Relay user equipment (UE) radio resource control (RRC) connection status indicator

Abstract

To provide a relay device that manages wireless communication links using relay devices.SOLUTION: A relay user equipment (UE) device 12 in a communication system 10 transmits a Radio Resource Control (RRC) connection status indicator indicating an RRC connection status of the relay UE device to a serving base station 20. The RRC connection status indicator is also used by a remote UE device 16 to manage relay communication to the base station. A remote UE device in direct communication with the base station transmits a measurement report to the base station. The measurement report includes measurements only for relay UE devices reporting the RRC connection status. The base station manages direct to indirect communication switching at least partially based on the measurement report. Remote UE devices manage relay reselection using a relay candidate prioritization at least partially based on the connection status of candidate relay UE devices.SELECTED DRAWING: Figure 1A

Description

Priority claims

[0001] This application claims priority to U.S. Provisional Application No. 63 / 186,574, filed May 10, 2021, with Attorney Docket No. TPRO00362US, entitled "Sidelink L2 Relay Reselection During Radio Link Failure," and U.S. Provisional Application No. 63 / 222,303, filed July 15, 2021, with Attorney Docket No. TPRO00363US, entitled "Service Continuity Under L2 Sidelink Relay." Both U.S. provisional applications are commonly assigned to the present application and are expressly incorporated by reference in their entireties. [Technical Field]

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

[0003] Many wireless communication systems employing several 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 through a base station. Such Proximity Services (ProSe) communication is sometimes referred to as device-to-device (D2D) communication. Furthermore, one or more UE devices can act as relay devices between the UE devices and a destination, where the relay device forwards data between the UE device and the destination. The destination can be a communication network or another UE device (the 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 cases, for example, a UE device may be outside the coverage area of ​​a base station, and a relay UE device provides a communication link from such out-of-coverage (OoC) UE device that is routed to the base station via 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. DISCLOSURE OF THE INVENTION

[0004] A relay user equipment (UE) device transmits a radio resource control (RRC) connection status indicator to a serving base station indicating the RRC connection status of the relay UE device. The RRC connection status indicator may be used by a remote UE device to manage relay communications to the base station. In one example, a remote UE device in direct communication with a base station transmits a measurement report to the base station, the measurement report including only measurements for relay UE devices reporting an RRC connection (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. [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 RRC connection status to a remote UE device.

[0006] [Figure 1B] 1 is a block diagram of an example communications system in which candidate relay UE devices each transmit an RRC connection state for reception by remote UE devices.

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

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

[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 UE device.

[0011] [Figure 4] FIG. 10 is a message diagram of an example of relay link management for direct to indirect switching where a remote UE device sends measurement reports for RRC connected candidate relay UE devices.

[0012] [Figure 5] FIG. 10 is a message diagram of an example of relay link management where a remote UE device maintains a recommended relay list based on the connectivity state of candidate relay UE devices. DETAILED DESCRIPTION OF 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 (destination UE device) or a network. If the destination is a network, the relay provides a connection to a cell provided by the network's base station (gNB). A relay connection between a remote UE device and a target UE device is sometimes referred to as a UE-to-UE (U2U) relay connection. A relay connection between a remote UE device and a base station (gNB) is sometimes referred to as a UE-to-network (U2N) relay connection. In some cases, the final destination is the target UE device via a base station. In conventional systems where a relay connects base stations (gNBs), a relay UE device must meet certain criteria to function as a relay. For example, a 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 relaying functionality.

[0014] The sidelink relaying function allows a remote UE that is out of coverage (OoC) to connect to a gNB or base station via a relay UE device. UE-to-Network (U2N) relaying requires that the relay UE is 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.

[0015] In some cases, 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 via the relay UE device. When switching to the indirect link, it may be advantageous for the base station to switch to an indirect relay link provided by a relay UE device in an RRC CONN state. For example, switching to a relay connection via a relay UE device in an RRC CONN state can minimize delay compared to switching to a relay connection via a relay UE device in an RRC IDLE state or an RRC INACTIVE state. In some examples herein, the remote UE device provides a measurement report including measurements of only candidate relay UE devices reporting an RRC CONN state. Thus, the base station evaluates only candidate relay UE devices in an RRC CONN state, selects a recommended relay UE device, and transmits an RRC reconfiguration message to the remote UE device identifying the recommended relay UE device.

