Switching to indirect communication via a relay user equipment (UE) device in a radio resource control (RRC) connected state other than RRC connected

Abstract

A base station transmits a radio resource control (RRC) reconfiguration message to a remote user equipment (UE) device to initiate a path switch from direct communication with the remote UE device to indirect communication through a relay UE device. When the path switch is initiated, the relay UE device is in an RRC connected state other than RRC CONN. The remote UE device transmits an RRC reconfiguration complete message to the base station via the relay UE device. In response to receiving the RRC reconfiguration complete message, the relay UE device performs an RRC connection establishment with the base station when the relay UE device is in an RRC idle state, and performs an RRC resumption with the base station when the relay UE device is in an RRC INACTIVE state. The relay UE device transmits the RRC reconfiguration complete message to the base station.

Description

Priority claims

[0001] This application claims priority to U.S. Provisional Application No. 63 / 222,303, filed July 15, 2021, and bearing Docket No. TPRO 00363 US, entitled "SERVICE CONTINUITY UNDER L2 SIDELINK RELAYING," which is assigned to the assignee of the present application and is expressly incorporated herein by reference in its entirety. [Technical Field]

[0002] The present invention relates generally to wireless communications, and more particularly to managing wireless communications links using relay devices. [Background technology]

[0003] Many wireless communication systems employing multiple base stations providing wireless services to user equipment (UE) devices enable sidelink communication between two or more UE devices, allowing UE devices to communicate directly with other UE devices. In sidelink communication, UE devices transmit data signals to each other over a communication link using cellular resources instead of via a base station. Such Proximity Services (ProSe) communication is sometimes referred to as device-to-device (D2D) communication. Additionally, one or more UE devices can be used as relay devices between the UE device and a destination, where the relay device forwards data between the UE device and the destination. The destination may be a communication network or another UE device (destination UE device). When the destination is a network, the relay function is typically referred to as UE-to-Network (U2N) relaying, where the relay UE device establishes a communication path between the remote UE and a base station (gNB) or cell. In some situations, for example, a UE device may be outside the coverage area of a base station, and a relay UE device provides a routed communication link from such an out-of-coverage (OoC) UE device to the base station through the relay UE device. When the destination device is another UE device (target UE device), the relay function is typically referred to as UE-to-UE (U2U) relaying. Summary of the Invention

[0004] A base station transmits a synchronous radio resource control (RRC) reconfiguration message to a remote user equipment (UE) device to initiate a path switch from direct communication with the UE device to indirect communication through a relay UE device. When the path switch is initiated, the relay UE device is in an RRC connection state other than RRC CONN. The remote UE device transmits an RRC reconfiguration complete message to the base station via the relay UE device. In response to receiving the RRC reconfiguration complete message, the relay UE device performs an RRC connection establishment with the base station when the relay UE device is in an RRC idle state, and performs an RRC resumption with the base station when the relay UE device is in an RRC INACTIVE state. The relay UE device transmits the RRC reconfiguration complete message to the base station via a Uu communication link. [Brief explanation of the drawings]

[0005] [Figure 1A] 1 is a block diagram of an example communication system in which a candidate relay UE device transmits a reference signal to be received by a remote UE device 108, where the candidate relay UE device may be in any one of the RRC connected states.

[0006] [Figure 1B] 1 is a block diagram of a communication system in which a remote UE device transmits measurement reports to a base station.

[0007] [Figure 1C] 1 is a block diagram of a communication system in which a remote UE device sends an RRC reconfiguration complete message to a target relay UE device for relay to a base station.

[0008] [Figure 1D] 1 is a block diagram of a communication system in which a target relay UE device forwards an RRC reconfiguration complete message to a base station as an RRC reconfiguration complete transmission.

[0009] [Figure 2] FIG. 2 is a block diagram of an example base station.

[0010] [Figure 3] 1 is a block diagram of an example of a UE device suitable for use as each of the UE devices.

[0011] [Figure 4A] FIG. 10 is a message diagram illustrating an example of relay link management for switching from a direct path to an indirect path when a target relay UE device is RRC INACTIVE.

