Security for sidelink (SL) multi-hop UE-to-network (U2N) relay discovery

Abstract

Embodiments include methods for a first user equipment (UE) arranged to discover intermediate UE-to-network (U2N) relays that facilitate access to a communication network via a U2N relay. Such methods include obtaining the following security material from the first UE's home public land mobile network (HPLMN): relay discovery security materials associated with a second UE configured to operate as the U2N relay, and intermediate relay discovery security materials associated with a third UE configured to operate as an intermediate U2N relay between the first UE and the second UE. Such methods include receiving from the third UE a message associated with multi-hop relay discovery. The message includes a first portion generated by the third UE and a second portion generated by the second UE. Such methods include verifying the first portion based on the intermediate relay discovery security materials and the second portion based on the relay discovery security materials and, based on successful verification of the first and second portions, processing the content of the message.

Description

[0001] SECURITY FOR SIDELINK (SL) MULTI-HOP UE-TO-NETWORK (U2N) RELAY DISCOVERY

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to wireless networks and devices, and more specifically to techniques that enable user equipment (UEs) to securely discover a multi-hop path of relay UEs that facilitate UE communication with a wireless network.

[0004] BACKGROUND

[0005] Currently the fifth generation (5G) of cellular systems, also referred to as New Radio (NR), is being standardized within the Third-Generation Partnership Project (3GPP). NR is developed for maximum flexibility to support multiple and substantially different use cases. These include enhanced mobile broadband (eMBB), machine type communications (MTC), ultra-reliable low latency communications (URLLC), side-link device-to-device (D2D), and several other use cases. NR was initially specified in 3GPP Release 15 (Rel-15) and continues to evolve through subsequent releases, such as Rel-16 and Rel-17.

[0006] 5G / NR technology shares many similarities with fourth-generation Long-Term Evolution (LTE). For example, NR uses CP-OFDM (Cyclic Prefix Orthogonal Frequency Division Multiplexing) in the downlink (DL) from network to user equipment (UE), and both CP-OFDM and DFT-spread OFDM (DFT-S-OFDM) in the uplink (UL) from UE to network. As another example, NR DL and UL time-domain physical resources are organized into equal-sized 1-ms subframes. A subframe is divided into multiple slots of equal duration, with each slot including multiple OFDM-based symbols. Even so, time-frequency resources can be configured much more flexibly for an NR cell than for an LTE cell.

[0007] Sidelink (SL) is a type of device-to-device (D2D) communication whereby UEs can communicate with each other directly rather than indirectly via a 3GPP RAN. The first 3GPP standardization of SL was in LTE Rel-12 targeting public safety use cases and proximity-based services (ProSe). Since then, a number of enhancements have been introduced to broaden the use cases that could benefit from D2D technology. For example, the D2D extensions in LTE Rel-14 and Rel-15 include supporting vehicle-to-everything (V2X) communication.

[0008] 3GPP Rel-16 specifies the NR SL interface. NR Rel-16 SL targets advanced V2X services, which can be categorized into four use case groups: vehicles platooning, extended sensors, advanced driving, and remote driving. The advanced V2X services require anew SL in order to meet the stringent requirements in terms of latency and reliability. The NR SL is designed to provide higher system capacity and better coverage, and to allow for extension to support the future development of even more advanced V2X services and other related services. Broadcast, groupcast, and unicast transmissions are desirable for the services targeted by NR SL. In groupcast (or multicast), the intended receiver of a message consists of only a subset of the possible recipients in proximity to the transmitter, whereas a unicast message is intended for only one recipient in proximity to the transmitter. For example, in the platooning service there are certain messages that are only of interest of the members of the platoon, for which groupcast can be used. Unicast is a natural fit for use cases involving only a pair of vehicles.

[0009] Two UE-based SL relay capabilities were studied for NR Rel-17: UE-to-Network (U2N) relay, where a UE extends the network connectivity to another nearby UE by using direct communication; and UE-to-UE (U2U) relay, where a UE uses two direct communication links to connect two UEs in its proximity that otherwise are not able to communicate.

[0010] 3GPP TR 23.752 (v2.0.0) section 6.10 describes ProSe 5G U2U Relay. A ProSe 5G U2U Relay is a (5G ProSe-enabled) UE that provides functionality to support connectivity between 5G ProSe U2U UEs. For UE-to-UE relay use cases, the source UE, the target UE, and the UE-to-UE relay may be in or out of 3GPP coverage. 3GPP TR 33.740 (v0.2.0) describes a security solution for PC5 links between source UE, U2U relay, and target UE when the U2U relay is in 3GPP coverage.

[0011] Typically, 5G ProSe UEs initially discover each other via 5G Prose Discovery procedure, then trigger ProSe Communication (aka PC5 link) establishment for each other. In other scenarios, 5G ProSe U2U Relay Communication is triggered without an explicit discovery procedure, but rather the discovery information is embedded into a PC5 link establishment request.

[0012] Each 5G ProSe discovery or direct communication message includes a specific code: a ProSe Restricted Code in the case of ProSe direct discovery or communication and a Relay Service Code (RSC) in the case of ProSe U2N relay. There is a one-to-one association between codes and security materials, e.g., each RSC is associated with a corresponding set of security materials including Code-Sending Security Parameters and Code-Receiving Security Parameters.

[0013] As described in 3GPP TR 23.700-03 (vO. 1.0), some ProSe enhancements being considered for Rel-19 include support of multi -hop U2U and U2N relaying, including layer-2 (L2) and layer- 3 (L3) relaying. In multi-hop U2N relaying, two endpoint UEs of the relaying path are referred to as “Remote UE” and “U2N Relay”, while the intermediate relays are referred to as “Intermediate U2N Relay” or more simply “Intermediate Relay.” Likewise, for multi-hop U2U relaying, two endpoint UEs of relaying path are referred to as “source end UE” and “target end UE”, or more generically “end UEs,” while the intermediate relays are referred to as “U2U Relays.” SUMMARY

[0014] To support multi -hop U2N relaying, a remote UE can discover a U2N Relay via one or more proximate Intermediate U2N Relays. These discovery messages used to discover either a proximate Intermediate U2N Relay or a target U2N Relay via a proximate Intermediate U2N Relay need to be security protected. Failure to protect the security of these discovery messages for multi-hop U2N relaying may lead to various attacks by unauthorized UEs, such as discovery message manipulation, replay, and / or capture of private or sensitive user information. Currently, however, there are no security mechanisms specified for these discovery messages used in multihop U2N relaying. Similar problems and / or difficulties exist for multi-hop U2U relaying.

[0015] An object of embodiments of the present disclosure is to provide, enable, and / or facilitate solutions to exemplary problems summarized above and described in more detail below, thereby improving security of multi-hop U2N relay discovery.

[0016] Embodiments include exemplary methods (e.g., procedures) for a first UE configured to discover intermediate U2N relays that facilitate access to a communication network via a U2N relay.

[0017] These exemplary methods include obtaining the following security material from the first UE’s PLMN: relay discovery security materials associated with a second UE configured to operate as the U2N relay, and intermediate relay discovery security materials associated with a third UE configured to operate as an intermediate U2N relay between the first UE and the second UE.

[0018] These exemplary methods also include receiving from the third UE a message associated with multi-hop relay discovery. The message includes a first portion generated by the third UE and a second portion generated by the second UE. These exemplary methods also include verifying the following: the first portion based on the intermediate relay discovery security materials associated with the third UE, and the second portion based on the relay discovery security materials associated with the second UE. These exemplary methods also include, based on successful verification of the first and second portions, processing the content of the message.

[0019] In some embodiments, the first portion includes a hop count that was generated by the second UE and updated by the third UE, and the second portion includes a relay service code (RSC). In some embodiments, the first UE is a Monitoring Remote UE and the message is an Announcement. In other embodiments, the first UE is a Discoverer Remote UE and the message is a Discovery Response.

[0020] Other variations of these exemplary methods are disclosed herein.

[0021] Other embodiments include exemplary methods (e.g., procedures) for a second UE configured to provide a U2N relay between intermediate U2N relays and a communication network. In general, these exemplary methods are complementary to the other exemplary methods summarized above.

[0022] These exemplary methods include obtaining the following security material from the second UE’s HPLMN relay discovery security materials associated with the second UE, and intermediate relay discovery security materials associated with a third UE configured to operate as an intermediate U2N relay. These exemplary methods also include receiving, from the third UE, a Discovery Solicitation message associated with multi-hop relay discovery. The Discovery Solicitation message includes a first portion generated by the third UE and a second portion generated by a first UE configured to operate as a Discoverer Remote UE. These exemplary methods also include verifying the following: the first portion based on the intermediate relay discovery security materials associated with the third UE, and the second portion based on the relay discovery security materials associated with the second UE. These exemplary methods also include based on successful verification of the first and second portions, processing the content of the Discovery Solicitation message.

[0023] Other variations of these exemplary methods are disclosed herein.

[0024] Other embodiments include exemplary methods (e.g., procedures) for a third UE configured to provide an intermediate U2N relay between remote UEs and a U2N relay coupled to communication network. In general, these exemplary methods are complementary to the other exemplary methods summarized above.

[0025] These exemplary methods include receiving a first message associated with multi-hop relay discovery. The first message includes a second portion generated by a message source UE and a first portion generated by one of the following: the message source UE, or a fourth UE arranged as an intermediate U2N relay between the message source UE and the third UE. These exemplary methods also include verifying the first portion based on one of the following: relay discovery security materials associated with a second UE arranged to provide the U2N relay, or intermediate relay discovery security materials associated with the fourth UE.

[0026] These exemplary methods also include verifying the second portion based on the relay discovery security materials associated with a second UE arranged to provide the U2N relay. These exemplary methods also include, based on successful verification of the first and second portions, updating the first portion and secures the updated first portion using the intermediate relay discovery security materials associated with the third UE. These exemplary methods also include sending a second message including the second portion and the secured updated first portion to one of the following: a message target UE, or a fifth UE arranged as an intermediate U2N relay between the message target UE and the third UE. In some embodiments, the first portion includes a hop count and the second portion includes a RS, and updating the first portion includes incrementing the hop count.

[0027] In some embodiments, the first and second messages are Announcement messages, and the message source UE is the second UE arranged as an Announcing U2N Relay. In other embodiments, the first and second messages are Discovery Response messages, and the message source UE is the second UE arranged as a Discoveree U2N Relay. In other embodiments, the first and second messages are Discovery Solicitation messages, and the message source UE is a first UE arranged as a Discoverer Remote UE.

[0028] Other variations of these exemplary methods are disclosed herein.

[0029] Other embodiments include UEs (e.g., wireless devices) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments include non-transitory, computer-readable media storing program instructions that, when executed by processing circuitry, configure such UEs to perform operations corresponding to any of the exemplary methods described herein.

[0030] These and other embodiments described herein may facilitate establishment of security on PC5 links used in multi-hop U2N relay arrangements, which facilitates end-to-end security between a remote UE and a U2N relay as well as hop-to-hop security between the remote UE, the intermediate U2N relay(s), and the U2N relay. At a high level, embodiments may improve discovery in multi-hop U2N relay arrangements, thereby improving SL functionality for UEs.

[0031] These and other objects, features, and advantages of embodiments of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 shows exemplary NR user plane (UP) and control plane (CP) protocol stacks.