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

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

[0018] 1A is a block diagram of an example communication system 10 in which a candidate relay UE device 12 transmits an RRC connection status 14 to a remote UE device 16. The candidate relay UE device 12 is within a cell coverage area 18 of a 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, including an RRC connected state (RRC CONN), an RRC idle state (RRC IDLE), and an RRC inactive state (RRC INACTIVE). The candidate relay UE device 12 transmits the RRC connection status 14 indicating its RRC connection state with the base station 20. Thus, for example, the remote UE device 16 may be within or outside the cell coverage area 18, or 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 not connected to the base station 20 when receiving the RRC connection status 14. The remote UE device 16 may be in an RRC connected state with a base station and / or an RRC connected state with a 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, as described below, the remote UE device is indirectly connected to a base station via an 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 state may be conveyed to the remote UE device using any suitable sidelink transmission. In some cases, the RRC connection state is transmitted as part of a sidelink discovery signal, which may be a Model A discovery announcement message or a Model B response message. In other situations, the RRC connection state is transmitted in a PC5-RRC message. Such a technique may be useful, for example, if the RRC connection state of the relay UE device changes after a PC5 connection is established with the remote UE device.

[0020] In another example where a PC5-RRC message may be utilized, a relay UE device serves as a U2U relay during OoC before moving into a cell 18 and becoming in-coverage. After establishing an RRC CONN with a base station 20, the relay UE device transmits an RRC connection status 14 to all source and destination UE devices for which the relay device is provided. The RRC connection status may then be utilized by the source and destination UE devices when performing relay reselection. For example, the relay UE device may notify the source UE device when the destination UE device is no longer directly reachable by the relay UE device; however, because the relay UE device is in RRC CONN with the base station, the source UE device may determine that a connection via the relay UE device and the base station is preferred over other options. Therefore, the source UE device remains with the same relay UE device to reach the destination UE device via U2N relaying because establishing a connection via RRC CONN relaying is faster than establishing a relay connection via a non-RRC CONN, in-coverage relay UE device. Furthermore, if the source UE device is already PC5 connected to the original relay UE, the process of performing relay reselection requires exchanging control messages several times on both the PC5 link and the Uu link before traffic data can be resumed (e.g., PC5-S message to disconnect the current relay UE device, direct communication request message towards the new relay UE device, etc.).

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

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

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

[0024] In this example, the remote UE device 108 receives RRC connection status 104-106 from three candidate relay UE devices, and the status information facilitates communication link management of the connection to the base station. In one example discussed below, the received RRC connection status information of the candidate relay UE devices facilitates switching from direct communication (without the relay UE device) to indirect communication (with the relay UE device) between the remote UE device 108 and the base station 112. In another example, the remote UE device prioritizes candidate relay UE devices for relay reselection based at least in part on the connection status. In addition to the increased delay for the remote UE device to connect to a base station, (re)selecting a relay UE device that is either RRC IDLE or RRC INACTIVE means that the relay UE device must still establish its own RRC connection with the base station, which may be rejected. The remote UE device would then need to find another candidate relay UE device to connect to the base station.

[0025] FIG. 1C is a block diagram of a system 100 for an example in which a remote UE device 108 transmits a measurement report 120 based on received RRC connection status of candidate relay UE devices 101-103. The scenario of FIG. 1C is an example of the situation of FIG. 1B in which RRC connection status information is used to generate the measurement report 120. For example, the RRC connection status 104-106 of each candidate relay UE device is received in a discovery signal transmitted by the candidate relay UE device providing the RRC connection status. The remote UE device measures the quality of the signal received from the candidate relay UE device 101-103. Suitable techniques include measuring the Sidelink Discovery Reference Signal Received Power (SD-RSRP) level of the discovery signal transmitted by the candidate relay UE device and received at the remote UE device. For example, the discovery signal containing the RRC connection status is measured, although measurements may also be made on other discovery signals in some circumstances. The remote UE device generates a measurement report based on the measured SD-RSRP level and the RRC connection status of the candidate relay UE devices 101-103. The measurement report includes at least the measured SD-RSRP level associated with a UE identifier identifying the candidate relay UE device that transmitted the measured signal. For example, the measurement report includes only the SD-RSRP measurements of the candidate relay UE devices and the candidate relay UE devices reporting the 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. Because 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 the RRC CONN. As described with reference to FIG. 1B, the second candidate relay UE device 102 is the only candidate relay UE device in the above example that is in the RRC CONN. As a result, 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 the measurement report may be triggered by a message from the gNB 112 or by an event detected at the remote UE device 108. For example, the remote UE device 108 may generate the measurement report in response to detecting certain criteria related to the quality of the connection to the gNB and the quality of alternative connections to the gNB. For example, the trigger for generating the measurement may be based on a determination that the Uu connection to the gNB is below a first threshold and the connections to the candidate relay UE devices are above a second threshold. In some circumstances, generation of the measurement report may be triggered if at least one candidate relay UE device has an SD-RSRP greater than a threshold, without evaluating the Uu connection.