[0012] [Figure 4B] FIG. 10 is a message diagram illustrating an example of relay link management for switching from a direct path to an indirect path when a target relay UE device is RRC IDLE.

[0013] [Figure 5] 1 is a flowchart of an example method for managing a path switch from a direct communication link to an indirect communication link. DETAILED DESCRIPTION OF THE INVENTION

[0014] As described above, a relay UE device provides a connection between a remote UE device and a destination, which can be another UE device (destination UE device) or a network. If the destination is a network, the relay provides a connection to a cell provided by a base station (gNB) of the network. A relay connection between a remote UE device and a target UE device may be referred to as a UE-to-UE (U2U) relay connection. A relay connection between a remote UE device and a base station (gNB) may be referred to as a UE-to-Network (U2N) relay connection. In some situations, the final destination is the target UE device via the base station. In conventional systems in which a relay connects to a base station (gNB), the relay UE device is required to meet certain criteria to function as a relay. For example, the relay UE device must be in coverage and have a cellular (Uu) communication link to the base station of sufficient quality to be available for U2N relay functionality.

[0015] The sidelink relay function allows a remote UE that is out of coverage (OoC) to connect with a gNB or base station via a relay UE device. In UE-to-Network (U2N) relaying, the relay UE must be in cell coverage and connected to a gNB. The relay connection from the remote UE device to the base station (gNB) includes a PC5 link (sidelink) between the remote UE device and the relay UE device and a Uu link between the relay UE device and the gNB.

[0016] In some situations, a remote UE device communicates directly with a base station (gNB) without communicating through a relay UE device, and the base station determines that the communication link to the remote UE device should be switched from the direct link to an indirect link through a relay UE device. However, when switching to the indirect link, the base station may choose to switch to an indirect relay link provided by a relay UE device in an RRC state other than RRC CONN. Compared to switching to a relay connection through a relay UE device in RRC IDLE or RRC INACTIVE, latency may be minimized when switching to a relay connection through a relay UE device in RRC CONN. However, in some situations, a path through a relay in RRC IDLE or RRC INACTIVE may be preferable. Therefore, the base station may select a better path at the expense of latency. In other situations, relaying in RRC CONN may not be available and the only indirect option involves relaying in IDLE or INACTIVE, as it is generally more power efficient to keep a relay UE device IDLE or INACTIVE when there are no remote UE devices PC5 connected to the relay UE device. Also, current communication standards do not specify that a remote UE device restrict the pool of candidate relay UE devices included in a measurement report to any particular RRC state, such as RRC CONN, nor do they specify that a remote UE device indicate the state of the candidate relay UE devices listed in a measurement report.

[0017] In the example herein, the base station sends a synchronized RRC reconfiguration message to the remote UE device to initiate a path switch from a direct link to an indirect link via a relay UE device currently in an RRC state other than RRC CONN. The remote UE sends an RRC reconfiguration complete message to the base station through the relay UE device, which triggers a procedure for transitioning the relay UE device to RRC CONN. In response to receiving the RRC reconfiguration complete message, the relay UE performs an RRC connection establishment with the base station when the relay UE device is in an RRC idle state, and performs an RRC resumption with the base station when the target relay UE device is in an RRC inactive state. The relay UE device sends the RRC reconfiguration complete message to the base station via a Uu communication link.

[0018] While the techniques described herein may be applied to various types of systems and communication specifications, the example device operates in accordance with at least one revision of the 3rd Generation Partnership Project (3GPP) New Radio (NR) V2X communication specification. Thus, while the techniques described herein may be adopted by one or more future revisions of the communication specification, the techniques may also be applied to other communication specifications in which sidelink or D2D is employed. More specifically, the techniques may be applied to current and future releases of the 3GPP NR specification. For example, the techniques may be applied to 3GPP NR (3GPP Rel-17) and 3GPP Rel-18.

[0019] 1A is a block diagram of an example communication system 100 in which candidate relay UE devices 101-103 transmit reference signals 104-106 to be received by a remote UE device 108, and the candidate relay UE devices 101-103 may be in any one of the RRC connected states. The candidate relay UE devices 101-103 are within a cell coverage area 110 of a base station (gNB) 112. In this example, a first candidate relay UE device 101 is in an RRC inactive state (RRC INACTIVE), a second candidate relay UE device 102 is in an RRC connected state (RRC CONN), and a third candidate relay UE device 103 is in an RRC idle state (RRC IDLE).