[0034] Figure 2 illustrates a high-level view of an exemplary 5G / NR network architecture.

[0035] Figure 3 shows three exemplary network coverage scenarios for two UEs and a gNB serving a cell.

[0036] Figure 4 shows a reference architecture for 5G ProSe U2U relay.

[0037] Figure 5 shows an example scenario of multi-hop 5G ProSe U2N relay.

[0038] Figure 6 shows an example scenario of multi-hop 5G ProSe U2U relay.

[0039] Figure 7 shows signaling for a model A discovery procedure supporting multi-hop U2N relay, according to some embodiments of the present disclosure.

[0040] Figure 8 shows signaling for a model B discovery procedure supporting multi-hop U2N relay, according to some embodiments of the present disclosure. Figure 9 shows a flow diagram of an exemplary method for a first UE (e.g, wireless device), according to various embodiments of the present disclosure.

[0041] Figure 10 shows a flow diagram of an exemplary method for a second UE (e.g., wireless device), according to various embodiments of the present disclosure.

[0042] Figure 11 shows a flow diagram of an exemplary method for a third UE (e.g., wireless device), according to various embodiments of the present disclosure.

[0043] Figure 12 shows a communication system according to various embodiments of the present disclosure.

[0044] Figure 13 shows a UE according to various embodiments of the present disclosure.

[0045] DETAILED DESCRIPTION

[0046] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0047] In general, all terms used herein are to be interpreted according to their ordinary meaning to a person of ordinary skill in the relevant technical field, unless a different meaning is expressly defined and / or implied from the context of use. All references to a / an / the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise or clearly implied from the context of use. The operations of any methods and / or procedures disclosed herein do not have to be performed in the exact order disclosed, unless an operation is explicitly described as following or preceding another operation and / or where it is implicit that an operation must follow or precede another operation. Any feature of any embodiment disclosed herein can apply to any other disclosed embodiment, as appropriate. Likewise, any advantage of any embodiment described herein can apply to any other disclosed embodiment, as appropriate.

[0048] Furthermore, the following terms are used throughout the description given below:

[0049] • Radio Access Node: As used herein, a “radio access node” (or equivalently “radio network node,” “radio access network node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., gNB in a 3GPP 5G / NR network or an enhanced or eNB in a 3 GPP LTE network), base station distributed components (e.g, CU and DU), a high-power or macro base station, a low-power base station (e.g., micro, pico, femto, or home base station, or the like), an integrated access backhaul (IAB) node, a transmission point (TP), a transmission reception point (TRP), a remote radio unit (RRU or RRH), and a relay node.

[0050] • Core Network Node: As used herein, a “core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a serving gateway (SGW), a PDN Gateway (P-GW), a Policy and Charging Rules Function (PCRF), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a Charging Function (CHF), a Policy Control Function (PCF), an Authentication Server Function (AUSF), a location management function (LMF), or the like.

[0051] • Wireless Device: As used herein, a “wireless device” (or “WD” for short) is any type of device that is capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other wireless devices. Communicating wirelessly can involve transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information through air. Unless otherwise noted, the term “wireless device” is used interchangeably herein with the term “user equipment” (or “UE” for short), with both of these terms having a different meaning than the term “network node”.

[0052] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0053] • Network Node: As used herein, a “network node” is any node that is either part of the radio access network (e.g., a radio access node or equivalent term) or of the core network (e.g., a core network node discussed above) of a cellular communications network. Functionally, a network node is equipment capable, configured, arranged, and / or operable to communicate directly or indirectly with a wireless device and / or with other network nodes or equipment in the cellular communications network, to enable and / or provide wireless access to the wireless device, and / or to perform other functions (e.g, administration) in the cellular communications network.

[0054] • Node: As used herein, the term “node” (without prefix) can be any type of node that can in or with a wireless network (including RAN and / or core network), including a radio access node (or equivalent term), core network node, or wireless device. However, the term “node” may be limited to a particular type (e.g., radio access node, IAB node) based on its specific characteristics in any given context.

[0055] The above definitions are not meant to be exclusive. In other words, various ones of the above terms may be explained and / or described elsewhere in the present disclosure using the same or similar terminology. Nevertheless, to the extent that such other explanations and / or descriptions conflict with the above definitions, the above definitions should control.

[0056] Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is generally used. However, the concepts disclosed herein are not limited to a 3GPP system, and can be applied in any system that can benefit from the concepts, principles, and / or embodiments described herein.

[0057] Figure 1 shows an exemplary configuration of NR user plane (UP) and control plane (CP) protocol stacks between a UE (110), a gNodeB (gNB, e.g., base station, 120), and an access and mobility management function (AMF, 130) in a 5G core network (5GC). Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP) layers between the UE and the gNB are common to UP and CP. PDCP provides ciphering / deciphering, integrity protection, sequence numbering, reordering, and duplicate detection for both CP and UP, as well as header compression and retransmission for UP data.

[0058] On the UP side, Internet protocol (IP) packets arrive to PDCP as service data units (SDUs), and PDCP creates protocol data units (PDUs) to deliver to RLC. The Service Data Adaptation Protocol (SDAP) layer handles quality-of-service (QoS) including mapping between QoS flows and Data Radio Bearers (DRBs) and marking QoS flow identifiers (QFI) in UL and DL packets. RLC transfers PDCP PDUs to MAC through logical channels (LCH). RLC provides error detection / correction, concatenation, segmentation / reassembly, sequence numbering, reordering of data transferred to / from the upper layers. MAC provides mapping between LCHs and PHY transport channels, LCH prioritization, multiplexing into or demultiplexing from transport blocks (TBs), hybrid ARQ (HARQ) error correction, and dynamic scheduling (in gNB). PHY provides transport channel services to MAC and handles transfer over the NR radio interface, e.g., via modulation, coding, antenna mapping, and beam forming.

[0059] On the CP side, the non-access stratum (NAS) layer between UE and AMF handles UE / gNB authentication, mobility management, and security control. RRC sits below NAS in the UE but terminates in the gNB rather than the AMF. RRC controls communications between UE and gNB at the radio interface as well as the mobility of a UE between cells in the NG-RAN. RRC also broadcasts system information (SI) and performs establishment, configuration, maintenance, and release of DRBs and Signaling Radio Bearers (SRBs) and used by UEs. Additionally, RRC controls addition, modification, and release of carrier aggregation (CA) and dual-connectivity (DC) configurations for UEs, and performs various security functions such as key management.

[0060] After a UE is powered ON it will be in the RRC IDLE state until an RRC connection is established with the network, at which time the UE will transition to RRC CONNECTED state (e.g., where data transfer can occur). The UE returns to RRC IDLE after the connection with the network is released. In RRC IDLE state, the UE’s radio is active on a discontinuous reception (DRX) schedule configured by upper layers. During DRX active periods (also referred to as “DRX On durations”), an RRC IDLE UE receives SI broadcast in the cell where the UE is camping, performs measurements of neighbor cells to support cell reselection, and monitors a paging channel on physical DL control channel (PDCCH) for pages from 5GC via gNB. A UE in RRC IDLE state is not known to the gNB serving the cell where the UE is camping. However, NR RRC includes an RRC INACTIVE state in which a UE is known (e.g., via context) by the serving gNB.

[0061] Figure 2 shows a high-level view of an exemplary 5G network architecture, including a Next Generation Radio Access Network (NG-RAN, 299) and a 5GC (298). As shown in the figure, the NG-RAN can include gNBs (e.g., 210a, b) and ng-eNBs (e.g, 220a, b) that are connected via respective Xn interfaces. The gNBs and ng-eNBs are also connected to the 5GC via the NG interfaces, more specifically to access and mobility management function (AMFs, e.g, 230a, b) via respective NG-C interfaces and to user plane functions (UPFs, e.g. , 240a, b) via respective NG- U interfaces. Moreover, the AMFs can communicate with one or more policy control functions (PCFs, e.g., 250a, b) and network exposure functions (NEFs, e.g., 260a, b).

[0062] Each of the gNBs can support the NR radio interface including frequency division duplexing (FDD), time division duplexing (TDD), or a combination thereof. In contrast, each of ng-eNBs can support the LTE radio interface but, unlike conventional LTE eNodeBs (eNBs), connect to the 5GC via the NG interface. Each of the gNBs and ng-eNBs can serve a geographic coverage area including one more cells (e.g., 211a-b, 221a-b). The gNBs and ng-eNBs can also use various directional beams to provide coverage in the respective cells. Depending on the cell in which it is located, a UE (205) can communicate with the gNB or ng-eNB serving that cell via the NR or LTE radio interface, respectively. Although Figure 2 shows gNBs and ng-eNBs separately, it is also possible that a single NG-RAN node provides both types of functionality.

[0063] Each gNB can include a central (or centralized) unit (CU or gNB-CU) and one or more distributed (or decentralized) units (DU or gNB-DU), which can be viewed as logical nodes. CUs host higher-layer protocols and perform various gNB functions such controlling the operation of DUs, which host lower-layer protocols and can include various subsets of the gNB functions. A CU connects to its associated DUs over respective Fl logical interfaces. Each of the CUs and DUs can include various circuitry needed to perform their respective functions, including processing circuitry, communication interface circuitry (e.g., for communication via Xn, NG, radio, etc. interfaces), and power supply circuitry.

[0064] As briefly mentioned above, 3GPP Rel-16 specifies the NR sidelink (SL) interface and targets advanced V2X services including use cases such as vehicles platooning, extended sensors, advanced driving, and remote driving. The advanced V2X services require anew SL to meet service requirements of low latency and high reliability. The NR SL is designed to provide higher system capacity and better coverage, and to allow for extension to support the future development of even more advanced V2X services and other related services.

[0065] In general, a V2X UE can support unicast communication via the uplink / downlink radio interface (also referred to as “Uu”) to a 3GPP RAN, such as the LTE Evolved-UTRAN (E- UTRAN) or the NG-RAN. A V2X UE can also support SL unicast over the PC5 interface. In addition to Uu and PC5 interfaces, the V2X UEs can communicate with a ProSe (PROximity- based SErvices) network function (NF) via respective PC3 interfaces. Communication with the ProSe NF requires a UE to establish a connection with the RAN, either directly via the Uu interface or indirectly via PC5 and another UE’s Uu interface. The ProSe function provides the UE various information for network related actions, such as service authorization and provisioning of PLMN- specific information (e.g., security parameters, group IDs, group IP addresses, out-of-coverage radio resources, etc.).

[0066] Figure 3 shows three exemplary network coverage scenarios for two UEs (310, 320) and a gNB (330) serving a cell. In the full coverage scenario (left), both UEs are in the coverage of the cell, such that they both can communicate with the gNB via respective Uu interfaces and directly with each other via the PC5 interface. In the partial coverage scenario (center), only one of the UEs is in coverage of the cell, but the out-of-coverage UE can still communicate with the gNB indirectly via the PC5 interface with the in-coverage UE. In the out-of-coverage scenario, both UEs can only communicate with each other via the PC5 interface.

[0067] In general, the term “SL standalone” refers to direct communication between two SL- capable UEs (e.g., via PC5) in which source and destination are the UEs themselves. In contrast, the term “SL relay” refers to indirect communication between a network node and a remote UE via a first interface (e.g., Uu) between the network node an intermediate (or relay) UE and a second interface (e.g., PC5) between the relay UE and the remote UE. In this case the relay UE is neither the source nor the destination.

