Relay User Equipment (UE) Wireless Resource Control (RRC) Connection Status Indicator

Abstract

A relay user equipment (UE) device transmits a radio resource control (RRC) connection status indicator to a serving base station indicating an RRC connection status of the relay UE device. The RRC connection status indicator may be used by a remote UE device to manage relay communication to the base station. In one example, a remote UE device that communicates directly with the base station transmits a measurement report to the base station, the measurement report including only measurements for relay UE devices that report an RRC CONN status. The base station manages a switch from direct to indirect communication based at least in part on the measurement report. In another example, the remote UE device manages relay reselection using relay candidate prioritization based at least in part on the connection status of the candidate relay UE devices.

Description

Claim of Priority ,

[0003] ,

[0001] This application claims priority to U.S. Provisional Application No. 63 / 186,574, filed on May 10, 2021, bearing docket number TPRO00362US and entitled "Sidelink L2 Relay Reselection during Radio Link Failure", and U.S. Provisional Application No. 63 / 222,303, filed on July 15, 2021, bearing docket number TPRO00363US and entitled "Service Continuity under L2 Sidelink Relay". Both U.S. provisional applications have been assigned to the assignee of this application and are hereby expressly incorporated by reference in their entirety.

Technical Field

[0002] The present invention generally relates to wireless communication and, more particularly, to the management of wireless communication links using relay devices.

[0003] Many wireless communication systems employing several base stations to provide 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 via a communication link using cellular resources instead of going through a base station. Such proximity services (ProSe) communication is sometimes also referred to as device-to-device (D2D). Furthermore, one or more UE devices can be used as relay devices between a UE device and a destination, and the relay device transfers 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 usually referred to as UE-to-Network (U2N) relay, and the relay UE device establishes a communication path between the remote UE and a base station (gNB) or cell. In some cases, for example, a UE device may be outside the service area of ​​a base station, and a relay UE device provides a communication link that is routed from such out-of-coverage (OoC) UE devices to the base station via the relay UE device. When the destination device is another UE device (target UE device), the relay function is usually called UE-to-UE (U2U) relaying. [Disclosure of the Invention]

[0004] A relay user equipment (UE) transmits a Radio Resource Control (RRC) connection status indicator to the serving base station, indicating the RRC connection status of the relay UE. The RRC connection status indicator may be used by a remote UE to manage relay communications to the base station. In one example, a remote UE communicating directly with the base station transmits a measurement report to the base station, which includes measurements only for relay UEs reporting RRC connection (RRC CONN) status. The base station manages the switch from direct to indirect communications based at least partially on the measurement report. In another example, the remote UE manages relay reselection using relay candidate prioritization based at least partially on the connection status of candidate relay UEs. [Brief explanation of the drawing]

[0005] [Figure 1A] This is a block diagram of an example communication system in which a candidate relay UE device transmits the RRC connection status to a remote UE device.

[0006] [Figure 1B] This is a block diagram of an example communication system in which each candidate relay UE device transmits the RRC connection status received by the remote UE device.

[0007] [Figure 1C] This is a block diagram of an example system in which a remote UE device sends a measurement report based on the RRC connection status of a received candidate relay UE device.

[0008] [Figure 1D] This is a block diagram of an example system in which a remote UE device is connected to a base station via a relay connection, and a candidate relay priority list is maintained, at least partially, based on the RRC connection status of the candidate relay UE device.

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

[0010] [Figure 3] This is a block diagram of an example of a UE device suitable for use as a UE device.

[0011] [Figure 4] This is a message diagram illustrating an example of relay link management for direct-to-indirect switching when a remote UE device sends a measurement report from a candidate relay UE device connected via RRC.

[0012] [Figure 5] This is a message diagram illustrating an example of relay link management when a remote UE device maintains a recommended relay list based on the connection status of candidate relay UE devices. [Modes for carrying out the invention]

[0013] As described above, a relay UE device provides a connection between a remote UE device and a destination, which may be another UE device (a 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. The relay connection between a remote UE device and a target UE device is sometimes called a UE-to-UE (U2U) relay connection. The relay connection between a remote UE device and a base station (gNB) is sometimes called a UE-to-network (U2N) relay connection. In some cases, the final destination is a target UE device via a base station. In conventional systems where the relay connects to a base station (gNB), the relay UE device must meet certain criteria to function as a relay. For example, the relay UE device must be within coverage and have a cellular (Uu) communication link to a base station of sufficient quality to be available for U2N relay functionality.