[0020] The remote UE device 108 is in communication with the base station 112 via a direct Uu communication link 114. Thus, the remote UE device 108 is within the cell coverage area 110 when the example scenario described with reference to Figures 1A-1D begins. The remote UE device 108 receives reference signals 104, 105, 106 from each of the candidate relay UE devices 101, 102, 103. In this example, the reference signals 104-106 are sidelink discovery signals, and the discovery signals may be Model A discovery announcement messages or Model B response messages.

[0021] FIG. 1B is a block diagram of a communication system 100 in which a remote UE device 108 transmits a measurement report 120 to a base station 112. The remote UE device 108 generates the measurement report 120 based on measurements of reference signals 104-106 received at the remote UE device 108. By way of example, the measurement report 120 is generated in accordance with at least one revision of the 3GPP communication specifications. The base station 112 receives the measurement report and determines that the remote UE device 108 should switch from a direct communication path to the base station 112 to an indirect communication path via a relay UE device. In this example, the base station 112 selects a candidate relay UE device 101 as a target relay UE device for the indirect communication path. The base station transmits a synchronized RRC reconfiguration message 122 instructing the remote UE device 108 to switch to the indirect path through the candidate relay UE device 101. Thus, in the example described with reference to FIGS. 1A-1D, when the remote UE device 108 receives the synchronized RRC reconfiguration message 122, the target relay UE device is RRC INACTIVE.

[0022] 1C is a block diagram of a communication system 100 in which a remote UE device 108 sends an RRC reconfiguration complete message 124 to a target relay UE device (candidate relay UE device 101) for relaying to a base station 112. In response to receiving the synchronous RRC reconfiguration message 122, the remote UE device establishes a side link (PC5 link) 126 with the candidate relay UE device 101. After the PC5 link is established, the remote UE device 108 sends an RRC reconfiguration complete message 124 to the candidate relay UE device 101 using a default setting of SL-RLC1, directed to the base station 112. In response to receiving the RRC reconfiguration complete message 124, the target relay UE device 101 performs a procedure to resume an RRC CONN state with the base station 112. In this example, the target relay UE device 101 performs a resumption procedure in accordance with at least one revision of the 3GPP communication specifications, which typically includes at least sending an RRC resume request message to the base station 112, receiving an RRC resume message from the base station 112, and sending an RRC resume complete message to the base station 112. After the procedure is performed, the RRC CONN state 128 is resumed.

[0023] In a situation where the target relay UE device is a candidate relay UE device in RRC IDLE, the candidate relay UE device performs an RRC connection establishment procedure. If the target relay UE device is a candidate relay UE device 103, for example, the candidate relay UE device 103 performs an RRC establishment procedure in accordance with at least one revision of the 3GPP communication specifications, which typically includes sending an RRC establishment request message to the base station 112, receiving an RRC reconfiguration message from the base station 112, and sending an RRC reconfiguration complete message to the base station 112.

[0024] 1D is a block diagram of a communication system 100 in which a target relay UE device (candidate relay UE device 101) forwards information related to an RRC reconfiguration complete message 124 in a remote reconfiguration complete relay transmission 130 to a base station 112. After the RRC CONN with the base station 112 is resumed, the target relay UE device (candidate relay UE device 101) relays the reconfiguration complete message 124 to the base station 112, and an indirect communication path 132 between the remote UE device 108 and the base station 112 via the relay UE device 101 is established. In this example, the remote reconfiguration complete relay transmission 130 is a signaling radio bearer 1 (SRB1) message transmitted using a sidelink relay adaptation protocol (SRAP) technique.