[0068] In general, an “out-of-coverage UE” is one that cannot establish a direct connection to the network and must communicate via either SL standalone or SL relay. UEs that are in coverage can be configured by the network (e.g., gNB) via RRC signaling and / or broadcast system information, either directly (via Uu interface) or indirectly (via PC5 interface and relay UE Uu interface). Out-of-coverage UEs rely on a (pre-)configuration available in their SIMs. These preconfigurations are generally static but can be updated by the network when a UE is in coverage. A “peer UE” refers to a UE that can communicate with the out-of-coverage UE via SL standalone or SL relay (in which case the peer UE is also a relay UE). 3GPP Rel-17 includes coverage extension for SL-based communication, including UE-to- network (U2N) relay for cellular coverage extension and UE-to-UE (U2U) relay for SL coverage extension. In U2N relay, a UE extends the network connectivity to another nearby UE by using direct communication. U2N relay functionality is fundamental for network coverage extension for public safety in remote areas, for wearable devices tethering in commercial use cases (e.g., sensors, virtual reality headsets), etc.

[0069] LTE U2N relay functionality uses a layer-3 (L3) architecture in which the relay of data packets via the PC5 interface is performed at the network layer, and UEs connected to a L3 U2N relay are transparent to the network. NR U2N relay uses two different architectures: a L3 architecture similar to LTE, and a newly defined architecture in which PC5 relaying occurs within layer 2 (L2), over the RLC sublayer.

[0070] 3GPP TR 23.752 (vl7.0.0) section 6.7 describes L2 -based U2N relay functionality, which includes forwarding functionality that can relay any type of traffic over the PC5 interface between two UEs. A L2 U2N Relay UE supports connectivity to the 5GS (i.e., NG-RAN and 5GC) for other UEs that have successfully established a PC5 link to the L2 U2N Relay UE. A UE connected to a L2 U2N relay will be seen by the network as a regular UE., as if it was directly connected to the network. This gives the network control of the connection and services, but requires the definition of several new mechanisms not present or needed in the L3 architecture.

[0071] 3GPP TR 23.752 (vl7.0.0) section 6.6 describes L3-based U2N relay functionality (also referred to as “ProSe 5G U2N Relay”) that can be used for both public safety and commercial services. A ProSe 5G U2N Relay UE supports connectivity to the 5GS (i.e., NG-RAN and 5GC) for other UEs that have successfully established a PC5 link to the ProSe 5G U2N Relay UE.

[0072] In U2U relay, a UE uses two direct communication links to connect two UEs in its proximity that otherwise are not able to communicate. U2U relay functionality was not part of the LTE ProSe specification, and its inclusion on NR ProSe can be beneficial for public safety communications range extension for both in-network and off-network use cases.

[0073] 3GPP TR 23.752 (v!7.0.0) section 6.10 describes ProSe 5G U2U Relay. A ProSe 5G U2U Relay is a (5G ProSe-enabled) UE that provides functionality to support L3 connectivity between 5G ProSe U2U UEs. For UE-to-UE relay use cases, the source UE, the target UE, and the UE-to- UE relay may be in or out of 3GPP coverage. Note that terms “UE-to-UE Relay” and “relay UE” are used interchangeably herein.

[0074] Figure 4 shows a reference architecture for 5G ProSe U2U relay. In this architecture, two 5G ProSe End UEs have respective PC5 links to a 5G ProSe U2U Relay UE, which enables the 5G ProSe End UEs communicate with each other via the 5G ProSe U2U Relay. 3GPP TS 23.304 (vl 8.1.0) provides the following definitions of technical terms often used in relation to ProSe:

[0075] • 5G ProSe-enabled UE: A UE that supports 5G ProSe requirements and associated procedures.

[0076] • 5G ProSe Direct Discovery: A procedure employed by a 5G ProSe-enabled UE to discover other 5G ProSe-enabled UEs in its vicinity based on direct radio transmissions between the two UEs with NR technology.

[0077] • 5G ProSe Direct Communication: A communication between two or more UEs in proximity that are 5G ProSe-enabled, by means of user plane transmission using NR technology via a path not traversing any network node.

[0078] • 5G ProSe UE-to-Network (U2N) Relay: A 5G ProSe-enabled UE that provides functionality to support connectivity to the network for 5G ProSe Remote UE(s).

[0079] • 5G ProSe Remote UE: A 5G ProSe-enabled UE that communicates with a DN via a 5G ProSe U2N Relay.

[0080] • 5G ProSe UE-to-UE (U2U) Relay: A 5G ProSe-enabled UE that provides functionality to support connectivity between 5G ProSe End UEs. Also called 5G ProSe Layer-3 U2U Relay.

[0081] • 5G ProSe End UE: A 5G ProSe-enabled UE that connects with another 5G ProSe-enabled UE(s) via a 5G ProSe UE-to-UE Relay. Also called 5G ProSe Layer-3 End UE.

[0082] • Application Layer ID: An identifier identifying a 5G ProSe-enabled UE within the context of a specific application. The format of this identifier is outside the scope of 3GPP.

[0083] • Direct Network Communication: One mode of network communication, where there is no 5G ProSe UE-to-Network Relay between a UE and the 5G network.

[0084] • Indirect Network Communication: One mode of network communication, where there is a 5G ProSe UE-to-Network Relay between a UE and the 5G network.

[0085] • Member ID: An identifier uniquely identifying a member in the Application Layer managed group and that is managed by the ProSe application layer.

[0086] • Mode of communication: Mode of communication to be used by the 5G ProSe-enabled UE over PC5 reference point, i.e. broadcast mode, groupcast mode or unicast mode.

[0087] • Open ProSe Discovery: ProSe Direct Discovery without explicit permission from the 5G ProSe-enabled UE being discovered, according to TS 22.278 [7],

[0088] • ProSe identifier: A globally unique identifier used to identify the ProSe Application associated with the ProSe operation in 5G ProSe Direct Discovery and 5G ProSe Direct Communication. In this Release, the "Application ID" defined in TS 23.303 [3] can be used as the ProSe identifier in 5G ProSe Direct Discovery and in a consequent 5G ProSe Direct Communication.

[0089] • Restricted ProSe Discovery: ProSe Direct Discovery that only takes place with explicit permission from the 5G ProSe-enabled UE being discovered, according to TS 22.278 [7],

[0090] • User Info ID: The User Info ID is configured for Model A or Model B Group Member Discovery and 5G ProSe UE-to-Network Relay Discovery either for public safety or commercial applications based on the policy of the HPLMN or via the ProSe application server that allocates it. The definition of values of User Info ID is out of scope of this specification.

[0091] 3GPP TR 33.740 (vl 8. 1.0) describes a security solution for PC5 links between source UE, U2U relay, and target UE. Hop by hop PC5 security establishment is to be supported as well as multiple security methods for each PC5 link. For example, a 5G Prose U2U relay may support a PC5 link security establishment procedure with network assistance. This is similar to security establishment for U2N relay as specified in 3GPP TS 33.503 (v!8.2.0) section 6.3.3, and can include UP-based security or CP-based security. The network-assisted security method could be used when a U2U relay is in 3GPP network coverage.

[0092] Additionally, a 5G Prose U2U relay may support a PC5 link security establishment procedure without network assistance. This is similar to V2X unicast security specified in 3GPP TS 33.536 (vl7.1.0) section 5.3. This non-assisted security method could be used when a U2U relay is out of 3GPP network coverage.

[0093] Typically, 5G ProSe UEs initially discover each other via 5G Prose Discovery procedure, then trigger ProSe Communication (aka PC5 link) establishment for each other. In other scenarios, 5G ProSe U2U Relay Communication is triggered without an explicit discovery procedure, but rather the discovery information is embedded into a PC5 link establishment request.

[0094] Each 5G ProSe discovery or direct communication message includes a specific code: a ProSe Restricted Code in the case of ProSe direct discovery or communication and a Relay Service Code (RSC) in the case of ProSe U2N relay. There is a one-to-one association between codes and security materials, e.g., each RSC is associated with a corresponding set of security materials including Code-Sending Security Parameters and Code-Receiving Security Parameters.

[0095] As described in 3GPP TR 23.700-03 (vO. 1.0), some ProSe enhancements being considered for Rel-19 include support of multi -hop U2U and U2N relaying, including L2 and L3 relaying. In multi-hop U2N relaying, two endpoint UEs of the relaying path are referred to as “Remote UE” and “U2N Relay”, while the intermediate relays are referred to as “Intermediate U2N Relay,” “5G ProSe Intermediate Relay,” or more simply “Intermediate Relay.” Likewise, for multi-hop U2U relaying, two endpoint UEs of relaying path are referred to as “source end UE” and “target end UE”, or more generically “end UEs,” while the intermediate relays are referred to as “U2U Relays.”

[0096] Figure 5 shows an example scenario of multi-hop 5G ProSe U2N relay. In this example, a 5G ProSe Remote UE has a PC5 link to an Intermediate U2N Relay, which also has a 5G ProSe U2N Relay UE, which also has Uu connection to the NG-RAN. By this arrangement, the 5G ProSe Remote UE can communicate with the NG-RAN, the coupled 5GC, and the data network.

[0097] Support for single-hop relay discovery, selection, authorization, connection establishment and data transfer for ProSe U2N Relay were addressed in Rel-17 and / or Rel-18. Although some of these features may need to be enhanced to support multi-hop U2N relay, other aspects that may need to be considered for Rel-19 multi-hop U2N relay support include the following:

[0098] • Whether and how to support the authorization of multi-hop U2N Relay and Remote UE authorization and policy and parameter provisioning.

[0099] • Whether and how to support the multi -hop U2N Relay discovery.

[0100] • Whether and how to perform multi-hop U2N Relay (re-)selection.

[0101] • Whether and how to enhance existing mechanisms for IP address / prefix allocation to support 3 multi -hop U2N Relay.

[0102] • Whether and how to control the maximum number of hops supported when using multihop L3 U2N relays.

[0103] • How to manage multi-hop PC5 links, including how to establish, modify and release L2 link over PC5 reference point for multi-hop U2N Relays.

[0104] • Whether and how to support end-to-end QoS requirements between Remote UE and network via multi-hop L3 U2N Relay.

[0105] Figure 6 shows an example scenario of multi-hop 5G ProSe U2U relay. In this example, a 5G ProSe Remote UE has a PC5 link to an Intermediate U2N Relay, which also has a 5G ProSe U2N Relay UE, which also has Uu connection to the NG-RAN. By this arrangement, the 5G ProSe Remote UE can communicate with the NG-RAN, the coupled 5GC, and the data network.

[0106] Support for single-hop relay discovery, selection, authorization, connection establishment and data transfer for ProSe U2U Relay were addressed in Rel-17 and / or Rel-18. Although some of these features may need to be enhanced to support multi-hop U2U relay, other aspects that may need to be considered for Rel-19 multi-hop U2U relay support include the following:

[0107] • Whether and how to enhance existing mechanisms for multi-hop U2U Relay discovery.

[0108] • Whether and how to enhance existing mechanisms for IP address / prefix allocation.