[0014] The sidelink relay function allows remote UEs located outside of coverage (OoC) to connect to a gNB or base station via a relay UE device. For UE-to-network (U2N) relay, the relay UE must be within cell coverage and connected to a gNB. The relay connection from a remote UE device to a 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.

[0015] In some cases, a remote UE may communicate directly with a base station (gNB) without going through a relay UE, and the base station may decide to switch the communication link to the remote UE from a direct link to an indirect link via a relay UE. When switching to an indirect link, it may be advantageous for the base station to switch to an indirect relay link provided by a relay UE in an RRC CONN state. For example, switching to a relay connection via a relay UE in an RRC CONN state can minimize latency compared to switching to a relay connection via a relay UE in an RRC IDLE or RRC INACTIVE state. In some examples here, the remote UE provides a measurement report that includes measurements only of candidate relay UEs reporting an RRC CONN state. Thus, the base station evaluates only the candidate relay UEs in RRC CONN, selects a recommended relay UE, and sends an RRC reconfiguration message to the remote UE identifying that recommended relay UE.

[0016] In other situations, when a decision is made to perform relay reselection to establish a new relay communication link with a base station, the remote UE equipment communicates indirectly with the base station (gNB) via the relay UE equipment. The remote UE equipment maintains a candidate relay priority list based at least partially on the connection status of the candidate relay equipment. Candidate relay UE equipment in the RRC CONN state is given higher priority than candidate relay UE equipment in the RRC INACTIVE state. Candidate relay UE equipment in the RRC IDLE state has the lowest priority. Prioritization may be based on additional factors. For example, prioritization may be based on the measured Sidelink Discovery Reference Signal Received Power (SD-RSRP) level of the discovery signal received from the candidate relay UE equipment. Thus, prioritization can be based on a combination of RRC connection status, SD-RSRP level, and other criteria. In other cases, if the remote UE equipment is already PC5-RRC connected to the relay UE equipment, the Sidelink Reference Signal Received Power (SL-RSRP) level may be used.

[0017] The techniques described herein may be applicable to various types of systems and communication specifications, but the equipment in this example operates in accordance with at least one revision of the 3GPP New Radio (NR) V2X communication specification. Therefore, the techniques described herein may be applicable to other communication specifications employing sidelink or D2D, but may be adopted in one or more future revisions of the communication specification. More specifically, this technique may be applicable to current and future releases of the 3GPP NR specification. For example, this technique may also be applicable to 3GPP NR (Rel-17).

[0018] Figure 1A is a block diagram of a communication system 10 in an example where a candidate relay UE device 12 transmits an RRC connection state 14 to a remote UE device 16. The candidate relay UE device 12 is located within the cell coverage area 18 of the base station (gNB) 20. For example, the candidate relay UE device 12 may be in one of three RRC connection states with the base station 20, where the three states are RRC CONN, RRC IDLE, and RRC INACTIVE. The candidate relay UE device 12 transmits an RRC connection state 14 indicating the RRC connection state with the base station 20. Therefore, for example, the remote UE device 16 may be located inside or outside the cell coverage area 18, and may be in any of several communication modes or transition states. For example, the remote UE device 16 may be directly connected to the base station 20, indirectly connected to the base station 20 via one or more relay UE devices, or may not be connected to the base station 20 when it receives the RRC connection state 14. The remote UE device 16 may be in an RRC connection state with the base station and / or with the relay UE device 12. In one example, as described below, the remote UE device 16 receives RRC connection state 14 messages from one or more candidate relay UE devices while directly connected to the base station 20, before switching to an indirect relay communication link via the candidate relay UE device. In another example described below, the remote UE device is indirectly connected to the base station via the original relay UE device before performing relay reselection based in part on the RRC connection state of the candidate relay UE device.

[0019] The RRC connection status can be transmitted to the remote UE device using any appropriate sidelink transmission. In some cases, the RRC connection status is transmitted as part of a sidelink discovery signal, which may be a Model A discovery notification message or a Model B response message. In other situations, the RRC connection status is transmitted in a PC5-RRC message. Such a technique may be useful, for example, when the RRC connection status of the relay UE device changes after the PC5 connection has been established with the remote UE device.