[0025] FIG. 2 is a block diagram of an example base station 200 suitable for use as the base station 112, and any base station that provides a cell or otherwise serves any of the UE devices. The base station 200 includes a controller 204, a transmitter 206, and a receiver 208, as well as other electronics, hardware, and code. The base station 200 is any fixed, mobile, or portable device that performs the functions described herein. The various functions and operations of the blocks described with reference to the base stations 112, 200 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated into a single device, and functions described as being performed in any single device may be implemented across multiple devices. The base station 200 may be a fixed device or equipment that is installed at a specific location during system deployment. Examples of such equipment include a fixed base station or fixed transceiver station. Although base stations may be referred to by different terms, they are generally referred to as gNodeBs or gNBs when operating in accordance with one or more communication specifications for 3GPP V2X operation. In some situations, the base station 200 may be a mobile device that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generation equipment such as 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.

[0026] The controller 204 includes any combination of hardware, software, and / or firmware for performing the functions described herein and facilitating the overall functionality of the base station 200. An example of a suitable controller 204 includes code executing on a microprocessor or processor configuration coupled 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 and the transmitter 206 receive and transmit signals, respectively, via an antenna 210. The antenna 210 may include separate transmit and receive antennas. In some situations, the antenna 210 may include multiple transmit and receive antennas.

[0027] The transmitter 206 and receiver 208 in the example of Figure 2 perform radio frequency (RF) processing, including modulation and demodulation. Accordingly, the receiver 208 may include components such as a low noise amplifier (LNA) and a filter. The transmitter 206 may include a filter and an amplifier. Other components may include an isolator, a matching circuit, and other RF components. These components, in combination with or in cooperation with other components, perform base station functions. The components required may depend on the specific functions required by the base station.

[0028] The transmitter 206 includes a modulator (not shown), and the receiver 208 includes a demodulator (not shown). The modulator modulates the signal transmitted as part of the downlink signal and can apply any one of a number of modulation orders. The demodulator demodulates any uplink signal received at the base station 200 according to one of a number of modulation orders.

[0029] The base station 200 includes a communication interface 212 for sending and receiving messages to and from other base stations. The communication interface 212 may be connected to a backhaul or network that enables communication with other base stations. In some situations, the link between base stations may include at least a portion wireless. Thus, the communication interface 212 may include wireless communication capabilities or may utilize some of the components of the transmitter 206 and / or receiver 208.

[0030] FIG. 3 is a block diagram of an example UE device 300 suitable for use as each of the UE devices 101-103, 108. In some examples, the UE device 300 is any wireless communication device, such as a mobile phone, walkie-talkie modem, personal digital assistant (PDA), tablet, or smartphone. In other examples, the UE device 300 is a machine-type communication (MTC) device or an Internet of Things (IoT) device. The UE device 300 is therefore any fixed, mobile, or portable device that performs the functions described herein. The various functions and operations of the blocks described with reference to the UE device 300 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated into a single device, and functions described as being performed in any single device may be implemented across multiple devices.

[0031] The UE device 300 includes at least a controller 302, a transmitter 304, and a receiver 306. The controller 302 includes any combination of hardware, software, and / or firmware for performing the functions described herein and facilitating the overall functionality of the communications device. An example of a suitable controller 302 includes code executing on a microprocessor or processor configuration coupled to memory. 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 the transmitter 304 receive and transmit signals, respectively, via an antenna 308. The antenna 308 may include separate transmit and receive antennas. In some situations, the antenna 308 may include multiple transmit and receive antennas.

[0032] The transmitter 304 and receiver 306 in the example of Figure 3 perform radio frequency (RF) processing, including modulation and demodulation. Accordingly, the receiver 306 may include components such as a low noise amplifier (LNA) and a filter. The transmitter 304 may include a filter and an amplifier. Other components may include an isolator, matching circuits, and other RF components. These components, in combination with or in cooperation with other components, perform communication device functions. The components required may depend on the specific functions required by the communication device.

[0033] 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 a signal transmitted as part of an uplink signal. The demodulator demodulates a downlink signal according to one of a plurality of modulation orders. In addition to the memory that is part of the controller 302, the UE device 300 includes a memory 310. Information such as a candidate relay prioritized list that may be included in the remote reconfiguration complete relay transmission 130 may be stored and maintained on the memory 310, the controller 302, or a combination of the two.

