Conditional service continuity (CSC) for relay communication links

Abstract

A remote terminal communicating with a serving cell over a multi-hop relay communication link receives a Conditional Service Continuity (CSC) configuration from the serving cell. The CSC configuration identifies at least a target cell for establishing an alternate communication link. In response to determining execution criteria have been met, the remote terminal establishes the alternate relay communication link to the target cell in accordance with the CSC configuration. The remote terminal may determine the execution criteria is met when determining the multi-hop relay communication link has suffered the RLF.

Description

CONDITIONAL SERVICE CONTINUITY (CSC) FOR RELAY COMMUNICATION LINKSCLAIM OF PRIORITY

[0001] The present application claims priority to Provisional Application No. 63 / 664,288, entitled “U2N Multihop Relay Failures” and filed June 26, 2024, assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety.FIELD

[0002] This invention generally relates to wireless communications and more particularly to Conditional Service Continuity (CSC) for relay communication links.BACKGROUND

[0003] Many wireless communication systems that employ several base stations (network nodes) that provide wireless service to terminals (user equipment (UE) devices) enable sidelink communication between two or more terminals where the terminals can communicate directly with other terminals. In addition, one or more terminal can be used as relay devices to form relay communication links between terminal and a cell of a base station or between a source UE device and a destination UE device. A relayed connection between a remote UE and the network through a relay device is often referred to as a UE-to-Network (U2N) link. The U2N link includes a PC5 link between the relay device and the remote UE and Uu link between the relay device and a cell of a base station in the network.

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

[0005] A remote terminal communicating with a serving cell over a multi-hop relay communication link receives a Conditional Service Continuity (CSC) configuration from the serving cell. The CSC configuration identifies at least a target cell for establishing an alternate communication link. In response to determining execution criteria have been met, the remote terminal establishes the alternate relay communication link to the target cell in accordance with the CSC configuration. The establishment may include transmitting a RRCReconfigurationComplete message to the target cell. The remote terminal may determine the execution criteria have been met by determining that the multi-hop relay communication link has suffered a radio link failure (RLF). The remote terminal may determine the multi-hop relay communication link has suffered the RLF by detecting the RLF on the PC5 link to the first relay terminal or by receiving a failure notification message from the first relay terminal indicating that the RLF has occurred on one of the other PC5 links or indicating that the Uu link to the serving cell has failed.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 A is a block diagram of an example of a communication system where a remote terminal is connected to a network node serving cell over a U2N relay communication link and the remote terminal performs a conditional path switch procedure to a target cell in accordance with a Conditional Service Continuity (CSC) configuration received from the serving cell.

[0007] FIG. 1 B is a block diagram of an example of the communication system where a remote terminal performs a CSC path switch procedure to a target cell after the second PC5 link (path B) experiences an RLF.

[0008] FIG. 1 C is a block diagram of an example of the communication system where a remote terminal performs a CSC path switch procedure to a target cell after the llu link (path C) experiences an RLF.

[0009] FIG. 1 D is a block diagram of an example of the communication system where a remote terminal performs a CSC path switch procedure to a target cell after the remote terminal detects an RLF of the first PC5 link (path A).

[0010] FIG. 2 is a block diagram of an example of a base station suitable for use as the network node providing the serving cell and as the network node providing the target cell, as well as network nodes providing the candidate target cells.

[0011] FIG. 3 is a block diagram of an example of a UE device suitable for use as each of the terminals including remote terminal and relay terminals including the relay terminals.

[0012] FIG. 4A is a message flow diagram for an example where a remote terminal performs a CSC path switch procedure to a target cell after the second PC5 link (path B) experiences an RLF.

[0013] FIG. 4B is a message flow diagram for an example where a remote terminal performs a CSC path switch procedure to a target cell after the Uu link (path C) experiences an RLF.

[0014] FIG. 4C is a message flow diagram for an example where a remote terminal performs a CSC path switch procedure to a target cell after the first PC5 link (path A) experiences an RLF.

[0015] FIG. 5 is a flow chart of an example of method of managing conditional service continuity (CSC) for relay communication links performed at a terminal.

[0016] FIG. 6 is a flow chart of an example of method of managing conditional service continuity (CSC) for relay communication links performed at a network node.DETAILED DESCRIPTION

[0017] As discussed above, a relay communication link can be established between a serving cell and a remote terminal (remote user equipment (UE) device) through oneor more relay terminals (relay UE devices). The relay communication link, often referred to as a UE-to-Network (U2N) communication link, includes PC5 links between the remote terminal and the relay terminal and between relay terminals when more than one relay terminal forms the U2N communication link. The remote terminal is connected through a first PC5 link to a first relay terminal. The first relay terminal is connected through a second PC5 link to the second relay terminal and the second relay terminal is connected to the serving cell over a Uu link. The relay communication link may include any number of internal relay terminals where a PC5 ingress link of each relay terminal is a PC5 egress link of an adjacent relay terminal. Except for the last relay terminal, therefore, each relay terminal in the U2N link has a PC5 ingress link to a terminal and a PC5 egress link to another terminal.