[0109] • Whether and how to control the maximum number of hops supported when using multihop U2U relays. • Whether and how to support path changes or Relay (re)selections, e.g., in case one or more U2U Relays become unavailable / suitable.

[0110] • Whether and how to support the network control 5G ProSe multi-hop U2U Relay operations, including at least, authorization, policy and parameters provisioning etc.

[0111] • How to manage multi-hop PC5 links, at least including how to establish, modify and release L2 link over PC5 reference point for multi-hop U2U Relays.

[0112] • How to establish the connection between source UE and target UE via multiple 5G ProSe U2U Relays.

[0113] • How to satisfy end-to-end QoS requirements for the End UEs over the path via 5G ProSe multi-hop U2U Relays, if needed.

[0114] To support multi -hop U2N relaying, a remote UE can discover a U2N Relay via one or more proximate Intermediate U2N Relays. These discovery messages used to discover either a proximate Intermediate U2N Relay or a target U2N Relay via a proximate Intermediate U2N Relay need to be security protected. Failure to protect the security of these discovery messages for multi-hop U2N relaying may lead to various attacks by unauthorized UEs, such as discovery message manipulation, replay, and / or capture of private or sensitive user information.

[0115] For example, if the discovery messages are not integrity protected and replay protected, the parameters included in the discovery messages (e.g., RSC, hop count) can be modified and / or replayed by an attacker. Consequently, a remote UE may fail to find a proper U2N Relay by which it can obtain desired services. As another example, if the discovery messages are not confidentiality protected (e.g., encrypted), the parameters (e.g., RSC) and any user information in the messages may be obtained by attackers.

[0116] Currently, however, there are no security mechanisms specified for these discovery messages used in multi-hop U2N relaying. Similar problems and / or difficulties exist for multihop U2U relaying.

[0117] Embodiments of the present disclosure address these problems, issues, and / or difficulties by providing flexible and efficient security procedures for multi-hop 5G ProSe U2N relay communication, including hop-by-hop security applied by intermediate U2N relays to discovery messages, thereby protecting integrity and / or confidentiality of discovery information inserted and / or updated by the intermediate U2N, such as hop count, route information, etc. Moreover, in addition to obtaining relay security material used to protect Remote UE / U2N Relay discovery security material, the intermediate U2N relays also obtain additional sets of relay discovery security material for each Intermediate Relay from their respective home public land mobile networks (HPLMNs). In this manner, embodiments facilitate establishment of security on PC5 links used in multi-hop U2N relay arrangements, which facilitates end-to-end security between a remote UE and a U2N relay, as well as hop-to-hop security between the remote UE, the intermediate U2N relay(s), and the U2N relay. At a high level, embodiments improve discovery in multi-hop U2N relay arrangements, thereby improving SL functionality for UEs.

[0118] In general, the following two models of relay discovery are specified:

[0119] A. announcement sent by announcing 5G ProSe U2N and received by monitoring 5G ProSe Remote UE; and

[0120] B. discovery solicitation sent by discoverer 5G ProSe Remote UE and received by discoveree 5G ProSe U2N.

[0121] Embodiments usable for each of these two models are discussed below.

[0122] In model A, the announcing 5G ProSe U2N and the monitoring 5G ProSe Remote UE performs protected relay discovery as specified in 3GPP TS 23.304 (vl 8.5.0) clause 6.3.2.3.2 and 3GPP TS 33.503 (v!8.2.0) clause 6.1.3.2.2.1. The announcing 5G ProSe U2N sends an Announcement message and protects it with relay discovery security material as specified in these clauses. The announcing 5G ProSe U2N may also include in or with this message "hop info", such as maximum hop limit, initial value of hop counter, visited route information (e.g., list of visited Relay IDs), etc. The announcing 5G ProSe U2N can protect the “hop info” by relay discovery security material. Alternatively, the announcing 5G ProSe U2N may also fetch intermediate discovery material associated with a first Intermediate U2N Relay and protects (twice) the original Announcement message plus the “hop info”.

[0123] The Intermediate U2N Relay(s) can forward the received discovery Announcement message sent by the announcing 5G ProSe U2N, and can also insert other information (e.g., hop count, route information, etc.) needed to support multi-hop U2N relay in the forwarded messages. Alternately, or in addition, the first Intermediate U2N Relay(s) can update information already in the received discovery Announcement message.

[0124] To protect the integrity and / or confidentiality of the updated and / or inserted information, each Intermediate U2N Relay also needs to obtain a set of relay discovery security material from its own HPLMN, referred to herein as “intermediate relay discovery security material.” As such, the forwarded discovery Announcement message contains both the original discovery Announcement message protected by the relay discovery security material associated with the announcing U2N Relay and the inserted / updated information protected by the intermediate relay discovery security material associated with the Intermediate U2N Relay. This set of operations may be repeated multiple times, according to how many Intermediate U2N Relays are in the discovery path between the announcing U2N Relay and the monitoring Remote UE. Figure 7 shows signaling for a model A discovery procedure supporting multi-hop U2N relay, according to some embodiments of the present disclosure. The procedure is between an Announcing U2N Relay (710), a first Intermediate U2N Relay (720), a second Intermediate U2N Relay (730), and a Monitoring Remote UE (740). Although the operations shown in Figure 7 are given numerical labels, this is intended to facilitate explanation rather than to require or imply any specific operational order, unless expressly stated otherwise.

[0125] In operation 0a, the announcing U2N Relay is provisioned by its HPLMN with the relay discovery security materials as specified in 3GPP TS 33.503 (vl 8.2.0) clause 6.1.3.2.2.1. Also, the intermediate U2N Relays and the Monitoring Remote UE are provisioned by their respective HPLMNs with relay discovery security materials associated with the Announcing U2N Relay, for their roles as Monitoring UEs as specified in 3GPP TS 33.503 (vl8.2.0) clause 6.1.3.2.2.1. For example, the Intermediate U2N Relays needs to be provisioned with U2N discovery security material to understand the RSC being announced by the Announcing U2N.

[0126] In operation 0b, the Intermediate U2N Relays are also provisioned by their respective HPLMNs with intermediate relay discovery security material used for protection of the forwarded announcement message, for their roles as announcing UEs as specified in 3GPP TS 33.503 (vl8.2.0) clause 6.1.3.2.2.1. The Intermediate U2N Relays, the Monitoring Remote UE, and / or the Announcing U2N Relay are also provisioned with intermediate relay discovery security materials associated with neighbouring intermediate U2Ns, for their roles as Monitoring UE as specified in 3 GPP TS 33.503 (vl8.2.0) clause 6.L3.2.2.1.

[0127] Note that the Intermediate U2N Relays, the Monitoring Remote UE, and / or the Announcing U2N Relay is / are not necessarily aware of the neighbouring intermediate U2N relays. In such case, they may just request intermediate relay discovery security materials for all possible neighbouring intermediate U2N relays, e.g., using PLMN IDs of the networks offering intermediate relaying service as input. Based on this input, they obtain intermediate relay discovery security materials for Intermediate Relay UEs belonging to those PLMN IDs.

[0128] In some embodiments, the intermediate U2N Relays (i.e., 720, 730) may also be able to function as conventional U2N Relays (e.g., 710). In such case, the intermediate relay discovery security materials provided by their HPLMNs may be the same as or different than the security material provided for conventional U2N relaying (e.g., operation 0a). In some variants, the relay discovery security materials provided in operation 0a can include an indication of whether they may also be used as intermediate relay discovery security materials. Alternately, when the UEs request intermediate relay security material from their PLMNs in operation 0b, the PLMNs can respond with an indication that the security material provided for conventional U2N relaying operation 0a may also be used as intermediate relay security material. In operation 1, the Announcing U2N Relay reuses the 5G ProSe UE-to-Network Relay Discovery Announcement message as specified in 3GPP TS 33.503 (vl8.2.0) clause 6.1.3.2.2.1 with additional information (e.g. hop count) required for multi-hop U2N relay, and protects the message with relay discovery security material obtained in operation 0a. The Announcing U2N Relay may also decide to protect the message with intermediate relay security material if it has obtained such material in operation Ob. If the Announcing U2N Relay applies such intermediate relay security material, then only Intermediate U2N Relays associated with that material can perform operation 2. If not, any intermediate U2N Relays could possibly process the announcement message sent by the announcing U2N Relay. Thus, by applying the additional protection, the announcing U2N Relay reduces its possible next hop Intermediate U2N Relays.

[0129] In operation 2, the first Intermediate U2N Relay receives the protected announcement message, obtains the RSC, and verifies the Announcement message based on the relay discovery security material associated with the announcing U2N, which it obtained in operation 0a. In this context, “Verify” includes decrypting the encryption applied to the message and its data elements by the sender, and checking the integrity of the message and data elements according to the integrity protection applied by the sender. Note that if the announcing U2N protects the message additionally with intermediate relay security material, the first Intermediate U2N Relay also performs verification using intermediate relay security material obtained from operation Ob.

[0130] If verification is successful, the first Intermediate U2N Relay updates the hop information (e.g. hop count) and forwards the original Announcement message with the additional information (e.g. updated hop count). The forwarded message is protected by the intermediate relay discovery security material that the first Intermediate U2N Relay obtained from its HPLMN in operation Ob.

[0131] In operation 3, the second Intermediate U2N Relay receives the protected message, obtains the RSC, and verifies the original Announcement message based on the relay discovery security material associated with the announcing U2N, which it obtained in operation 0a. The second Intermediate U2N Relay also verifies the additional information based on intermediate relay discovery security material associated with the first Intermediate U2N Relay, which it obtained in operation Ob.

[0132] If the verification is successful, the second Intermediate U2N Relay updates the hop information (e.g. hop count) and forwards the original Announcement message with the additional information (e.g. updated hop count). The forwarded message is protected by the intermediate relay discovery security material that the second Intermediate U2N Relay obtained from its HPLMN in operation Ob.

[0133] In operation 4, upon receiving the Announcement message from the second Intermediate U2N Relay, the monitoring Remote UE verifies the received Announcement message using the relay discovery security material associated with the announcing U2N, which it obtained in operation Oa. The monitoring Remote UE also verifies the additional information based on the intermediate relay discovery security material associated with the second Intermediate U2N Relay, which it obtained in operation Ob. If the verification is successful, the monitoring 5G ProSe Remote UE processes the relay announcement message as specified in 3GPP TS 33.503 (vl 8.2.0) clause 6.1.3.2.2.1.

[0134] In model B, the Discoveree 5G ProSe U2N and the Discoverer 5G ProSe Remote UE performs protected relay discovery as specified in 3GPP TS 23.304 (vl 8.5.0) clause 6.3.2.3.3 and 3GPP TS 33.503 (v!8.2.0) clause 6.1.3.2.2.2. The Intermediate U2N Relay(s) can relay and forward the Discovery Solicitation / Response messages sent by the Discoveree 5G ProSe U2N and the Discoverer 5G ProSe Remote UE, respectively. The intermediate U2N can also insert other information (e.g., hop count, route information, etc.) needed to support multi-hop U2N relay in the forwarded messages.

