Fault monitoring and recovery mechanism for SL relays

Abstract

Disclosed herein are systems and methods for fault monitoring and fault recovery. In one embodiment, a method implemented by a remote wireless communication device in a communication system includes performing a fault recovery procedure. The fault recovery procedure includes selecting either a prepared cell or a prepared relay wireless communication device as a target cell or a target relay wireless communication device for fault recovery.

Description

[Technical field]

[0001] The present disclosure relates to wireless communication systems, such as cellular communication systems, and more particularly to failure monitoring and recovery in wireless communication systems in which wireless communication devices may be used as relays. [Background technology]

[0002] 1 NR Frame Structure Similar to Long Term Evolution (LTE), New Radio (NR) uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink (i.e., from a network node, gNB, eNB, or base station, to a user equipment or UE). Thus, the basic NR physical resource on an antenna port can be viewed as a time-frequency grid as shown in FIG. 1, where resource blocks (RBs) in 14 symbol slots are shown. A resource block corresponds to 12 consecutive subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain starting with 0 from one end of the system bandwidth. Each resource element corresponds to one OFDM subcarrier in one OFDM symbol interval.

[0003] Different subcarrier spacing values ​​are supported in NR. The supported subcarrier spacing values ​​(also called different numerologies) are given by Δf = (15 × 2^μ) kHz, where μ ∈ (0, 1, 2, 3, 4). Δf = 15 kHz is the basic (or reference) subcarrier spacing, also used in LTE.

[0004] In the time domain, downlink and uplink transmissions in NR will be organized into equal-sized subframes of 1 ms each, similar to LTE. Subframes are further divided into multiple slots of equal duration. The slot length is 1 / 2μms for subcarrier spacing Δf=(15×2^μ)kHz. There is only one slot per subframe for Δf=15kHz, and a slot consists of 14 OFDM symbols.

[0005] Downlink transmissions are dynamically scheduled, i.e., in each slot, the gNB transmits downlink control information (DCI) regarding which UEs data should be transmitted to and on which resource blocks in the current downlink slot the data is transmitted. This control information is typically transmitted in the first one or two OFDM symbols in each slot in NR. The control information is carried on a physical control channel (PDCCH) and the data is carried on a physical downlink shared channel (PDSCH). If the UE detects and decodes the PDCCH first, and if the PDCCH is successfully decoded, the UE decodes the corresponding PDSCH based on the downlink allocation provided by the decoded control information in the PDCCH.

[0006] In addition to the PDCCH and PDSCH, there are also other channels and reference signals transmitted in the downlink, including synchronization signal blocks (SSBs), channel state information reference signals (CSI-RS), etc.

[0007] Uplink data transmissions carried on the physical uplink shared channel (PUSCH) can also be dynamically scheduled by the gNB by transmitting a DCI (transmitted in the downlink (DL) domain) that indicates a scheduling time offset such that the PUSCH is always transmitted in a slot in the uplink (UL) domain.

[0008] 2 Radio Link Monitoring in LTE and NR One of the main intentions of the Radio Link Failure (RLF) procedure in LTE was to help the UE perform fast and reliable recovery without going through RRC_IDLE. It is beneficial to avoid unnecessary latency due to RACH access and RRC connection establishment from RRC IDLE. Radio link monitoring of the serving cell followed by Radio Resource Control (RRC) re-establishment to the target cell in LTE is shown in Figure 2.

[0009] In LTE, there are several reasons that can lead to radio link failure, including the following: 1) Timer T310 expires 2) The maximum number of RLC retransmissions in the uplink is reached 3) Handover failure and timer T304 expiry

[0010] Regarding radio link failure due to timer T310 expiry, while the UE is in RRC connected mode, the UE monitors the downlink radio channel quality based on the downlink reference symbols. The UE compares the measured downlink channel quality with an out-of-sync and in-sync threshold, Qout and Qin, respectively. The physical layer in the UE evaluates the downlink channel quality and periodically sends an indication of an out-of-sync or in-sync to the layer 3. The layer 3 in the UE then evaluates whether a radio link failure has occurred based on the in-sync and out-of-sync indications output from the layer 3. When the number of consecutively received out-of-sync indications exceeds the counter N310, the timer T310 is started. The radio link shall be considered restored if the UE receives N311 in-sync indications from the physical layer consecutively while T310 is running. However, if the timer T310 expires before the radio link is restored, a radio link failure is declared by the UE.

[0011] Regarding radio link failure due to timer T304 expiry, during the handover procedure, timer T304 is started when the UE receives a handover command from the source cell. The value of timer T304 should be set to allow the UE to attempt a maximum number of random access channel (RACH) access attempts (e.g., a maximum number of random access preamble transmissions) to the target cell. When timer T304 expires, a radio link failure due to handover is detected.

[0012] When a radio link failure is triggered, a radio connection re-establishment is triggered. The UE first performs a cell search to determine the best cell for radio link re-establishment. According to 3GPP TS36.300 v15.7.0, the UE can select as the target cell the same cell, a different cell from the same eNB, or a prepared cell from a different eNB, in which activity can be resumed via a radio connection re-establishment procedure (i.e., the UE stays in connected mode) since the previous UE context can be retrieved by inter-cell communication. However, when a prepared cell is not available, the UE selects a non-prepared cell. In this case, the UE must go into idle mode and then try to set up a radio connection. In this case, the UE activity cannot be resumed. Table 1 below is a reproduction of Table 10.1.6-1 from 3GPP TS36.300, which guides the UE behavior for target cell selection. TIFF0007636554000001.tif102170

[0013] 3. Sidelink Transmission in NR For Release 16, sidelink transmissions over NR are specified. These are extensions of the Proximity-Based Services (ProSe) specified for LTE. Four new extensions are introduced to NR sidelink transmissions, among others: Support is added for unicast and groupcast transmissions in the NR sidelink. For unicast and groupcast, a Physical Sidelink Feedback Channel (PSFCH) is introduced for the receiver UE to report the decoding status back to the transmitter UE. To improve latency performance, grant-free communication is also provided for NR sidelink transmissions, which are employed in NR uplink transmissions. To mitigate resource collisions between different sidelink transmissions launched by different UEs, it enhances the channel sensing and resource selection procedures, which also leads to a new design of the PSCCH. Support for achieving high connection density, congestion control, and therefore Quality of Service (QoS) management in NR sidelink transmissions.

[0014] To enable the above enhancements, new physical channels and reference signals are introduced in NR (previously available in LTE). PSSCH (Physical Sidelink Shared Channel, SL version of PDSCH): The PSSCH is transmitted by the sidelink transmitter UE and carries the sidelink transmission data, the System Information Blocks (SIBs) for Radio Resource Control (RRC) configuration and part of the Sidelink Control Information (SCI). PSFCH (Physical Sidelink, SL version of PUCCH): PSFCH is transmitted by the sidelink receiver UE for unicast and groupcast, and it carries 1 bit information on 1 RB for HARQ acknowledgment (ACK) and negative ACK (NACK). In addition, channel state information (CSI) is carried in the Medium Access Control (MAC) control element (CE) on PSSCH instead of PSFCH. PSCCH (Physical Sidelink Common Control Channel, SL version of PDCCH): When traffic to be sent to the receiver UE arrives at the transmitter UE, the transmitter UE should first send the PSCCH, which conveys part of the SCI (Sidelink Control Information, SL version of DCI) to be decoded by any UE for channel sensing purposes, including reserved time-frequency resources for transmission, Demodulation Reference Signal (DMRS) pattern and antenna ports, etc. Sidelink Primary Synchronization Signal / Secondary Synchronization Signal (S-PSS / S-SSS): Similar to downlink transmission in NR, primary and secondary synchronization signals (referred to as S-PSS and S-SSS, respectively) are supported in sidelink transmission. Through detecting S-PSS and S-SSS, the UE can identify the sidelink synchronization identity (SSID) from the UE sending the S-PSS / S-SSS. Through detecting S-PSS / S-SSS, the UE can thus know the characteristics of the UE transmitter S-PSS / S-SSS. The series of processes of collecting timing and frequency synchronization along with the UE's SSID is called initial cell search. It should be noted that the UE sending the S-PSS / S-SSS may not necessarily be involved in the sidelink transmission, and the node (UE / eNB / gNB) sending the S-PSS / S-SSS is called the synchronization source. There are two S-PSS sequences and 336 S-SSS sequences, forming a total of 672 SSIDs in the cell. Physical Sidelink Broadcast Channel (PSBCH): The PSBCH is transmitted together with the S-PSS / S-SSS as a synchronization signal / PSBCH block (SSB). The SSB has the same numerology as the PSCCH / PSSCH on that carrier and the SSB should be transmitted within the bandwidth of the configured BWP. The PSBCH carries information related to synchronization such as the Direct Frame Number (DFN), an indication of slot and symbol level time resources for sidelink transmissions, and an in-coverage indicator. The SSB is transmitted periodically every 160 ms. DMRS, Phase Tracking Reference Signal (PT-RS), Channel State Information Reference Signal (CSIRS): These physical reference signals supported by NR downlink / uplink transmissions are also adopted by sidelink transmissions. Similarly, PT-RS is only applicable to FR2 transmissions.

[0015] Another new feature is the two-stage Sidelink Control Information (SCI). This is a version of DCI for SL. Unlike DCI, only a part of the SCI (first stage) is sent on the PSCCH. This part (including reserved time-frequency resources for transmission, demodulation reference signal (DMRS) pattern and antenna ports, etc.) is used for channel sensing purposes and can be read by all UEs, while the remaining (second stage) scheduling and control information, such as 8-bit source identification (ID) and 16-bit destination ID, NDI, RV and HARQ process ID, is sent on the PSSCH to be decoded by the receiver UE.

[0016] In a similar manner to ProSe in LTE, NR sidelink transmission has two modes of resource allocation: Mode 1: Sidelink resources are scheduled by the gNB. Mode 2: The UE autonomously selects sidelink resources from (one or more) (pre-)configured sidelink resource pools based on a channel sensing mechanism. For an in-coverage UE, the gNB may be configured to employ Mode 1 or Mode 2. For an out-of-coverage UE, only Mode 2 may be employed.

[0017] As in LTE, scheduling over the sidelink in NR is done differently for Mode 1 and Mode 2. Mode 1 supports two types of grants: Dynamic grant: When traffic to be sent via sidelink arrives at the transmitter UE, the UE should launch a four-message exchange procedure (SR on UL, grant, BSR on UL, grant for data on SL sent to the UE) to request sidelink resources from the gNB. During the resource request procedure, the gNB may assign a Sidelink Radio Network Temporary Identifier (SL-RNTI) to the transmitter UE. If this sidelink resource request is granted by the gNB, the gNB indicates the resource allocation for PSCCH and PSSCH in a Downlink Control Information (DCI) carried by the PDCCH with a scrambled CRC using the SL-RNTI. When the transmitter UE receives such a DCI, the transmitter UE can obtain the grant only if the scrambled CRC of the DCI can be successfully resolved by the allocated SL-RNTI. The transmitter UE then indicates the time-frequency resources and transmission scheme of the assigned PSSCH in the PSCCH and launches the PSCCH and PSSCH on the assigned resources for sidelink transmission. When a grant is obtained from a gNB, the transmitter UE can transmit only a single TB, so this type of grant is suitable for traffic with loose latency requirements. · Configured grant: For traffic with strict latency requirements, performing a four-message exchange procedure to request sidelink resources may induce unacceptable latency. In this case, prior to traffic arrival, the transmitter UE may perform a four-message exchange procedure and request a set of resources. If a grant can be obtained from the gNB, the requested resources are reserved in a periodic manner. Once the traffic arrives at the transmitter UE, the UE can launch PSCCH and PSSCH on the upcoming resource occasion. In effect, this type of grant is also known as grant-free communication.

[0018] In both dynamic and configured grants, the sidelink receiver UE cannot receive the DCI (as it is addressed to the transmitter UE) and therefore should perform blind decoding to identify the presence of PSCCH and find the resources for PSSCH through the SCI.

[0019] When the transmitter UE launches the PSCCH, the CRC is also inserted into the SCI without scrambling.

[0020] In Mode 2 resource allocation, when traffic arrives at the transmitter UE, the transmitter UE should autonomously select resources for PSCCH and PSSCH. To further minimize the latency of feedback HARQ ACK / NACK transmission and then retransmission, the transmitter UE may also reserve resources for PSCCH / PSSCH for retransmission. To further enhance the probability of successful TB decoding in one shot and thus suppress the probability of performing retransmission, the transmitter UE may repeat TB transmission along with the initial TB transmission. This mechanism is also known as blind retransmission. As a result, when traffic arrives at the transmitter UE, the transmitter UE should select resources for the following transmission. 1) A PSSCH associated with the PSCCH for initial transmission and blind retransmission. 2) A PSSCH associated with the PSCCH for retransmission.

[0021] Since each transmitter UE in a sidelink transmission should autonomously select resources for said transmission, it turns out that how to prevent different transmitter UEs from selecting the same resources is an important issue in Mode 2. Therefore, a specific resource selection procedure is imposed for Mode 2 based on channel sensing. The channel sensing algorithm involves measuring RSRP on different subchannels and requires knowledge of different UE power levels of DMRS on PSSCH or DMRS on PSCCH depending on the configuration. This information is known only after the receiver SCI has been launched by (all) other UEs. The sensing and selection algorithm is somewhat complex.

[0022] 4 Discovery Procedure There is a device to device (D2D) discovery procedure for discovery of services and applications offered by other UEs in close proximity. It is part of LTE Release 12 and Release 13. The discovery procedure has two modes: Mode A, which is based on open announcement (broadcast), and Mode B, which is request / response. The discovery mechanism is controlled by the application layer (ProSe). Discovery messages are sent on the Physical Sidelink Discovery Channel (PSDCH), which is not available in NR. There is also a specific resource pool for announcement and monitoring of discovery messages. The discovery procedure can be used to discover UEs that support some services or applications before initiating direct communication.

[0023] 5 Layer 2 (L2) UE-Network Relay In TR23.752 v0.3.0 clause 6.7, Layer 2 based UE-network relay is described.

[0024] 5.1 General information In TR23.752 v0.3.0 clause 6.7, a protocol architecture supporting L2 UE-Network Relay UE is provided.

[0025] L2 UE - Network Relay UE provides a forwarding function that can relay any type of traffic on the PC5 link.

[0026] The L2 UE-Network Relay UE provides functionality to support connectivity to a fifth generation system (5GS) for a remote UE. A UE is considered to be a remote UE if the UE successfully establishes a side link (i.e., a PC5 link in 3GPP NR) to the L2 UE-Network Relay UE (also referred to herein as a "Relay UE"). A remote UE may be located within Next Generation Radio Access Network (NG-RAN) coverage or outside of NG-RAN coverage.

[0027] Figure 3 shows the protocol stack for user plane transport related to a Protocol Data Unit (PDU) session, including Layer 2 UE-Network Relay UE. The PDU layer corresponds to the PDUs carried between the remote UE and the Data Network (DN) over the PDU session. It is important to note that the two endpoints of the Packet Data Convergence Protocol (PDCP) link are the remote UE and the gNB. The relay function is implemented under PDCP. This means that data security between the remote UE and the gNB is ensured without exposing raw data at the UE-Network Relay UE.

