Centralized unit-distributed unit communication associated to radio link failure report and beam failure recovery attempts

According to certain embodiments, a method is performed by a network node comprising a CU. The method comprises receiving assistance information for mobility robustness optimization and forwarding the assistance information, configuration changes related to mobility robustness optimization, or both to a DU or to a second CU. According to certain embodiments, a method is performed by a network node comprising a DU. The method comprises receiving assistance information for mobility robustness optimization. The assistance information indicates that a failure may have originated in a cell of the DU. The method further comprises performing one or more parameter changes in one or more functions handled by the DU.

BACKGROUND

The 3rdGeneration Partnership Project (3GPP) develops various technical specifications (TS), including technical specifications for Radio Access Network (RAN) architectures. For example, 3GPP describes a RAN architecture for 5thGeneration (5G-RAN) or Next Generation (NG-RAN) systems in TS 38.401 v15.4.0 (http://www.3gpp.org/ftp//Specs/archive/38_series/380.401/38401-f40.zip).

FIG.1illustrates the current 5G-RAN (NG-RAN) architecture. The NG-RAN consists of a set of base stations (referred to as gNBs) connected to the 5G Core Network (5GC) through the NG interface. A gNB can support Frequency Division Duplex (FDD) mode, Time Division Duplex (TDD) mode or dual mode operation. gNBs can be interconnected through the Xn interface. A gNB may consist of a gNB Central Unit (gNB-CU) and gNB-Distributed Units (gNB-DUs). A gNB-CU and a gNB-DU are connected via F1 logical interface. One gNB-DU is connected to only one gNB-CU. For resiliency, a gNB-DU may be connected to multiple gNB-CU by appropriate implementation. NG, Xn and F1 are logical interfaces. The NG-RAN is layered into a Radio Network Layer (RNL) and a Transport Network Layer (TNL). The NG-RAN architecture (i.e., the NG-RAN logical nodes and interfaces between them) is defined as part of the RNL. For each NG-RAN interface (NG, Xn, F1) the related TNL protocol and the functionality are specified. The TNL provides services for user plane transport and signalling transport.

A gNB may also be connected to a Long Term Evolution (LTE) eNodeB (eNB) via the X2 interface. Another architectural option is that where an LTE eNB connected to the Evolved Packet Core (EPC) network is connected over the X2 interface with a so called nr-gNB. The latter is a gNB not connected directly to a Core Network (CN) and connected via X2 to an eNB for the sole purpose of performing dual connectivity.

The architecture inFIG.1can be expanded by spitting the gNB-CU into two entities. One gNB-CU-User Plane (gNB-CU-UP), which serves the user plane and hosts the Packet Data Convergence Protocol (PDCP) protocol and one gNB-CU-Control Plane (gNB-CU-CP), which serves the control plane and hosts the PDCP and Radio Resource Control (RRC) protocol. For completeness it should be noted that a gNB-DU hosts the Radio Link Control (RLC)/Medium Access Control (MAC)/PHY protocols.

1.2 Introduction of RLF (LTE and New Radio (NR))

In connected mode, the network typically configures the user equipment (UE) to perform and report Radio Resource Management (RRM) measurements to assist network-controlled mobility decisions (i.e., handovers, which is network control). That is done via handovers, where the network decides to hand over the UE from one cell to another. As a fallback, in case handovers do not work properly, a failure detection and counter-action at the UE has been specified, the co-called Radio Link Failure (RLF) handling (described below). That RLF procedure is typically triggered when something unexpected happens in any of the mobility related procedures (as described below in section 1.3). That is detected thanks to some interactions between RRC and lower layer protocols such as L1, MAC, RLC, etc. In the case of L1, a procedure called radio link monitoring has been introduced.

In the context of the present disclosure, it is important to describe what triggers RLF and the content of RLF reports, to support Mobility Robustness Optimization (MRO). Among different issues that may trigger RLF in LTE and NR, two of them are of particular note for the present disclosure:RLF due to radio link problem (expiry of timer T301) (i.e., RLF due to problems indicated by physical layer); andRLF due to random access problem (i.e., RLF indicated by MAC layer).
RLF triggered by other reasons (e.g., RLC) are not described in detail herein.
1.3 RLF Triggered by Radio Link Problems (L1) in LTE

In LTE, lower layers provide to upper layer Out-of-Sync (OOS) and In-Sync (IS), internally by the UE's physical layer, which in turn may apply RRC/layer 3 (i.e., higher layer) filtering for the evaluation of RLF. The procedure is illustrated inFIG.2(higher layer RLF related procedures in LTE).

The details of UE actions related to RLF are captured in the RRC specifications (36.331), described in relevant part below:5.2.2.9 Actions upon reception of SystemInformationBlockType2Upon receiving SystemInformationBlockType2, the UE shall:1> apply the configuration included in the radioResourceConfigCommon;. . .1> if in RRC_CONNECTED and UE is configured with RLF timers and constants values received within rlf-TimersAndConstants:2> not update its values of the timers and constants in ue-TimersAndConstants except for the value of timer T300;. . .5.3.10.0 GeneralThe UE shall:. . .1> if the received radioResourceConfigDedicated includes the rlf-TimersAndConstants:2> reconfigure the values of timers and constants as specified in 5.3.10.7;. . .5.3.10.7 Radio Link Failure Timers and Constants reconfigurationThe UE shall:1> if the received rlf-TimersAndConstants is set to release:2> use values for timers T301, T310, T311 and constants N310, N311, as included in ue-TimersAndConstants received in SystemInformationBlockType2 (or SystemInformationBlockType2-NB in NB-IoT);1> else:2> reconfigure the value of timers and constants in accordance with received rlf-TimersAndConstants;1> if the received rlf-TimersAndConstantsSCG is set to release:2> stop timer T313, if running, and2> release the value of timer t313 as well as constants n313 and n314;1> else:2> reconfigure the value of timers and constants in accordance with received rlf-TimersAndConstantsSCG;. . .5.3.10.11 SCG dedicated resource configurationThe UE shall:. . .1> if the received radioResourceConfigDedicatedSCG includes the rlf-TimersAndConstantsSCG:2> reconfigure the values of timers and constants as specified in 5.3.10.7;. . .5.3.11.1 Detection of physical layer problems in RRC_CONNECTEDThe UE shall:1> upon receiving N310 consecutive “out-of-sync” indications for the PCell from lower layers while neither T300, T301, T304 nor T311 is running:2> start timer T310;1> upon receiving N313 consecutive “out-of-sync” indications for the PSCell from lower layers while T307 is not running:2> start T313;NOTE: Physical layer monitoring and related autonomous actions do not apply to SCells except for the PSCell.5.3.11.2 Recovery of physical layer problemsUpon receiving N311 consecutive “in-sync” indications for the PCell from lower layers while T310 is running, the UE shall:1> stop timer T310;1> stop timer T312, if running;NOTE 1: In this case, the UE maintains the RRC connection without explicit signalling, i.e. the UE maintains the entire radio resource configuration.NOTE 2: Periods in time where neither “in-sync” nor “out-of-sync” is reported by layer 1 do not affect the evaluation of the number of consecutive “in-sync” or “out-of-sync” indications.Upon receiving N314 consecutive “in-sync” indications for the PSCell from lower layers while T313 is running, the UE shall:1> stop timer T313;RLF-TimersAndConstantsThe IE RLF-TimersAndConstants contains UE specific timers and constants applicable for UEs in RRC_CONNECTED.

RLF-TimersAndConstants Information Element

RLF-TimersAndConstants field descriptionsn3xyConstants are described in section 7.4. n1 corresponds with 1, n2corresponds with 2 and so on.t3xyTimers are described in section 7.3. Value ms0 corresponds with 0 ms,ms50 corresponds with 50 ms and so on.E-UTRAN configures RLF-TimersAndConstants-r13 only if UE supportsce-ModeB. UE shall use the extended values t3xy-v1310 andt3xy-v1330, if present, and ignore the values signaled by t3xy-r9.
Timers (Informative)

ConstantUsageN310Maximum number of consecutive “out-of-sync” indicationsfor the PCell received from lower layersN311Maximum number of consecutive “in-sync” indicationsfor the PCell received from lower layersN313Maximum number of consecutive “out-of-sync” indicationsfor the PSCell received from lower layersN314Maximum number of consecutive “in-sync” indicationsfor the PSCell received from lower layers

When Discontinuous Reception (DRX) is in use, in order to enable sufficient UE power saving the out-of-sync and in-sync evaluation periods are extended and depend upon the configured DRX cycle length. The UE starts in-sync evaluation whenever out-of-sync occurs. Therefore, the same period (TEvaluate_Qout_DRX) is used for the evaluation of out-of-sync and in-sync. However, upon starting the RLF timer (T310) until its expiry, the in-sync evaluation period is shortened to 100 ms, which is the same as without DRX. If the timer T310 is stopped due to N311 consecutive in-sync indications, the UE performs in-sync evaluation according to the DRX based period (TEvaluate_Qout_DRX).

The whole methodology used for RLM in LTE (i.e. measuring the Cell-specific Reference Signal (CRS) to “estimate” the Physical Downlink Control Channel (PDCCH) quality) relies on the fact that the UE is connected to an LTE cell which is the single connectivity entity transmitting PDCCH and CRSs.

In summary, RLM in LTE has been specified so that the network does not need to configure any parameter i.e. UE generates IS/OOS events internally from lower to higher layers to control the detection of radio link problems. On the other hand, RLF/SCG Failure procedures are controlled by RRC and configured by the network via counters N310, N311, N313, N314 (which works as filters to avoid too early RLF triggering) and timers T310, T311, T313 and T314.

Radio Link Monitoring (RLM) and the L1 Input to RLF Function

The purpose of the RLM function in the UE is to monitor the downlink radio link quality of the serving cell in RRC_CONNECTED state and is based on the CRSs, which is always associated to a given LTE cell and derived from the Physical Cell Identifier (PCI). This in turn enables the UE when in RRC_CONNECTED state to determine whether it is in-sync or out-of-sync with respect to its serving cell.

The UE's estimate of the downlink radio link quality is compared with out-of-sync (OOS) and in-sync (IS) thresholds, Qout and Qin respectively, for the purpose of RLM. These thresholds are expressed in terms of the Block Error Rate (BLER) of a hypothetical PDCCH transmission from the serving cell. Specifically, Qout corresponds to a 10% BLER while Qin corresponds to a 2% BLER. The same threshold levels are applicable with and without DRX.

The mapping between the CRS based downlink quality and the hypothetical PDCCH BLER is up to the UE implementation. However, the performance is verified by conformance tests defined for various environments. Also, the downlink quality is calculated based on the Reference Signal Received Power (RSRP) of CRS over the whole band since the UE does not necessarily know where PDCCH is going to be scheduled, which is illustrated inFIG.3. That is,FIG.3illustrates that PDCCH can be scheduled anywhere over the whole downlink transmission bandwidth.

When no DRX is configured, OOS occurs when the downlink radio link quality estimated over the last 200 ms period becomes worse than the threshold Qout. Similarly, without DRX the IS occurs when the downlink radio link quality estimated over the last 100 ms period becomes better than the threshold Qin. Upon detection of out-of-sync, the UE initiates the evaluation of in-sync.

1.4 RLF Triggered by Random Access Problems (MAC) in LTE

Random Access Channel (RACH) is a MAC layer procedure. Hence, it is MAC that indicates to RRC a RACH failure, which happens, for example, when the maximum number of preamble retransmissions is reached (i.e., after the UE has tried to perform power ramping a number of times and/or went through failed contention resolutions). The portions below explain how the UE may reach a maximum number of preamble retransmissions.

In LTE, a UE performs random access for many different purposes, both in RRC_CONNECTED and RRC_IDLE. LTE uses the RACH for initial network access, but in LTE the RACH cannot carry any user data, which is exclusively sent on the Physical Uplink Shared Channel (PUSCH). Instead, the LTE RACH is used to achieve uplink time synchronization for a UE which either has not yet acquired, or has lost, its uplink synchronization. Once uplink synchronization is achieved for a UE, the eNodeB can schedule orthogonal uplink transmission resources for it. Relevant scenarios in which the RACH is used are therefore:(1) A UE in RRC_CONNECTED state, but not uplink-synchronized, needing to send new uplink data or control information (e.g. an event-triggered measurement report);(2) A UE in RRC_CONNECTED state, but not uplink-synchronized, needing to receive new downlink data, and therefore to transmit corresponding ACKnowledgement/Negative ACKnowledgement (ACK/NACK) in the uplink;(3) A UE in RRC_CONNECTED state, handing over from its current serving cell to a target cell;(4) For positioning purposes in RRC_CONNECTED state, when timing advance is needed for UE positioning;(5) A transition from RRC_IDLE state to RRC_CONNECTED, for example for initial access or tracking area updates;(6) Recovering from radio link failure; andOne additional exceptional case is that an uplink-synchronized UE is allowed to use the RACH to send a Scheduling Request (SR) if it does not have any other uplink resource

Random access in LTE may either be configured as contention-based random access (CBRA), which implies an inherent risk of collision, or contention-free RACH (CFRA), where resources are reserved by the network to a given UE at a given time.

Preamble Retransmission Due to Collision Detection of RAR not Received

Random access is captured in the MAC specifications (TS 36.321). In CBRA the UE randomly selects a preamble and transmits with a configurable initial power. Then, it waits for a Random-Access Response (RAR) in a configurable time window. That RAR contains a Temporary Cell Radio Network Temporary Identifier (TC-RNTI) and an UL grant for MSG.3. If the UE receives a RAR within the time window, it transmits MSG.3. If the UE has a Cell Radio Network Temporary Identifier (C-RNTI) allocated by the cell, the UE addresses MSG.3 with that, otherwise it uses the TC-RNTI received in the RAR. As a preamble collision might have happened, different UEs might have received the same RAR, hence, the network sends a MSG.4 to possibly solve contention. If the UE has used the allocated C-RNTI in MSG.4, that is echoed back in MSG.4 to indicate that collision is resolved. Otherwise, the network addresses the UE with the TC-RNTI and includes in the MAC payload the UE identity used in MSG.3. If the UE identity matches the one the UE has the UE considers the contention resolved.