[0135] To protect the integrity and / or confidentiality of the updated and / or inserted information, each Intermediate U2N Relay also needs to obtain a set of relay discovery security material from its own HPLMN, i.e., the “intermediate relay discovery security material” discussed above. As such, the forwarded Discovery Solicitation / Response messages contain both the original discovery message protected by the relay discovery security material associated with the message source and the inserted information protected by the intermediate relay discovery security material associated with the Intermediate U2N Relay. This set of operations may be repeated multiple times, according to how many Intermediate U2N Relays are in the discovery path between the announcing U2N Relay and the monitoring Remote UE.

[0136] Figure 8 shows signaling for a model B discovery procedure supporting multi-hop U2N relay, according to some embodiments of the present disclosure. The procedure is between a Discoverer Remote UE (810), a first Intermediate U2N Relay (820), a second Intermediate U2N Relay (830), and a Discoveree U2N Relay (840). Although the operations shown in Figure 8 are given numerical labels, this is intended to facilitate explanation rather than to require or imply any specific operational order, unless expressly stated otherwise.

[0137] In operation 0a, the discoveree U2N Relay is provisioned with relay discovery security materials from its HPLMN as specified in 3GPP TS 33.503 (v!8.2.0) clause 6.1.3.2.2.2. The intermediate U2N Relays and the Discoverer Remote UE are provisioned with the relay discovery security materials associated with the discoveree U2N for their roles as discoverer UE as specified in 3GPP TS 33.503 (vl 8.2.0) clause 6.1.3.2.2.2. For example, the intermediate U2N Relays need to be provisioned with U2N discovery security material to understand the RSC being discovered. In operation Ob, the intermediate U2N Relays are also provisioned by their respective HPLMNs with intermediate relay discovery security material used for protection of forwarded discovery Solicitation / Response messages, for their roles as discoveree UE as specified in 3GPP TS 33.503 (vl8.2.0) clause 6.1.3.2.2.2. The 5GProSe intermediate U2N, the discoveree 5GProSe U2N and the discoverer remote UE are also provisioned with the intermediate relay discovery security materials associated with the neighbouring intermediate U2Ns, for their roles as discoverer UE as specified in 3GPP TS 33.503 (vl8.2.0) clause 6.1.3.2.2.2.

[0138] Note that the Intermediate U2N Relays, the Discoverer Remote UE, and / or the Discoveree U2N Relay is / are not necessarily aware of the neighbouring intermediate U2N relays. In such case, they may just request intermediate relay discovery security materials for all possible neighbouring intermediate U2N relays, e.g., using PLMN IDs of the networks offering intermediate relaying service as input. Based on this input, they obtain intermediate relay discovery security materials for Intermediate Relay UEs belonging to those PLMN IDs.

[0139] In some embodiments, the intermediate U2N Relays (i.e., 820, 830) may also be able to function as conventional U2N Relays (e.g., 840). In such case, the intermediate relay discovery security materials provided by their HPLMNs may be the same as or different than the security material provided for conventional U2N relaying (e.g., operation 0a). In some variants, the relay discovery security materials provided in operation 0a can include an indication of whether they may also be used as intermediate relay discovery security materials. Alternately, when the UEs request intermediate relay security material from their PLMNs in operation 0b, the PLMNs can respond with an indication that the security material provided for conventional U2N relaying operation 0a may also be used as intermediate relay security material.

[0140] In operation 1, the discoverer Remote UE reuses the 5G ProSe U2N Relay Discovery Solicitation message as specified in 3GPP TS 33.503 (v!8.2.0) clause 6.1.3.2.2.2 with additional information (e.g. hop count) required for multi-hop U2N relay, and protects the message with relay discovery security material obtained in operation 0a. The discoverer Remote UE may also decide to protect the message with intermediate relay security material if it has obtained such material in operation 0b. If the discoverer Remote UE applies such intermediate relay security material, then only Intermediate U2N Relays associated with that material can perform operation 2. If not, any intermediate U2N Relays could possibly process the announcement message sent by the announcing U2N Relay. Thus, by applying the additional protection, the discoverer Remote UE reduces its possible next hop Intermediate U2N Relays.

[0141] In operation 2, the first Intermediate U2N Relay receives the protected Discovery Solicitation message, verifies the security (i.e., decryption, integrity check) based on the relay discovery security material associated with the discoveree U2N (obtained in operation 0a), and obtains the RSC. If verification is successful, the first Intermediate U2N Relay updates the hop information (e.g. hop count, route info) and forwards the original Discovery Solicitation message with the updated information. The forwarded message is now protected not only by the relay discovery security material associated with the discoveree U2N (applied in operation 1) but also by the intermediate relay discovery security material that the first Intermediate U2N Relay obtained from its HPLMN in operation Ob.

[0142] In operation 3, the second Intermediate U2N Relay receives the protected Discovery Solicitation message, obtains the RSC, verifies the original Discovery Solicitation message based on the relay discovery security material associated with the discoveree U2N (obtained in operation Oa), and verifies the updated information (e.g., updated hop count) based on intermediate relay discovery security material associated with the first Intermediate U2N Relay (obtained in operation Ob). If verification is successful, the second Intermediate U2N Relay again updates the hop information (e.g. hop count) and forwards the original Relay Discovery Solicitation message with the updated information (e.g. updated hop count). The forwarded message is protected by the intermediate relay discovery security material that the second Intermediate U2N Relay obtained from its HPLMN in operation Ob.

[0143] In operation 4, upon receiving the Discovery Solicitation message from the second Intermediate U2N Relay , the discoveree 5G ProSe U2N verifies the received Relay Discovery Solicitation message using the relay discovery security material associated with the discoveree U2N obtained in operation Oa and the updated information based on the intermediate relay discovery security material associated with the second Intermediate U2N Relay obtained in operation Ob. If verification is successful, the discoveree U2N Relay processes the Discovery Solicitation message as specified in 3GPP TS 33.503 (v!8.2.0) clause 6.1.3.2.2.2.

[0144] In operation 5, the discoveree U2N Relay sends a 5G ProSe UE-to-Network Relay Discovery Response message as specified in 3GPP TS 33.503 (vl 8.2.0) clause 6.1.3.2.2.2 with additional information (e.g. hop count) required for multi-hop U2N relay. The discoveree U2N Relay protects the message with relay discovery security material obtained in operation Oa. Optionally, the discoveree U2N relay also protects the message with intermediate relay discovery security material associated with the second Intermediate U2N Relay, which it obtained in operation Ob.

[0145] In operation 6, the second Intermediate U2N Relay verifies the protected Discovery Response message received from discoveree U2N Relay, updates the additional information (e.g., updated hop count), and forwards the message with the updated information to the discoverer Remote UE. The second Intermediate U2N Relay protects the forwarded message with the intermediate relay discovery security material that it obtained from its HPLMN in operation Ob, in a similar manner as in operation 3.

[0146] In operation 7, the first Intermediate U2N Relay verifies the protected Discovery Response message received from the second Intermediate U2N Relay, updates the additional information (e.g., updated hop count), and forwards the message with the updated information to the discoverer Remote UE. The first Intermediate U2N Relay protects the forwarded message with the intermediate relay discovery security material that it obtained from its HPLMN in operation Ob, same as in operation 2.

[0147] In operation 8, upon receiving the Discovery Response message from the first Intermediate U2N Relay, the discoverer Remote UE verifies the received message using the relay discovery security material associated with the discoveree U2N obtained in operation Oa and verifies the additional information based on the intermediate relay discovery security material associated with the first Intermediate U2N Relay, which it obtained in operation Ob. If the verification is successful, the discoverer 5G ProSe Remote UE processes the Discovery Response message as specified in 3 GPP TS 33.503 (v!8.2.0) clause 6.I.3.2.2.2.

[0148] Various features of the embodiments described above correspond to various operations illustrated in Figures 9-11, which show exemplary methods (e.g., procedures) for a first UE, a second UE, and an third UE, respectively. In other words, various features of the operations described below correspond to various embodiments described above, including the exemplary procedures shown in Figures 9-11. Furthermore, the exemplary methods shown in Figures 9-11 can be used cooperatively to provide various benefits, advantages, and / or solutions to problems described herein. Although Figures 9-11 show specific blocks in particular orders, the operations of the exemplary methods can be performed in different orders than shown and can be combined and / or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

[0149] In addition, Figure 9 shows an exemplary method (e.g., procedure) for a first UE configured to discover intermediate U2N relays that facilitate access to a communication network via a U2N relay, according to various embodiments of the present disclosure. The exemplary method can be performed by a remote UE (e.g, wireless device) such as described elsewhere herein.

[0150] The exemplary method includes the operations of block 910, where the first UE obtains the following security material from the first UE’s PLMN: relay discovery security materials associated with a second UE configured to operate as the U2N relay, and intermediate relay discovery security materials associated with a third UE configured to operate as an intermediate U2N relay between the first UE and the second UE. The exemplary method also includes the operations of block 920, where the first UE receives from the third UE a message associated with multi-hop relay discovery. The message includes a first portion generated by the third UE and a second portion generated by the second UE. The exemplary method also includes the operations of block 930, where the first UE verifies the following: the first portion based on the intermediate relay discovery security materials associated with the third UE, and the second portion based on the relay discovery security materials associated with the second UE. The exemplary method also includes the operations of block 940, where based on successful verification of the first and second portions, the first UE processes the content of the message.

[0151] In some embodiments, the first portion includes a hop count that was generated by the second UE and updated by the third UE, and the second portion includes a relay service code (RSC).

[0152] In some embodiments, the intermediate relay discovery security materials associated with the third UE include a third encryption key and a third integrity protection key and the relay discovery security materials associated with the second UE include a second encryption key and a second integrity protection key. In some of these embodiments, verifying the first portion in block 930 includes the operations of sub-block 931, where the first UE decrypts the first portion using the third encryption key and verifies integrity of the decrypted first portion using the third integrity protection key. Also, verifying the second portion in block 930 includes the operations of sub-block 932, where the first UE decrypts the second portion using the second encryption key and verifies integrity of the decrypted second portion using the second integrity protection key.

[0153] In some of these embodiments, the first UE is a Monitoring Remote UE and the message is an Announcement. In other of these embodiments, the first UE is a Discoverer Remote UE and the message is a Discovery Response. In some variants of these embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0154] • (950) generating a secure Discovery Solicitation message using the relay discovery security materials associated with the second UE; and

[0155] • (960) sending the secure Discovery Solicitation message to at least the third UE. The Discovery Response message is responsive to the Discovery Solicitation message.

[0156] In addition, Figure 10 shows an exemplary method (e.g., procedure) for a second UE configured to provide a U2N relay between intermediate U2N relays and a communication network, according to various embodiments of the present disclosure. The exemplary method can be performed by a U2N relay UE (e.g., wireless device) such as described elsewhere herein. In embodiments, the second UE is a Discoveree U2N Relay UE. The exemplary method includes the operations of block 1010, where the second UE obtains the following security material from the second UE’s HPLMN: relay discovery security materials associated with the second UE, and intermediate relay discovery security materials associated with a third UE configured to operate as an intermediate U2N relay. The exemplary method also includes the operations of block 1020, where the second UE receives, from the third UE, a Discovery Solicitation message associated with multi-hop relay discovery that includes a first portion generated by the third UE and a second portion generated by a first UE configured to operate as a Discoverer Remote UE. The exemplary method also includes the operations of block 1030, where the second UE verifies the following: the first portion based on the intermediate relay discovery security materials associated with the third UE, and the second portion based on the relay discovery security materials associated with the second UE. The exemplary method also includes the operations of block 1040 where the second UE, based on successful verification of the first and second portions, processes the content of the Discovery Solicitation message.