[0020] In another example where the PC5-RRC message can be used, the relay UE device is provided as a U2U relay during OoC before moving into cell 18 and coming within coverage. After establishing RRC CONN with the base station 20, the relay UE device transmits the RRC connection state 14 to all source UE devices and destination UE devices for which the relay device is provided. Then, the RRC connection state can be used by the source UE device and the destination UE device when performing relay reselection. For example, the relay UE device may notify the source UE device when the destination UE device becomes no longer directly reachable by the relay UE device. However, since the relay UE device is in RRC CONN with the base station, the source UE device may determine that the connection via the relay UE device and the base station is recommended over other options. Therefore, establishing a connection via RRC CONN relay is faster than establishing a relay connection via a relay UE device within coverage without RRC CONN, so the source UE device stays with the same relay UE device to reach the destination UE device via U2N relay. Further, if the source UE device is already PC5-connected to the original relay UE, during the process of performing relay reselection, it is necessary to exchange control messages several times on both the PC5 link and the Uu link before traffic data is resumed (for example, a PC5-S message to disconnect the current relay UE device, a direct communication request message for the new relay UE device, etc.).

[0021] In a third example where the PC5-RRC message can be used to transmit the RRC connection state, the relay UE device is released to RRC IDLE or RRC INACTIVE by the gNB after the PC5 connection is established with the remote UE device but before the remote UE device is in RRC CONN with the base station. Such a scenario may include a relay UE device that transmits a discovery signal indicating that the relay UE device is in the RRC CONN state, and a remote UE device that establishes a PC5 connection before the gNB releases the relay UE device from RRC CONN.

[0022] Figure 1B is a block diagram of a communication system 100 in which candidate relay UE devices 101-103 each transmit RRC connection statuses 104-106 to be received by a remote UE device 108. System 100 in Figure 1B is an example of system 10 in Figure 1A. Candidate relay UE devices 101-103 are located within the cell coverage area 110 of the base station (gNB) 112. For example, candidate relay UE devices 101-103 may be in one of three RRC connection statuses with base station 100. Here, the three statuses are RRC CONN, RRC IDLE, and RRC INACTIVE. Each candidate relay UE device 101-103 transmits an RRC connection status 104-106 indicating the RRC connection status with base station 20.

[0023] For example, each RRC connection state 104 to 106 is transmitted in a sidelink discovery message. For example, the first candidate relay UE device 101 is in the RRC IDLE state to base station 112 and transmits RRC connection state 104 indicating that relay UE device 101 is in the RRC IDLE state. The second candidate relay UE device 102 is in the RRC CONN state to base station 112 and transmits RRC connection state 105 indicating that relay UE device 102 is in the RRC CONN state. The third candidate relay UE device 103 is in the RRC INACTIVE state to base station 112 and transmits RRC connection state 106 indicating that relay UE device 103 is in the RRC INACTIVE state.

[0024] In the example here, the remote UE device 108 receives RRC connection states 104 to 106 from three candidate relay UE devices, and the state information facilitates the communication link management of the connection to the base station. In one example discussed below, the received RRC connection state information of the candidate relay UE device facilitates the switching from direct communication (without a relay UE device) between the remote UE device 108 and the base station 112 to indirect communication (with a relay UE device). In another example, the remote UE device ranks the candidate relay UE devices for relay reselection, at least partially based on the connection state. In addition to the increased latency for the remote UE device to connect to the base station, selecting (reselecting) a relay UE device that is either in RRC IDLE or RRC INACTIVE means that the relay UE device needs to continue to establish its own RRC connection with the base station, which may be rejected. And then, the remote UE device needs to find another candidate relay UE device for connecting to the base station.