FIG.4illustrates an example of the CBRA procedure. In the case collision is detected, the UE shall perform preamble re-transmission and initiates random access again. And, collision is considered to be detected in the following cases:After transmitting a MSG.3 using a C-RNTI assigned by target cell (e.g. in handover or when UE is in RRC_CONNECTED), UE detects a MSG.4 not addressing its C-RNTI and contention resolution timer expires; andAfter transmitting a MSG.3 using a TC-RNTI assigned to it in the RAR, UE detects a MSG.4 addressing the same TC-RNTI but the UE Identity in the MSG.4 payload does not match the UE's identity transmitted on MSG.3.
Notice that collision is not considered in MAC as a failure case. Hence, upper layers are not aware that a collision has occurred.

Preamble retransmission is also triggered when the UE sends a preamble and does not receive a RAR within the RAR time window. In that case, the UE performs preamble power ramping and transmits the preamble again. In LTE, the network may also configure contention-free random access, such as in handover and resumption of downlink traffic for a UE, by allocating a dedicated signature to the UE on a per-need basis.

In all these cases, when RAR time window expires (for CFRA or CBRA) or when collision is detected, the UE performs preamble retransmission.

A configured parameter controls how many times the UE shall do that, as shown below as part of the RACH-ConfigCommon:RACH-ConfigCommonThe IE RACH-ConfigCommon is used to specify the generic random access parameters.

RACH-ConfigCommon Information Element

Seamless handovers are a key feature of 3GPP technologies. Successful handovers ensure that the UE moves around in the coverage area of different cells without causing too much interruptions in the data transmission. However, there will be scenarios when the network fails to handover the UE to the ‘correct’ neighbor cell in time and in such scenarios the UE will declare the radio link failure (RLF) or Handover Failure (HOF).

Upon HOF and RLF, the UE may take autonomous actions (i.e., trying to select a cell and initiate reestablishment procedure so that we make sure the UE is trying to get back as soon as it can so that it can be reachable again). The RLF will cause a poor user experience as the RLF is declared by the UE only when it realizes that there is no reliable communication channel (radio link) available between itself and the network. Also, reestablishing the connection requires signaling with the newly selected cell (random access procedure, RRC Reestablishment Request, RRC Reestablishment RRC Reestablishment Complete, RRC Reconfiguration and RRC Reconfiguration Complete) and adds some latency, until the UE can exchange data with the network again.

According to the specifications (TS 36.331), the possible causes for the radio link failure could be one of the following:1) Expiry of the radio link monitoring related timer T310;2) Expiry of the measurement reporting associated timer T312 (not receiving the handover command from the network within this timer's duration despite sending the measurement report when T310 was running);3) Upon reaching the maximum number of RLC retransmissions;4) Upon receiving random access problem indication from the MAC entity.
As RLF leads to reestablishment, which degrades performance and user experience, it is in the interest of the network to understand the reasons for RLF and try to optimize mobility related parameters (e.g., trigger conditions of measurement reports) to avoid later RLFs. Before the standardization of MRO related report handling in the network, only the UE was aware of some information associated to how did the radio quality looked like at the time of RLF, what is the actual reason for declaring RLF, etc. For the network to identify the reason for the RLF, the network needs more information, both from the UE and also from the neighboring base stations.

As part of the MRO solution in LTE, the RLF reporting procedure was introduced in the RRC specification in Rel-9 RAN2 work. That has impacted the RRC specifications (TS 36.331) in the sense that it was standardized that the UE would log relevant information at the moment of an RLF and later report to a target cell the UE succeeds to connect (e.g., after reestablishment). That has also impacted the inter-gNodeB interface (i.e., X2AP specifications (TS 36.423)), as an eNodeB receiving an RLF report could forward to the eNodeB where the failure has been originated.

For the RLF report generated by the UE, its contents have been enhanced with more details in the subsequent releases. The measurements included in the measurement report based on the latest LTE RRC specification are:1) Measurement quantities (RSRP, Reference Signal Received Quality (RSRQ)) of the last serving cell (PCell).2) Measurement quantities of the neighbor cells in different frequencies of different radio access technologies (RATs) (e.g., EUTRA, UTRA, GERAN, CDMA2000).3) Measurement quantity (e.g., Received Signal Strength Indicator (RSSI)) associated to WLAN Aps.4) Measurement quantity (e.g., RSSI) associated to Bluetooth beacons.5) Location information, if available (including location coordinates and velocity)6) Globally unique identity of the last serving cell, if available, otherwise the PCI and the carrier frequency of the last serving cell.7) Tracking area code of the PCell.8) Time elapsed since the last reception of the ‘Handover command’ message.9) C-RNTI used in the previous serving cell.10) Whether or not the UE was configured with a data radio bearer (DRB) having Quality of Service Class Identifier (QCI) value of 1.
The detection and logging of the RLF related parameters is captured in section 5.3.11.3 of LTE RRC specification (bolded text refers to RLF detection part and the underlined text refers to RLF reporting aspects):
5.3.11.3 Detection of Radio Link Failure
The UE shall:1> upon T310 expiry; or1> upon T312 expiry; or1> upon random access problem indication from MCG MAC while neither T300, T301, T304 nor T311 is running; or1> upon indication from MCG RLC, which is allowed to be send on PCell, that the maximum number of retransmissions has been reached for an SRB or DRB:2> consider radio link failure to be detected for the MCG i.e. RLF;2> except for NB-IoT, store the following radio link failure information in the VarRLF Report by setting its fields as follows:3> clear the information included in VarRLF-Report, if any;3> set the plmn-IdentityList to include the list of EPLMNs stored by the UE (i.e. includes the RPLMN);3> set the measResultLastServCell to include the RSRP and RSRQ, if available, of the PCell based on measurements collected up to the moment the UE detected radio link failure;3> set the measResultNeighCells to include the best measured cells, other than the PCell, ordered such that the best cell is listed first, and based on measurements collected up to the moment the UE detected radio link failure, and set its fields as follows;4> if the UE was configured to perform measurements for one or more EUTRA frequencies, include the measResultListEUTRA,4> if the UE was configured to perform measurement reporting for one or more neighbouring UTRA frequencies, include the measResultListUTRA,4> if the UE was configured to perform measurement reporting for one or more neighbouring GERAN frequencies, include the measResultListGERAN;4> if the UE was configured to perform measurement reporting for one or more neighbouring CDMA2000 frequencies, include the measResultsCDMA2000;4> for each neighbour cell included, include the optional fields that are available;NOTE 1: The measured quantities are filtered by the L3 filter as configured in the mobility measurement configuration. The measurements are based on the time domain measurement resource restriction, if configured. Blacklisted cells are not required to be reported.3> if available, set the logMeasResultListWLAN to include the WLAN measurement results, in order of decreasing RSSI for WLAN APs;3> if available, set the logMeasResultListBT to include the Bluetooth measurement results, in order of decreasing RSSI for Bluetooth beacons;3> if detailed location information is available, set the content of the locationInfo as follows:4> include the locationCoordinates;4> include the horizontal Velocity, if available;3> set the failedPCellId to the global cell identity, if available, and otherwise to the physical cell identity and carrier frequency of the PCell where radio link failure is detected;3> set the tac-FailedPCell to the tracking area code, if available, of the PCell where radio link failure is detected;3> if an RRCConnectionReconfiguration message including the mobilityControlInfo was received before the connection failure:4> if the last RRCConnectionReconfiguration message including the mobilityControlInfo concerned an intra E-UTRA handover:a 5> include the previousPCellId and set it to the global cell identity of the PCell where the last RRCConnectionReconfiguration message including mobilityControlInfo was received;b 5> set the timeConnFailure to the elapsed time since reception of the last RRCConnectionReconfiguration message including the mobilityControlInfo;4> if the last RRCConnectionReconfiguration message including the mobilityControlInfo concerned a handover to E-UTRA from UTRA and if the UE supports Radio Link Failure Report for Inter-RAT MRO:c 5> include the previousUTRA-CellId and set it to the physical cell identity, the carrier frequency and the global cell identity, if available, of the UTRA Cell in which the last RRCConnectionReconfiguration message including mobilityControlInfo was received;d 5> set the timeConnFailure to the elapsed time since reception of the last RRCConnectionReconfiguration message including the mobilityControlInfo;3> if the UE supports QCI1 indication in Radio Link Failure Report and has a DRB for which QCI is 1:4> include the drb-EstablishedWithQCI-1;3> set the connectionFailureType to rlf,3> set the c-RNTI to the C-RNTI used in the PCell;3> set the rlf-Cause to the trigger for detecting radio link failure;2> if AS security has not been activated:3> if the UE is a NB-IoT UE:4> if the UE supports RRC connection re-establishment for the Control Plane CIoT EPS optimisation:e 5> initiate the RRC connection re-establishment procedure as specified in 5.3.7;4> else:f 5> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;3> else:4> perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘other’;2> else:3> initiate the connection re-establishment procedure as specified in 5.3.7;
In case of DC, the UE shall:1> upon T313 expiry; or1> upon random access problem indication from SCG MAC; or1> upon indication from SCG RLC, which is allowed to be sent on PSCell, that the maximum number of retransmissions has been reached for an SCG or split DRB:2> consider radio link failure to be detected for the SCG i.e. SCG-RLF;2> initiate the SCG failure information procedure as specified in 5.6.13 to report SCG radio link failure;
In case of CA PDCP duplication, the UE shall:1> upon indication from an RLC entity, which is restricted to be sent on SCell only, that the maximum number of retransmissions has been reached:2> consider radio link failure to be detected for the RLC entity;2> initiate the failure information procedure as specified in 5.6.21 to report PDCP duplication failure;
The UE may discard the radio link failure information, i.e. release the UE variable VarRLF-Report, 48 hours after the radio link failure is detected, upon power off or upon detach.

After the RLF is declared, the RLF report is logged and, once the UE selects a cell and succeeds with a reestablishment, it includes an indication that it has an RLF report available in the RRC Reestablishment Complete message, to make the target cell aware of that availability. Then, upon receiving an UEInformationRequest message with a flag “rlf-ReportReq-r9” the UE shall include the RLF report (stored in a UE variable VarRLF-Report, as described above) in an UEInformationResponse message and send to the network.

UEInformationRequest field descriptionsrach-ReportReqThis field is used to indicate whether the UE shall report informationabout the random access procedure.UEInformationResponseThe UEInformationResponse message is used by the UE to transfer the information requested by the E-UTRAN.Signalling radio bearer: SRB1 or SRB2 (when logged measurement information is included)RLC-SAP: AMLogical channel: DCCHDirection: UE to E-UTRAN

Based on the contents of the RLF report (e.g., the Globally unique identity of the last serving cell, where the failure was originated), the cell in which the UE reestablishes can forward the RLF report to the last serving cell. This forwarding of the RLF report is done to aid the original serving cell with tuning of the handover related parameters (e.g., measurement report triggering thresholds) as the original serving cell was the one who had configured the parameters associated to the UE that led to the RLF.

Two different types of inter-node messages have been standardized in LTE for that purpose, the Radio link failure indication and the handover report (in 36.423). The Radio link failure indication procedure is used to transfer information regarding RRC re-establishment attempts or received RLF reports between eNBs. This message is sent from the eNB in which the UE performs reestablishment to the eNB which was the previous serving cell of the UE. The contents of the RLF indication message is given below:

This message is sent by the eNB2to indicate an RRC re-establishment attempt or a reception of an RLF Report from a UE that suffered a connection failure at eNB1.

Based on the RLF report from the UE and the knowledge about in which cell did the UE reestablished itself, the original source cell can deduce whether the RLF was caused due to a coverage hole or due to handover associated parameter configurations. If the RLF was deemed to be due to handover associated parameter configurations, the original serving cell can further classify the handover related failure as too-early, too-late or handover to wrong cell classes. These handover failure classes are explained in brief below.1) Whether the handover failure occurred due to the ‘too-late handover’ casesa. The original serving cell can classify a handover failure to be ‘too late handover’ when the original serving cell fails to send the handover command to the UE associated to a handover towards a particular target cell and if the UE reestablishes itself in this target cell post RLF. Notice that this also comprises the case where the UE has not triggered a measurement report (because the thresholds were not properly set) and/or the case the UE sends the measurement report in poor radio conditions and the network is not able to decoded it and, based on that trigger a handover. These two possible cases are shown below inFIGS.5A and5B.b. An example corrective action from the original serving cell could be to initiate the handover procedure towards this target cell a bit earlier by decreasing the CIO (cell individual offset) towards the target cell that controls when the IE sends the event triggered measurement report that leads to taking the handover decision.2) Whether the handover failure occurred due to the ‘too-early handover’ casesa. The original serving cell can classify a handover failure to be ‘too early handover’ when the original serving cell is successful in sending the handover command to the UE associated to a handover however the UE fails to perform the random access towards this target cell (i.e. UE receives the HO command, starts timer T304 but timer expires before the UE is able to succeed with random access).b. An example corrective action from the original serving cell could be to initiate the handover procedure towards this target cell a bit later by increasing the CIO (cell individual offset) towards the target cell that controls when the IE sends the event triggered measurement report that leads to taking the handover decision. This also needs to consider RACH parameters (e.g. maximum number of preamble retransmissions, RAR time window, contention resolution timer, etc.) and the settings of timer T304.3) Whether the handover failure occurred due to the ‘handover-to-wrong-cell’ casesa. The original serving cell can classify a handover failure to be ‘handover-to-wrong-cell’ when the original serving cell intends to perform the handover for this UE towards a particular target cell but the UE declares the RLF and reestablishes itself in a third cell.b. A corrective action from the original serving cell could be to initiate the measurement reporting procedure that leads to handover towards the target cell a bit later by decreasing the CIO (cell individual offset) towards the target cell or via initiating the handover towards the cell in which the UE reestablished a bit earlier by increasing the CIO towards the reestablishment cell.

To aid the serving cell to classify a handover as ‘too-late’ handover, the RLF reporting (via RLF indication message) from the reestablishment cell to the original source cell is enough. To classify a handover as ‘too early’ or ‘handover to wrong cell’, the serving cell may further benefit from receiving the ‘handover report’ message (from either the cell that re-establishment happened, or the wrong cell the UE handed over but failed while the UE Context Release message is sent to the source cell) which includes the following parameters:

This message is sent by the eNB1to report a handover failure event or other critical mobility problem.