[0028] UE-Network Relay An adaptation relay layer in the UE can distinguish between the Signaling Radio Bearers (SRBs) and Data Radio Bearers (DRBs) for a particular remote UE. The adaptation relay layer is also responsible for mapping PC5 traffic to one or more DRBs of the Uu. The specification of the adaptation relay layer is under the responsibility of the RAN Working Group 2 (WG2).

[0029] Figure 4 shows the protocol stack for NAS connectivity for a remote UE to the Non-Access Stratum (NAS) Mobility Management (NAS-MM) and NAS Session Management (NAS-SM) components. NAS messages are transparently forwarded between the remote UE and the 5G-RAN via Layer 2 UE-Network Relay UE using: UE-Network Relay PDCP end-to-end connection, where the role of the UE is to relay PDUs on the signalling radio bearer without any modification. N2 connectivity between 5G-AN and 5G-AMF via N2. N3 connected AMF and SMF over N11.

[0030] UE-Network Relay The role of the UE is to relay the PDUs from the signaling radio bearer without modification.

[0031] 5.2 Procedure Figure 5 is a reproduction of Figure 6.7.3-1 from TR 23.752, showing the procedure for connection establishment for indirect communication via UE-Network Relay UE. Section 6.7 of TR 23.752 describes this procedure as follows: 0. When in coverage, the remote UE and the UE-Network Relay UE may independently perform initial registration to the network according to the registration procedure in TS 23.502 [2]. The assigned 5G GUTI of the remote UE is maintained when subsequent NAS signaling between the remote UE and the network is exchanged via the UE-Network Relay UE. NOTE: The current procedures presented here assume a single-hop relay. 1. When in coverage, the remote UE and the UE-network relay UE independently obtain service authorization for indirect communication from the network. 2~3. The remote UE and UE-network relay UE perform UE-network relay UE discovery and selection. 4. The remote UE initiates a one-to-one communication connection with the selected UE-Network Relay UE via PC5 by sending an indirect communication request message to the UE-Network Relay. 5. When the UE-network relay UE is in CM_IDLE state and triggered by a communication request received from a remote UE, the UE-network relay UE sends a service request message to the serving AMF of the UE-network relay UE via PC5. The AMF of the relay may perform UE-network relay UE authentication based on the NAS message validation, and if necessary, the AMF will check the subscription data. UE-Network Relay If the UE is already in CM_CONNECTED state and is authorized to implement relay service, step 5 is omitted. 6. The UE-Network Relay UE sends an indirect communication response message to the remote UE. 7. The remote UE sends a NAS message to the serving AMF. The NAS message is encapsulated in an RRC message sent to the UE-Network Relay UE via PC5, which forwards the message to the NG-RAN. The NG-RAN derives the serving AMF of the remote UE and forwards the NAS message to this AMF. NOTE: It is assumed that the PLMN of the remote UE is reachable by the PLMN of the UE-network relay and that the UE-network relay UE AMF supports all S-NSSAIs to which the remote UE may wish to connect. If the remote UE did not perform initial registration with the network in step 0, the NAS message is an initial registration message. Otherwise, the NAS message is a service request message. When the remote UE performs initial registration via the UE-network relay, the serving AMF of the remote UE may perform authentication of the remote UE based on NAS message validation, and if necessary, the AMF of the remote UE checks the subscription data. In the service request case, the user plane connection for the PDU session may also be activated. Other steps follow clause 4.2.3.2 in TS 23.502 [2]. 8. The remote UE may trigger the PDU session establishment procedure as specified in clause 4.3.2.2 of TS 23.502[2]. 9. Data is transmitted between the remote UE and the UPF via the UE-Network Relay UE and the NG-RAN. The UE-Network Relay UE forwards all data messages between the remote UE and the NG-RAN using the RAN-specified L2 relay method.

[0032] 5.3 Service Continuity As described in section 4.5.4 of TR38.836, the L2 UE-Network Relay uses the RAN2 principles of the Rel-15 NR handover procedure as a baseline Access Stratum (AS) layer solution to ensure service continuity (i.e., the gNB hands over the remote UE to the target cell or target relay UE, including (1) a handover preparation type of procedure between the gNB and relay UE (if necessary), (2) an RRCReconfiguration to the remote UE, where the remote UE switches to the target, and (3) a handover complete message, similar to the legacy procedure).

[0033] The exact content of the messages (e.g. handover commands) will be discussed in the 3GPP WI phase. This does not imply that inter-node messages will be sent over Uu.

[0034] Below, the intersection between the intra-gNB and inter-gNB cases is captured.

[0035] a. Switching from indirect to direct routes For L2 UE-network relay service continuity, when a remote UE switches directly to a Uu cell, the baseline procedure shown in Figure 6 is used. The steps of the procedure in Figure 6 are described in 3GPP TR38.836 V1.0.0 as follows: Step 1: Set up and report measurements Step 2: gNB decides to switch directly to the cell Step 3: RRC Reconfiguration message to remote UE Step 4: The remote UE performs random access to the gNB Step 5: The remote UE feeds back RRCReconfigurationComplete to the gNB via the target route using the target configuration provided in the RRC reconfiguration message. Step 6: RRC reconfiguration to relay UE Step 7: If necessary, the PC5 link between the remote UE and the relay UE is released. Step 8: Data path switching. Note: The order of steps 6 / 7 / 8 is not restricted. The following will be discussed further in the WI phase, which includes: - whether the remote UE suspends data transmission over the relay link after step 3; - whether step 6 can be before or after step 3 and the necessity of step 6; - whether step 7 can be after step 3 or after step 5 and the necessity of step 7 / can be replaced by PC5 reconfiguration; - Whether step 8 can come after step 5.

[0036] b. Switching from direct to indirect routes For L2 UE-network relay service continuity, when a remote UE switches to an indirect relay UE, the baseline procedure shown in Figure 7 is used. The steps of the procedure in Figure 7 are described in TR38.836 as follows: Step 1: A remote UE reports its (one or more) candidate relay UEs after the remote UE measures / discovers one or more candidate relay UEs. - In step 1, when reporting, the remote UE may filter suitable relay UE(s) that meet higher layer criteria. - In step 1, the report may include the relay UE's ID and SL RSRP information, where the measurement details for PC5 may be left to the WI phase. Step 2: The gNB decides to switch to the target relay UE and a target (re)configuration is optionally sent to the relay UE (similar preparation). Step 3: An RRC reconfiguration message to the remote UE, which may contain the following information: 1) target relay UE identity, 2) target Uu and PC5 configuration. Step 4: The remote UE establishes a PC5 connection with the target relay UE if one has not been set up yet. Step 5: The remote UE feeds back RRCReconfigurationComplete to the gNB via the target route using the target configuration provided in RRCReconfiguration. Step 6: Data path switching. NOTE: The following will be discussed further in the WI phase, including: - whether step 2 should be after the relay UE connects to the gNB (e.g. after step 4) if not already before; - Whether step 4 can come before step 2 / 3. Summary of the Invention

[0037] SUMMARY OF THE DISCLOSURE Disclosed herein are systems and methods for fault monitoring and fault recovery.

[0038] A first aspect of the present disclosure provides a method implemented by a remote wireless communication device in a communication system, the method including implementing a failure recovery procedure, the failure recovery procedure including selecting either a prepared cell or a prepared relay wireless communication device as a target cell or a target relay wireless communication device for failure recovery.

[0039] A second aspect of the disclosure provides a method implemented by a relay wireless communication device in a communication system, the method including transmitting, to a remote wireless communication device, cell information including an indication of one or more cells to which the relay wireless communication device is connected.

[0040] In one embodiment, a method performed by a remote wireless communication device in a communication system includes receiving a message from a network node that configures the remote wireless communication device to perform a path switch. The message includes a value for a first timer. The method further includes setting the first timer to the value included in the message and determining whether the path switch has failed based on whether the first timer expires before the path switch is successfully completed. In this manner, behavior of the remote wireless communication device with respect to a path switch failure is clearly defined.

[0041] In one embodiment, the path switching is either (a) a path switching from an indirect path between the remote wireless communication device and the serving cell via the serving relay wireless communication device to a direct path between the remote wireless communication device and the target cell for the path switching, (b) a path switching from a direct path between the remote wireless communication device and the serving cell to an indirect path between the remote wireless communication device and the target cell for the path switching via the target relay wireless communication device for the path switching, or (c) a path switching from a first indirect path between the remote wireless communication device and the serving cell via the serving relay wireless communication device to a second indirect path between the remote wireless communication device and the target cell for the path switching via the target relay wireless communication device for the path switching.

[0042] In one embodiment, the method further includes initiating a first timer in response to receiving the message and initiating implementation of a path switching procedure.

[0043] In one embodiment, the message is a Radio Resource Control (RRC) message.

[0044] In one embodiment, the first timer is an existing timer or a new timer.

[0045] In one embodiment, the path switching is from an indirect path between the remote wireless communication device and the serving cell through the serving relay wireless communication device to a direct path between the remote wireless communication device and the target cell. In one embodiment, the value of the first timer is a value that allows the remote wireless communication device to perform a defined or configured maximum number of random access attempts to the target cell. In one embodiment, the method further includes stopping the first timer upon successful completion of the random access to the target cell.

[0046] In one embodiment, the path switching is either a path switching from a direct path between the remote wireless communication device and the serving cell to an indirect path between the remote wireless communication device and the target cell via the target relay wireless communication device, or a path switching from a first indirect path between the remote wireless communication device and the serving cell via the serving relay wireless communication device to a second indirect path between the remote wireless communication device and the target cell via the target relay wireless communication device. In one embodiment, the value of the first timer is a value that enables the remote wireless communication device to complete a Layer 2 link establishment and / or a sidelink connection setup towards the target relay wireless communication device.

[0047] In one embodiment, the message is an RRC reconfiguration message for a conditional reconfiguration execution, and the RRC reconfiguration message includes reconfigurationWithSync.

[0048] In one embodiment, determining whether the path switch has failed includes determining that the path switch has failed in response to an expiration of a first timer before the path switch is successfully completed. The method further includes performing a failure recovery procedure in response to determining that the path switch has failed. In one embodiment, the failure recovery procedure is an RRC re-establishment procedure.

[0049] In one embodiment, performing the failure recovery procedure includes starting a second timer, performing a selection procedure for selecting either a target cell or a target relay wireless communication device for failure recovery while the second timer is running, and attempting to connect to the selected target cell or the selected target relay wireless communication device for failure recovery. In one embodiment, the second timer is an existing timer or a new timer. In one embodiment, the second timer is set to a value that allows the remote wireless communication device to access the selected target cell or the selected target relay wireless communication device for failure recovery.

[0050] In one embodiment, performing the selection procedure includes performing measurements on one or more potential target cells and selecting a target cell for failure recovery from the one or more potential target cells based on the performed measurements. In one embodiment, the one or more potential target cells include one or more previous serving cells of the remote wireless communication device and / or one or more neighboring cells of the serving cell of the remote wireless communication device. In one embodiment, performing measurements on the one or more potential target cells includes performing measurements on the one or more potential target cells based on a measurement configuration received by the remote wireless communication device from a network node before a path switch is requested.

[0051] In one embodiment, performing the selection procedure includes performing measurements on one or more potential target relay wireless communication devices and selecting a target relay wireless communication device for failure recovery from the one or more potential target relay wireless communication devices based on the performed measurements. In one embodiment, performing measurements on the one or more potential target relay wireless communication devices includes performing, for each potential target relay wireless communication device, measurements on an existing sidelink connection between the remote wireless communication device and the potential target relay wireless communication device or on a discovery message received by the remote wireless communication device from the potential target relay wireless communication device.

[0052] In one embodiment, performing the selection procedure includes performing measurements on one or more potential target cells, performing measurements on one or more potential target relay wireless communication devices, and selecting a target cell or a target relay wireless communication device for failure recovery from the one or more potential target cells and the one or more potential target wireless communication devices based on the performed measurements. In one embodiment, selecting a target cell or a target relay wireless communication device for failure recovery includes selecting a target cell or a target relay wireless communication device for failure recovery based on at least one of the following conditions: preferring a potential target cell, preferring a potential target wireless communication device, selecting one of the potential target cells or the potential target wireless communication devices based on a measured wireless channel quality. In one embodiment, selecting a target cell or a target relay wireless communication device for failure recovery includes selecting a target cell or a target relay wireless communication device for failure recovery based on a measured wireless channel quality taking into account a defined or configured offset.

[0053] In one embodiment, the one or more potential target cells are one or more prepared cells. In one embodiment, the one or more potential target relay wireless communication devices are one or more potential target relay wireless communication devices connected to a prepared cell.

[0054] In one embodiment, performing the selection procedure includes performing one of two or more defined selection schemes based on the indicator received from the network node.

[0055] In one embodiment, performing the failure recovery procedure further includes stopping the second timer upon successfully connecting to the selected target cell or the selected target relay wireless communication device for failure recovery.

[0056] In one embodiment, the method further includes sending a message to the network node, the message including information indicating that the path switch has failed, information indicating the wireless communication device, the failed target wireless node of the path switch, or the failed target cell served by the target wireless node, and / or the failed target relay wireless communication device, information indicating a cause of the path switch failure, information indicating a pair relationship between the target wireless communication node of the wireless communication device path switch, one or more measurement results for a neighboring cell or device (e.g., regarding RSRP, RSRQ, RSSI, SINR, SIR, channel occupancy, etc.), a buffer status report, and / or a power headroom report.

[0057] In one embodiment, performing the failure recovery procedure further includes determining that recovery has failed in response to expiration of a second timer before a connection to the selected target cell or selected target relay wireless communication device for failure recovery is successfully made, and transitioning to an idle mode and performing a search procedure in response to determining that recovery has failed.

[0058] Corresponding embodiments of a remote wireless communication device are also disclosed. In one embodiment, a remote wireless communication device in a communication system is adapted to receive a message from a network node to configure the remote wireless communication device to perform a path switch. The message includes a value for a first timer. The remote wireless communication device is further adapted to set the first timer to the value included in the message and determine whether the path switch has failed based on whether the first timer expires before the path switch is successfully completed.

[0059] In another embodiment, a remote wireless communication device in a communication system comprises one or more transmitters, one or more receivers, and a processing circuit associated with the one or more transmitters and the one or more receivers. The processing circuit is configured to cause the remote wireless communication device to receive a message from a network node configuring the remote wireless communication device to perform a path switch. The message includes a value for a first timer. The processing circuit is further configured to cause the remote wireless communication device to set the first timer to the value included in the message and to determine whether the path switch has failed based on whether the first timer expires before the path switch is successfully completed.

[0060] Also disclosed are computer program embodiments. In one embodiment, a computer program is provided comprising instructions that, when executed on at least one processor, cause the at least one processor to perform a method of operation of a remote wireless communication device according to any of the embodiments disclosed herein. In one embodiment, a carrier is provided that contains the computer program, the carrier being one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

[0061] Also disclosed herein are embodiments of a method implemented by a network node. In one embodiment, a method implemented by a network node in a communication system includes sending a message to a remote wireless communication device to configure the remote wireless communication device to perform a path switch. The message includes a value for a first timer.