[0025] Figure 1C is a block diagram of System 100 for an example in which a remote UE device 108 transmits a measurement report 120 based on the received RRC connection status of candidate relay UE devices 101-103. The scenario in Figure 1C is an example of the situation in Figure 1B in which RRC connection status information is used to generate the measurement report 120. For example, the RRC connection statuses 104-106 of each candidate relay UE device are received in discovery signals transmitted by the candidate relay UE devices that provide the RRC connection status. The remote UE device measures the quality of the signals received from candidate relay UE devices 101-103. Appropriate techniques include measuring the Sidelink Discovery Reference Signal Received Power (SD-RSRP) level of the discovery signal transmitted by the candidate relay UE devices and received by the remote UE device. For example, the discovery signal containing the RRC connection status is measured, but in some circumstances, measurements may be taken on other discovery signals. The remote UE device generates a measurement report based on the measured SD-RSRP level and the RRC connection status of candidate relay UE devices 101-103. The measurement report includes at least the measured SD-RSRP level associated with a UE identifier that identifies the candidate relay UE device that transmitted the measured signal. For example, the measurement report includes only the candidate relay devices and the SD-RSRP measurements of the candidate relay UE devices that report their status or RRC connection (RRC CONN). In one example, the measurement report is used by the base station 112 to select a target relay UE device for switching from direct communication to indirect communication via the target relay UE device. Since the measurement report identifies only RRC-connected candidate relay UE devices, the target relay UE device selected by the base station from the candidate relay UE devices is in RRC CONN. As illustrated with reference to Figure 1B, the second candidate relay UE device 102 is the only candidate relay UE device in the above example that is in RRC CONN. Consequently, in this example, the second candidate relay UE device 102 is the only candidate relay UE device identified in the measurement report 120.

[0026] The transmission of a measurement report may be triggered by a message from gNB112 or by an event detected by the remote UE device 108. For example, the remote UE device 108 may generate a measurement report in response to the detection of specific criteria regarding the quality of the connection to the gNB and the quality of alternative connections to the gNB. For example, the trigger for generating a measurement may be based on the determination that the Uu connection to the gNB is below a first threshold and the connection to the candidate relay UE device is above a second threshold. In some situations, the generation of a measurement report may be triggered without evaluating the Uu connection if at least one candidate relay UE device has an SD-RSRP greater than the threshold.

[0027] Figure 1D is a block diagram of System 100 relating to an example in which a remote UE device 108 is connected to a base station 112 via a relay connection and maintains a candidate relay priority list 130 based at least partially on the RRC connection status of candidate relay UE devices 101-103. The remote UE device 108 uses the candidate relay priority list 130 for relay reselection. In some situations, the candidate relay priority list 130 is generated when the relay reselection procedure is initiated. In other situations, the candidate relay priority list 130 is generated before the trigger that initiates the relay reselection procedure.

[0028] The example begins with a remote UE device 108 connected to a serving base station (gNB) 112 via an initial relay UE device 132 that is out of coverage (OoC). Thus, the remote UE device 108 is outside the coverage cell 110 provided by the base station 112. In other situations, the remote UE device 108 may be within the coverage of cell 110. The relay connection between the remote UE device 108 and the base station 112 includes a PC5 communication link 134 between the remote UE device 108 and the initial relay UE device 132, and a Uu link 136 between the initial relay UE device 132 and the base station (gNB) 112.

[0029] For example, RRC connection status indicators 104-106 are transmitted as part of a discovery message, which can be a Model A message or a Model B response message. Depending on the circumstances, the transmission of RRC connection status indicators may occur in response to a change in the RRC connection status at a relay UE device. For example, a change in the RRC connection status may trigger the transmission of a Model A discovery message containing the RRC connection status indicators. The RRC connection status indicators 104-106 can be any information or identifiers that indicate the current RRC connection status of the relay UE device transmitting the indicators to another UE device (e.g., remote UE device 108). For example, the RRC connection status indicators indicate one of three status states according to one or more revisions of the 3GPP New Radio (NR) V2X communication specification: RRC CONN, RRC IDLE, or RRC INACTIVE. As per the example in Figure 1B above, the remote UE device 108 maintains a candidate relay priority list 130 in which candidate relay UE devices 101-103 are prioritized for relay services based at least partially on their RRC connection status. Candidate relay UE devices in the RRC CONN state are given higher priority than those in the RRC INACTIVE state. Candidate relay UE devices in the RRC IDLE state have the lowest priority. Prioritization may also be based on additional factors. For example, prioritization may be based on the measured SD-RSRP level of the discovery signal received from the candidate relay UE device. Thus, prioritization can be based on a combination of connection status, SD-RSRP level, and other criteria. If two candidate relay UE devices have the same connection status, the candidate relay UE device with a higher measured SD-RSRP is assigned a higher priority. Typically, in network planning, cell edges correspond to RSRP levels better than -120 dBm.Similarly, for SD-RSRP, it is recommended to select candidate relay UEs with an SD-RSRP level above -120 dBm, although lower levels may also work as long as the level exceeds the UE's sensitivity level. Therefore, if a candidate relay UE in RRC CONNECTED has a measured SD-RSRP below -120 dBm, while another candidate relay UE in RRC IDLE has an SD-RSRP above -120 dBm, the remote UE may decide to connect with the candidate UE in RRC IDLE. This is especially possible if the remote UE and the candidate relay UE are in relative motion.

