Relay reselection by intermediate relay terminals for multi-hop relay communication

Abstract

In response to determining an initial parent terminal PCS connection with an initial parent relay terminal has become unavailable, an intermediate relay terminal maintains a child terminal PCS connection with a child terminal and performs a relay reselection procedure to select a target parent relay terminal for facilitating communication to a target cell. The intermediate relay terminal refrains from notifying the child terminal that the initial parent terminal PCS connection had become unavailable while performing the relay reselection procedure.

Description

TUTL 00414 PC-1- RELAY RESELECTION BY INTERMEDIATE RELAY TERMINALS FOR MULTI-HOP RELAY COMMUNICATIONCLAIM OF PRIORITY

[0001] The present application claims priority to Provisional Application No.63 / 779,009, entitled “Relay Reselection by the Intermediate Relay UE” and filed March 27, 2025, assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety.FIELD

[0002] This invention generally relates to wireless communications and more particularly to relay reselection by intermediate relay terminals for multi-hop relay communication.BACKGROUND

[0003] Many wireless communication systems that employ several base stations (network nodes) that provide wireless service to terminals (user equipment (UE) devices) enable sidelink communication between two or more terminals where the terminals can communicate directly with other terminals. In addition, one or more terminal can be used as relay devices to form relay communication links between terminal and a cell of a base station or between a source UE device and a destination UE device. A relayed connection between a remote UE and the network through a relay device is often referred to as a UE-to-Network (U2N) link. The U2N link includes a PC5 link between the relay device and the remote UE and Uu link between the relay device and a cell of a base station in the network. Accordingly, a remote terminal (remote UE) may be connected to a cell of a network node through one or more intermediate relay terminals (relay UEs) forming the U2N link. The relay terminal directly connected to the cell is typically referred to as the last relay terminal or last relay UE (LRU). In some situations, multiple relay terminals can form a connection from the remote terminal toTUTL 00414 PC-2-the network. Such an arrangement is typically referred to as a multi-hop relay communication link where each relay terminal provides one hop.

[0004] In some conventional systems, the U2N communication links use a Sidelink Relay Adaptation Protocol (SRAP) defined by one or more revisions of the 3rdGeneration Partnership Project (3GPP) standards to transmit control and data signals over the PC5 link and the llu link. The SRAP is used to perform bearer mapping (signaling radio bearers (SRBs) and data radio bearers (DRBs)) between the two links. For U2N relays, a local Remote UE ID is included in both the PC5 SRAP header and the Uu SRAP header. The Layer 2 (L2) U2N Relay UE is configured by the gNB (network node) with the local Remote UE ID to be used in SRAP headers. In some situations, the U2N communication link may include more than one relay terminal.

[0005] In conventional systems, terminals establish, reestablish, or resume connections to a cell of a network. In accordance with 3GPP standards, for example, a terminal may be in one of three Radio Resource Control (RRC) states when the terminal attempts to connect or reconnect to a cell of the network. When in an RRC IDLE state, a terminal establishes a new connection using an RRC setup procedure. When a terminal is in an RRC CONNECTED state and the link fails, the terminal restores the connection through an RRC reestablishment procedure. When a terminal is in an INACTIVE state, the terminal resumes the suspended connection using an RRC resume procedure. The RRC IDLE and RRC INACTIVE states can be collectively referred to as a nonconnected state.

[0006] With a multi-hop relay communication path between a child terminal and an initial cell through an intermediate relay terminal and parent terminal of the intermediate relay terminal, situations arise where the child terminal is connected to the intermediate relay terminal over a child PC5 link when a parent PC5 link becomes unavailable. The multi-hop relay communication path may be a multi-hop relay communication link where the terminals are in RRC CONNECTED and data is transmitted over the path. The multi-hop relay communication path may also be a potential multi-hop relay communication link where the child terminal initiates a procedure to establish RRC CONNECTED through the intermediate relay terminal and the parent relay terminal.TUTL 00414 PC-3-

[0007] For the case when the child terminal and / or the intermediate relay terminal is in RRC CONNECTED, conventional systems require the intermediate relay terminal to notify the child terminal when the parent PC5 link becomes unavailable (e.g., the intermediate relay terminal detects RLF of the PC5 link to the parent relay terminal). It is also possible for the intermediate relay terminal to report the RLF when the child terminal attempts to establish RRC CONNECTED when the PC5 link becomes unavailable.SUMMARY

[0008] In response to determining an initial parent terminal PC5 connection with an initial parent relay terminal has become unavailable, an intermediate relay terminal maintains a child terminal PC5 connection with a child terminal and performs a relay reselection procedure to select a target parent relay terminal for facilitating communication to a target cell. The intermediate relay terminal refrains from notifying the child terminal that the initial parent terminal PC5 connection had become unavailable while performing the relay reselection procedure.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 A is a block diagram of an example of a communication system where an intermediate relay terminal performs relay reselection while refraining from notifying a child terminal that an initial parent relay terminal PC5 link to an initial parent terminal has become unavailable.

[0010] FIG. 1 B is a block diagram of communication system for an example where the child terminal is a remote terminal 104 and the initial parent relay terminal is an initial last relay terminal and where the intermediate relay terminal performs relay reselection while in the RRC non-CONNECTED state and while refraining from notifying the remote terminal that an initial last relay terminal PC5 link to the initial last terminal has become unavailable.

[0011] FIG. 1 C is a block diagram of the communication system for an example where the intermediate relay terminal informs the remote terminal that the intermediateTUTL 00414 PC-4-relay terminal cannot perform functions of a relay terminal after a failed relay reselection attempt while in the RRC non-CONNECTED state.

[0012] FIG. 1 D is a block diagram of communication system for an example where the child terminal is a remote terminal and the initial parent relay terminal is an initial last relay terminal and where the intermediate relay terminal performs relay reselection while in the RRC CONNECTED state and while refraining from notifying the remote terminal that an initial last relay terminal PC5 link to the initial last terminal has become unavailable.

[0013] FIG. 1 E is a block diagram of communication system for an example where the child terminal is a remote terminal and the initial parent relay terminal is an initial last relay terminal and where the intermediate relay terminal performs relay reselection to connect to the initial cell while in the RRC CONNECTED state and while refraining from notifying the remote terminal that an initial last relay terminal PC5 link to the initial last terminal has become unavailable.

[0014] FIG. 2 is a block diagram of an example of a base station suitable for use as the network node providing the serving cell.

[0015] FIG. 3 is a block diagram of an example of a UE device suitable for use as each of the terminals including remote terminals and relay terminals.

[0016] FIG. 4A is a message flow diagram for an example where the intermediate relay terminal performs relay reselection while in the RRC CONNECTED state and while refraining from notifying the remote terminal that an initial last relay terminal PC5 link to the initial last terminal has become unavailable.

[0017] FIG. 4B is a message flow diagram for an example where the intermediate relay terminal performs relay reselection to connect to the initial cell while in the RRC CONNECTED state and while refraining from notifying the remote terminal that an initial last relay terminal PC5 link to the initial last terminal has become unavailable.

[0018] FIG. 4C is a message flow diagram for an example where the intermediate relay terminal fails at an attempt of relay reselection and / or RRC Reestablishment for the examples of FIG. 4A and FIG. 4B.TUTL 00414 PC-5-

[0019] FIG. 5 is a message flow diagram 500 for an example where the intermediate relay terminal performs a path switch service continuity procedure to connect to a target relay terminal while in the RRC CONNECTED state and while refraining from notifying the remote terminal that an initial last relay terminal PC5 link to the initial last terminal has become unavailable.