[0018] In some situations, a U2N relay communication link fails such that the serving cell cannot continue to provide service to the remote terminal. One of the PC5 links or the Uu link may experience an RLF. Conventional systems are limited in that the remote terminal must perform a (re)establishment procedure to continue communication with the network after an RLF occurs on one of the paths (links) of a multi-hop relay communication link. Such a requirement is inefficient and results in delays. For the examples herein, however, the serving cell sends a Conditional Service Continuity (CSC) configuration to the remote terminal communicating with a serving cell over the multi-hop relay communication link where the CSC configuration identifies at least one target cell for establishing an alternate communication link. In some situations, a target cell is identified by identifying a candidate relay terminal that is being served by the target cell. The target cell may be provided by the same network node providing the serving cell or by a different network node. In some situations, the serving cell is the target cell. Accordingly, the alternate communication link may include different relay terminals to the original serving cell in some situations. For the examples, the CSC configuration also includes execution criteria indicating to the remote terminal when an alternate communication link should be established. In response a determination that the execution criteria have been met, the remote terminal establishes the alternate relay communication link to the target cell in accordance with the CSC configuration. The execution criteria may include authorization to perform the CSC path switch when aradio link failure (RLF) is detected by or reported to the remote terminal. In some situations, the execution criteria may only include an RLF determination. In such situations, therefore, the remote terminal establishes the alternate relay communication link to the target cell at least partially in response to determining the multi-hop relay communication link has suffered a radio link failure (RLF). A CSC path switch for communication links without relay terminals based on such criteria is typically referred to as a “Subsequent CSC path switch”. The terminology is derived from the situation where a first attempt to perform CSC path switch without an RLF condition fails which leads to an RLF and the terminal “subsequently” performing another CSC path switch. The remote terminal may evaluate multiple alternate communication links to the target cell where the candidate alternate communication links may include the direct Uu link to the target cell and one or more candidate alternate relay communication links to the target cell. The selection of the alternate communication link is based on measurements from the target cell or relay terminal meeting the threshold requirements. The candidate alternate relay communication links may include any number of relay terminals. In some situations, the CSC configuration may include information identifying one or more candidate relay terminals in addition to one or more target cells.

[0019] A network node is any apparatus, equipment, device, or combination of devices, on the network side of the communication system that is connected to the communication network or is part of communication network. Some examples of a network node include a base station, a node B, an E-UTRA Node B, Evolved Node B, eNodeB, eNB, a New Generation eNB (ng-eNB), a gNodeB (also known as a gNB) in new radio (NR) technology, a macro station, pico station, and a femto station. The network node may form, or be a part of, the radio access network (RAN) that provides a connection between the core network and terminal communication devices. A RAN may be organized into three functional blocks including a Radio Unit (RU), a Distributed Unit (DU) and a Centralized Unit (CU). The RU transmits, receives, amplifies, and digitizes radio frequency signals and typically located near, or integrated into, the antenna. The DU and CU perform computations and / or processing to send and receive digitalized radio signals to and from the core network. The DU is typically located at or near the RU and the CU may be closer to the core network. The infrastructure orconnection between the RU and the DU is often referred to as fronthaul and the infrastructure or connection between the DU and the CU is often referred to as a midhaul. The communication node, therefore, may perform the functions of one or more of the RU, DU and / or CU depending on the particular implementation.

[0020] A terminal communication device (terminal), such as a remote terminal and a relay terminal, is a communication device on the terminal side of the communication system and is sometimes referred to as user equipment (UE), a UE device, a terminal device, wireless mobile device, wireless communication device and other terms. Some examples of a terminal communication device include a mobile phone, a smart phone, a personal digital assistant (PDA), tablet, and laptop computer. In some situations, the terminal communication device is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. In addition, the terminal communication device may be, or may be a part of, a wearable device or a vehicle where the vehicle may be terrestrial vehicle, watercraft, or aircraft (including unmanned aerial vehicles). The terminal communication device, therefore, is any fixed, mobile, or portable equipment that performs the functions of the terminal device described herein.

[0021] FIG. 1 A is a block diagram of an example of a communication system 100 where a remote terminal 102 is connected to a network node serving cell 104 over a U2N relay communication link 106 and the remote terminal 102 performs a conditional path switch procedure to a target cell 108 in accordance with a Conditional Service Continuity (CSC) configuration 110 received from the serving cell 104. For the example, the remote terminal 102 is connected to a first relay terminal 112 over a first PC5 link 114 which may be referred to as path A. The first relay terminal 112 is connected to a second relay terminal 116 over a second PC5 link 118 (path B) and the second relay terminal 116 is connected to the serving cell 104 over a Uu link 120 (path C). The relay communication link 106 may include any number of relay terminals and the techniques discussed herein for two relay terminals 112, 116 may be expanded to multi-hop relay communication links having three or more relay terminals. A network node, such as a gNB, provides one or more serving cells including the serving cell 104. The network node providing the serving cell 104, therefore, may provide other cells including one or more target cells.

[0022] The remote terminal 102 is in a Radio Resource Control (RRC) Connected state with the serving cell 104 and can transmit and receive data and other signals to and from the serving cell 104 over the relay communication link 106 in accordance with known techniques. For the example, the remote terminal 102 provides measurement reports 124 to the serving cell 104. The measurement reports may be periodic, event based, or a combination of the periodic and event-based measurement reports. Examples of event-based measurement report criteria include the following events:

[0023] Event X1 (Serving L2 U2N Relay UE becomes worse than thresholdl and NR Cell becomes better than threshold2);

[0024] Event X2 (Serving L2 U2N Relay UE becomes worse than threshold);

[0025] Event Y1 (PCell becomes worse than thresholdl and candidate L2 U2NRelay UE becomes better than threshold2);

[0026] Event Y2 (Candidate L2 U2N Relay UE becomes better than threshold); and

[0027] Event Z1 (Serving L2 U2N Relay UE becomes worse than thresholdl and Candidate L2.

