U2U relay discovery and (re) selection

Abstract

Embodiments provide a UE [e.g., a source UE] of a wireless [e.g., radio-based] communication system [e.g., a 5G / NR communication system] wherein the UE is configured to operate in a sidelink operating mode [e.g., 5G / NR sidelink mode 1 or mode 2] wherein the UE is configured to transmit [e.g., via a sidelink] to discover [e.g., via a sidelink], the UE is configured to discover [e.g., via the sidelink], and the UE is configured to discover [e.g., via the 5G / NR sidelink mode 1 or mode 2]. A discovery message of one or more candidate relay UEs connected or capable of being connected to a target UE or a set of target UEs [e.g., a set of target UEs having a set ID] via a UE-to-UE relay is provided to establish a connection with the target UE or the set of target UEs [e.g., a set of target UEs having a set ID] via a UE-to-UE relay.

Description

[0001] Embodiments of the present application relate to the field of wireless communications, and more particularly, to wireless communications between two UEs (eg, a source UE and a target UE) via a UE-to-UE relay. Some embodiments relate to U2U relay discovery and selection.

[0002] FIG1 is a schematic diagram of an example of a terrestrial wireless network 100, as shown in FIG1(a), including a core network 102 and one or more radio access networks RAN1, RAN2, ... RANN. FIG1(b) is a schematic diagram of a radio access network RAN n A schematic diagram of an example of a radio access network RAN n One or more base stations gNB1 to gNB5 may be included, each serving a specific area around the base station, schematically represented by corresponding cells 1061 to 1065. Base stations are provided to serve users within the cells. The term base station, BS, refers to a gNB in ​​a 5G network, an eNB in ​​UMTS / LTE / LTE-A / LTE-A Pro, or a BS in other mobile communication standards. Users can be fixed devices or mobile devices. The wireless communication system can also be accessed by mobile or fixed IoT devices connected to the base station or user. Mobile devices or IoT devices can include physical devices, ground-based vehicles such as robots or cars, aerial vehicles such as manned or unmanned aerial vehicles (UAVs), the latter also known as drones, buildings and other items or devices, which have embedded electronic devices, software, sensors, actuators, etc., and network connectivity that enables these devices to collect and exchange data on existing network infrastructure. Figure 1(b) shows an exemplary view of five cells, however, the RAN n More or fewer such cells may be included, and the RAN nIt is also possible to include only one base station. Figure 1(b) shows two users UE1 and UE2, also referred to as user equipment UE, which are in cell 1062 and served by base station gNB2. Another user UE3 is shown in cell 1064 served by base station gNB4. Arrows 1081, 1082 and 1083 schematically represent uplink / downlink connections for transmitting data from users UE1, UE2 and UE3 to base stations gNB2, gNB4 or for transmitting data from base stations gNB2, gNB4 to users UE1, UE2, UE3. In addition, Figure 1(b) shows two IoT devices 1101 and 1102 in cell 1064, which can be fixed or mobile devices. IoT device 1101 accesses the wireless communication system via base station gNB4 to receive and send data, as schematically represented by arrow 1121. IoT device 1102 accesses the wireless communication system via user UE3, as schematically represented by arrow 1122. The respective base stations gNB1 to gNB5 may be connected to the core network 102, for example via an S1 interface, via respective backhaul links 1141 to 1145, which are schematically represented in FIG. 1( b) by arrows pointing to “core”. The core network 102 may be connected to one or more external networks. In addition, some or all of the respective base stations gNB1 to gNB5 may be connected to each other, for example via an S1 or X2 interface or an XN interface in NR, via respective backhaul links 1161 to 1165, which are schematically represented in FIG. 1( b) by arrows pointing to “gNB”.

[0003] For data transmission, a physical resource grid may be used. The physical resource grid may include a set of resource elements to which various physical channels and physical signals are mapped. For example, a physical channel may include a physical downlink, uplink and sidelink shared channel (PDSCH, PUSCH, PSSCH) carrying user-specific data (also referred to as downlink, uplink and sidelink load data), a physical broadcast channel (PBCH) carrying, for example, a master information block (MIB), a physical downlink shared channel (PDSCH) carrying, for example, a system information block (SIB), and a physical downlink, uplink and sidelink control channel (PDCCH, PUCCH, PSSCH) carrying, for example, downlink control information (DCI), uplink control information (UCI) and sidelink control information (SCI). For the uplink, the physical channel, or more precisely, the transport channel according to 3GPP, may further include a physical random access channel (PRACH or RACH) used by the UE to access the network after synchronization and obtaining the MIB and SIB. The physical signal may include a reference signal or symbol (RS), a synchronization signal, etc. The resource grid may include frames or radio frames with a specific duration in the time domain and a given bandwidth in the frequency domain. A frame may have a certain number of subframes of a predetermined length, for example, 1 millisecond. Each subframe may include one or more time slots of 12 or 14 OFDM symbols, depending on the cyclic prefix (CP) length. All OFDM symbols may be used for DL ​​or UL or only for a subset, for example, when utilizing a shortened transmission time interval (sTTI) or a microslot / non-slot based frame structure comprising only a few OFDM symbols.

[0004] The wireless communication system may be any single tone or multi-carrier system using frequency division multiplexing, such as an orthogonal frequency division multiplexing (OFDM) system, an orthogonal frequency division multiple access (OFDMA) system, or any other IFFT-based signal with or without CP, such as DFT-s-OFDM. Other waveforms may be used, such as non-orthogonal waveforms for multiple access, such as filter bank multi-carrier (FBMC), generalized frequency division multiplexing (GFDM), or universal filtering multi-carrier (UFMC). The wireless communication system may operate according to the LTE-Advancedpro standard or the NR (5G, New Radio) standard.

[0005] The wireless network or communication system depicted in Figure 1 can be a heterogeneous network with different overlapping networks, such as a macro cell network, each macro cell including a macro base station, such as base stations gNB1 to gNB5, and a small cell base station network (not shown in Figure 1), such as a femto base station or a pico base station.

[0006] In addition to the above-mentioned terrestrial wireless networks, there are also non-terrestrial wireless communication networks NTN, including space-borne transceivers, such as satellites, and / or airborne transceivers, such as unmanned aircraft systems. The non-terrestrial wireless communication network or system can operate in a similar manner to the terrestrial system described above with reference to Figure 1, for example according to the LTE-Advanced Pro standard or the NR (5G, New Radio) standard.

[0007] In a mobile communication network, for example, in a network similar to the network described above with reference to FIG. 1 , such as an LTE or 5G / NR network, there may be UEs that communicate directly with each other via one or more side link (SL) channels, for example, using a PC5 interface. UEs that communicate directly with each other via side links may include vehicles that communicate directly with other vehicles (V2V communication), vehicles that communicate with other entities of a wireless communication network (V2X communication), other entities being, for example, roadside entities such as traffic lights, traffic signs, or pedestrians. Other UEs may not be vehicle-related UEs and may include any of the above-mentioned devices. These devices may also communicate directly with each other (D2D communication) using SL channels.

[0008] When considering two UEs communicating directly with each other via a sidelink, the two UEs may be served by the same base station so that the base station can provide sidelink resource allocation configuration or assistance to the UEs. For example, the two UEs may be within the coverage of a base station, such as one of the base stations shown in FIG1 . This is referred to as the “in coverage” scenario. Another scenario is referred to as the “out of coverage” scenario. It should be noted that “out of coverage” does not mean that the two UEs are not within a cell as shown in FIG1 , but rather that the UEs

[0009] - may not be connected to the base station, for example, not in the RRC connected state, resulting in the UE being unable to receive any sidelink resource allocation configuration or assistance from the base station, and / or

[0010] - may be connected to a base station, but due to one or more reasons, the base station may not provide sidelink resource allocation configuration or assistance to the UE, and / or

[0011] -It is possible to connect to base stations that do not support NR V2X services, such as GSM, UMTS, LTE base stations.

[0012] When considering two UEs communicating directly with each other via a side link, for example using a PC5 interface, one of the UEs can also be connected to the BS and can relay information from the BS to the other UE via the side link interface. Relaying can be performed in the same frequency band (in-band relaying), or another frequency band can be used (out-of-band relaying). In the first case, the communication on the Uu and side link can be decoupled using different time slots, such as a time division duplex system TDD system.

[0013] Figure 2 is a schematic diagram of a scenario within coverage, in which two UEs in direct communication with each other are both connected to a base station. The coverage of the base station gNB is schematically represented by a circle 200, which substantially corresponds to the cell schematically represented in FIG1 . The UEs in direct communication with each other include a first vehicle 202 and a second vehicle 204, both of which are located within the coverage 200 of the base station gNB. Both vehicles 202, 204 are connected to the base station gNB, and in addition, they are directly connected to each other via a PC5 interface. Via control signaling on the Uu interface (which is a radio interface between the base station and the UE), the gNB can assist in the scheduling and / or interference management of V2V traffic. That is, the gNB provides SL resource allocation configuration or assistance to the UE, and the gNB allocates resources for V2V communication on the side link. This configuration is also referred to as a mode 1 configuration for NR V2X or a mode 3 configuration for LTE V2X.

[0014] Figure 3 is a schematic diagram of an out-of-coverage scenario, where the UEs communicating directly with each other are either not connected to the base station, although they may be physically located within a cell of the wireless communication network, or some or all of the UEs communicating directly with each other are connected to the base station, but the base station does not provide SL resource allocation configuration or assistance. The figure shows that three vehicles 206, 208 and 210 communicate directly with each other via a side link, for example using a PC5 interface. The scheduling and / or interference management of V2V traffic is based on algorithms implemented between vehicles. This configuration is also called Mode 2 configuration in NR V2X, or Mode 4 configuration in LTE V2X. As described above, Figure 3 The out-of-coverage scenario in does not necessarily mean that the corresponding Mode 2 UE (in NR) or Mode 4 UE (in LTE) is outside the coverage 200 of the base station, but means that the corresponding Mode 2 UE (in NR) or Mode 4 UE (in LTE) is not served by the base station, is not connected to a base station in coverage, or is connected to a base station but does not receive SL resource allocation configuration or assistance from the base station. Therefore, there may be such a situation: Figure 2 In the coverage area 200 shown, in addition to NR mode 1 or LTE mode 3 UEs 202, 204, there are also NR mode 2 or LTE mode 4 UEs 206, 208, 210.

[0015] Of course, it is also possible that the first vehicle 202 is covered by the gNB, that is, connected to the gNB via Uu, wherein the second vehicle 204 is not covered by the gNB and is only connected to the first vehicle 202 via the PC5 interface, or the second vehicle is connected to the first vehicle 202 via the PC5 interface, but connected to another gNB via Uu, through Figure 4 and Figure 5 The discussion will make this clear.

[0016] Figure 4 is a schematic diagram of a scenario in which two UEs communicate directly with each other, where only one of the two UEs is connected to a base station. The coverage area of ​​the base station gNB is schematically represented by a circle 200, which basically corresponds to the cell schematically represented in Figure 1. The UEs that communicate directly with each other include a first vehicle 202 and a second vehicle 204, where only the first vehicle 202 is located within the coverage area 200 of the base station gNB. The two vehicles 202, 204 are directly connected to each other via the PC5 interface.

