Recovery via sidelink

Abstract

Radio link failure (RLF) recovery via a sidelink (SL) is provided. Disclosed herein are systems and methods for avoiding a user equipment (UE) from triggering a radio resource control (RRC) reestablishment procedure upon RLF, thereby avoiding unnecessary signaling overhead and connectivity disruption. In some embodiments, a UE (UE1) communicates with another UE (UE2) via a SL, and UE1 detects RLF via a radio link. Upon detecting the RLF, UE1 sends a failure message to UE2 via a SL channel identifying the detected RLF. Upon receiving the failure message from UE1, UE2 forwards the message to the network via an available Uu link between UE2 and the network. In some embodiments, before sending the failure message to the network, if no Uu radio link is available and active, UE2 performs a random access procedure to a selected cell.

Description

[0001] Related Applications

[0002] This application claims the benefit of provisional patent application serial number 62 / 891,004, filed on August 23, 2019, the disclosure of which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present disclosure relates to recovery from Radio Link Failure (RLF) in a wireless communication network. Background Art

[0004] In the 3rd Generation Partnership Project (3GPP), a dual connectivity (DC) solution has been specified for Long Term Evolution (LTE) and between LTE and the fifth generation (5G) new air interface (NR). In DC, two nodes are involved: a primary node (MN, or primary enhanced or evolved Node B (eNB) (MeNB)) and a secondary node (SN, or secondary eNB (SeNB)). Multi-connectivity (MC) is the case when more than two nodes are involved. In addition, the use of DC in ultra-reliable low-latency communication (URLLC) scenarios has been proposed in 3GPP to enhance robustness and avoid connection interruptions.

[0005] 3GPP DC

[0006] Figure 1 Different ways to deploy a 5G NR network with or without interworking with LTE radio access (also known as Evolved Universal Terrestrial Radio Access (E-UTRA)) and Evolved Packet Core (EPC) are shown. In principle, NR and LTE can be deployed without any interworking, which is represented by NR Standalone (SA) operation. That is, an NR base station (gNB) in NR can be connected to a 5G Core Network (CN) (5GCN) and an eNB in ​​LTE can be connected to the EPC, without any interconnection between the two ( Figure 1 On the other hand, the first supported version of NR is the so-called Evolved Universal Terrestrial Radio Access Network (E-UTRAN) NR DC (EN-DC), which consists of Figure 1 Option 3 in is shown. In such a deployment, DC between NR and LTE is applied with LTE as the primary node and NR as the secondary node. A radio access network (RAN) node (e.g. gNB) supporting NR may not have a control plane connection to the core network (e.g. EPC); instead, it relies on LTE as a MN (MeNB). This is also called "non-standalone NR". Note that in this case, the functionality of the NR cell is limited and will be used as a booster and / or diversity branch for connected mode user equipment (UE), but RRC_IDLE UEs cannot camp on these NR cells.

[0007] With the introduction of 5GCN, other options may also be valid. As mentioned above, option 2 supports standalone NR deployments with gNBs connected to 5GCN. Similarly, LTE can also be connected to 5GCN using option 5 (also known as enhanced LTE (eLTE), E-UTRA / 5GCN, or LTE / 5GCN, and the nodes can be referred to as next-generation eNBs (NG-eNBs)). In these cases, both NR and LTE are considered part of the next-generation RAN (NG-RAN) (and both NG-eNBs and gNBs can be referred to as NG-RAN nodes). It is worth noting that options 4 and 7 are other variants of DC between LTE and NR, which will be standardized as part of the NG-RAN connected to 5GCN, represented by multi-radio DC (MR-DC). The content under the MR-DC umbrella is as follows:

[0008] EN-DC (Option 3): LTE is the MN and NR is the SN (using EPC CN),

[0009] NR E-UTRA DC (NE-DC) (Option 4): NR is the MN and LTE is the SN (using 5GCN),

[0010] NG-RAN E-UTRA NR DC (NGEN-DC) (Option 7): LTE is the MN and NR is the SN (using 5GCN),

[0011] NR-DC (a variant of Option 2): DC, where both MN and SN are NR (using 5GCN).

[0012] Since the migration of these options may be different for different operators, it is possible that multiple options may be deployed in parallel in the same network. For example, there may be eNBs supporting options 3, 5, and 7 in the same network as NR base stations supporting options 2 and 4. In conjunction with the DC solution between LTE and NR, it is also possible to support carrier aggregation (CA) in each cell group (i.e., primary cell group (MCG) and secondary cell group (SCG)) and DC (e.g., NR-NR DC) between nodes on the same radio access technology (RAT). For LTE cells, the result of these different deployments is the coexistence of LTE cells associated with eNBs connected to EPC, 5GCN, or both EPC / 5GCN.

[0013] As mentioned before, DC is standardized for both LTE and EN-DC. LTE DC and EN-DC are designed differently when it comes to which nodes control what. Basically, there are two options:

[0014] 1. Centralized solutions (such as LTE DC),

[0015] 2. Decentralized solutions (such as EN-DC).

[0016] Figure 2 A schematic control plane architecture 200-1 of DC in LTE DC and a control plane architecture 200-2 of EN-DC are shown. In the control plane architecture 200-1 of LTE DC, MN 202 has an LTE radio resource control (RRC) entity (LTERRC) 204 to control UE 206 (which stores LTE RRC state 208). MN 202 communicates with SN 210-1 via an Xn-C interface. UE 206 communicates with both MN 202 and SN 210-1 via a Uu interface.

[0017] The main difference of the control plane architecture 200-2 of EN-DC is that SN 210-2 has a separate NR RRC entity (NRRRC) 212. This means that SN 210-2 can also control UE 206, sometimes without knowing MN 202, but usually SN 210-2 needs to coordinate with MN 202. MN 202 communicates with SN 210-2 via the Xx-C interface. In the control plane architecture 200-1 of LTE DC, RRC decisions always come from MN 202 (MN to UE). However, note that SN 210-1 still decides the configuration of SN 210-1, because only SN 210-1 itself knows the resources, capabilities, etc. of SN 210-1.

[0018] For EN-DC, the main changes compared to LTE DC are:

[0019] Introducing a split bearer from SN 210-2 (called SCG split bearer),

[0020] Introducing split bearers for RRC, and

[0021] • Introducing direct RRC (also called SCG Signalling Radio Bearer (SRB)) from SN 210-2.

[0022] Figure 3 and Figure 4 The user plane (UP) 300 and control plane (CP) 400 architecture of EN-DC are shown. Specifically, Figure 3 Network side protocol termination options for MCG, SCG and split bearers in MR-DC (EN-DC) with EPC are shown. Figure 4 The network structure of CP 400 in EN-DC is shown.

[0023] SN 210 is sometimes referred to as a secondary gNB (SgNB) (where gNB is an NR base station), and in the case where LTE is MN 202 and NR is SN 210, MN 202 is referred to as MeNB. In another case where NR is MN 202 and LTE is SN 210, the corresponding terms are SeNB and master gNB (MgNB).

[0024] Splitting RRC messages is mainly used to create diversity, and the sender can decide to select one of the links for scheduling the RRC message, or it can duplicate the message on both links. In the downlink, path switching between MCG or SCG branches or duplication on both is left to the network implementation. On the other hand, for the uplink, the network configures the UE to use MCG, SCG or both branches. The terms "branch", "path" and "Radio Link Control (RLC) bearer" are used interchangeably throughout this document.

[0025] CA

[0026] When CA is configured, the UE has only one RRC connection with the network. In addition, one serving cell provides non-access stratum (NAS) mobility information upon RRC connection establishment / reestablishment / switching, and one serving cell provides security input upon RRC connection reestablishment / switching. This cell is called the primary cell (PCell). In addition, depending on the UE capabilities, a secondary cell (SCell) can be configured to form a serving cell set together with the PCell. Therefore, the serving cell set configured for the UE always consists of one PCell and one or more SCells. In addition, when DC is configured, it may be the case that one carrier under the SCG is used as the primary SCell (PSCell). Therefore, in this case, there is one PCell and one or more SCells on the MCG, and one PSCell and one or more SCells on the SCG.

[0027] Reconfiguration, addition and removal of SCells can be performed via RRC. RRC can also add, remove or reconfigure SCells for use with the target PCell when switching within a RAT. When adding a new SCell, dedicated RRC signaling is used to send all required system information for the SCell, i.e., when in connected mode, the UE does not need to obtain the broadcasted system information directly from the SCell.

[0028] Vehicle to Everything (V2X)

[0029] Figure 5A cellular intelligent transport system (ITS) (C-ITS) environment is shown. C-ITS aims to define a new cellular ecosystem for the delivery of vehicle services and their propagation. Such an ecosystem includes both short-range V2X service transmissions and long-range V2X service transmissions. Specifically, short-range communications involve transmissions towards other vehicle UEs or roadside units (RSUs) via device-to-device (D2D) links (also defined as sidelink (SL) or PC5 interfaces in 3GPP). On the other hand, for long-range transmissions, transmissions on the Uu interface between the UE and the base station are considered, in which case the packets can be propagated to different ITS service providers, which can be road traffic authorities, road operators, motor vehicle original equipment manufacturers (OEMs), cellular operators, etc.