[0028] The measurement report may include candidate cell(s) and / or candidate relay terminals that exceed the configured threshold requirements that triggered the measurement report. In one example, the remote terminal periodically provides measurement reports which include measurements of signals from potential candidate relay terminals and potential candidate target cells. Where candidate relay terminals are included in a measurement report, the Cell ID of the serving cell of each candidate relay terminal is included in the measurement report along with an identifier of the candidate relay terminal, such as the L2ID. Other terminals, including the relay terminals 112, 116, may also provide measurement reports to the serving cell 104. Based at least partially on the measurement reports, the serving cell 104 generates the CSC configuration 110 which at least identifies one candidate target cell for an alternate communication link 122 to the network. As discussed below, the CSC configuration may provide additional information which may include candidate relay terminals and / or execution criteria for performing the CSC path switch. A target cell may be identified implicitly in the CSC configuration by the identification of a candidate relay terminal. The remote terminal can consider an identified candidate relay terminal for the CSC path switch where theserving cell of the identified candidate relay terminal has not changed. The CSC configuration 110, therefore, at least provides information that allows the remote terminal 102 to establish the alternate communication link 122 to the network. For the examples herein, the CSC configuration 110 authorizes the remote terminal 102 to perform a path switch to the target cell 108 in response to receiving an CSC activation message or in response to a determination that the execution criteria have been met where the criteria may include a determination by the remote terminal 102 that the multihop relay communication link 106 has suffered a failure. In response to determining the criteria have been met, the remote terminal establishes the alternate communication link 122 to the target cell 108 where the alternate communication link 122 may by a direct llu link to the target cell or may include one or more relay terminals connecting the remote terminal 102 to the target cell 108. The execution criteria may include events such as the Event X1 , Event X2, Event Y1 , Event Y2; and Event Z1 discussed above for measurement reports. The execution criteria may be in accordance with handover decision criteria used by a serving cell for non-conditional handovers. In other words, the remote terminal performs the CSC path switch when the same conditions would have prompted a serving cell to perform a non-conditional handover. In some situations, the remote terminal determines a CSC path switch should be performed when a radio link failure (RLF) has occurred on Path A, Path B or Path C. The remote terminal evaluates the quality of the links to the candidate target cell(s) and any candidate relay terminal(s) to identify the preferred alternate communication link 122. As discussed below, the serving cell 104 performs a handover preparation procedure with the candidate target cell(s) identified in the CSC configuration 110 which facilitates a path switch to the target cell 104 without a re-establishment procedure required with conventional techniques after an RLF.

[0029] FIG. 1 B is a block diagram of an example of the communication system 100 where a remote terminal 102 performs a path switch procedure to a target cell 108 after the second PC5 link 118 (path B) experiences an RLF. Accordingly, the CSC path switch of FIG. 1 B is an example of the CSC path switch of FIG. 1 A. For the example of FIG. 1 B, the first relay terminal 112 detects the RLF of the second PC5 link 118. In response, the first relay terminal 112 sends a failure notification message 130 to theremote terminal 102. For the example, the failure notification message is a PC5-RRC message in accordance with 3GPP standards. In conventional systems, remote terminals initiate an RRC reestablishment procedure to reconnect to the network in response to a failure notification. For the examples herein, however, the remote terminal 102 performs a CSC path switch in accordance with the CSC configuration to establish the alternate communication link 122. The second relay terminal 116 also detects the RLF on the second PC5 link 118 and, in response, sends failure report message 132 to the serving cell 104. The failure report message 132 is an RRC message in the example. In some situations, the failure report message 132 triggers the serving cell 104 to perform additional HO preparation where the serving cell 104 confirms the HO request(s) previously sent to the target cell(s).

[0030] FIG. 1 C is a block diagram of an example of the communication system 100 where a remote terminal 102 performs a path switch procedure to a target cell 108 after the Uu link 120 (path C) experiences an RLF. Accordingly, the CSC path switch of FIG.1 C is an example of the CSC path switch of FIG. 1 A. For the example of FIG. 1 C, the second relay terminal 116 detects the RLF of the Uu link 120. In response, the second relay terminal 118 sends a failure notification message 134 to the first relay terminal 112. The first relay terminal 112 processes the failure notification message 134 and, in response, sends another failure notification message 136 to the remote terminal 102. For the example, the failure notification messages 134,136 are a PC5-RRC messages in accordance with 3GPP standards. In conventional systems, remote terminals initiate an RRC reestablishment procedure to reconnect to the network in response to a failure notification. For the examples herein, however, the remote terminal 102 performs a CSC path switch in accordance with the CSC configuration to establish the alternate communication link 122. The serving cell 104 also detects the RLF on the Uu link 120. In some situations, the detection of the RLF triggers the serving cell 104 to perform additional HO preparation where the serving cell 104 confirms the HO request(s) previously sent to the target cell(s).

[0031] FIG. 1 D is a block diagram of an example of the communication system 100 where a remote terminal 102 performs a path switch procedure to a target cell 108 after the remote terminal 102 detects an RLF of the first PC5 link 114. Accordingly, the CSCpath switch of FIG. 1 D is an example of the CSC path switch of FIG. 1 A. For the example of FIG. 1 D, the first relay terminal 112 also detects the RLF of the first PC5 link 114. In response, the first relay terminal 112 sends a failure notification message 138 to the second relay terminal 116. The second relay terminal 116 processes the failure notification message 138 and, in response, sends failure report message 140 to the serving cell 104. For the example, the failure notification messages 138, 140 are PC5- RRC messages in accordance with 3GPP standards. In conventional systems, remote terminals initiate an RRC reestablishment procedure to reconnect to the network in response to detecting an RLF of the first hop (first PC5 link). For the examples herein, however, the remote terminal 102 performs a CSC path switch in accordance with the CSC configuration to establish the alternate communication link 122. The failure report message 140 is an RRC message for the example. In some situations, the failure report message 140 triggers the serving cell 104 to perform additional HO preparation where the serving cell 104 confirms the HO request(s) previously sent to the target cell(s).