[0030] Figure 2 is a block diagram of an example of a base station 200 suitable for use as base station 112, and any base station that provides a cell or services to any of the UE equipment. Base station 200 includes a control unit 204, a transmitter 206, and a receiver 208, as well as other electronic equipment, hardware, and code. Base station 200 is any fixed, mobile, or portable device that performs the functions described herein. Various functions and operations of the blocks described with reference to base stations 112, 200 can be implemented in any number of devices, circuits, or elements. Two or more functional blocks may be integrated into a single device, and functions described to be performed in any single device may be implemented across multiple devices. Base station 200 may be a fixed device or equipment installed in a specific location during system deployment. Examples of such equipment include a fixed base station or fixed transceiver station. While base stations may be referred to in different terms, when operating according to one or more communication specifications of 3GPP V2X operation, a base station is usually referred to as a gNodeB or gNB. In some cases, base station 200 may be a mobile device that is temporarily installed in a specific location. Some examples of such equipment include mobile transceivers 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 yet another case, the base station 106 may be a portable device that is not fixed to a specific location.

[0031] The control unit 204 includes any combination of hardware, software, and / or firmware not only for performing the functions described herein but also for making all the functions of the user equipment more efficient. An example of a suitable control unit 204 includes software code that runs on a microprocessor or processor array connected to memory. The transmitter 206 includes electronic equipment configured to transmit radio signals. In some cases, the transmitter 206 may include multiple transmitters. The receiver 208 includes electronic equipment configured to receive radio signals. In some cases, the receiver 208 may include multiple receivers. The receiver 208 and the transmitter 206 receive and transmit signals via an antenna 210, respectively. The antenna 210 may include separate transmitting and receiving antennas. In some cases, the antenna 210 may include multiple transmitting and receiving antennas.

[0032] In the example in Figure 2, the transmitter 206 and receiver 208 perform radio frequency (RF) processing, including modulation and demodulation. Therefore, the receiver 208 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 with or in conjunction with other components, perform the functions of the user equipment. The required components may depend on the specific functions required by the user equipment.

[0033] 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 one of several modulation orders. The demodulator demodulates the uplink signal received at the base station 200 according to one of the several modulation orders.

[0034] The base station 200 includes a communication interface 212 for sending and receiving messages with other base stations. The communication interface 212 may be connected to a backhaul or network that enables communication with other base stations. In some cases, the link between base stations may include at least some radio components. Thus, the communication interface 212 may include radio communication functionality and may utilize some components of the transmitter 206 and / or receiver 208.

[0035] Figure 3 is a block diagram of an example of a UE device 300 suitable for use as UE devices 12, 16, 101-103, 108, and 132, respectively. In some examples, the UE device 300 is any wireless communication device such as a mobile phone, transceiver modem, personal digital assistant (PDA), tablet, or smartphone. In other examples, the UE device 300 is a machine-type communications (MTC) communication device or an Internet of Things (IoT) device. Thus, the UE device 300 is any stationary, 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 can be implemented in any number of devices, circuits, or elements. Two or more functional blocks may be integrated into a single device, and functions described to be performed in any single device may be implemented across multiple devices.

[0036] The UE device 300 includes at least a control unit 302, a transmitter 304, and a receiver 306. The control unit 302 includes any combination of hardware, software, and / or firmware to perform the functions described herein, as well as to facilitate the overall function of the communication device. A suitable example of the control unit 302 includes code that runs on a microprocessor or processor configuration connected to memory. The transmitter 304 includes electronic equipment configured to transmit radio signals. Depending on the circumstances, the transmitter 304 may include multiple transmitters. The receiver 306 includes electronic equipment configured to receive radio signals. Depending on the circumstances, the receiver 306 may include multiple receivers. The receiver 304 and the transmitter 306 receive and transmit signals via an antenna 308, respectively. The antenna 308 may include separate transmitting and receiving antennas. Depending on the circumstances, the antenna 308 may include multiple transmitting and receiving antennas.