[0020] FIG. 6 is a flow chart of an example of a method of performing relay selection for a multi-hop relay communication path.

[0021] FIG. 7 is a flow chart of an example of method of establishing RRC CONNECTED without notifying a remote terminal of the unavailability of the PC5 link to an initial last relay terminal.DETAILED DESCRIPTION

[0022] As discussed above, a relay communication link can be established between a serving cell and a remote terminal (remote user equipment (UE) device) through one or more relay terminals (relay UE devices). The relay communication link, often referred to as a UE-to-Network (U2N) communication link, includes PC5 links between the remote terminal and the relay terminal and between relay terminals when more than one relay terminal forms the U2N communication link. The remote terminal is connected through a first PC5 link to a first relay terminal. The first relay terminal is connected through a second PC5 link to the second relay terminal and the second relay terminal is connected to the serving cell over a Uu link. The relay communication link may include any number of intermediate relay terminals where a PC5 ingress link of each relay terminal is a PC5 egress link of an adjacent relay terminal. Except for the last relay terminal, therefore, each relay terminal in the U2N link has a PC5 ingress link to a terminal and a PC5 egress link to another terminal. The last relay terminal (LRT) may be referred to as the U2N relay terminal or the last relay UE (LRU). The relay terminals connected within the multi-hop relay communication link between the remote terminal and the last relay terminal may be referred to as intermediate relay terminals and / or intermediate relay UEs (IRUs).

[0023] As discussed above, conventional systems require an intermediate relay terminal to notify a child terminal when the PC5 link to the parent terminal of theTUTL 00414 PC-6-intermediate relay terminal becomes unavailable. Such a technique, however, is inefficient in some situations. When the intermediate relay terminal successfully performs relay reselection, for example, the child terminal may unnecessarily perform relay resection in response to the failure notification. Accordingly, even though the intermediate relay terminal reestablished communication through a target relay terminal to the network and is capable of continuing to facilitate a multi-hop relay communication link for the child terminal, the child terminal evaluates candidate relay terminals. For the examples herein, however, the intermediate relay terminal refrains from notifying the child terminal while performing the relay reselection and RRC reestablishment procedures at least until the procedures are completed.

[0024] In some examples, the intermediate relay terminal is in a non-connected RRC state, such as RRCJDLE or RRCJNACTIVE, when detecting the unavailability (e.g, RLF) of the PC5 link to the parent relay terminal. The intermediate relay terminal performs relay reselection without notifying the child terminal. Where the child terminal is a remote terminal that has sent a RRC Setup Request, the intermate relay terminal establishes RRC CONNECTED and forwards the remote terminal RRC Setup Request through the multi-hop relay communication link to the serving cell.

[0025] In some other examples, the intermediate relay terminal is in the RRC CONNECTED state when detecting the unavailability (e.g, RLF) of the PC5 link to the parent relay terminal. The intermediate relay terminal performs relay reselection without notifying the child terminal. The child terminal may be remote terminal, the parent terminal may be an initial last relay terminal, and the intermediate relay terminal may be facilitating a multi-hop relay communication link when detecting the PC5 link unavailability. The intermediate relay terminal sends a suspend data notification to the remote terminal and performs relay reselection RRC connection reestablishment without notifying the remote terminal. After a multi-hop relay communication link is reestablished, the remote terminal can continue with data transmission over the new reestablished link.

[0026] A network node is any apparatus, equipment, device, or combination of devices, on the network side of the communication system that is connected to the communication network or is part of communication network. Some examples of aTUTL 00414 PC-7-network node include a base station, a node B, an E-UTRA Node B, Evolved Node B, eNodeB, eNB, a New Generation eNB (ng-eNB), a gNodeB (also known as a gNB) in new radio (NR) technology, a macro station, pico station, and a femto station. The network node may form, or be a part of, the radio access network (RAN) that provides a connection between the core network and terminal communication devices. A RAN may be organized into three functional blocks including a Radio Unit (RU), a Distributed Unit (DU) and a Centralized Unit (CU). The RU transmits, receives, amplifies, and digitizes radio frequency signals and typically located near, or integrated into, the antenna. The DU and CU perform computations and / or processing to send and receive digitalized radio signals to and from the core network. The DU is typically located at or near the RU and the CU may be closer to the core network. The infrastructure or connection between the RU and the DU is often referred to as fronthaul and the infrastructure or connection between the DU and the CU is often referred to as a midhaul. The communication node, therefore, may perform the functions of one or more of the RU, DU and / or CU depending on the particular implementation.

[0027] A terminal communication device (terminal), such as a remote terminal and a relay terminal, is a communication device on the terminal side of the communication system and is sometimes referred to as user equipment (UE), a UE device, a terminal device, wireless mobile device, wireless communication device and other terms. Some examples of a terminal communication device include a mobile phone, a smart phone, a personal digital assistant (PDA), tablet, and laptop computer. In some situations, the terminal communication device is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. In addition, the terminal communication device may be, or may be a part of, a wearable device or a vehicle where the vehicle may be terrestrial vehicle, watercraft, or aircraft (including unmanned aerial vehicles). The terminal communication device, therefore, is any fixed, mobile, or portable equipment that performs the functions of the terminal device described herein.

[0028] A parent terminal is a terminal that is connected to a child terminal where the parent terminal is typically closer within the multi-hop communication link to the cell of the network node. The parent terminal, therefore, has one less hop to the network than the child terminal. For example, an intermediate relay terminal is a child terminal of aTUTL 00414 PC-8- U2N relay terminal that is Uu connected to the cell of the network node and the U2N relay terminal is parent terminal of the intermediate relay terminal. Similarly, a remote terminal is a child terminal of an intermediate relay terminal and the intermediate relay terminal is parent terminal of the remote terminal.

[0029] An access node is a terminal or a cell that provides access to the network. Accordingly, a cell may be an access node for a terminal. A U2N relay terminal may be an access node as well as an intermediate relay terminal that is connected (or can connect) to the cell via a U2N relay terminal or via one or more intermediate relay terminals and a U2N relay terminal. For the examples herein, the relay terminals, child terminals, parent terminals, and remote terminals are User Equipment (UE) devices that may perform particular functions and services in the examples. The relay terminals may be referred to as first, second, intermediate, and last in accordance with the particular functions and / or position within a relay communication link. A first relay terminal and second relay terminal may be referred to as an intermate relay terminal (IRT) or intermediate relay UE (IRU). A U2N relay terminal connected to cell over a Uu link and may be referred to as a last relay terminal (RLT) or last relay UE (LRU). The last relay terminal, therefore, is connected to a cell of the network over a Uu link.

[0030] FIG. 1 A is a block diagram of an example of a communication system 10 where an intermediate relay terminal 12 performs relay reselection while refraining from notifying a child terminal 14 that an initial parent relay terminal PC5 link 16 to an initial parent terminal 18 has become unavailable. For the example, the intermediate relay terminal 12 is initially connected to the child terminal 14 through a child PC5 link 20 and is connected to its parent relay terminal (initial parent relay terminal) 18 through an initial PC5 link 16. The intermediate relay terminal 12, therefore, is initially configured to at least potentially facilitate a multi-hop relay communication path 22 from the child terminal 14 to an initial cell 26 through the initial parent terminal PC5 link 16. For the example of Fig. 1A, the intermediate relay terminal may be in a Radio Resource Configuration (RRC) Connected state or an RRC non-connected state (IDLE or INACTIVE). The multi-hop relay communication path 22 may be a portion of a multi-hop relay communication link between a remote terminal and the network 24 or may be a portion of an identified potential multi-hop relay communication link between a remoteTUTL 00414 PC-9-terminal and the network 24. For example, the child terminal 14 may be a remote terminal in the RRC IDLE state initiating a connection procedure to establish RRC CONNECTED to the initial cell 26 through a multi-hop relay communication link through the intermediate relay terminal 12 and the initial parent relay terminal 18. Examples with additional details for RRC CONNECTED and RRC non-CONNECTED states are discussed below.