ConditionExplanationifHandoverReportTypeThis IE shall be present if the Handover ReportHoToWrongCellType IE is set to the value “HO to wrong cell”ifHandoverReportTypeThis IE shall be present if the Handover ReportInterRATpingpongType IE is set to the value “InterRAT ping-pong”
1.6 RLF Triggered by Radio Link Problems (L1) in NR

As described, RLF handling is similar in LTE and NR. However, the RLF triggered by radio link problems in NR has quite some differences compared to LTE i.e. in the way that OOS and IS indications are generated by L1. We start by describing the cell concept in NR and the changes due to beamforming, to later introduce RLM in NR and its differences compared to LTE.

Cell and Beam-Based Mobility Concept in NR

In LTE, each cell broadcasts a primary and secondary synchronization signal (PSS/SSS) that encodes a physical cell identifier. This is how a UE identifies a cell in LTE. In NR, equivalent signals also exist. In addition, as NR is designed to be possibly deployed in higher frequencies (e.g., above 6 GHz) where beamforming is massively used, these should be possibly beamformed for the same cell (and possibly in a time-domain manner, in a beam sweeping). And, when transmitted in different beams, each of these PSS/SSS for the same cell has its own identification, in what is called an Synchronization Signal and PBCH Block (SSB), as in addition, Master Information Block (MIB) is also included in each beam.

Hence, one could say that a cell in NR is basically defined by a set of these SSBs that may be transmitted in one (typical implementation for lower frequencies such as below 6 GHz) or multiple downlink beams (typical implementation for lower frequencies such as below 6 GHz). For the same cell, these SSBs carry the same physical cell identifier (PCI). For standalone operation (i.e., to support UEs camping on an NR cell), they also carry in System Information Block Type 1 (SIB1) the RACH configuration, which comprises a mapping between the detected SSB covering the UE at a given point in time and the PRACH configuration (e.g., time, frequency, preamble, etc.) to be used. For that, each of these beams may transmit its own SSB which may be distinguished by an SSB index. An example of this is shown inFIG.6.

These SSBs may be used for many different purposes, including RRM measurements (to assist connected and idle mode mobility), beam selection upon random access, and last, but not least, which is one of the main topics of the present disclosure, beam failure detection and radio link monitoring. In addition to SSBs, for most of these purposes listed above, the network may also configure CSI-RS resources via dedicated signaling to each UE, where each resource may also be beamformed and transmitted in multiple beams.

Radio Link Monitoring (RLM) and the L1 Input to RLF Function in NR

In NR, RLM is also defined for a similar purpose as in LTE (i.e., monitor the downlink radio link quality of the serving cell in RRC_CONNECTED state, in particular the quality of control channels so that the network can contact the UE to schedule information). However, differently from LTE, some level of configurability has been introduced for RLM in NR in terms of RS type/beam/RLM resource configuration and BLER thresholds for IS/OOS generation.

Explicit RLM Resource Configuration

In the previous section it was shown that in NR, two different reference signal (RS) types (SSBs and CSI-RSs) are defined for RRM measurements for mobility assistance, RLM, beam failure detection, etc. There are different reasons to define the two RS types, one of them being the possibility to transmit SSBs in wide beams while CSI-RSs in narrow beams and the other being the ability to change the beamformer of CSI-RS dynamically without affecting the idle mode coverage of the cell (which would have changed if SSB beamformer is changed).

In NR, the RS type used for RLM is also configurable (both CSI-RS based RLM and SS block based RLM are supported) and the RS type for RLM should be configured via RRC signaling. As NR can operate in quite high frequencies (above 6 GHs, but up to 100 GHz) these RS types used for RLM can be beamformed. In other words, depending on deployment or operating frequency, the UE can be configured to monitor beamformed reference signals regardless which RS type is selected for RLM. Hence, differently from LTE, RS for RLM can be transmitted in multiple beams.

As there can be multiple beams, the UE needs to know which ones to monitor for RLM and how to generate IS/OOS events to be indicated to upper layers (so upper layers are able to control the triggering of RLF). In the case of SSB, each beam can be identified by an SSB index (derived from a time index in PBCH and/or a PBCH/DRMS scrambling), while in case of CSI-RS, a resource index is also defined (signaled with the CSI-RS configuration).

In NR the network can configure by RRC signaling, X RLM resources to be monitored, either related to SS blocks or CSI-RS, as follows:One RLM-RS resource can be either one SS/PBCH block or one CSI-RS resource/port;The RLM-RS resources are UE-specifically configured;When UE is configured to perform RLM on one or multiple RLM-RS resource(s),Periodic IS is indicated if the estimated link quality corresponding to hypothetical PDCCH BLER based on at least one RLM-RS resource among all configured X RLM-RS resource(s) is above Q_in threshold;Periodic OOS is indicated if the estimated link quality corresponding to hypothetical PDCCH BLER based on all configured X RLM-RS resource(s) is below Q_out threshold;That points in the direction that only the quality of best beam really matters at every sample to generate OOS/IS events. In other words, if the best beam is below the threshold (i.e. all others would also be), then an OOS event is generated. Same for IS event, as long as the best is above (all other do not matter).

One observation is that changing bandwidth part (BWP) may lead to changes in the RLM resources the UE monitors, especially if the PDCCH configuration also changes. And, in addition, there could be a need to change the RS type the UE monitors as the target active BWP may not include the RS type/resources the UE was monitoring in the previous active BWP. Each BWP is associated with its own set of RLM-RSs.

The RLM configuration provided to the UE with dedicated signalling is shown below, reproduced as in the RRC specifications where the parameters we have discussed above are bolded:RadioLinkMonitoringConfigThe IE RadioLinkMonitoringConfig is used to configure radio link monitoring for detection of beam- and/or cell radio link failure. See also TS 38.321 [3], clause 5.1.1.

RadioLinkMonitoringConfig Information Element

RLM Resource Configuration Via Transmission Configuration Indicator (TCI) States

NR has yet another way to perform RLM, which is using the concept of TCI states. The field failureDetectionResourcesToAddModList in the RLM configuration above is described as a list of reference signals for performing RLM but if no RSs are provided in this list for the purpose of RLF detection, the UE performs Cell-RLM based on the activated TCI-State of PDCCH as described in TS 38.213 [13], clause 5. The network ensures that the UE has a suitable set of reference signals for performing cell-RLM.

As noted above, the term TCI state stands for Transmission Configuration Indicator state. It is used to introduce dynamics in beam selection. The UE can be configured through RRC signaling with N TCI states, where N is up to 64, and depends on UE capabilities. Each state contains a Quasi-Co-Location (QCL) information, i.e. one or two source DL RSs, each combined with a QCL type. Since a TCI state contains QCL Type D information for one of the RSs, the N TCI states can be interpreted as a list of N possible beams transmitted from the network. The other source DL RS in the TCI state may be used for time/frequency QCL purposes. A first list of available TCI states is configured for PDSCH, and a second list of TCI states is configured for PDCCH contains pointers, known as TCI State IDs, to a subset of the TCI states configured for PDSCH. The network then activates one TCI state for PDCCH (i.e. provides a TCI for PDCCH) and up to eight active TCI states for PDSCH. Each configured TCI state contains parameters for the QCL associations between source reference signals (CSI-RS or SS/PBCH) and target reference signals (e.g., PDSCH/PDCCH DMRS ports). TCI states are also used to convey QCL information for the reception of CSI-RS.

Another important concept in NR is the CORESET (Control resource set), where some of the parameters of PDCCH configuration are provided. The CORESET defines the length (1, 2, or 3 OFDM symbols) as well as a frequency-domain allocation of the PDCCH allocation. It is the CORESET configuration that defines the TCI state that is used to receive the PDCCH candidates transmitted in that CORESET. Each CORESET can have a different TCI state configured/activated, enabling the possibility to use different transmit beams for different PDCCH candidates.

In total, it is possible to configure the UE with 3 CORESETs.ControlResourceSetThe IE ControlResourceSet is used to configure a time/frequency control resource set (CORESET) in which to search for downlink control information (see TS 38.213 [13], clause FFS_Section).

ControlResourceSet Information Element

Notice that for each CORESET one can configure a list of TCI states, where each state is defined as follows:TCI-StateThe IE TCI-State associates one or two DL reference signals with a corresponding quasi-colocation (QCL) type.

TCI-State Information Element

The UE needs to know which resources to monitor, but also how to generate IS/OOS events to be reported internally to higher layers. While LTE the SINR maps to a 10% BLER for the generation of OOS events and the SINR maps to a BLER of 2% for the generation of IS events, configurable values can be defined in NR. Currently LTE like 10% and 2% BLER can be configured for OOS and IS events and another pair of X % and Y % will be standardized once a URLLC type of application related requirements are put in place and RAN4 has evaluated the feasibility of these requirements. Hence, differently from LTE, the BLER thresholds for IS/OOS generation will be configurable.

Concept of BW (Bandwidth) Parts and Multi-SSBs

RAN1 introduced the concept of Bandwidth Parts (BWP) which intends to configure the UE with an operation bandwidth that can be less than the actual carrier bandwidth. This has similarities to the handling of “bandwidth reduced” UEs in LTE (Cat-M1) which are not able to operate on the entire carrier bandwidth. Note that the discussion is primarily about carriers spanning several 100 MHz and UEs supporting, for example, “only” carriers of 100 MHz. In other words, this concept addresses UEs supporting an operating bandwidth that is 100 times wider than for Cat-M1. Like in LTE Cat-M1 the configured BWP may not coincide with the carrier's SSB (PSS/SSS/MIB) and it must be discussed how the UE acquires cell sync, performs measurements and acquires SIB in such cases. Besides this core part of the BWP functionality, RAN1 also discussed other flavors e.g. with additional SSBs in the same carrier or in the same BWP as well as the possibility to configure a UE with several possibly overlapping BWPs among which the network can switch by means of L1 control signals (DCI).

FIG.7illustrates an example configuration of bandwidth parts. The downlink and uplink bandwidth parts determine the frequency range in which the UE is required to receive and transmit data channels (PDSCH and PUSCH) and corresponding control channels (PDCCH and PUCCH). As a starting point, a BWP cannot span more than the configured carrier bandwidth.

A key aspect of the BWP concept (as opposed to using only the carrier bandwidth) is to support UEs that cannot handle the entire carrier bandwidth. UEs supporting the full carrier bandwidth can also utilize the entire carrier. Hence, we envision that in dedicated signalling, the NW configures the DL BWP and the UL BWP in accordance with the UE capabilities.

The BWPs can be configured by dedicated signalling in the first RRCReconfiguration after connection establishment (i.e., when the NW knows the UE capabilities). However, already before that point in time the UE must read PDCCH and PDSCH to acquire SIB1, to receive Paging messages and to receive Msg2, Msg4 and the above-mentioned RRCReconfiguration. Hence, the UE must be configured with an “initial BWP”.

A network may still decide to configure a wider initial BWP than some UEs support. This may be the case if the NW wants to optimize the SIB acquisition time or connection establishment time by using a wider bandwidth. But this situation may also occur if a legacy network does not yet support UEs with lower complexity. The UE discovers this based on the initial BWP configured in MIB and since it cannot acquire SIB1 it should consider the cell as barred.

Upon successful connection establishment, the network should configure a BWP in accordance with the UE capabilities. The BWP configuration is specific for a serving cell, i.e., the network must at least configure a DL BWPs for each serving cell. And UL BWP is configured for PCells and for SCells with configured UL.

FIG.8illustrates an example configuration of bandwidth parts. In LTE, each cell was characterized by its center frequency (UL+DL for FDD), by the carrier bandwidth, and by the physical cell ID conveyed in PSS/SSS. The PSS/SSS used to be at the carrier's center frequency. In NR, the SSB-frequency is not necessarily the center frequency which will require signaling both values or one value and an offset (as already discussed in the context of RRM measurements). Upon initial access, the UE must discover the (one) SSB, acquire sync, acquire MIB and then attempt to read SIB1. At this point the UE has selected the cell, i.e., an SSB on a certain frequency.

When the UE establishes an RRC connection, the NW may configure a dedicated BWP. That BWP may overlap with the SSB's frequency. If so, the UE is able to (re-)acquire the SSB at any time in order to re-gain sync and to perform SS-based measurements.

However, if operating bandwidth of a cell (carrier) is wide and if many UEs have an operation bandwidth which is significantly narrower than the carrier bandwidth, the network will allocate UEs to BWPs that do not coincide the with SSB frequency to balance the load and to maximize the system capacity. As in LTE Cat-M1 this implies that these UEs need (inter-frequency, intra-carrier) measurement gaps to re-sync with their serving cell's SSB and to detect and measure neighbor cells. At the same time, the RLM related measurements are performed by the UE more often than the RRM related measurements. Therefore, the network is expected to provide the RLM-RS in the active BWP for a given UE. So, there is no measurement gaps associated to performing RLM measurements.

1.7 RLF Triggered by Random Access Problems (MAC) in NR—Beam Failure Recovery (BFR)

In LTE, random access is used by different procedures. In NR, a procedure called Beam Failure Recovery (BFR) has been defined and relies on random access to indicate eicajer. Hence, a failure in the BFR procedure leads to a random-access failure that is indicated to the higher layers so that RLF is triggered. Below we describe the BFR procedure.

Beam Failure Detection (BFD) and Beam Failure Recovery (BFR) Mechanism

In NR, a new mechanism aiming to avoid RLF was introduced: Beam Failure Recovery (BFR), which relies on beam selection and random-access procedure. The procedure is assisted by the monitoring procedure called Beam Failure Detection (BFD) that, when it occurs, triggers BFR. Making an analogy, RLF is a RRC procedure triggered when the UE is out of cell coverage in connected mode, because L3 mobility may have failed, and shall perform autonomous actions to re-gain connectivity with the network, possibly in another cell. On the other hand, BFR is a L1/MAC procedure triggered when the UE is out of beam coverage (or at least out of coverage of a pre-determined set of beams e.g. beams overlapping coverage with beams used for PDCCH transmission for that UE) because beam management procedures may have failed, and UE shall perform autonomous actions to re-gain connectivity with the same cell (i.e. also in configured candidate beams covered by the same cell).

The UE is configured with BFD resources to be monitored, i.e., a subset of beams in cell coverage, and BFR resources, another set of beams in cell coverage. These BFD and BFR resources can be associated to either SSBs or CSI-RSs, similar to RLM. The UE continuously monitors the BFD resources to check if it is still within the coverage of these beams. If the UE is not under the coverage (as defined with certain Qout threshold), the UE performs the beam recovery using the BFR related UL resources. In this way, the UE and the network maintain a set of beams using at least one of which they can reach each other. When the UE fails to reach the network using any of the BFR resources, the UE declares RLF.