[0030] When it comes to the SL interface, the first standardization work in 3GPP dates back to Release (Rel) 12, targeting public safety use cases. Since then, many enhancements have been introduced to expand the use cases that can benefit from D2D technology. Specifically, in LTE Rel-14 and Rel-15, the extension of the D2D work includes support for V2X communications, including any combination of direct communications between vehicles (vehicle-to-vehicle (V2V)), pedestrians (vehicle-to-pedestrian (V2P)), and infrastructure (vehicle-to-infrastructure (V2I)).

[0031] While LTE V2X is primarily targeted at traffic safety services, NR V2X has a wider scope, including not only basic safety services, but also non-safety applications, such as extended sensor / data sharing between vehicles, where the goal is to enhance the perception of the vehicle's surroundings. Therefore, a new set of applications has been captured in 3GPP Technical Report (TR) 22.886 V16.2.0, which will require an enhanced NR system and a new NR SL architecture. These applications include advanced driving, vehicle platooning, cooperative maneuvering between vehicles, and remote driving.

[0032] In this new context, it becomes more urgent to meet the expected requirements of required data rate, capacity, reliability, latency, communication range, and speed. In addition, considering the radio conditions and the environment in which enhanced V2X (eV2X) scenarios occur, both communication interfaces PC5 and Uu can be used to support advanced V2X use cases. For example, given the various services that can be transmitted over SL, a robust Quality of Service (QoS) framework that considers the different performance requirements of different V2X services seems to be needed. In addition, the NR protocol should be designed to handle more robust and reliable communications. All these issues are currently under 3GPP study in NR Rel-16.

[0033] Radio Link Failure (RLF) due to physical layer issues

[0034] Figure 6 RLF due to physical layer problems is shown. It may happen that the UE loses coverage to the cell to which the UE is currently connected. This may happen when the UE enters a fade dip, or when a handover is required as described above, but the handover fails for one reason or another. This is especially true if the "handover region" is very short, as will be described further below.

[0035] The quality of the radio link is typically monitored in the UE, for example on the physical layer, as described in 3GPP Technical Specifications (TS) 38.300 V15.6.0, TS 38.331 V15.6.0 and TS 38.133 V15.6.0, and is summarized here in a very brief description.

[0036] When the physical layer detects that it has experienced a problem according to the criteria defined in TS 38.133, the physical layer sends an indication of the detected problem (Out-of-Sync indication) to the RRC protocol. After a configurable number (N310) of such consecutive indications, a timer (T310) starts. If the link quality does not improve (recover) while T310 is running (i.e., there are no N311 consecutive "In-Sync" indications from the physical layer), RLF is declared in the UE, see Figure 6 .

[0037] The above-mentioned relevant timers and counters are listed here for reference. The UE reads the timer value from the system information broadcast in the cell. Alternatively, the UE can be configured with UE-specific values ​​and constants of the timer using dedicated signaling, i.e., where a specific value is given to a specific UE, where the message only concerns each specific UE.

[0038]

[0039]

[0040] Now, if T310 expires for the MCG, and as seen above, the UE initiates connection re-establishment to resume the ongoing RRC connection. The procedure now includes a cell selection by the UE. That is, the RRC_CONNECTED UE will now try to autonomously find a better cell to connect to since, according to the described measurements, the connection to the previous cell failed (it may happen that the UE returns to the first cell anyway, but then also performs the same procedure). Once a suitable cell has been selected (as further described, for example, in TS 38.304), the UE requests re-establishment of the connection in the selected cell. It is important to note that there is a difference in the mobility behavior as the RLF results in UE-based cell selection compared to the normally applied network controlled mobility.

[0041] If the re-establishment is successful (which depends inter alia on whether the selected cell and the gNB controlling that cell are ready to maintain the connection to the UE), the connection between the UE and the gNB can be restored.

[0042] Failure to reestablish means that the UE enters RRC_IDLE and the connection is released. In order to continue communication, a new RRC connection must be requested and established.

[0043] The reason for introducing the above timer T31x and counter N31x is to add some freedom and hysteresis for configuring the criteria for when the radio link should be considered failed (and restored). This is desirable because if the connection is abandoned prematurely, if the loss of link quality proves to be temporary, and the UE successfully recovers the connection without any further action or procedure (e.g. before T310 expires, or before the count reaches the value N310), this will impair the end-user performance.

[0044] The procedure for NR RLF detection related actions is as follows (text reproduced from 3GPP TS 38.331 V15.6.0):

[0045]

[0046]

[0047] NR SL unicast link

[0048] Figure 7 An NR SL unicast link between a pair of UEs is shown. For NR SL, unicast at the access layer is supported for services that require high reliability. There can be multiple SL unicast links between the same UE pair, and each link can support multiple SL QoS flows / radio bearers. At the access layer, each link can be identified by a source and destination L2 identity (ID). For example, Figure 7The PC5 unicast link 1 in can be identified by a pair of L2 ID1 (ie, corresponding to application ID1) and L2 ID2 (ie, corresponding to application ID2).

[0049] More specifically, at the physical layer, the hybrid automatic repeat request (HARQ) acknowledgement / negative acknowledgement (ACK / NACK) feedback can be configured so that the receiver UE in the SL unicast pair will send an ACK when a transport block (TB) is successfully received, or send a NACK when a TB reception fails. In addition to the RLC unacknowledged mode (UM), the RLC acknowledged mode (AM) can also be configured for NR SL unicast transmission / reception. When the RLC AM is configured depending on the RLC protocol data unit (PDU) reception failure, the receiving (RX) UE will send an RLC status report to the transmitting (TX) UE and request retransmission of the lost RLC PDU.

[0050] Similar RLF procedures as in NR Uu are also supported for NR SL unicast with the following possible criteria:

[0051] • expiry of a timer started following an indication of a radio problem (e.g. out-of-sync) from the physical layer; or

[0052] The maximum number of RLC retransmissions is reached; or

[0053] The maximum number of consecutive HARQ NACK feedbacks is reached; or

[0054] The channel busy ratio (CBR) is higher than the threshold.

[0055] Figure 8 Shows Figure 7 Figure 2 shows the link release procedure for an NR SL unicast link. Finally, a UE may release an established unicast link due to poor link quality or due to out-of-service. The link release procedure shown is based on PC5-S signaling.

[0056] SL Resource Allocation

[0057] There are two different resource allocation (RA) procedures for V2X over SL, namely network-controlled RA (so-called "mode 3" in LTE and "mode 1" in NR) and autonomous RA (so-called "mode 4" in LTE and "mode 2" in NR). Transmission resources are selected within a resource pool predefined or configured by the network.

[0058] With network controlled RA, the NG-RAN is responsible for scheduling the SL resource(s) to be used by the UE for SL transmission(s). The UE sends a SL Buffer Status Report (BSR) to the network to notify the SL data available for transmission in the SL buffer associated with the Medium Access Control (MAC) entity. The network then signals the RA to the UE using Downlink Control Information (DCI). Network controlled (or Mode 1) RA can be implemented via dynamic scheduling signaling via the Physical Downlink Control Channel (PDCCH) or by semi-persistent scheduling where the gNB provides one or more configured SL grants. Both Type 1 and Type 2 configured SL grants are supported.

[0059] With autonomous RA, each device independently decides which SL radio resources to use for SL operation based on, for example, reading the received SL control information (SCI) or energy detection. For both RA modes, the SCI is transmitted on the physical sidelink control channel (PSCCH) to indicate the SL resources allocated for the physical sidelink shared channel (PSSCH). Unlike network-controlled RA, which can be performed only when the UE is in RRC_CONNECTED state, autonomous RA (or mode 2) can be performed when the UE is in RRC_CONNECTED mode and when the UE is in INACTIVE / IDLE state, and also when the UE is in Uu coverage and out of coverage. Specifically, when the UE is in RRC_CONNECTED mode, the SL resource pool can be configured with dedicated RRC signaling, while for IDLE / INACTIVE mode operation, the UE will rely on the SL resource pool provided in the broadcast signal (i.e., the system information block (SIB)).

[0060] There are certain challenges currently. In non-SA (NSA) or SA NR deployment scenarios, SL operation and transmission between UEs can be network controlled (i.e., SL Mode 1 transmission) or not network controlled (i.e., SL Mode 2 transmission). In the case of SL Mode 2 transmission, even if the SL UEs operate autonomously without assistance from the network, they may still be under network coverage (i.e., under the coverage of the primary node, the secondary node, or both).

[0061] When RLF is experienced in NR, different actions are performed based on whether DC or CA is activated and based on whether RLF has been detected on MCG, SCG, PCell / PSCell, or SCell. Specifically:

[0062] If DC replication is activated:

[0063] o If RLF occurs on the SCG, the UE sends an SCGFailureInformation message to the MCG and does not trigger RRC reestablishment.

[0064] o If RLF occurs on MCG, the UE triggers RRC re-establishment according to 3GPP Rel-15.

[0065] o If RLF occurs on MCG, according to 3GPP Rel-16, the UE sends an MCGFailureInformation message to the network and does not trigger RRC re-establishment.

[0066] If CA replication is activated:

[0067] o If RLF occurs in the RLC entity mapped to the PCell (i.e., on the MCG side), the RRC re-establishment procedure is triggered. This may also occur in the NR standalone case.