[0027] 1D is a block diagram of an example system 100 in which a remote UE device 108 is connected to a base station 112 via a relay connection and maintains a candidate relay preference list 130 based at least in part on the RRC connection status of the candidate relay UE devices 101-103. The remote UE device 108 uses the candidate relay preference list 130 for relay reselection. In some situations, the candidate relay preference list 130 is generated when a relay reselection procedure is initiated. In other situations, the candidate relay preference list 130 is generated prior to a 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 where the remote UE device 108 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 the 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, the RRC connection status indicators 104-106 are transmitted as part of a discovery message, which may be a Model A message or a Model B response message. In some circumstances, transmission of the RRC connection status indicator occurs in response to a change in the RRC connection status at the relay UE device. For example, a change in the RRC connection status may trigger transmission of a Model A discovery message including the RRC connection status indicator. The RRC connection status indicators 104-106 may be any information or identifier that indicates to another UE device (e.g., a remote UE device 108) the current RRC connection status of the relay UE device transmitting the indicator. For example, the RRC connection status indicator indicates one of three status states in accordance with one or more revisions of the 3GPP New Radio (NR) V2X communication specification: RRC CONN, RRC IDLE, or RRC INACTIVE. 1B, the remote UE device 108 maintains a candidate relay priority list 130 in which candidate relay UE devices 101-103 are prioritized for relay service based at least in part on their RRC connection status. Candidate relay UE devices in the RRC CONN state are given higher priority than candidate relay UE devices 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 discovery signals received from candidate relay UE devices. Thus, prioritization may 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 the higher measured SD-RSRP is assigned a higher priority. Typically, in network planning, cell edge corresponds to an RSRP level better than -120 dBm.Similarly, for SD-RSRP, it is recommended to select a candidate relay UE device with an SD-RSRP level above -120 dBm, although lower levels may work as long as the level exceeds the sensitivity level of the UE device. Thus, if a candidate relay UE device in RRC CONNECTED has a measured SD-RSRP below -120 dBm while another candidate relay UE device in RRC IDLE has a measured SD-RSRP above -120 dBm, the remote UE device may decide to connect with the candidate UE device in RRC IDLE. This may be especially the case when the remote UE device and the candidate relay UE device are in relative motion.

[0030] FIG. 2 is a block diagram of an example of a base station 200 suitable for use as the base station 112, and any base station that provides a cell or services any UE device. 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 may be 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 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 device that is installed at a specific location during system deployment. Examples of such devices include a fixed base station or a fixed transceiver station. Although base stations may be referred to by different terms, when operating in accordance with one or more communications specifications for 3GPP V2X operations, base stations are typically referred to as gNodeBs or gNBs. In some cases, the base station 200 may be a mobile device that is temporarily installed at a specific location. Some examples of such equipment include mobile transceiver stations, which may include power generation equipment such as generators, solar panels, and / or batteries. Larger and heavier versions of such equipment may be transported on trailers. In still other cases, the base station 106 may be a portable device that is not fixed to a particular location.

[0031] The controller 204 may include any combination of hardware, software, and / or firmware for performing the functions described herein as well as for making all functions of the user equipment device more efficient. An example of a suitable controller 204 includes software code executing on a microprocessor or processor array coupled to memory. The transmitter 206 includes electronics configured to transmit wireless signals. In some cases, the transmitter 206 may include multiple transmitters. The receiver 208 includes electronics configured to receive wireless signals. In some cases, 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 cases, the antenna 210 may include multiple transmit and receive antennas.

[0032] 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 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 device. The required components may depend on the specific functionality required by the user equipment device.

[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 any one of a number of modulation orders. The demodulator demodulates the uplink signal received at the base station 200 according to one of a number of modulation orders.

[0034] 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 cases, the link between base stations may include at least some wireless portion. Thus, the communication interface 212 may include wireless communication capabilities and may utilize some of the components of the transmitter 206 and / or receiver 208.