[0157] In some embodiments, the exemplary method also includes the operations in block 1050 where the second UE generates a Discovery Response message. The Discovery Response message is secured using the relay discovery security materials associated with the second UE. In some embodiments, the exemplary method also includes the operations of block 1060, where the second UE sends the secure message to at least the third UE. The Discovery Response message is sent in block 1060 based on processing the content of the Discovery Solicitation message.

[0158] In some embodiments, the relay discovery security materials associated with the second UE include a second encryption key and a second integrity protection key. Also, the intermediate relay discovery security materials associated with the third UE include a third encryption key and a third integrity protection key.

[0159] The first potion includes, for example, a hop count and the second portion includes a relay service code (RSC).

[0160] In some further variants, verifying the first portion of the Discovery Solicitation message in block 1030 includes the operations of sub-block 1031, where the second UE decrypts the first portion using the third encryption key and verifies integrity of the decrypted first portion using the third integrity protection key. Also, verifying the second portion of the Discovery Solicitation message in block 1030 includes the operations of sub-block 1032, where the second UE decrypts the second portion using the second encryption key and verifying integrity of the decrypted second portion using the second integrity protection key. In some embodiments, the relay discovery security materials associated with the second UE include an indication for the relay discovery security materials to be used also as intermediate relay discovery security materials.

[0161] In addition, Figure 11 shows an exemplary method (e.g., procedure) for a third UE configured to provide an intermediate U2N relay between remote UEs and a U2N relay coupled to communication network, according to various embodiments of the present disclosure. The exemplary method can be performed by an intermediate U2N relay UE (e.g., wireless device) such as described elsewhere herein.

[0162] The exemplary method includes the operations of block 1120, where the third UE receives a first message associated with multi-hop relay discovery. The first message includes a second portion generated by a message source UE and a first portion generated by one of the following: the message source UE, or a fourth UE arranged as an intermediate U2N relay between the message source UE and the third UE. The exemplary method also includes the operations of block 1130, where the third UE verifies the first portion based on one of the following: relay discovery security materials associated with a second UE arranged to provide the U2N relay, or intermediate relay discovery security materials associated with the fourth UE.

[0163] The exemplary method also includes the operations of block 1140, where the third UE verifies the second portion based on the relay discovery security materials associated with a second UE arranged to provide the U2N relay. The exemplary method also includes the operations of block 1150, where based on successful verification of the first and second portions, the third UE updates the first portion and secures the updated first portion using the intermediate relay discovery security materials associated with the third UE. The exemplary method also includes the operations of block 1160, where the third UE sends a second message including the second portion and the secured updated first portion to one of the following: a message target UE, or a fifth UE arranged as an intermediate U2N relay between the message target UE and the third UE.

[0164] In some embodiments, the first portion includes a hop count and the second portion includes a relay service code (RSC), and updating the first portion in block 1150 includes the operations of sub-block 1151, where the third UE increments the hop count. In some of these embodiments, the hop count was generated by the message source UE and updated by the fourth UE, i.e., prior to being received by the third UE.

[0165] In some embodiments, the relay discovery security materials associated with the second UE include a second encryption key and a second integrity protection key and the intermediate relay discovery security materials associated with the fourth UE include a fourth encryption key and a fourth integrity protection key. In some of these embodiments, verifying the first portion based on the relay discovery security materials associated with the second UE in block 1130 includes the operations of sub-block 1131, where the third UE decrypts the first portion using the second encryption key and verifying integrity of the decrypted first portion using the second integrity protection key.

[0166] In some of these embodiments, verifying the first portion based on the intermediate relay discovery security materials associated with the fourth UE in block 1130 includes the operations of sub-block 1132, where the third UE decrypts the first portion using the fourth encryption key and verifying integrity of the decrypted first portion using the fourth integrity protection key. In some of these embodiments, verifying the second portion in block 1140 includes the operations of sub-block 1141, where the third UE decrypts the second portion using the second encryption key and verifying integrity of the decrypted second portion using the second integrity protection key.

[0167] In some embodiments, the exemplary method also includes the operations of block 1110, where the third UE obtaining the following from the third UE’s HPLMN: the relay discovery security materials associated with the second UE, the intermediate relay discovery security materials associated with the third UE, and the intermediate relay discovery security materials associated with the fourth UE. In some of these embodiments, one of the following applies:

[0168] • the intermediate relay discovery security materials associated with the third UE include an indication for use also as relay discovery security materials; or

[0169] • the intermediate relay discovery security materials associated with the third UE are derived from or based on relay discovery security materials associated with the third UE.

[0170] In some embodiments, the intermediate relay discovery security materials associated with the third UE include a third encryption key and a third integrity protection key. In such case, securing the updated first portion in block 1150 includes the operations of sub-block 1152, where the third UE protects integrity of the first portion using the third integrity protection key and encrypts the integrity-protected first portion using the third encryption key.

[0171] In some embodiments, the first and second messages are Announcement messages, and the message source UE is the second UE arranged as an Announcing U2N Relay. In other embodiments, the first and second messages are Discovery Response messages, and the message source UE is the second UE arranged as a Discoveree U2N Relay. In other embodiments, the first and second messages are Discovery Solicitation messages, and the message source UE is a first UE arranged as a Discoverer Remote UE.

[0172] Although various embodiments are described above in terms of methods, techniques, and / or procedures, the person of ordinary skill will readily comprehend that such methods, techniques, and / or procedures can be embodied by various combinations of hardware and software in various systems, communication devices, computing devices, control devices, apparatuses, non-transitory computer-readable media, computer program products, etc. Figure 12 shows an example of a communication system 1200 in accordance with some embodiments. In this example, communication system 1200 includes a telecommunication network 1202 that includes an access network 1204 (e.g., RAN) and a core network 1206, which includes one or more core network nodes 1208. Access network 1204 includes one or more access network nodes, such as network nodes 1210a-b (one or more of which may be generally referred to as network nodes 1210), or any other similar 3GPP access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, telecommunication network 1202 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1202 that supports an ORAN specification (e.g., a specification published by the O-RAN Alliance, or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in telecommunication network 1202, including one or more network nodes 1210 and / or core network nodes 1208.

[0173] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU- CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adj ective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an O-2 interface defined by the O-RAN Alliance or comparable technologies. Network nodes 1210 facilitate direct or indirect connection of UEs, such as by connecting UEs 1212a-d (one or more of which may be generally referred to as UEs 1212) to core network 1206 over one or more wireless connections.

[0174] Example wireless communications over a wireless connection include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, communication system 1200 may include any number of wired or wireless networks, network nodes, UEs, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals whether via wired or wireless connections. Communication system 1200 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0175] UEs 1212 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 1210 and other communication devices. Similarly, network nodes 1210 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 1212 and / or with other network nodes or equipment in telecommunication network 1202 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 1202.

[0176] In the depicted example, core network 1206 connects network nodes 1210 to one or more hosts, such as host 1216. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. Core network 1206 includes one or more core network nodes (e.g., 1208) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and / or hosts, such that the descriptions thereof are generally applicable to the corresponding components of core network node 1208. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0177] Host 1216 may be under the ownership or control of a service provider other than an operator or provider of access network 1204 and / or telecommunication network 1202, and may be operated by the service provider or on behalf of the service provider. Host 1216 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio / video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server. As a whole, communication system 1200 of Figure 12 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[0178] In some examples, telecommunication network 1202 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 1202 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1202. For example, telecommunication network 1202 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive loT services to yet further UEs.

[0179] In some examples, UEs 1212 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to access network 1204 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1204. Additionally, a UE may be configured for operating in single- or multi-RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

[0180] In the example, hub 1214 communicates with access network 1204 to facilitate indirect communication between one or more UEs (e.g., UE 1212c and / or 1212d) and network nodes (e.g., network node 1210b). In some examples, hub 1214 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1214 may be a broadband router enabling access to core network 1206 for the UEs. As another example, hub 1214 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1210, or by executable code, script, process, or other instructions in hub 1214. As another example, hub 1214 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, hub 1214 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1214 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1214 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 1214 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0181] Hub 1214 may have a constant / persistent or intermittent connection to network node 1210b. Hub 1214 may also allow for a different communication scheme and / or schedule between hub 1214 and UEs (e.g., UE 1212c and / or 1212d), and between hub 1214 and core network 1206. In other examples, hub 1214 is connected to core network 1206 and / or one or more UEs via a wired connection. Moreover, hub 1214 may be configured to connect to an M2M service provider over access network 1204 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1210 while still connected via hub 1214 via a wired or wireless connection. In some embodiments, hub 1214 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to network node 1210b. In other embodiments, hub 1214 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1210b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0182] In some embodiments hub 1214 may be configured to operate as a UE-to-network (U2N) relay, including performing operations attributed to U2N relays in any of the exemplary methods or procedures described above.

[0183] Figure 13 shows a UE 1300 in accordance with some embodiments. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by 3 GPP, including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0184] A UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and / or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

[0185] UE 1300 includes processing circuitry 1302 that is operatively coupled via a bus 1304 to an input / output interface 1306, a power source 1308, a memory 1310, a communication interface 1312, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 13. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0186] Processing circuitry 1302 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in memory 1310. Processing circuitry 1302 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, processing circuitry 1302 may include multiple central processing units (CPUs).

[0187] In the example, input / output interface 1306 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into UE 1300. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device. In some embodiments, power source 1308 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. Power source 1308 may further include power circuitry for delivering power from power source 1308 itself, and / or an external power source, to the various parts of UE 1300 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging power source 1308. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1308 to make the power suitable for the respective components of UE 1300 to which power is supplied.

[0188] Memory 1310 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, memory 1310 includes one or more application programs 1314, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1316. Memory 1310 may store, for use by UE 1300, any of a variety of various operating systems or combinations of operating systems.

[0189] Memory 1310 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and / or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ Memory 1310 may allow UE 1300 to access instructions, application programs and the like, stored on transitory or non- transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in memory 1310, which may be or comprise a device-readable storage medium.

[0190] Processing circuitry 1302 may be configured to communicate with an access network or other network using communication interface 1312. Communication interface 1312 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1322. Communication interface 1312 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1318 and / or a receiver 1320 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1318 and receiver 1320 may be coupled to one or more antennas (e.g., antenna 1322) and may share circuit components, software or firmware, or alternatively be implemented separately.

[0191] In the illustrated embodiment, communication functions of communication interface 1312 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / intemet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0192] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1312, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., an alert is sent when moisture is detected), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0193] As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input.

[0194] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to UE 1300 shown in Figure 13.

[0195] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements, and transmits the results of such monitoring and / or measurements to another UE and / or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0196] In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g. by controlling an actuator) to increase or decrease the drone’s speed. The first and / or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

[0197] The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the spirit and scope of the disclosure. Various embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art. The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and / or electronic devices and can include, for example, electrical and / or electronic circuitry, devices, modules, processors, memories, logic solid state and / or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and / or displaying functions, and so on, as such as those that are described herein.

[0198] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according to one or more embodiments of the present disclosure.