[0062] In one embodiment, the path switching is either (a) a path switching from an indirect path between the remote wireless communication device and the serving cell via the serving relay wireless communication device to a direct path between the remote wireless communication device and the target cell for the path switching, (b) a path switching from a direct path between the remote wireless communication device and the serving cell to an indirect path between the remote wireless communication device and the target cell for the path switching via the target relay wireless communication device for the path switching, or (c) a path switching from a first indirect path between the remote wireless communication device and the serving cell via the serving relay wireless communication device to a second indirect path between the remote wireless communication device and the target cell for the path switching via the target relay wireless communication device for the path switching.

[0063] In one embodiment, the message is an RRC message.

[0064] In one embodiment, the first timer is an existing timer or a new timer.

[0065] In one embodiment, the path switch is from an indirect path between the remote wireless communication device and the serving cell through the serving relay wireless communication device to a direct path between the remote wireless communication device and the target cell. In one embodiment, the value of the first timer is a value that allows the remote wireless communication device to perform a defined or configured maximum number of random access attempts to the target cell.

[0066] In one embodiment, the path switching is either a path switching from a direct path between the remote wireless communication device and the serving cell to an indirect path between the remote wireless communication device and the target cell via the target relay wireless communication device, or a path switching from a first indirect path between the remote wireless communication device and the serving cell via the serving relay wireless communication device to a second indirect path between the remote wireless communication device and the target cell via the target relay wireless communication device. In one embodiment, the value of the first timer is a value that enables the remote wireless communication device to complete a Layer 2 link establishment and / or a sidelink connection setup towards the target relay wireless communication device.

[0067] In one embodiment, the message is an RRC reconfiguration message for a conditional reconfiguration execution, and the RRC reconfiguration message includes reconfigurationWithSync.

[0068] In one embodiment, the method further includes receiving a message from the remote wireless communication device, the message including information indicating that the path switch has failed, information indicating the wireless communication device, the failed target wireless node of the path switch, or the failed target cell served by the target wireless node, and / or the failed target relay wireless communication device, information indicating a cause of the path switch failure, information indicating a pair relationship between the target wireless communication nodes of the wireless communication device path switch, one or more measurement results for a neighboring cell or device (e.g., regarding RSRP, RSRQ, RSSI, SINR, SIR, channel occupancy, etc.), a buffer status report, and / or a power headroom report.

[0069] In one embodiment, the method further includes storing information regarding a pair relationship between the remote wireless communication device and the selected target relay wireless communication device for path switching. In one embodiment, the method further includes sending information regarding the pair relationship to another network node. In one embodiment, the method further includes clearing information regarding the pair relationship upon receiving a message from the remote wireless communication device indicating that a new connection has been established.

[0070] In one embodiment, the network node is a RAN node serving a serving cell of a remote wireless communication device, and the method further includes storing a UE context of the remote wireless communication device and / or sending the UE context of the remote wireless communication device to another RAN node serving a target cell of the path switch.

[0071] In one embodiment, the network node is a RAN node serving a serving cell of a remote wireless communication device, and the UE context of the remote wireless communication device is stored in the network node and / or in another RAN node serving a target cell of the path switch until a third timer expires.

[0072] In one embodiment, the method further includes clearing the stored UE context upon receiving a message from the remote wireless communication device indicating that a new connection has been established.

[0073] Corresponding embodiments of a network node are also disclosed. In one embodiment, a network node for a communication system is adapted to send a message to a remote wireless communication device to configure the remote wireless communication device to perform a path switch. The message includes a value for a first timer.

[0074] In one embodiment, a network node for a communication system comprises processing circuitry configured to cause the network node to send a message to a remote wireless communication device, the message configuring the remote wireless communication device to perform a path switch, the message including a value for a first timer.

[0075] In one embodiment, a computer program is provided comprising instructions which, when executed on at least one processor, cause the at least one processor to perform a method of network node operation according to any of the embodiments disclosed herein. In one embodiment, a carrier is provided containing the computer program, the carrier being one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

[0076] Also disclosed herein are embodiments of a communication system and a method of operation of the communication system. In one embodiment, a communication system including a host computer comprises a processing circuit configured to provide user data and a communication interface configured to forward the user data to a cellular network for transmission to the UE, the UE comprising a radio interface and a processing circuit. The processing circuit of the UE is configured to perform the method of operation of a remote wireless communication device according to any of the embodiments disclosed herein. In one embodiment, the cellular communication system further comprises a UE. In one embodiment, the cellular network further comprises a base station configured to communicate with the UE. In one embodiment, the processing circuit of the host computer is configured to execute a host application and thereby provide user data, and the processing circuit of the UE is configured to execute a client application associated with the host application.

[0077] In one embodiment, a method implemented in a communication system including a host computer, a base station, and a UE includes providing user data at the host computer and initiating a transmission at the host computer conveying the user data to the UE over a cellular network including the base station. The UE performs a method of operation of a remote wireless communication device according to any of the embodiments disclosed herein. In one embodiment, the method further includes receiving the user data from the base station at the UE.

[0078] In another embodiment, a communication system including a host computer comprises a communication interface configured to receive user data originating from a transmission from a UE to a base station, the UE comprising a wireless interface and a processing circuit. The processing circuit of the UE configured to perform the method of operation of a remote wireless communication device according to any of the embodiments disclosed herein. In one embodiment, the communication system further comprises a UE. In one embodiment, the communication system further comprises a base station, the base station comprising a wireless interface configured to communicate with the UE and a communication interface configured to forward user data carried by the transmission from the UE to the base station to the host computer. In one embodiment, the processing circuit of the host computer is configured to execute a host application, and the processing circuit of the UE is configured to execute a client application associated with the host application, thereby providing the user data. In one embodiment, the processing circuit of the host computer is configured to execute a host application, thereby providing the requested data, and the processing circuit of the UE is configured to execute a client application associated with the host application, thereby providing the user data in response to the requested data.

[0079] In one embodiment, a method implemented in a communication system including a host computer, a base station, and a UE includes receiving, at the host computer, user data transmitted from the UE to the base station, the UE performing a method of operation of a remote wireless communication device according to any of the embodiments disclosed herein. In one embodiment, the method further includes providing, at the UE, the user data to the base station. In one embodiment, the method further includes executing, at the UE, a client application, thereby providing the user data to be transmitted, and executing, at the host computer, a host application associated with the client application. In one embodiment, the method further includes executing, at the UE, the client application, and receiving, at the UE, input data to the client application, the input data being provided at the host computer by executing a host application associated with the client application, the user data to be transmitted being provided by the client application in response to the input data.

[0080] In one embodiment, a communication system including a host computer comprises a processing circuit configured to provide user data and a communication interface configured to forward the user data to a cellular network for transmission to a UE, the cellular network comprising a base station having a radio interface and a processing circuit. The processing circuit of the base station configured to perform the method of operation of the network node according to any of the embodiments disclosed herein. In one embodiment, the communication system further comprises a base station. In another embodiment, the communication system further comprises a UE, the UE configured to communicate with the base station. In one embodiment, the processing circuit of the host computer is configured to execute a host application and thereby provide user data, and the UE comprises a processing circuit configured to execute a client application associated with the host application.

[0081] In one embodiment, a method implemented in a communication system including a host computer, a base station, and a UE includes providing user data at the host computer and initiating a transmission at the host computer conveying the user data to the UE over a cellular network comprising the base station. The base performs a method of operation of a network node according to any of the embodiments disclosed herein. In one embodiment, the method further includes transmitting the user data at the base station. In one embodiment, the user data is provided at the host computer by executing a host application, and the method further includes executing, at the UE, a client application associated with the host application.

[0082] In one embodiment, a communication system includes a host computer with a communication interface configured to receive user data originating from a transmission from a UE to a base station, the base station comprising a wireless interface and processing circuitry. The processing circuitry of the base station is configured to perform the method of operation of a network node according to any of the embodiments disclosed herein. In one embodiment, the communication system further comprises a base station. In one embodiment, the communication system further comprises a UE, the UE configured to communicate with the base station. In one embodiment, the processing circuitry of the host computer is configured to execute a host application, and the UE is configured to execute a client application associated with the host application, thereby providing the user data to be received by the host computer.

[0083] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects of the present disclosure and, together with the description, serve to explain the principles of the disclosure. [Brief description of the drawings]

[0084] [Figure 1] FIG. 1 illustrates basic New Radio (NR) physical resources. [Diagram 2] FIG. 1 illustrates Radio Link Failure (RLF) monitoring of a serving cell and subsequent Radio Resource Control (RRC) re-establishment to a target cell in Long Term Evolution (LTE). [Diagram 3] 1 illustrates a protocol stack for user plane transport involving a Protocol Data Unit (PDU) session, including a Layer 2 UE - Network Relay UE, where the PDU layer corresponds to the PDUs carried between the remote UE and the Data Network (DN) over the PDU session. [Figure 4] A diagram showing the protocol stacks of NAS connection for a remote UE to Non-Access Stratum (NAS) Mobility Management (NAS-MM) and NAS Session Management (NAS-SM) components. [Diagram 5] FIG. 6.7.3-1 is a reproduction of FIG. 6.7.3-1 from 3GPP TR23.752, showing a procedure for connection establishment for indirect communication via UE-Network Relay UE. [Figure 6] A diagram showing a baseline procedure for service continuity for L2 UE-network relay when a remote UE switches directly to a Uu cell. [Figure 7] A diagram showing baseline procedures for L2 UE-network relay service continuity when a remote UE switches to an indirect relay UE. [Figure 8] FIG. 1 illustrates an example of a cellular communication system in which embodiments of the present disclosure may be implemented. [Figure 9A] 1A-1C illustrate examples of direct-indirect path switching, indirect-indirect path switching, and indirect-direct path switching in which path switching fault monitoring and fault recovery are implemented, according to some exemplary embodiments of the present disclosure. [Figure 9B] 1A-1C illustrate examples of direct-indirect path switching, indirect-indirect path switching, and indirect-direct path switching in which path switching fault monitoring and fault recovery are implemented, according to some exemplary embodiments of the present disclosure. [Figure 9C]1A-1C illustrate examples of direct-indirect path switching, indirect-indirect path switching, and indirect-direct path switching in which path switching fault monitoring and fault recovery are implemented, according to some exemplary embodiments of the present disclosure. [Figure 10] FIG. 1 illustrates an example of a remote UE experiencing a path switching failure and triggering a failure recovery procedure, according to an embodiment of the present disclosure. [Figure 11] 5 is a flowchart illustrating the operation of a remote wireless communication device according to an embodiment of the present disclosure. [Figure 12] 1 is a flowchart illustrating a path switching failure recovery procedure according to an exemplary embodiment of the present disclosure. [Figure 13] 4 is a flowchart illustrating the operation of a network node according to an embodiment of the present disclosure. [Figure 14] FIG. 2 is a schematic block diagram of a network node according to some embodiments of the present disclosure. [Figure 15] 15 is a schematic block diagram illustrating a virtualized embodiment of the network node of FIG. 14 in accordance with some embodiments of the present disclosure. [Figure 16] FIG. 15 is a schematic block diagram of the network node of FIG. 14 in accordance with some other embodiments of the present disclosure. [Figure 17] 1 is a schematic block diagram of a wireless communication device according to some embodiments of the present disclosure. [Figure 18] 18 is a schematic block diagram of the wireless communication device of FIG. 17 according to some other embodiments of the present disclosure. [Figure 19] FIG. 1 illustrates a communication network connected to a host computer through an intermediate network in accordance with some embodiments of the present disclosure. [Figure 20] FIG. 2 is a generalized block diagram of a host computer communicating with a UE via a base station over a partial wireless connection in accordance with some embodiments of the present disclosure. [Figure 21] 1 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. [Figure 22]1 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. [Diagram 23] 1 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. [Figure 24] 1 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. [Diagram 25] 4 is a flowchart illustrating the operation of a relay wireless communication device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0085] The embodiments described below represent information to enable those skilled in the art to practice the embodiments and show the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and recognize applications of these concepts not specifically addressed herein. It is to be understood that these concepts and applications fall within the scope of the present disclosure.

[0086] Wireless Node: As used herein, a "wireless node" is either a wireless access node or a wireless communication device.

[0087] Radio Access Node: As used herein, a "radio access node" or "radio network node" or "radio access network node" is any node in a radio access network (RAN) of a cellular communications network that operates to transmit and / or receive signals wirelessly. Some examples of radio access nodes include, but are not limited to, a base station (e.g., a New Radio (NR) base station (gNB) in a 3rd Generation Partnership Project (3GPP) fifth generation (5G) NR network, or an enhanced or evolved Node B (eNB) in a 3GPP Long Term Evolution (LTE) network), a high power or macro base station, a low power base station (e.g., a micro base station, a pico base station, a home eNB, etc.), a relay node, a network node implementing part of the functionality of a base station, or a network node implementing a gNB distributed unit (gNB-DU), or a network node implementing part of the functionality of some other type of radio access node.

[0088] Core Network Node: As used herein, a "core network node" is any type of node in a core network or any node that implements a core network function. Some examples of core network nodes include, for example, a Mobility Management Entity (MME), a Packet Data Network Gateway (P-GW), a Service Capability Publication Function (SCEF), a Home Subscriber Server (HSS), etc. Some other examples of core network nodes include nodes that implement an Access and Mobility Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Publication Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), etc.

[0089] Communication Device: As used herein, a "communication device" is any type of device that has access to an access network. Some examples of communication devices include, but are not limited to, a mobile phone, a smartphone, a sensor device, a meter, a vehicle, a household appliance, a medical appliance, a media player, a camera, or any type of consumer electronic device, such as, but not limited to, a television, a radio, a lighting device, a tablet computer, a laptop computer, or a personal computer (PC). A communication device may be a portable, handheld, computer-equipped, or vehicle-mounted mobile device enabled to communicate voice and / or data over a wireless or wired connection.

[0090] Wireless Communication Device: One type of communication device is a wireless communication device, which may be any type of wireless device having access to (i.e., served by) a wireless network (e.g., a cellular network). Some examples of wireless communication devices include, but are not limited to, user equipment devices (UE) in 3GPP networks, machine-type communication (MTC) devices, and Internet of Things (IoT) devices. Such wireless communication devices may be or may be integrated into mobile phones, smartphones, sensor devices, meters, vehicles, household appliances, medical appliances, media players, cameras, or any type of consumer electronics, such as, but not limited to, televisions, radios, lighting devices, tablet computers, laptop computers, or PCs. Wireless communication devices may be portable, handheld, computer-equipped, or vehicle-mounted mobile devices enabled to communicate voice and / or data over a wireless connection.

[0091] Network Node: As used herein, a "network node" is any node that is part of either the RAN or the core network of a cellular communications network / system.

[0092] Transmitting / Receiving Point (TRP): In some embodiments, a TRP can be either a network node, a radio head, a spatial relationship, or a transmission configuration indicator (TCI) state. A TRP can be represented in some embodiments by a spatial relationship or a TCI state. In some embodiments, a TRP may use multiple TCI states.

[0093] Path Switching: As used herein, a path switching is a switching of a wireless communication device's (WCD's) connection from one path (e.g., a direct path or an indirect path) to another path (e.g., an indirect path or a direct path). The two paths may be to the same or different cells.

[0094] Remote WCD: As used herein, a remote WCD is a WCD for which a path switch is initiated and the source path and / or the target path for the path switch is through a relay WCD.

[0095] Relay WCD: As used herein, a relay WCD is a WCD that acts as a relay (eg, an L2 UE-to-network relay) between a remote WCD and a network node or another WCD.