[0035] FIG. 3 is a block diagram of an example UE device 300 suitable for use as each of the UE devices 12, 16, 101-103, 108, and 132. 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) communication device or an Internet of Things (IoT) device. Thus, the UE device 300 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 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 as being performed in any single device may be implemented across multiple devices.

[0036] The UE device 300 includes at least a controller 302, a transmitter 304, and a receiver 306. The controller 302 facilitates the overall functionality of the communications device as well as includes any combination of hardware, software, and / or firmware for performing the functions described herein. Examples of suitable controllers 302 include code executing on a microprocessor or processor architecture coupled to memory. The transmitter 304 includes electronics configured to transmit wireless signals. In some circumstances, the transmitter 304 may include multiple transmitters. The receiver 306 includes electronics configured to receive wireless signals. In some circumstances, the receiver 306 may include multiple receivers. The receiver 304 and the transmitter 306 receive and transmit signals, respectively, via an 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.

[0037] The transmitter 304 and receiver 306 in the example of Figure 3 perform radio frequency (RF) processing, including modulation and demodulation. Accordingly, the receiver 304 may include components such as a low noise amplifier (LNA) and a filter. The transmitter 306 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 conjunction with other components, perform communication device functions. The required components may vary depending on the specific functions required for the communication device.

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

[0039] The communications device 300 includes a memory 310 in addition to the memory that is part of the controller 302. Information such as the candidate relay priority list 130 may be stored and maintained in the memory 310, the controller, 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 a remote UE device 108 sends measurement reports for RRC connected candidate relay UE devices. While Figure 4 shows three candidate relay UE devices 101-103, any number of candidate relay devices can be involved in the messaging. The example begins with a remote UE device 108 connected to a 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 Uu communication link 402.

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

[0042] At transmission 406, a discovery message is transmitted from the candidate relay UE device 101. At transmission 408, a discovery message is transmitted from the candidate relay UE device 102. At transmission 410, a discovery message is transmitted from the candidate relay UE device 103. The discovery messages at transmissions 406, 408, and 410 may be Model A discovery announcement messages or Model B discovery response messages. For example, the discovery message includes an RRC connection status notification indicating the RRC connection status of the relay UE device that transmitted the discovery message. The remote UE device 108 receives the discovery message and evaluates the received signaling and information as part of a relay reselection procedure. For example, the remote UE device measures the SD-RSRP level of the received discovery message to evaluate the RRC connection status of the candidate relay UE devices 101-103.

[0043] At transmission 412, the remote UE device transmits a measurement report to the gNB 112, the measurement report including signal quality measurements of the 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. Thus, the measurement report includes signal quality measurements, such as the SD-RSRP level of the discovery signal 408, for the second candidate relay UE device 102. The measurement report may also include signal quality measurements of other gNBs, depending on the circumstances.

[0044] 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 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, the RRC connection state, 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), etc.

[0045] At event 416, the remote UE device 108 and the gNB 112 perform a measurement configuration and reporting procedure. The line representing event 416 is dashed to indicate that the procedure is not necessary if the gNB 112 already has the information that would be obtained from the measurement configuration and reporting procedure.

[0046] The gNB 112 selects a relay UE device (target relay UE device) after obtaining measurement reports from the second candidate relay UE device and any other candidate relay UE devices included in the measurement report 120 provided by the remote UE device. For example, the gNB 112 selects the second candidate UE device 102 for the relay connection.

[0047] At transmission 418, the gNB 112 transmits an RRC reconfiguration message to the remote UE device. The RRC reconfiguration message initiates a switch from the direct communication link 402 to an indirect communication link via the second candidate relay UE device 102. In some circumstances, the order of transmissions 416, 418 can be switched.

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

[0049] At transmission 422, the remote UE device 108 transmits an RRC reconfiguration complete message to the gNB 112. Communication between the remote UE device 108 and the gNB 112 continues via an indirect communication link 424 that includes a relay connection through the second candidate relay UE device 102.

[0050] FIG. 5 is a message diagram 500 of an example of relay link management in which a remote UE device 108 maintains a recommended relay list based on the connection states of candidate relay UE devices. While FIG. 5 shows three candidate relay UE devices 101-103, any number of candidate relay devices can be involved in the messaging. This example begins with a remote UE device 108 connected to a base station via a relay connection through an initial relay UE device 102 that includes a PC5 link 502 to a first relay UE device 132. At event 504, the remote UE device 108 begins maintaining a 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 candidate relay UE devices 101-103 are prioritized for relay service based at least in part on their RRC connection states and measured SD-RSRP levels. The remote UE device 108 uses the discovery procedures of transmissions 508, 510, and 512 to identify and prioritize relay UE devices. In some circumstances, the remote UE device 108 waits for another event before performing reselection. In other circumstances, other events 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 otherwise determined to be unavailable.