There is a relation between RLM and BFD. The UE may be configured to only perform RLM with a set of resources. In that case, the UE monitor these resources to generate OOS indications to upper layers so RLF may be triggered under certain conditions. The UE may be configured to only perform BFD or both BFD+RLM, where each configured resource is indicated to be associated to either RLM, BFD or both BFD/RLM, as shown below:RadioLinkMonitoringConfigThe IE RadioLinkMonitoringConfig is used to configure radio link monitoring for detection of beam- and/or cell radio link failure. See also TS 38.321 [3], clause 5.1.1.

RadioLinkMonitoringConfig Information Element

If no RSs are provided for the purpose of beam failure detection, the UE performs beam monitoring based on the activated TCI-State for PDCCH. In other words, if no RSs for beam failure detection are not explicitly configured, the UE defaults to use the RSs which the UE uses as QCL reference for the reception of the PDCCH DMRS, which is identical to the RSs in the activated TCI state(s). If RSs for RLM are not explicitly configured, the UE defaults to use the RSs which the UE uses as QCL reference for the reception of the PDCCH DMRS, which is identical to the RSs in the activated TCI state(s).

Beam recovery and radio link monitoring (RLM) are related to beam management. Radio link monitoring is a well-known procedure from LTE, where the UE is monitoring the quality of its serving cell to determine if the NW is unable to reach the UE. In LTE, the UE performs measurements on the CRS, and uses these measurements to estimate what the BLER of PDCCH would be if it were transmitted. In practice, the UE estimates the channel quality, e.g., Signal-to-Interference-plus-Noise ratio (SINR). The UE then triggers an internal out-of-sync (OOS) event if the BLER of a PDCCH received at this SINR level would be higher than 10%. When the UE has detected a certain number of consecutive OOS indications, the UE starts the T310 timer, and when the T310 expires, the UE declares radio link failure (RLF). Radio link failure is a severe failure case, where the UE essentially has no coverage from its serving cell. One situation where this may happen is if the network has failed to perform a handover to a new cell. After declaring RLF, the UE can establish connection with the new cell. In some cases, the UE has simply moved out of coverage, in which case the UE is unable to establish connection to a new cell.

In NR, RLM is similar to the LTE RLM. The only difference is that since there is no CRS, the UE uses another RS to perform RLM. In NR, the UE can be configured to use either a set of SS/PBCH blocks and/or a set of periodic CSI-RSs to perform RLM. L1 in the UE would generate an OOS indication when the quality of all the configured RSs fall below a certain threshold; otherwise an IS indication would be generated. The beam recovery procedure was designed to handle a situation where the beams of the UE and the gNB have become misaligned, and normal beam management procedures have become ineffective. During beam recovery, the UE initiates a realignment of the beams, by performing either contention-based or contention-free random access. One situation where this may happen is when the beam management algorithms have failed to update the active TCI state, leading to that the UE's Rx beam is misaligned.

To discover the beam misalignment, the UE will monitor a set of periodic reference signals, either SS/PBCH blocks or CSI-RS. The monitoring procedure is similar to RLM, but a different set of reference signals may be used. Also, for beam monitoring, there is no generation of in-sync indications, only out-of-sync indications are generated. The MAC layer in the UE interprets the absence of an out-of-sync indication as an in-sync indication. The UE generates an out-of-sync indication if all the monitored RSs fall below a certain threshold.

RLM and beam monitoring have some similarities: both procedures try to detect when the channel quality is below a certain threshold. Once the channel quality is below the threshold, the UE determines that it is unreachable by the NW and takes action. The main difference is the actions taken: for beam recovery, the UE quickly initiates a random access procedure in the serving cell. For RLM, the UE starts the T310 timer, and once the timer expires, the UE will declare radio link failure, perform cell reselection, and RRC reestablishment. The NW configures the UE to independently perform RLM and/or beam recovery, and there is currently no relation between the procedures. In particular, in case the UE attempts to perform beam recovery, but fails to find any suitable RS in the serving cell, the UE will not declare RLF: RLF will be triggered once T310 expires.

The number of RSs (X) the UE can be configured to monitor for RLM depends on the frequency band:For carrier frequencies below 3 GHz, X=2;For carrier frequencies between 3 GHz and 6 GHz, X=4;For carrier frequencies above 6 GHz, X=8.

For beam monitoring, the UE can be configured with 1 or 2 RSs. The underlying idea is that each RSs is associated with one CORESET.

If RSs for beam failure detection are not explicitly configured, the UE defaults to use the RSs which the UE uses as QCL reference for the reception of the PDCCH DMRS, which is identical to the RSs in the activated TCI state(s). If RSs for RLM are not explicitly configured, the UE defaults to use the RSs which the UE uses as QCL reference for the reception of the PDCCH DMRS, which is identical to the RSs in the activated TCI state(s).

How the UE combines the two RSs in one TCI state is still unclear, but it is likely that it will be up to UE implementation.

For both RLM and beam monitoring, the UE monitors UE-specifically configured periodic RS resource(s) to estimate the quality of a hypothetical PDCCH. For both RLM and beam monitoring, there are two options:The RS is not reconfigured in the UE as it moves: the NW transparently updates the Tx beam of the RS. This would require a CSI-RS, which DL beam can be dynamically updated.The UE derives the RS from the active TCI state of the CORESET(s): as the UE moves, different TCI states are activated for the CORESET(s), leading to an implicit update of the RSs used for RLM and beam monitoring.

As previously described, BFR is basically triggered when certain conditions are fulfilled. Below we show the configuration of BFR, which is very similar to a RACH configuration:BeamFailureRecoveryConfigThe BeamFailureRecoveryConfig IE is used to configure the UE with RACH resources and candidate beams for beam failure recovery in case of beam failure detection. See also TS 38.321 [3], clause 5.1.1.

BeamFailureRecoveryConfig Information Element

BeamFailureRecoveryConfig field descriptionsbeamFailureRecoveryTimerTimer for beam failure recovery timer. Upon expiration of the timerthe UE does not use CFRA for BFR. Value in ms. ms10 corresponds to10 ms, ms20 to 20 ms, and so on.candidateBeamRSListA list of reference signals (CSI-RS and/or SSB) identifying thecandidate beams for recovery and the associated RA parameters. Thenetwork configures these reference signals to be within the linkedDL BWP (i.e., within the DL BWP with the same bwp-Id) of the UL BWPin which the BeamFailureRecoveryConfig is provided.msg1-SubcarrierSpacingSubcarrier spacing for contention free beam failure recovery. Onlythe values 15 or 30 kHz (<6 GHz), 60 or 120 kHz (>6 GHz) areapplicable. See TS 38.211 [16], clause 5.3.2.rsrp-ThresholdSSBL1-RSRP threshold used for determining whether a candidate beammay be used by the UE to attempt contention free Random Accessto recover from beam failure. (see TS 38.213 [13], clause 6)ra-prioritizationParameters which apply for prioritized random access procedurefor BFR (see TS 38.321 [3], clause 5.1.1).ra-ssb-OccasionMaskIndexExplicitly signalled PRACH Mask Index for RA Resource selectionin TS 38.321 [3]. The mask is valid for all SSB resourcesrach-ConfigBFRConfiguration of contention free random access occasions for BFRrecoverySearchSpaceIdSearch space to use for BFR RAR. The network configures this searchspace to be within the linked DL BWP (i.e., within the DL BWP withthe same bwp-Id) of the UL BWP in which theBeamFailureRecoveryConfig is provided. The CORESETassociated with the recovery search space cannot be associatedwith another search space.ssb-perRACH-OccasionNumber of SSBs per RACH occasion for CF-BFR (L1 parameter‘SSB-per-rach-occasion’)
1.8 Split Architecture Background

In Rel-15 work, a split architecture of RAN is introduced for the Next Generation RAN (NG-RAN). In the split architecture option, the RAN protocol stack functionality is separated in different parts. The CU-CP is expected to handle the RRC layer, the CU-UP will handle the PDCP layer and the DU will handle the RLC, MAC and PHY layer of the protocol stack. In some further split the DU can have separated unit that handles the PHY parts separately compared to RLC and MAC layers that are handled in a DU.

FIG.9illustrates an example of a split architecture. As different units handle different protocol stack functionalities, there will be a need for inter-node communication between the DU and CU. This is achieved via F1-C interface related to control plane signaling and via F1-U interface related to user plane signaling.

In the context of the present disclosure, that would mean that there may be different functions in different locations responsible for the lower layer functionalities, like RLM, BFD, BFR and RACH (e.g. in the DU where RLC/MAC/PHY are terminated), and higher layer functionalities like handling of Self-Organizing Network (SON) related reports (e.g., RLF reports), RLF parameter settings, or MRO parameters (e.g., thresholds for triggering measurement reports and handovers).

SUMMARY

According to certain embodiments, a method is performed by a network node comprising a CU. The method comprises receiving assistance information for mobility robustness optimization and forwarding the assistance information, configuration changes related to mobility robustness optimization, or both to a DU or to a second CU.

According to certain embodiments, a network node comprising a CU comprises processing circuitry configured to receive assistance information for mobility robustness optimization, and to forward the assistance information, configuration changes related to mobility robustness optimization, or both to a DU or to a second CU. In certain embodiments, the network node further comprises power supply circuitry configured to supply power to the network node.

According to certain embodiments, a computer program comprises instructions that, when executed on a computer, perform steps comprising receiving assistance information for mobility robustness optimization and forwarding the assistance information, configuration changes related to mobility robustness optimization, or both to a DU or to a second CU.

In certain embodiments, the above-described method, network node, and/or computer program may include one or more additional features. For example, the above-described method, network node, and/or computer program may include one or more of the following features:

In certain embodiments, the assistance information comprises a radio link failure report.

In certain embodiments, the assistance information comprises a handover report.

In certain embodiments, a failure cause is determined based on the received assistance information.

In certain embodiments, a location where a failure originated is determined based on the received assistance information. For example, in certain embodiments, the location where the failure originated is determined based on one or more of: the failure cause determined based on the received assistance information; and location information provided in the assistance information.

In certain embodiments, the assistance information, the configuration changes related to mobility robustness optimization, or both are forwarded to the location where the failure originated.

In certain embodiments, the assistance information indicates that a failure may have originated in a cell of a DU associated with the CU, and the forwarding comprises forwarding the assistance information, the configuration changes related to mobility robustness optimization, or both to the DU comprising the cell where the failure may have originated. In certain embodiments, a mapping is determined between a cell identifier and the DU.

In certain embodiments, configuration changes related to mobility robustness optimization are determined based on the received assistance information.

In certain embodiments, the assistance information is received from a wireless device.

In certain embodiments, the assistance information is received from another CU (e.g., another CU of the same network node or a CU of another network node).

Certain embodiments select a portion of the assistance information to forward and the selected portion of the assistance information is forwarded to the DU or to the second CU.

According to certain embodiments, a method is performed by a network node comprising a DU. The method comprises receiving assistance information for mobility robustness optimization. The assistance information indicates that a failure may have originated in a cell of the DU. The method further comprises performing one or more parameter changes in one or more functions handled by the DU.

According to certain embodiments, a network node comprising a DU comprises processing circuitry configured to receiving assistance information for mobility robustness optimization. The assistance information indicates that a failure may have originated in a cell of the DU. The processing circuitry is further configured to perform one or more parameter changes in one or more functions handled by the DU. In certain embodiments, the network node further comprises power supply circuitry configured to supply power to the network node.

According to certain embodiments, a computer program comprises instructions that, when executed on a computer, perform steps comprising receiving assistance information for mobility robustness optimization. The assistance information indicates that a failure may have originated in a cell of the DU. The steps further comprise performing one or more parameter changes in one or more functions handled by the DU.

In certain embodiments, the above-described method, network node, and/or computer program may include one or more additional features. For example, the above-described method, network node, and/or computer program may include one or more of the following features:

In certain embodiments, the assistance information is received from a CU.

In certain embodiments, the assistance information comprises a radio link failure report.

In certain embodiments, the one or more functions may comprise one or more of: random access; beam failure detection; beam failure recovery; radio link monitoring; cell quality derivation; beam management; and one or more other functions affected by beamforming parameters.

In certain embodiments, a failure cause is determined based on the received assistance information.

In certain embodiments, a location where a failure originated is determined based on the received assistance information. In certain embodiments, the location where the failure originated is determined based on one or more of: the failure cause determined based on the received assistance information; and location information provided in the assistance information.

In certain embodiments, a mapping is determined between a cell identifier and the DU.

In certain embodiments, parameter changes performed in the one or more functions handled by the DU are indicated to the CU.

DETAILED DESCRIPTION

There currently exist certain challenge(s). One problem is the lack of observability in the exact network location handling the function to be optimized provided in the existing MRO solutions in LTE if applied to NR. That comes from new issues that may occur in NR such as: misconfiguration of RLM, misconfiguration of cell quality derivation and beam reporting parameters, misconfiguration of beam failure detection and beam recovery and, in more general terms, the effects of beam-based monitoring (i.e., based on beam measurements) in NR in different procedures.

Misconfiguration of RLM

Differently from LTE, RLM is a highly configurable procedure in NR. First, the network may choose between two different RLM mechanisms (i.e., either explicit configuration of RSs to be monitored (i.e., downlink beams to be monitored, and RS resources signals, like SSBs and/or CSI-RSs), or an implicit configuration based on TCI states and QCLs RSs according to the UE's CORESET configuration(s)), which in turn have their own configuration. Other different parameters are also configurable, regardless of the method above, such as the BLER threshold for the generation of OOS and IS indication from L1 to upper layers so that RLF may be triggered when a radio link problem is detected.

Related to that, the first problem that the present disclosure aims to solve is the lack of observability when an RLF is triggered due to a problem related to a misconfigured RLM functionality such as the usage of a method not suitable for some scenarios (e.g., network uses a TCI state based method, while it could have used an explicit configuration of RSs, the network has configured too few RLM resources to save UE power, and/or network has configured too many RLM resources unnecessarily and not matching the PDCCH coverage, etc.).

As RLF aims to counter-act failed mobility decisions, RLM shall detect issues in the serving cell when L1 does not perform mobility properly. However, with an RLM misconfiguration the opposite may occur: the UE may have a very good cell coverage (e.g., because cell quality is derived from its whole cell set of SSBs and best beams/SSB is quite good), but, if the proper resources are not configured for RLM (e.g., because beam management is not operating as expected), the UE may not trigger measurement reports (and network may not trigger handovers, because serving cell is actually good), but the UE may trigger RLF. In other words, there may be an RLF even if the UE is still under cell coverage if RLM is not properly configured.