[0037] In the example shown in Figure 3, the transmitter 304 and receiver 306 perform radio frequency (RF) processing, including modulation and demodulation. Therefore, the receiver 304 may include components such as a low-noise amplifier (LNA) and filters. The transmitter 306 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components work together or in conjunction with other components to perform the functions of the communication device. The required components may vary depending on the specific functions required of the communication device.

[0038] The transmitting unit 306 includes a modulator (not shown), and the receiving unit 304 includes a demodulator (not shown). The modulator can modulate the signal transmitted as part of the uplink signal by applying any one of a plurality of modulation orders. The demodulator demodulates the downlink signal according to one of the plurality of modulation orders.

[0039] The communication device 300 includes memory 310 in addition to the memory which is part of the control unit 302. Information such as the candidate relay priority list 130 may be stored and maintained in memory 310, the control unit, or a combination of the two.

[0040] Figure 4 is a message diagram 400 of an example of relay link management for direct-to-indirect switching, in which the remote UE device 108 sends a measurement report about a candidate relay UE device connected via RRC. Figure 4 shows three candidate relay UE devices 101-103, but any number of candidate relay devices can be involved in messaging. The example starts with the remote UE device 108 connected to the base station (gNB) 108 via a direct connection 402. Uplink and downlink data are exchanged between the remote UE device 108 and the gNB 112 via the direct UE communication link 402.

[0041] In transmission 404, a Model B discovery request is sent to the nearest candidate relay UE. In some circumstances, the Model B discovery request may be omitted. Therefore, the arrow representing the Model B discovery request is shown with a dashed line to indicate that transmission may not be necessary. For example, if a Model A discovery message is received from the candidate relay UE, a Model B request may not be necessary.

[0042] Transmit 406 transmits a discovery message from candidate relay UE device 101. Transmit 408 transmits a discovery message from candidate relay UE device 102. Transmit 410 transmits a discovery message from candidate relay UE device 103. The discovery messages in transmits 406, 408, and 410 may be Model A discovery notification messages or Model B discovery response messages. For example, a discovery message may include an RRC connection status notification indicating the RRC connection status of the relay UE device that sent the discovery message. As part of the relay reselection procedure, the remote UE device 108 receives the discovery messages and evaluates the received signals and information. For example, the remote UE device measures the SD-RSRP level of the received discovery message and evaluates the RRC connection status of candidate relay UE devices 101-103.

[0043] In transmission 412, the remote UE device sends a measurement report to gNB 112, which includes signal quality measurements of candidate relay devices reporting the RRC connection status of the RRC connection (RRC CONN). According to the example discussed above, the second candidate relay UE device 102 reports its status as RRC CONN. Therefore, the measurement report includes signal quality measurements for the second candidate relay UE device 102, such as the SD-RSRP level of the discovery signal 408. The measurement report may also include signal quality measurements of other gNBs, depending on the circumstances.

[0044] In event 414, gNB112 decides that communication with remote UE device 108 should be switched from a direct connection to an indirect connection via a relay UE device. gNB112's decision 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, the RRC connection status, and the congestion level of the candidate relay UE (gNB may know how many remote UE devices are already connected to a particular candidate relay UE).

[0045] In event 416, the remote UE device 108 and gNB112 perform the measurement setup and reporting procedure. The line representing event 416 is shown as a dashed line to indicate that the procedure is not necessary if gNB112 already has the information that would be obtained from the measurement setup and reporting procedure.

[0046] gNB112 selects a relay UE (target relay UE) after obtaining measurement reports from any other candidate relay UEs included in the measurement report 120 provided by the second candidate relay UE and the remote UE. For example, gNB112 selects the second candidate UE 102 for the relay connection.

[0047] In transmission 418, gNB112 sends an RRC reconfiguration message to the remote UE device. The RRC reconfiguration message initiates the switching from the direct communication link 402 to the indirect communication link via the second candidate relay UE device 102. Depending on the situation, the order of transmissions 416 and 418 can be reversed.