[0031] The example of FIG. 1 A begins with the child PC5 link 20 established between the child terminal 14 and the intermediate relay terminal 12 as well as the initial parent relay PC5 link 16 established between the intermediate relay terminal 12 and the initial parent relay terminal 18. The intermediate relay terminal 12 determines that the initial parent relay PC5 link 16 has become unavailable. In some situations, the determination is based on a detection that the PC5 link 16 has suffered a radio link failure (RLF). In other situations, the intermediate relay terminal may receive a notification from the parent terminal 18 indicating that the parent relay terminal 18 is no longer able to serve as a relay terminal. For example, the parent relay terminal 18 may indicate that a connection to another relay terminal or a Uu connection to the serving cell has failed or has otherwise become unavailable. For a situation where the parent relay terminal 18 is last relay terminal connected to the serving cell, the parent relay terminal 18 may indicate that the Uu link to the serving cell has suffered an RLF. In still other examples, the parent relay terminal 18 may become unavailable because parent relay terminal 18 (or a relay terminal in the multi-hop relay path) has performed a Handover (HO) to another cell or has performed relay reselection.

[0032] In response to determining that the initial parent relay PC5 link 16 has become unavailable, the intermediate relay terminal 12 performs a relay reselection procedure 27 while maintaining the child PC5 link 20 and while refraining from notifying the child terminal 14 that reselection is being performed or that the initial parent relay terminal PC5 link 16 had become unavailable. The intermediate relay terminal 12 refrains from notifying the child terminal 14 of the reselection at least until the reselection procedure is completed and, in some situations, may provide a notification to the child terminal 14 after RRC CONNECTED is reestablished with the target parent relay terminal 28. In other situations, no notification is sent to the child terminal 14TUTL 00414 PC-10-indicating that reselection will be, is being, or has been performed before, during, or after relay reselection. In still other situations, no notification is sent except for a failure notification in response to a failed relay reselection or a failed RRC reestablishment procedure.

[0033] The target parent relay terminal 28 is connected to the network 24 through a target cell 30 where the target parent relay terminal 28 may be connected directly to the target cell 30 over Uu link or may be connected through one or more relay terminals. In some situations, the target cell 30 is the initial cell 26. Accordingly, the block representing the target cell 30 is shown with dashed lines in FIG. 1A.

[0034] FIG. 1 B is a block diagram of communication system 100 for an example where the child terminal 14 is a remote terminal 104 and the initial parent relay terminal 18 is an initial last relay terminal 108 and where the intermediate relay terminal 12 performs relay reselection while in the RRC non-CONNECTED state and while refraining from notifying the remote terminal 104 that an initial last relay terminal PC5 link 112 to the initial last terminal 108 has become unavailable. Accordingly, the system 100 of FIG. 1 B is an example of the system 10 of FIG. 1A where the initial multi-hop relay communication path 22 is a potential multi-hop relay communication link between the remote terminal 104 and the initial cell 26 including the intermediate relay terminal 12 and the initial last relay terminal 108. For the example, the intermediate relay terminal 12 is initially connected to the remote terminal 104 through a PC5 link 110 and is connected to the last relay terminal 108 through the initial PC5 link 112. The intermediate relay terminal 12 is in a non-RRC CONNECTED state, such as the RRC IDLE or RRC INACTIVE states. The initial last relay terminal 108 is connected to the initial cell 26 over a Uu link 114.

[0035] The remote terminal 104, which is initially not in RRC CONNECTED, sends a remote terminal RRC Setup Request (RT RRC Setup Request) 116, to the intermediate relay terminal 12 over the Signaling Radio Bearer 0 (SRB0) used for transmission of Radio Resource Control (RRC) messages using the Common Control Channel (CCCH). Before the intermediate relay terminal 12 is able to establish the RRC CONNECTED state and forward the RT Setup Request 116, the intermediate relay terminal 12 detects that the PC5 link 112 to the last relay terminal 108 is no longer available (e.g., hasTUTL 00414 PC-11-suffered an RLF). The RT Setup Request 116 may be received before or after the intermediate relay terminal 12 detects the unavailability of the PC5 link 112 since the intermediate relay terminal 12 does not notify the remote terminal 104 of the unavailability of the initial relay PC5 link 112 to the initial last relay terminal 108.

[0036] In response to detecting the unavailability of the initial PC5 link 112, the intermediate relay terminal 12 performs a relay selection procedure 118 while maintaining the remote PC5 link 110 and while refraining from notifying the remote terminal 104 that reselection is being performed or that the initial last relay terminal PC5 link 112 had become unavailable. After selecting the target last relay terminal 120 and establishing a target PC5 link 121 with the target last relay terminal 120, the intermediate relay terminal 12 sends an RRC Setup Request to initiate a procedure to establish RRC CONNECTED with the target cell 30. The target cell configures the intermediate relay terminal 12 with the Local ID and SL-RLC channels to support SRAP and the intermediate relay terminal 12 establishes RRC CONNECTED. After the intermediate relay terminal 12 is in RRC CONNECTED, the intermediate relay terminal 12 forwards the RT RRC Setup Request to the target cell 30 through the target last relay terminal 120. For the example, the intermediate relay terminal 12 sends the RT RRC Setup Request via a Sidelink UE Information (Sill) RRC message 126 to the target last relay terminal 120 using the configured Local ID and SRAP protocol. .The target last relay terminal 120 forwards the RT RRC Setup Request information via the configured RLC to the target cell 30. While performing the relay reselection procedure 118, the intermediate relay terminal 12 does not notify the remote terminal 104 that the initial parent relay PC5 link 112 to the initial last relay terminal 108 has become unavailable or that the intermediate relay terminal 12 is performing relay reselection. In some situations, the intermediate relay terminal 12 notifies the remote terminal 104 if the reselection and / or the RRC establishment fails. For the example of FIG. 1 B, the target cell 30 is provided by the same network node (e.g, gNB) that provides the initial cell 26.

[0037] FIG. 1 C is a block diagram of the communication system 100 for an example where the intermediate relay terminal 12 informs the remote terminal 104 that the intermediate relay terminal 12 cannot perform functions of a relay terminal after a failedTUTL 00414 PC-12-relay reselection attempt while in the RRC non-CONNECTED state. The scenario described with reference to FIG. 1 C is an example the system 100 of FIG. 1 B where the intermediate relay terminal 12 is unsuccessful in establishing RRC CONNECTED after attempting the relay reselection procedure 118 that includes refraining from notifying the remote terminal 104 that the PC5 link 110 has become unavailable.

[0038] If the intermediate relay terminal 12 is unable to successfully perform relay reselection or if relay selection is successful but RRC CONNECTED cannot be established, the intermediate relay terminal 12 determines access failure 130 has occurred. In response, the intermediate relay terminal 12 sends an access failure message 132 to the remote terminal 104. For the example, the access failure message is a PC5-RRC message. In some situations, different messages may be sent based on the type of failure where a relay selection failure message is sent in response to unsuccessful relay reselection and a RRC CONNECTION failure message is sent in response to unsuccessful RRC CONNECTION establishment event after a successful relay reselection.