Such issue could be named an RLF from good cell or a too early RLF.FIG.10illustrates an example of such a scenario.

Currently, for MRO related problems, the network may be assisted by RLF reports, where the UE logs information when a failure has occurred and a cause value (i.e., what has caused the failure), which may include measurements performed for RRM purposes, as shown below:

Notice that one information that is logged is the RRM measurements performed at the serving cell (and neighbour cells). That allows the source receiving that report to understand the serving cell quality compared to the neighbors and how it could later adjust its settings so that under certain conditions a measurement report would have been triggered. However, with the new RLM scheme in NR only informing latest RRM measurements when the failure occurred (e.g., serving cell quality) does not reveal at all failures that may be caused by misconfigured RLM parameters e.g. RLM resources.

Misconfiguration of Cell Quality Derivation (CQD) and Beam Reporting Parameters

One difference in NR compared to LTE is the possible usage of different reference signals (SSBs and/or CSI-RSs) for handover decisions (while in LTE only cell-specific reference signals are used for cell quality derivation). Also, the way the UE computes cell quality in NR (Cell Quality derivation procedure) is quite configurable.

In NR, these reference signals for CQD are transmitted in different beams and when more than one beam is used for the transmission of these reference signals, the UE receives these reference signals in different time instances. There are also other parameters as in LTE, but possibly configurable per beam (e.g. filter parameters). In RRC, cell quality derivation is described as follows:

5.3.3 Derivation of Cell Measurement Results

The network may configure the UE to derive RSRP, RSRQ and SINR measurement results per cell associated to NR measurement objects based on parameters configured in the measObject (e.g. maximum number of beams to be averaged and beam consolidation thresholds) and in the reportConfig (rsType to be measured, SS/PBCH block or CSI-RS).

The UE shall:

1> for each cell measurement quantity to be derived based on SS/PBCH block:2> if nrofSS-BlocksToAverage in the associated measObject is not configured; or2> if absThreshSS-BlocksConsolidation in the associated measObject is not configured; or2> if the highest beam measurement quantity value is below or equal to absThreshSS-BlocksConsolidation:3> derive each cell measurement quantity based on SS/PBCH block as the highest beam measurement quantity value, where each beam measurement quantity is described in TS 38.215 [9];2> else:3> derive each cell measurement quantity based on SS/PBCH block as the linear power scale average of the highest beam measurement quantity values above absThreshSS-BlocksConsolidation where the total number of averaged beams shall not exceed nrofSS-BlocksToAverage;2> apply layer 3 cell filtering as described in 5.5.3.2;1> for each cell measurement quantity to be derived based on CSI-RS:2> consider a CSI-RS resource to be applicable for deriving cell measurements when the concerned CSI-RS resource is included in the csi-rs-CellMobility including the physCellId of the cell in the CSI-RS-ResourceConfigMobility in the associated measObject;2> if nrofCSI-RS-ResourcesToAverage in the associated measObject is not configured; or2> if absThreshCSI-RS-Consolidation in the associated measObject is not configured; or2> if the highest beam measurement quantity value is below or equal to absThreshCSI-RS-Consolidation:3> derive each cell measurement quantity based on applicable CSI-RS resources for the cell as the highest beam measurement quantity value, where each beam measurement quantity is described in TS 38.215 [9];2> else:3> derive each cell measurement quantity based on CSI-RS as the linear power scale average of the highest beam measurement quantity values above absThreshCSI-RS-Consolidation where the total number of averaged beams shall not exceed nrofCSI-RS-ResourcesToAverage;2> apply layer 3 cell filtering as described in 5.5.3.2.

In the example ofFIG.11, the cell-A's coverage is identified based on the coverage area of SSB beams A1and A2whereas the coverage area of cell-B's is identified based on the coverage area of SSB beams B1, B2and B3. When the UE computes the cell quality of these cells, then the UE needs to consider the additional configuration as to how to combine these beam level measurements into a cell level measurement. This is captured in the section 5.5.3.3 of the NR RRC specification TS 38.321 [3], as shown above. In a nut shell, the cell quality can be derived either based on the strongest beam or based on the average of up to ‘X’ strongest beams that are above a threshold ‘T’. These options were introduced to prevent potential ping-pong handover related issues that can arise when only the strongest beam is used for cell quality derivation. It was also discussed that having an averaging based configuration can result in a UE being in a sub optimal cell due to the process of averaging. In the end, both options were supported stating that the network can configure the UE with any of these options depending on which option suits best in terms of the radio condition within the cell's coverage area. Therefore, depending how CQD parameter are set, measurement reports may be triggered later or earlier. Triggering too early may lead to too early or pingo-pong handover, while triggering too late may lead to RLF.

Notice also that beam reporting based on L3 filtered beam measurements in connected mode has also been introduced to possibly improve ping-pong handover rate, especially if one trigger measurement reports on best beam quality. In other words, the network would benefit in getting early measurement reports based on best beam cell quality, but also knowing the quality of individual beams (e.g., SSBs and/or CSI-RS) in neighbour cells before taking mobility decisions. For example, a good candidate may be the one with very good best beam, but also where multiple other beams may be detected (known thanks to the reported information). On the other hand, beam report may not always be activated. Hence, the mistuning of beam reporting parameters (together with the mistuning of CQD parameters) may lead to either a solution where the UE unnecessarily has more efforts (in case beam reporting is activated) and larger measurement reports needs to be transmitted; or the network lacks beam observability to take handover decisions. Hence, current MRO solution only based on the existing measurements is not suitable to solve these potential issues. Beam reporting parameters may be number of beams to report (e.g. per cell), thresholds for beam reporting, reporting quantities per beam, etc.

Misconfiguration of Beam Failure Detection and Beam Recovery

In LTE, a RACH failure indicated from lower layers may trigger RLF. The baseline solution for MRO assistance is an indication in the RLF report that RLF was triggered due to RACH failure. However, as described in the background, for NR random access is used when beam failure detection is triggered, in a procedure called Beam Failure Recovery (BFR). Before that is triggered the UE is monitoring a set of configured RLM/BFD resource and, when a condition is fulfilled the UE triggers BFR, which consists of a flavor of random access, where the network needs to configure a set of RSs (i.e., a set of beams) that the UE may select before mapping to a RACH resource and send the preamble.

RACH failure due to BFR happens when the UE reaches the maximum number of RACH attempts, but many things depending on configurable parameters, contention, etc. Only knowing that RACH failure occurred limits quite a lot the root cause analyses possibilities on the network side (i.e., limited observability).

Examples of misconfigurations related to BFD and BR may be the resource for BFD, its relation to RLM resources, or the resources for candidate beams when BFR is triggered. In the case of misconfigured candidate beams resource, upon BFD, the UE starts to search on a configured candidate set and may not find a candidate beam in the configured set, which would lead to an RLF. However, it might be the case that the UE is still under cell coverage (i.e. CQD of serving cell is still quite good and measurement reports/mobility is not triggered by the network), something that would be quite bad.

Provision of MRO Assistance Information to the Correct Network Function

In the current handling of the RLF, upon receiving the RLF report from the UE the reestablishment cell forwards the RLF report (along with other parameters as captured in section 0) to the last serving cell of the UE. This communication happens on the interface between two RRC entities. In legacy LTE this interface has been the X2. However, if such communication had to happen in the NG RAN, it might happen over the Xn interface (between two CU-CPs or between a CU-CP and an eNB) or it might happen over the NG interface, in cases where the RLF report needs to be forwarded to nodes not connected via the Xn interface.

The current information exchange upon RLF declaration is between CU-CPs or CU-CP and eNB i.e., those units that handle RRC in respective nodes. The information exchanged is via either new or existing Xn messages. For example, new RLF indication message or Handover report message could be defined.

In LTE this information exchange was sufficient to identify the too late HO, too early HO and handover to wrong cell scenarios. However, in NR, as described above, there can be other issues that lead to RLF from the UE. One of them is the sub-optimal configuration of radio link monitoring related parameters, the BFD (beam failure detection) and BFR (beam failure recovery) parameters such as the RS resources, CQD and beam reporting parameters, misconfiguration of beam management procedures in general, etc. These resources are configured by the RRC. However, the exact way of managing these resources is up to the DUs that are handling the beam management and the beamforming functionalities.

In NR, there are new causes for RLF declaration via sub-optimal BFD and BFR resources.

The reference signals (e.g. SSBs and/or CSI-RSs) configured as part of the BFD and BFR could be beamformed dynamically and this dynamicity is controlled by the DUs

The RLF report upon failure to perform BFR is sent to RRC (CU) and thus the DU is unaware of the failure cause and cannot tune its beamforming parameters associated to RSs that are used for BFD and BFR.

Certain aspects of the present disclosure and their embodiments may provide solutions to these or other challenges. As one example, the present disclosure addresses the issue related to CU/DU split and the lack of observability in the correct functions handling certain related functionality (e.g., beamforming related functionality in the DU).

There are, proposed herein, various embodiments which address one or more of the issues disclosed herein.

According to one example embodiment, a method performed by a first Centralized Unit (CU) in the network side (e.g., implemented in a node, in the cloud, etc.) for Mobility Robustness Optimization is disclosed. In certain embodiments, the method may comprise:Receiving from a wireless terminal/user equipment (UE) assistance information from a UE for mobility robustness optimization (MRO), such as an RLF report and/or a Handover report (or any other assistance information for MRO);Determining the failure cause (e.g., by checking what is indicated in the assistance information reported by the UE). In certain embodiments, failure causes that may be in the assistance information (e.g., RLF report) may be one or more of the following: T310 expiry, Random Access Problem (possibly including additional information that this was triggered by Beam Failure Recovery, and further details about the procedure), maximum number of RLC retransmissions, Expiry of timer T312, RLM problem, Beam Failure Detection problem, Beam Management problem, cell quality derivation problem, etc.;Determining the location where the failure may be originated (e.g., its own CU, one of its associated DUs, another CU, or a DU associated to another CU). In certain embodiments, that determination may be performed based on the failure cause described in the previous step and/or location information also provided in the assistance report (e.g., RLF report) like a cell/node/DU/CU identifier. In certain embodiments, this may also be done at the network side by a look-up function where the CU receiving the report from the UE looks up a mapping between a reported identifier known by the UE (e.g., cell identifier) and CU/DU addressing information.Forwarding assistance information for MRO (e.g., an RLF report) or configuration changes related to MRO to the location where the failure may be originated, upon (or in response to) the previous determination step (e.g., its own CU, one of its associated DUs, another CU, or a DU associated to another CU).In certain embodiments, the location may be a DU associated to the CU receiving the assistance information from the UE (e.g. RLF report). This is shown inFIG.12(for the case where assistance information is provided).FIG.13shows an arrangement of a CU, a DU, and a UE that may perform the steps ofFIG.12.In certain embodiments, the location may be a second CU (and, in that case the second CU is responsible to forward the assistance information to a second DU where the failure was originated, in case the function that led to RLF is handled by the second DU). This is shown inFIG.14(for the case where assistance information is provided).FIG.15shows an arrangement of a CUs, DUs, and a UE that may perform the steps ofFIG.14.

According to another example embodiment, a method performed by a second Centralized Unit (CU) in the network side (e.g., implemented in a node, in the cloud, etc.) for Mobility Robustness Optimization is disclosed. In certain embodiments, the method comprises:Receiving assistance information for MRO (e.g., a RLF report) indicating that a failure may be originated in a cell of a DU associated to the second CU; andForwarding assistance information for MRO (e.g., the RLF report) or configuration changes related to MRO to the DU where the failure may be originated upon determining a mapping between a cell identifier and the DU.

According to another example embodiment, a method performed by a Distributed Unit (DU) in the network side (e.g., implemented in a node, in the cloud, etc.) for Mobility Robustness Optimization is disclosed. In certain embodiments, the method comprises:Receiving assistance information for MRO (e.g., a RLF report) indicating that a failure may be originated in a cell of that DU (e.g., that may be received from a CU, as described above);Performing one or more parameter changes in at least one of the functions handled by that DU (possibly using forwarded assistance information). In certain embodiments, these functions may include one or more of Random-Access, BFD, BFR, RLM, cell quality derivation, beam management, or any other function affected by beamforming parameters handled by that DU;Indicating to the DU any parameter changes performed in at least one of the functions handled by that DU. In certain embodiments, these functions may include one or more of Random-Access, BFD, BFR, RLM, cell quality derivation, beam management, or any other function affected by beamforming parameters handled by that DU.

Some examples of how the various embodiments described herein may be implemented are described below.

In certain embodiments, if the cell in which the UE performs re-establishment is the same as the last serving cell indicated in the assistance information (e.g., the RLF report), and if the failure cause is associated to RLF caused by procedures handled by the DU (which is the same DU since both cells are the same), such as sub optimum beam configuration for procedures like cell quality derivation, RLM parameters, contention free random-access resources, BFD, BFR, beam reporting, etc., the CU may perform one or more of the following actions:Indicate the beam configuration related issues to DU (e.g., possibly forwarding assistance information to the DU, like the RLF report or parts of it);Indicate one or more changes in the beam configuration related parameters for at least one of the described procedures (e.g., resources for BFR, BFD, RLM, CQD settings, activation of beam reporting, etc.); andConfigure one or more beam related parameters for at least one of the described procedures (e.g., resources for BFR, BFD, RLM, CQD settings, activation of beam reporting, etc.).

In certain embodiments, if the cell in which the UE performs re-establishment is not the same as the last serving cell indicated in the assistance information (e.g., the RLF report), and if the failure cause is associated to RLF caused by procedures handled by a DU (and, the re-establishment cell is associated to the same DU as the last serving cell), such as sub optimum beam configuration for procedures like cell quality derivation, RLM parameters, contention free random-access resources, BFD, BFR, beam reporting, etc., the CU may perform one or more of the following actions:Indicate the beam configuration related issues to DU (e.g., possibly forwarding assistance information to the DU, like the RLF report or parts of it);Indicate one or more changes in the beam configuration related parameters for at least one of the described procedures (e.g., resources for BFR, BFD, RLM, CQD settings, activation of beam reporting, etc.); andConfigure one or more beam related parameters for at least one of the described procedures (e.g., resources for BFR, BFD, RLM, CQD settings, activation of beam reporting, etc.).