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

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

[0053] At event 514, the remote UE device selects a recommended candidate relay UE device for establishing a relay connection to the gNB 112. Event 514 may be part of a relay reselection procedure. In some circumstances, the remote UE device 108 maintains a list of recommended candidate relay UE devices and selects the most recommended relay UE device for reselection in response to the event. For example, if an RLF occurs and the connection cannot be reestablished through the original relay UE device 132, the remote UE device 108 may determine that a new relay connection should be established through a recommended relay UE device.

[0054] At event 516, a PC5 link is established with a recommended candidate relay UE device, for example, the recommended candidate relay UE device is the second candidate relay UE device 102. Subsequently, a relay connection 518 is established with the gNB 112.

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

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

[0057] Clearly, other forms and modifications of the present invention will occur to those skilled in the art in light of these teachings. The foregoing description is intended to be illustrative 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 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 transceiver having a transmitter and a receiver and configured to initially communicate with a base station over a communication link; the receiving unit is configured to receive, from a first candidate relay UE device, a first Radio Resource Control (RRC) connection status indicator indicating a current connection status of the first candidate relay UE device to a base station, and to receive, from a second candidate relay UE device, a second RRC connection status indicator indicating a current connection status of the second candidate relay UE device to the base station; The transceiver is further configured to switch communication from the original communication link to the relay communication link communicating with the base station via 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 based at least in part on the first RRC connection status indicator and the second RRC connection status indicator. A remote user equipment (UE) device.

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

3. the initial communication link is a direct communication link between the remote UE device and the base station; 3. The remote UE device of claim 2, further comprising: a controller configured to, in response to the quality of the direct communication link falling below a direct link quality threshold, transmit an RRC connection status indicator indicating an RRC CONN state; and generate a measurement report including link quality measurements associated with relay UE device identifiers of each candidate relay UE device in a connected state and omitting link quality measurements of all other candidate relay UE devices.

4. 2. The remote UE device of claim 1, wherein the controller 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 is above a relay threshold.

5. 5. The remote UE device of claim 4, wherein the controller is further configured to: determine that the quality of the direct communication link has fallen below the direct link quality threshold; and determine, based on measurements at the remote UE device, that at least one link to a candidate relay UE device is above a relay threshold.

6. the receiver is configured to receive from the base station a measurement report configuration identifying criteria for generating the measurement report; The remote UE device of claim 4 , wherein the controller is configured to generate the measurement report in response to determining that the criteria for generating the measurement report are met.

7. the receiver is further configured to receive an RRC reconfiguration message from the base station, the RRC reconfiguration message identifying the recommended candidate relay UE device; The remote UE device of claim 4 , wherein the controller 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 reconfiguration message.

8. the initial communication link is a first relay communication link via an initial relay UE device; The remote UE device of claim 2 , wherein the controller is configured to select the recommended candidate relay UE device.

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

10. a transceiver and a control unit; the transceiver having a transmitter and a receiver and configured to communicate with a remote user equipment (UE) device over a direct communication link; The receiving unit is configured to receive, from a remote UE device measurement report at the remote UE device including link quality measurements of signals received from candidate relay UE devices, link quality measurements including only link quality measurements of signals received from candidate relay UE devices whose Radio Resource Control (RRC) connection state with the base station is connected (RRC CONN); the controller is configured to identify one of the candidate relay UE devices as a target relay UE device; The base station, wherein the transmitter 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 of claim 10, wherein the measurement report is generated based on RRC status indicators transmitted by the candidate relay UE devices.

12. 12. The base station of claim 11, wherein the measurement report is generated based on RRC status indicators transmitted by other candidate relay UE devices by omitting measurements of signals transmitted by the other candidate relay UE devices that are not in the RRC connected state.

13. 13. The base station of claim 12, wherein the RRC state 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 of claim 13, wherein the transmitter is further configured to transmit a measurement configuration message to the remote UE device indicating criteria for triggering generation of the measurement report.

15. The base station of claim 14 , wherein the criteria includes a direct link minimum quality threshold for the direct communication link.

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

Images