[0034] Figure 4A is a message diagram 400 for an example of relay link management for switching from a direct path to an indirect path when the target relay UE device is in RRC INACTIVE. While Figure 4A shows three candidate relay UE devices 101-103, any number of candidate relay devices may be involved in the messaging. This example begins with a remote UE device 108 in direct communication (402) with a base station (gNB) 112, with a first candidate relay UE device 101 in an RRC INACTIVE state, a second candidate relay UE device 102 in an RRC CONN state, and a third candidate relay UE device 103 in an RRC IDLE state. Uplink and downlink data are exchanged between the remote UE device 108 and the gNB 112 via the direct Uu communication link 402.

[0035] At transmission 404, a Model B discovery request is transmitted from the remote UE device 108 to nearby candidate relay UE devices. In some circumstances, the Model B discovery request may be omitted. Thus, the arrow representing the Model B discovery request is shown dashed to indicate that transmission may not be required. For example, if a Model A discovery message is received from a candidate relay UE device, a Model B request may not be required.

[0036] At transmission 406, a discovery message is transmitted from the candidate relay UE device 102. At transmission 408, a discovery message is transmitted from the candidate relay UE device 101. At transmission 410, a discovery message is transmitted from the candidate relay UE device 103. The discovery messages of transmissions 406, 408, and 410 may be Model A discovery announcement messages or Model B discovery response messages. The remote UE device 108 receives the discovery messages and evaluates the received signals and information as part of a relay reselection procedure. For example, the remote UE device 108 measures the sidelink discovery reference signal received power (SD-RSRP) level of the received discovery messages.

[0037] At transmission 412, the remote UE device 108 transmits a measurement report to the gNB 112, where the measurement report includes signal quality measurements of the candidate relay devices. Thus, the measurement report includes signal quality measurements, such as SD-RSRP levels, of the discovery signals 406, 408, 410.

[0038] At event 414, the gNB 112 determines that communication with the remote UE device 108 should be switched from a direct connection to an indirect connection via a target relay UE device. The decision by the gNB 112 to switch to indirect communication may be based on any combination of factors, such as which event triggered the measurement report, the SD-RSRP level(s), the RRC connection status, and the congestion level of the candidate relay UE (the gNB may know how many remote UE devices are already connected to a particular candidate relay UE). In the example of FIG. 4A, the gNB 112 selects candidate relay UE device (UE1) 101 as the target UE device.

[0039] At transmission 416, the gNB 112 transmits a synchronized RRC reconfiguration message to the remote UE device 108. The synchronized RRC reconfiguration message initiates a switch from the direct communication link 402 to an indirect communication link via the target candidate relay UE device 101.

[0040] At event 418, a PC5 connection is established between the remote UE device 108 and the target-candidate relay UE device 101. In some situations, a PC5 connection may already be established and event 418 is not required.

[0041] At transmission 420, the remote UE device 108 transmits an RRC reconfiguration complete message directed to the gNB 112 via the candidate relay UE device 101. The RRC reconfiguration complete message 420 is received at the target relay UE device 101 via the PC5 link.

[0042] In response to receiving the RRC reconfiguration complete message 420, the target relay UE device 101 initiates the RRC resumption procedure by sending an RRC resumption request at transmission 422.

[0043] The target relay UE device 101 and the gNB 112 exchange messages to resume the RRC CONN. In this example, the gNB 112 sends an RRC resume message in transmission 424, and the target relay UE device 101 sends an RRC resume complete message 426. When the target relay UE device 101 is in the RRC CONN, a Uu communication link 428 is established between the target relay UE device 101 and the gNB 112.

[0044] At transmission 429, the gNB 112 sends an RRC reconfiguration message to the target relay UE device 101 to configure both the sidelink radio link control (RLC) configuration, the RLC configuration on the Uu link, and the remote UE identifier (ID) to be used for relay operation.

[0045] The target relay UE device 101 relays the RRC reconfiguration complete message received from the remote UE device 108 to the gNB 112 in transmission 430. Communication between the remote UE device 108 and the gNB 112 continues via an indirect communication link 432 that includes a relayed connection through the relay UE device 101.