[0068] o If RLF occurs in the RLC entity mapped to the PSCell (ie, on the SCG side), the SCGFailureInformation procedure is used, and the RLF is reported to the MCG, and RRC re-establishment is not triggered.

[0069] o If RLF occurs in the RLC entity mapped to the SCell (ie, whether on the MCG side or the SCG side), the UE sends a report to the network (ie, FailureInformation message) and does not trigger RRC re-establishment.

[0070] According to the situation, if the prior art is applied, as a general rule, the RRC reestablishment process is applied when RLF is detected on the PCell. In addition, in another case, when the UE does not have an available link to the network through which an RLF RRC message (e.g., MCGFailureInformation, SCGFailureInformation, or FailureInformation message) can be sent, RRC reestablishment is also triggered.

[0071] If an RRC re-establishment is performed, this will result in connectivity disruption and high latency due to the time consuming nature of the RRC procedure. Summary of the invention

[0072] A method is provided for detecting and handling a radio link failure in a cellular communication system by performing a radio link failure (RLF) recovery via a sidelink (SL). In some embodiments, a method is performed by a first wireless device for detecting and handling a radio link failure in a cellular communication system, the method comprising: detecting a radio link failure of a first radio link between the first wireless device and a radio access network of the cellular communication system; and sending a failure message to the second wireless device via a sidelink between the first wireless device and the second wireless device.

[0073] In some embodiments, the method further comprises receiving a response from the second wireless device via the sidelink. In some embodiments, the method further comprises receiving a response from a radio access node in the radio access network via a second radio link between the first wireless device and the radio access node. In some embodiments, the response is a radio resource control (RRC) message that triggers a specific RRC procedure. In some embodiments, the method further comprises performing one or more actions based on the response.

[0074] In some embodiments, the failure message is a FailureInformation message. In some embodiments, the failure message is a MCGFailureInformation message or a SCGFailureInformation message. In some embodiments, the failure message includes a wireless device context of the first wireless device. In some embodiments, the failure message includes information related to the radio link failure.

[0075] In some embodiments, the failure message is an RRC message, and the radio resource control RRC message is used to handle radio link failure in carrier aggregation (CA), dual connectivity (DC), or standalone operation with the help of the sidelink.

[0076] In some embodiments, the failure message includes an indication of a failure condition, the indication directly or indirectly indicating one or more conditions that caused the radio link failure.

[0077] In some embodiments, the failure message includes one or more recent measurements made by the first wireless device related to the first radio link.

[0078] In some embodiments, a method is performed by a second wireless device for handling a radio link failure at a first wireless device in a cellular communication system, the method comprising: receiving a failure message from the first wireless device via a sidelink between the first wireless device and the second wireless device, the failure message being related to a radio link failure at the first wireless device of a first radio link between the first wireless device and a radio access network of the cellular communication system; and sending the failure message to a radio access node in the radio access network of the cellular communication system via a second radio link between the second wireless device and the radio access node.

[0079] In some embodiments, the method further comprises performing a radio access procedure to establish the second radio link between the second wireless device and the radio access node. In some embodiments, the radio access procedure is a random access procedure.

[0080] In some embodiments, the method further comprises: receiving a response from the radio access node; and sending the response to the first wireless device via the sidelink. In some embodiments, the method further comprises: receiving a response from a second radio access node; and sending the response to the first wireless device via the sidelink. In some embodiments, the response is an RRC message that triggers a specific RRC procedure.

[0081] In some embodiments, the failure message is a FailureInformation message. In some embodiments, the failure message is a MCGFailureInformation message or a SCGFailureInformation message. In some embodiments, the failure message includes a wireless device context of the first wireless device. In some embodiments, the failure message includes information related to the radio link failure.

[0082] In some embodiments, the failure message is an RRC message, and the radio resource control RRC message is used to handle the radio link failure in CA, DC, or standalone operation with the help of the sidelink.

[0083] In some embodiments, the failure message includes an indication of a failure condition, the indication directly or indirectly indicating one or more conditions that caused the radio link failure.

[0084] In some embodiments, the failure message includes one or more recent measurements made by the first wireless device related to the first radio link.

[0085] In some embodiments, a UE including a processor is configured to execute a method as described in any one of the above embodiments.

[0086] In some embodiments, a method for handling a radio link failure is performed by a first base station, the method comprising: receiving a failure message from a second wireless device, the failure message being related to a radio link failure at the first wireless device of a first radio link between the first wireless device and a radio access network of a cellular communication system; and any one of: sending a response to the second wireless device; or the first wireless device sending a response; or sending the failure message, a response to the failure message, an indication to trigger a specific process, or a request for a specific process to the second base station.

[0087] In some embodiments, the method further comprises performing a radio access procedure to establish a second radio link between the second wireless device and the first base station. In some embodiments, the radio access procedure is a random access procedure.

[0088] In some embodiments, the response is an RRC message that triggers a specific RRC procedure.

[0089] In some embodiments, the fault message is a FailureInformation message.

[0090] In some embodiments, the failure message is a MCGFailureInformation message or a SCGFailureInformation message. In some embodiments, the failure message includes a wireless device context of the first wireless device. In some embodiments, the failure message includes information related to the radio link failure.

[0091] In some embodiments, the failure message is an RRC message, and the radio resource control RRC message is used to handle radio link failure in CA, DC, or standalone operation with the help of a sidelink.

[0092] In some embodiments, the failure message includes an indication of a failure condition, the indication directly or indirectly indicating one or more conditions that caused the radio link failure.

[0093] In some embodiments, the fault message includes one or more recent measurements made by the first wireless device.

[0094] In some embodiments, a radio access node comprises a processor configured to execute the method as described in any one of the above embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0095] The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0096] Figure 1 Different ways to deploy a fifth generation (5G) New Radio (NR) network with or without interworking with Long Term Evolution (LTE) radio access (also known as Evolved Universal Terrestrial Radio Access (E-UTRA)) and Evolved Packet Core (EPC) are shown.

[0097] Figure 2 A schematic control plane architecture of dual connectivity (DC) in LTE DC and a control plane architecture of Evolved Universal Terrestrial Radio Access Network (E-UTRAN) NR DC (EN-DC) are shown.

[0098] Figure 3 Network-side protocol termination options for a Master Cell Group (MCG), a Secondary Cell Group (SCG), and split bearers in a Multi-Radio DC (MR-DC) (EN-DC) with EPC are shown.

[0099] Figure 4 The network architecture of the control plane (CP) in EN-DC is shown.

[0100] Figure 5 A Cellular Intelligent Transmission System (ITS) (C-ITS) environment is shown.

[0101] Figure 6 A radio link failure (RLF) due to a physical layer problem is shown.

[0102] Figure 7 An NR sidelink (SL) unicast link between a pair of user equipment (UE) is shown.

[0103] Figure 8 Shows Figure 7 Link release procedure for NR SL unicast link.

[0104] Fig. 9 An example of a cellular communication system is shown in which embodiments of the present disclosure may be implemented.

[0105] Fig. 10A and Fig. 10B shows at least some aspects of at least some of the embodiments described herein Fig. 9 operation of a cellular communication system.

[0106] Fig.11 is a schematic block diagram of a radio access node according to some embodiments of the present disclosure.

[0107] Fig.12 is a schematic block diagram illustrating a virtualized embodiment of a radio access node according to some embodiments of the present disclosure.

[0108] Fig.13 is a schematic block diagram of a radio access node according to some other embodiments of the present disclosure.

[0109] Fig.14 is a schematic block diagram of a UE according to some embodiments of the present disclosure.

[0110] Fig.15 is a schematic block diagram of a UE according to some other embodiments of the present disclosure. DETAILED DESCRIPTION

[0111] The embodiment of setting forth below represents the information for enabling those skilled in the art to practice the embodiment, and shows the best mode of practicing the embodiment. When reading the following description according to the accompanying drawings, those skilled in the art will understand the concept of the present disclosure and will recognize the application of these concepts that are not specifically addressed herein. It should be understood that these concepts and applications fall within the scope of the present disclosure.

[0112] Radio node: As used herein, a "radio node" is a radio access node or a wireless device.

[0113] Radio access node: As used herein, a "radio access node" or "radio network node" is any node in a radio access network (RAN) of a cellular communication network that operates to transmit and / or receive signals wirelessly. Some examples of radio access nodes include, but are not limited to, base stations (e.g., NR base stations (gNBs) in a 3rd Generation Partnership Project (3GPP) 5th Generation (5G) New Radio (NR) network or enhanced or evolved Node Bs (eNBs) in a 3GPP Long Term Evolution (LTE) network), high power or macro base stations, low power base stations (e.g., micro base stations, pico base stations, home eNBs, or the like), and relay nodes.

[0114] Core network node: As used herein, a "core network node" is any type of node in a core network (CN) or any node that implements a CN function. Some examples of CN nodes include, for example, a mobility management entity (MME), a packet data network gateway (P-GW), a service capability exposure function (SCEF), a home subscriber server (HSS), etc. Some other examples of CN nodes include nodes that implement an access and mobility function (AMF), a user plane (UP) function (UPF), a session management function (SMF), an authentication server function (AUSF), a network slice selection function (NSSF), a network exposure function (NEF), a network function (NF) repository function (NRF), a policy control function (PCF), a unified data management (UDM), etc.