[0039] FIG. 1 D is a block diagram of communication system 100 for an example where the child terminal 14 is a remote terminal 104 and the initial parent relay terminal 18 is an initial last relay terminal 108 and where the intermediate relay terminal 12 performs relay reselection while in the RRC CONNECTED state and while refraining from notifying the remote terminal 104 that an initial last relay terminal PC5 link 112 to the initial last terminal 108 has become unavailable. Accordingly, the system 100 of FIG. 1D is an example of the system 10 of FIG. 1 A where the initial multi-hop relay communication path 22 is a multi-hop relay communication link between the remote terminal 104 and the initial cell 26 including the intermediate relay terminal 12 and the initial last relay terminal 108. For the example, the intermediate relay terminal 12 is initially connected to the remote terminal 104 through a remote PC5 link 110 and is connected to the last relay terminal 108 through the initial PC5 link 112. The intermediate relay terminal 12 is in the RRC CONNECTED state with the initial cell 26 where the initial last relay terminal 108 is connected to the initial cell 26 over a Uu link 114. The remote terminal 104 is also in the RRC CONNECTED state with the initial cell 26.TUTL 00414 PC-13-

[0040] In response to detecting the unavailability of the PC5 link 112, the intermediate relay terminal 12 performs a relay selection procedure 118 while maintaining the remote PC5 link 110 and while refraining from notifying the remote terminal 104 that reselection is being performed or that the initial last relay terminal PC5 link 112 had become unavailable. For the example, the intermediate relay terminal 12 sends a suspend sidelink data message 140 to the remote terminal 104 instructing the remote terminal 104 to temporarily suspend sidelink data transmission. An example of a suitable message for conveying the instruction is a PC5-RRC message that is sent in response to detecting the unavailability of the PC5 link 112 and the determination that relay reselection will be performed. The intermediate relay terminal 12 performs the relay reselection procedure 118 and identifies the target last relay terminal 120 which is connected to (or connects to) a target cell 30 over a Uu link 122. For the example of FIG. 1 D, the target cell 30 is not the initial cell 26 and may be provided by the same network node (gNB) 142 providing the initial cell 26 or by a different network node (gNB) 144. Accordingly, the block representing the network node 144 is illustrated with dashed lines to indicate the target network node 144 may be the initial network node 142 in some situations.

[0041] After a PC5 link 146 is established between the intermediate relay terminal 12 and the intermediate last relay terminal 120, the intermediate relay terminal 12 reestablishes RRC CONNECTED with the target cell 30. The intermediate relay terminal exchanges messages with the target cell and is reconfigured with Packet Data Convergence Protocol (PDCP) parameters in a reestablishment procedure 148 in accordance with known techniques except that the reestablishment is transparent to the remote terminal 104. In other words, the remote terminal 104 is unaware that the PC5 link 112 had become unavailable and that the intermediate relay terminal 12 is performing relay reselection followed by RRC reestablishment. In conventional systems, the intermediate relay terminal informs the remote terminal of the PC5 link 112 failure. As a result, both the intermediate relay terminal and the remote terminal may perform relay reselection. With the techniques herein, however, the remote terminal is unaware of the link failure and does not perform relay selection in response to a notification that the initial parent relay PC5 link is unavailable.TUTL 00414 PC-14-

[0042] After reestablishing RRC CONNECTED, the intermediate relay terminal 12, sends a reestablishment notification 150 to the remote terminal 104 indicating that the intermediate relay terminal has successfully performed relay reselection and connection reestablishment. An example of suitable technique for sending the reestablishment notification 150 includes sending a NotificationMessageSidelink message with an indication type of “relayllE-reestablished”. After receiving the notification message 150, the remote terminal determines whether to remain PC5 connected to the intermediate relay terminal 12 and send a RRC Reestablishment Request to the target cell via the IRU or whether to perform relay reselection. Therefore, the remote terminal 104 sends a reestablishment request to initiate the reestablishment procedure 152 to establish the RRC CONNECTED with the target cell 30 where the target cell 30 reestablishes PDCP with the remote terminal 104. In conventional systems, the intermediate relay terminal sends a notification message before the intermediate relay terminal performs reselection and reestablishment where the message prompts the remote terminal to also perform its own relay reselection followed by reestablishment.

[0043] FIG. 1 E is a block diagram of communication system 100 for an example where the child terminal 14 is a remote terminal 104 and the initial parent relay terminal 18 is an initial last relay terminal 108 and where the intermediate relay terminal 12 performs relay reselection to connect to the initial cell 26 while in the RRC CONNECTED state and while refraining from notifying the remote terminal 104 that an initial last relay terminal PC5 link 112 to the initial last terminal 108 has become unavailable. Accordingly, the system 100 of FIG. 1E is an example of the system 10 of FIG. 1 A where the initial multi-hop relay communication path is a multi-hop relay communication link between the remote terminal 104 and the initial cell 26 including the intermediate relay terminal 12 and the initial last relay terminal 108. For the example, the intermediate relay terminal 12 is initially connected to the remote terminal 104 through a remote PC5 link 110 and is connected to the last relay terminal 108 through the initial parent relay PC5 link 112. The intermediate relay terminal 12 is in the RRC CONNECTED state with the initial cell 26 where the initial last relay terminal 108 is connected to the initial cell 26 over a Uu link 114. The remote terminal 104 is also in the RRC CONNECTED state with the initial cell 26. The initial states and connections inTUTL 00414 PC-15-the example of FIG. 1E, therefore, are the same as the initial states and connections in the example of FIG. 1D. For the example of FIG. 1E, however, the selected target last relay terminal 120 is connected to (or will be connected to) the initial cell 26 via a Uu link 160.

[0044] In response to detecting the unavailability of the PC5 link 112, the intermediate relay terminal 12 performs a relay selection procedure 118 while maintaining the remote PC5 link 110 and while refraining from notifying the remote terminal 104 that reselection is being performed or that the initial last relay terminal PC5 link 112 had become unavailable. For the example, the intermediate relay terminal sends a suspend sidelink data message 140 to the remote terminal 104 instructing the remote terminal 104 to temporarily suspend data transmission. An example of a suitable message for conveying the instruction is a PC5-RRC message that is sent in response to detecting the unavailability of the PC5 link 112 and the determination that relay reselection will be performed. The intermediate relay terminal 12 performs the relay reselection procedure 118 and identifies the target last relay terminal 120 which is connected to (or connects to) the initial cell 26 over the Uu link 160. For the example of FIG. 1 E, the target cell is the initial cell 26 is provided by the initial network node (gNB) 142.