[0199] As described herein, device and / or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and / or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

[0200] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0201] In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood, that although these terms (and / or other terms that can be synonymous to one another) can be used synonymously herein, there can be instances when such words can be intended to not be used synonymously.

[0202] Embodiments of the present disclosure also include, but are not limited to, the following enumerated examples.

[0203] Al . A method for a first user equipment (UE) arranged to discover intermediate UE-to- network (U2N) relays that facilitate access to a communication network via a U2N relay, the method comprising: obtaining the following security material from the first UE’s home public land mobile network (HPLMN): relay discovery security materials associated with a second UE configured to operate as the U2N relay; and intermediate relay discovery security materials associated with a third UE configured to operate as an intermediate U2N relay between the first UE and the second UE; receiving from the third UE a message associated with multi-hop relay discovery, wherein the message includes a first portion generated by the third UE and a second portion generated by the second UE; verifying the following: the first portion based on the intermediate relay discovery security materials associated with the third UE, and the second portion based on the relay discovery security materials associated with the second UE; and based on successful verification of the first and second portions, processing the content of the message.

[0204] A2. The method of embodiment Al, wherein the first portion includes a hop count that was generated by the second UE and updated by the third UE, and the second portion includes a relay service code (RSC).

[0205] A3. The method of any of embodiments A1-A2, wherein: the intermediate relay discovery security materials associated with the third UE include a third encryption key and a third integrity protection key; and the relay discovery security materials associated with the second UE include a second encryption key and a second integrity protection key.

[0206] A4. The method of embodiment A3, wherein: verifying the first portion comprises decrypting the first portion using the third encryption key and verifying integrity of the decrypted first portion using the third integrity protection key; and verifying the second portion comprises decrypting the second portion using the second encryption key and verifying integrity of the decrypted second portion using the second integrity protection key.

[0207] A5. The method of any of embodiments A3-A4, wherein the first UE is a Monitoring Remote UE and the message is an Announcement.

[0208] A6. The method of any of embodiments A3-A4, wherein the first UE is a Discoverer Remote UE and the message is a Discovery Response.

[0209] A7. The method of embodiment A6, further comprising: generating a secure Discovery Solicitation message using the relay discovery security materials associated with the second UE and the intermediate relay discovery security materials associated with the third UE; and sending the secure Discovery Solicitation message to at least the third UE, wherein the Discovery Response message is responsive to the Discovery Solicitation message.

[0210] A8. The method of embodiment A9, wherein generating the secure Discovery Solicitation message comprises: protecting integrity of a first portion of the Discovery Solicitation message using the third integrity protection key and encrypting the integrity-protected first portion using the third encryption key; and protecting integrity of a second portion of the Discovery Solicitation message using the second integrity protection key and encrypting the integrity-protected second portion using the second encryption key. A9. The method of embodiment A8, wherein the first potion includes a second hop count and the second portion includes a relay service code (RSC).

[0211] Bl . A method for a second user equipment (UE) arranged to provide a UE-to-network (U2N) relay between intermediate U2N relays and a communication network, the method comprising: obtaining the following security material from the second UE’s home public land mobile network (HPLMN): relay discovery security materials associated with the second UE; and intermediate relay discovery security materials associated with a third UE configured to operate as an intermediate U2N relay; generating a secure message associated with multi-hop relay discovery, wherein the message is secured using the relay discovery security materials associated with the second UE and the intermediate relay discovery security materials associated with the third UE; and sending the secure message to at least the third UE.

[0212] B2. The method of embodiment Bl, wherein: the relay discovery security materials associated with the second UE include a second encryption key and a second integrity protection key; and the intermediate relay discovery security materials associated with the third UE include a third encryption key and a third integrity protection key.

[0213] B3. The method of embodiment B2, wherein generating the secure message comprises: protecting integrity of a first portion of the message using the third integrity protection key and encrypting the integrity -protected first portion using the third encryption key; and protecting integrity of a second portion of the message using the second integrity protection key and encrypting the integrity -protected second portion using the second encryption key.

[0214] B4. The method of embodiment B3, wherein the first potion includes a hop count and the second portion includes a relay service code (RSC). B5. The method of any of embodiments B2-B4, wherein the second UE is an Announcing U2N relay UE and the secure message is an Announcement.

[0215] B6. The method of any of embodiments B2-B4, wherein the second UE is a Discoveree U2N Relay UE and the secure message is a Discovery Response.

[0216] B7. The method of embodiment B6, further comprising: receiving, from the third UE, a Discovery Solicitation message that includes a first portion generated by the third UE and a second portion generated by a first UE configured to operate as a Discoverer Remote UE; verifying the following: the first portion based on the intermediate relay discovery security materials associated with the third UE, and the second portion based on the relay discovery security materials associated with the second UE; and based on successful verification of the first and second portions, processing the content of the Discovery Solicitation message, wherein the Discovery Response message is sent based on processing the content of the Discovery Solicitation message.

[0217] B8. The method of embodiment B7, wherein: verifying the first portion of the Discovery Solicitation message comprises decrypting the first portion using the third encryption key and verifying integrity of the decrypted first portion using the third integrity protection key; and verifying the second portion of the Discovery Solicitation message comprises decrypting the second portion using the second encryption key and verifying integrity of the decrypted second portion using the second integrity protection key.

[0218] B9. The method of any of embodiments B1-B8, wherein the relay discovery security materials associated with the second UE include an indication for the relay discovery security materials to be used also as intermediate relay discovery security materials.

[0219] Cl . A method for a third user equipment (UE) arranged to provide an intermediate UE-to- network (U2N) relay between remote UEs and a U2N relay coupled to communication network, the method comprising: receiving a first message associated with multi-hop relay discovery, wherein the first message includes a second portion generated by a message source UE and a first portion generated by one of the following: the message source UE, or a fourth UE arranged as an intermediate U2N relay between the message source UE and the third UE; verifying the first portion based on one of the following: relay discovery security materials associated with a second UE arranged to provide the U2N relay; or intermediate relay discovery security materials associated with the fourth UE; verifying the second portion based on the relay discovery security materials associated with the message source UE; based on successful verification of the first and second portions, updating the first portion and securing the updated first portion using the intermediate relay discovery security materials associated with the third UE; and sending a second message including the second portion and the secured updated first portion to one of the following: a message target UE, or a fifth UE arranged as an intermediate U2N relay between the message target UE and the third UE.

[0220] C2. The method of embodiment Cl, wherein the first portion includes a hop count and the second portion includes a relay service code (RSC), and updating the first portion includes incrementing the hop count.

[0221] C3. The method of embodiment C2, wherein the hop count was generated by the message source UE and updated by the fourth UE.

[0222] C4. The method of any of embodiments C1-C3, wherein: the relay discovery security materials associated with the second UE include a second encryption key and a second integrity protection key; and the intermediate relay discovery security materials associated with the fourth UE include a fourth encryption key and a fourth integrity protection key.

[0223] C5. The method of embodiment C4, wherein: verifying the first portion based on the relay discovery security materials associated with the second UE comprises decrypting the first portion using the second encryption key and verifying integrity of the decrypted first portion using the second integrity protection key; verifying the first portion based on the intermediate relay discovery security materials associated with the fourth UE comprises decrypting the first portion using the fourth encryption key and verifying integrity of the decrypted first portion using the fourth integrity protection key; and verifying the second portion comprises decrypting the second portion using the second encryption key and verifying integrity of the decrypted second portion using the second integrity protection key.

[0224] C6. The method of any of embodiments C1-C5, further comprising obtaining the following from the third UE’s home public land mobile network (HPLMN): the relay discovery security materials associated with the second UE; the intermediate relay discovery security materials associated with the third UE; and the intermediate relay discovery security materials associated with the fourth UE.

[0225] C7. The method of embodiment C7, wherein one of the following applies: the intermediate relay discovery security materials associated with the third UE include an indication for use also as relay discovery security materials; or the intermediate relay discovery security materials associated with the third UE are derived from or based on relay discovery security materials associated with the third UE.

[0226] C8. The method of any of embodiments C1-C7, wherein: the intermediate relay discovery security materials associated with the third UE include a third encryption key and a third integrity protection key; and securing the updated first portion comprises protecting integrity of the first portion using the third integrity protection key and encrypting the integrity -protected first portion using the third encryption key.

[0227] C9. The method of any of embodiments C1-C8, wherein the first and second messages are Announcement messages, and the message source UE is the second UE arranged as an Announcing U2N Relay.

[0228] CIO. The method of any of embodiments C1-C8, wherein the first and second messages are Discovery Response messages, and the message source UE is the second UE arranged as a Discoveree U2N Relay. Cl 1. The method of any of embodiments C1-C8, wherein the first and second messages are Discovery Solicitation messages, and the message source UE is a first UE arranged as a Discoverer Remote UE.

[0229] DI . A first user equipment (UE) arranged to discover intermediate UE-to-network (U2N) relays that facilitate access to a communication network via a U2N relay, the first UE comprising: communication interface circuitry configured to communicate with other UEs configured as intermediate U2N relays; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments A1-A9.

[0230] D2. A first user equipment (UE) arranged to discover intermediate UE-to-network (U2N) relays that facilitate access to a communication network via a U2N relay, the first UE being configured to perform operations corresponding to any of the methods of embodiments A1-A9.

[0231] D3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a first user equipment (UE) arranged to discover intermediate UE-to-network (U2N) relays that facilitate access to a communication network via a U2N relay, configure the first UE to perform operations corresponding to any of the methods of embodiments A1-A9.

[0232] D4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a first user equipment (UE) arranged to discover intermediate UE-to-network (U2N) relays that facilitate access to a communication network via a U2N relay, configure the first UE to perform operations corresponding to any of the methods of embodiments A1-A9.

[0233] El. A second user equipment (UE) arranged to provide a UE-to-network (U2N) relay between intermediate U2N relays and a communication network, the second UE comprising: communication interface circuitry configured to communicate with other UEs configured as intermediate U2N relays; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments B1-B9.

[0234] E2. A second user equipment (UE) arranged to provide a UE-to-network (U2N) relay between intermediate U2N relays and a communication network, the second UE being configured to perform operations corresponding to any of the methods of embodiments B1-B9.

[0235] E3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a second user equipment (UE) arranged to provide a UE-to-network (U2N) relay between intermediate U2N relays and a communication network, configure the UE to perform operations corresponding to any of the methods of embodiments B1-B9.

[0236] E4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a second user equipment (UE) arranged to provide a UE-to- network (U2N) relay between intermediate U2N relays and a communication network, configure the UE to perform operations corresponding to any of the methods of embodiments B1-B9.

[0237] Fl . A third user equipment (UE) arranged to provide an intermediate UE-to-network (U2N) relay between remote UEs and a U2N relay coupled to communication network, the third UE comprising: communication interface circuitry configured to communicate with other UEs configured as remote UEs, intermediate U2N relays, or U2N relays coupled to communication network; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments C 1 -C 11.

[0238] F2. A third user equipment (UE) arranged to provide an intermediate UE-to-network (U2N) relay between remote UEs and a U2N relay coupled to communication network, the third UE being configured to perform operations corresponding to any of the methods of embodiments Cl-Cll. F3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a third user equipment (UE) arranged to provide an intermediate UE-to-network (U2N) relay between remote UEs and a U2N relay coupled to communication network, configure the third UE to perform operations corresponding to any of the methods of embodiments Cl-Cl 1.