[0115] Wireless Device: As used herein, a "wireless device" is any type of device that has access to (i.e., is served by) a cellular communication network by wirelessly transmitting and / or receiving signals to (one or more) radio access nodes. Some examples of wireless devices include, but are not limited to, user equipment devices (UEs) and machine type communication (MTC) devices in 3GPP networks.

[0116] Sidelink wireless device: As used herein, a "sidelink wireless device," "sidelink-capable wireless device," "sidelink UE," or "sidelink-capable UE" is a wireless device or UE capable of sidelink (SL) communications.

[0117] Network node: As used herein, a "network node" is any node that is part of the CN or RAN of a cellular communication network / system.

[0118] Note that the description given herein focuses on 3GPP cellular communication systems, and as such, 3GPP terminology or terminology similar to 3GPP terminology is often used. However, the concepts disclosed herein are not limited to 3GPP systems.

[0119] Note that in the description of this document, reference may be made to the term "cell"; however, particularly with respect to 5G NR concepts, beams may be used instead of cells, and therefore it is important to note that the concepts described herein are equally applicable to both cells and beams.

[0120] Radio link failure (RLF) recovery via SL is provided. Disclosed herein are systems and methods for avoiding a UE from triggering a radio resource control (RRC) reestablishment procedure upon RLF, thereby avoiding unnecessary signaling overhead and connectivity disruption. In some embodiments, a UE (UE1) communicates with another UE (UE2) via SL, and UE1 detects RLF via a radio link (e.g., a Uu radio link with a base station). Upon detecting RLF, UE1 sends a fault message to UE2 via a SL channel identifying the detected RLF. In some embodiments, the fault message includes additional information, such as UE1 context and UE1 related information (e.g., measurements that UE1 has performed, fault type, UE identity, and / or service frequency), or other information that helps the network understand what conditions caused the fault. Upon receiving the fault message from UE1, UE2 forwards the message to the network via an available Uu link between UE2 and the network (e.g., an associated base station). In some embodiments, before sending the fault message to the network, if no Uu radio link is available and active (i.e., UE2 is operating in SL mode 2), UE2 performs a random access procedure to a selected cell.

[0121] In some embodiments, RLF recovery is provided through SL in carrier aggregation (CA). When RLF on the primary cell PCell is detected, if the UE (UE1) is involved in SL operation with another UE (UE2), UE1 sends a FailureInformation message to UE2, and if there is a Uu link between UE2 and the network, UE2 forwards the FailureInformation message to the network. If there is no Uu link between UE2 and the network, UE2 performs random access through the network before sending the FailureInformation message (i.e., if the random access procedure is successful).

[0122] In some other embodiments, RLF recovery is provided by activating a dual connectivity (DC) replicated SL. When the UE detects an RLF on a master cell group (MCG) (or a secondary cell group (SCG)) and no available Uu link toward the network is available (i.e., Uu link failure on the MCG and SCG), if the UE (UE1) is involved in SL operation with another UE (UE2), UE1 sends a MCGFailureInformation (i.e., for RLF detected on the MCG) or SCGFailureInformation (i.e., for RLF detected on the SCG) message to UE2, and if there is a Uu link between UE2 and the network, UE2 forwards the message to the network (i.e., to the MCG or SCG). If there is no Uu link between UE2 and the network, UE2 performs random access through the network (i.e., on the MCG or SCG) before sending the FailureInformation message (i.e., if the random access procedure is successful).

[0123] Certain embodiments may provide one or more of the following technical advantages. For example, in the case of DC and CA duplication, the systems and methods disclosed herein avoid the UE triggering the RRC reestablishment process when RLF is detected. As a result, unnecessary signaling overhead and connectivity interruption caused by the RRC reestablishment process are avoided.

[0124] As another example, when RLF is detected on the PCell or when the UE detecting RLF has no Uu link available to the network, an embodiment of the present disclosure avoids the RRC reestablishment process by allowing a failure report to be sent to the network via the SL UE (if SL operation is ongoing). In this way, the UE is not forced to trigger the RRC reestablishment process, and once notified of the RLF, the network can decide to take action to avoid connectivity interruption.

[0125] At this point, Fig. 9An example of a cellular communication system 900 in which embodiments of the present disclosure may be implemented is shown. In the embodiments described herein, the cellular communication system 900 is, for example, a 5G system (5GS) including an NR RAN or an evolved packet system (EPS) including an LTE RAN. In this example, the RAN includes base stations 902-1 and 902-2, which are referred to as eNBs in LTE and gNBs or next generation RAN (NG-RAN) nodes in 5G NR, and the base stations 902-1 and 902-2 control corresponding (macro) cells 904-1 and 904-2. The base stations 902-1 and 902-2 are generally referred to as base stations 902 herein, and are individually referred to as base stations 902. Similarly, the (macro) cells 904-1 and 904-2 are generally referred to as (macro) cells 904 herein, and are individually referred to as (macro) cells 904. The RAN may also include a plurality of low power nodes 906-1 to 906-4 that control corresponding small cells 908-1 to 908-4. The low power nodes 906-1 to 906-4 may be small base stations (such as pico or femto base stations) or remote radio heads (RRHs) or the like. It is noteworthy that, although not shown, one or more of the small cells 908-1 to 908-4 may alternatively be provided by the base station 902. The low power nodes 906-1 to 906-4 are generally referred to as low power nodes 906 herein, and are individually referred to as low power nodes 906. Similarly, the small cells 908-1 to 908-4 are generally referred to as small cells 908 herein, and are individually referred to as small cells 908. The cellular communication system 900 also includes a core network 910. The base station 902 (and optionally the low power node 906) is connected to the core system 910.

[0126] Base station 902 and low power node 906 provide services to wireless devices 912-1 through 912-5 in corresponding cells 904 and 908. Wireless devices 912-1 through 912-5 are generally referred to herein as wireless devices 912, and individually as wireless devices 912. Wireless devices 912 are also sometimes referred to herein as UEs.

[0127] In the embodiments described herein, at least some of the UEs 912 have SLs with other UEs 912. For example, Fig. 9 A SL between UE 912-1 and UE 912-3 and another SL between UE 912-4 and UE 912-5 are shown.In addition, at least some of the UEs 912 are within the coverage of the RAN and have a cellular link, also referred to herein as a radio link, such as, for example, a Uu link.

[0128] Now, a description of some example embodiments of the present disclosure will be provided. Note that the following embodiments are described for NR, but they can be applied to LTE or any other radio access technology (RAT). In addition, the proposed methods and solutions work independently of the core network used (Evolved Packet Core (EPC) or 5G CN (5GCN)) and the multi-radio dual connectivity (DC) (MR-DC) architecture options considered (Evolved Universal Terrestrial Radio Access Network (E-UTRAN) NR DC (EN-DC), NR Evolved Universal Terrestrial Radio Access (E-UTRA) DC (NE-DC), NG-RAN E-UTRA NR DC (NGEN-DC), or NR-DC).

[0129] When MR-DC operation is configured, SL transmissions between two (or more) UEs may be fully controlled by the network (i.e., SL Mode 1 transmissions), or may operate autonomously without network assistance (i.e., SL Mode 2 transmissions). Note that the latter case does not imply that all SL UEs involved in the transmission are out-of-coverage (by operating in SL Mode 1, one or more UEs may still be in network coverage).

[0130] The scenario targeted herein is when a UE (ie, hereinafter referred to as UE1) performs normal Uu operation with the network and simultaneously has ongoing SL operation with another UE (ie, hereinafter referred to as UE2). Fig. 9 , UE1 and UE2 may be UE 912-1 or UE 912-3 connected via SL, or UE1 and UE2 may be UE 912-4 or UE 912-5 connected via SL. In addition, UE2 is in the coverage of a cell, even though it does not necessarily involve any Uu operation with (one or more) cells (UE2 is in its coverage). The terms "UE1" and "UE2" are used interchangeably throughout this document.

[0131] In one embodiment, the triggers for RLF are the same as defined in 3GPP Technical Specification (TS) 38.331 V15.6.0 Section 5.3.10.3 "Detection of radio link failure". These include RLF detected when the maximum number of RLC retransmissions is reached. Alternatively, RLF is detected if the measured reference signal received power (RSRP) is too low (given a relevant threshold) or when the physical downlink control channel (PDCCH) / physical downlink shared channel (PDSCH) fails to be decoded due to low power signal quality (e.g., low RSRP, reference signal received quality (RSRQ)). In addition, RLF is detected when N out-of-coverage indications are received from lower layers in a manner similar to the RLF / Radio Link Management (RLM) process in LTE, or when an indication is received from the Medium Access Control (MAC) that random access has failed.

[0132] In another embodiment, upon detecting RLF on the Uu radio link, UE1 sends a failure message to UE2 via the SL channel (i.e., if no Uu radio link to the network is available), wherein the failure message is about the RLF detected on the Uu link. In one embodiment, the failure message is a FailureInformation message (e.g., in the case of carrier aggregation (CA) duplication). However, in another embodiment, the failure message is a MCGFailureInformation or SCGFailureInformation message (e.g., in the case of DC duplication). In an alternative embodiment, the failure message is a new RRC message for handling RLF in CA, DC or standalone operation with the help of SL.