[0045] After a PC5 link 146 is established between the intermediate relay terminal 12 and the intermediate last relay terminal 120, the intermediate relay terminal 12 reestablishes RRC CONNECTED with the target cell (initial cell 26). The intermediate relay terminal exchanges messages with the initial cell and is reconfigured with PDCP parameters in a reestablishment procedure 162 in accordance with known techniques except that the reestablishment is transparent to the remote terminal 104. In other words, the remote terminal 104 is unaware that the PC5 link 112 had become unavailable and that the intermediate relay terminal 12 is performing reestablishment. In conventional systems, the intermediate relay terminal informs the remote terminal of the PC5 link 112 failure. As a result, both the intermediate relay terminal and the remote terminal may perform relay reselection. With the techniques herein, however, the remote terminal is unaware of the link failure and does not perform relay selection.TUTL 00414 PC-16-

[0046] After reestablishing RRC CONNECTED, the intermediate relay terminal 12, sends a remote terminal PC5 connected notification 164 to the target cell indicating that the remote terminal is connected to the intermediate relay terminal over the PC5 link 110. For the example, the notification 164 also indicates that the remote terminal 104 was not notified that the PC5 link to the initial last relay terminal had become unavailable or that the intermediate relay terminal had performed RRC reestablishment. An example of suitable technique for sending the notification 162 includes sending a SidelinkllEInformation message. After the intermediate relay terminal 12 reestablishes RRC CONNECTED, the intermediate relay terminal 12 also sends a Resume Data message (sidelink restored message) 166 to the remote terminal 104 indicating to the remote terminal 104 that sidelink data transmission can be resumed. An example of suitable message for conveying the Resume Data notification is a PC5-RRC message. In some situations, the target cell (initial cell) 26 may determine that the remote terminal should be RRC reconfigured and may perform RRC Reconfiguration 168. The RRC Reconfiguration 168 is shown with a dashed line to indicate that the reconfiguration is not required in some situations. For the examples herein, the intermediate relay terminal 170 notifies the remote terminal if the reestablishment fails with a reestablishment failed notification 170.

[0047] FIG. 2 is a block diagram of an example of a base station 200 suitable for use as a network node providing the initial cell 26 or target cell 30. Accordingly, the first network node 142 and the second network node 144 may be a base station 200. The base station 200 includes a controller 204, transceiver 205 that includes a transmitter 206 and receiver 208, and an antenna 210, as well as other electronics, hardware, and code. The base station 200 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to the network nodes providing cells and base station 200 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. The base station 200 may be a fixed device or apparatus that is installed at a particular location at the time of system deployment. Examples of such equipment include fixed baseTUTL 00414 PC-17-stations or fixed transceiver stations. Although the base station 200 may be referred to by different terms, the base station 200 is typically referred to as a gNodeB or gNB when operating in accordance with one or more communication specifications of the 3GPP V2X operation. In some situations, the base station 200 may be mobile equipment that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generating equipment such as electric generators, solar panels, and / or batteries. Larger and heavier versions of such equipment may be transported by trailer. In still other situations, the base station 200 may be a portable device that is not fixed to any particular location.

[0048] The controller 204 includes any combination of hardware, software, and / or firmware for executing the functions described herein as well as facilitating the overall functionality of the base station 200. An example of a suitable controller 204 includes code running on a microprocessor or processor arrangement connected to memory. The transmitter 206 includes electronics configured to transmit wireless signals. In some situations, the transmitter 206 may include multiple transmitters. The receiver 208 includes electronics configured to receive wireless signals. In some situations, the receiver 208 may include multiple receivers. The receiver 208 may receive signals through multiple antennas or through a selected antenna of a plurality of antennas of the antenna 210. The antenna 210 may include separate transmit and receive antennas or separate arrays in some situations.

[0049] The transmitter 206 and receiver 208 in the example of FIG. 2 perform radio frequency (RF) processing including modulation and demodulation. The receiver 208, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 206 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the base station functions. The required components may depend on the particular functionality required by the base station.

[0050] The transmitter 206 includes a modulator (not shown), and the receiver 208 includes a demodulator (not shown). The modulator modulates the signals to beTUTL 00414 PC-18-transmitted as part of the downlink signals and can apply any one of a plurality of modulation orders. The demodulator demodulates any uplink signals received at the base station 200 in accordance with one of a plurality of modulation orders.

[0051] The base station 200 includes a communication interface 212 for transmitting and receiving messages with other base stations such as the network nodes providing target cells and / candidate target cells. The communication interface 212 may be connected to a backhaul or network enabling communication with other base stations. In some situations, the link between base stations may include at least some wireless portions. The communication interface 212, therefore, may include wireless communication functionality and may utilize some of the components of the transmitter 206 and / or receiver 208.

[0052] FIG. 3 is a block diagram of an example of a UE device 300 suitable for use as each of the terminals including child terminals, parent terminals, last relay terminals, remote terminals, and intermediate relay terminals., Accordingly, such as the intermediate relay terminal 12, child terminal 14, initial parent relay terminal 18, the target parent relay terminal 28, the remote terminal 104, initial last relay terminal 108, and the target last relay terminal 120 may be a UE device 300. In some examples, the UE device 300 is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone. In other examples, the UE device 300 is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. The UE device 300, therefore is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to UE device 300 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

[0053] The UE device 300 includes at least a controller 302 and a transceiver 303 that includes a transmitter 304 and a receiver 306. The controller 302 includes any combination of hardware, software, and / or firmware for executing the functions described herein as well as facilitating the overall functionality of a communicationTUTL 00414 PC-19-device. An example of a suitable controller 302 includes code running on a microprocessor or processor arrangement connected to memory 310. The transmitter 304 includes electronics configured to transmit wireless signals. In some situations, the transmitter 304 may include multiple transmitters. The receiver 306 includes electronics configured to receive wireless signals. In some situations, the receiver 306 may include multiple receivers. The receiver 306 and transmitter 304 receive and transmit signals, respectively, through the antenna 308. The antenna 308 may include separate transmit and receive antennas. In some circumstances, the antenna 308 may include multiple transmit and receive antennas.

[0054] The transmitter 304 and receiver 306 in the example of FIG. 3 perform radio frequency (RF) processing including modulation and demodulation. The receiver 306, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 304 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the communication device functions. The required components may depend on the particular functionality required by the communication device.

[0055] The transmitter 304 includes a modulator (not shown), and the receiver 306 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as part of the uplink signals. The demodulator demodulates the downlink signals in accordance with one of a plurality of modulation orders.

[0056] The UE device 300 is capable of transmitting and receiving sidelink signals to and from other UE devices as well as communicating with a base station. The controller 302, in conjunction with the receiver 306, measures signals, such as discovery signals, transmitted by nearby UE devices to generate the neighbor list that includes neighbor UE devices within the maximum distance. The neighbor list is stored in the memory 310 and transmitted to a base station 200 when the UE device 300 is a reporting UE device.

[0057] FIG. 4A is a message flow diagram 400 for an example where the intermediate relay terminal 12 performs relay reselection while in the RRCTUTL 00414 PC-20- CONNECTED state and while refraining from notifying the remote terminal 104 that an initial last relay terminal PC5 link 110 to the initial last terminal 108 has become unavailable. Accordingly, the message flow 400 of FIG. 4A is an example of suitable message flow for the scenario discussed with reference to FIG. 1 D. For the example, the intermediate relay terminal 12 is initially connected to the remote terminal 104 through a remote PC5 link 110 and is connected to the last relay terminal 108 through the initial PC5 link 112. The intermediate relay terminal 12 is in the RRC CONNECTED state with the initial cell 26 where the initial last relay terminal 108 is connected to the initial cell 26 over a llu link 114. The remote terminal 104 is also in the RRC CONNECTED state with the initial cell 26.

[0058] At event 402, the remote terminal 104 and the initial cell 26 exchange uplink and downlink data over a multi-hop communication link including the intermediate relay terminal 12 and the initial last relay terminal 108 where the intermediate relay terminal 12 is connected to the initial last relay terminal 108 over the initial PC5 link.

[0059] At event 404, the intermediate relay terminal 12 determines that the initial PC5 link 112 to the initial last relay terminal 108 has become unavailable. In most situations, the intermediate relay terminal 12 detects a radio link failure (RLF) although the PC5 link may become unavailable in other ways.