[0096] Direct Path: As used herein, the terms "direct connection" or "indirect path" refer to a connection between a WCD and a network node (eg, a RAN node such as a base station).

[0097] Indirect Path: As used herein, the term "indirect connection" or "indirect path" refers to a connection between a remote WCD and a network node (eg, a RAN node such as a base station) via a relay WCD.

[0098] Prepared Cell: As used herein, a prepared cell for a particular WCD is a cell that has previously admitted the WCD (e.g., during an earlier performed handover preparation phase) or that obtains the UE context of the WCD (e.g., during the second phase of a Radio Link Failure (RLF) procedure).

[0099] Provisioned Relay WCD: As used herein, a provisioned relay WCD for a particular remote WCD is a relay WCD candidate that is connected to the provisioned cell of the remote WCD. In other words, this WCD has a serving cell that is the provisioned cell of the remote WCD.

[0100] It should be noted that the description provided herein focuses on 3GPP cellular communication systems, and therefore 3GPP terminology or terminology similar to 3GPP terminology is often used, however, the concepts disclosed herein are not limited to 3GPP systems.

[0101] It should be noted that in the description herein, reference may be made to the term "cell." However, it is important to note that, particularly with respect to 5G NR concepts, a beam may be used in place of a cell, and thus the concepts described herein are equally applicable to both cells and beams.

[0102] In the 3GPP Release 17 Study Item (SI) on NR sidelink relay (RP-193253, “New SID: Study on NR sidelink relay”), the following objectives will be studied during the 3GPP Rel-17 time frame: This research item targets to study single-hop NR sidelink based relaying. 1. Investigate mechanism(s) with minimal specification impact to support SA requirements for sidelink based UE-network and UE-UE relays, focusing on the following aspects (where applicable) for Layer 3 relays and Layer 2 relays [RAN2]: A. Relay (re)selection criteria and procedures; B. Relay / Remote UE Authorization, C. QoS for relay function; D. Service Continuity; E. The security of the relayed connection after SA3 has provided its conclusions; F. Impact on user plane protocol stack and control plane procedures, e.g. connection management of relayed connections; According to the above research objectives, Layer 2 (L2) relay should be studied as an important relay mechanism.

[0103] Service continuity during path switching is one research objective for sidelink (SL) relay SI. During the recent RAN2 meeting, RAN2 discussed as a baseline a basic procedure for mobility scenarios where a remote UE switches between direct and indirect paths based on NR Rel-15 handover (HO) procedures. The procedure was described in section 5.3 of the Background Art above. When a remote UE switches from a serving path (direct or indirect) to another indirect path after receiving RRCReconfiguration from a gNB, the remote UE needs to set up a PC5 unicast link towards the selected target relay UE if there is no PC5 unicast link available. The remote UE can use the existing L2 link establishment procedure as in Release 16 to set up the link (as captured in clause 6.3.3.1 of TS23.287 v16.3.0). After that, the remote UE sends RRCReconfigurationSidelink to the target relay UE to establish / modify the sidelink DRB. During the entire procedure, the remote UE may trigger a sidelink RLF due to one of the following events: 1) The maximum number of consecutive HARQ DTXs is reached 2) The maximum number of RLC retransmissions is reached. 3) PC5-RRC AS configuration failure due to receiving RRCReconfigurationFailureSidelink

[0104] If a sidelink RLF is triggered, the reroute procedure will be impaired, however, it is unclear how the remote UE will react to the reroute failure.

[0105] Embodiments of the systems and methods disclosed herein provide solutions to the above-mentioned and other problems. In particular, systems and methods for failure monitoring and recovery as may occur following a path switching failure are disclosed herein. In one embodiment, at least one of the paths involved in the path switching is an indirect link through a relay WCD using a side link between a remote WCD (e.g., a remote UE) and a relay WCD (e.g., a relay UE). In one embodiment, the relay WCD is a layer 2 relay UE (i.e., a layer 2 UE-network relay UE).

[0106] In one embodiment, a fault monitoring and recovery procedure is proposed for a remote WCD (e.g., a remote UE) in case of, for example, a path switch, particularly when the remote WCD is passing a fault in the case where the remote WCD performs a path switch from either a direct path or an indirect path to an indirect path.

[0107] Rerouting to an indirect path may fail, for example, due to any of the following events: 1) The maximum number of consecutive HARQ DTXs is reached 2) The maximum number of RLC retransmissions is reached. 3) PC5-RRC AS configuration failure due to receiving RRCReconfigurationFailureSidelink

[0108] In one embodiment, in response to determining that a path switch has failed (e.g., by expiration of an associated timer), the remote WCD triggers a failure recovery procedure. In a path switch failure recovery procedure, the remote WCD initially remains in a connected mode (e.g., an RRC connected mode). In one embodiment, the remote WCD performs a search procedure to search for a potential target cell (or potential target RAN node) or target relay WCD with which to perform connection re-establishment. If the remote WCD is unable to find and re-establish a connection to a target RAN node (or target cell) or target relay WCD within a configured amount of time, the remote WCD transitions to an idle mode (e.g., RRC idle).

[0109] In some embodiments, one or more timers are utilized during a path switching failure recovery procedure to control the behavior of a remote WCD.

[0110] Although not limited to or by a particular advantage, some example advantages that may be provided by some of the embodiments described herein are as follows. · The remote WCD may implement appropriate recovery procedures upon detection of an RLF on the SL link and / or Uu link during a route switch (eg, during a route switch from either a direct or indirect link to an indirect path). · The remote WCD is able to select either a target cell (or target RAN node) or a target relay WCD based on set conditions and measurement results. · Unnecessary down-switching from connected mode (e.g. RRC connected) to idle mode (e.g. RRC idle) is avoided. · Service QoS satisfaction for remote WCDs in case of RLF occurrence during route switching (eg, during route switching from either a direct or indirect link to an indirect path) is better ensured.

[0111] FIG. 8 illustrates an example of a cellular communication system 800 in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communication system 800 is a 5G system (5GS) including a Next Generation RAN (NG-RAN) and a 5G Core (5GC), although the present disclosure is not limited thereto. The embodiments of the present disclosure may be implemented in other types of cellular communication systems (e.g., EPS) or in other types of wireless networks in which sidelink relaying is used. In this example, the RAN includes base stations 802-1 and 802-2, including NR base stations (gNBs) in 5GS and optionally Next Generation eNBs (ng-eNBs) (e.g., LTE RAN nodes connected to 5GC), which control corresponding (macro) cells 804-1 and 804-2. The base stations 802-1 and 802-2 are generally referred to herein collectively as base stations 802 and individually as base stations 802. Similarly, (macro) cells 804-1 and 804-2 are generally referred to herein collectively as (macro) cells 804 and individually as (macro) cells 804. The RAN also includes several low power nodes 806-1-806-4, which may control corresponding small cells 808-1-808-4. The low power nodes 806-1-806-4 may be small base stations (such as pico or femto base stations), or remote radio heads (RRHs), etc. Although not specifically shown, one or more of the small cells 808-1-808-4 may alternatively be provided by the base station 802. The low power nodes 806-1-806-4 are generally referred to herein collectively as low power nodes 806 and individually as low power nodes 806. Similarly, small cells 808-1 through 808-4 are generally referred to herein collectively as small cells 808 and individually as small cells 808. The cellular communication system 800 also includes a core network 810, referred to in 5GS as 5GC. The base stations 802 (and optionally the low power nodes 806) are connected to the core network 810.

[0112] Base station 802 and low power node 806 serve wireless communication devices 812-1 through 812-5 in corresponding cells 804 and 808. Wireless communication devices 812-1 through 812-5 are generally referred to herein collectively as wireless communication devices 812 and individually as wireless communication devices 812. In the following description, wireless communication devices 812 are often UEs and therefore may sometimes be referred to as UEs 812, although the disclosure is not limited thereto.

[0113] Next, embodiments of the present disclosure will be described in more detail. These embodiments relate to path switching failure monitoring and recovery. In this regard, FIGS. 9A-9C show three examples of path switching in a cellular communication system 900. The cellular communication system 900 may be, for example, but is not limited to, the cellular communication system 800 of FIG. 8. The cellular communication system 900 includes a network node 902 (e.g., a RAN node, such as, for example, a base station 802) associated with (e.g., serving) a serving cell 904-S of a remote WCD 906-RM and a target cell 904-T for path switching for the remote WCD 906-RM. It should be noted that, although the examples of FIGS. 9A-9C show the source cell 904-S and the target cell 904-T as associated with (e.g., served by) the same network node 902, the present disclosure is not limited thereto. It should also be noted that although the source cell 904-S and the target cell 904-T are shown in these examples as being different cells, the source cell and the target cell could alternatively be the same cell.

[0114] In particular, FIG. 9A illustrates a path switch from a direct path to an indirect path. As illustrated, a remote WCD 906-RM is initially connected to the network via a direct path from the remote WCD 906-RM to a serving cell 904-S (i.e., to a network node 902 on the serving cell 904-S). In response to a request from the network node 902, the remote WCD 906-RM attempts to implement a path switch from the direct path between the remote WCD 906-RM and the serving cell 904-S to an indirect path between the remote WCD 906-RM and a target cell 904-T for the path switch via a target relay WCD 906-RE-T. It should be noted that the path switch may be faulty. Disclosed herein are embodiments for monitoring for such path switch failures and, in some embodiments, for implementing a path switch failure recovery procedure to attempt to recover from a detected path switch failure.

[0115] FIG. 9B illustrates a path switch from one indirect path to another indirect path. As shown, a remote WCD 906-RM is initially connected to the network via a first indirect path from the remote WCD 906-RM to a serving cell 904-S (i.e., to a network node 902 on the serving cell 904-S) via a serving relay WCD 906-RE-S. In response to a request from the network node 902, the remote WCD 906-RM attempts to implement a path switch from the first indirect path to a second indirect path between the remote WCD 906-RM and a target cell 904-T for the path switch via a target relay WCD 906-RE-T. It should be noted that the path switch may be faulty. Disclosed herein are embodiments for monitoring for such path switch failures and, in some embodiments, for implementing a path switch failure recovery procedure to attempt to recover from a detected path switch failure.

[0116] FIG. 9C illustrates a path switch from an indirect path to a direct path. As shown, a remote WCD 906-RM is initially connected to the network via an indirect path from the remote WCD 906-RM to a serving cell 904-S (i.e., to a network node 902 on the serving cell 904-S) via a serving relay WCD 906-RE-S. In response to a request from the network node 902, the remote WCD 906-RM attempts to implement a path switch from the indirect path to a direct path between the remote WCD 906-RM and a target cell 904-T for the path switch. It should be noted that the path switch may be faulty. Disclosed herein are embodiments for monitoring for such path switch failures and, in some embodiments, for implementing a path switch failure recovery procedure to attempt to recover from a detected path switch failure.

[0117] Next, embodiments related to monitoring for path switching failure (e.g., path switching failure for any of the three path switching scenarios shown in FIG. 9A-FIG. 9C) are described. The embodiments are described in the context of NR, i.e., the remote WCD and relay WCD are deployed in the same NR cell or different NR cells. The embodiments are also applicable to other relay scenarios including WCD-network relay or WCD-WCD relay, where the remote WCD 906-RM and relay WCD (e.g., relay WCD 906-RE-S or 906-T) may be based on LTE sidelink or NR sidelink, and the connection between the relay WCD (e.g., relay WCD 906-RE-S or 906-RE-T) and the network node 902 (e.g., base station) may be LTE Uu or NR Uu.

[0118] In the embodiments described below, it is assumed that a remote WCD 906-RM connected to the network node 902 via a relay WCD (e.g., a relay WCD 906-RE-S or 906-RE-T) is based on an L2 relay mechanism. The remote WCD 906-RM is in a connected mode (e.g., an RRC connected mode).

[0119] In a first embodiment, upon receiving a message (e.g., an RRC message or RRC signaling) from a (serving) network node 902 (e.g., a serving gNB) indicating a path switch, the remote WCD 906-RM switches from a serving path (i.e., a direct or indirect path) to another target path (i.e., an indirect or direct path). The received message not only carries the necessary parameters for setting the target path, but also carries the value of a first timer, based on which the remote WCD 906-RM starts the first timer after receiving the message. The first timer can be a newly defined timer or an existing timer, e.g., T304. If the remote WCD906-RM is unable to successfully access the target entity (i.e., the target cell 904-T or associated target RAN node if the target path is a direct path, or the target relay WCD906-RE-T if the target path is an indirect path) before the first timer expires, the remote WCD906-RM considers the path switching to have failed.

[0120] NOTE: In the case of a path switch from a serving direct path to another direct path, the remote WCD 906-RM will simply rely on existing handover procedures. Therefore, the embodiments described herein focus only on other path switch cases, including direct-indirect path switch, indirect-direct path switch, and indirect-indirect path switch.

[0121] The remote WCD 906-RM performs the following actions for different path switching cases: When the remote WCD 906-RM switches to a direct path, the WCD 906-RM may perform similar actions as if the remote WCD 906-RM performs a handover to the target cell. That is, a first timer (e.g., T304) may be set to a value that allows the remote WCD 906-RM to perform a maximum number of random access attempts (e.g., a maximum number of random access preamble transmissions) on the corresponding target cell 904-T. The remote WCD 906-RM stops the first timer upon successful completion of the random access on the corresponding target cell 904-T. If the remote WCD 906-RM cannot successfully complete the random access on the target cell 904-T before the first timer expires, the remote WCD 906-RM determines that the path switching has failed.

[0122] When the remote WCD906-RM switches to an indirect path, the remote WCD906-RM starts a first timer upon receiving a message indicating a path switch. The first timer is set to a value that allows the remote WCD906-RM to complete a layer 2 link establishment and / or a sideline connection (e.g., PC5-RRC connection) setup toward the corresponding target UE906-RE-T. For example, the remote WCD906-RM stops the first timer when the remote WCD906-RM receives an RRCReconfigurationCompleteSidelink to establish the necessary sidelink DRBs and / or SRBs. If the remote WCD906-RM cannot successfully connect to the target relay WCD906-RE-T before the first timer expires, the remote WCD906-RM determines that the path switch has failed (i.e., due to a sidelink RLF during the path switch procedure).

[0123] In a second embodiment, the first embodiment is also applicable when the remote WCD 906-RM performs a conditional reconfiguration execution, i.e., when applying a stored RRCReconfiguration message including reconfigurationWithSync, which indicates a route switch for the remote WCD 906-RM.

[0124] In a third embodiment, if, during a path switching procedure, the remote WCD 906-RM determines that the path switching procedure has failed, as described above, the remote WCD 906-RM initiates a failure recovery procedure, referred to herein as a path switching failure recovery procedure.

[0125] In a fourth embodiment, the failure recovery procedure is an RRC re-establishment procedure that is the same or similar to a conventional RRC re-establishment procedure in LTE or NR, but may be modified to take into account the indirect path.

[0126] In a fifth embodiment, upon initiating a path switching failure recovery procedure, the remote WCD 906-RM starts a second timer. The second timer can be a new timer or an existing timer such as T311. The second timer is set to a value that allows the remote WCD 906-RM to access a selected target cell or a selected target UE for path switching failure recovery. While the second timer is running, the remote WCD 906-RM stays in a connected mode (e.g., RRC connected mode). Upon expiration of the second timer, the remote WCD 906-RM goes into an idle mode (e.g., RRC idle). The second timer is stopped by the remote WCD 906-RM upon selection of a preferred cell or a preferred target relay UE.