[0032] FIG. 2 is a block diagram of an example of a base station 200 suitable for use as the network node providing the serving cell 104 and as the network node providing the target cell 108, as well as network nodes providing the candidate target cells. The base station 200 includes a controller 204, transceiver 205 that includes a transmitter 206 and receiver 208, and an antenna 108, as well as other electronics, hardware, and code. The base station 200 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to the network nodes providing cells and base station 200 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. The base station 200 may be a fixed device or apparatus that is installed at a particular location at the time of system deployment. Examples of such equipment include fixed base stations or fixed transceiver stations. Although the base station 200 may be referred to by different terms, the base station 200 is typically referred to as a gNodeB or gNB when operating in accordance with one or more communication specifications of the 3GPP V2X operation. In some situations, the base station 200 may be mobileequipment that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generating equipment such as electric generators, solar panels, and / or batteries. Larger and heavier versions of such equipment may be transported by trailer. In still other situations, the base station 200 may be a portable device that is not fixed to any particular location.

[0033] The controller 204 includes any combination of hardware, software, and / or firmware for executing the functions described herein as well as facilitating the overall functionality of the base station 200. An example of a suitable controller 204 includes code running on a microprocessor or processor arrangement connected to memory. The transmitter 206 includes electronics configured to transmit wireless signals. In some situations, the transmitter 206 may include multiple transmitters. The receiver 208 includes electronics configured to receive wireless signals. In some situations, the receiver 208 may include multiple receivers. The receiver 208 may receive signals through multiple antennas or through a selected antenna of a plurality of antennas of the antenna 108. The antenna 108 may include separate transmit and receive antennas or separate arrays in some situations.

[0034] The transmitter 206 and receiver 208 in the example of FIG. 2 perform radio frequency (RF) processing including modulation and demodulation. The receiver 208, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 206 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the base station functions. The required components may depend on the particular functionality required by the base station.

[0035] The transmitter 206 includes a modulator (not shown), and the receiver 208 includes a demodulator (not shown). The modulator modulates the signals to be transmitted as part of the downlink signals and can apply any one of a plurality of modulation orders. The demodulator demodulates any uplink signals received at the base station 200 in accordance with one of a plurality of modulation orders.

[0036] The base station 200 includes a communication interface 212 for transmitting and receiving messages with other base stations such as the network nodes providing target cells and / candidate target cells. The communication interface 212 may be connected to a backhaul or network enabling communication with other base stations. In some situations, the link between base stations may include at least some wireless portions. The communication interface 212, therefore, may include wireless communication functionality and may utilize some of the components of the transmitter 206 and / or receiver 208.

[0037] FIG. 3 is a block diagram of an example of a UE device 300 suitable for use as each of the terminals including remote terminal and relay terminals including the relay terminals 112, 116. In some examples, the UE device 300 is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone. In other examples, the UE device 300 is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. The UE device 300, therefore is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to UE device 300 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

[0038] The UE device 300 includes at least a controller 302, a transmitter 304 and a receiver 306. The controller 302 includes any combination of hardware, software, and / or firmware for executing the functions described herein as well as facilitating the overall functionality of a communication device. An example of a suitable controller 302 includes code running on a microprocessor or processor arrangement connected to memory 310. The transmitter 304 includes electronics configured to transmit wireless signals. In some situations, the transmitter 304 may include multiple transmitters. The receiver 306 includes electronics configured to receive wireless signals. In some situations, the receiver 306 may include multiple receivers. The receiver 306 and transmitter 304 receive and transmit signals, respectively, through the antenna 308.The antenna 308 may include separate transmit and receive antennas. In some circumstances, the antenna 308 may include multiple transmit and receive antennas.

[0039] The transmitter 304 and receiver 306 in the example of FIG. 3 perform radio frequency (RF) processing including modulation and demodulation. The receiver 306, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 304 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the communication device functions. The required components may depend on the particular functionality required by the communication device.

[0040] The transmitter 304 includes a modulator (not shown), and the receiver 306 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as part of the uplink signals. The demodulator demodulates the downlink signals in accordance with one of a plurality of modulation orders.

[0041] The UE device 300 is capable of transmitting and receiving sidelink signals to and from other UE devices as well as communicating with a base station. The controller 302, in conjunction with the receiver 306, measures signals, such as discovery signals, transmitted by nearby UE devices to generate the neighbor list that includes neighbor UE devices within the maximum distance. The neighbor list is stored in the memory 310 and transmitted to the base station 106 when the UE device 300 is a reporting UE device. The receiver 306 and controller 302 also measure signals transmitted by the base station to determine the wide-beam precoder and the UE-specific precoder information.