[0133] In one embodiment, a FailureInformation, MCGFailureInformation, or SCGFailureInformation message sent by UE1 to UE2 is enhanced by including UE1 context and (e.g., all) UE1 related information (e.g., measurements that UE1 has performed, fault type, UE identity, and / or service frequency). In another embodiment, a FailureInformation, MCGFailureInformation, or SCGFailureInformation message sent by UE1 to UE2 is enhanced by including a fault condition that helps the network understand what conditions caused the failure. However, in another embodiment, a FailureInformation, MCGFailureInformation, or SCGFailureInformation message sent by UE1 to UE2 is enhanced by including some or all of the latest available UE1 measurements.

[0134] In one embodiment, upon receiving a failure message from UE1, UE2 forwards the message to the network via an available Uu link between UE2 and the network (e.g., an associated base station 902 or a low power node 906). In another embodiment, before sending the failure message to the network, if no Uu radio link is available and active (i.e., UE2 operates in SL mode 2), UE2 performs a random access procedure to the selected cell. Specifically, if UE2 has been allocated a contention-free random access resource, UE2 performs a contention-free random access procedure. If UE2 has not been allocated a contention-free resource, UE2 performs a contention-based random access procedure.

[0135] In one embodiment, in case of MR-DC, UE2 forwards the fault message to MCG via SRB1. Furthermore, in case of MR-DC, in another embodiment, UE2 forwards the fault message to SCG via SRB3. Alternatively, in case of MR-DC, in one embodiment, UE2 forwards the fault message to SCG embedded in the MCG RRC message via SRB1. In another embodiment, in case of MR-DC, UE2 forwards the fault message to the network via a split signaling radio bearer (SRB).

[0136] In one embodiment, if CA replication is enabled between UE2 and the network, UE2 forwards the fault message to the network via PCell. In another embodiment, if CA replication is enabled between UE2 and the network, UE2 forwards the fault message to the network via primary secondary cell (PSCell). However, in another embodiment, if CA replication is enabled between UE2 and the network, UE2 forwards the fault message to the network via one (or more) secondary cells (SCells).

[0137] In another embodiment, upon receiving the failure message from UE2, the network generates an RRC message according to the determined RRC procedure and sends the generated RRC message to UE2. In one embodiment, upon receiving the failure message from UE2, the network generates an RRC message according to the determined RRC procedure and sends the generated RRC message to UE1 (if it is reachable). Here, the RRC signaling message may simply be an RRC reconfiguration message.

[0138] In another embodiment, if MR-DC is enabled, upon receiving a fault message, the master node (MN) sends an RRC message to the secondary node (SN) via an inter-node RRC message, and the secondary node (SN) forwards such message to UE1 (or UE2) via SRB3. In one embodiment, if MR-DC is enabled, upon receiving a fault message, the SN sends an RRC message to UE1 (or UE2) via SRB3. However, in another embodiment, if MR-DC is enabled, upon receiving a fault message, the SN sends an RRC message to the MN via an inter-node RRC message, and the MN forwards such message to UE1 (or UE2) via SRB1. In one embodiment, if MR-DC is enabled, upon receiving a fault message, the MN sends an RRC message to UE1 (or UE2) via SRB1.

[0139] However, in another embodiment, if MR-DC is enabled, upon receiving a failure message, the MN sends an indication to the SN by requesting to perform a specific RRC procedure (e.g., handover, reconfiguration, or reconstruction). In another embodiment, if MR-DC is enabled, upon receiving a failure message, the MN forwards such message to the SN (i.e., via an inter-node RRC message), and the SN decides on its own what action to perform.

[0140] In one embodiment, upon receiving an RRC message from the network, UE2 forwards the message to UE1 via the SL. In addition, in another embodiment, upon receiving an RRC message from UE2, UE1 performs a process triggered by the RRC message. Alternatively, in one embodiment, upon receiving an RRC message from the network, UE1 performs a process triggered by the RRC message.

[0141] Fig. 10A and Fig. 10B shows at least some aspects of at least some of the above-described embodiments. Fig. 9 Operation of a cellular communication system 900 of the present invention. Note that optional steps are represented by dashed lines or dashed boxes. In this example, SL exists between two UEs 912, which are represented here as UE1 912-1 and UE2 912-2. UE1 912-1 detects RLF of a cellular link (e.g., Uu link) between UE1 912-1 and the RAN of the cellular communication system 900 (step 1000). As described above, in one embodiment, UE1 912-1 detects RLF based on any one of a plurality of predefined triggers for RLF. In one embodiment, the predefined triggers for RLF are the same as those defined in Section 5.3.10.3 “Detection of radio link failure” of 3GPP TS 38.331 V15.6.0. These include RLF detected when the maximum number of radio link control (RLC) retransmissions is reached. Alternatively, RLF is detected if the measured RSRP is too low (given a relevant threshold) or when PDCCH / PDSCH cannot be decoded due to low power signal quality (e.g., low RSRP, RSRQ). In addition, RLF is detected when N out-of-coverage indications are received from lower layers in a manner similar to the RLF / RLM procedure in LTE, or when an indication is received from the MAC that random access has failed.

[0142] Upon detecting an RLF, UE1 912-1 sends a fault message to UE2 912-2 via the SL between UE1 912-1 and UE2 912-2 (step 1002). As described above, in one embodiment, upon detecting an RLF on a cellular radio link (e.g., no Uu radio link), UE1 912-1 sends a fault message to UE2 912-2 via the SL channel (e.g., if no Uu radio link to the network is available). The fault message is about the RLF detected on the cellular link (e.g., Uu radio link). As described above, in one embodiment, the fault message is a FailureInformation message (e.g., in the case of CA duplication). However, in another embodiment, the fault message is a MCGFailureInformation or SCGFailureInformation message (e.g., in the case of DC duplication). In an alternative embodiment, the fault message is a new RRC message for handling RLF in CA, DC, or standalone operation with the help of SL.

[0143] In one embodiment, the failure message is a FailureInformation, MCGFailureInformation, or SCGFailureInformation message, and the FailureInformation, MCGFailureInformation, or SCGFailureInformation message sent by UE1 912-1 to UE2 912-2 is enhanced by including the UE1 context and (e.g., all) UE1 related information. In another embodiment, the FailureInformation, MCGFailureInformation, or SCGFailureInformation message sent by UE1 912-1 to UE2 912-2 is enhanced by including a failure condition that helps the network understand what conditions caused the failure. However, in another embodiment, the FailureInformation, MCGFailureInformation, or SCGFailureInformation message sent by UE1 912-1 to UE2 912-2 is enhanced by including some or all of the latest available UE1 measurements.

[0144] Upon receiving the failure message from UE1 912-1, UE2 912-2 optionally performs a random access procedure to establish a cellular radio link (e.g., a Uu radio link) to the network (step 1004). Note that if UE2 912-2 already has an existing cellular radio link (e.g., a Uu radio link), step 1004 may not be performed. More specifically, before sending the failure message to the network, if no Uu radio link is available and active (i.e., UE2 912-2 operates in SL mode 2), UE2 912-2 performs a random access procedure to the selected cell. Specifically, if UE2 912-2 has been allocated a contention-free random access resource, UE2 912-2 performs a contention-free random access procedure. If UE2 912-2 has not been allocated a contention-free random access resource, U2E performs a contention-based random access procedure. In this example, UE2 912-2 already has a cellular radio link to the base station 902 (here represented as BS1 902-1) or establishes a cellular radio link to BS1 902-1 via a random access procedure.

[0145] UE2 912-2 sends a fault message to the network via a cellular radio link (e.g., via a Uu radio link) (step 1006). As described above, in one embodiment, in the case of MR-DC, UE2 912-2 forwards the fault message to MCG via SRB1 (i.e., forwards the fault message to the base station 902 serving MCG via SRB1, in this example, the base station 902 is BS1 902-1). In addition, in the case of MR-DC, in another embodiment, UE2 912-2 forwards the fault message to SCG via SRB3 (i.e., forwards the fault message to the base station 902 serving SCG via SRB3, in this example, the base station 902 is BS1902-1). Alternatively, in the case of MR-DC, in one embodiment, UE2 912-2 forwards the fault message to the SCG embedded in the MCG RRC message via SRB1 (i.e., the fault message is forwarded to the base station 902 serving the SCG embedded in the MCG RRC message via SRB1, in this example, the base station 902 is BS1 902-1). In another embodiment, in the case of MR-DC, UE2 912-2 forwards the fault message to the network (e.g., BS1 902-1) via a split SRB.

[0146] In one embodiment, if CA replication is enabled between UE2 912-2 and the network, UE2 912-2 forwards the fault message to the network via the PCell (which is served by BS1 902-1 in this example). In another embodiment, if CA replication is enabled between UE2 912-2 and the network, UE2 912-2 forwards the fault message to the network via the PSCell (which is served by BS1 902-1 in this example). However, in another embodiment, if CA replication is enabled between UE2 912-2 and the network, UE2 912-2 forwards the fault message to the network via one (or more) SCells (which are served by BS1 902-1 in this example).