[0127] While the second timer is running, the remote WCDs 906-RM perform a selection procedure for each to select a target cell (or a target RAN node serving the target cell) or a target relay for failure recovery. The selection procedure is performed according to at least one of the following options in some embodiments:

[0128] Option 1: The remote WCD 906-RM is configured to search only for the target cell according to the cell search procedure as if the remote WCD 906-RM triggered an RLF on its direct Uu connection. The remote WCD 906-RM may measure its previous serving cell (i.e., the serving cell connected via a direct or directed connection when the path switch was triggered) and / or neighboring cells. Those measurements may be performed according to a measurement configuration received by the remote WCD 906-RM from a (serving) network node 902 (e.g., the remote WCD 906-RM's serving gNB) when the remote WCD 906-RM was connected to the serving cell 904-S (i.e., directly or indirectly via a relay WCD 906-RE-S) before the path switch was triggered.

[0129] Option 2: The remote WCD 906-RM is configured to search only for the target relay WCD. During this search procedure, the remote WCD 906-RM measures the radio channel quality towards a neighboring WCD (e.g., another WCD with which the remote WCD 906-RM has an existing connection, or another WCD for which the remote WCD 906-RM is able to detect ProSe or D2D discovery signals). The measurement may be performed on an existing sidelink (e.g., an existing PC5 unicast link) for the neighboring WCD if there is already such a link established towards the neighboring WCD. In that case, the remote WCD 906-RM may measure the radio signal strength of possible reception on that link (e.g., RSRP of reception on PSSCH, PSCCH, or PSFCH). In other cases, the remote WCD 906-RM may monitor the radio signal strength for possible discovery message reception. The remote WCD 906-RM may send discovery messages in its vicinity. Based on receiving discovery messages from neighboring WCDs, the remote WCD 906-RM measures the wireless channel quality on each neighboring sidelink (i.e., between the remote WCD 906-RM and each neighboring WCD) with respect to metrics such as, for example, RSRP, RSRQ, RSSI, SINR, SIR, channel occupancy / channel busy ratio, etc. Based on the measurement results, the remote WCD 906-RM selects the best target WCD (i.e., with the strongest wireless channel quality) as the target relay WCD for failure recovery. If multiple suitable target relay WCDs are found (e.g., multiple target relay UEs have measured wireless channel qualities above a specified or configured threshold), the remote WCD 906-RM may select any one of those target relay UEs as the target for failure recovery.

[0130] Option 3: The remote WCD 906-RM is configured to search for both a target cell and a target relay WCD. After the search, the remote WCD 906-RM may find both one or more best target cells and / or best target relay WCDs. To enable selection when there are multiple suitable target cells / relay WCDs available, some selection criteria may be further configured in the remote WCD 906-RM, which may include at least one of the following: Condition 1: Prefer target cell. In this case, the remote WCD906-RM will only select the target cell, if any. Condition 2: Prioritize target relay WCD. In this case, the remote WCD 906-RM will only select the target relay WCD, if any. Condition 3: Select either the target cell or the target relay WCD in terms of the measured radio channel quality. In one embodiment, a certain offset may be set for the remote WCD 906-RM to account for differences in communication range and / or transmission power to compare between the target cell and the target relay WCD.

[0131] For any of the above options, the relevant setting is signaled to the remote WCD 906-RM when the remote WCD 906-RM has a connection to the serving cell 904-S (i.e., directly or indirectly via the relay WCD 906-RE-S). The setting regarding which option the remote WCD 906-RM should apply may be signaled as an indicator (e.g., an option index) of one of these options or as a threshold of the radio channel quality of the radio link. Furthermore, the remote WCD 906-RM may stop measuring the target cell for a while if its measured strongest target cell (e.g., the previous serving cell, i.e., the serving cell connected via a direct or indicated connection when the path switch was triggered, or any neighboring cell) falls below a configured threshold. In this case, the remote WCD 906-RM indicates that there is no neighboring cell with a sufficiently good connection. Therefore, there is no point in wasting WCD power to measure neighboring cells.

[0132] During the selection procedure, in one embodiment, the remote WCD 906-RM first selects a prepared target cell or a prepared target relay WCD, if any (i.e., prioritizes the selection of a prepared target cell or a prepared target relay WCD). Furthermore, each relay WCD may indicate cell information (e.g., information indicating which cell(s) the relay WCD is connected to, or information indicating whether the relay WCD is connected to the prepared cell(s) of the remote WCD 906-RM) in the signaling, which is sent to the remote WCD 906-RM. This cell information may be taken into account when the remote WCD 906-RM selects the target relay WCD(s). This cell information may be signaled via at least one of the following signaling mechanisms: Discovery signaling RRC signaling (e.g. PC5-RRC) MAC CE L1 signaling (e.g. SCI) Control PDUs of a protocol layer (e.g. SDAP, PDCP, RLC or adaptation layer)

[0133] After connecting to the target cell or target relay WCD for failure recovery, the remote WCD 906-RM activity may be resumed (i.e., the remote WCD 906-RM stays in connected mode) since the previous UE context may be retrieved by inter-cell communication. However, when a prepared cell or a prepared relay WCD is not available, the remote WCD 906-RM selects a non-prepared cell or a non-prepared relay WCD. In this case, the remote WCD 906-RM may not successfully recover from the failure before the second timer expires, in which case the remote WCD 906-RM transitions to RRC idle and then tries to set up a radio connection. In this case, the activity of the remote WCD 906-RM may not be resumed.

[0134] When the remote WCD 906-RM selects a target cell or a target relay WCD in which to perform recovery, the second timer is stopped.

[0135] In one embodiment, after the remote WCD 906-RM recovers from a path switching failure, e.g., after re-establishing an RRC, the remote WCD 906-RM sends signaling (e.g., a message) to the network (e.g., to the serving network node 902 or the serving gNB) that conveys one or more of the following: - indicators for failed rerouting; Information indicating the involved nodes, including the remote WCD 906-RM and the failed target cell 904-T or failed target relay WCD 906-RE-T; Information indicating one or more causes of the path switching failure (e.g. reaching the maximum number of consecutive HARQ DTXs, reaching the maximum number of RLC retransmissions, or PC5-RRC AS configuration failure due to receiving an RRCReconfigurationFailureSidelink). Where the failed path switch is for the remote WCD906-RM to set up a relay connection via a target relay WCD906-RE-T of the failed path switch, pairing information regarding the pairing relationship between the remote WCD906-RM and this target relay WCD906-RE-T may be stored, for example, in the serving network node 902 (e.g., a serving gNB) and / or provided to another network node (e.g., a target gNB of successful recovery). Measurements of other nearby cells or WCDs, for example, regarding RSRP, RSRQ, RSSI, SINR, SIR, channel occupancy, etc. Buffer status reporting Power Headroom Reporting

[0136] The signaling described above may be, for example, the RRC signaling SidelinkUEInformationNR. The signaling may be another RRC signaling.

[0137] An example of a remote UE experiencing a path switching failure and triggering a failure recovery procedure according to the embodiment described above is shown in FIG.

[0138] In the sixth embodiment, if the remote WCD 906-RM goes into an idle mode (e.g., RRC idle) when the failed path switch cannot be restored by the failure recovery procedure, the remote WCD 906-RM performs a search procedure similar to that described in the fifth embodiment. Using this selection procedure, the remote WCD 906-RM selects an unprepared target cell or an unprepared target relay WCD to set up a connection. After the connection is established, the remote WCD 906-RM may report similar information as covered in the fifth embodiment to the network (e.g., to the serving network node 902 or serving gNB, or to a network node or gNB after reconnection).

[0139] In a seventh embodiment, when a path switch to an indirect path is triggered for a remote WCD 906-RM, before sending a message (e.g., RRC reconfiguration) to the remote WCD 906-RM indicating the path switch, the serving network node 902 (e.g., serving gNB) stores pair relationship information about the pair relationship between the remote WCD 906-RM and the selected target relay WCD 906-RE-T for the path switch. If the target relay WCD 906-RE-T belongs to a different network node (e.g., different gNB), the serving network node 902 may also send the pair relationship information to the target network node (e.g., target gNB). In one embodiment, the pair relationship information includes information indicating that the target relay WCD 906-RE-T serves as a relay to the remote WCD 906-RM. In one embodiment, the pair relationship information is stored in the associated network node (e.g., associated gNB) until the relay path is released. In the case of a path switching failure, the remote WCD 906-RM is not able to connect to the new (target) path. In this case, the pair relationship information is maintained in the target network node (e.g., target gNB) for a set amount of time. For example, a timer may be started in the target network node when the target network node receives a request message from the serving network node 902 indicating that a path switching needs to be prepared. Similarly, a timer may be started in the serving network node when the serving network node sends RRC signaling to the remote WCD 906-RM indicating that a path switching is initiated. When the timer expires, the pair relationship information is cleared. The timer is stopped when the remote WCD 906-RM successfully completes a path switching while the timer is running.

[0140] In the eighth embodiment, as described in the previous embodiment, in case of a path switch failure, the remote WCD 906-RM triggers a failure recovery procedure (e.g., an RRC re-establishment procedure), and the UE context of the remote WCD 906-RM is stored in the relevant network node (i.e., the serving network node 902 (e.g., the serving gNB) and / or the target network node (e.g., the target gNB)) for a set amount of time. When the target network node receives a request message from the serving network node 902 indicating that a path switch needs to be prepared, a timer may be started in the target network node. Similarly, when the serving network node 902 sends a message (e.g., an RRC message or RRC signaling) to the remote WCD 906-RM indicating that a path switch is initiated, a timer may be started in the serving network node 902. The stored UE context of the remote WCD 906-RM is cleared if the timer expires. The timer is stopped when the remote WCD 906-RM successfully completes a route switch while the timer is running.

[0141] In a ninth embodiment, for the seventh and eighth embodiments, the stored context and / or stored pairing relationship information of the remote WCD 906-RM may be cleared at the node in question (i.e., serving and / or target network node) only if signaling is received indicating that the stored information of the remote WCD 906-RM needs to be cleared. The signaling may be sent by the remote WCD 906-RM after the remote WCD 906-RM establishes a new connection, i.e., after the remote WCD 906-RM goes idle (e.g., RRC idle) and establishes a new connection. The signaling may also be generated by the target network node (e.g., target gNB). For example, the target network node fails to receive a completion message from the remote WCD 906-RM within an expected period of time. The target network node will then clear all stored information related to the remote WCD 906-RM. Meanwhile, the target network node may send signaling to the serving network node to clear stored information relating to the remote WCD 906-RM.

[0142] FIG. 11 is a flow chart illustrating the operation of a remote WCD 906-RM according to at least some of the embodiments described above. As shown, the remote WCD 906-RM receives a message from the network node 902 that triggers or indicates a path switch for the remote WCD 906-RM (step 1100). The message, in some embodiments, is an RRC message (e.g., an RRC reconfiguration message), as described above, or an RRC message for a conditional reconfiguration execution, i.e., when applying a stored RRCReconfiguration message including reconfigurationWithSync, which indicates a path switch for the remote WCD 906-RM. The received message includes a value for a first timer to use to determine a path switch failure, as described above. Additionally, the message may include additional parameters related to the path switch, such as, for example, one or more parameters that enable the remote WCD 906-RM to connect to a target entity (i.e., a target cell 904-T or a target relay WCD 906-RE-T) for the path switch. Additional details regarding the message received in step 1100 and the value of the first timer contained therein are provided above and are equally applicable here. As also described above, in one embodiment, either the source path or the target path for the path switch is an indirect path. More specifically, in one embodiment, the path switch is either a direct-indirect path switch, an indirect-indirect path switch, or an indirect-direct path switch, as described above.

[0143] In response to the received message, the remote WCD 906-RM sets a first timer to a value included in the received message (step 1102), starts the first timer (step 1104), and starts implementing the triggered path switch (step 1106). The remote WCD 906-RM stops the first timer if the remote WCD 906-RM successfully completes the path switch (e.g., stops the first timer upon successful random access to the target cell 904-T if the target path is a direct path, or successfully connects to the target relay WCD 906-RE-T if the target path is an indirect path) (step 1108). The remote WCD 906-RM determines whether there is a path switch failure for the path switch based on the first timer (step 1110). More specifically, as described above, the remote WCD 906-RM determines that the path switch failed if the first timer expires before the remote WCD 906-RM is able to successfully connect to the target entity for the path switch (step 1110A). Conversely, the remote WCD 906-RM determines that the path switch was successful if the first timer was stopped in step 1108 prior to expiration of the first timer (step 1110B).

[0144] In some embodiments, in response to determining in step 1110A that the path switching has failed, the remote WCD 906-RM performs a path switching failure recovery procedure (step 1112). The recovery procedure may be according to any of the respective embodiments described above. Details of those embodiments are equally applicable here. For example, in one embodiment, the failure recovery procedure is an RRC re-establishment procedure. As another example, in an embodiment, the failure recovery procedure is according to the fifth embodiment described above. If the failure recovery has failed, the remote WCD 906-RM may transition to an idle mode and take one or more additional actions (e.g., perform a cell search) as described above with respect to the sixth embodiment (step 1113). It should be noted that one or more aspects of step 1113 may alternatively be performed within step 1112.

[0145] In some embodiments, the remote WCD 906-RM sends a message to the network (e.g., to the serving network node 902, e.g., after successful path switching failure recovery, or to some other network node, e.g., a target network node) (step 1114). This message may include various information, as described in the above embodiments (e.g., the fifth embodiment).

[0146] FIG. 12 illustrates the path switching failure recovery procedure of step 1112 in more detail, according to one exemplary embodiment of the present disclosure. As shown, in response to determining that there is a path switching failure, the remote WCD 906-RM starts a second timer (step 1200). The details of the second timer and the value of the second timer described above are equally applicable here. While the second timer is running, the remote WCD 906-RM performs a selection procedure to select a target entity (e.g., a target cell or a target relay WCD) for failure recovery (step 1202). Details regarding one exemplary embodiment of this selection procedure are provided above, for example, with respect to the fifth embodiment. For example, the selection procedure includes, in one embodiment, performing measurements on one or more potential target relay WCDs and / or one or more potential target cells for failure recovery (step 1202-1), and then selecting a target relay WCD or a target cell for failure recovery based on the measurements (step 1202-2), according to, for example, any of the variations of the fifth embodiment described above.

[0147] The remote WCD 906-RM attempts to connect to the selected target relay WCD or target cell (step 1204). The remote WCD 906-RM stops a second timer upon successful connection to the selected target relay WCD or target cell, as described above (step 1206). In response to expiration of the second timer, the remote WCD 906-RM determines that recovery has failed, transitions to an idle mode, and initiates a cell search procedure in the idle mode, as described above (step 1208).

[0148] FIG. 13 is a flow chart illustrating the operation of a network node (e.g., serving network node 902) of a remote WCD 906-RM according to at least some of the embodiments described above. As shown, the network node stores pairing information and / or sends pairing information to another network node (steps 1300 and 1302), for example according to the seventh and / or eighth embodiments described above. The network node sends a message to the remote WCD 906-RM triggering or instructing a path switch for the remote WCD 906-RM (step 1304), as described above. The message includes a value for a first timer, as described above (step 1306). The network may receive a message related to a path switch or path switch failure recovery from the remote WCD 906-RM, in some embodiments, as described above (step 1308). The details provided above regarding storing / sending UE context information, storing / sending pair information, messages indicating path switching, and messages received from a remote WCD 906-RM are equally applicable here.