[0017] Figure 5 2001, wherein the coverage of the first base station gNB1 is schematically represented by a first circle 2001, wherein the coverage of the second base station gNB2 is schematically represented by a second circle 2002. The UEs that directly communicate with each other include a first vehicle 202 and a second vehicle 204, wherein the first vehicle 202 is located within the coverage 2001 of the first base station gNB1 and is connected to the first base station gNB1 via a Uu interface, wherein the second vehicle 204 is located within the coverage 2002 of the second base station gNB2 and is connected to the second base station gNB2 via a Uu interface.

[0018] In the wireless communication system described above, in UE-to-network relay, the target / destination of the remote UE is clear - it is the network. In UE-to-UE relay, the target UE can connect to any relay UE. For UE-to-UE relay, there is the problem of how to find the correct relay UE to connect to the target / destination UE.

[0019] Therefore, there is a need to improve UE-to-UE relay.

[0020] It should be noted that the information in the previous section is only for enhancing understanding of the background technology of the present invention and therefore, it may contain information that does not constitute the prior art known to a person of ordinary skill in the art.

[0021] Embodiments of the present invention are described herein with reference to the accompanying drawings.

[0022] FIG1 is a schematic diagram showing an example of a wireless communication system;

[0023] Figure 2 is a schematic diagram of a scenario within coverage, where UEs communicating directly with each other are connected to a base station;

[0024] Figure 3 is a schematic diagram of an out-of-coverage scenario, where UEs communicating directly with each other do not receive SL resource allocation configuration or assistance from the base station;

[0025] Figure 4is a schematic diagram of a partial out-of-coverage scenario, where a portion of the UEs directly communicating with each other do not receive SL resource allocation configuration or assistance from the base station;

[0026] Figure 5 is a schematic diagram of a scenario within coverage, where UEs communicating directly with each other are connected to different base stations;

[0027] Figure 6 is a schematic diagram of a wireless communication network;

[0028] Figure 7 is a schematic diagram of an end-to-end user plane protocol stack using layer 2 UE-to-UE relay [1];

[0029] Figure 8 is a schematic diagram of an end-to-end control plane protocol stack using layer 2 UE-to-UE relay [1];

[0030] Fig. 9 is a schematic diagram of three different scenarios of discovering a target UE via a relay UE;

[0031] Fig.10 is a schematic diagram of a wireless communication system including a transceiver, such as a base station or a relay, and a plurality of communication devices, such as UEs, according to an embodiment;

[0032] Fig.11 is a schematic diagram of a wireless communication system, where a source UE, a relay UE and a destination UE are within coverage [2];

[0033] Fig.12 is a schematic diagram of a wireless communication system, wherein a source UE, a relay UE, and a destination UE are out of coverage [2];

[0034] Fig.13 is a schematic diagram of a wireless communication system, wherein at least one of the UEs involved in the relay (e.g., source UE, relay UE, destination UE) is in coverage, and at least one of the UEs involved in the relay is out of coverage (partial coverage) [2];

[0035] Fig.14 is a schematic diagram of a wireless communication system including UEs within coverage and UEs outside coverage;

[0036] Fig.15 is a schematic diagram of a wireless communication system including UEs within coverage and UEs outside coverage;

[0037] Fig.16 It is a schematic diagram of the U2U relay scenario;

[0038] Fig.17 is a schematic diagram of a source UE initiating a discovery process; and

[0039] Fig.18 An example of a computer system is shown on which the units or modules and the steps of the method described according to the method of the present invention can be executed.

[0040] In the following description, equal or equivalent elements or elements having equal or equivalent functions are denoted by equal or equivalent reference numerals.

[0041] In the following description, a number of details are set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other cases, in order to avoid obscuring embodiments of the present invention, well-known structures and devices are shown in block diagram form rather than in detail. In addition, unless otherwise specifically stated, the features of the following different embodiments may be combined with each other.

[0042] As already shown in the introduction, in UE-to-network relay, the target / destination of the remote UE is clear - it is the network. In UE-to-UE relay, the target UE can connect to any relay UE. For UE-to-UE relay, there is the problem of how to find the right relay UE to connect to the target / destination UE.

[0043] Unlike the U2N relay scenario, discovering the third, potentially unknown target UE is more challenging, especially in out-of-coverage scenarios. If the source UE has not been connected to the target UE before, then the remote UE does not know which remote UEs can be reached via the relay UE and must first "discover" this. On the other hand, the relay UE only knows about UEs that it has already discovered or that have an existing connection with the relay UE.

[0044] The existing solution is to relay the discovery message through the relay UE, the response of the target remote UE and the reply of the relay UE to the source remote UE.

[0045] This approach introduces additional delay in the communication part due to the two necessary PC5 message flows. On the other hand, if the target remote UE is discoverable by the source remote UE, no modification of the protocol is required.

[0046] If the remote source UE receives only replies from relay UEs, the path to the target remote UE is obvious. If more relay UEs reply, a relay needs to be selected. The criteria for how to select the appropriate relay UE is unclear / unspecified.

[0047] Before describing the embodiments of the present invention in detail in Section 2, a background of sidelink relay is first provided in Section 1.

[0048] 1. Background

[0049] Depending on the SL mode (in coverage or out of coverage), the UE has to make the decision itself or can be guided by the gNodeB. For the in coverage scenario, the gNodeB allocates resources and is aware of the relay UEs in the cell. The source UE can request relay information and / or allocation of relays. The current specification only defines U2N relays.

[0050] In TR38.836, the basic process of U2U relay discovery is based on TS23.303.

[0051] 1.1 PC5 Basic Information

[0052] Then, based on [4], basic information that may be useful for understanding the context is described.

[0053] Two sidelink resource allocation modes are supported: Mode 1 and Mode 2.

[0054] In Mode 1, the sidelink resource allocation is provided by the network.

[0055] In mode 2, the UE determines the SL transmission resources in the resource pool.

[0056] The Physical Sidelink Control Channel (PSCCH) indicates to the UE the resources and other transmission parameters to be used for the PSSCH. The PSCCH transmission is associated with the DM-RS.

[0057] The physical sidelink shared channel (PSSCH) transmits the TB of the data itself, as well as control information triggered by the HARQ process and CSI feedback, etc. At least 6 OFDM symbols in a time slot are used for PSSCH transmission. PSSCH transmission is associated with DM-RS and can be associated with PT-RS.

[0058] The Physical Sidelink Feedback Channel (PSFCH) carries HARQ feedback over the sidelink from the UE that is the intended recipient of the PSSCH transmission to the UE that performs the transmission. The PSFCH sequence is transmitted in one PRB that is repeated over two OFDM symbols near the end of the sidelink resource in a slot.

[0059] The sidelink synchronization signal consists of the sidelink primary synchronization signal and the sidelink secondary synchronization signal (S-PSS, S-SSS), each occupying 2 symbols and 127 subcarriers. The physical sidelink broadcast channel (PSBCH) occupies 9 and 5 symbols in the normal CP and extended CP cases, respectively, including the related DM-RS.

[0060] For unicast, the sidelink supports a channel state information reference signal (CSI-RS) for CSI measurement and reporting. CSI reporting is performed in the sidelink MAC CE.

[0061] Logical channels are divided into two groups: control channels and traffic channels. Control channels are used only to transmit control plane information.

[0062] The Common Control Channel (CCCH) is a channel for transmitting control information between the UE and the network. This channel is used for UEs that do not have an RRC connection with the network[4].

[0063] The following identifiers are used for NR sidelink communications:

[0064] ■ Source Layer-2 ID: Identifies the transmitter of data in NR sidelink communication. The Source Layer-2 ID is 24 bits long and is split into two bit strings at the MAC layer:

[0065] o One bit string is the LSB portion (8 bits) of the Source Layer-2 ID and is forwarded to the physical layer of the transmitter. This identifies the source of the expected data in the sidelink control information and is used to filter packets at the physical layer of the receiver.

[0066] o The second bit string is the MSB portion (16 bits) of the Source Layer-2 ID, carried in the MAC header. This is used to filter packets at the receiver's MAC layer.

[0067] ■ Destination Layer-2 ID: Identifies the destination of the data in NR sidelink communications. For NR sidelink communications, the destination Layer-2 ID is 24 bits long and is split into two bit strings at the MAC layer:

[0068] o A bit string is the LSB portion (16 bits) of the destination layer-2 ID and is forwarded to the physical layer of the transmitter. This identifies the destination of the expected data in the sidelink control information and is used to filter packets at the physical layer of the receiver.

[0069] o The second bit string is the MSB part (8 bits) of the destination layer-2 ID, carried in the MAC header. This is used to filter packets at the receiver's MAC layer.

[0070] ■ PC5 Link Identity: Uniquely identifies a PC5 unicast link in the UE during its lifetime, as specified in [5]. The PC5 Link Identity is used to indicate to higher layers that a sidelink RLF has been declared and the corresponding PC5-RRC connection has been released.

[0071] 1.2 General Sidelink Description

[0072] For a source Layer-2 ID and destination Layer-2 ID pair within an AS, NR sidelink communications may support one of three transmission modes:

[0073] ■Unicast transmission, characterized by:

[0074] o Support one PC5-RRC connection between peer UEs for a pair;

[0075] ○ Send and receive control information and user traffic between peer UEs in the sidelink;

[0076] ○Support side link HARQ feedback;

[0077] ○Support side link transmit power control;

[0078] ○Support RLC AM;

[0079] ○ Detect radio link failure of PC5-RRC connection.

[0080] ■Multicast transmission, characterized by:

[0081] ○ Transmission and reception of user traffic between UEs belonging to the same group in the side link;

[0082] ○Support sidelink HARQ feedback.

[0083] ■Broadcast transmission, characterized by:

[0084] ○ Transmission and reception of user traffic between UEs in the sidelink.

[0085] Figure 6 is a schematic diagram of a wireless communication network. Figure 6 1 shows two base stations 182 and 180 communicating via an Xn interface. The two base stations 182 and 184 constitute a next-generation radio access network NG-RAN. Therefore, it is assumed that the first base station 182 is a gNode B (gNB), and the second base station 184 is a next-generation evolved Node B (ng-eNB). In addition, Figure 6 , three UEs 202, 204, and 206 are shown, wherein UEs 202 and 204 are within the coverage of base stations 182 and 184 (e.g., within the NG-RAN coverage), and UE 206 is outside the coverage of base stations 182 and 184 (e.g., outside the NG-RAN coverage). Each UE 202, 204 communicates with the corresponding base station via a Uu interface, wherein UEs 202, 204, 206 communicate directly with each other via a PC5 interface.

[0086] 1.3 U2N Discovery Process[1]

[0087] ProSe direct discovery consists of two parts (see [1] clause 6.2.2.2, which is based on [5] clause 6.3.3).

[0088] The first part is monitoring. This process includes the UE monitoring broadcast data. Depending on the ProSe application ID that the UE wants to use, the UE may need to monitor one or more (e.g., any one or all) of the following:

[0089] 1. Destination layer 2-ID;

[0090] 1.ProSe application ID;

[0091] 2. Source user information (ProSe application layer ID of the source UE, ProSe application layer group ID);

[0092] Note 1: The broadcasting UE is the source UE.

[0093] 3. Target user information (ProSe application layer ID of the target UE);

[0094] Note 2: The target UE is the monitoring UE.

[0095] 4. Relay service code (used for UE to network relay discovery);

[0096] 5. Discovery group ID (for group member discovery).