[0147] Once a fault message is sent from UE2 912-2 to BS1 902-1, multiple alternative solutions are proposed. In the first alternative solution (ALT#1), upon receiving the fault message from UE2 912-2, BS1 902-1 generates a response and sends the response to UE2 912-2 (step 1008). As described above, in some embodiments, the response is an RRC message for the RRC process that BS1 902-1 has decided to perform in response to the fault message. UE2 912-2 forwards the response to UE1 912-1 (step 1010). Upon receiving the response, UE1 912-1 performs one or more actions according to the response (step 1012). For example, if the response is an RRC message for a specific RRC process, UE1 912-1 continues the specific RRC process. Here, the RRC signaling message can be, for example, an RRC reconfiguration message, so that the RRC process is an RRC reconfiguration process.

[0148] In the second alternative solution (ALT#2), upon receiving the failure message from UE2 912-2, if UE1 912-1 is reachable, BS1 902-1 generates a response and sends the response to UE1 912-1 (step 1014). As described above, the response is an RRC message according to the RRC process that BS1 902-1 has decided to perform in response to the failure message. Upon receiving the response, UE1 912-1 performs one or more actions according to the response (step 1016). For example, if the response is an RRC message for a specific RRC process, UE1 912-1 continues the specific RRC process. Here, the RRC signaling message can be, for example, an RRC reconfiguration message, so that the RRC process is an RRC reconfiguration process.

[0149] In the third alternative solution (ALT#3), upon receiving the failure message from UE2 912-2, BS1 902-1 sends a failure message, a response generated to the failure message, or an indication or request for a specific RRC process to another base station 902 (represented here as BS2 902-2) (step 1018). Then, BS2 902-2 generates a response and sends the response to UE2 912-2 directly or via BS1902-1 (step 1020). UE2 912-2 forwards the response to UE1 912-1 (step 1022). Upon receiving the response, UE1 912-1 performs one or more actions according to the response (step 1024). For example, if the response is an RRC message for a specific RRC process, UE1 912-1 continues the specific RRC process.

[0150] In the fourth alternative solution (ALT#4), upon receiving the failure message from UE2 912-2, BS1 902-1 sends a failure message, a response generated to the failure message, or an indication or request for a specific RRC process to another base station 902 (represented here as BS2 902-2) (step 1026). Then, BS2 902-2 generates a response and sends the response to UE1 912-1 directly or via BS1902-1 (step 1028). Upon receiving the response, UE1 912-1 performs one or more actions according to the response (step 1030). For example, if the response is an RRC message for a specific RRC process, UE1 912-1 continues the specific RRC process.

[0151] As described above, in one embodiment, if MR-DC is enabled, when a fault message is received at the MN (BS1 902-1 in this example), the MN sends an RRC message to the SN (BS2 902-2 in this example) via an inter-node RRC message, and the SN forwards such message to UE1 912-1 (ALT#4) or UE2 912-2 (ALT#3) via SRB3. In another embodiment, if MR-DC is enabled, when a fault message is received at the SN (BS1 902-1 in this example), the SN sends an RRC message that triggers the desired RRC process to UE1 912-1 (ALT#2) or UE2 912-2 (ALT#1) via SRB3. However, in another embodiment, if MR-DC is enabled, when a fault message is received at the SN (BS1 902-1 in this example), the SN sends an RRC message that triggers the desired RRC process to the MN (BS2 902-2 in this example) via an inter-node RRC message, and the MN forwards the RRC message to UE1 912-1 (ALT#4) or UE2 912-2 (ALT#3) via SRB1. In one embodiment, if MR-DC is enabled, when a fault message is received at the MN (BS1 902-1 in this example), the MN sends an RRC message for the desired RRC process to UE1 912-1 (ALT#2) or UE2 912-2 (ALT#1) via SRB1.

[0152] However, in another embodiment, if MR-DC is enabled, when a fault message is received at the MN (BS1 902-1 in this example), the MN sends an indication to the SN (BS2 902-2 in this example) by requesting to perform a specific RRC process (e.g., handover, reconfiguration, or reconstruction). In another embodiment, if MR-DC is enabled, when a fault message is received at the MN (BS1 902-1 in this example), the MN forwards such message to the SN (BS2 902-2 in this example), for example, via an inter-node RRC message, and the SN decides by itself what action to perform.

[0153] In one embodiment, upon receiving the RRC message from the network, UE2 912-2 forwards the message to UE1 912-1 via the SL between UE1 912-1 and UE2 912-2. In addition, in another embodiment, upon receiving the RRC message from UE2 912-2, UE1 912-1 performs a process triggered by the RRC message. Alternatively, in one embodiment, upon receiving the RRC message from the network, UE1 912-1 performs a process triggered by the RRC message.

[0154] Fig.11 1 is a schematic block diagram of a radio access node 1100 according to some embodiments of the present disclosure. The radio access node 1100 may be, for example, a base station 902 or 906. As shown, the radio access node 1100 includes a control system 1102, the control system 1102 including one or more processors 1104 (e.g., a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and / or the like), a memory 1106, and a network interface 1108. The one or more processors 1104 are also referred to herein as processing circuits. In addition, the radio access node 1100 includes one or more radio units 1110, each of which includes one or more transmitters 1112 and one or more receivers 1114 coupled to one or more antennas 1116. The radio unit 1110 may be referred to as or be part of a radio interface circuit. In some embodiments, the radio unit(s) 1110 is external to the control system 1102 and is connected to the control system 1102 via, for example, a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) 1110 and potentially also the antenna(s) 1116 are integrated with the control system 1102. The one or more processors 1104 operate to provide one or more functions of the radio access node 1100 as described herein (e.g., as described above with respect to Fig. 10A and Fig. 10BIn some embodiments, the function(s) are implemented using software, which is stored in the memory 1106 and executed by the one or more processors 1104, for example.

[0155] Fig.12 1 is a schematic block diagram illustrating a virtualized embodiment of a radio access node 1100 according to some embodiments of the present disclosure. This discussion is equally applicable to other types of network nodes. In addition, other types of network nodes may have similar virtualized architectures.

[0156] As used herein, a "virtualized" radio access node is an implementation of a radio access node 1100 in which at least a portion of the functionality of the radio access node 1100 is implemented as virtual component(s) (e.g., via virtual machine(s) executing on physical processing node(s) in network(s)). As shown, in this example, the radio access node 1100 includes a control system 1102 (which includes one or more processors 1104 (e.g., CPU, ASIC, FPGA, etc.)), a memory 1106, a network interface 1108, and one or more radio units 1110, each of which includes one or more transmitters 1112 and one or more receivers 1114 coupled to one or more antennas 1116, as described above. The control system 1102 is connected to the radio unit(s) 1110 via, for example, an optical cable or the like. The control system 1102 is connected to one or more processing nodes 1200 via the network interface 1108, which are coupled to or included as part of the network(s) 1202. Each processing node 1200 includes one or more processors 1204 (eg, CPUs, ASICs, FPGAs, and / or the like), memory 1206 , and a network interface 1208 .

[0157] In this example, the functionality 1210 of the radio access node 1100 described herein (eg, as described above with respect to Fig. 10A and Fig. 10BThe described one or more functions of BS1 902-1 or BS2 902-2) are distributed across or implemented at the control system 1102 and the one or more processing nodes 1200 in any desired manner. In some specific embodiments, some or all of the functions 1210 of the radio access node 1100 described herein are implemented as virtual components executed by one or more virtual machines, which are implemented in (one or more) virtual environments hosted by (one or more) processing nodes 1200. As will be appreciated by those of ordinary skill in the art, additional signaling or communication between (one or more) processing nodes 1200 and the control system 1102 is used in order to implement at least some of the desired functions 1210. It is worth noting that in some embodiments, the control system 1102 may not be included, in which case the (one or more) radio units 1110 communicate directly with the (one or more) processing nodes 1200 via (one or more) appropriate network interfaces.

[0158] In some embodiments, a computer program comprising instructions is provided, which, when executed by at least one processor, causes the at least one processor to implement the functionality of a radio access node 1100 according to any embodiment described herein or a node (e.g., processing node 1200) that implements one or more functions 1210 of the radio access node 1100 in a virtual environment. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of the following: 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).

[0159] Fig.13 1 is a schematic block diagram of a radio access node 1100 according to some other embodiments of the present disclosure. The radio access node 1100 includes one or more modules 1300, each of which is implemented in software. The module(s) 1300 provide the functionality of the radio access node 1100 described herein (e.g., the above description of the Fig. 10A and Fig. 10B This discussion is equally applicable to one or more functions of BS1 902-1 or BS2 902-2 described herein. Fig.12 1200, wherein module 1300 may be implemented at one of processing nodes 1200, or distributed across multiple processing nodes 1200, and / or distributed across (one or more) processing nodes 1200 and control system 1102.