[0149] FIG. 25 is a flow chart illustrating the operation of a relay WCD (e.g., relay WCD 906-RE-S) according to at least some of the embodiments described above. As shown, in step 2500, the relay WCD transmits cell information to a remote WCD (e.g., remote WCD 906-RM) including an indication of one or more cells to which the relay WCD is connected. The indication may include an indication that the relay WCD is connected to a prepared cell of the remote WCD. In this manner, the remote WCD is provided with information that enables the remote WCD to select the relay WCD as part of a failure recovery procedure following a path switching failure. The cell information may be signaled via one or more of discovery signaling, RRC signaling, a MAC control element, Layer 1 signaling, and one or more control PDUs of a protocol layer. FIG. 14 is a schematic block diagram of a network node 1400 according to some embodiments of the present disclosure. The network node 1400 may be, for example, a RAN node, such as a base station 802 or 806, or a network node implementing all or a portion of the functionality of a base station 802 or gNB described herein. As shown, the network node 1400 includes a control system 1402 including one or more processors 1404 (e.g., a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc.), a memory 1406, and a network interface 1408. The one or more processors 1404 are also referred to herein as processing circuits. Additionally, when the network node 1400 is a RAN node, the network node 1400 may include one or more radio units 1410 each including one or more transmitters 1412 and one or more receivers 1414 coupled to one or more antennas 1416. The radio units 1410 may be referred to as or be part of an air interface circuit.In some embodiments, the radio unit(s) 1410 are external to the control system 1402, e.g., connected to the control system 1402 via a wired connection (e.g., optical cable). However, in some other embodiments, the radio unit(s) 1410 and potentially the antenna(s) 1416 are integrated together with the control system 1402. The one or more processors 1404 operate to provide one or more functions of the network node 1400 described herein (e.g., one or more functions of a network node, such as network node 902, serving network node, serving gNB, target network node, or target gNB, as described herein). In some embodiments, the function(s) are implemented in software, e.g., stored in the memory 1406 and executed by the one or more processors 1404.

[0150] FIG. 15 is a schematic block diagram illustrating a virtualized embodiment of a network node 1400, according to some embodiments of the disclosure. As used herein, a "virtualized" network node is an implementation of a network node 1400 in which at least a portion of the functionality of the network node 1400 is implemented as virtual component(s) (e.g., via virtual machine(s) executing on physical processing node(s) in the network(s)). As shown, the network node 1400 includes one or more processing nodes 1500 coupled to or included as part of the network(s) 1502. Each processing node 1500 includes one or more processors 1504 (e.g., CPU, ASIC, FPGA, etc.), memory 1506, and a network interface 1508. If the network node 1400 is a RAN node, the network node 1400 may include a control system 1402 and / or one or more radio units 1410, as described above. The control system 1402 may be connected to wireless unit(s) 1410, such as via an optical cable.

[0151] In this example, the functions 1510 of the network node 1400 described herein (e.g., one or more functions of a network node, such as network node 902, serving network node, serving gNB, target network node, or target gNB, as described herein) are implemented in one or more processing nodes 1500 or distributed in any desired manner across one or more processing nodes 1500 and the control system 1402 and / or radio unit(s) 1410. In some particular embodiments, some or all of the functions 1510 of the network node 1400 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 1500. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) 1500 and the control system 1402 is used to perform at least some of the desired functions 1510. In particular, in some embodiments, the control system 1402 may not be included, in which case the wireless unit(s) 1410 communicate directly with the processing node(s) 1500 via an appropriate network interface(s).

[0152] In some embodiments, a computer program or computer program product is provided that includes instructions that, when executed by at least one processor, cause the at least one processor to perform functions of the radio access node 1400 or a node (e.g., processing node 1500) implementing one or more of the functions 1510 of the radio access node 1400 in a virtual environment in accordance with any of the embodiments described herein. In some embodiments, a carrier is provided that comprises the computer program product described above. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as a memory).

[0153] 16 is a schematic block diagram of a network node 1400 according to some other embodiments of the disclosure. The network node 1400 includes one or more modules 1600, each of which is implemented in software. The module(s) 1600 provide the functionality of the network node 1400 described herein (e.g., one or more functionality of a network node, such as a network node 902, a serving network node, a serving gNB, a target network node, or a target gNB, as described herein). This description is equally applicable to the processing node 1500 of FIG. 15, where the module 1600 may be implemented in one of the processing nodes 1500 or distributed across multiple processing nodes 1500 and / or distributed across the processing node(s) 1500 and the control system 1402.

[0154] FIG. 17 is a schematic block diagram of a WCD 1700 according to some embodiments of the disclosure. The WCD 1700 may be, for example, a remote WCD 906-RM or a relay WCD, such as, for example, a target relay WCD or a source relay WCD, as described herein. As shown, the WCD 1700 includes one or more processors 1702 (e.g., CPU, ASIC, FPGA, etc.), a memory 1704, and one or more transceivers 1706, each including one or more transmitters 1708 and one or more receivers 1710 coupled to one or more antennas 1712. The transceiver(s) 1706 includes a radio front-end circuit connected to the antenna(s) 1712 configured to condition signals communicated between the antenna(s) 1712 and the processor(s) 1702, as will be appreciated by those skilled in the art. The processor 1702 is also referred to herein as a processing circuit. The transceiver 1706 is also referred to herein as a radio circuit. In some embodiments, the functionality of WCD 1700 described above (e.g., one or more functions of a remote WCD 906-RM or a relay WCD described herein, such as, e.g., a target relay WCD or a source relay WCD) may be implemented fully or partially in software, e.g., stored in memory 1704 and executed by processor(s) 1702. It should be noted that WCD 1700 may include additional components not shown in FIG. 17 , such as, for example, one or more user interface components (e.g., input / output interfaces including a display, buttons, a touch screen, a microphone, a speaker(s), etc., and / or any other components for enabling input of information into and / or output of information from WCD 1700), a power supply (e.g., a battery and associated power circuitry), etc.

[0155] In some embodiments, a computer program or computer program product is provided that includes instructions that, when executed by at least one processor, cause the at least one processor to perform functions of a WCD 1700 (e.g., a remote WCD 906-RM, or one or more functions of a relay WCD, such as, for example, a target relay WCD or a source relay WCD, as described herein) in accordance with any of the embodiments described herein. In some embodiments, a carrier is provided that comprises the computer program product described above. The carrier is one of an electronic signal, an optical signal, a wireless signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium, such as a memory).

[0156] 18 is a schematic block diagram of a WCD 1700 according to some other embodiments of the disclosure. The WCD 1700 includes one or more modules 1800, each of which is implemented in software. The module(s) 1800 provide the functionality of the WCD 1700 described herein (e.g., one or more functions of a remote WCD 906-RM or a relay WCD described herein, e.g., a target relay WCD or a source relay WCD).

[0157] Referring to Figure 19, according to one embodiment, a communication system includes a communication network 1900, such as a 3GPP type cellular network, comprising an access network 1902, such as a RAN, and a core network 1904. The access network 1902 comprises a number of base stations 1906A, 1906B, 1906C, such as Node Bs, eNBs, gNBs, or other types of wireless access points (APs), each defining a corresponding coverage area 1908A, 1908B, 1908C. Each base station 1906A, 1906B, 1906C is connectable to the core network 1904 via a wired or wireless connection 1910. A first UE 1912 located in the coverage area 1908C is configured to wirelessly connect to or be paged by the corresponding base station 1906C. A second UE 1914 in the coverage area 1908A can wirelessly connect to the corresponding base station 1906A. Although multiple UEs 1912, 1914 are shown in this example, the disclosed embodiments are equally applicable to situations where only one UE is in the coverage area or connects to the corresponding base station 1906.

[0158] The communication network 1900 is itself connected to a host computer 1916, which may be embodied in hardware and / or software of a standalone server, a cloud-implemented server, a distributed server, or as a processing resource in a server farm. The host computer 1916 may be owned or under the control of a service provider, or may be operated by or on behalf of the service provider. Connections 1918 and 1920 between the communication network 1900 and the host computer 1916 may extend directly from the core network 1904 to the host computer 1916, or may proceed through an optional intermediate network 1922. The intermediate network 1922 may be one of a public network, a private network, or a hosted network, or a combination of two or more of them, and the intermediate network 1922 may be a backbone network or the Internet, if any, and in particular the intermediate network 1922 may comprise two or more sub-networks (not shown).

[0159] The communication system of FIG. 19 as a whole enables connectivity between connected UEs 1912, 1914 and a host computer 1916. The connectivity may be described as an over-the-top (OTT) connection 1924. The host computer 1916 and connected UEs 1912, 1914 are configured to communicate data and / or signaling via the OTT connection 1924 using the access network 1902, the core network 1904, any intermediate networks 1922, and possible further infrastructure (not shown) as intermediaries. The OTT connection 1924 may be transparent in the sense that the participating communication devices through which the OTT connection 1924 passes are unaware of the routing of the uplink and downlink communications. For example, the base station 1906 may not be or need not be informed of the past routing of incoming downlink communications involving data originating from the host computer 1916 to be forwarded (e.g., handed over) to the connected UE 1912. Similarly, the base station 1906 does not need to be aware of the future routing of outgoing uplink communications originating from the UE 1912 and destined for the host computer 1916 .

[0160] Next, an exemplary implementation of the UE, base station, and host computer described in the previous paragraph according to an embodiment will be described with reference to FIG. 20. In the communication system 2000, the host computer 2002 comprises hardware 2004 including a communication interface 2006 configured to set up and maintain wired or wireless connections with interfaces of different communication devices of the communication system 2000. The host computer 2002 further comprises a processing circuit 2008, which may have storage and / or processing capabilities. In particular, the processing circuit 2008 may comprise one or more programmable processors, ASICs, FPGAs, or combinations thereof (not shown) adapted to execute instructions. The host computer 2002 further comprises software 2010, which is stored in or accessible by the host computer 2002 and executable by the processing circuit 2008. The software 2010 includes a host application 2012. The host application 2012 may be operable to provide services to a remote user, such as the UE 2014 connecting via an OTT connection 2016 that terminates at the UE 2014 and the host computer 2002. In providing services to the remote user, the host application 2012 may provide user data that is transmitted using the OTT connection 2016.

[0161] The communication system 2000 further includes a base station 2018 provided in the communication system, the base station 2018 comprising hardware 2020 enabling the base station 2018 to communicate with the host computer 2002 and the UE 2014. The hardware 2020 may include a communication interface 2022 for setting up and maintaining wired or wireless connections with interfaces of different communication devices of the communication system 2000, as well as a wireless interface 2024 for setting up and maintaining at least a wireless connection 2026 with a UE 2014 located in a coverage area (not shown in FIG. 20) served by the base station 2018. The communication interface 2022 may be configured to facilitate a connection 2028 to the host computer 2002. The connection 2028 may be direct, or the connection 2028 may pass through a core network (not shown in FIG. 20) of the communication system and / or one or more intermediate networks outside the communication system. In the illustrated embodiment, the hardware 2020 of the base station 2018 further includes processing circuitry 2030, which may comprise one or more programmable processors, ASICs, FPGAs, or combinations thereof (not shown) adapted to execute instructions. The base station 2018 further has software 2032 stored internally or accessible via an external connection.

[0162] The communication system 2000 further includes the UE 2014 already mentioned. The hardware 2034 of the UE 2014 may include a radio interface 2036 configured to set up and maintain a radio connection 2026 with a base station serving a coverage area in which the UE 2014 is currently located. The hardware 2034 of the UE 2014 further includes a processing circuit 2038, which may comprise one or more programmable processors, ASICs, FPGAs, or combinations thereof (not shown) adapted to execute instructions. The UE 2014 further includes software 2040 stored in or accessible by the UE 2014 and executable by the processing circuit 2038. The software 2040 includes a client application 2042. The client application 2042, with the support of the host computer 2002, may be operable to provide services to a human or non-human user via the UE 2014. At the host computer 2002, a running host application 2012 may communicate with a running client application 2042 via an OTT connection 2016 that terminates at the UE 2014 and the host computer 2002. In providing services to a user, the client application 2042 may receive request data from the host application 2012 and provide user data in response to the request data. The OTT connection 2016 may transfer both the request data and the user data. The client application 2042 may interact with the user to generate the user data that the client application 2042 provides.

[0163] It should be noted that the host computer 2002, base station 2018, and UE 2014 shown in Figure 20 may be similar or equivalent to the host computer 1916, one of the base stations 1906A, 1906B, 1906C, and one of the UEs 1912, 1914, respectively, of Figure 19. That is, the inner workings of these entities may be as shown in Figure 20, and separately, the surrounding network topology may be that of Figure 19.

[0164] In Figure 20, the OTT connection 2016 is depicted abstractly to show communication between the host computer 2002 and the UE 2014 via the base station 2018, without explicit reference to intermediary devices and the exact routing of messages through these devices. The network infrastructure may determine the routing, which may be configured to be hidden from the UE 2014 or from the service provider operating the host computer 2002, or both. While the OTT connection 2016 is active, the network infrastructure may also make decisions to dynamically change the routing (e.g., based on load balancing considerations or reconfiguration of the network).

[0165] The wireless connection 2026 between the UE 2014 and the base station 2018 follows the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of the OTT service provided to the UE 2014 using the OTT connection 2016 of which the wireless connection 2026 forms the final segment. More precisely, the teachings of these embodiments may improve, for example, data rates and / or latency, thereby providing benefits such as, for example, reduced user latency, relaxed restrictions on file sizes, and / or better responsiveness.

[0166] Measurement procedures may be provided for the purpose of monitoring data rates, latency, and other factors that one or more embodiments improve upon. There may further be an optional network function for reconfiguring the OTT connection 2016 between the host computer 2002 and the UE 2014 in response to fluctuations in the measurement results. The measurement procedures and / or the network function for reconfiguring the OTT connection 2016 may be implemented in the software 2010 and hardware 2004 of the host computer 2002 or in the software 2040 and hardware 2034 of the UE 2014, or both. In some embodiments, sensors (not shown) may be deployed in or in association with the communication devices through which the OTT connection 2016 passes, and the sensors may participate in the measurement procedures by providing values ​​of the monitored quantities exemplified above, or other physical quantities from which the software 2010, 2040 may calculate or estimate the monitored quantities. The reconfiguration of the OTT connection 2016 may include message formats, retransmission settings, preferred routing, etc., and the reconfiguration need not affect the base station 2018, and the reconfiguration may be unknown or imperceptible to the base station 2018. Such procedures and functions may be known and practiced in the art. In some embodiments, the measurements may involve proprietary UE signaling that facilitates the host computer 2002 measurements of throughput, propagation time, latency, etc. The measurements may be implemented in that the software 2010 and 2040 cause the software 2010 and 2040 to send messages, particularly empty or "dummy" messages, using the OTT connection 2016 while the software 2010 and 2040 monitors propagation times, errors, etc.