[0042] FIG. 4A is a message flow diagram 400 for an example where a remote terminal 102 performs a path switch procedure to a target cell 108 after the second PC5 link 118 (path B) experiences an RLF. Accordingly, the messaging example of FIG. 4A CSC path switch is an example of messaging in the CSC path switch of FIG. 1 B. At transmission exchange 402, the remote terminal 201 transmits uplink (UL) data to the serving cell 104 and receives downlink (DL) data from the serving cell 104 over themultiple-hop relay communication link 106. Accordingly, UL signals are transmitted by the remote terminal 102, received by the first relay terminal 112, forwarded to the second relay terminal 116, and forwarded by the second relay terminal 116 to the serving cell 104. DL signals are transmitted by the serving cell 104, received by the second relay terminal 116, forwarded to the first relay terminal 112, and forwarded by the first relay terminal 112 to the remote terminal 102.

[0043] At transmission 404, measurement reports are transmitted by the remote terminal 102 and the relay terminals 112, 116 to the serving cell via the SRAP layer that is established when the remote UE transitioned to RRC CONNECTED. This allows the data and RRC messages to be delivered transparently to the serving cell, without decoding at the relay terminals. The measurement reports are periodic measurement reports that provide information regarding signals received at each device. The measurement reports transmitted by the remote terminal are relayed through the relay communication link 106. The measurement reports from the second relay terminal 116 are transmitted directly to the serving cell 104 over the Uu link 120. The measurement reports from the first relay terminal may be relayed by the second relay terminal 116 to the serving cell 104 or transmitted directly to the serving cell 104 over a Uu link when the first relay terminal 112 is in coverage. In addition, measurement reports from other terminals may be received at the serving cell 104. One or more of such terminals may be identified by the serving cell 104 as candidate relay terminals for the alternate communication link based, at least partially, on the measurement reports.

[0044] The serving cell 104 evaluates the measurement reports to identify one or more candidate target cells. For the example, the serving cell 104 identifies the target cell 108 as a candidate target cell. Based at least partially on the measurement reports, the serving cell 104 makes a CSC decision at event 406. The serving cell 104 determines that the remote terminal 102 should be configured with a CSC configuration. The serving cell only configures CSC to a remote terminal that is capable of supporting CSC. This information is provided to the serving cell as part of the capability signaling during the initial RRC Connection procedure.

[0045] At transmissions 408, 410, 412, the serving cell performs handover (HO) preparation for each candidate target cell. Depending on the HO REQUEST ACK in412 the serving cell 104 determines whether the target cell 108 is an appropriate cell to be included in the CSC configuration to the remote terminal. In order for a target cell to be included in the CSC configuration there needs to be resource availability from the target cell. This includes both PUSCH resources and RACH resource (e.g., CFRA resource for contention-free access). For the examples, the CSC configuration also includes the target cell’s Cell ID, the candidate relay terminal’s L2ID, the carrier frequency of the target cell (if appropriate), SSB information of the target cell and the measurement criteria for satisfying the execution condition for CSC (e.g., Event A3, A5 for the Uu link and / or Event Y2 (Candidate relay terminal becomes better than threshold)). For the example of FIG. 4A, only the target cell 108 is shown. The HO preparation confirms the ability of the candidate target cell process the HO of the remote terminal 102 to the candidate target cell.

[0046] At transmission 408, the serving cell sends a HO request message to the target cell 108. At event 410, the target cell performs admission control. At transmission 412, the target cell 108 sends a HO request acknowledgment indicating that the target cell 108 can accept the remote terminal 102.

[0047] At transmission 414, the serving cell 104 sends the CSC configuration 110 in a CSC RRC reconfiguration message. The CSC RRC reconfiguration message is transmitted over the relay communication link. Accordingly, the second relay terminal 116 forwards the message to the first relay terminal 112 and the first relay terminal 112 forwards the message to the remote terminal 102.

[0048] At event 416, the first relay terminal 112 detects an RLF on the second PC5 link. At event 418, the second relay terminal also detects the RLF on the second PC5 link.

[0049] At transmission 420, the first relay terminal 112 transmits a failure notification message indicating to the remote terminal 102 that the relay communication link has suffered an RLF. In some situations, the message may further specify that the RLF occurred on the second PC5 link.

[0050] At transmission 422, the second relay terminal 116 transmits a failure report indicating to the serving cell 104 that the relay communication link has suffered an RLF. In some situations, the failure report may further specify that an RLF occurred on thesecond PC5 link. For the example, the failure report is a SidelinkUEInformation message that includes at least the remote terminal’s (102) L2ID and the cause for sending the message i.e. , PC5 RLF detected. The message may optionally include the particular PC5 link that experienced the RLF.

[0051] At event 424, the serving cell executes HO preparation where the serving cell confirms that the target cell(s) 106 that the target cell 106 can process the handover of the remote UE to the target cell. The event 424 may be omitted in some circumstances. Accordingly, the oval representing the event in FIG. 4A is illustrated with a dashed line to indicate that the preparation is optional. In some situations, event 424 may facilitate the allocation of resources by the target cell. Event 424 may include an “activation” request from the serving cell to the target cells indicating the CSC path switch will be executed. For example, the target cell may wait for an activation request before allocating the resources for the remote terminal even though the target cell 108 had previously agreed to accept the remote terminal, including the resource configuration to be used. Such a technique may result in more efficient resource usage.

[0052] At event 426, the remote UE determines that a CSC path switch is required. In response to the failure notification received from the first relay terminal 112, the remote terminal 102 determines that the CSC path switch procedure should be initiated in accordance with the CSC configuration. The remote terminal measures signals from the target cell(s) and any candidate relay terminals and executes a CSC path switch to the target cell over the most appropriate alternate communication link to the target cell 108. For the examples, each candidate relay terminal broadcasts the identify of its serving cell in a discovery message. Accordingly, the remote terminal can determine whether a candidate relay terminal is being served by a target cells. Where the target cells are identified in the CSC configuration with candidate relay terminals, the remote terminal determines whether a candidate relay terminal is still being served by the target cell. After the alternate Uu link and PC5 links are established, the remote terminal 102 transmits an RRC Reconfiguration Complete message to the target cell 108 at event 428. Data communication continues over the alternate communication link at communication event 430.