[0160] Fig.141400 is a schematic block diagram of a UE 1400 according to some embodiments of the present disclosure. As shown, the UE 1400 includes one or more processors 1402 (e.g., CPU, ASIC, FPGA, and / or the like), a memory 1404, and one or more transceivers 1406, each transceiver 1406 including one or more transmitters 1408 and one or more receivers 1410 coupled to one or more antennas 1412. As will be appreciated by those skilled in the art, the (one or more) transceiver 1406 includes a radio front-end circuit connected to the (one or more) antennas 1412, the radio front-end circuit being configured to condition signals transmitted between the (one or more) antennas 1412 and the (one or more) processors 1402. The processor 1402 is also referred to herein as a processing circuit. The transceiver 1406 is also referred to herein as a radio circuit. In some embodiments, the functionality of the UE 1400 described above (e.g., the above with respect to Fig. 10A and Fig. 10B One or more functions of the described UE1 912-1 or UE2 912-2) may be implemented in whole or in part using software, which is stored in the memory 1404 and executed by the processor(s) 1402, for example. Note that the UE 1400 may include Fig.14 Additional components not shown in the figure, such as, for example, one or more user interface components (e.g., including a display, buttons, a touch screen, a microphone, (one or more) speakers, and / or input / output interfaces such as the like, and / or any other components for allowing information to be input into UE 1400 and / or allowing information to be output from UE 1400), a power supply (e.g., a battery and associated power circuits), etc.

[0161] In some embodiments, a computer program is provided comprising instructions that, when executed by at least one processor, cause the at least one processor to implement the functionality of the UE 1400 according to any embodiment described herein (e.g., the above description of the Fig. 10A and Fig. 10B In some embodiments, a carrier including the aforementioned computer program product is provided. The carrier is one of the following: 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).

[0162] Fig.151 is a schematic block diagram of a UE 1400 according to some other embodiments of the present disclosure. The UE 1400 includes one or more modules 1500, each of which is implemented using software. The (one or more) modules 1500 provide the functionality of the UE 1400 described herein (e.g., the above description of Fig. 10A and Fig. 10B One or more functions of UE1 912-1 or UE2 912-2 described).

[0163] Any suitable steps, methods, features, functions or benefits disclosed herein may be performed by one or more functional units or modules of one or more virtual devices. Each virtual device may include a plurality of these functional units. These functional units may be implemented via a processing circuit, which may include one or more microprocessors or microcontrollers and other digital hardware, which may include a digital signal processor (DSP), dedicated digital logic, etc. The processing circuit may be configured to execute program codes stored in a memory, which may include one or more types of memory, such as a read-only memory (ROM), a random access memory (RAM), a cache memory, a flash memory device, an optical storage device, etc. The program code stored in the memory includes program instructions for executing one or more telecommunications and / or data communication protocols and instructions for executing one or more of the technologies described herein. In some implementations, the processing circuit may be used to cause the corresponding functional unit to perform the corresponding function according to one or more embodiments of the present disclosure.

[0164] Although the processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform operations in a different order, combine certain operations, overlap certain operations, etc.).

[0165] In the following, some further exemplary embodiments are listed:

[0166] Embodiment 1: A method for detecting and handling a radio link failure in a cellular communication system, performed by a first wireless device, the method comprising: detecting (1000) a radio link failure of a radio link between the first wireless device and a radio access network of the cellular communication system; and sending (1002) a failure message to the second wireless device via a side link between the first wireless device and the second wireless device.

[0167] Embodiment 2: The method as described in Embodiment 1 also includes receiving (1010, 1022) a response from the second wireless device via the sidelink.

[0168] Embodiment 3: The method of embodiment 1 further comprises receiving (1014, 1028) a response from a radio access node in the radio access network via a radio link between the first wireless device and the radio access node.

[0169] Embodiment 4: A method as described in Embodiment 2 or 3, wherein the response is an RRC message that triggers a specific RRC process.

[0170] Embodiment 5: The method as described in any one of embodiments 2 to 4 further includes performing (1012, 1016, 1024, 1030) one or more actions according to the response.

[0171] Embodiment 6: A method as described in any one of Embodiments 1 to 5, wherein the fault message is a FailureInformation message.

[0172] Embodiment 7: The method as described in any one of Embodiments 1 to 5, wherein the fault message is a MCGFailureInformation message or a SCGFailureInformation message.

[0173] Embodiment 8: The method of embodiment 6 or 7, wherein the fault message includes a wireless device context of the first wireless device.

[0174] Embodiment 9: The method as described in Embodiment 6, 7, or 8, wherein the fault message includes information related to the radio link failure.

[0175] Embodiment 10: A method as described in any one of Embodiments 1 to 5, wherein the failure message is an RRC message, and the radio resource control RRC message is used to handle radio link failure in CA, DC, or independent operation with the help of a side link.

[0176] Embodiment 11: The method as described in any one of Embodiments 1 to 10, wherein the fault message includes an indication of the fault condition, and the indication directly or indirectly indicates one or more conditions that caused the radio link failure.

[0177] Embodiment 12: The method as described in any one of Embodiments 1 to 10, wherein the fault message includes one or more latest measurements performed by the first wireless device (for example, one or more latest measurements related to the radio link).

[0178] Embodiment 13: A method for handling a radio link failure at a first wireless device in a cellular communication system, performed by a second wireless device, the method comprising: receiving (1002) a fault message from the first wireless device via a side link between the first wireless device and the second wireless device, the fault message being related to a radio link failure at the first wireless device in a radio link between the first wireless device and a radio access network of the cellular communication system; and sending (1006) the fault message to a radio access node in the radio access network of the cellular communication system via a radio link between the second wireless device and the radio access node.

[0179] Embodiment 14: The method of Embodiment 13 further includes performing (1004) a radio access procedure to establish the radio link between the second wireless device and the radio access node.

[0180] Embodiment 15: The method of embodiment 13 or 14 further comprises: receiving (1008) a response from the radio access node; and sending (1010) the response to the first wireless device via the sidelink.

[0181] Embodiment 16: The method of Embodiment 13 or 14 further comprises: receiving (1008) a response from a second radio access node; and sending (1010) the response to the first wireless device via the sidelink.

[0182] Embodiment 17: The method as described in Embodiment 15 or 16, wherein the response is an RRC message that triggers a specific RRC process.

[0183] Embodiment 18: A method as described in any one of Embodiments 13 to 17, wherein the fault message is a FailureInformation message.

[0184] Embodiment 19: A method as described in any one of Embodiments 13 to 17, wherein the fault message is a MCGFailureInformation message or a SCGFailureInformation message.

[0185] Embodiment 20: The method of Embodiment 18 or 19, wherein the fault message includes a wireless device context of the first wireless device.

[0186] Embodiment 21: The method as described in Embodiment 18, 19, or 20, wherein the fault message includes information related to the radio link failure.

[0187] Embodiment 22: A method as described in any one of Embodiments 13 to 17, wherein the failure message is an RRC message, and the radio resource control RRC message is used to handle radio link failure in CA, DC, or independent operation with the help of a side link.

[0188] Embodiment 23: The method as described in any one of Embodiments 13 to 22, wherein the fault message includes an indication of the fault condition, and the indication directly or indirectly indicates one or more conditions that caused the radio link failure.

[0189] Embodiment 24: A method as described in any one of Embodiments 13 to 23, wherein the fault message includes one or more latest measurements made by the first wireless device (e.g., one or more latest measurements related to the radio link).

[0190] Embodiment 25: A method for handling a radio link failure performed by a base station, the method comprising: receiving (1006) a fault message from a second wireless device, the fault message being related to a radio link failure at a first wireless device of a radio link between the first wireless device and a radio access network of a cellular communication system; and any of the following: sending (1008) a response to the second wireless device; or sending (1014) a response to the first wireless device; or sending (1018, 1026) the fault message, a response to the fault message, an indication of triggering a specific process (e.g., a specific RRC process), or a request for a specific process (e.g., a specific RRC process) to a second base station.

[0191] Embodiment 26: The method as described in Embodiment 25, wherein the response is an RRC message that triggers a specific RRC process.

[0192] Embodiment 27: A method as described in any one of Embodiments 25 or 26, wherein the fault message is a FailureInformation message.

[0193] Embodiment 28: A method as described in any one of Embodiments 25 or 26, wherein the fault message is a MCGFailureInformation message or a SCGFailureInformation message.

[0194] Embodiment 29: The method of Embodiment 27 or 28, wherein the fault message includes a wireless device context of the first wireless device.

[0195] Embodiment 30: The method as described in Embodiment 27, 28, or 29, wherein the fault message includes information related to the radio link failure.

[0196] Embodiment 31: A method as described in any one of Embodiments 25 or 26, wherein the failure message is an RRC message, and the radio resource control RRC message is used to handle radio link failure in CA, DC, or independent operation with the help of a side link.

[0197] Embodiment 32: The method as described in any one of Embodiments 25 to 31, wherein the fault message includes an indication of the fault condition, and the indication directly or indirectly indicates one or more conditions that caused the radio link failure.

[0198] Embodiment 33: A method as described in any one of Embodiments 25 to 32, wherein the fault message includes one or more latest measurements made by the first wireless device (e.g., one or more latest measurements related to the radio link).

[0199] Embodiment 34: A wireless device, comprising: a processing circuit, the processing circuit being configured to perform any one of the steps of any one of Group A embodiments; and a power supply circuit, the power supply circuit being configured to supply power to the wireless device.