[0097] The second part is broadcasting: This process consists of a UE broadcasting data that other UEs will listen to. Depending on the ProSe application that the broadcasting UE wants to use, in addition to broadcasting the source and destination Layer-2-IDs, the broadcasting UE may also need to broadcast one or more (e.g., any one) of the following:

[0098] 1.ProSe application ID;

[0099] 2. Source user information (ProSe application layer ID of the source UE, ProSe application layer group ID);

[0100] 3. Target user information (ProSe application layer ID of the target UE);

[0101] 4. Relay service code;

[0102] 5. Discover the group ID.

[0103] 1.4 UE-to-UE Relay Information from TR

[0104] For L2 UE to UE relay architecture, the protocol stack is similar to L2 UE to network relay, except that the termination points are two remote UEs.

[0105] An adaptation layer is supported on the second PC5 link (i.e. the PC5 link between the relay UE and the target / destination UE) for L2 UE to UE relay. For L2 UE to UE relay, the adaptation layer is placed on the RLC sublayer for CP and UP on the second PC5 link. Sidelink SDAP / PDCP and RRC are terminated between the two remote UEs, and RLC, MAC and PHY are terminated on each PC5 link.

[0106] The adaptation layer on the first PC5 hop between the source remote UE and the relay UE supports identification of traffic destined for different target / destination remote UEs.

[0107] The identity information of the remote UE end-to-end radio bearers is included in the adaptation layer of the first and second PC5 hops.

[0108] In addition, the identity information of the source remote UE and / or the identity information of the destination remote UE are candidate information to be included in the adaptation layer, which will be decided in the WI stage [2].

[0109] 1.4.1 Control and User Plane Protocols for Layer 2 UE-to-UE Relay

[0110] Figure 7 A schematic diagram of an end-to-end user plane protocol stack using Layer 2 UE-to-UE relay [1] is shown.

[0111] like Figure 7 As shown, the first UE (UE1) includes an IP / non-IP layer or entity, a service data adaptation protocol (SDAP) layer or entity, a packet data convergence protocol (PDCP) layer or entity, an adaptation layer or entity, a radio link control (RLC) layer or entity, a medium access control (MAC) layer or entity, and a physical (PHY) layer or entity. The UE-to-UE relay includes two adaptation layers or entities, two RLC layers or entities, two MAC layers or entities, and two PHY layers or entities. The second UE (UE2) includes an IP / non-IP layer or entity, an SDAP layer or entity, a PDCP layer or entity, an adaptation layer or entity, an RLC layer or entity, a MAC layer or entity, and a PHY layer or entity.

[0112] Figure 8 A schematic diagram of an end-to-end control plane protocol stack using Layer 2 UE-to-UE relay [1] is shown.

[0113] like Figure 8As shown, the first UE (UE1) includes a PC5 signaling (PC5-S) layer or entity, a packet data convergence protocol (PDCP) layer or entity, an adaptation layer or entity, a radio link control (RLC) layer or entity, a media access control (MAC) layer or entity, and a physical (PHY) layer or entity. The UE-to-UE relay includes two adaptation layers or entities, two RLC layers or entities, two MAC layers or entities, and two PHY layers or entities. The second UE (UE2) includes a PC5-S layer or entity, a PDCP layer or entity, an adaptation layer or entity, an RLC layer or entity, a MAC layer or entity, and a PHY layer or entity.

[0114] In [2], discovery mode refers to Mode A and Mode B defined in [3], i.e., the “I am here” and “who is there” approaches of ProSe discovery.

[0115] 1.5 Target UE Discovery via UE-to-UE Relay

[0116] According to [1], there are three methods for UE-to-UE discovery:

[0117] 1. The source UE attempts direct communication. If this fails, it finds a relay UE and attempts to reach the target UE via the relay.

[0118] 2. Alternative 1: UE-to-UE relay discovery and selection can be integrated into the unicast link establishment process as described in clause 6.3.3 of [5].

[0119] 3. Alternative 2: UE-to-UE relay discovery and selection is integrated into the Mode B (“who’s there”) direct discovery process.

[0120] When a source UE wants to communicate with a target UE, it first tries to find the target UE by sending:

[0121] Direct communication request, or

[0122] • Solicitation message with target UE information.

[0123] If the source UE cannot reach the target UE directly, it will try to discover the UE-to-UE relay to reach the target UE, which may also trigger the relay to discover the target UE. To be more efficient, this scheme attempts to integrate target UE discovery and UE-to-UE relay discovery and selection, including two alternatives:

[0124] -Alternative 1: UE-to-UE relay discovery and selection can be integrated into the unicast link establishment process, such as TS

[0125] As described in clause 6.3.3 of 23.287.

[0126] -Alternative 2: UE-to-UE relay discovery and selection is integrated into Mode B direct discovery process.

[0127] In this scheme, the source UE can discover the target UE via the relay, allowing the target UE to select the relay and the source UE to select the relay path or the direct path.

[0128] There may be situations where multiple UE-to-UE relays can be used to reach the target UE, or the target UE may also directly receive a direct communication request or solicitation message from the source UE. The target UE may choose which one to reply to based on, for example, signal strength, local policy (e.g., traffic load on UE-to-UE relays), relay service code (if any), or operator policy (e.g., always prefer direct communication or only use certain specific UE-to-UE relays).

[0129] The source UE may receive responses from multiple UE-to-UE relays or directly from the target UE, with the source UE selecting the communication path based on, for example, signal strength or operator policy (e.g., always preferring direct communication or only using certain specific UE-to-UE relays) (see [1], 6.8 Solution #8: UE-to-UE relay selection without relay discovery).

[0130] Fig. 9 It is a schematic diagram of three different scenarios of discovering the target UE via the relay UE.

[0131] According to the first scenario 900 , the source UE 202 sends a direct communication request or solicitation message to the destination UE 204 , wherein in the first scenario, it is exemplarily assumed that the source UE 202 cannot reach the destination UE 204 directly.

[0132] According to the second scenario 902, the source UE 202 discovers two UE-to-UE (U2U) relays 206 and 208, each of which sends a broadcast direct communication request in its vicinity. Therefore, in the second scenario, it is exemplarily assumed that the first UE-to-UE relay 206 reaches the destination UE 204.

[0133] According to the third scenario, the destination UE 204 sends a direct communication accept message to the first UE-to-UE relay 206 , wherein the first UE-to-UE relay 206 sends a direct communication accept message to the source UE 202 .

[0134] Therefore, the PC5 communication channel can be used to transmit the discovery message.

[0135] Mode A is suitable for UEs that are not sensitive to power consumption, because the notification UE will periodically broadcast direct discovery messages.

[0136] When a UE-to-UE relay is out of coverage, it can act as a UE-to-UE relay based on preconfigured policies and parameters [1].

[0137] 1.6 Information Content in UE-to-UE Relay Discovery and Selection

[0138] During the UE-to-UE relay discovery and selection process, the following information content may be sent (e.g., broadcast) from the source UE to the relay UE: source UE information, target UE information, application ID and / or, if any, relay service code (e.g., layer-2 ID, ProSe application ID, UE's application layer ID, target UE's application layer ID and / or relay applicability indication).

[0139] During the UE-to-UE relay discovery and selection process, the following information content is sent from the relay UE to the target / destination UE and optionally also to the source UE: source UE information, target UE information and relay UE information (e.g., relay UE ID) and / or the L2 address of the relay as the source layer-2 ID.

[0140] In the UE-to-UE relay discovery and selection process, the following information contents may be sent from the target / destination UE to the relay UE: source UE information, relay UE information and / or target / destination UE information.

[0141] During UE-to-UE relay discovery and selection, the following information content may be sent from the relay UE to the source UE: source UE information, relay UE information, and / or target / destination UE information. 2. Example

[0142] The embodiments of the present invention can be shown in FIG. 1 to FIG. Figure 5 The wireless communication system or network shown is implemented in the figure, and the system or network includes a transceiver, such as a base station, a gNB or a relay, and multiple communication devices, such as a user equipment (UE). Fig.10 is a schematic diagram of a wireless communication system, the wireless communication system includes a transceiver 200 such as a relay and a plurality of communication devices 202 such as UEs 1 and 202 2 The UE may communicate directly with the relay 200 via a wireless communication link or channel 203, such as a radio link (eg, using a PC5 interface (side link)). The relay 200 may be located between the UE 202 and the relay 200. 1 and 202 2 relay messages between the UE 202 1 and 202 2The UE 202 may communicate with each other via the relay 200. The relay 200 may include one or more antennas ANT or an antenna array having multiple antenna units, a signal processor 200a, and a transceiver unit 200b. The UE 202 may include one or more antennas ANT or an antenna array having multiple antenna units, a processor 202a, and a receiver unit 200b. 1 To 202a 2 and transceiver (eg, receiver and / or transmitter) unit 202b 1 To 202b 2 Base station 200 and / or one or more UEs 202 may operate in accordance with the inventive teachings described herein.

[0143] An embodiment provides a UE [e.g., a source UE] of a wireless [e.g., radio-based] communication system [e.g., a 5G / NR communication system], wherein the UE is configured to operate in a sidelink operation mode [e.g., 5G / NR sidelink mode 1 or mode 2], wherein the UE is configured to send [e.g., via a sidelink] a discovery message for discovering [e.g., via a sidelink] one or more candidate relay UEs that are connected to or capable of connecting to a target UE or a group of target UEs, so as to establish a connection with the target UE or a group of target UEs [e.g., a group of target UEs with a group ID] via a UE-to-UE relay.

[0144] In an embodiment, the discovery message includes information about a target UE or a group of target UEs [eg, a layer 2 destination ID], a source UE, and / or other relevant information.

[0145] In an embodiment, the UE is configured to receive a discovery response message from one or more candidate relay UEs connected or capable of connecting to a target UE or a group of target UEs, wherein the UE is configured to select a relay UE from the one or more candidate relay UEs.

[0146] In an embodiment, the UE is configured to establish a connection with a target UE or a group of target UEs via the selected relay UE.

[0147] In an embodiment, the UE is configured to select a relay UE from one or more candidate relay UEs according to a selection criterion, wherein the selection criterion is preconfigured or signaled by a base station of the wireless communication network, or configured by a higher layer.

[0148] In an embodiment, the selection criterion is at least one of:

[0149] - the signal strength of the link between the UE and the corresponding relay UE [e.g., Reference Signal Received Power (RSRP)],

[0150] - the signal strength of the link between the corresponding relay UE and the target UE [e.g., Reference Signal Received Power (RSRP)],

[0151] - The load of the corresponding relay UE [e.g., CPU, memory, temperature, channel busy rate (CBR), buffer status, channel occupancy],

[0152] - the number of remote UEs connected to the corresponding relay UE,

[0153] - the data rate supported by the corresponding relay UE,

[0154] - Capabilities of the corresponding relay UE,

[0155] - Information received from higher levels,

[0156] - received Radio Resource Control (RRC) messages,

[0157] -Signal strength of the discovery message.

[0158] In an embodiment, the UE is configured to select a relay UE from one or more candidate relay UEs according to auxiliary information or control information received from the base station when the UE is within the coverage of a base station of the wireless communication system.

[0159] In an embodiment, the UE is configured to, when the UE is within the coverage of a base station of the wireless communication system, send discovery messages only to those candidate relay UEs indicated by the control information received from the base station.