In certain embodiments, if the cell in which the UE performs re-establishment is not the same as the last serving cell, and they are associated to different DUs (but under the same CU), forward the RLF report (including, for example, RLM/BFD-BFR related info) via an available interface such as the Xn interface to DU associated to the last serving cell indicated in the assistance information where RLF is declared.

In certain embodiments, the DU may either receive an indication of the issue detected by the CU (e.g., the indication may suggest that a reconfiguration of BDF and/or BFR is needed). Alternatively, in certain embodiments the CU may send to the DU the RLF and/or handover report. In certain embodiments, upon receiving (or in response to receiving) such information concerning failure cases or cases where a reconfiguration for the purpose of mobility optimization is needed, the DU may change the beamforming configuration(s) associated to BFD and/or BFR resources and beam configuration associated to cell quality derivation, RACH resource allocation and handover.

FIG.16is a flow chart of an embodiment for CU-CP associated to using RLF report for RLM/BFD-BFR resource beamforming modifications. The method inFIG.16comprises receiving an RLF report (step1.1), determining an RLF due to beam failure reasons (step1.2a) and/or determining re-establishment is in the same cell as the last serving cell (step1.2b), and indicating to the DU about the RM/BFD-BFR issues (step1.3a) and/or changing the RLM or BFD-BFR resources based on the contents of the RLF report (step1.3b).

FIG.17is a flow chart of an embodiment for DU associated to using RLF report for RLM/BFD-BFR resource beamforming modifications. The method comprises receiving an RLM/BFD-BFR indication (step2.1) and changing a beamforming configuration associated to RLM/BFD-BFR resources (step2.2).

In addition to the above-described communication from CU to DU, in certain embodiments there can be scenarios where DU might do the learning based on the statistics associated to successful BFR attempts and thus indicate to the CU about the optimal RLM or BFD/BFR resource configurations that shall be used for the UEs in that area in the future.

FIG.18is a flow chart of an embodiment for DU associated to using BFR attempts-based BFD/BFR resource configurations. The method comprises collecting statistics associated to the usage of RLM/BFD-BFR related resources (step3.1) and performing an optimality check (threshold based or ML based) for the RLM/BFD-BFR associated resources' usage (step3.2). The method further comprises determining changes required for RLM/BFD-BFR resources (step3.3) and informing CU of the changes related to RLM/BFD-BFR resources' allocation (step3.4).

FIG.19is a flow chart of an embodiment for CU associated to using BFR attempts-based RLM/BFD-BFR resource reconfigurations. The method comprises receiving RLM/BFD-BFR reconfiguration request from DU (step4.1) and changing BFD/BFR configuration associated to BFD and/or BFR resources (step4.2).

In addition to the above-described communications, there can be scenarios where the CU might do the learning based on the statistics associated to successful BFR attempts as well as other beam measurement/configuration of the neighboring cells, and thus via leveraging a more thorough information (including nonboring cells information) the CU may reconfigure the DU with the optimal BFD/BFR resource configurations that shall be used for the UEs in that area in the future.

FIG.20is a flow chart of an embodiment for CU associated to using BFR attempts' based RLM/BFD-BFR resource reconfigurations. The method comprises collecting statistics associated to the usage of RLM/BFD-BFR related resources, including the source cells and the neighboring cells (step3.1) and performing optimality check (threshold based or ML based) for BFD/BFR associated resources' usage (step3.2). The method further comprises determining changes required for BFD/BFR resources (step3.3) and informing DU the new configuration for RLM/BFD-BFR resources' allocation (step3.4).

Certain embodiments may provide one or more of the following technical advantage(s). As one example, certain embodiments may enable the CU and DU to exchange the information associated to RLF, Handover reports-based learning (from CU to DU) and the successful BFR, cell quality derivation and RACH resource allocation related learning (from DU to CU). This may advantageously enable fine tuning tuning of the BFD and/or BFR resources configurations as well as the configuration of beam configuration for cell quality derivation, dedicated RACH resource allocation (CFRA) and beams configuration for handovers. This fine tuning may advantageously reduce the network overhead by using only the ‘optimal’ RLM/BFD-BFR resources and also reduce the RLF declaration from the UE thus reducing the UE interruption times due to RLFs along with ensuring optimum beams for cell quality derivation, dedicated RACH resource allocation and beam configuration for handovers.

Additional Explanation

2.1 RLF Report Related Information from CU to DU

In certain embodiments, the CU can inform the DU about the statistics derived from the intra cell RLF reports and RLF reports contained in Handover reports associated to the beam failure related aspects that led to RLF. The flow charts associated to this feature are provided inFIGS.16-17.

In certain embodiments, the CU receives the RLF report associated to a UE that was served by a cell connected to this CU before declaring RLF.

2.1.2 Step1.2(CU Determines if the RLF Occurred Due to RLM/BFD/FR or Beam Related Configurations)

In this step, the CU identifies that the RLF was declared by the UE due to the beam failure related reasons.

In certain embodiments, the identification may be performed based on the contents of the RLF report. In some cases, the reason for RLF may be a maximum number of RACH attempts being reached.

In certain embodiments, the identification may be based on the fact that the cell in which the UE performed the re-establishment is the same cell which was the last serving cell of the UE. In certain embodiments, the identification may be further based on the beam through which the UE performs the RA as part of the reestablishment and comparing this beam with the UEs configured and lastly activated beam failure recovery resources (the active BWP of the UE). In certain embodiments, the DU may be mandated to inform the CU about the changes in the active BWP of the UE. In certain embodiments, if the CU is not aware of these activated beam failure recovery resources, then the CU may request the DU to provide the last active BWP of the UE (in such a scenario, the DU is expected to retain the UE's active BWP history for a “duration” even after the UE becomes non-reachable from the network side). In certain embodiments, the CU declares that the previously configured RLM/BFD-BFR resources are sub-optimal if the beam from which the UE re-establishes is not amongst the beams assigned to be used for the RLM/BFD-BFR purposes.

In certain embodiments, both of the above conditions may be taken into consideration to realize that the issues are related to RLM/BFDBFR resource allocations. In some cases, this could be based on statistics from a single UE's RLM/BFDBFR related RLF or based on the statistics from multiple UEs' RLM/BFD-BFR related RLF declarations.

In certain embodiments, the CU may determine that the RLF occurred since beams configured to measure the cell quality were not optimum since the UE reports alternative better beams. For example, this could happen due to two reasons:Case 1: UE is configured to base the cell quality on specific beam which is below the required threshold for an acceptable cell but there are other strong beams available.Case 2: UE is configured to base the cell quality based on the average of multiple configured or strongest beams, but the average of the beams is below the required threshold for an acceptable cell.

In certain embodiments, the DU uses the RLF report from the CU and performs the following actions.Case 1: DU configured the UE with alternative strong beam reported from the UE or the UE is configured to base the cell quality on the average of multiple beams.Case 2: DU configured the UE with specific strong beam instead of utilizing the average of multiple beams for cell quality derivation.

In certain embodiments, the CU may determine that the UE reports RLF since the beams allocated as CFRA resources were not optimum. In some cases, the RLF report could also be included inside the Handover report in case of handover failure scenarios. In such a scenario, the CU may then report its finding to the DU.

In certain embodiments, the DU may determine from the RLF report that the CFRA resources were not optimum but the UE reports alternative beams that could have been optimum. In such a scenario, the DU may then reconfigure the UE with CFRA resources based on strong beam reported by the UE.

2.1.3 Step1.3(Step2.1and2.2as Well) (Informing DU about the Change in the RLM/BFD-BFR, Cell Quality Beam, Beam for RACH Configurations and/or Informing DU about the Possible Need to Change Beamforming Configurations Associated to RLM/BFD-BFR RSs, Cell Quality Beam, Beams for CFRA)

In certain embodiments, the CU may decide to change the RLM/BFD-BFR resources (e.g., new beam addition, some beams removal, etc.) associated to certain BWPs and use the new configuration to the UEs that will come to connected in the cell in which the UE had declared RLF.

In certain embodiments, the CU may inform the DU about the beam through which the UE performed the reestablishment so that this information can be used by the DU to modify the beamforming configurations of the RLM/BFD-BFR related beams or cell quality beams or beams for CFRA.

2.2 BFR (and RLM) Related Information from DU to CU

When there is a successful beam failure recovery, there is no notification given to CU as to which beams are mostly used for BFR and which beams are not used at all. This is what is proposed inFIGS.18-19and the steps captured in these figures.

In certain embodiments, the DU may use the beam which was used by the UE for BFR as part of the statistics.

In certain embodiments, upon (or in response to) BFR the UE sends a measurement report associated to the successful BFR. This report can be obtained from the UE upon request from the network (e.g., something similar to UEInformationRequest and UEInformationResponse framework but from the lower layer like L1 reporting used in CSI framework). In such a report, the UE may include the RSRP measurements associated to one or more of the configured BFD and/or BFR RSs. Additionally, the UE may also include the beams that are measured to be better than the configured BFD related RSs (these additional beams might be related to BFR related RSs and/or those RSs that were blindly detected by the UE and/or those RSs that were configured for RRM measurements). Additionally, in certain embodiments the collected information may include the L1 RSRP reporting included as part of the CSI framework. Moreover, in certain embodiments the UE can include measurements of the resources associated to the RLM in parallel with the measurement associated to the resources used for BFD-BFR

In certain embodiments, both of the above-described embodiments' associated information may be collected.

In certain embodiments, the above-mentioned statistics may be collected in DU. In certain embodiments, these statistics may be collected in a centralized storage (as shown inFIG.20, this centralized storage can be CU and in that case the step3.4may be more of execution of the decision obtained from step3.3and a communication from CU to DU rather than communication from DU to CU).

2.2.2 Step3.2(Checking Whether the Configured BFD/BFR Resources are Optimal)

In certain embodiments, the usage of certain BFR resources can be checked based on:How often a beam has been used for BFR?Whether any other beam was available at the time of using a particular beam for BFR?Based on both above statistics.Other suitable criteria

In certain embodiments, the statistics so collected may be checked against a predefined threshold. In certain embodiments, the statistics may be compared relatively against one another to decide which beams are most beneficial for BFR purposes and which beams are least beneficial. In certain embodiments, the statistics so collected may be given to a machine learning algorithm that can output most suitable ‘X’ beams for BFR.

In certain embodiments, as part of the BFD related configuration enhancement, based on the UEs reported beams that were part of the measurement report sent by the UE after BFR, the need for adding new BFD resources to the existing BFD resources can be checked. For example, if an RS that is not currently included in the BFD configuration but is reported by UEs as an RS that was audible (e.g., beams above certain threshold), then it can be a candidate for addition for BFD resources in the future.

2.2.3 Step3.3(Check if there is a Need for Changing the BFD/BFR Resources)

In certain embodiments, based on the already available BFD/BFR resource configurations and comparing it with the optimality information obtained from step3.2, the DU may decide if the current list of BFR resources can be updated or not.

2.2.4 Step3.4(Informing CU about the Changes Related to BFD/BFR Resource Allocation)

In certain embodiments, if the decision in Step3.3was to change the BFD/BFR resources, then this may be informed to the CU

2.3 Handover Report Related Information from CU to DU

In certain embodiments, the CU may inform the DU about the statistics derived from the handover reports associated to the beam failure related aspects that led to handover failure or could potentially avoid future handover failures.

In certain embodiments, the CU may receive the Handover report associated to a UE that was served by a cell connected to this CU before declaring RLF or handover failure or even after successful handover.

2.3.2 Step1.2(CU Determines if the Handover Report Contains Possibilities for Beam Configuration Optimization)

In this step, the CU may identify that the Handover report contains RLF reports which were caused by beam-related reasons or in case of successful handover CU may notice there is a possibility for beam configuration improvement as indicated by UE.

In certain embodiments, the target DU for a handover may use the successful handover report from CU which includes UE report of alternative better beams to adjust the handover configuration including selection of target beams for UE in cell edge situations.

In certain embodiments, the CU may determine and inform the source DU that the RLF indicator in handover reports indicates that there were stronger beams available during Handover other than the ones configured for this purpose in source DU.

2.4 RLM/BFD Parameters that May be Tuned Based on Assistance Information

In certain of the example embodiments disclosed herein, it has been described that assistance information reported by the UE and forwarded to the DU where the failure has been originated may be used to optimize RLM parameters. In certain embodiments, these parameters may be one or more of the following:

RadioLinkMonitoringConfig Information Element

beamFailureDetectionTimer: This is the timer for beam failure detection as defined in TS 38.321, clause 5.17. The value is in number of “Qout,LRreporting periods of Beam Failure Detection” Reference Signal. Value pbfd1 corresponds to 1 Qout,LRreporting period of Beam Failure Detection Reference Signal, value pbfd2 corresponds to 2 Qout,LRreporting periods of Beam Failure Detection Reference Signal and so on.

The usage of the timer is described in the MAC specifications as follows:

The MAC entity shall:

1> if beam failure instance indication has been received from lower layers:2> start or restart the beamFailureDetectionTimer;2> increment BFI_COUNTER by 1;2> if BFI_COUNTER>=beamFailureInstanceMaxCount:3> initiate a Random Access procedure (see subclause 5.1) on the SpCell.1> if the beamFailureDetectionTimer expires; or1> if beamFailureDetectionTimer, beamFailureInstanceMaxCount, or any of the reference signals used for beam failure detection is reconfigured by upper layers:2> set BFI_COUNTER to 0.1> if the Random Access procedure is successfully completed (see subclause 5.1):2> set BFI_COUNTER to 0;2> stop the beamFailureRecoveryTimer, if configured;2> consider the Beam Failure Recovery procedure successfully completed.

This is somehow equivalent to the in-sync indications in RLF handling that indicates that after the reception of an OSS event the link is getting recovered. In BFD, the absence of an OOS indication is somehow an indication that beam(s) monitored are getting better and beam recovery shall not be triggered.

If the timer is too short (e.g., a single OSS event received), the UE triggers BFR upon a single OOS event. That may possibly be due to fast fading effect and, network may not really want the UE to trigger BFR (i.e. random access) every time it happens, since that might be fixed by the network via ordinary beam management procedures. The consequence of a too short timer value is a higher than necessary number of BFR attempts, which may lead to RLF due to the maximum number of retransmissions in RACH being reached.