[0060] At transmission 406, the intermediate relay terminal 12 sends a suspend data message 140 to the remote terminal 104. In response to detecting the unavailability of the PC5 link 112 and determining that relay reselection will be performed, the intermediate relay terminal 12 sends a PC5-RRC message conveying the suspend data message 140. The suspend data message 140 instructs the remote terminal 104 to temporarily suspend uplink data transmission. For the example, the suspend data message 140 does not indicate a reason for the data transmission suspension and does not indicate that the PC5 link 112 has become unavailable.

[0061] At event 408, the intermediate relay terminal 12 initiates relay reselection. The relay reselection procedure includes refraining from notifying the remote terminal 104 that relay reselection is being performed or that the PC5 link 112 is unavailable. In response to detecting the unavailability of the PC5 link 112, therefore, the intermediate relay terminal 12 performs the relay selection procedure 118 while maintaining theTUTL 00414 PC-21-remote PC5 link 110 and while refraining from notifying the remote terminal 104 that reselection is being performed or that the initial last relay terminal PC5 link 112 had become unavailable. The target last relay terminal is connected to (or is capable of connecting to) a target cell 30 over a Uu link 122. For the example of FIG. 4A, the target cell 30 is not the initial cell 26 and may be provided by the same network node (gNB) 142 providing the initial cell 26 or by a different network node (gNB) 144.

[0062] At event 410, the remote terminal 104 suspends data transmission.

[0063] At transmission 412, the target relay last relay terminal 120 sends a discovery message that is received by the intermediate relay terminal 12. The intermediate relay terminal may receive discovery messages from multiple candidate relay terminals.Based on the discovery messages and other criteria, the intermediate relay terminal selects the target last relay terminal 120 at event 414.

[0064] At event 416, a PC5 link is established between the intermediate relay terminal 12 and the target last relay terminal 120. In accordance with known techniques, the intermediate relay terminal sends a direct Communication request message which initiates the PC5 Signaling (PC5-S) procedure to establish a PC5 link.

[0065] At transmission 418, the intermediate relay terminal 12 sends an RRC Reestablishment request to the target cell 30. After a PC5 link 146 is established between the intermediate relay terminal 12 and the intermediate last relay terminal 120, the intermediate relay terminal 12 initiates the procedure to reestablish RRC CONNECTED with the target cell 30 by sending the RRC Reestablishment request.

[0066] At transmission 420, the target cell 30 sends an RRC Reconfiguration message to the target last relay terminal 120. The RRC Reconfiguration message includes PDCP parameters and SRAP parameters for the target last relay terminal.

[0067] At transmission 422, the target cell 30 sends an RRC Reconfiguration message to the intermediate relay terminal 12. The RRC Reconfiguration message includes PDCP parameters and SRAP parameters for the intermediate relay terminal 12. The intermediate relay terminal 12 exchanges messages with the target cell and is reconfigured with the SRAP and PDCP parameters in a reestablishment procedure in accordance with known techniques except that the reestablishment is transparent to the remote terminal 104.TUTL 00414 PC-22-

[0068] At transmission 424, the intermediate relay terminal 12, sends a reestablishment notification to the remote terminal 104 indicating that the intermediate relay terminal has successfully performed relay reselection and RRC reestablishment. For the example, the reestablishment notification is sent as a NotificationMessageSidelink message with an indication type of “relayUE-reestablished”. After receiving the Relay UE reestablished notification, the remote terminal determines whether to remain PC5 connected to the intermediate relay terminal 12 and send a RRC Reestablishment Request to the target cell via the IRU or whether to perform relay reselection. For the example, the remote terminal 104 sends a reestablishment request to initiate the reestablishment procedure at transmission 426.

[0069] At transmission 428, the target cell 30 sends an RRC Reconfiguration message to the remote terminal 104. The RRC Reconfiguration message includes PDCP parameters and SRAP parameters for the remote terminal 104.

[0070] Uplink and downlink data communication continue over the multi-hop wireless communication link between the remote terminal 104 and the target cell 30 at transmission 430. The multi-hop wireless communication link includes the intermediate relay terminal and the target last relay terminal 120.

[0071] FIG. 4B is a message flow diagram 440 for an example where the intermediate relay terminal 12 performs relay reselection to connect to the initial cell 26 while in the RRC CONNECTED state and while refraining from notifying the remote terminal 104 that an initial last relay terminal PC5 link 110 to the initial last terminal 108 has become unavailable. Accordingly, the message flow of FIG. 4B is an example of a message flow for the scenario of FIG. 1 E discussed above. For the scenario of FIG. 4B, therefore, the initial multi-hop relay communication path is a multi-hop relay communication link between the remote terminal 104 and the initial cell 26 including the intermediate relay terminal 12 and the initial last relay terminal 108. The intermediate relay terminal 12 is initially connected to the remote terminal 104 through a remote PC5 link 110 and is connected to the last relay terminal 108 through the initial PC5 link 112. The intermediate relay terminal 12 is in the RRC CONNECTED state with the initial cell 26 where the initial last relay terminal 108 is connected to the initial cell 26 over a Uu link 114. The remote terminal 104 is also in the RRC CONNECTED state with the initialTUTL 00414 PC-23-cell 26. The initial states and connections in the example of FIG. 4B, therefore, are the same as the initial states and connections in the example of FIG. 4A. For the example of FIG. 4B, however, the selected target last relay terminal 120 is connected to (or will be connected to) the initial cell 26 via a Uu link 160. For the example of FIG. 4B, the transmissions 404-422 are performed as discussed with reference to FIG. 4A above except that the target cell is the initial cell.

[0072] At transmission 442, the remote terminal 104 sends a Remote PC5 Connected notification to the initial cell (target cell) 26. After reestablishing RRC CONNECTED, the intermediate relay terminal 12, sends a remote terminal PC5 connected notification 164 to the initial cell 26 indicating that the remote terminal 104 is connected to the intermediate relay terminal 12 over the PC5 link 110. For the example, the notification 164 also indicates that the remote terminal 104 was not notified that the PC5 link to the initial last relay terminal 108 had become unavailable or that the intermediate relay terminal had performed RRC reestablishment. For the example, the Remote PC5 Connected notification is a SidelinkUEInformation message.

[0073] At transmission 444, the intermediate relay terminal 12 sends a remote-not-notified notification to the target cell 26 indicating that the remote terminal 104 was not notified of the unavailability of the PC5 link to the initial last relay terminal or that reestablishment was being performed. Transmission 444 is omitted if the Remote PC5 Connected notification includes the remote-not-notified information. Accordingly, transmission 444 is shown with a dashed line in FG. 4B to illustrate that the transmission 444 may be omitted in some situations.

[0074] After the intermediate relay terminal reestablishes RRC CONNECTED, the intermediate relay terminal 12 also sends a Resume Data message 166 at transmission 446 which indicates to the remote terminal 104 that the sidelink is restored and that data transmission can be resumed. For the example, the Resume Data notification is transmitted as an PC5-RRC message.

[0075] In some situations, the target cell (initial cell) 26 may determine that the remote terminal should be RRC reconfigured and may perform RRC Reconfiguration. In such situations, the target cell 26 initiates RRC reconfiguration with transmission 448.TUTL 00414 PC-24- The RRC Reconfiguration transmission 448 is shown with a dashed line to indicate that the reconfiguration is not required in some situations.

[0076] At event 460, the remote terminal 104 resumes data transmissions. Uplink and downlink communication over the multi-hop relay communication link continues at event 462 where the multi-hop relay communication link is facilitated by the intermediate relay terminal 12 and the target last relay terminal 120 between the remote terminal and the target cell (initial cell) 26.