[0160] In an embodiment, the UE is configured to select another relay UE for communicating with a target UE or a group of target UEs if reselection criteria are met and / or in response to reception of a reselection control message [e.g., received from a base station, a current relay UE, a target UE] [e.g., controlling the UE to reselect the relay UE].

[0161] In an embodiment, the UE is configured to select another relay from one or more candidate relays UE when a reselection criterion is met or in response to receipt of a reselection control message.

[0162] In an embodiment, the UE is configured to, when a reselection criterion is met or in response to receipt of a reselection control message, send an additional discovery message for discovering one or more candidate relay UEs connected or capable of connecting to a target UE or a group of target UEs [e.g., via a side link], wherein the UE is configured to receive an additional discovery response message from one or more candidate relay UEs connected or capable of connecting to the target UE or a group of target UEs, wherein the UE is configured to select another relay UE from the one or more candidate relay UEs.

[0163] In an embodiment, the UE is configured to send a reselection information message to the relay UE, the reselection information message notifying the relay UE of another relay UE selected to switch to another relay UE, or wherein the UE is configured to send a reselection information message to the base station, the reselection information message notifying the base station of another relay UE selected and requesting the base station to coordinate the switch to the selected another UE.

[0164] In an embodiment, the reselection criterion is at least one of the following:

[0165] -Signal strength of the link between the UE and the relay UE [e.g., Reference Signal Received Power (RSRP)] [e.g.,

[0166] below the threshold],

[0167] - the signal strength of the link between the relay UE and the remote UE [e.g., Reference Signal Received Power (RSRP)] [e.g., below a threshold],

[0168] - one or more QoS parameters [e.g. below or above a threshold],

[0169] - the load of relay UEs [e.g. above a threshold],

[0170] - battery status of the relay UE [e.g. below a threshold],

[0171] - Information received from higher levels,

[0172] - A control message received from the relay UE or the base station instructing the relay UE to stop the relay operation.

[0173] A further embodiment provides a relay UE [e.g., UE-to-UE relay] of a wireless [e.g., radio-based] communication system [e.g., a 5G / NR communication system], wherein the relay UE is configured to operate in a sidelink operation mode [e.g., 5G / NR sidelink mode 1 or mode 2], wherein the relay UE is configured to receive a discovery message from a source UE, the discovery message indicating a target UE or a group of target UEs [e.g., a group of target UEs with a group ID; for example, the relay UE is part of the group of UEs] to which the source UE requests relay of a message, wherein the relay UE is configured to, if the relay UE is capable of relaying the message between the source UE and the target UE or the group of target UEs, send a discovery message response to the source UE, the discovery message response indicating that the relay UE is capable of relaying the message between the source UE and the target UE or the group of target UEs.

[0174] In an embodiment, the discovery message includes information about a target UE or a group of target UEs [eg, a layer 2 destination ID], a source UE, and / or other relevant information.

[0175] In an embodiment, the relay UE is configured to send a target UE or target UE group discovery message for discovering a target UE or a group of target UEs in response to receipt of a discovery message.

[0176] In an embodiment, the relay UE is configured to send a discovery message response to the source UE in response to receiving a target UE or target UE group discovery message response from the target UE or a group of target UEs.

[0177] In an embodiment, the relay UE is configured to maintain a list of remote UEs to which the relay UE is connected or can be connected, wherein the relay UE is configured to send the discovery message response directly to the source UE if the target UE is included in the remote UE list.

[0178] In an embodiment, the relay UE is configured to share the remote UE list with a base station of the wireless communication network in case the relay UE is within the coverage of the base station.

[0179] In an embodiment, the relay UE is configured to send remote UE discovery messages for discovering remote UEs [e.g., periodically or at predefined or random time instances], wherein the relay UE is configured to update the remote UE list based on remote UE discovery response messages received from discovered remote UEs.

[0180] In an embodiment, the relay UE is configured to save additional information about the remote UE in the remote UE list to further support relaying of messages and / or reply to discovery messages.

[0181] In an embodiment, the discovery response message further includes information about the target UE.

[0182] In an embodiment, the discovery response message further includes a list of one or more remote UEs to which the relay UE is connected or can be connected.

[0183] In an embodiment, the discovery response message further includes information about the one or more remote UEs.

[0184] In an embodiment, for each of the one or more remote UEs, the information about the one or more remote UEs is at least one of:

[0185] - Supported application IDs,

[0186] -Activity Group ID

[0187] - Received Signal Strength Indicator (RSSI) readings,

[0188] - Address information [e.g., Layer 2 ID of Layer 3 address information],

[0189] - UE type,

[0190] -UE speed or mobility indication,

[0191] -UE position (relative or absolute).

[0192] In an embodiment, the discovery response message further includes information about the relay UE.

[0193] In an embodiment, the information about the relay UE is at least one of the following:

[0194] - Relay the remaining charge or battery status of the UE,

[0195] - Discontinuous Reception (DRX) configuration of the relay UE,

[0196] - the number of remote UEs connected to the relay UE,

[0197] - a list of remote UEs to which the relay UE is connected or capable of connecting,

[0198] - List of supported service application IDs,

[0199] - a list of supported groups or an indication that all groups are supported,

[0200] - a list of supported Public Land Mobile Networks (PLMNs) and / or Standalone Non-Public Networks (SNPNs),

[0201] - buffer status information,

[0202] - Type of relay UE (e.g. L2 or L3, UE to UE or UE to network),

[0203] - Network connection information [e.g., whether the relay UE is connected to the network, cell ID],

[0204] - Channel Busy Rate (CBR) at the relay.

[0205] In an embodiment, the relay UE is configured to, when receiving a reselection information message from one of the source UE, the target UE and the base station, send another reselection information message to another of the source UE, the target UE and the base station, the reselection information message notifying the relay UE to switch to another relay UE, and the another reselection information message notifying the selected other relay UE.

[0206] In an embodiment, the relay UE is configured to switch the traffic between the source UE and the target UE to another relay UE at a time indicated in the reselection information message.

[0207] In an embodiment, the relay UE is configured to send a relay reselection control message to the source UE and / or target UE and / or base station when the relay reselection criteria are met, and the relay reselection control message controls the source UE and / or target UE and / or base station to select another relay UE.

[0208] In an embodiment, the relay reselection criterion is at least one of the following:

[0209] -Signal strength of the link between the UE and the relay UE [e.g., Reference Signal Received Power (RSRP)] [e.g.,

[0210] below the threshold],

[0211] - the signal strength of the link between the relay UE and the remote UE [e.g., Reference Signal Received Power (RSRP)] [e.g., below a threshold],

[0212] - one or more QoS parameters [e.g. below or above a threshold],

[0213] - the load of relay UEs [e.g. above a threshold],

[0214] - battery status of the relay UE [e.g. below a threshold],

[0215] - Information received from higher levels,

[0216] - information or control information from a base station,

[0217] - Relay operation termination criteria.

[0218] In an embodiment, the relay UE is configured to stop relaying if a relay operation termination criterion is reached.

[0219] In an embodiment, the relay UE is configured to send a control message to the source UE and / or the target UE and / or the base station to instruct the relay UE to stop relaying when a relay operation termination criterion is reached.

[0220] In an embodiment, the relay operation termination criterion is one of the following:

[0221] -The critical power of the relay UE,

[0222] - Restart of the operating system of the relay UE,

[0223] - Hardware failure of the relay UE,

[0224] - Reconfiguration of the relay UE [eg by higher layers].

[0225] - one or more QoS parameters [e.g. below or above a threshold],

[0226] - the load of relay UEs [e.g. above a threshold],

[0227] - battery status of the relay UE [e.g. below a threshold],

[0228] - Information received from higher levels,

[0229] - information or control information from a base station,

[0230] - Relay operation termination criteria.

[0231] A further embodiment provides a target UE of a wireless [e.g., radio-based] communication system [e.g., a 5G / NR communication system], wherein the target UE is configured to operate in a sidelink operation mode [e.g., 5G / NR sidelink mode 1 or mode 2], wherein the target UE is configured to communicate with a source UE of a wireless communication network via a relay UE of the wireless communication network, wherein the target UE is configured to, when a reselection criterion is met,

[0232] -Reselect another relay UE

[0233] - Alternatively, a relay reselection control message is sent to the source UE, where the relay reselection control message controls the source UE and / or the base station to select another relay UE.

[0234] In an embodiment, the reselection criterion is at least one of the following:

[0235] -Signal strength of the link between the UE and the relay UE [e.g., Reference Signal Received Power (RSRP)] [e.g.,

[0236] below the threshold],

[0237] - the signal strength of the link between the relay UE and the remote UE [e.g., Reference Signal Received Power (RSRP)] [e.g., below a threshold],

[0238] - one or more QoS parameters [e.g. below or above a threshold],

[0239] - the load of relay UEs [e.g. above a threshold],

[0240] - battery status of the relay UE [e.g. below a threshold],

[0241] - Information received from higher levels,

[0242] - A control message received from the relay UE, instructing the relay UE to stop the relay operation.

[0243] In an embodiment, the target UE is configured to reselect another relay by sending a discovery message for discovering one or more candidate relay UEs that are connected to or capable of connecting to the source UE [e.g., via a side link], wherein the target UE is configured to select another relay UE from one or more candidate relay UEs that are connected to or capable of connecting to the source UE [e.g., via a side link].

[0244] In an embodiment, the target UE is configured to reselect another relay UE from one or more candidate relay UEs according to a selection criterion.

[0245] In an embodiment, the target UE is configured to send a reselection information message to the relay UE, the reselection information message notifying the relay UE of another relay UE selected to switch to another relay UE, or wherein the target UE is configured to send a reselection information message to the base station, the reselection information message notifying the base station of another relay UE selected and requesting the base station to coordinate the switch to the selected another UE.

[0246] A further embodiment provides a wireless [e.g., radio-based] communication system [e.g., a 5G / NR communication system]. The communication system includes a source UE according to one of the embodiments of the present invention, a relay UE according to one of the embodiments of the present invention, and a target UE according to one of the embodiments of the present invention.

[0247] A further embodiment provides a method for operating a UE [e.g., a source UE] of a wireless [e.g., radio-based] communication system [e.g., a 5G / NR communication system]. The method includes the step of operating the UE in a sidelink operation mode [e.g., 5G / NR sidelink mode 1 or mode 2]. In addition, the method includes sending a discovery message for discovering one or more candidate relay UEs that are connected or capable of connecting to a target UE or a group of target UEs [e.g., via a sidelink], for establishing a connection with the target UE or a group of target UEs via a UE-to-UE relay.

[0248] A further embodiment provides a method for operating a relay UE [e.g., UE-to-UE relay] of a wireless [e.g., radio-based] communication system [e.g., a 5G / NR communication system]. The method includes the step of operating the relay UE in a sidelink operation mode [e.g., 5G / NR sidelink mode 1 or mode 2]. In addition, the method includes the step of receiving a discovery message from a source UE, the discovery message indicating a target UE or a group of target UEs to which the source UE requests message relay. In addition, the method includes, in the event that the relay UE is capable of relaying messages between the source UE and the target UE or a group of target UEs, the step of sending a discovery message response to the source UE, the discovery message response indicating that the relay UE is capable of relaying messages between the source UE and the target UE or a group of target UEs.