[0053] FIG. 4B is a message flow diagram 440 for an example where a remote terminal 102 performs a CSC path switch procedure to a target cell 108 after the Uu link 120 (path C) experiences an RLF. Accordingly, the messaging example of FIG. 4B CSC path switch is an example of messaging in the CSC path switch of FIG. 1 C. The events and transmissions labeled with the same reference numbers as in FIG. 4A are performed in the same manner as described with reference to FIG. 4A. For the example of FIG. 4B, therefore, the measurement reports, the HO request and the CSC RRC configuration are transmitted at the transmissions 404, 408, 414.

[0054] At event 442, the second relay terminal 116 determines that the Uu link to the serving cell has suffered an RLF. At event 444, the serving cell 102 also determines that Uu link has failed. At event 446, the serving cell performs HO preparation. As discussed above with reference to event 424, the HO preparation is optional.

[0055] At transmission 448, a failure notification message is sent by the second relay terminal 116 to the first relay terminal 112. For the example, the failure notification message is a PC5-RRC message that is received and deciphered by the first relay terminal 112. In response to the failure notification message received from the second relay terminal 116, the first relay terminal 112 generates and transmits failure notification message to the remote terminal 102 at transmission 450. For the example, the failure notification message is a PC5-RRC message. In some situations, the failure notification message may be transmitted using a different technique. For example, the failure notification message may be sent using application layer signaling, such as PC5- S signaling. The contents of the second failure notification message transmitted by the first relay terminal 112 may be same as the contents of the first failure notification message transmitted by the second relay terminal 116. In other situations, the transmitted information may be different.

[0056] In another example, the failure notification messages take the form of discovery messages. For example, the AS layer of the second relay terminal 116 informs the upper layer (application layer) of the PC5 RLF. In response, the upper layer indicates in a discovery message (an upper layer message) that the relay terminal performed relay reselection. Therefore, the discovery message indicates the “relay reselection” which may be due to an RLF. The discovery message prompts the firstrelay terminal 112 to perform relay reselection and send its own discovery message which is received by the remote terminal 102 indicating the relay reselection by the first relay terminal 112. The remote terminal performs CSC. Therefore, a failure notification message or discover signal indicating relay reselection received by the remote terminal 102 prompts the remote terminal to execute the relay selection in accordance with the CSC configuration and establish the alternate communication link as discussed above.

[0057] FIG. 4C is a message flow diagram 460 for an example where a remote terminal 102 performs a CSC path switch procedure to a target cell 108 after the first PC5 link 114 (path A) experiences an RLF. Accordingly, the messaging example of FIG. 4C CSC path switch is an example of messaging in the CSC path switch of FIG. 1 D. The events and transmissions labeled with the same reference numbers as in FIG. 4A are performed in the same manner as described with reference to FIG. 4A. For the example of FIG. 4C, therefore, the measurement reports, the HO request and the CSC RRC configuration are transmitted at the transmissions 404, 408, 414.

[0058] At event 462, the remote terminal 102 determines that that PC5 link to the first relay terminal 112 has suffered an RLF. At event 464, the first relay terminal 112 also detects the RLF on the PC5 link to the remote terminal 102

[0059] At transmission 466, the first relay terminal 116 sends a failure notification message to the second relay terminal 116. For the example, the failure notification message is a PC5-RRC message that is received and deciphered by the second relay terminal 116. In response to the failure notification message received from the first relay terminal 112, the second relay terminal 116 generates and transmits a failure report to the serving cell 104 at transmission 468. For the example, failure report is a transmitted in an RRC message, such as a SidelinkUEInformation message. In situations where there are more than two relay terminals, each relay terminal generates a failure notification message in response to the failure notification message received from prior relay terminal. The last relay terminal transmits the failure report in the RRC message to the serving cell.

[0060] In response to the RLF at event 462, the remote terminal performs CSC. Therefore, the RLF detected by the remote terminal 102 prompts the remote terminal toexecute the relay selection in accordance with the CSC configuration and establish the alternate communication link as discussed above.

[0061] FIG. 5 is a flow chart of an example of method of managing conditional service continuity (CSC) for relay communication links. The method may be performed in a system such as the system 100 discussed herein. For the example, the method is performed by a remote terminal, such as the remote terminal 102. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the terminal may facilitate the generation, formatting, reception and transmission of signals and messages. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 5. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 5.

[0062] At step 502, the remote terminal 102 communicates with the serving cell 104 over the multi-hop relay communication link. As discussed above, the multi-hop relay communication link comprises a first PC5 link between the remote terminal and a first relay terminal, a second PC5 link between the first relay terminal and the second relay terminal, and a Uu link between the second relay terminal and the serving cell.

[0063] At step 504, the remote terminal receives, from the serving cell over the multihop relay communication link, a Conditional Service Continuity (CSC) configuration identifying a target cell for establishing an alternate communication link.