Else, if the timer is too long, for example BFR is only triggered when a high number of OOS events come in a quite short window, there could be a misdetection of problems if here and there the link gets recovered (and OOS events are absent just sometimes), which may possibly happen due to fast fading effect. Hence, BFR may not be triggered, even when needed, even though RLM may anyway trigger RLF, depending how the RLF parameters for the IS and OSS counter thresholds are set.

According to certain of the embodiments described herein, information regarding OSS events for BFD and RLM and beam measurements on reference signals configured for RLM may assist the network to either increase the timer value when too many BFRs are happening (e.g. based on collected statistics from one or multiple UEs). That may be known thanks to the reported assistance information (e.g., RLF report) containing information that RACH failure occurred due to BFR being triggered and reaching a maximum number of retransmissions.

beamFailureInstanceMaxCount: This field determines after how many beam failure events the UE triggers beam failure recovery (see TS 38.321, clause 5.17). Value n1 corresponds to 1 beam failure instance, n2 corresponds to 2 beam failure instances and so on. This is basically the number of OOS events within the time window that triggers BFR.

If this value is too low, there may be too many BFRs triggered due to a fast fading event and/or blocking, which will trigger the UE to perform random access and possibly lead to RLF if maximum number of attempts is reached. Notice that the risk here is to trigger BFR due to a fast fading and/or blockage effect that may likely be recovered anyway. The content of RLF report including beam measurements on BFD resources (and event measurements beyond that) may assist the network to understand that too many BFRs may be happening due to too low values for this counter.

Else, if this value is too high, UE may not trigger BFRs even though the situation is not very good.

The risk is that RLM is being performed anyway and RLF is triggered, even though there is still some good coverage in the cell that was not really detected since UE has not triggered BFR and has not had the chance to find a candidate beam (assuming a correct configuration of candidate beams). Hence, too high value may lead to too late BFR.

The reported information in the RLF report may assist the network to detect RLF due to RACH failure (maximum number of retransmissions) due to too many BFR attempts, possibly due to a too low value of the counter. Or, RLF due to expiry of timer T310 due to the fact BFR is not being triggered (or is slower than RLF) due to the fact that the counter is set too high.

failureDetectionResourcesToAddModList: This field is a list of reference signals for detecting beam failure and/or cell level radio link failure (RLF). The limits of the reference signals that the network can configure are specified in TS 38.213, in Table 5-1. The network configures at most two detectionResources per BWP for the purpose “beamFailure” or “both”. If no RSs are provided for the purpose of beam failure detection, the UE performs beam monitoring based on the activated TCI-State for PDCCH as described in TS 38.213, clause 6. If no RSs are provided in this list for the purpose of RLF detection, the UE performs Cell-RLM based on the activated TCI-State of PDCCH as described in TS 38.213, clause 5. The network ensures that the UE has a suitable set of reference signals for performing cell-RLM.

Basically, this list determines the exact resources for BFD and/or RLM, but also the exact RLM/BFD method to be used (implicitly based on TCI states configurations or explicitly based on RS configurations).

If a UE is configured with sub optimum of RS resources for BFD or RLM, RLF may either be triggered too early or never be triggered. That is especially important in the case the resources monitored for RLM/BFD are not the same ones used for cell quality derivation. In that case, the network may not trigger handovers (because UE does not trigger measurements reports taken based on SSBs, which have good coverage) but triggers RLF due to the expiry of timer T310 due to misconfigured RS resources for RLM, in the sense that they may not really translate that the UE is still under cell coverage (but monitoring resources/beams that are not the best ones covering the UE). Hence, when an RLF happens due to timer T310 and UE logs BFD/RLM information, such as beam measurements of BFD/RLM resources, but possibly other beams from the serving cell (e.g. available SSB measurements, or CSI-RS measurements) the UE basically indicates to the network that the UE was under cell coverage but it was monitoring resources with not so good coverage (hence, RLF happened).

Similar issues may occur in BFR triggered by a misconfiguration of BFD resources. If the network detects RLF due to RACH failure due to too many RACH retransmissions due to too many BFR procedures, it may be a sign of too many BFD events, due to misconfigured BFD resources.

Possible network actions based on an enhanced RLF report with information regarding beam measurements on serving cell of BFD/RLM resources, and possibly including beam measurements on serving cell of other resources not configured for BFD/RLM, such as serving cell SSB measurements for RRM, may be taken. For example, the network may know that it should have configured other BFD/RLM resources/beams, and even change the method being used from the one based on TCIs to something that matches the reference signals used for cell quality derivation (e.g., use the same RS and instruct the UE to do RLM/BFD based on SSBs, as in the case of RRM measurements).

Another possible optimization is the activation of BFR itself. It might be the case the network starts its operation without BFR until it starts to detect RLFs and realize that something may be done. For example, when the UE declares RLFs and RLF report indicates that these could be avoided with BFR e.g. the RLF report shows that there were other good beams not configured for RLM that could have been configured as candidate beams for BFR. Hence, based on that information, network activates BFR and knows which beam it may configure as candidate beams.

2.5 BFR Parameters that May be Tuned Based on Assistance Information

In certain of the example embodiments disclosed herein, it has been described that assistance information reported by the UE and forwarded to the DU where the failure has been originated may be used to optimize BFR parameters. In certain embodiments, these parameters may be one or more of the following:

BeamFailureRecoveryConfig Information Element

beamFailureRecoveryTimer: Timer for beam failure recovery timer that starts when BFR is triggered (i.e. when random access due to BFR is started and stops if things are successful. Upon expiration of the timer the UE does not use CFRA for BFR. Value in ms. ms10 corresponds to 10 ms, ms20 to 20 ms, and so on.

Hence, upon the expiry of the timer the UE may still perform beam selection for Beam Failure Recovery (BFR) (i.e., RACH resource selection), but for contention-free random access resources. Longer this timer is, longer is the amount of time the UE is allowed to use CFRA. Hence, based on beam measurement information reported in RLF report when RLF happens (e.g., due to RACH failure (due to maximum number of attempts reached)) the network may know what beams the UE has tried to select, for example, whether these were CFRA or CBRA resources and, possibly increase the value of this timer so the UE may take more time to select a CFRA resource. Else, if failure occurs even if that time is set with a quite high value.

candidateBeamRSList: This is a list of reference signals (CSI-RS and/or SSB) identifying the candidate beams for recovery and the associated RA parameters. The network configures these reference signals to be within the linked DL BWP (i.e., within the DL BWP with the same bwp-Id) of the UL BWP in which the BeamFailureRecoveryConfig is provided.

Upon BFD, the UE needs to select one of the configured beams. If upon BFD the UE is under the coverage of beams that are not in the list of these resources, the UE is not able to perform BFR, which may lead to RLF. Hence, RLF report may include beam measurements (e.g., based on SSBs and CSI-RSs) to indicate the network that these resources are possibly misconfigured.

Hence, based on these reports, the network may add and/or replace resources in that configuration. For example, if in RLF report the UE indicates the RLF due to expiry of timer T310, even though it indicates that BFD was triggered (e.g., thanks to a flag in RLF report for BFD or other information enabling network to detect that), but no BFR was triggered because the lack of resources, and network also has beam measurements for beams that were not configured as candidate resources, network knows that these reported beams, if providing good measurements (e.g., high RSRP, RSRQ or SINR values), are good to be configured as candidates for beam recovery so that RLF may be avoided next time thanks to the fact that the UE would have an opportunity to select a beam of the cell that is providing good coverage to the UE so the UE can try to perform BFR. Notice that these beams measurements may be RRM measurements based on SSBs.

msg1-SubcarrierSpacing: Subcarrier spacing for contention free beam failure recovery. Only the values 15 or 30 kHz (<6 GHz), 60 or 120 kHz (>6 GHz) are applicable. See TS 38.211, clause 5.3.2.

rsrp-ThresholdSSB: This is a L1-RSRP threshold used for determining whether a candidate beam may be used by the UE to attempt contention free Random Access to recover from beam failure (see TS 38.213, clause 6). By receiving an RLF report including beam measurements at the moment the failure has occurred, the network knows which beams are above or below a threshold. Notice that in this sense, the UE may report beams in RLF report regardless of their quality (i.e., possibly including beams below that threshold). That would allow the network to possibly lower that threshold in case it is set too high.

ra-prioritization: These are parameters which apply for prioritized random access procedure for BFR. They comprise the following parameters:powerRampingStepHighPrioritiy: Power ramping step applied for prioritized random access procedure; This is to be used in case prioritization is used for BFR.scalingFactorBI: Scaling factor for the backoff indicator (BI) for the prioritized random access procedure. (see TS 38.321 [3], clause 5.1.4). Value zero corresponds to 0, value dot25 corresponds to 0.25 and so on.

Upon the reception of an RLF report including information that BFR failure has occurred (e.g., maximum number of RACH attempts) and beam measurements when the procedure occurs, the network is able to understand that prioritization of BFR could have make the procedure succeed. Then, upon receiving an RLF report with that information the network may turn on the prioritization feature (i.e., configure UEs with that configuration) and provide parameter accordingly, such as power ramping step high priority and scaling factor.

ra-ssb-OccasionMaskIndex: Explicitly signalled PRACH Mask Index for RA Resource selection in TS 38.321 [3]. The mask is valid for all SSB resources.

rach-ConfigBFR: This is the configuration of contention free random access occasions for BFR. If the network receives an RLF report including information that RLF is triggered due to RACH failure, and that this occurred due to BFR and that contention is detected, the network may configure CFRA resources.

recoverySearchSpaceId: Search space to use for BFR RAR. The network configures this search space to be within the linked DL BWP (i.e., within the DL BWP with the same bwp-Id) of the UL BWP in which the BeamFailureRecoveryConfig is provided. The CORESET associated with the recovery search space cannot be associated with another search space.

ssb-perRACH-Occasion: This is defining the number of SSBs per RACH occasion for CF-BFR (L1 parameter ‘SSB-per-rach-occasion’). If the network receives an RLF report including information that RLF is triggered due to RACH failure, and that this occurred due to BFR and that contention is detected, the network may reconfigure the distribution of SSBs per RACH occasion and/or configure more CBRA resources to avoid the RLFs.

Similar parameters may be tuned for CSI-RS related configurations.

2.6 CQD Parameters that May be Tuned Based on Assistance Information

In certain of the example embodiments disclosed herein, it has been described that assistance information reported by the UE and forwarded to the DU where the failure has been originated may be used to optimize CQD parameters. These parameters may be one or more of the following bolded ones in the measurement object:

MeasObjectNR Information Element

absThreshCSI-RS-Consolidation: This is the absolute threshold for the consolidation of measurement results per CSI-RS resource(s) from L1 filter(s). The field is used for the derivation of cell measurement results as described in 5.5.3.3 and the reporting of beam measurement information per CSI-RS resource as described in 5.5.5.2 of TS 38.331.

absThreshSS-BlocksConsolidation: Absolute threshold for the consolidation of measurement results per SS/PBCH block(s) from L1 filter(s). The field is used for the derivation of cell measurement results as described in 5.5.3.3 and the reporting of beam measurement information per SS/PBCH block index as described in 5.5.5.2 of TS 38.331.

nrofCSInrofCSI-RS-ResourcesToAverage: Indicates the maximum number of measurement results per beam based on CSI-RS resources to be averaged. The same value applies for each detected cell associated with this MeasObjectNR.

nrofSS-BlocksToAverage: Indicates the maximum number of measurement results per beam based on SS/PBCH blocks to be averaged. The same value applies for each detected cell associated with this MeasObject.

These parameters define per RS how the UE uses beams to compute cell quality. Averaging multiple beams has the potential to reduce handover ping-pong rate but may delay the triggering of measurement reports in case the UE detects multiple beams per cell. Hence, if the network receives an RLF reporting including information that RLF has happened and additional beam measurements (with beams not necessarily used for CQD), network may figure out that RLF has occurred due to too late measurement reports due to CQD based on averages. Hence, receiving these reports may lead the network to disable averaging and/or reduce the number of averaged beams and/or raising the consolidation thresholds so that less beams are used for averaging.

2.7 Beam Reporting Parameters that May be Tuned Based on Assistance Information

RLFs may be happening (e.g., due to too early handovers) because the network hands over the UE to cells with a very good beam (e.g., CQD was very strong) but a very unstable beam, for example in cells with many narrow beams but not very stable. Hence, UE may drop right after performing the handover. That could be avoided by beam reporting for triggered cells. Hence, upon receiving an RLF report containing beam measurements, for example for the serving cell, the network may activate beam reporting, or possibly increase number of beams to be reported or lower consolidation thresholds so more beam measurements are included in measurement reports. These parameters are included in the reportConfig, as shown below:

ReportConfigNR Information Element

maxNrofRS-IndexesToReport: This indicates to the UE the maximum number of RS indexes to include in the measurement report for A1-A6 events. This value may be increased in case RLFs are being triggered due to the network deciding to perform handovers to cells with too few good beams (i.e., providing good cell coverage due to best beam, but not so stable).

FIG.21illustrates an example of a method performed by a network node comprising a Centralized Unit, in accordance with certain embodiments. Examples of a network node, in general, are further described below with respect toFIGS.24-30(see e.g., network node160, which comprises processing circuitry170and power circuitry187, in accordance with certain embodiments). As described above, a network node may be arranged in a split-architecture comprising one or more CUs and one or more DUs (see e.g.,FIGS.1,9, and12-15).

At step2110, the method comprises receiving assistance information for mobility robustness optimization. Examples of assistance information may include a radio link failure report or a handover report. In certain embodiments, the assistance information is received from a wireless device, an example of which is shown inFIGS.12-13. In certain other embodiments, the assistance information is received from another CU, an example of which is shown inFIGS.14-15. The CUs may be part of the same network node or different network nodes, depending on the embodiment.

At step2120, the method comprises forwarding the assistance information, configuration changes related to mobility robustness optimization, or both to a DU or to a second CU. For example, in certain embodiments, the first CU determines a location where a failure may have originated and forwards the assistance information and/or configuration changes to the location where the failure may have originated. In certain embodiments, the location where the failure may have originated may comprise a location within a network, such as a network node (e.g., gNB), a CU, a DU, and/or a cell where the failure may have originated. If the failure may have originated in a cell of a DU associated with the first CU, the first CU forwards the assistance information and/or configuration changes to the DU comprising the cell where the failure may have originated. If the failure may have originated in a cell of DU associated with the second CU, the first CU forward the assistance information and/or configuration changes to the second CU (and the second CU may then forward the assistance information to its DU comprising the cell where the failure may have originated). In certain embodiments, the first CU determines the location where the failure originated is determined based on the assistance information. For example, the first CU determines the location where the failure originated one or more of: a failure cause determined based on the received assistance information; and location information provided in the assistance information.