[0249] A further embodiment provides a method for operating a target UE of a wireless [e.g., radio-based] communication system [e.g., a 5G / NR communication system]. The method includes the step of operating the target UE in a sidelink operation mode [e.g., 5G / NR sidelink mode 1 or mode 2]. In addition, the method includes the step of communicating with a source UE of a wireless communication network via a relay UE of the wireless communication network. In addition, the method includes the step of reselecting another relay UE or sending a relay reselection control message to the source UE when a reselection criterion is met, the relay reselection control message controlling the source UE to select another relay UE.

[0250] Embodiments provide mechanisms to support single-hop L2 and / or L3 UE-to-UE relaying for unicast transmissions.

[0251] In an embodiment, a source UE is defined as a UE that identifies a candidate UE-to-UE relay and initiates relay reselection via an existing connection. A message is sent to a target UE directly or via a relay UE. The source UE is a remote UE.

[0252] In an embodiment, the target UE is a remote UE that receives a message from a source UE or from a relay UE. It is also called a destination UE.

[0253] In an embodiment, a target group is a group of UEs, for example, destinations in a multicast communication, which may have a single group ID as a target address.

[0254] In an embodiment, a remote UE is a UE that is connectable to a relay UE. The source UE and the target / destination UE are remote UEs, and the relay UE is not a remote UE.

[0255] In an embodiment, a UE-to-UE relay sends / receives a discovery message to / from a source UE or a target UE [1] (6.50.3 Impact on services, entities and interfaces).

[0256] In an embodiment, the user information ID is defined as follows. For mode A, when the UE acts as a notifying UE, this corresponds to the notifier information parameter. For mode B, when the UE acts as a discoverer or discoverer UE, respectively, this corresponds to the discoverer information in the solicitation message and the discoverer information in the response message.

[0257] In an embodiment, the relay service code (TS23.303) may be used to identify the connection service provided by the ProSe UE to network relay and the authorized user to whom the ProSe UE to network relay will provide the service, and may select related security policies or information, such as information on authentication and authorization between the remote UE and the ProSe UE to network relay.

[0258] In an embodiment, the Relay Service Code (TR23.752) identifies the connectivity service provided by the ProSe UE-to-UE Relay to the application. The Relay Service Code is configured in the ProSe UE-to-UE Relay that provides connectivity services to the application. The Relay Service Code is configured in the remote UE that is interested in the related connectivity service [1] (6.36.2.4 5G ProSe UE-to-UE Relay Discovery Parameters).

[0259] In an embodiment, Relay_indication is a flag for indicating whether relay can be used in communication (eg, when the source UE wishes to broadcast a direct communication request or solicitation message, it indicates in the message whether UE-to-UE relay can be used).

[0260] In an embodiment, relay selection is the process of selecting or reselecting a relay.

[0261] Subsequently, embodiments of the present invention are described in further detail.

[0262] 2.1 Use Cases

[0263] The embodiments described herein mainly focus on one or more of the following scenarios.

[0264] In an embodiment, the source UE has a PC5 connection with the target UE and the link quality no longer allows reliable communication. The source UE decides to use a relay UE to reach the target UE, if possible.

[0265] In an embodiment, the source UE is looking for reachable target UEs supporting specific services / applications in order to connect with these UEs. Examples of this could be: PTT applications for special groups (i.e. firefighters); multiplayer gaming; road services using RSUs as relay UEs.

[0266] In an embodiment, the source UE is aware of the existence of another target UE and wishes to connect to that specific UE, either because the target ID is already known to the application, or because there are multiple group IDs known to multiple devices, some of which can be connected directly, but some may only be reachable via a relay UE.

[0267] In an embodiment, the basic setup is that a source UE is connected to a relay UE, where the relay UE is connected to a target UE (ie, source UE (S) <-> relay UE (R) <-> target UE (T)).

[0268] In an embodiment, there may also be a scenario where the source and target UEs are completely unaware of the relay UE. In other words, there may be a PC5 link between the source UE and the relay UE, and there may be a PC5 link between the relay UE and the target UE, where the source UE and the target UE are unaware of the relay UE. In this case, discovering the relay can help both parties "discover" the connection between the source UE and the target UE.

[0269] In an embodiment, in a relay UE, an adaptation layer may map an incoming PC5 message to an outgoing PC5 message so as to relay the message to the correct target UE.

[0270] In an embodiment, route planning decisions may be determined by:

[0271] ■Target UE (destination UE) and / or

[0272] ■ Source UE, and / or

[0273] ■Relay UE, and / or

[0274] ■Base station.

[0275] The embodiment considers three coverage scenarios (see [2], 5.1). According to the first coverage scenario, both UEs are within the coverage area, such as Fig.11 shown. Specifically, Fig.11 A schematic diagram of a wireless communication network having a base station 182, a source UE 202, a destination UE 204, and a UE-to-UE relay 206 is shown, wherein the source UE 202, the destination UE 204, and the UE-to-UE relay 206 are within the coverage of the base station 182 [2]. According to the second coverage scenario, both UEs are out of coverage, such as Fig.12 shown. Specifically, Fig.12 A schematic diagram of a wireless communication network having a base station 182, a source UE 202, a destination UE 204, and a UE-to-UE relay 206 is shown, wherein the source UE 202, the destination UE 204, and the UE-to-UE relay 206 are located outside the coverage of the base station 182 [2]. According to the third coverage scenario, at least one UE is within the coverage, and at least one UE is outside the coverage, such as Fig.13 shown. Specifically, Fig.13 A schematic diagram of a wireless communication network having a base station 182, a source UE 202, a destination UE 204 and a UE-to-UE relay 206 is shown, wherein the UE-to-UE relay 206 is located within the coverage of the base station 182, and wherein the source UE 202 and the destination UE 204 are located outside the coverage of the base station 182 [2].

[0276] In addition, there may be a situation where one UE is within the coverage of one cell, and another UE is within the coverage of another cell.

[0277] Fig.14 A schematic diagram of a wireless communication system including UEs within coverage and outside coverage is shown. Fig.14 In the exemplary embodiment, it is assumed that UE 202, 204 and 206 are within the coverage of base station 182 (gNB) of the wireless communication network, while UE 208, 210 and 212 are out of coverage. For example, the out-of-coverage remote UE 202 and 204 can communicate with each other using the corresponding PC5 link via the out-of-coverage relay UE 206. In addition, the in-coverage UE 208 and 210 can be connected to the base station 182 (gNB) of the wireless communication network via the corresponding Uu link. The two in-coverage UEs 208 and 210 can also be directly connected to each other via the PC5 link. In this case, the out-of-coverage UE 212 can communicate with UE 208 via UE 210, where UE 210 can act as a U2N relay (i.e., the message is relayed by UE 210 to UE 208 via the base station using the corresponding Uu link) or a U2U relay (i.e., the message is relayed by UE 210 directly to UE 208 via the PC5 link).

[0278] Fig.15 A schematic diagram of a wireless communication system including UEs within coverage and outside coverage is shown. Fig.15 In the exemplary embodiment, it is assumed that UEs 202, 204, and 206 are within the coverage of a base station 182 (gNB) of a wireless communication network, while UEs 208, 210, and 212 are out of coverage. Therefore, UEs 202, 204, and 206 are connected to base station 182 via a Uu link, wherein UEs 204 and 206 may also be directly connected to each other via a PC5 link. Out-of-coverage UEs 208, 210, and 212 may perform a discovery process for detecting UEs that may be used as relays for communicating with other UEs of the wireless communication network.

[0279] In the wireless communication system as described above, such as in Fig.14 and 15 In the exemplary illustrated wireless communication system, embodiments allow a UE to be aware of other UEs available via a side link.

[0280] In addition, embodiments allow the remote UE to know which relay UE is connected to or can be connected to which other remote UEs. Therefore, in an embodiment, the UE can know the destination ID before selecting the relay UE. In addition, in an embodiment, the UE can select the relay UE and then ask the relay UE which other UEs are connected. In addition, in an embodiment, it is also possible that the UE does not know the target IP. In this case, the selection of the relay UE is random. In addition, in an embodiment, the UE-to-UE relay can be a unicast link or broadcast to all connected remote UEs.

[0281] It is worth noting in this regard that in UE-to-UE relay, U2N discovery cannot be fully reused because the target ID may be lost. The target ID of the target UE does not need to be known in advance. In Mode B, the source UE can ask "who is there" to discover this.

[0282] The embodiment provides auxiliary information in PC5.

[0283] An embodiment provides a list of target UEs.

[0284] The embodiment defines the content of the relay UE response in the Mode B (Who's There) discovery message.

[0285] In an embodiment, the relay UE may only forward the discovery message from the source UE to the target UE.

[0286] In an embodiment, the relay UE may modify the discovery message (eg, source ID) and then forward the modified discovery message to the target UE.

[0287] An embodiment provides a relay indication flag, wherein if the flag is true, the message may be relayed.

[0288] In an embodiment, the remote UE may obtain a list of possible relay nodes from the U2N, wherein the UE may select a relay UE from the possible relay UEs in the list.

[0289] 2.2 Example 1-Discovery

[0290] It is worth noting that, although the following embodiments are described by referring to examples of relay selection and single-hop scenarios, the embodiments described below are also applicable to relay reselection and / or multi-hop scenarios.

[0291] In the example, three options are found:

[0292] - The source UE initiates discovery,

[0293] - The target / destination UE initiates discovery, and / or

[0294] -Relay UE initiates discovery.

[0295] 2.2.1 Example 1.1: Discovery process for UE-to-UE relay

[0296] The embodiments solve the problem of UE to UE endpoint (or UE to UE relay scenario), ie how the source UE knows the most suitable relay UE to reach a specific target UE. Furthermore, the embodiments allow the source UE to select the correct relay UE.

[0297] In an embodiment, a source UE sends a "Reverse Discovery Message" to request a relay to connect with a specific UE.

[0298] Note that this process is applicable to in-coverage, out-of-coverage, and PC5; L2 and L3 relaying and Mode 1 and Mode 2 resource allocation (see [1] Mode A (“I am here”) and Mode B (“Who is here”)).

[0299] In an embodiment, discovery may be initiated by one of the following:

[0300] - source UE,

[0301] - target UE,

[0302] - Relay UE,

[0303] -gNodeB (trigger discovery).

[0304] Fig.16 FIG. 1 shows a schematic diagram of a U2U relay. In particular, Fig.16 , five UEs are shown, exemplarily assuming that the first UE 202 is connected to the second UE 204 and the fourth UE 204 via corresponding PC5 links, wherein the second UE 204 is connected to the third UE 206 and the fifth UE 210 via corresponding PC5 links. In this case, the second UE 204 can act as a U2U relay for the first UE 202 as a source UE, which wants to communicate with the third UE 206 as a target UE.

[0305] In an embodiment, when a source UE (which may be within or outside the coverage of a gNodeB) decides to connect to a target UE via a UE-to-UE relay (e.g., it has lost the PC5 connection to the target UE), it first broadcasts / multicasts its request (Mode B discovery) to find potential UE-to-UE relays in its vicinity. Among these relays, some may be good candidates (e.g., they have already discovered the target UE, discovered the target UE based on a discovery message, or they have already established a PC5 connection with the target UE). At this stage, the source UE compares the radio signal strength measurements of the "Side Link Discovery Response Messages" received from different UE-to-UE relays and selects the best UE-to-UE relay based on a threshold preconfigured or signaled by the gNodeB. In addition to RSRP, other criteria are possible. See Example 2.1: Selection criteria for SL relays for details.