[0077] FIG. 4C is a message flow diagram 480 for an example where the intermediate relay terminal 12 fails at an attempt of relay reselection and / or RRC Reestablishment for the examples of FIG. 4A and FIG. 4B. Therefore, the message flow of FIG. 4C is an example when the intermediate relay terminal is the RRC CONNECTED state when determining that the PC5 link 110 has become unavailable and attempts to identify a target cell and reestablish the RRC CONNECTED state while refraining from notifying the remote terminal 104 that an initial last relay terminal PC5 link 110 to the initial last terminal 108 has become unavailable. For the example of FIG.4C, the transmissions / events 402, 404, 406, 410 are performed as discussed with reference to FIG. 4A.

[0078] At event 482, the intermediate relay attempt to perform relay resection without notifying the remote terminal 104 that the PC5 link to the initial last relay terminal is unavailable. If the relay reselection procedure fails, the intermediate relay sends a failure notification to the remote terminal at transmission 488. If a target relay is selected and a PC5 link is established with the target last relay terminal, the intermediate relay terminal attempts to reestablish RRC CONNECTED at event 484.

[0079] If either the relay reselection or the reestablishment procedure is unsuccessful, the intermediate relay terminal 12 determines reestablishment has failed at event 486. The intermediate relay terminal sends an access failure notification to the remote terminal at transmission 488. For the example, access failure notification is a NotificationMessageSidelink message with an indication type “relayUE-Uu-RLF”.Another suitable example of conveying the access failure notification includes a NotificationMessageSidelink message with an indication type “relayUE-Reestablishment-failure”.TUTL 00414 PC-25-

[0080] The intermediate relay terminal 12, therefore, may initially be in RRC Connected state or an RRC non-connected state and performs relay reselection and establishes the RRC CONNECTED state with the target cell without notifying its child terminal of an RLF of the PC5 to the intermediate relay terminal’s parent terminal. The target cell may be the initial cell, a cell provided by the same gNB (initial gNB) that provides the initial cell, or a cell provided by another gNB. The techniques discussed for relay reselection may also be applied to a path switch service continuity procedure.

[0081] FIG. 5 is a message flow diagram 500 for an example where the intermediate relay terminal performs a path switch service continuity procedure to connect to a target relay terminal while in the RRC CONNECTED state and while refraining from notifying the remote terminal 104 that an initial last relay terminal PC5 link 110 to the initial last terminal 108 has become unavailable.

[0082] At event 502, the remote terminal 104 and the initial cell 26 exchange uplink and downlink data over a multi-hop communication link including the intermediate relay terminal 12 and the initial last relay terminal 108 where the intermediate relay terminal 12 is connected to the initial last relay terminal 108 over the initial PC5 link.

[0083] At transmission 504, the intermediate relay terminal 12 sends a measurement report to the initial cell 26.

[0084] At transmission 506, the remote terminal 104 sends a measurement report to the initial cell 26.

[0085] At event 508, the network node (gNB) providing the initial cell determines that the intermediate relay terminal should be configured for a conditional path switch and identifies at least the target last relay terminal as a path switch candidate. The network node determines the conditional path switch parameters for the intermediate relay terminal.

[0086] At transmission 510, the network node configures the target last relay terminal for the conditional path switch for the intermediate relay terminal.

[0087] At transmission 512, the network node configures intermediate relay terminal for the conditional path switch. The RRC reconfiguration with conditional path switch includes the candidate terminals which includes the target relay terminal.TUTL 00414 PC-26-

[0088] At event 514, the intermediate relay terminal determines that the PC5 link to the initial last relay terminal has become unavailable.

[0089] At event 516, the intermediate relay terminal initiates the conditional path switch to the target last relay terminal. Without notifying the remote terminal that the PC5 link to the initial last relay terminal is no longer available, the intermediate relay terminal determines if the conditions are met for the conditional path switch and initiates the conditional path switch. Accordingly, the intermediate relay terminal maintains the child PC5 link to the remote terminal while executing the path switch.

[0090] At transmission 518, the intermediate relay terminal transmits an RRC Reconfiguration complete message to the target cell to complete the path switch. For the example, the target cell is the initial cell. If the target cell is not the initial cell, the intermediate relay terminal notifies the remote terminal of the change in cell.

[0091] At event 520, the remote terminal 104 resumes data transmissions. Uplink and downlink communication over the multi-hop relay communication link continues at event 520 where the multi-hop relay communication link is facilitated by the intermediate relay terminal 12 and the target last relay terminal 120 between the remote terminal and the target cell (initial cell) 126.

[0092] FIG. 6 is a flow chart of an example of a method of performing relay selection for a multi-hop relay communication path. The method may be performed in a system such as the system 10 discussed herein. For the example, the method is performed by a terminal, such as the intermediate relay terminal 12. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the terminal may facilitate the generation, formatting, reception and transmission of signals and messages. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 6. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 6.

[0093] At step 602, the intermediate relay terminal maintains a PC5 link with a child terminal.TUTL 00414 PC-27-

[0094] At step 604, the intermediate relay terminal determines whether the PC5 link to the parent terminal is available. If the PC5 link is no longer available because, for example, the link has suffered an RLF, the method provides to step 606. Otherwise, the method returns to step 602.

[0095] At step 606, the intermediate relay terminal performs relay reselection to select a target relay terminal for facilitating communication with a target cell while refraining from notifying the child terminal that the initial parent relay terminal PC5 link has become unavailable. The intermediate relay terminal refrains from notifying the child terminal at least until the relay resection procedure is complete.

[0096] FIG. 7 is a flow chart of an example of method of establishing RRC CONNECTED without notifying a remote terminal of the unavailability of the PC5 link to an initial last relay terminal. The method may be performed in a system such as the system 100 discussed herein. For the example, the method is performed by a terminal that may be selected to perform the functions of an intermediate relay terminal, such as the intermediate relay terminal 12. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the terminal may facilitate the generation, formatting, reception and transmission of signals and messages. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 7. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 7.

[0097] At step 702, the intermediate relay terminal 12 facilitates an initial relay communication link between the network and a remote terminal through an initial last relay terminal.

[0098] At step 704, the intermediate relay terminal 12 determines that the initial parent terminal PC5 link to the initial last relay terminal is no longer available.TUTL 00414 PC-28-

[0099] At step 706, the intermediate relay terminal 12 transmits a system data message to the remote terminal and maintains the child PC5 link with the remote terminal 104.

[0100] At step 708, the intermediate relay terminal 12 performs relay reselection to select a target last relay terminal without notifying the remote terminal that the PC5 link is no longer available or that relay reselection is being performed.

[0101] At step 710, the intermediate relay terminal 12 determines whether the PC5 link to the target last relay terminal has been successfully established. If the PC5 link has not been established, the method proceeds to step 712. Otherwise, the method continues at step 714.

[0102] At step 712, the intermediate relay terminal 12 sends an access failure notification to the remote terminal. The access failure notification invokes the remote terminal to perform relay reselection.

[0103] At step 714, the intermediate relay terminal 12 determines whether RRC CONNECTED has been successfully reestablished. If RRC CONNECTED has not been reestablished, the method proceeds to step 712. Otherwise, the method continues at step 716.

[0104] At step 716, the intermediate relay terminal 12 determines whether the target cell is the initial cell. If the target cell is the initial cell, the method provides proceeds to step 718. Otherwise, the method continues at step 720.

[0105] At step 718, the intermediate relay terminal 12 sends a resume data notification to the remote terminal.

[0106] At step 720, the intermediate relay terminal 12 sends a relay reestablished notification to the remote terminal.