[0200] Embodiment 35: A base station, comprising: a processing circuit, the processing circuit being configured to execute any one of the steps described in any one of Embodiments in Group B; and a power supply circuit, the power supply circuit being configured to supply power to the base station.

[0201] Embodiment 36: A UE, comprising: an antenna, the antenna being configured to send and receive wireless signals; a radio front-end circuit, the radio front-end circuit being connected to the antenna and to a processing circuit, and being configured to regulate signals transmitted between the antenna and the processing circuit; the processing circuit, the processing circuit being configured to perform any one of the steps described in any one of the embodiments in Group A; an input interface, the input interface being connected to the processing circuit, and being configured to allow information to be input into the UE for processing by the processing circuit; an output interface, the output interface being connected to the processing circuit, and being configured to output information that has been processed by the processing circuit from the UE; and a battery, the battery being connected to the processing circuit, and being configured to supply power to the UE.

[0202] At least some of the following abbreviations may be used in this disclosure:

[0203] 3GPP Third Generation Partnership Project

[0204] 5G fifth generation

[0205] 5GCN Fifth Generation Core Network

[0206] 5GS Fifth Generation System

[0207] ACK

[0208] AM confirmation mode

[0209] AMF access and mobility functions

[0210] ASIC Application-Specific Integrated Circuit

[0211] AUSF authentication server function

[0212] BSR Buffer Status Report

[0213] CA Carrier Aggregation

[0214] CBR Channel Busy Ratio

[0215] ·C-ITS Cellular Intelligent Transmission System

[0216] CN Core Network

[0217] CP Control Plane

[0218] CPU Central Processing Unit

[0219] D2D Device to Device

[0220] DC Dual Connectivity

[0221] DCI Downlink Control Information

[0222] DSP Digital Signal Processor

[0223] eNB Enhanced or evolved Node B

[0224] EN-DC Evolved Universal Terrestrial Radio Access Network New Radio Dual Connectivity

[0225] eLTE Enhanced Long Term Evolution

[0226] EPC Evolved Packet Core

[0227] EPS Evolved Packet System

[0228] E-UTRA Evolved Universal Terrestrial Radio Access

[0229] E-UTRAN Evolved Universal Terrestrial Radio Access Network

[0230] eV2X enhances transportation to everything

[0231] FPGA Field Programmable Gate Array

[0232] gNB new air interface base station

[0233] HARQ Hybrid Automatic Repeat Request

[0234] HSS Home Subscriber Server

[0235] ID

[0236] ITS Intelligent Transportation System

[0237] LTE Long Term Evolution

[0238] MAC Media Access Control

[0239] MC Multi-Connectivity

[0240] MCG Master Cell Group

[0241] MeNB Master enhanced or evolved Node B

[0242] MgNB main new air interface base station

[0243] MME Mobility Management Entity

[0244] MN Master Node

[0245] MR-DC multi-radio dual connectivity

[0246] MTC Machine Type Communication

[0247] NACK Negative Acknowledgement

[0248] NAS Non-Access Stratum

[0249] NE-DC New Radio Evolution Common Terrestrial Radio Access Dual Connectivity

[0250] NEF network open function

[0251] NF Network Function

[0252] NG-eNB Next Generation Enhanced or Evolved Node B

[0253] NGEN-DC Next Generation Radio Access Network Evolution Universal Terrestrial Radio Access New Air Interface Dual Connectivity

[0254] NG-RAN Next Generation Radio Access Network

[0255] NR New Radio

[0256] NRF Network Function Repository function

[0257] NSA is not independent

[0258] NSSF network slice selection function

[0259] OEM Original Equipment Manufacturer

[0260] PCell Primary Cell

[0261] PCF policy control function

[0262] PDCCH Physical Downlink Control Channel

[0263] PDSCH Physical Downlink Shared Channel

[0264] PDU Protocol Data Unit

[0265] P-GW Packet Data Network Gateway

[0266] PSCCH Physical Sidelink Control Channel

[0267] PSCell primary and secondary cells

[0268] PSSCH Physical Sidelink Shared Channel

[0269] QoS Quality of Service

[0270] RA resource allocation

[0271] RAM Random Access Memory

[0272] RAN Radio Access Network

[0273] RAT Radio Access Technology

[0274] Rel version

[0275] RLC Radio Link Control

[0276] RLF Radio Link Failure

[0277] RLM Radio Link Management

[0278] ROM Read Only Memory

[0279] RRC Radio Resource Control

[0280] RRH Remote Radio Head

[0281] RSRP Reference Signal Received Power

[0282] RSRQ Reference Signal Received Quality

[0283] RSU Roadside Unit

[0284] RX

[0285] SA Independence

[0286] SCEF service capability exposure function

[0287] SCG Secondary Cell Group

[0288] SCell

[0289] SCI Sidelink Control Information

[0290] SeNB Secondary enhanced or evolved Node B

[0291] SgNB auxiliary new air interface base station

[0292] SIB System Information Block

[0293] SL Sidelink

[0294] SMF session management function

[0295] SN Auxiliary Node

[0296] SRB Signalling Radio Bearer

[0297] TB transmission block

[0298] TR Technical Report

[0299] TS Technical Specification

[0300] TX Transmit

[0301] UDM unified data management

[0302] UE User Equipment

[0303] UM unconfirmed mode

[0304] UP User Plane

[0305] UPF User Plane Function

[0306] URLLC Ultra-Reliable Low Latency Communication

[0307] V2I Vehicle to Infrastructure

[0308] V2P vehicles to pedestrians

[0309] V2V vehicle to vehicle

[0310] V2X vehicles to everything

Claims

1. A method for detecting and handling a radio link failure in a cellular communication system, performed by a first wireless device, the method comprising: detecting a radio link failure of a first radio link between the first wireless device and a radio access node of a radio access network of the cellular communication system; sending a fault message to the second wireless device via a sidelink between the first wireless device and the second wireless device, the fault message to be forwarded to the radio access node; as well as A response message is received from the radio access node, the response message requesting a radio resource control (RRC) reconfiguration, wherein the response message is a radio resource control (RRC) message that triggers a specific RRC procedure.

2. The method of claim 1, further comprising receiving a response from the second wireless device via the sidelink. 3 . The method of claim 1 , wherein the response message is received from a radio access node in the radio access network via a second radio link between the first wireless device and the radio access node.

4. The method of any one of claims 2 to 3, further comprising performing one or more actions based on the response.

5. The method according to any one of claims 1 to 3, wherein: The fault message is a FailureInformation message.

6. The method according to any one of claims 1 to 3, wherein: The fault message is a MCGFailureInformation message or a SCGFailureInformation message.

7. The method of claim 5, wherein: The failure message includes a wireless device context of the first wireless device.

8. The method of claim 5, wherein: The failure message includes information related to the radio link failure.

9. The method according to any one of claims 1 to 3, wherein: The failure message is a radio resource control RRC message used to handle a radio link failure in carrier aggregation CA, dual connectivity DC, or standalone operation with the help of the sidelink.

10. The method according to any one of claims 1 to 3, wherein: The failure message includes an indication of a failure condition, the indication directly or indirectly indicating one or more conditions that caused the radio link failure.

11. The method according to any one of claims 1 to 3, wherein: The failure message includes one or more recent measurements made by the first wireless device related to the first radio link.

12. A user equipment UE, comprising a processor, wherein the processor is configured to execute the method according to any one of claims 1 to 11.

13. A method for handling a radio link failure performed by a first base station, the method comprising: receiving a failure message from a second wireless device, the failure message being sent to the second wireless device via a sidelink between the first wireless device and the second wireless device, and the failure message relating to a radio link failure of a first radio link between the first wireless device and a radio access network of a cellular communication system; as well as sending a response message to the first wireless apparatus, the response message requesting the first wireless apparatus to perform a radio resource control (RRC) reconfiguration, The response message is a radio resource control RRC message that triggers a specific RRC process.

14. The method of claim 13, further comprising: Any of the following: · sending the response message to the second wireless device; or • Sending the fault message, a response to the fault message, an indication to trigger a specific procedure, or a request for a specific procedure to the second base station.

15. The method of claim 14, further comprising performing a radio access procedure to establish a second radio link between the second wireless device and the first base station.

16. The method of claim 15, wherein: The radio access procedure is a random access procedure.

17. The method according to any one of claims 13 to 16, wherein: The fault message is a FailureInformation message.

18. The method according to any one of claims 13 to 16, wherein: The fault message is a MCGFailureInformation message or a SCGFailureInformation message.

19. The method of claim 17, wherein: The fault message includes a wireless device context of the first wireless device.

20. The method of claim 17, wherein: The failure message includes information related to the radio link failure.

21. The method of any one of claims 13 to 16, wherein: The failure message is a radio resource control RRC message used to handle a radio link failure in carrier aggregation CA, dual connectivity DC, or standalone operation with the help of a sidelink.

22. The method of any one of claims 13 to 16, wherein: The failure message includes an indication of a failure condition, the indication directly or indirectly indicating one or more conditions that caused the radio link failure.

23. The method of any one of claims 13 to 16, wherein: The fault message includes one or more recent measurements made by the first wireless device.

24. A radio access node comprising a processor configured to perform the method of any one of claims 13 to 23.

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