[0306] In an embodiment, after the PC5 connection is established, the UE-to-UE relay can maintain a list of remote UE (source and target) IDs in case another source UE intends to establish a connection with them. Therefore, one source UE may be the target UE of another source UE. In this way, the signaling between the UE-to-UE relay and the remote UE can be reduced.

[0307] In an embodiment, if the relay UE is within the coverage area, a list of connected and discovered remote UEs may also be sent to the gNodeB to assist other remote UEs in selecting the correct relay UE.

[0308] In addition, the gNodeB may assign a relay to a source UE or a target UE. The gNodeB may send additional assistance information to the remote UEs to enable them to find a suitable relay, for example, one or more of the selection criteria that may be used in the discovery response (see Section 2.3.1, Example 2.1: Selection criteria for SL relays).

[0309] In an embodiment, in a coverage scenario, a source UE in coverage can inform the gNodeB of discovery, can receive the configuration of discovery from the gNodeB and obtain information about relay selection. The gNodeB or UE can make a decision with the help of auxiliary information (e.g., from the gNodeB or relay UE) to help find an appropriate relay UE. The UE in coverage can also query the gNB for known relays before sending any discovery. For example, this may allow whitelisting or blacklisting relays based on policy or security settings.

[0310] In an embodiment, in an out-of-coverage scenario, a UE (eg, source UE) may autonomously select a relay UE based on preconfigured parameters (one or more). The preconfiguration may also be obtained from a previous connection with a gNodeB, which is valid for a certain period of time.

[0311] In an embodiment, in a partial coverage scenario, at least one of the UEs is out of coverage and at least one of the UEs is in coverage. In this case, the devices in coverage are able to receive parameters from the gNodeB, while the devices out of coverage rely on pre-configured parameters or parameters saved from a previous connection with the gNodeB.

[0312] In an embodiment, the source UE may also discover a target group (= a group of UEs) which may be identified by a group ID, instead of a single target UE. A relay node (or relay UE) may be a member of this group.

[0313] 2.2.2 Example 1.2: Source UE initiates discovery process (out-of-coverage scenario)

[0314] In addition to Embodiment 1.1: Discovery process for UE to UE relay, a remote UE may also initiate a discovery process. This may be particularly useful if the UE has no other connection at all (out of coverage). The remote UE then sends information about the type of application or group it wants to join. It may include an indication of whether it wants to communicate with the network or other UEs or both.

[0315] In an embodiment, other UEs, such as UE-to-UE relays, may respond to the message informing it that it can satisfy the remote UE's request and connect it to other UEs or networks if the UE is a U2N relay and is within coverage.

[0316] In addition to the discovery process described in Section 1.4 (UE-to-UE relaying information from TR), another alternative can be as follows:

[0317] In an embodiment, it is assumed that a UE-to-UE relay UE has a list of connected / discovered remote UEs (source or target or target group) or even other relay UEs.

[0318] In an embodiment, a source UE not connected to a relay UE broadcasts / multicasts a discovery message containing a target UE L2 ID (Mode B). All potential relay UEs will receive this discovery message, and relay UEs connected to the target UE will respond to the source UE.

[0319] Fig.17 FIG. 2 shows a schematic diagram of a source UE initiating a discovery process. Fig.17 As shown in the exemplary embodiment, the source UE 202 may send a broadcast discovery with a target layer 2 ID to the first and second potential relay UEs 206 and 208, wherein only the first potential relay UE 206 is connected to the target UE 204 described by the target layer 2 ID. Thus, the potential relay UEs may have a list of remote UEs to which they are connected or can be connected.

[0320] Since the relay UE already has a connection to the target UE (ie PC5), there is no need to relay a discovery message or initiate a discovery procedure to discover the target UE.

[0321] To make an informed decision, the relay UE may request the connected UE for its supported application IDs, and thus may choose to forward the discovery message from the source UE to the target UE if the application ID does not match the remote UE's current supported ID list.

[0322] 2.2.3 Example 1.3: Relay UE initiates discovery process

[0323] In an embodiment, it is assumed that a UE-to-UE relay UE has a list of connected remote UEs (source or target).

[0324] In an embodiment, the relay UE may periodically broadcast / multicast discovery messages (mode A) to receive discovery response messages from remote UEs. Based on RRSI and / or other criteria, the relay UE may add appropriate UEs (L2 IDs) to its list of "available" remote UEs.

[0325] If the L2 ID in its list matches the L2 ID to which the source UE is to connect, a PC5 connection can be established.

[0326] 2.2.4 Example 1.4: Contents of the Discovery (Response) Message

[0327] In an embodiment, the target UE information may be placed in the discovery message from the relay UE.

[0328] Regarding discovery, [1] mentions: "Alternative 2: UE-to-UE relay discovery and selection is integrated into the Mode B (“who’s there”) direct discovery process."

[0329] This alternative could also actually have a list of connected / discovered UEs in the relay to respond to requests faster (without explicit discovery).

[0330] In an embodiment, the discovery (response) message sent by the relay UE may include additional information about the remote UE. The relay UE saves a list of all discovered (and not timed out) remote UEs supporting the relay UE, a list of all remote UEs with active PC5 connections to the relay UE, and additional data from the remote UE configuration and capabilities.

[0331] In an embodiment, the list of remote UEs (target UEs from the relay's perspective) may include at least one of the following information for each remote UE:

[0332] - Supported application IDs,

[0333] - Activity Group ID,

[0334] - RSSI readings,

[0335] - L2 ID (see [6] - e.g. source / destination L2 ID),

[0336] - UE type (e.g. bicycle, car, pedestrian, industrial machine),

[0337] -UE speed or mobility indication,

[0338] -UE position (relative or absolute).

[0339] If the relay UE receives a discovery message mode B ("Who's there"), the relay UE may - instead of forwarding the message - directly reply with a list of remote UEs that are possible target UEs discovered by the source UE.

[0340] If the remote UE in the list has "disappeared", the PC5 RLF between the source and target UE captures the resolution.

[0341] Since the source UE knows the relay, the relay can also inform the source UE of the RLF between the relay UE and the target UE.

[0342] The relay may include information that facilitates relay selection, such as one or more of the following:

[0343] - Relay remaining power or low battery status indication,

[0344] -Relay DRX configuration,

[0345] - the number of connected UEs,

[0346] - a list of remote UEs (e.g. in case of multi-hop operation, for each UE the list may include the number of hops and the maximum number of hops),

[0347] - a list of source UEs (e.g. in case of multi-hop operation, for each UE the list may include the number of hops and the maximum number of hops),

[0348] - List of supported service application IDs,

[0349] - a list of supported groups, or a special indication that all groups are supported,

[0350] - List of supported PLMNs and / or SNPNs.

[0351] If the relay is initiating a discovery process (Example 1.3: Relay UE initiates discovery process) or generally needs to send a discovery message, such as forwarding discovery information from a source UE to a target UE, such relay information can be sent by the relay on the discovery message. In the case where other nodes initiate the discovery process (Example 1.2: Source UE initiates discovery process (out-of-coverage scenario) and Example 2.1: Selection criteria for SL relay): Relay information can be sent in response to a discovery message. The discovery message can also be sent as a broadcast message with additional information to keep the original discovery message compact.

[0352] 2.3 Example 2 - (Re)selection

[0353] 2.3.1 Example 2.1: Selection criteria for SL relay

[0354] In an embodiment, discovery may be initiated by one of the following:

[0355] - source UE,

[0356] - target UE,

[0357] - Relay UE,

[0358] -gNodeB (trigger discovery).

[0359] In an embodiment, the decision which relay to use is made by the source UE, the target UE or the gNodeB. However, the relay may overrule the decision based on security parameters, network policies or internal settings (e.g. a relay UE may reject a relay connection in the following cases: low battery, too many UEs, blacklisted devices (UEs on the blacklist due to "bad" behavior, etc.). This is a local setting of the relay UE. Regarding SL relays, no signaling of the battery status is sent to the gNodeB yet). The rejected request may have been signaled by the relay during the discovery phase or at a later stage. The relay UE may inform the gNodeB of the decision and may "deregister" as a relay node.

[0360] Internal settings can be one or more of the following:

[0361] - Blacklist of blocked UEs,

[0362] - settings from the top,

[0363] - Unsupported App IDs (app ids are known to increase the load and relays are not willing to do that)

[0364] -Battery status,

[0365] - Load (similar to selection criteria).

[0366] In general, all criteria / events for selection may result in a relay UE being unable / unwilling to act as a relay UE, even if assigned by a gNodeB. Further handling of this situation is required.

[0367] The parameters / information / events considered in the (re)selection criteria may be at least one of the following:

[0368] RSRP thresholds, such as minimum and maximum RSRP thresholds,

[0369] o The threshold may apply to both radio links: source UE-relay UE and / or target UE-relay UE,

[0370] oThese two thresholds can be set separately or together;

[0371] Load, e.g. relay UE load (to avoid relay UE overload),

[0372] o A threshold value may be defined, such as an upper limit on the load of the relay UE.

[0373] o Load can be based on the number of remote UEs connected, the processing power or resource indicator required to handle the connections,

[0374] o It is also possible to use internal system parameters available to the modem, such as free memory, (chip) temperature, power consumption, etc.;

[0375] The number of remote UEs connected to this relay UE;

[0376] ·The supported data rate of the relay UE;

[0377] UE capabilities (e.g. energy saving, coverage enhancement, etc.);

[0378] Relay UE: Maximum number of source and / or target UEs or UE-to-UE relay links to be supported;

[0379] ·Through senior management;

[0380] RRC messages;

[0381] RLF (for reselection).

[0382] These criteria can also be used for the (re)selection of relays.

[0383] 2.3.2 Example 2.2: Relay Reselection

[0384] In an embodiment, when a remote UE selects a U2U relay UE, there is reason to select another relay. Termination and reselection of a new relay may be initiated by:

[0385] - source UE,

[0386] - target UE,

[0387] - Relay UE, and / or

[0388] -gNodeB (trigger discovery) (e.g., applicable to scenarios with in-coverage or partial coverage).

[0389] In an embodiment, a connected remote UE wishes to select a new relay based on channel quality or other measurements or indications and performs SL relay discovery. Selection of a suitable new U2U relay is then prepared (since only one relay can be connected currently).

[0390] In an embodiment, the remote UE tells the current relay UE and / or the base station (eg, gNodeB (if within coverage)) that it will reselect and connect to a different relay UE with a specific ID.

[0391] In an embodiment, the relay UE takes this information into account and informs this UE and / or the base station (e.g. gNodeB) of the reselection. This information may be independent of further messages from the reselection remote UE to another remote UE, but may also be tied to a specific (last) message sent.

[0392] In an embodiment, a (connected) remote UE (e.g., target UE) notifies the relay UE and / or base station (e.g., gNodeB) that it is selecting a new relay UE so that the relay UE can indicate this to other remote UEs (e.g., source UEs) trying to contact the remote UE so that they can switch / select / discover the same new relay UE, or try to discover the remote UE directly.

[0393] In an embodiment, this "relay UE modification" information may include, for example, a timestamp and an ID of the new relay UE, so that the target and source UEs may be changed to the new relay UE at the same point in time.