[0107] At step 722, the intermediate relay terminal 12 facilitates a multi-hop relay communication link between the remote terminal and the network where the target last relay terminal facilitates the multi-hop relay communication link.

[0108] To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, modules, circuits, and steps have beenTUTL 00414 PC-29-described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. The described functionality may be implemented in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure. In accordance with various embodiments, a processor, device, component, circuit, structure, machine, module, etc. can be configured to perform one or more of the functions described herein. The term "configured to" or "configured for" as used herein with respect to a specified operation or function refers to processors, devices, components, circuits, electronics, and equipment that are physically constructed, programmed, instructed and / or arranged to perform the specified operation or function. Furthermore, the various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), other electronics or combinations thereof. (ASIC), a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, electronics, and circuits can further include antennas and / or transceivers to communicate with various components within the network or within the device. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein.

[0109] When implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method or algorithm disclosed herein can be implemented as software stored on a computer-readable medium. Computer readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be anyTUTL 00414 PC-30-available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.

[0110] Therefore, the methods and apparatus of this invention may take the form, at least partially, of program logic or program code (i.e., instructions) embodied in tangible media, such as a machine-readable storage medium. When the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. The methods and apparatus of the present invention may also be embodied in the form of program code that is transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via any other form of transmission. When the program code is received and loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code combines with the processor to provide a unique apparatus that operates analogously to specific logic circuits.

[0111] Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the present disclosure. It will be appreciated that, for clarity purposes, the above description has described embodiments of the present disclosure with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processing logic elements or domains may be used without detracting from the present disclosure. For example, functionality illustrated to be performed by separate processing logic elements, or controllers, may be performed by the same processing logic element, or controller. Therefore, references to specific functional units are only references to a suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

[0112] Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by theTUTL 00414 PC-31-following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims

TUTL 00414 PC-32- CLAIMS1. A method comprising:maintaining a child terminal PC5 connection with a child terminal; determining a parent terminal PC5 connection with an initial parent relay terminal has become unavailable;in response to determining the initial parent terminal PC5 connection with the initial parent relay terminal has become unavailable, performing a relay reselection procedure to select a target parent relay terminal for facilitating communication to a target cell;refraining, at least until the relay reselection procedure has been completed, from notifying the child terminal that the initial parent terminal PC5 connection had become unavailable.

2. The method of claim 1 , further comprising:notifying, in response to a failure of the relay reselection procedure, the child terminal that the relay reselection procedure has failed.

3. The method of claim 2, wherein the notifying comprises transmitting a PC5-Radio Resource Control (RRC) message comprising an access failure cause value.

4. The method of claim 2, wherein the notifying comprises refraining from forwarding Model A discovery signals.

5. The method of claim 1 , further comprising:performing, while maintaining the child PC5 connection, a Radio Resource Control (RRC) re-establishment procedure; andin response to a failure of the RRC re-establishment procedure, notifying the child terminal that the RRC re-establishment procedure has failed.

6. The method of claim 1, further comprising:TUTL 00414 PC-33- performing, while maintaining the child PC5 connection, a Radio Resource Control (RRC) re-establishment procedure; andin response to a successful RRC re-establishment procedure, notifying the child terminal that the RRC re-establishment procedure was successful.

7. The method of claim 6, wherein the successful RRC re-establishment procedure is to a target cell of a target network node that is different from an initial network node providing an initial cell initially serving the initial parent relay terminal.

8. The method of claim 1 , further comprising:performing, while maintaining the child PC5 connection, a Radio Resource Control (RRC) re-establishment procedure;transmitting a system data notification message to the child terminal instructing the child terminal to suspend sidelink data transmission;in response to a successful RRC re-establishment procedure to the initial cell, refraining from notifying the child terminal that the RRC re-establishment procedure was successful; andtransmitting a resume data message to the child terminal instructing the child terminal to resume sidelink data transmission.

9. The method of claim 8, wherein the successful RRC re-establishment procedure is to an initial cell initially serving the initial parent relay terminal.

10. The method of claim 9, further comprising:transmitting, to the initial cell, a remote terminal PC5 connected notification indicating that the child terminal is connected via the child PC5 link.

11. The method of claim 8, wherein the successful RRC re-establishment procedure is to a target cell of an initial network node providing an initial cell initially serving the initial parent relay terminal.TUTL 00414 PC-34- 12. The method of claim 1 , further comprising:receiving a remote terminal (RT) Radio Resource Control (RRC) Setup Request from the child terminal;performing a RRC reestablishment procedure to establish RRC CONNECTED with the target cell; andtransmitting a SidelinkUEInformation message with the RT RRC Setup request to the target cell.

13. A method comprising:facilitating an initial multi-hop relay communication link between a remote terminal and an initial cell through an initial last relay terminal, the initial multi-hop relay communication link comprising a child PC5 link to the remote terminal and an initial parent PC5 link to the initial last relay terminal;determining that the initial parent PC5 link has become unavailable; transmitting a suspend data message to the remote terminal instructing the remote terminal to suspend sidelink data transmission;while maintaining the child PC5 link and in response to determining the initial parent PC5 link has become unavailable, performing a relay reselection procedure to select a target parent relay terminal for facilitating communication to a target cell;performing a Radio Resource Control (RRC) reestablishment procedure to establish RRC CONNECTED with a target cell serving the target parent relay terminal;refraining from notifying the remote terminal that the initial parent terminal PC5 connection had become unavailable;transmitting a resume data message to the remote terminal when the target cell is the initial cell;transmitting a reestablishment notification message to the remote terminal when the target cell is provided by a target network node different from an initial network node that provided the initial; andfacilitating a reestablished multi-hop relay communication link between the remote terminal and the target cell through the target last relay terminal.TUTL 00414 PC-35- 14. The method of claim 13, further comprising:transmitting the resume data message to the remote terminal when the target cell is provided by the initial network node.

15. The method of claim 9, further comprising:when the target cell is the initial cell, transmitting, to the initial cell, a remote terminal PC5 connected notification indicating that the remote terminal is connected via the child PC5 link.

16. An intermediate relay terminal comprising:a transceiver configured to maintain a child terminal PC5 connection with a child terminal; anda controller configured to:determine that a parent terminal PC5 connection with an initial parent relay terminal has become unavailable;in response to determining the initial parent terminal PC5 connection with the initial parent relay terminal has become unavailable, perform a relay reselection procedure to select a target parent relay terminal for facilitating communication to a target cell; andrefrain, at least until the relay reselection procedure has been completed, from notifying the child terminal that the initial parent terminal PC5 connection had become unavailable.

17. The intermediate relay terminal of claim 16, wherein the controller is configured to determine that the relay reselection procedure has failed and wherein the transceiver is configured to transmit a failure notification to the child terminal indicating the relay reselection procedure has failed.

18. The intermediate relay terminal of claim 16, wherein:the controller is configured to perform, while maintaining the child PC5 connection, a Radio Resource Control (RRC) re-establishment procedure; andTUTL 00414 PC-36- in response to a failure of the RRC re-establishment procedure, to notify the child terminal that the RRC re-establishment procedure has failed.

19. The intermediate relay terminal of claim 16, wherein:the controller is configured to perform, while maintaining the child PC5 connection, a Radio Resource Control (RRC) re-establishment procedure; andin response to a successful RRC re-establishment procedure, to notify the child terminal that the RRC re-establishment procedure was successful.

20. The intermediate relay terminal of claim 19, wherein the successful RRC reestablishment procedure is to a target cell of a target network node that is different from an initial network node providing an initial cell initially serving the initial parent relay terminal.

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