[0064] At step 506, the remote terminal 102 determines whether execution criteria authorizing the CSC path switch have been met. In some situations, the criteria includes a determination that the multi-hop relay communication link has failed. For the example, the remote terminal may determine the link has failed by detecting that the PC5 link to the first relay terminal has failed or by receiving a signal from the first relay terminal indicating the multi-hop relay communication link is no longer available. The signal may include a failure notification message indicating an RLF. As discussed above, the signal may be a discovery signal transmitted by the first relay terminal indicating that the first relay terminal is executing a relay reselection procedure implying that the multi-hoprelay communication link is no longer available. If it is determined that the multi-hop relay communication link has failed, the method continues to step 508. Otherwise, the method returns to step 502.

[0065] At step 508, the remote terminal establishes the alternate relay communication link to the target cell in accordance with the CSC configuration. For the example, the remote terminal evaluates signals from one or more target cells and / or from candidate relay terminals to select the best alternative relay communication link to a target cell. The target cell(s), and possibly candidate relay terminals, are provided in the CSC configuration previously received from the serving cell. Therefore, in response to determining execution criteria has been met, such as determining the multi-hop relay communication link has failed after the CSC configuration has been received, the remote terminal establishes the alternate relay communication link to the target cell in accordance with the CSC configuration.

[0066] FIG. 6 is a flow chart of an example of method of managing conditional service continuity (CSC) for relay communication links. The method may be performed in a system such as the system 100 discussed herein. For the example, the method is performed by a network node providing a serving cell to remote terminal. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the terminal may facilitate the generation, formatting, reception and transmission of signals and messages. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 6. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 6.

[0067] At step 602, the serving cell 104 of a network node communicates with the remote terminal 102 over the multi-hop relay communication link. As discussed above, the multi-hop relay communication link comprises a first PC5 link between the remote terminal and a first relay terminal, a second PC5 link between the first relay terminal and the second relay terminal, and a Uu link between the second relay terminal and the serving cell.

[0068] At step 604, measurements are received from terminals. Measurement reports may be received from the remote terminal 102, the relay terminals 112, 116 and other terminals in the area. For the example, the measurement reports may be periodic measurement reports that provide information regarding signals received at each device. The measurement reports transmitted by the remote terminal are relayed through the relay communication link 106. The measurement reports from the second relay terminal 116 are transmitted directly to the serving cell 104 over the Uu link 120. The measurement reports from the first relay terminal may be relayed by the second relay terminal 116 to the serving cell 104 or transmitted directly to the serving cell 104 over a Uu link when the first relay terminal 112 is in coverage. In addition, measurement reports from other terminals may be received at the serving cell 104. One or more of such terminals may be identified by the serving cell 104 as candidate relay terminals for the alternate communication link based, at least partially, on the measurement reports.

[0069] At step 606, the network node determines whether CSC should be configured for the remote terminal 102. Based at least partially on the measurement reports, the network node makes a CSC decision. The network node evaluates the measurement reports to identify one or more candidate target cells and may identify candidate relay terminals. If the network node determines that the remote terminal 102 should be configured with a CSC configuration, the method proceeds to step 608. Otherwise, the method returns to step 602.

[0070] At step 608, network node sends a HO request message to the target cell(s). The one or more target cells perform admission control and send a HO request acknowledgment indicating that the target cell can accept the remote terminal 102. The one or more HO request acknowledgments are received at step 610.

[0071] At step 612, the network node sends the CSC configuration to the remote terminal 102. For the example, the network node sends the CSC configuration in a CSC RRC reconfiguration message over the relay communication link. Accordingly, the second relay terminal 116 forwards the message to the first relay terminal 112 and the first relay terminal 112 forwards the message to the remote terminal 102.

[0072] At step 614, the network node receives a HO success message from the target cell indicating that the CSC path switch was successfully completed. The remoteterminal continues communication over the established alternate communication link to the target cell.

[0073] To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. The described functionality may be implemented in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure. In accordance with various embodiments, a processor, device, component, circuit, structure, machine, module, etc. can be configured to perform one or more of the functions described herein. The term "configured to" or "configured for" as used herein with respect to a specified operation or function refers to processors, devices, components, circuits, electronics, and equipment that are physically constructed, programmed, instructed and / or arranged to perform the specified operation or function. Furthermore, the various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), other electronics or combinations thereof, a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, electronics, and circuits can further include antennas and / or transceivers to communicate with various components within the network or within the device. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein.

[0074] When implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method oralgorithm disclosed herein can be implemented as software stored on a computer- readable medium. Computer readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.

[0075] Therefore, the methods and apparatus of this invention may take the form, at least partially, of program logic or program code (i.e., instructions) embodied in tangible media, such as a machine-readable storage medium. When the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. The methods and apparatus of the present invention may also be embodied in the form of program code that is transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via any other form of transmission. When the program code is received and loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code combines with the processor to provide a unique apparatus that operates analogously to specific logic circuits.

[0076] Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the present disclosure. It will be appreciated that, for clarity purposes, the above description has described embodiments of the present disclosure with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processing logic elements or domains may be used without detracting from the present disclosure. For example, functionality illustrated to be performed by separate processing logic elements, or controllers, may be performed by the same processing logic element, or controller. Therefore, references to specificfunctional units are only references to a suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

[0077] Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims

CLAIMS1 . A method comprising: communicating, by a remote terminal, with a serving cell over a multi-hop relay communication link comprising a first PC5 link between the remote terminal and a first relay terminal, a second PC5 link between the first relay terminal and the second relay terminal, and a llu link between the second relay terminal and the serving cell; receiving, from the serving cell over the multi-hop relay communication link, a Conditional Service Continuity (CSC) configuration identifying a target cell for establishing an alternate communication link; in response to determining execution criteria have been met after the CSC configuration has been received, establishing the alternate relay communication link to the target cell in accordance with the CSC configuration.