[0394] In an embodiment, the same process may be applied to the source UE.

[0395] In an embodiment, the relay UE may send, for example, a measurement report using "assistance information" or any other format to inform the source and target UEs, for example, of signal strength / quality. Based on a threshold (for example, typically the threshold may be a minimum threshold and a maximum threshold), the source and / or target UE may initiate a relay UE change procedure.

[0396] In an embodiment, the reason for reselection of the relay may be at least one or more of the following:

[0397] - RSRP is below or above a threshold (min / max),

[0398] - Insufficient QOS parameters, for example:

[0399] oHigh transmission / packet / forwarding latency,

[0400] o Fragmented packets,

[0401] o Low data rates,

[0402] o Limited,

[0403] - the load on the relay node (e.g. number of connected UEs, data rate, processing, low memory),

[0404] - indication of the (low) battery status,

[0405] -Instructed by the top management,

[0406] - Based on other events, the relay UE wishes to stop the relay service.

[0407] In an embodiment, a relay UE may wish to stop providing relay services because its own applications require a higher quality of service, such as V2X fleet control. This may also be triggered by higher layers, such as applications that require a lot of processing power, low latency or other QoS characteristics. A relay UE may stop providing services if it moves from IC to OOC because it cannot coordinate itself. This may be due to a lack of capabilities, limited processing power and memory, limited measurement capabilities, or any other attribute of the UE.

[0408] In an embodiment, in a coverage scenario, all information about relay termination, reselection and timing can be shared with a base station (e.g., gNodeB) to enable proper control of resources and selection criteria, thereby helping remote UEs to discover / select and / or schedule resources accordingly.

[0409] 2.3.3 Example 2.3: Termination and rediscovery of relay triggering

[0410] In an embodiment, a UE-to-UE relay may have emergency reasons to terminate its operation as a relay, for example:

[0411] Critical battery level,

[0412] Restart of the operating system;

[0413] Hardware failure, and / or

[0414] Reconfigure (disable relay operation).

[0415] In an embodiment, in case a UE-to-UE relay needs to complete its relay operation, it should send a message to the source and target UEs that are using this relay. This message can be broadcast, multicast or unicast.

[0416] In an embodiment, the message may indicate an imminent termination and may include how long the relay operation may still continue. An immediate termination (0 ms remaining) may also be indicated.

[0417] In an embodiment, when the source UE or target UE receives the relay termination message, they can start the discovery process again or use the previously acquired information to perform reselection. A special code can be sent to the new relay to indicate that the affected UE is trying to reestablish the previous operating connection.

[0418] 2.4 Further Examples

[0419] The various elements and features of the present invention can be implemented in hardware using analog and / or digital circuits, can be implemented in software by executing instructions through one or more general or special processors, or as a combination of hardware and software. For example, embodiments of the present invention can be implemented in the environment of a computer system or another processing system. Fig.18 An example of a computer system 500 is shown. These units or modules and the method steps performed by these units can be executed on one or more computer systems. The computer system 500 includes one or more processors 502, such as special purpose or general purpose digital signal processors. The processor 502 is connected to a communication infrastructure 504, such as a bus or network. The computer system 500 includes a main memory 506, such as a random access memory (RAM), and a secondary memory 508, such as a hard drive and / or a removable storage drive. The secondary memory 508 can allow computer programs or other instructions to be loaded into the computer system 500. The computer system 500 can also include a communication interface 510 to allow software and data to be transmitted between the computer system 500 and external devices. The communication can be in the form of electronic, electromagnetic, optical or other signals that can be processed by the communication interface. The communication can use wires or cables, optical fibers, telephone lines, cellular phone links, RF links and other communication channels 512.

[0420] The terms "computer program medium" and "computer readable medium" are generally used to refer to tangible storage media, such as a removable storage unit or a hard disk installed in a hard drive. These computer process products are a means of providing software to the computer system 500. Computer programs, also known as computer control logic, are stored in the main memory 506 and / or the secondary memory 508. The computer program can also be received via the communication interface 510. When the computer program is executed, the computer system 500 is enabled to implement the present invention. In particular, when the computer program is executed, the processor 502 is enabled to implement the process of the present invention, such as any method described in the present invention. Accordingly, such a computer program can represent a controller of the computer system 500. In the case of using software to implement the disclosure, the software can be stored in a computer program product and loaded into the computer system 500 using an interface of a removable storage drive, such as the communication interface 510.

[0421] The implementation in hardware or software can be performed using a digital storage medium, such as cloud storage, floppy disk, DVD, Blu-ray, CD, ROM, PROM, EPROM, EEPROM or flash memory, which has electronically readable control signals stored thereon, which cooperate with (or can cooperate with) a programmable computer system to perform the corresponding method. Therefore, the digital storage medium can be computer-readable.

[0422] Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

[0423] Generally, embodiments of the present invention can be implemented as a computer program product with a program code, when the computer program product runs on a computer, the program code is operative to perform one of the methods.For example, the program code can be stored on a machine readable carrier.

[0424] Other embodiments comprise a computer program for performing one of the methods described herein, stored on a machine readable carrier. In other words, therefore, an embodiment of the inventive method is a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

[0425] Therefore, a further embodiment of the method of the present invention is a data carrier (or a digital storage medium or a computer-readable medium) comprising a computer program recorded thereon for performing one of the methods described herein. Therefore, a further embodiment of the method of the present invention is a data stream or a signal sequence representing a computer program for performing one of the methods described herein. For example, the data stream or signal sequence can be configured to be transmitted via a data communication connection, such as via the Internet. Further embodiments include processing means, such as a computer or a programmable logic device configured to or adapted to perform one of the methods described herein. Further embodiments include a computer having installed thereon a computer program for performing one of the methods described herein.

[0426] In some embodiments, a programmable logic device (e.g., a field programmable gate array) may be used to perform some or all of the functions of the methods described herein. In some embodiments, a field programmable gate array may be used in conjunction with a microprocessor to perform one of the methods described herein. Typically, the method is preferably performed by any hardware device.

[0427] The above embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to other persons skilled in the art. Therefore, it is intended that the present invention be limited only by the scope of the forthcoming patent claims and not by the specific details presented herein by way of description and explanation of the embodiments.

[0428] References

[0429] [1]TR 23.752v17.0.0-Study on system enhancement for Proximity basedServices in 5G System

[0430] [2]TR 38.836v17.0.0-Study on Sidelink Relay Rel-17

[0431] [3]TS 23.303v17.0.0-Proximity-based services(ProSe)

[0432] [4]TS 38.300v17.0.0-NR Overall Description-Discovery

[0433] [5]TS 23.287v17.3.0-Architecture enhancements for 5G System(5GS)tosupport Vehicle-to-Everything(V2X)servicesV2X Architecture

[0434] [6]TS 38.331v17.1.0-NR; Radio Resource Control (RRC); Protocol specification

[0435] abbreviation

[0436] 3GPP Third Generation Partnership Project

[0437] ACK

[0438] AIM auxiliary information message

[0439] AMF Access and Mobility Management Function

[0440] BS Base Station

[0441] BWP Bandwidth Part

[0442] CA Carrier Aggregation

[0443] CC Component Carrier

[0444] CBG Coded Block Group

[0445] CBR Channel Busy Rate

[0446] CQI Channel Quality Indicator

[0447] CSI-RS Channel State Information Reference Signal

[0448] CN Core Network

[0449] D2D Device to Device

[0450] DAI Downlink Allocation Index

[0451] DCI Downlink Control Information

[0452] DL Downlink

[0453] DRX Discontinuous Reception

[0454] FFT Fast Fourier Transform

[0455] FR1 Frequency Range 1

[0456] FR2 Frequency Range 2

[0457] GMLC Gateway Mobile Location Center

[0458] gNB Evolved Node B (NR base station) / Next Generation Node B base station

[0459] GSCN Global Synchronization Channel Number

[0460] HARQ Hybrid Automatic Repeat Request

[0461] IC Coverage

[0462] ICS Initial Cell Search

[0463] IoT

[0464] LCS Location Services

[0465] LMF location management function

[0466] LPP LTE Positioning Protocol

[0467] LTE Long Term Evolution

[0468] MAC Medium Access Control

[0469] MCR Minimum communication range

[0470] MCS Modulation and Coding Scheme

[0471] MIB Master Information Block

[0472] NACK Negative Acknowledgement

[0473] NB Node B

[0474] NES Network Energy Saving

[0475] NR New Radio

[0476] NTN Non-Terrestrial Network

[0477] NW Network

[0478] OFDM Orthogonal Frequency Division Multiplexing

[0479] OFDMA Orthogonal Frequency Division Multiple Access

[0480] OOC Out of coverage

[0481] PBCH Physical Broadcast Channel

[0482] P-UE Pedestrian UE; not limited to pedestrian user equipment, but refers to any UE with energy saving requirements, such as electric vehicles, cyclists

[0483] PC5 Interface for D2D communication using sidelink channel

[0484] PDCCH Physical Downlink Control Channel

[0485] PDSCH Physical Downlink Shared Channel

[0486] PLMN Public Land Mobile Network

[0487] PPP Point-to-Point Protocol

[0488] PPP Precision Point Positioning

[0489] PRACH Physical Random Access Channel

[0490] PRB Physical Resource Block

[0491] ProSe Proximity Services

[0492] PSFCH Physical Sidelink Feedback Channel

[0493] PSCCH Physical Sidelink Control Channel

[0494] PSSCH Physical Sidelink Shared Channel

[0495] PUCCH Physical Uplink Control Channel

[0496] PUSCH Physical Uplink Shared Channel

[0497] RAIM Receiver Autonomous Integrity Monitoring

[0498] RAN Radio Access Network

[0499] RAT Radio Access Technology

[0500] RB Resource Block

[0501] RNTI Radio Network Temporary Identifier

[0502] RP Resource Pool

[0503] RRC Radio Resource Control

[0504] RS Reference Symbol / Signal

[0505] RTT Round Trip Time

[0506] SBI Service-Based Interface

[0507] SCI Side Link Control Information

[0508] SI System Information

[0509] SIB Side Link Information Block

[0510] SL Side Link

[0511] SPI System Presence Indicator

[0512] SSB Synchronous Signal Block

[0513] SSR State Space Representation

[0514] TB Transfer Block

[0515] TTI short transmission time interval

[0516] TDD Time Division Duplex

[0517] TDOA Time Difference of Arrival

[0518] TIR target integrity risk

[0519] TRP Transmit Receive Point

[0520] TTA Alarm Time

[0521] TTI Transmission Time Interval

[0522] U2N UE to Network

[0523] U2U UE to UE

[0524] UCI Uplink Control Information

[0525] UE User equipment, such as a smartphone or IoT node

[0526] UL Uplink

[0527] UMTS Universal Mobile Telecommunications System

[0528] V2x

[0529] V2V Vehicle to Vehicle

[0530] V2I Vehicle to Infrastructure

[0531] V2P Vehicle to Pedestrian

[0532] V2N Vehicle-to-Network

[0533] V-UE Vehicle UE

[0534] VRU Vulnerable Road User

[0535] WUS wake-up signal

Claims

1. A UE of a wireless communication system, in, The UE is configured to operate in a sidelink mode of operation, Therein, the UE is configured to send a discovery message for discovering one or more candidate relay UEs connected to or capable of connecting to a target UE or a group of target UEs, so as to establish a connection with the target UE or a group of target UEs via a UE-to-UE relay.