[0239] F4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a third user equipment (UE) arranged to provide an intermediate UE-to-network (U2N) relay between remote UEs and a U2N relay coupled to communication network, configure the third UE to perform operations corresponding to any of the methods of embodiments Cl-Cl 1.

Claims

CLAIMS1. A method for a first user equipment, UE (740, 810), arranged to discover intermediate UE-to-network, U2N, relays that facilitate access to a communication network via a U2N relay, the method comprising: obtaining (910) the following security material from the first UE’s home public land mobile network, HPLMN: relay discovery security materials associated with a second UE (710, 840) configured to operate as the U2N relay; and intermediate relay discovery security materials associated with a third UE (730, 820) configured to operate as an intermediate U2N relay between the first UE (740, 810) and the second UE (710, 840); receiving (920) from the third UE (730, 820) a message associated with multi-hop relay discovery, wherein the message includes a first portion generated by the third UE (730, 820) and a second portion generated by the second UE (710, 840); verifying (930) the following: the first portion based on the intermediate relay discovery security materials associated with the third UE (730, 820), and the second portion based on the relay discovery security materials associated with the second UE (710, 840); and based on successful verification of the first and second portions, processing (940) the content of the message.

2. The method of claim 1, wherein the first portion includes a hop count that was generated by the second UE (710, 840) and updated by the third UE (730, 820), and the second portion includes a relay service code, RSC.

3. The method of any of claims 1-2, wherein: the intermediate relay discovery security materials associated with the third UE (730, 820) include a third encryption key and a third integrity protection key; and the relay discovery security materials associated with the second UE (710, 840) include a second encryption key and a second integrity protection key.

4. The method of claim 3, wherein:verifying the first portion comprises decrypting (931) the first portion using the third encryption key and verifying integrity of the decrypted first portion using the third integrity protection key; and verifying the second portion comprises decrypting (932) the second portion using the second encryption key and verifying integrity of the decrypted second portion using the second integrity protection key.

5. The method of any of claims 3-4, wherein the first UE (740) is a Monitoring Remote UE and the message is an Announcement.

6. The method of any of claims 3-4, wherein the first UE (810) is a Discoverer Remote UE and the message is a Discovery Response.

7. The method of claim 6, further comprising: generating (950) a secure Discovery Solicitation message using the relay discovery security materials associated with the second UE (840); and sending (960) the secure Discovery Solicitation message to at least the third UE (820), wherein the Discovery Response message is responsive to the Discovery Solicitation message.

8. A method for a second user equipment, UE (840), arranged to provide a UE-to-network, U2N, relay between intermediate U2N relays and a communication network, the method comprising: obtaining (1010) the following security material from the second UE’s home public land mobile network, HPLMN: relay discovery security materials associated with the second UE (840); and intermediate relay discovery security materials associated with a third UE (830) configured to operate as an intermediate U2N relay; receiving (1020), from the third UE (830), a Discovery Solicitation message associated with multi-hop relay discovery that includes a first portion generated by the third UE (830) and a second portion generated by a first UE (810) configured to operate as a Discoverer Remote UE; verifying (1030) the following: the first portion based on the intermediate relay discovery security materials associated with the third UE (830), and the secondportion based on the relay discovery security materials associated with the second UE (840); and based on successful verification of the first and second portions, processing (1040) the content of the Discovery Solicitation message.

9. The method of claim 8, further comprising: generating (1050) a Discovery Response message, wherein the Discovery Response message is secured using the relay discovery security materials associated with the second UE; and sending (1060) the secure message to at least the third UE (830), wherein the Discovery Response message is sent based on processing the content of the Discovery Solicitation message.

10. The method of claims 8-9, wherein: the relay discovery security materials associated with the second UE (840) include a second encryption key and a second integrity protection key; and the intermediate relay discovery security materials associated with the third UE (830) include a third encryption key and a third integrity protection key.

11. The method of claim 10, wherein the first portion includes a hop count and the second portion includes a relay service code, RSC.

12. The method of claims 8-11, wherein: verifying the first portion of the Discovery Solicitation message comprises decrypting (1031) the first portion using the third encryption key and verifying integrity of the decrypted first portion using the third integrity protection key; and verifying the second portion of the Discovery Solicitation message comprises decrypting (1032) the second portion using the second encryption key and verifying integrity of the decrypted second portion using the second integrity protection key.

13. The method of any of claims 8-12, wherein the relay discovery security materials associated with the second UE (840) include an indication for the relay discovery security materials to be used also as intermediate relay discovery security materials.

14. A method for a third user equipment, UE (720, 730, 820, 830), arranged to provide an intermediate UE-to-network, U2N, relay between remote UEs and a U2N relay coupled to communication network, the method comprising: receiving (1120) a first message associated with multi-hop relay discovery, wherein the first message includes a second portion generated by a message source UE and a first portion generated by one of the following: the message source UE, or a fourth UE arranged as an intermediate U2N relay between the message source UE and the third UE (720, 730, 820, 830); verifying (1130) the first portion based on one of the following: relay discovery security materials associated with a second UE (710, 840) arranged to provide the U2N relay; or intermediate relay discovery security materials associated with the fourth UE; verifying (1040) the second portion based on: relay discovery security materials associated with the second UE (710, 840); based on successful verification of the first and second portions, updating (1050) the first portion and securing the updated first portion using the intermediate relay discovery security materials associated with the third UE (720, 730, 820, 830); and sending (1060) a second message including the second portion and the secured updated first portion to one of the following: a message target UE, or a fifth UE arranged as an intermediate U2N relay between the message target UE and the third UE (720, 730, 820, 830).

15. The method of claim 14, wherein the first portion includes a hop count and the second portion includes a relay service code, RSC, and updating the first portion includes incrementing the hop count.

16. The method of claim 15, wherein the hop count was generated by the message source UE and updated by the fourth UE.

17. The method of any of claims 14-16, wherein: the relay discovery security materials associated with the second UE (710, 840) include a second encryption key and a second integrity protection key; and the intermediate relay discovery security materials associated with the fourth UE include a fourth encryption key and a fourth integrity protection key.

18. The method of claim 17, wherein: verifying the first portion based on the relay discovery security materials associated with the second UE (710, 840) comprises decrypting (1131) the first portion using the second encryption key and verifying integrity of the decrypted first portion using the second integrity protection key; verifying the first portion based on the intermediate relay discovery security materials associated with the fourth UE comprises decrypting (1132) the first portion using the fourth encryption key and verifying integrity of the decrypted first portion using the fourth integrity protection key; and verifying the second portion comprises decrypting (1141) the second portion using the second encryption key and verifying integrity of the decrypted second portion using the second integrity protection key.

19. The method of any of claims 14-18, further comprising obtaining (1110) the following from the third UE’s home public land mobile network, HPLMN: the relay discovery security materials associated with the second UE (710, 840); the intermediate relay discovery security materials associated with the third UE (720, 730, 820, 830); and the intermediate relay discovery security materials associated with the fourth UE.

20. The method of claim 19 wherein one of the following applies: the intermediate relay discovery security materials associated with the third UE (720, 730, 820, 830) include an indication for use also as relay discovery security materials; or the intermediate relay discovery security materials associated with the third UE (720, 730, 820, 830) are derived from or based on relay discovery security materials associated with the third UE (720, 730, 820, 830).

21. The method of any of claims 14-20, wherein: the intermediate relay discovery security materials associated with the third UE (720, 730, 820, 830) include a third encryption key and a third integrity protection key; andsecuring the updated first portion comprises protecting integrity of the first portion using the third integrity protection key and encrypting the integrity -protected first portion using the third encryption key.

22. The method of any of claims 14-21, wherein the first and second messages are Announcement messages, and the message source UE is the second UE (710) arranged as an Announcing U2N Relay.

23. The method of any of claims 14-21, wherein the first and second messages are Discovery Response messages, and the message source UE is the second UE (840) arranged as a Discoveree U2N Relay.

24. The method of any of claims 14-21, wherein the first and second messages are Discovery Solicitation messages, and the message source UE is a first UE (810) arranged as a Discoverer Remote UE.

25. A first user equipment, UE (740, 810), arranged to discover intermediate UE-to-network, U2N, relays that facilitate access to a communication network via a U2N relay, the first UE (740, 810) comprising: communication interface circuitry configured to communicate with other UEs configured as intermediate U2N relays; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of claims 1-7.

26. A first user equipment, UE (740, 810), arranged to discover intermediate UE-to-network, U2N, relays that facilitate access to a communication network via a U2N relay, the first UE (740, 810) being configured to perform operations corresponding to any of the methods of claims 1-7.

27. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a first user equipment, UE (740, 810), arranged to discover intermediate UE-to-network, U2N, relays that facilitate access to a communicationnetwork via a U2N relay, configure the first UE (740, 810) to perform operations corresponding to any of the methods of claims 1-7.

28. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a first user equipment, UE (740, 810), arranged to discover intermediate UE-to-network, U2N, relays that facilitate access to a communication network via a U2N relay, configure the first UE (740, 810) to perform operations corresponding to any of the methods of claims 1-7.

29. A second user equipment, UE (840), arranged to provide a UE-to-network, U2N, relay between intermediate U2N relays and a communication network, the second UE (840) comprising: communication interface circuitry configured to communicate with other UEs configured as intermediate U2N relays; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of claims 8-13.

30. A second user equipment, UE (840), arranged to provide a UE-to-network, U2N, relay between intermediate U2N relays and a communication network, the second UE (840) being configured to perform operations corresponding to any of the methods of claims 8-13.

31. A non-transitory , computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a second user equipment, UE (840), arranged to provide a UE-to-network, U2N, relay between intermediate U2N relays and a communication network, configure the UE to perform operations corresponding to any of the methods of claims 8-13.

32. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a second user equipment, UE (840), arranged to provide a UE-to-network, U2N, relay between intermediate U2N relays and a communication network, configure the UE to perform operations corresponding to any of the methods of claims 8-13.

33. A third user equipment, UE (720, 730, 820, 830), arranged to provide an intermediateUE-to-network, U2N, relay between remote UEs and a U2N relay coupled to communication network, the third UE (720, 730, 820, 830) comprising: communication interface circuitry configured to communicate with other UEs configured as remote UEs, intermediate U2N relays, or U2N relays coupled to communication network; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of claims 14-24.

34. A third user equipment, UE (720, 730, 820, 830), arranged to provide an intermediate UE-to-network, U2N, relay between remote UEs and a U2N relay coupled to communication network, the third UE (720, 730, 820, 830) being configured to perform operations corresponding to any of the methods of claims 14-24.

35. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a third user equipment, UE (720, 730, 820, 830), arranged to provide an intermediate UE-to-network, U2N, relay between remote UEs and a U2N relay coupled to communication network, configure the third UE (720, 730, 820, 830) to perform operations corresponding to any of the methods of claims 14-24.

36. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a third user equipment, UE (720, 730, 820, 830), arranged to provide an intermediate UE-to-network, U2N, relay between remote UEs and a U2N relay coupled to communication network, configure the third UE (720, 730, 820, 830) to perform operations corresponding to any of the methods of claims 14-24.

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