[0046] Figure 4B is a message diagram 450 for an example of relay link management for switching from a direct path to an indirect path when the target relay UE device is in RRC IDLE. While Figure 4B shows three candidate relay UE devices 101-103, any number of candidate relay devices may be involved in the messaging. This example begins with a remote UE device 108 in direct communication 402 with a base station (gNB) 112, with a first candidate relay UE device 101 in an RRC inactive state (RRC INACTIVE), a second candidate relay UE device 102 in an RRC connected state (RRC CONN), and a third candidate relay UE device 103 in an RRC idle state (RRC IDLE). Uplink and downlink data are exchanged between the remote UE device 108 and the gNB 112 via the direct Uu communication link 402.

[0047] At transmission 404, a Model B discovery request is transmitted from the remote UE device 108 to nearby candidate relay UE devices. In some circumstances, the Model B discovery request may be omitted. Thus, the arrow representing the Model B discovery request is shown dashed to indicate that transmission may not be required. For example, if a Model A discovery message is received from a candidate relay UE device, a Model B request may not be required.

[0048] At transmission 406, a discovery message is transmitted from candidate relay UE device 102. At transmission 408, a discovery message is transmitted from candidate relay UE device 101. At transmission 410, a discovery message is transmitted from candidate relay UE device 103. The discovery messages of transmissions 406, 408, and 410 may be Model A discovery announcement messages or Model B discovery response messages. The remote UE device 108 receives the discovery messages and evaluates the received signals and information as part of a relay reselection procedure. By way of example, the remote UE device 108 measures the SD-RSRP level of the received discovery messages.

[0049] At transmission 412, the remote UE device transmits a measurement report to the gNB 112, where the measurement report includes signal quality measurements of the candidate relay devices. Thus, the measurement report includes signal quality measurements, such as SD-RSRP levels, of the discovery signals 406, 408, 410.

[0050] At event 414, the gNB 112 determines that communication with the remote UE device 108 should be switched from a direct connection to an indirect connection via a target relay UE device. The decision by the gNB 112 to switch to indirect communication may be based on any combination of factors, such as which event triggered the measurement report, the SD-RSRP level(s), the RRC connection status, and the congestion level of the candidate relay UE (the gNB may know how many remote UE devices are already connected to a particular candidate relay UE). In the example of FIG. 4B, the gNB 112 selects candidate relay UE device (UE3) 103 as the target UE device.

[0051] At transmission 416, the gNB 112 transmits an RRC reconfiguration message to the remote UE device 108. The RRC reconfiguration message initiates a switch from the direct communication link 402 to an indirect communication link via the target candidate relay UE device 103.

[0052] At event 418, a PC5 connection is established between the remote UE device 108 and the target-candidate relay UE device 103. In some situations, a PC5 connection may already be established and event 418 is not required.

[0053] At transmission 420, the remote UE device 108 transmits an RRC reconfiguration complete message directed to the gNB 112 via the candidate relay UE device 103. The RRC reconfiguration complete message 420 is received at the target relay UE device 103 via the PC5 link.

[0054] In response to receiving the RRC reconfiguration complete message 420, the target relay UE device 103 initiates the RRC establishment procedure by sending an RRC establishment request in transmission 452.

[0055] The target relay UE device 103 and the gNB 112 exchange messages to establish an RRC CONN. In this example, the gNB 112 sends an RRC reconfiguration message in transmission 454, and the target relay UE device 103 sends an RRC reconfiguration complete message 456. When the target relay UE device 103 is in the RRC CONN, a Uu communication link 428 is established between the target relay UE device 103 and the gNB 112. In transmission 429, the gNB 112 sends an RRC reconfiguration message to the target relay UE device 103 to configure both the sidelink RLC configuration, the RLC configuration on the Uu link, and the remote UE ID to be used for relay operation.

[0056] The target relay UE device 103 relays the RRC reconfiguration complete message received from the remote UE device 108 to the gNB 112 in transmission 430. Communication between the remote UE device 108 and the gNB 112 continues via an indirect communication link 432 that includes a relayed connection through the relay UE device 103.

[0057] 5 is a flowchart of an example method for managing a path switch from a direct communication link to an indirect communication link. The method is performed by a UE device that is capable of providing relay services to one or more remote UE devices and that is in an RRC connection state other than RRC CONN. Thus, in this example, the method may be performed by candidate relay UE devices such as candidate relay UE device (UE1) 101 and candidate relay UE device (UE3) 103.