2. A UE as claimed in any preceding claim, in, The discovery message includes information about a target UE or a group of target UEs, a source UE, and / or other relevant information.

3. The UE as claimed in one of the preceding claims, in, The UE is configured to receive a discovery response message from one or more candidate relay UEs connected or capable of connecting to a target UE or a group of target UEs, The UE is configured to select a relay UE from one or more candidate relay UEs.

4. A UE as claimed in any preceding claim, in, The UE is configured to establish a connection with a target UE or a group of target UEs via the selected relay UE.

5. The UE according to any one of claims 3 to 4, in, The UE is configured to select a relay UE from one or more candidate relay UEs according to a selection criterion, The selection criteria are pre-configured or signaled by a base station of the wireless communication network, or configured by a higher layer.

6. A UE as claimed in any preceding claim, in, The selection criteria are at least one of the following: - the signal strength of the link between the UE and the corresponding relay UE, - the signal strength of the link between the corresponding relay UE and the target UE, - The load of the corresponding relay UE, - the number of remote UEs connected to the corresponding relay UE, - the data rate supported by the corresponding relay UE, - Capabilities of the corresponding relay UE, - Information received from higher levels, - received Radio Resource Control (RRC) messages, - one or more QoS parameters, -Signal strength of the discovery message.

7. A UE as claimed in any one of the preceding claims, in, The UE is configured to select a relay UE from one or more candidate relay UEs according to auxiliary information or control information received from the base station when the UE is within the coverage of a base station of the wireless communication system.

8. A UE as claimed in any one of the preceding claims, in, The UE is configured to, when the UE is within the coverage of a base station of the wireless communication system, send discovery messages only to those candidate relay UEs indicated by the control information received from the base station.

9. A UE as claimed in any one of the preceding claims, in, The UE is configured to, if a reselection criterion is met and / or in response to receipt of a reselection control message, select another relay UE for communicating with the target UE or a group of target UEs.

10. The UE according to claim 9, in, The UE is configured to select another relay from one or more candidate relays when a reselection criterion is met or in response to receipt of a reselection control message.

11. The UE according to claim 9, in, The UE is configured to, when a reselection criterion is met or in response to receipt of a reselection control message, send a further discovery message for discovering one or more candidate relay UEs connected or capable of connecting to the target UE or a group of target UEs, wherein the UE is configured to receive a further discovery response message from one or more candidate relay UEs connected or capable of connecting to the target UE or a group of target UEs, The UE is configured to select another relay UE from one or more candidate relay UEs.

12. The UE according to any one of claims 9 to 11, in, The UE is configured to send a reselection information message to the relay UE, the reselection information message notifying the relay UE of another relay UE selected to switch to another relay UE, Or wherein the UE is configured to send a reselection information message to the base station, the reselection information message notifying the base station of another relay UE selected and requesting the base station to coordinate handover to the selected another UE.

13. The UE according to any one of claims 9 to 12, in, The re-selection criteria are at least one of the following: -Signal strength of the link between the UE and the relay UE, - the signal strength of the link between the relay UE and the remote UE, - one or more QoS parameters, -Relay UE load, - Relay UE's battery status, - Information received from higher levels, - A control message received from the relay UE or the base station instructing the relay UE to stop the relay operation.

14. A relay UE of a wireless communication system, in, The relay UE is configured to operate in a sidelink operation mode, The relay UE is configured to receive a discovery message from a source UE, the discovery message indicating a target UE or a group of target UEs to which the source UE requests message relay, Among them, the relay UE is configured to send a discovery message response to the source UE when the relay UE is capable of relaying messages between the source UE and the target UE or a group of target UEs, and the discovery message response indicates that the relay UE is capable of relaying messages between the source UE and the target UE or a group of target UEs.

15. A relay UE as claimed in the preceding claim, in, The discovery message includes information about a target UE or a group of target UEs, a source UE, and / or other relevant information.

16. The relay UE according to any one of claims 14 to 15, in, The relay UE is configured to send a target UE or target UE group discovery message for discovering a target UE or a group of target UEs in response to receipt of the discovery message.

17. The relay UE according to claim 16, in, The relay UE is configured to send a discovery message response to the source UE in response to receiving a target UE or target UE group discovery message response from the target UE or a group of target UEs.

18. The relay UE according to any one of claims 14 to 15, in, the relay UE being configured to maintain a list of remote UEs to which the relay UE is connected or capable of connecting, The relay UE is configured to directly send a discovery message response to the source UE when the target UE is included in the list of remote UEs.

19. The relay UE according to claim 18, in, The relay UE is configured to share the list of remote UEs with a base station of the wireless communication network in case the relay UE is within the coverage of the base station.

20. The relay UE according to any one of claims 18 to 19, in, The relay UE is configured to send a remote UE discovery message for discovering a remote UE. The relay UE is configured to update the list of remote UEs according to a remote UE discovery response message received from the discovered remote UE.

21. The relay UE according to any one of claims 18 to 20, in, The relay UE is configured to save additional information about the remote UE in the list of remote UEs to further support relaying of messages and / or to reply to discovery messages.

22. A relay UE as claimed in any one of the preceding claims, in, The discovery response message further includes information about the target UE.

23. A relay UE as claimed in any one of the preceding claims, in, The discovery response message further includes a list of one or more remote UEs to which the relay UE is connected or can be connected.

24. A relay UE as claimed in the preceding claim, in, The discovery response message further includes information about the one or more remote UEs.

25. A relay UE as claimed in the preceding claim, in, For each of the one or more remote UEs, the information about the one or more remote UEs is at least one of: - Supported application IDs, -Activity Group ID - Received Signal Strength Indicator (RSSI) readings, - Address information, - UE type, -UE speed or mobility indication, - one or more QoS parameters, -UE location.

26. A relay UE as claimed in any one of the preceding claims, in, The discovery response message further includes information about the relay UE.

27. A relay UE as claimed in the preceding claim, in, The information about the relay UE is at least one of the following: - Relay the remaining charge or battery status of the UE, - Discontinuous Reception (DRX) configuration of the relay UE, - the number of remote UEs connected to the relay UE, - a list of remote UEs to which the relay UE is connected or can be connected, - List of supported service application IDs, - a list of supported groups or an indication that all groups are supported, - a list of supported Public Land Mobile Networks (PLMNs) and / or Standalone Non-Public Networks (SNPNs), - buffer status information, - Type of relay UE, - Network connection information, - one or more QoS parameters, - Channel Busy Rate (CBR) at the relay UE.

28. The relay UE according to any one of claims 14 to 27, in, The relay UE is configured to, when receiving a reselection information message from one of the source UE, the target UE and the base station, send another reselection information message to another of the source UE, the target UE and the base station, the reselection information message notifying the relay UE to switch to another relay UE, and the another reselection information message notifying the selected other relay UE.

29. The relay UE according to claim 28, in, The relay UE is configured to switch the traffic between the source UE and the target UE to another relay UE at the time indicated in the reselection information message.

30. The relay UE according to any one of claims 14 to 27, in, The relay UE is configured to send a relay reselection control message to the source UE and / or the target UE and / or the base station when the relay reselection criterion is met, and the relay reselection control message controls the source UE and / or the target UE and / or the base station to select another relay UE.

31. The relay UE according to claim 30, in, The relay reselection criteria is at least one of the following: -Signal strength of the link between the UE and the relay UE, - the signal strength of the link between the relay UE and the remote UE, - one or more QoS parameters, -Relay UE load, -Relay UE's battery status, - Information received from higher levels, - information or control messages from base stations, - Relay operation termination criteria.

32. A relay UE as claimed in any one of the preceding claims, in, The relay UE is configured to stop relaying if a relay operation termination criterion is reached.

33. The relay UE according to claim 32, in, The relay UE is configured to send a control message to the source UE and / or the target UE and / or the base station, instructing the relay UE to stop relaying when a relay operation termination criterion is reached.

34. The relay UE as claimed in any one of claims 32 and 33, in, The relay operation termination criteria is one of the following: -The critical power of the relay UE, - Restart of the operating system of the relay UE, - Hardware failure of the relay UE, - Reconfiguration of relay UE, - one or more QoS parameters, -Relay UE load, - Relay UE's battery status, - Information received from higher levels, - information or control information from a base station, - Relay operation termination criteria.

35. A target UE of a wireless communication system, in, The target UE is configured to operate in a sidelink operation mode, The target UE is configured to communicate with the source UE of the wireless communication network via the relay UE of the wireless communication network, The target UE is configured to, when the reselection criteria are met, -Reselect another relay UE - Alternatively, a relay reselection control message is sent to the source UE, where the relay reselection control message controls the source UE and / or the base station to select another relay UE.

36. The target UE according to claim 35, in, The reselection criteria are at least one of the following: -Signal strength of the link between the UE and the relay UE, - the signal strength of the link between the relay UE and the remote UE, - one or more QoS parameters, -Relay UE load, - Relay UE's battery status, - Information received from higher levels, - A control message received from the relay UE instructing the relay UE to stop the relay operation.

37. The target UE according to claim 35, in, The target UE is configured to reselect another relay by sending a discovery message for discovering one or more candidate relay UEs that are connected or capable of connecting to the source UE, Therein, the target UE is configured to select another relay UE from one or more candidate relay UEs that are connected to or can be connected to the source UE.

38. The target UE according to claim 37, in, The target UE is configured to reselect another relay UE from one or more candidate relay UEs according to a selection criterion.

39. The target UE according to any one of claims 37 to 38, in, The target UE is configured to send a reselection information message to the relay UE, the reselection information message notifying the relay UE of another relay UE selected to switch to another relay UE, Or wherein the target UE is configured to send a reselection information message to the base station, the reselection information message notifying the base station of another relay UE selected and requesting the base station to coordinate handover to the selected another UE.

40. A wireless communication system, comprising: The source UE as claimed in any one of claims 1 to 13, The relay UE as claimed in any one of claims 14 to 34, and A target UE as claimed in any one of claims 35 to 38.

41. A method for operating a UE of a wireless communication system, the method comprising: operating the UE in a sidelink operation mode, A discovery message is sent for discovering one or more candidate relay UEs connected or capable of connecting to a target UE or a group of target UEs, for establishing a connection with the target UE or a group of target UEs via a UE-to-UE relay.

42. A method for operating a relay UE of a wireless communication system, the method comprising: operating a relay UE in a sidelink operation mode, receiving a discovery message from a source UE, the discovery message indicating a target UE or a group of target UEs to which the source UE requests message relay, In case the relay UE is capable of relaying messages between the source UE and the target UE or a group of target UEs, a discovery message response is sent to the source UE, the discovery message response indicating that the relay UE is capable of relaying messages between the source UE and the target UE or a group of target UEs.

43. A method for operating a target UE of a wireless communication system, the method comprising: operating the target UE in a sidelink operation mode, communicating with a source UE of a wireless communication network via a relay UE of the wireless communication network, When the reselection criterion is met, another relay UE is reselected or a relay reselection control message is sent to the source UE, and the relay reselection control message controls the source UE to select another relay UE.

44. A computer program for performing the method as claimed in any one of claims 41 to 43 when the computer program is run on a computer, a microprocessor or a software defined radio.

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