[0048] In event 420, a PC5 connection is established with the second candidate relay UE device 102. Depending on the situation, the PC5 connection may already be established, and event 420 may not be necessary.

[0049] In transmission 422, the remote UE device 108 sends an RRC reconstruction complete message to the gNB 112. Communication between the remote UE device 108 and the gNB 112 continues via an indirect communication link 424, which includes a relay connection via the second candidate relay UE device 102.

[0050] Figure 5 is a message diagram 500 of an example of relay link management in which the remote UE device 108 maintains a recommended relay list based on the connection status of candidate relay UE devices. Figure 5 shows three candidate relay UE devices 101-103, but any number of candidate relay devices can be involved in messaging. This example begins with the remote UE device 108 connected to the base station via a relay connection through the initial relay UE device 102, which includes a PC5 link 502 to the first relay UE device 132. In event 504, the remote UE device 108 begins maintaining the recommended candidate relay UE device list. Event 504 may be part of a relay reselection procedure and / or may be triggered by an event such as a radio link failure (RLF). The remote UE device 108 maintains a candidate relay priority list 130 in which the candidate relay UE devices 101-103 are prioritized for relay services, at least in part based on their RRC connection status and measured SD-RSRP levels. The remote UE device 108 uses the discovery procedures of transmits 508, 510, and 512 to identify and prioritize relay UE devices. In some situations, the remote UE device 108 waits for another event before performing reselection. In other situations, another event may trigger the remote UE device to perform reselection. For example, the remote UE device 108 may perform relay reselection if the elapsed time since receiving the RLF notification exceeds a time threshold. In another example, the remote UE device 108 performs relay reselection if the PC5 link with the original relay UE device 132 is released, falls below a minimum quality threshold, or is determined to be in another unusable state.

[0051] In transmission 506, a Model B discovery request is sent to the nearest candidate relay UE. In some circumstances, the Model B discovery request may be omitted. Therefore, the arrow representing the Model B discovery request is shown with a dashed line to indicate that transmission may not be necessary. For example, if a Model A discovery message is received from the candidate relay UE, a Model B request may not be necessary.

[0052] In transmission 508, a discovery message is sent from candidate relay UE device 101. In transmission 510, a discovery message is sent from candidate relay UE device 102. In transmission 512, a discovery message is sent from candidate relay UE device 103. The discovery messages in transmissions 508, 510, and 512 may be Model A discovery announcement messages or Model B discovery response messages. For example, a discovery message may include an RRC connection status notification indicating the RRC connection status of the relay UE device sending the discovery message. As part of the relay reselection procedure, the remote UE device 108 receives the discovery messages and evaluates the received signals and information. For example, the remote UE device measures the SD-RSRP level of the received discovery message and evaluates the RRC connection status of candidate relay UE devices 101-103.

[0053] In event 514, the remote UE device selects a recommended candidate relay UE device for establishing a relay connection to gNB112. Event 514 may also be part of a relay reselection procedure. Depending on the circumstances, the remote UE device 108 maintains a list of recommended candidate relay UE devices and, in response to the event, selects the most recommended relay UE device for reselection. For example, if an RLF occurs and the connection cannot be re-established via the original relay UE device 132, the remote UE device 108 may decide that a new relay connection should be established via a recommended relay UE device.

[0054] In event 516, the PC5 link is established with the recommended candidate relay UE device. For example, the recommended candidate relay UE device is the second candidate relay UE device 102. Subsequently, the relay connection 518 is established with gNB112.

[0055] In transmission 520, the remote UE device 108 transmits an RRC re-establishment request message via the second relay UE device 102.

[0056] In transmission 522, the PC5-S message is sent to the original relay UE device, releasing the PC5 connection.

[0057] Clearly, other forms and modifications of the present invention will be readily conceivable to those skilled in the art in consideration of these teachings. The foregoing description is descriptive and not limiting. The present invention is limited only by the claims, which include all such forms and modifications, when viewed in conjunction with the foregoing specification and the accompanying drawings. Therefore, the scope of the present invention should not be determined by reference to the foregoing description, but rather by reference to the entire scope of the accompanying claims and their equivalents.