2. The method of claim 1 , wherein the target cell is the serving cell.

3. The method of claim 1 , wherein the CSC configuration identifying a candidate relay terminal being served by the target cell, the CSC configuration indicating the target cell by indicating the candidate relay terminal.

4. The method of claim 1 , wherein establishing the alternate relay communication link comprises sending a RRCReconfigurationComplete message to the target cell.

5. The method of claim 1 , wherein the determining execution criteria have been met comprises determining the multi hop relay communication link has failed.

6. The method of claim 5, wherein determining the multi-hop relay communication link has failed comprises detecting the first PC5 link has suffered a radio link failure (RLF).

7. The method of claim 5, wherein determining the multi-hop relay communication link has failed comprises receiving a failure notification message form the first relay terminal.

8. The method of claim 7, wherein failure notification message indicates that the second PC5 link has suffered a radio link failure (RLF).

9. The method of claim 7, wherein failure notification message indicates that the Uu link has suffered a radio link failure (RLF).

10. The method of claim 1 , wherein establishing the alternate communication link to the target cell comprises establishing an alternate PC5 link to a target relay terminal, the alternate communication link comprising the alternate PC5 link to the target relay terminal.11 . The method of claim 10, wherein the alternate communication link comprises another alternate PC5 link between the target relay terminal and another relay terminal and an alternate Uu link between the another relay terminal and the target cell.

12. The method of claim 11 , wherein the CSC configuration identifies the target relay terminal.

13. The method of claim 12, wherein the CSC configuration identifies a plurality of candidate relay terminals, the method further comprising: measuring a signal quality of a candidate relay signal transmitted from each candidate relay terminal; selecting the target relay terminal at least partially based on signal quality measurements of the candidate relay signals.

14. The method of claim 1 , wherein establishing the alternate communication link comprises:measuring a signal quality of a signal transmitted from the target cell; and in response to determining the signal is above a threshold, establishing an alternate Uu link with the target cell.

15. The method of claim 14, wherein CSC configuration identifies a plurality of candidate target cells, the method further comprising: measuring a signal quality of a candidate target cell signal transmitted from each candidate target cell; selecting the target cell at least partially based on signal quality measurements of the candidate target cells.

16. A method comprising: communicating, by a serving cell of a network node, with a remote terminal over a multi-hop relay communication link comprising a first PC5 link between the remote terminal and a first relay terminal, a second PC5 link between the first relay terminal and a second relay terminal, and a Uu link between the second relay terminal and the serving cell; receiving measurement reports from terminals; identifying a target cell based on the measurement reports; transmitting a handover request message to the target cell for a handover of the remote terminal to the target cell; receiving a handover request acknowledge message from the target cell; transmitting, from the serving cell over the multi-hop relay communication link, a Conditional Service Continuity (CSC) configuration identifying the target cell for establishing an alternate communication link between the remote terminal to the target cell, the CSC configuration indicating a conditional path switch is authorized when execution criteria is met; and receiving, from the target cell, a handover success message indicating the remote terminal has established the alternate communication link to the target cell.

17. The method of claim 16, further comprising: receiving a failure report from the second relay terminal indicating a radio link failure has occurred between the second relay terminal and the first relay terminal.

18. The method of claim 16, further comprising: receiving a failure report from the second relay terminal indicating a radio link failure has occurred between the first relay terminal and the remote terminal.

19. The method of claim 16, wherein the CSC configuration identifies the target cell by identifying a candidate relay terminal being served by the target cell.

20. The method of claim 16, wherein the execution criteria comprise detection of a radio link failure (RLF) on the multi-hop relay communication link.21 . A remote terminal comprising: a transceiver comprising a receiver and a transmitter, the transceiver configured to communicate with a serving cell over a multi-hop relay communication link comprising a first PC5 link between the remote terminal and a first relay terminal, a second PC5 link between the first relay terminal and a second relay terminal, and a llu link between the second relay terminal and the serving cell, the receiver configured to receive, from the serving cell over the multi-hop relay communication link, a Conditional Service Continuity (CSC) configuration identifying a target cell for establishing an alternate communication link; and a controller configured to determine execution criteria have been met after the CSC configuration is received and, in response to determining the radio link failure has occurred, establish the alternate communication link to the target cell in accordance with the CSC configuration.

22. The remote terminal of claim 21 , wherein the transmitter is configured to send a RRCReconfigurationComplete message to the target cell.

23. The remote terminal of claim 22, wherein the controller is configured to determine the execution criteria has been met when a radio link failure is determined to have occurred.

24. The remote terminal of claim 23, wherein the controller is configured to determine the radio link failure has occurred by detecting the radio link failure has occurred on the first PC5 link.

25. The remote terminal of claim 23, wherein the receiver is configured to receiver a failure notification message indicating the radio link failure has occurred on one of the llu link or the second PC5 link, the controller determining the radio link failure has occurred based on the failure notification message.

26. The remote terminal of claim 21 , wherein establishing the alternate communication link to the target cell comprises establishing an alternate PC5 link to a target relay terminal, the alternate communication link comprising the alternate PC5 link to the target relay terminal.

27. The remote terminal of claim 26, wherein the controller is configured to measure a signal quality of a signal transmitted from the target relay terminal and to establish the alternate communication link by establishing the alternate PC5 link with the target relay terminal at least partially in response to determining the signal is above a threshold.

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