[0058] In step 502, an RRC connection state other than RRC CONN with the base station 112 is maintained. Thus, in this example, the candidate relay UE device remains in RRC IDLE or RRC INACTIVE.

[0059] In step 504, a PC5 link is established with the remote UE device 108. For example, the candidate relay UE device receives a message according to one or more revisions of the 3GPP communications specifications to initiate the PC5 link.

[0060] In step 506, it is determined whether an RRC reconfiguration complete message has been received from the remote UE device 108. The destination of the RRC reconfiguration complete is the base station 112. By way of example, the relay UE device determines whether an RRC reconfiguration complete has been sent on the SL-RLC1 channel and then received from the remote UE device 108. If an RRC reconfiguration complete message has not been received from the remote UE device 108, the method returns to step 502. Otherwise, the method proceeds to step 508.

[0061] In step 508, it is determined whether the candidate relay UE device is in RRC IDLE or RRC INACTIVE. If the candidate relay UE device is RRC INACTIVE, the method proceeds to step 510. If the candidate relay UE device is in RRC IDLE, the method proceeds to step 512.

[0062] In step 510, the relay UE device sends an RRC Resume Request message to the gNB 112. Thus, when INACTIVE, the relay UE device initiates a connection resumption procedure in response to receiving an RRC Reconfiguration Complete message from the remote UE device 108.

[0063] In step 512, the relay UE device sends an RRC Establishment Request message to the gNB 112. Thus, when in IDLE, the relay UE device initiates the connection establishment procedure in response to receiving an RRC Reconfiguration Complete message from the remote UE device 108.

[0064] After the relay UE device enters the RRC CONN, the relay UE device relays the RRC reconfiguration complete message received from the remote UE device to the gNB 112 in step 514. Communication between the remote UE device 108 and the gNB 112 continues via an indirect path through the relay UE device.

[0065] The techniques described above provide at least a mechanism for switching from direct communication to indirect communication through a candidate relay UE device in an RRC connection state other than RRC CONN. When the relay UE device is IDLE or INACTIVE, the relay UE device initiates a procedure to transition to RRC CONN in response to receiving an RRC reconfiguration complete message from a remote UE device.

[0066] Clearly, other embodiments and modifications of the present invention will occur readily to those skilled in the art in view of these teachings. The foregoing description is illustrative, and not limiting. The present invention is to be limited only by the appended claims, which claims include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. Therefore, the scope of the present invention should be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with their full scope of equivalents.

Claims

1. A relay user equipment (UE) device, comprising: a control unit that maintains the relay UE device in a radio resource control (RRC) state with a base station other than an RRC connected state; a receiver for receiving an RRC reconfiguration complete message from a remote UE device directed to said base station via a PC5 communication link; a transmitter unit, The transmission unit When the relay UE device is in an RRC idle state, in response to receiving the RRC reconfiguration complete message, sending a first RRC message used for RRC connection establishment to the base station; When the relay UE device is in an RRC INACTIVE state, in response to receiving the RRC reconfiguration complete message, sending a second RRC message used for RRC connection resumption to the base station; sending the RRC reconfiguration complete message to the base station over an available Uu communication link in response to one of the first RRC message and the second RRC message. Relay User Equipment (UE) device.

2. the RRC reconfiguration complete message is sent by the remote UE device in response to receiving at the remote UE device an RRC reconfiguration message sent from the base station via a Uu direct communication link between the base station and the remote UE device, the RRC reconfiguration message initiating a path switch from the direct communication link between the remote UE device and the base station to an indirect communication link between the remote UE device and the base station via the relay UE device. The relay UE device of claim 1 .

3. the receiving unit receives an RRC resumption message after transmitting the second RRC message; The transmitter transmits an RRC resumption complete message after receiving the RRC resumption message. The relay UE device of claim 1 .

4. The transmitter and the receiver operate in accordance with at least one revision of a 3rd Generation Partnership Project (3GPP) New Radio (NR) V2X communication specification. The relay UE device of claim 1 .

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