Claims

1. A transceiver having a transmitting unit and a receiving unit, and initially configured to communicate with a base station via a communication link, The receiving unit is configured to receive a first radio resource control (RRC) connection status indicator from the first candidate relay UE device indicating the current connection status of the first candidate relay UE device to the base station, and to receive a second RRC connection status indicator from the second candidate relay UE device indicating the current connection status of the second candidate relay UE device to the base station. The transceiver is further configured to switch communication from the initial communication link to the relay communication link that communicates with the base station via a relay communication link through a recommended candidate relay UE, the recommended candidate relay UE being selected from the first candidate relay UE device and the second candidate relay UE device, at least partially based on the first RRC connection status indicator and the second RRC connection status indicator. Remote user equipment (UE) device.

2. The remote UE device according to claim 1, wherein each of the RRC connection status indicators indicates one of a plurality of RRC connection states, including connected (RRC CONN), idle (RRC IDLE), or inactive (RRC INACTIVE).

3. The aforementioned initial communication link is a direct communication link between the remote UE device and the base station. The remote UE device according to claim 2, further comprising a control unit that generates a measurement report omitting link quality measurements for all other candidate relay UE devices, which includes a link quality measurement associated with the relay UE device identifier of each candidate relay UE device that is in a connected state, and which transmits an RRC connection state indicator indicating an RRC CONN state in response to the quality of the direct communication link being below a direct link quality threshold, and which transmits an RRC connection state indicator.

4. The remote UE device according to claim 3, wherein the control unit is configured to generate a measurement report in response to determining that the quality of the direct communication link is below a direct link quality threshold and that at least one link to a candidate relay UE device exceeds a relay threshold.

5. The remote UE device according to claim 4, wherein the control unit is further configured to determine that the quality of the direct communication link falls below the direct link quality threshold, and to determine, based on measurements at the remote UE device, that at least one link to a candidate relay UE device exceeds the relay threshold.

6. The receiving unit is configured to receive a measurement report setting from the base station that identifies the criteria for generating the measurement report. The remote UE device according to claim 4, wherein the control unit is configured to generate the measurement report in response to a determination that the criteria for generating the measurement report have been met.

7. The receiving unit is further configured to receive an RRC reconstruction message from the base station that identifies the recommended candidate relay UE device. The remote UE device according to claim 4, wherein the control unit is further configured to establish the relay communication link to the base station via the recommended candidate relay UE device in response to the RRC reconstruction message.

8. The initial communication link is a first relay communication link via an initial relay UE device, The remote UE device according to claim 3, wherein the control unit is configured to select the recommended candidate relay UE device.

9. The remote UE device according to claim 2, wherein the first RRC connection status indicator is received in a first discovery message from the first candidate relay UE device, and the second RRC connection status indicator is received in a second discovery message from the second candidate relay UE device.

10. It comprises a transceiver and a control unit, The transceiver has a transmitting unit and a receiving unit and is configured to communicate with a remote user equipment (UE) device via a direct communication link. The receiving unit is configured to receive a link quality measurement from a remote UE device measurement report, which includes link quality measurement of signals received from a candidate relay UE device, where the radio resource control (RRC) connection status with the base station is connected (RRC CONN). The control unit is configured to identify one of the candidate relay UE devices as the target relay UE device. The base station is further configured to transmit an RRC reconfiguration message to the remote UE device for the remote UE device to switch from the direct communication link to an indirect communication link via the target relay UE device.

11. The base station according to claim 10, wherein the measurement report is generated based on the RRC status indicator transmitted by the candidate relay UE device.

12. The base station according to claim 11, wherein the measurement report is generated based on an RRC status indicator transmitted by the other candidate relay UE device, by omitting the measurement of signals transmitted by the other candidate relay UE device that is not in the RRC connection (RRC CONN) state.

13. The base station according to claim 12, wherein the RRC status indicator indicates one of a plurality of RRC connection states, including connected (RRC CONN), idle (RRC IDLE), or inactive (RRC INACTIVE).

14. The base station according to claim 13, wherein the transmitting unit is further configured to transmit a measurement setting message indicating a criterion for triggering the generation of the measurement report to the remote UE device.

15. The base station according to claim 14, wherein the criteria include a direct link minimum quality threshold for the direct communication link.

16. The base station according to claim 15, wherein the criteria include a minimum quality threshold for candidate relaying of a PC5 link.

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