[0167] FIG. 21 is a flow chart illustrating a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be as described with reference to FIG. 19 and FIG. 20. For simplicity of the disclosure, only drawing references to FIG. 21 are included in this section. In step 2100, the host computer provides user data. In sub-step 2102 (which may be optional) of step 2100, the host computer provides the user data by executing a host application. In step 2104, the host computer initiates a transmission carrying the user data to the UE. In step 2106 (which may be optional), the base station transmits the user data carried in the host computer initiated transmission to the UE, according to the teachings of the embodiments described throughout this disclosure. In step 2108 (which may also be optional), the UE executes a client application associated with the host application executed by the host computer.

[0168] FIG. 22 is a flow chart illustrating a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be as described with reference to FIG. 19 and FIG. 20. For simplicity of the disclosure, only drawing references to FIG. 22 are included in this section. In step 2200 of the method, the host computer provides user data. In an optional sub-step (not shown), the host computer provides the user data by executing a host application. In step 2202, the host computer initiates a transmission carrying the user data to the UE. The transmission may proceed via the base station according to the teachings of the embodiments described throughout this disclosure. In step 2204 (which may be optional), the UE receives the user data carried in the transmission.

[0169] FIG. 23 is a flow chart illustrating a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be as described with reference to FIG. 19 and FIG. 20. For simplicity of the disclosure, only drawing references to FIG. 23 are included in this section. In step 2300 (which may be optional), the UE receives input data provided by the host computer. Additionally or alternatively, in step 2302, the UE provides user data. In sub-step 2304 (which may be optional) of step 2300, the UE provides the user data by executing a client application. In sub-step 2306 (which may be optional) of step 2302, the UE executes a client application that provides the user data in response to the received input data provided by the host computer. In providing the user data, the executed client application may further take into account user input received from the user. Regardless of the particular manner in which the user data is provided, the UE initiates transmission of the user data to the host computer in sub-step 2308 (which may be optional). In method step 2310, the host computer receives user data transmitted from the UE according to the teachings of the embodiments described throughout this disclosure.

[0170] FIG. 24 is a flow chart illustrating a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be as described with reference to FIG. 19 and FIG. 20. For simplicity of the disclosure, only a drawing reference to FIG. 24 is included in this section. In step 2400 (which may be optional), the base station receives user data from the UE according to the teachings of the embodiments described throughout this disclosure. In step 2402 (which may be optional), the base station initiates transmission of the received user data to the host computer. In step 2404 (which may be optional), the host computer receives the user data carried in the transmission initiated by the base station.

[0171] Any suitable steps, methods, features, functions, or benefits disclosed herein may be implemented through one or more functional units or modules of one or more virtual devices. Each virtual device may comprise several of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessors or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), dedicated digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory, such as read-only memory (ROM), random access memory (RAM), cache memory, flash memory devices, optical storage devices, and the like. The program code stored in memory includes program instructions for implementing one or more communication and / or data communication protocols, as well as instructions for performing one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause each functional unit to perform a corresponding function according to one or more embodiments of the present disclosure.

[0172] Although the processes in the figures may indicate a particular order of operations performed by some embodiments of the present disclosure, it should be understood that such orders are exemplary (e.g., alternative embodiments may perform operations in a different order, combine some operations, overlap some operations, etc.).

[0173] At least some of the following abbreviations may be used in this disclosure. In case of inconsistencies between abbreviations, how the abbreviation is used above should be preferred. If listed multiple times below, the first listing should be preferred over subsequent listing(s). · 3GPP 3rd Generation Partnership Project 5G (fifth generation) ACK Acknowledgement AMF access and mobility management capabilities BWP Bandwidth Part CE control element CP Cyclic Prefix CSI-RS Channel State Information Reference Signal DCI Downlink Control Information DFN Direct Frame Number DMRS demodulation reference signal gNB gNode B HARQ Hybrid Automatic Repeat Request IE Information Elements LTE Long Term Evolution MAC Media Access Control MCS modulation coding scheme NACK Negative acknowledgment NDI New Data Indicator · NR new radio OFDM Orthogonal Frequency Division Multiplexing PDCCH Physical Downlink Control Channel PDCP Packet Data Convergence Protocol PDSCH Physical Downlink Shared Channel ProSe Proximity-based Services PSBCH Physical Sidelink Broadcast Channel PSCCH Physical Sidelink Common Control Channel PSFCH Physical sidelink feedback channel PT-RS tracking reference signal PUCCH Physical Uplink Control Channel PUSCH Physical Uplink Shared Channel QoS Quality of Service RAN Radio Access Network RB Resource Block RLC Radio Link Control RLF Radio Link Failure RLM Radio Link Monitoring RNTI Radio Network Temporary Identifier RRC Radio Resource Control RRC Radio Resource Control RSRP reference signal received power RSRQ Reference signal reception quality RSSI Received Signal Strength Indicator RV redundant version SCI Sidelink Control Information SCS Subcarrier Spacing SI System Information SL side link SMF session management function S-PSS Sidelink Primary Synchronization Signal SSB sync signal block SSID Sidelink Synchronization Identifier S-SSS Sidelink secondary synchronization signal UCI Uplink Control Information UE User Equipment UPF user plane function

[0174] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure, and all such improvements and modifications are considered within the scope of the concepts disclosed herein.

[0175] For the avoidance of doubt, the following numbered sentences present embodiments of the present disclosure. 1. A method implemented by a remote wireless communication device (906-RM) in a communication system (900), the method comprising: receiving (1100) a message from a network node (802) for configuring a remote wireless communication device (906-RM) to perform a path switch, the message including a value for a first timer; Setting (1102) a first timer to a value included in the message; determining (1110) whether the path switching has failed based on whether a first timer expires before the path switching is successfully completed; A method comprising: 2. Route switching, a) switching from an indirect path between the remote wireless communication device (906-RM) and the serving cell (904-S) via a serving relay wireless communication device (905-RE-S) to a direct path between the remote wireless communication device (906-RM) and a target cell (904-T) for the path switching; or b) a path change from a direct path between the remote wireless communication device (906-RM) and the serving cell (904-S) to an indirect path between the remote wireless communication device (906-RM) and a target cell (904-T) for the path change via a target relay wireless communication device (906-RE-T) for the path change; or A path switch from a first indirect path between a remote wireless communication device (906-RM) and a serving cell (904-S) via a serving relay wireless communication device (906-S) to a second indirect path between the remote wireless communication device (906-RM) and a target cell (904-T) for the path switch via a target relay wireless communication device (906-RE-T) for the path switch. 2. The method of embodiment 1, wherein 3. In response to receiving (1100) the message: Starting a first timer (1104); Initiating the implementation of a route switching procedure (1106); 3. The method of embodiment 1 or 2, further comprising: 4. The method of any one of embodiments 1 to 3, wherein the message is a radio resource control (RRC) message. 5. The method of any one of embodiments 1 to 4, wherein the first timer is an existing timer or a new timer. 6. A method according to any one of embodiments 1 to 5, wherein the path switching is a path switching from an indirect path between the remote wireless communication device (906-RM) and the serving cell (904-S) via a serving relay wireless communication device (905-RE-S) to a direct path between the remote wireless communication device (906-RM) and the target cell (904-T). 7. The method of embodiment 6, wherein the value of the first timer is a value that enables the remote wireless communication device (906-RM) to perform a specified or configured maximum number of random access attempts to the target cell (904-T). 8. The method of embodiment 7, further comprising stopping (1108) the first timer upon successful completion of random access to the target cell (904-T). 9. Route switching, A path switch from a direct path between the remote wireless communication device (906-RM) and the serving cell (904-S) to an indirect path between the remote wireless communication device (906-RM) and the target cell (904-T) via a target relay wireless communication device (906-RE-T), or A path switch from a first indirect path between the remote wireless communication device (906-RM) and the serving cell (904-S) via a serving relay wireless communication device (906-S) to a second indirect path between the remote wireless communication device (906-RM) and the target cell (904-T) via a target relay wireless communication device (906-RE-T). 6. The method of any one of embodiments 1 to 5, wherein 10. The method of embodiment 9, wherein the value of the first timer is a value that enables the remote wireless communication device (906-RM) to complete layer 2 link establishment and / or sidelink connection setup toward the target relay wireless communication device (906-RE-T). 11. A method as in any one of embodiments 1 to 10, wherein the message is an RRC reconfiguration message for a conditional reconfiguration execution, and the RRC reconfiguration message includes reconfigurationWithSync. 12. Determining whether the path switch has failed (1110) includes determining that the path switch has failed (1110A) in response to expiration of a first timer before the path switch is successfully completed; The method further includes, in response to determining (1110A) that the path switching has failed, performing (1112) a failure recovery procedure in response to determining (1110A) that the path switching has failed. 12. The method according to any one of embodiments 1 to 11. 13. The method of embodiment 12, wherein the failure recovery procedure is an RRC re-establishment procedure. 14. Implementing disaster recovery procedures (912) starting (1200) a second timer; While the second timer is running, performing a selection procedure for selecting either a target cell or a target relay wireless communication device for fault recovery (1202); and Attempting to connect to a selected target cell or a selected target relay wireless communication device for fault recovery (1204); 14. The method of embodiment 12 or 13, comprising: 15. The method of embodiment 14, wherein the second timer is an existing timer or a new timer. 16. The method of embodiment 14 or 15, wherein the second timer is set to a value that enables the remote wireless communication device (906-RM) to access the selected target cell or the selected target relay wireless communication device for failure recovery. 17. The step of performing a selection procedure (1202) comprises: performing measurements on one or more potential target cells (1202-1); selecting a target cell for fault recovery from one or more potential target cells based on the measurements performed (1202-2); 17. The method of any one of embodiments 14 to 16, comprising: 18. The method of embodiment 17, wherein the one or more potential target cells include one or more previous serving cells of the remote wireless communication device (906-RM) and / or one or more neighboring cells of the serving cell (904-S) of the remote wireless communication device (906-RM). 19. The method of embodiment 17 or 18, wherein performing measurements on one or more potential target cells (1202-1) includes performing measurements on one or more potential target cells based on a measurement configuration received by the remote wireless communication device (906-RM) from a network node before a path switch is requested (1202-1). 20. The step of performing a selection procedure (1202) comprises: performing measurements on one or more potential target relay wireless communication devices (1202-1); selecting a target relay wireless communication device for fault recovery from one or more potential target relay wireless communication devices based on the performed measurements (1202-2); 17. The method of any one of embodiments 14 to 16, comprising: 21. The method of embodiment 20, wherein performing measurements on one or more potential target relay wireless communication devices (1202-1) includes, for each potential target relay wireless communication device, performing measurements on an existing sidelink connection between the remote wireless communication device (906-RM) and the potential target relay wireless communication device, or on a discovery message received by the remote wireless communication device (906-RM) from the potential target relay wireless communication device. 22. The step of performing a selection procedure (1202) comprises: performing measurements on one or more potential target cells (1202-1); performing measurements on one or more potential target relay wireless communication devices (1202-1); selecting a target cell or a target relay wireless communication device for fault recovery from one or more potential target cells and one or more potential target wireless communication devices based on the performed measurements (1202-2); 17. The method of any one of embodiments 14 to 16, comprising: 23. Selecting a target cell or a target relay wireless communication device for fault recovery (1202-2) satisfies the following conditions: Prioritize potential target cells, Prioritizing potential target wireless communication devices; selecting either a potential target cell or a potential target wireless communication device based on the measured wireless channel quality; 23. The method of claim 22, further comprising: selecting a target cell or a target relay wireless communication device for failure recovery based on at least one of the following: 24. The method of embodiment 22, wherein selecting a target cell or a target relay wireless communication device for fault recovery (1202-2) includes selecting a target cell or a target relay wireless communication device for fault recovery based on a measured wireless channel quality taking into account a specified or configured offset (1202-2). 25. The method of any one of embodiments 14 to 24, wherein the one or more potential target cells are one or more prepared cells. 26. The method of any one of embodiments 14 to 25, wherein the one or more potential target relay wireless communication devices are one or more potential target relay wireless communication devices connected to one or more prepared cells. 27. The method of any one of embodiments 14 to 26, wherein performing the selection procedure (1202) includes performing one of two or more defined selection schemes based on the indicator received from the network node (1202). 28. Implementing disaster recovery procedures (1112) Stopping the second timer upon successfully connecting to the selected target cell or the selected target relay wireless communication device for failure recovery (1206). 28. The method of any one of embodiments 14 to 27, further comprising: 29. The method further comprising sending a message to the network node (1114), the message comprising: - Information indicating that a route switch has failed; and information indicating a failed target wireless node or a failed target cell served by the target wireless node and / or a failed target relay wireless communication device for a wireless communication device (906-RM) for a reroute; Information indicating the cause of the path switching failure; and Information indicating a pair relationship between target wireless nodes of a wireless communication device (906-RM) route switching; one or more measurements on neighboring cells or neighboring wireless communication devices (e.g., regarding RSRP, RSRQ, RSSI, SINR, SIR, channel occupancy, etc.); Buffer status reporting; Power headroom reporting and 29. The method of any one of embodiments 14 to 28, comprising one or more of: 30. Implementing disaster recovery procedures (1112) determining (1208) that recovery has failed in response to expiration of a second timer before a connection to the selected target cell or the selected target relay wireless communication device for recovery is successfully made; In response to determining (1208) that recovery was impaired, Transitioning to an idle mode (1208), and Conducting a search procedure (1208) 29. The method of any one of embodiments 14 to 28, further comprising: 31. A remote wireless communication device (906-RM) for a communication system (900), the remote wireless communication device (906-RM) comprising: receiving (1100) a message from a network node (802) for configuring a remote wireless communication device (906-RM) to perform a path switch, the message including a value for a first timer; Setting (1102) a first timer to a value included in the message; determining (1110) whether the path switching has failed based on whether a first timer expires before the path switching is successfully completed; A remote wireless communication device (906-RM) adapted to perform the above. 32. The remote wireless communication device (906-RM) of embodiment 31, wherein the remote wireless communication device (906-RM) is further adapted to perform the method according to any one of embodiments 2 to 30. 33. A remote wireless communication device (906-RM) for a communication system (900), the remote wireless communication device (906-RM) comprising: one or more transmitters (1708); one or more receivers (1710); A processing circuit (1702) associated with one or more transmitters (1708) and one or more receivers (1710); The processing circuit (1702) - receiving (1100) a message from a network node (802) for configuring a remote wireless communication device (906-RM) to perform a path switch, the message including a value for a first timer; Setting (1102) a first timer to a value contained in the message; determining whether the path switch has failed based on whether a first timer expires before the path switch is successfully completed (1110); A remote wireless communication device (906-RM) configured to: 34. A computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to perform a method according to any one of embodiments 1 to 30. 35. A carrier containing the computer program of embodiment 34, the carrier being one of an electronic signal, an optical signal, a radio signal, or a computer-readable storage medium. 36. A communication system including a host computer, the host computer comprising: processing circuitry configured to provide user data; a communications interface configured to forward user data to a cellular network for transmission to a user equipment (UE); Equipped with A communication system, wherein a UE comprises a radio interface and a processing circuit, the processing circuit of the UE being configured to perform a method according to any one of embodiments 1 to 30. 37. The communication system of embodiment 36, further comprising a UE. 38. The communication system of embodiment 37, wherein the cellular network further includes a base station configured to communicate with the UE. 39. processing circuitry of the host computer configured to execute a host application thereby providing user data; a processing circuit in the UE configured to execute a client application associated with the host application; A communication system as described in embodiment 37 or 38. 40. A method implemented in a communications system including a host computer, a base station, and a user equipment (UE), the method comprising: providing user data at a host computer; Initiating, in a host computer, a transmission carrying user data to a UE via a cellular network including a base station, the UE performing a method according to any one of embodiments 1 to 30. A method comprising: 41. Receiving user data from a base station at a UE 41. The method of embodiment 40, further comprising: 42. A communication system including a host computer, the host computer comprising: A communications interface configured to receive user data originating from a transmission from a user equipment (UE) to a base station Equipped with A communication system, wherein a UE comprises a radio interface and a processing circuit, the processing circuit of the UE being configured to perform a method according to any one of embodiments 1 to 30. 43. The communication system of embodiment 42, further comprising a UE. 44. The communication system of embodiment 43, further comprising a base station, the base station having a radio interface configured to communicate with the UE and a communication interface configured to forward user data carried by transmissions from the UE to the base station to a host computer. 45. processing circuitry of the host computer is configured to execute a host application; a processing circuit in the UE configured to execute a client application associated with the host application and thereby provide user data; A communication system as described in embodiment 43 or 44. 46. processing circuitry of the host computer configured to execute the host application and thereby provide the requested data; a processing circuit in the UE configured to execute a client application associated with the host application, thereby providing user data in response to the request data; A communication system as described in embodiment 43 or 44. 47. A method implemented in a communications system including a host computer, a base station, and a user equipment (UE), the method comprising: Receiving user data transmitted from a UE to a base station at a host computer, the UE performing a method according to any one of embodiments 1 to 30. A method comprising: 48. Providing user data to a base station in a UE 48. The method of embodiment 47, further comprising: 49. executing, at the UE, a client application thereby providing user data to be transmitted; executing, at the host computer, a host application associated with the client application; 49. The method of embodiment 48, further comprising: 50. executing, in the UE, a client application; receiving, at the UE, input data for a client application, the input data being provided at a host computer by executing a host application associated with the client application; Further comprising: 49. The method of embodiment 48, wherein the user data to be transmitted is provided by a client application in response to the input data. 51. A method implemented by a network node (902) in a communication system (900), the method comprising: Sending (1304) a message to a remote wireless communication device (906-RM) to configure the remote wireless communication device (906-RM) to perform a path switch, the message including a value for a first timer (1304). A method comprising: 52. Route switching, a) switching from an indirect path between the remote wireless communication device (906-RM) and the serving cell (904-S) via a serving relay wireless communication device (905-RE-S) to a direct path between the remote wireless communication device (906-RM) and a target cell (904-T) for the path switching; or b) a path change from a direct path between the remote wireless communication device (906-RM) and the serving cell (904-S) to an indirect path between the remote wireless communication device (906-RM) and a target cell (904-T) for the path change via a target relay wireless communication device (906-RE-T) for the path change; or A path switch from a first indirect path between a remote wireless communication device (906-RM) and a serving cell (904-S) via a serving relay wireless communication device (906-S) to a second indirect path between the remote wireless communication device (906-RM) and a target cell (904-T) for the path switch via a target relay wireless communication device (906-RE-T) for the path switch. 52. The method of embodiment 51, wherein either 53. The method of embodiment 51 or 52, wherein the message is a radio resource control (RRC) message. 54. The method of any one of embodiments 51 to 53, wherein the first timer is an existing timer or a new timer. 55. A method according to any one of embodiments 51 to 54, wherein the path switching is a path switching from an indirect path between the remote wireless communication device (906-RM) and the serving cell (904-S) via a serving relay wireless communication device (905-RE-S) to a direct path between the remote wireless communication device (906-RM) and the target cell (904-T). 56. The method of embodiment 55, wherein the value of the first timer is a value that enables the remote wireless communication device (906-RM) to perform a specified or configured maximum number of random access attempts to the target cell (904-T). 57. Route switching, A path switch from a direct path between the remote wireless communication device (906-RM) and the serving cell (904-S) to an indirect path between the remote wireless communication device (906-RM) and the target cell (904-T) via a target relay wireless communication device (906-RE-T), or A path switch from a first indirect path between the remote wireless communication device (906-RM) and the serving cell (904-S) via a serving relay wireless communication device (906-S) to a second indirect path between the remote wireless communication device (906-RM) and the target cell (904-T) via a target relay wireless communication device (906-RE-T). 55. The method of any one of embodiments 51 to 54, wherein 58. The method of embodiment 57, wherein the value of the first timer is a value that enables the remote wireless communication device (906-RM) to complete layer 2 link establishment and / or sidelink connection setup toward the target relay wireless communication device (906-RE-T). 59. The method of any one of embodiments 51-58, wherein the message is an RRC reconfiguration message for a conditional reconfiguration execution, and the RRC reconfiguration message includes reconfigurationWithSync. 60. The method further includes receiving (1306) a message from a remote wireless communication device (906-RM), the message comprising: - Information indicating that a route switch has failed; and information indicating a failed target wireless node or a failed target cell served by the target wireless node and / or a failed target relay wireless communication device for a wireless communication device (906-RM) for a reroute; Information indicating the cause of the path switching failure; and Information indicating a pair relationship between target wireless nodes of a wireless communication device (906-RM) route switching; one or more measurements on neighboring cells or neighboring wireless communication devices (e.g., regarding RSRP, RSRQ, RSSI, SINR, SIR, channel occupancy, etc.); Buffer status reporting; Power headroom reporting and 60. The method of any one of embodiments 51 to 59, comprising one or more of: 61. The method of any one of embodiments 51 to 60, further comprising storing (1300) information regarding a pair relationship between a remote wireless communication device (906-RM) and a selected target relay wireless communication device (906-RE-T) for path switching. 62. The method of embodiment 61, further comprising sending information regarding the pair relationship to another network node (1300). 63. The method of embodiment 61 or 62, further comprising clearing information regarding the pair relationship upon receiving a message from the remote wireless communication device (906-RM) indicating that a new connection has been established. 64. The method of any one of embodiments 51 to 62, wherein the network node (902) is a RAN node serving a serving cell (904-S) of a remote wireless communication device (906-RM), and the method further comprises storing (1302) a UE context of the remote wireless communication device (906-RM) and / or sending (1302) the UE context of the remote wireless communication device (906-RM) to another RAN node serving a target cell (904-T) of the path switch. 65. The method of any one of embodiments 51 to 62, wherein the network node (902) is a RAN node serving a serving cell (904-S) of a remote wireless communication device (906-RM), and the UE context of the remote wireless communication device (906-RM) is stored in the network node (902) and / or in another RAN node serving a target cell (904-T) of the path switch until a third timer expires. 66. The method of embodiment 64 or 65, further comprising clearing the stored UE context upon receiving a message from the remote wireless communication device (906-RM) indicating that a new connection has been established. 67. A network node (902) for a communication system (900), the network node (902) comprising: Sending (1304) a message to a remote wireless communication device (906-RM) to configure the remote wireless communication device (906-RM) to perform a path switch, the message including a value for a first timer (1304). A network node (902) adapted to perform the following: 68. The network node (902) of embodiment 67, wherein the network node (902) is further adapted to perform a method according to any one of embodiments 52 to 66. 69. A network node (902) for a communication system (900), the network node (902) comprising processing circuitry (1404, 1504), the processing circuitry (1404, 1504) configured to: Sending (1304) a message to a remote wireless communication device (906-RM) to configure the remote wireless communication device (906-RM) to perform a path switch, the message including a value for a first timer (1304). A network node (902) configured to cause 70. A computer program comprising instructions that, when executed on at least one processor, cause the at least one processor to perform a method according to any one of embodiments 51 to 66. 71. A carrier containing the computer program of embodiment 70, the carrier being one of an electronic signal, an optical signal, a radio signal, or a computer-readable storage medium. 72. A communication system including a host computer, the host computer comprising: processing circuitry configured to provide user data; a communications interface configured to forward user data to a cellular network for transmission to a user equipment (UE); Equipped with A communication system in which a cellular network comprises a base station having a radio interface and a processing circuit, the processing circuit of the base station being configured to perform a method according to any one of embodiments 51 to 66. 73. The communication system of embodiment 72, further comprising a base station. 74. The communication system of embodiment 73, further comprising a UE, the UE being configured to communicate with the base station. 75. processing circuitry of the host computer configured to execute a host application thereby providing user data; the UE comprising processing circuitry configured to execute a client application associated with the host application; A communication system as described in embodiment 74. 76. A method implemented in a communications system including a host computer, a base station, and a user equipment (UE), the method comprising: providing user data at a host computer; Initiating, in a host computer, a transmission carrying user data to a UE through a cellular network including a base station, the base station performing the method according to any one of embodiments 51 to 66. A method comprising: 77. Transmitting user data at a base station 77. The method of embodiment 76, further comprising: 78. A method according to claim 1, wherein user data is provided in a host computer by executing a host application, the method comprising: Executing, in the UE, a client application associated with the host application 78. The method of embodiment 77, further comprising: 79. A communications system including a host computer, the host computer having a communications interface configured to receive user data originating from a transmission from a user equipment (UE) to a base station, the base station having a wireless interface and processing circuitry, the processing circuitry of the base station configured to perform a method according to any one of embodiments 51 to 66. 80. The communication system of embodiment 79, further comprising a base station. 81. The communication system of embodiment 80, further comprising a UE, the UE being configured to communicate with the base station. 82. processing circuitry of the host computer is configured to execute a host application; the UE is configured to execute a client application associated with the host application, thereby providing user data to be received by the host computer; A communication system as described in embodiment 81.

