session is associated with a second V2X service different than the first, wherein the processor <NUM> modifies a Unicast Link Profile of the already-existing active unicast session to add the first V2X service. In certain examples, the Unicast Link Profile is associated with an RRC connection, wherein re-using the already-existing active unicast session further comprises re-using an existing RRC connection between the apparatus <NUM> and the target UE.

In some examples, the processor <NUM> generates a link identifier for the requested unicast session. In such examples, the link identifier maps the source and target application-layer identifiers to the unicast session.

In some examples, the processor <NUM> transmits a second request to the target UE to establish a unicast session and receives a response from the target UE, the response containing a set of link identifiers. In such examples, determining whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists already exists is based on the response from the target UE. In certain examples, the response from the includes as metadata all existing active unicast sessions of the target UE.

In some examples, the processor <NUM> maintains a second set of link identifiers of the apparatus, each link identifier associated with a pair of source and target application-layer identifiers, wherein determining from the response whether an active unicast session with the target UE already exists comprises determining whether a matching link identifier exists among the set of link identifiers contained in the response and the second set of link identifiers.

In certain examples, the second request includes as metadata the second set of link identifiers. In certain examples, the response includes an indication of matching link identifiers. In certain examples, re-using the already-existing active unicast session comprises selecting a matching link identifier and constructing a Unicast Link Profile that maps the unicast session requested in the first request to the already-existing active unicast session.

The memory <NUM> is a computer readable storage medium. In some examples, the memory <NUM> includes volatile computer storage media. In some examples, the memory <NUM> includes non-volatile computer storage media. In some examples, the memory <NUM> includes both volatile and non-volatile computer storage media.

In some examples, the memory <NUM> stores data related to SL HARQ operation. For example, the memory <NUM> may store V2X communication resources, ULI, and the like. In certain examples, the memory <NUM> also stores program code and related data, such as an operating system or other controller algorithms operating on the remote unit <NUM>.

The input device <NUM> may include any known computer input device including a touch panel, a button, a keyboard, a stylus, a microphone, or the like. The input device <NUM> may be integrated with the output device <NUM>, for example, as a touchscreen or similar touch-sensitive display. In some examples, the input device <NUM> includes a touchscreen such that text may be input using a virtual keyboard displayed on the touchscreen and/or by handwriting on the touchscreen. In some examples, the input device <NUM> includes two or more different devices, such as a keyboard and a touch panel.

The output device <NUM>, in one example, is designed to output visual, audible, and/or haptic signals. In some examples, the output device <NUM> includes an electronically controllable display or display device capable of outputting visual data to a user.

In certain examples, the output device <NUM> includes one or more speakers for producing sound. In some examples, the output device <NUM> includes one or more haptic devices for producing vibrations, motion, or other haptic feedback. In some examples, all or portions of the output device <NUM> may be integrated with the input device <NUM>. In other examples, the output device <NUM> may be located near the input device <NUM>.

The transceiver <NUM> includes at least transmitter <NUM> and at least one receiver <NUM>. One or more transmitters <NUM> may be used to send messages to the RAN, as described herein. Similarly, one or more receivers <NUM> may be used to receive messages from the RAN, as described herein. Although only one transmitter <NUM> and one receiver <NUM> are illustrated, the user equipment apparatus <NUM> may have any suitable number of transmitters <NUM> and receivers <NUM>. Further, the transmitter(s) <NUM> and the receiver(s) <NUM> may be any suitable type of transmitters and receivers.

Disclosed herein is a first apparatus for determining whether an active unicast session can be re-used. The first apparatus may be implemented by a source UE, such as the remote unit <NUM>, the UE-A <NUM>, the source UE <NUM>, and/or the user equipment apparatus <NUM>. The first apparatus includes a transceiver and a processor that receives, e.g., from an internal application or operating system, a first request to establish a unicast session over a direct communication link to a first UE (i.e., target UE). Here, the first request indicates a source application-layer identifier of the apparatus and a target application-layer identifier of the first UE. The processor determines determining whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists. The processor re-uses an already-existing active unicast session between the apparatus and the first UE in response to determining that an active unicast session between the source application-layer identifier and the target application-layer identifier already exists. Otherwise, the processor establishes a new unicast session between the apparatus and the first UE in response to determining that an active unicast session between the source application-layer identifier and the target application-layer identifier does not exist.