Claims

1. A method implemented by a remote wireless communication device (906-RM) in a communication system (900), the method comprising: receiving (1100) a message from a network node (802) configuring said remote wireless communication device (906-RM) to perform a path switch; determining 1110 whether there has been a failure in the path switching; and performing (1112) a failure recovery procedure, the failure recovery procedure being performed (1112) in response to determining (1110A) that the path switching has failed, the failure recovery procedure comprising: Selecting either a suitable cell or a suitable relay wireless communication device as a target cell or a target relay wireless communication device for failure recovery (1202). A method comprising:

2. The method of claim 1 , wherein the failure recovery procedure is an RRC re-establishment procedure.

3. The method according to claim 1 or 2, wherein the suitable cell or the suitable relay wireless communication device is a prepared cell or a prepared relay wireless communication device.

4. 4. The method of claim 3, further comprising selecting an unprepared cell or an unprepared relay wireless communication device when a prepared cell or a prepared relay wireless communication device is not available.

5. The path switching is a) switching a path from an indirect path between the remote wireless communication device (906-RM) and a serving cell (904-S) via a serving relay wireless communication device (905-RE-S) to a direct path between the remote wireless communication device (906-RM) and a target cell (904-T) for the path switching; b) a path switch from a direct path between the remote wireless communication device (906-RM) and the serving cell (904-S) to an indirect path between the remote wireless communication device (906-RM) and the target cell (904-T) for the path switch via a target relay wireless communication device (906-RE-T) for the path switch; or c) switching a path from a first indirect path between the remote wireless communication device (906-RM) and the serving cell (904-S) via a serving relay wireless communication device (906-S) to a second indirect path between the remote wireless communication device (906-RM) and the target cell (904-T) for the path switching via a target relay wireless communication device (906-RE-T) for the path switching. The method according to any one of claims 1 to 4, wherein

6. The failure recovery procedure includes: performing measurements on one or more potential target cells (1202-1); selecting the target cell for failure recovery from the one or more potential target cells based on the performed measurements (1202-2); The method of any one of claims 1 to 5, comprising:

7. The method of claim 6, wherein performing (1202-1) the measurements on the one or more potential target cells comprises performing (1202-1) the measurements on the one or more potential target cells based on a measurement configuration received by the remote wireless communication device (906-RM) from a network node.

8. The failure recovery procedure includes: performing measurements on one or more potential target relay wireless communication devices (1202-1); selecting (1202-2) the target relay wireless communication device for fault recovery from the one or more potential target relay wireless communication devices based on the performed measurements; The method of any one of claims 1 to 5, comprising:

9. The method of claim 8, wherein performing the measurements on the one or more potential target relay wireless communication devices (1202-1) includes, for each potential target relay wireless communication device, performing measurements on an existing sidelink connection between the remote wireless communication device (906-RM) and the potential target relay wireless communication device or on a discovery message received by the remote wireless communication device (906-RM) from the potential target relay wireless communication device.

10. The method according to claim 8 or 9, wherein the one or more potential target relay wireless communication devices are one or more potential target relay wireless communication devices connected to one or more previous serving cells of the remote wireless communication device (906-RM).

11. The failure recovery procedure includes: performing measurements on one or more potential target cells (1202-1); performing measurements on one or more potential target relay wireless communication devices (1202-1); selecting a target cell or a target relay wireless communication device for fault recovery from the one or more potential target cells and the one or more potential target wireless communication devices based on the performed measurements (1202-2); The method of any one of claims 1 to 5, comprising:

12. The step of selecting the target cell or the target relay wireless communication device for fault recovery (1202-2) satisfies the following conditions: Prioritize potential target cells, Prioritizing potential target wireless communication devices; selecting either a potential target cell or a potential target wireless communication device based on the measured wireless channel quality; The method of claim 11, further comprising: selecting (1202-2) the target cell or the target relay wireless communication device for failure recovery based on at least one of:

13. 13. The method of claim 1, wherein performing the failure recovery procedure (912) further comprises starting a second timer (1200), and the selecting step is performed while the second timer is running.

14. Implementing the fault recovery procedure (1112) and stopping the second timer upon successfully selecting the selected target cell or the selected target relay wireless communication device for failure recovery (1206). The method of claim 13 further comprising:

15. Implementing the fault recovery procedure (1112) includes: determining that recovery has failed in response to expiration of the second timer before successful selection of the selected target cell or the selected target relay wireless communication device for recovery (1208); In response to determining 1208 that recovery has been impaired, Transitioning to an idle mode (1208); and performing a search procedure (1208); 15. The method of claim 13 or 14, further comprising:

16. and sending a message to the network node (1114), the message including: - information indicating that said path switching has failed; and - information indicating the remote wireless communication device (906-RM), a failed target wireless node or a failed target cell served by the target wireless node, and / or a failed target relay wireless communication device of the path change; information indicating the cause of the failure of said path switching; - information indicating a pairing relationship between said remote wireless communication device (906-RM) and said target wireless node of said path switching; one or more measurements (related to RSRP, RSRQ, RSSI, SINR, SIR or channel occupancy) on neighbouring cells or neighbouring wireless communication devices; Buffer status reporting; and Power headroom reporting and 16. The method of claim 1 , comprising one or more of the following:

17. 17. The method of claim 1, wherein the message includes a value for a first timer, the method further including setting the first timer to the value included in the message, and determining whether there has been a failure to switch paths includes determining whether there has been a failure to switch paths based on whether the first timer expires before the switch paths are successfully completed.

18. In response to receiving the message (1100), Starting the first timer (1104); Initiating the implementation of a path switching procedure (1106); 20. The method of claim 17, further comprising:

19. A remote wireless communication device (906-RM) for a communication system (900), said remote wireless communication device (906-RM) adapted to perform the method according to any one of claims 1 to 18.

20. A computer-readable storage medium comprising instructions that, when executed on at least one processor, cause the at least one processor to perform the method of any one of claims 1 to 18.

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