In some examples, the first request is for a first V2X service and wherein the already-existing active unicast session is associated with a second V2X service different than the first, wherein the processor modifies a Unicast Link Profile of the already-existing active unicast session to add the first V2X service. In certain examples, the Unicast Link Profile is associated with an RRC connection, wherein re-using the already-existing active unicast session further comprises re-using an existing RRC connection between the apparatus and the first UE.

In some examples, the processor generates a link identifier for the requested unicast session. In such examples, the link identifier maps the source and target application-layer identifiers to the unicast session.

In some examples, the processor transmits a second request to the first UE to establish a unicast session and receives a response from the first UE, the response containing a set of link identifiers. In such examples, determining whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists already exists is based on the response from the first UE. In certain examples, the response from the includes as metadata all existing active unicast sessions of the first UE.

In some examples, the processor maintains a second set of link identifiers of the apparatus, each link identifier associated with a pair of source and target application-layer identifiers, wherein determining from the response whether an active unicast session with the first UE already exists comprises determining whether a matching link identifier exists among the set of link identifiers contained in the response and the second set of link identifiers.

Disclosed herein is a first method for determining whether an active unicast session can be re-used. The first method may be performed by a source UE, such as the remote unit <NUM>, the UE-A <NUM>, the source UE <NUM>, and/or the user equipment apparatus <NUM>. The first method includes receiving, from an internal application (e.g., a V2X application or OS running on the source UE), a first request to establish a unicast session over a direct communication link to a target UE (i.e., a second UE). Here, the first request indicates a source application-layer identifier of the source UE and a target application-layer identifier of the target UE. The first method includes determining whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists. The first method includes re-using an already-existing active unicast session between the source UE and the target UE in response to determining that an active unicast session between the source application-layer identifier and the target application-layer identifier already exists. Otherwise, the first method includes establishing a new unicast session between the source UE and target UE in response to determining that an active unicast session between the source application-layer identifier and the target application-layer identifier does not exist.

In some examples, the first request is for a first V2X service and the already-existing active unicast session is associated with a second V2X service different than the first. In such examples, the first method includes modifying a Unicast Link Profile of the already-existing active unicast session to add the first V2X service. In certain examples, the Unicast Link Profile is associated with an RRC connection. In such examples, re-using the already-existing active unicast session further comprises re-using an existing RRC connection between the source UE and the target UE.

In some examples, the first method includes generating a link identifier for the requested unicast session. In such examples, the link identifier maps the source and target application-layer identifiers to the unicast session.

In some examples, the first method further includes transmitting a second request to the target UE to establish a unicast session and receiving a response from the target UE, the response containing a set of link identifiers (e.g., a set of ULIs). In such examples, determining whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists already exists is based on the response from the target UE. In certain examples, the response from the includes as metadata all existing active unicast sessions of the target UE.

In some examples, the first method further includes maintaining a second set of link identifiers of the source UE, each link identifier associated with a pair of source and target application-layer identifiers. In such examples, determining from the response whether an active unicast session with the target UE already exists includes determining whether a matching link identifier exists among the set of link identifiers contained in the response and the second set of link identifiers.

Claim 1:
A method (<NUM>) of a first user equipment device, UE, the method comprising:
receiving (<NUM>), from an internal application, a first request to establish a unicast session over a direct communication link to a second UE, wherein the first request indicates a source application-layer identifier of the first UE and a target application-layer identifier of the second UE;
characterized by:
determining (<NUM>) whether an active unicast session between the source application-layer identifier and the target application-layer identifier already exists; and
re-using (<NUM>) an already-existing active unicast session between the first and the second UE in response to determining that an active unicast session between the source application-layer identifier and the target application-layer identifier already exists; and
establishing (<NUM>) a new unicast session between the first and second UE in response to determining that an active unicast session between the source application-layer identifier and the target application-layer identifier does not exist.