In certain embodiments, the first CU determines a mapping between a cell identifier the DU. As an example, in certain embodiments, the assistance information indicates a cell identifier of a cell where the failure may have originated, and the first CU determines the DU associated with that cell. The first CU may use the mapping to determine where to forward the assistance information and/or configuration changes.

The first CU may determine the assistance information and/or configuration changes to forward in step2120in any suitable manner. In certain embodiments, the first CU selects a portion of the assistance information received in step2110to forward and then forwards the selected portion to the DU or the second CU in step2120. In certain embodiments, the first CU uses the assistance information received in step2110to determine the configuration changes related to mobility robustness optimization. As an example, the first CU may determine a failure cause based on the assistance information received in step2110, and may then determine the configuration changes that may reduce the likelihood of a similar failure occurring in the future. The first CU may then forward the configuration changes in step2120, for example, so that the configuration changes can be applied in the cell where the failure may have originated.

In the examples described above, the network node comprising the first CU may also comprise the second CU, or another network node may comprise the second CU, depending on the embodiment.

Although certain embodiments have described the location where the failure may have originated as comprising a location in a network, in other embodiments, the location where the failure may have originated may comprise a physical or geographical location where the failure may have originated. The physical or geographical location may be in addition to or as an alternative to the location in the network. In certain embodiments, a location where the failure may have originated generally refers to a location that satisfies one or more criteria indicating a likelihood that the failure originated in that location. As an example, a failure within a coverage area of a cell may indicate a likelihood that the failure originated in a DU associated with that cell, which may in turn indicate a likelihood that the failure originated in a CU associated with that DU.

FIG.22illustrates an example of a method performed by a network node comprising a Distributed Unit, in accordance with certain embodiments. Examples of a network node, in general, are further described below with respect toFIGS.24-30(see e.g., network node160, which comprises processing circuitry170and power circuitry187, in accordance with certain embodiments). As described above, a network node may be arranged in a split-architecture comprising one or more CUs and one or more DUs (see e.g.,FIGS.1,9, and12-15).

At step2210, the method comprises receiving assistance information for mobility robustness optimization. The assistance information indicates that a failure may have originated in a cell of the DU. For example, in certain embodiments, the assistance information comprises a radio link failure report. In certain embodiments, the DU receives the assistance information from a CU.FIGS.12-13illustrate an example where the DU receives the assistance information from a first CU (a CU that receives the assistance information from a wireless device).FIGS.14-15illustrate an example where the DU receives the assistance information from a second CU (a CU that receives the assistance information from another CU).

At step2220, the method comprises performing one or more parameter changes in one or more functions handled by the DU. Examples of functions handled by the DU include one or more of: random access; beam failure detection; beam failure recovery; radio link monitoring; cell quality derivation; beam management; and one or more other functions affected by beamforming parameters.

In certain embodiments, the DU may determine the one or more parameter changes to perform based at least in part on the assistance information. As an example, the DU may determine a failure cause based on the received assistance information. In certain embodiments, the DU may determine the one or more parameter changes to perform based at least in part on the determined failure cause (e.g., changing one or more parameters that are determined based on the failure cause may reduce the likelihood of a similar failure happening in the future). As another example, in certain embodiments, the DU may determine a location where a failure originated based on the received assistance information. In certain embodiments, the location where the failure may have originated may comprise a location within a network, such as a network node (e.g., gNB), a CU, a DU, and/or a cell where the failure may have originated. In certain embodiments, the location where the failure originated is determined based on one or more of the failure cause determined based on the received assistance information and location information provided in the assistance information. The DU may then determine a location (e.g., a cell) where to perform the parameter change based on the location where the failure originated.

In certain embodiments, the DU may determine a mapping between a cell identifier and the Distributed Unit. The DU may use the mapping when determining the location of the failure. As an example, the DU may receive assistance information indicating a cell identifier of a cell where a failure occurred, map the cell identifier to a cell associated with the DU, and perform a parameter change in the cell.

In certain embodiments, the method further comprises indicating to a CU any parameter changes performed in the one or more functions handled by the DU. In this manner, the CU may be kept informed of parameter changes in the network.

Although certain embodiments have described the location where the failure may have originated as comprising a location in a network, in other embodiments, the location where the failure may have originated may comprise a physical or geographical location where the failure may have originated. The physical or geographical location may be in addition to or as an alternative to the location in the network. In certain embodiments, a location where the failure may have originated generally refers to a location that satisfies one or more criteria indicating a likelihood that the failure originated in that location. As an example, a failure within a coverage area of a cell may indicate a likelihood that the failure originated in a DU associated with that cell, which may in turn indicate a likelihood that the failure originated in a CU associated with that DU.

InFIG.23, network node160includes processing circuitry170, device readable medium180, interface190, auxiliary equipment184, power source186, power circuitry187, and antenna162. Although network node160illustrated in the example wireless network ofFIG.23may represent a device that includes the illustrated combination of hardware components, other embodiments may comprise network nodes with different combinations of components. It is to be understood that a network node comprises any suitable combination of hardware and/or software needed to perform the tasks, features, functions and methods disclosed herein. Moreover, while the components of network node160are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, a network node may comprise multiple different physical components that make up a single illustrated component (e.g., device readable medium180may comprise multiple separate hard drives as well as multiple RAM modules).

Processing circuitry170may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and/or encoded logic operable to provide, either alone or in conjunction with other network node160components, such as device readable medium180, network node160functionality. For example, processing circuitry170may execute instructions stored in device readable medium180or in memory within processing circuitry170. Such functionality may include providing any of the various wireless features, functions, or benefits discussed herein. In some embodiments, processing circuitry170may include a system on a chip (SOC).

Interface190is used in the wired or wireless communication of signalling and/or data between network node160, network106, and/or WDs110. As illustrated, interface190comprises port(s)/terminal(s)194to send and receive data, for example to and from network106over a wired connection. Interface190also includes radio front end circuitry192that may be coupled to, or in certain embodiments a part of, antenna162. Radio front end circuitry192comprises filters198and amplifiers196. Radio front end circuitry192may be connected to antenna162and processing circuitry170. Radio front end circuitry may be configured to condition signals communicated between antenna162and processing circuitry170. Radio front end circuitry192may receive digital data that is to be sent out to other network nodes or WDs via a wireless connection. Radio front end circuitry192may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters198and/or amplifiers196. The radio signal may then be transmitted via antenna162. Similarly, when receiving data, antenna162may collect radio signals which are then converted into digital data by radio front end circuitry192. The digital data may be passed to processing circuitry170. In other embodiments, the interface may comprise different components and/or different combinations of components.

Power circuitry187may comprise, or be coupled to, power management circuitry and is configured to supply the components of network node160with power for performing the functionality described herein. Power circuitry187may receive power from power source186. Power source186and/or power circuitry187may be configured to provide power to the various components of network node160in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source186may either be included in, or external to, power circuitry187and/or network node160. For example, network node160may be connectable to an external power source (e.g., an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry187. As a further example, power source186may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry187. The battery may provide backup power should the external power source fail. Other types of power sources, such as photovoltaic devices, may also be used.

Antenna111may include one or more antennas or antenna arrays, configured to send and/or receive wireless signals, and is connected to interface114. In certain alternative embodiments, antenna111may be separate from WD110and be connectable to WD110through an interface or port. Antenna111, interface114, and/or processing circuitry120may be configured to perform any receiving or transmitting operations described herein as being performed by a WD. Any information, data and/or signals may be received from a network node and/or another WD. In some embodiments, radio front end circuitry and/or antenna111may be considered an interface.

As illustrated, interface114comprises radio front end circuitry112and antenna111. Radio front end circuitry112comprise one or more filters118and amplifiers116. Radio front end circuitry114is connected to antenna111and processing circuitry120, and is configured to condition signals communicated between antenna111and processing circuitry120. Radio front end circuitry112may be coupled to or a part of antenna111. In some embodiments, WD110may not include separate radio front end circuitry112; rather, processing circuitry120may comprise radio front end circuitry and may be connected to antenna111. Similarly, in some embodiments, some or all of RF transceiver circuitry122may be considered a part of interface114. Radio front end circuitry112may receive digital data that is to be sent out to other network nodes or WDs via a wireless connection. Radio front end circuitry112may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters118and/or amplifiers116. The radio signal may then be transmitted via antenna111. Similarly, when receiving data, antenna111may collect radio signals which are then converted into digital data by radio front end circuitry112. The digital data may be passed to processing circuitry120. In other embodiments, the interface may comprise different components and/or different combinations of components.

As illustrated, processing circuitry120includes one or more of RF transceiver circuitry122, baseband processing circuitry124, and application processing circuitry126. In other embodiments, the processing circuitry may comprise different components and/or different combinations of components. In certain embodiments processing circuitry120of WD110may comprise a SOC. In some embodiments, RF transceiver circuitry122, baseband processing circuitry124, and application processing circuitry126may be on separate chips or sets of chips. In alternative embodiments, part or all of baseband processing circuitry124and application processing circuitry126may be combined into one chip or set of chips, and RF transceiver circuitry122may be on a separate chip or set of chips. In still alternative embodiments, part or all of RF transceiver circuitry122and baseband processing circuitry124may be on the same chip or set of chips, and application processing circuitry126may be on a separate chip or set of chips. In yet other alternative embodiments, part or all of RF transceiver circuitry122, baseband processing circuitry124, and application processing circuitry126may be combined in the same chip or set of chips. In some embodiments, RF transceiver circuitry122may be a part of interface114. RF transceiver circuitry122may condition RF signals for processing circuitry120.

Processing circuitry120may be configured to perform any determining, calculating, or similar operations (e.g., certain obtaining operations) described herein as being performed by a WD. These operations, as performed by processing circuitry120, may include processing information obtained by processing circuitry120by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored by WD110, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination.

User interface equipment132may provide components that allow for a human user to interact with WD110. Such interaction may be of many forms, such as visual, audial, tactile, etc. User interface equipment132may be operable to produce output to the user and to allow the user to provide input to WD110. The type of interaction may vary depending on the type of user interface equipment132installed in WD110. For example, if WD110is a smart phone, the interaction may be via a touch screen; if WD110is a smart meter, the interaction may be through a screen that provides usage (e.g., the number of gallons used) or a speaker that provides an audible alert (e.g., if smoke is detected). User interface equipment132may include input interfaces, devices and circuits, and output interfaces, devices and circuits. User interface equipment132is configured to allow input of information into WD110, and is connected to processing circuitry120to allow processing circuitry120to process the input information. User interface equipment132may include, for example, a microphone, a proximity or other sensor, keys/buttons, a touch display, one or more cameras, a USB port, or other input circuitry. User interface equipment132is also configured to allow output of information from WD110, and to allow processing circuitry120to output information from WD110. User interface equipment132may include, for example, a speaker, a display, vibrating circuitry, a USB port, a headphone interface, or other output circuitry. Using one or more input and output interfaces, devices, and circuits, of user interface equipment132, WD110may communicate with end users and/or the wireless network, and allow them to benefit from the functionality described herein.

Auxiliary equipment134is operable to provide more specific functionality which may not be generally performed by WDs. This may comprise specialized sensors for doing measurements for various purposes, interfaces for additional types of communication such as wired communications etc. The inclusion and type of components of auxiliary equipment134may vary depending on the embodiment and/or scenario.

Power source136may, in some embodiments, be in the form of a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic devices or power cells, may also be used. WD110may further comprise power circuitry137for delivering power from power source136to the various parts of WD110which need power from power source136to carry out any functionality described or indicated herein. Power circuitry137may in certain embodiments comprise power management circuitry. Power circuitry137may additionally or alternatively be operable to receive power from an external power source; in which case WD110may be connectable to the external power source (such as an electricity outlet) via input circuitry or an interface such as an electrical power cable. Power circuitry137may also in certain embodiments be operable to deliver power from an external power source to power source136. This may be, for example, for the charging of power source136. Power circuitry137may perform any formatting, converting, or other modification to the power from power source136to make the power suitable for the respective components of WD110to which power is supplied.

RAM217may be configured to interface via bus202to processing circuitry201to provide storage or caching of data or computer instructions during the execution of software programs such as the operating system, application programs, and device drivers. ROM219may be configured to provide computer instructions or data to processing circuitry201. For example, ROM219may be configured to store invariant low-level system code or data for basic system functions such as basic input and output (I/O), startup, or reception of keystrokes from a keyboard that are stored in a non-volatile memory. Storage medium221may be configured to include memory such as RAM, ROM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, floppy disks, hard disks, removable cartridges, or flash drives. In one example, storage medium221may be configured to include operating system223, application program225such as a web browser application, a widget or gadget engine or another application, and data file227. Storage medium221may store, for use by UE200, any of a variety of various operating systems or combinations of operating systems.

InFIG.24, processing circuitry201may be configured to communicate with network243busing communication subsystem231. Network243aand network243bmay be the same network or networks or different network or networks. Communication subsystem231may be configured to include one or more transceivers used to communicate with network243b. For example, communication subsystem231may be configured to include one or more transceivers used to communicate with one or more remote transceivers of another device capable of wireless communication such as another WD, UE, or base station of a radio access network (RAN) according to one or more communication protocols, such as IEEE 802.2, CDMA, WCDMA, GSM, LTE, UTRAN, WiMax, or the like. Each transceiver may include transmitter233and/or receiver235to implement transmitter or receiver functionality, respectively, appropriate to the RAN links (e.g., frequency allocations and the like). Further, transmitter233and receiver235of each transceiver may share circuit components, software or firmware, or alternatively may be implemented separately.

In some embodiments, some signalling can be effected with the use of control system3230which may alternatively be used for communication between the hardware nodes330and radio units3200.

With reference toFIG.26, in accordance with an embodiment, a communication system includes telecommunication network410, such as a 3GPP-type cellular network, which comprises access network411, such as a radio access network, and core network414. Access network411comprises a plurality of base stations412a,412b,412c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area413a,413b,413c. Each base station412a,412b,412cis connectable to core network414over a wired or wireless connection415. A first UE491located in coverage area413cis configured to wirelessly connect to, or be paged by, the corresponding base station412c. A second UE492in coverage area413ais wirelessly connectable to the corresponding base station412a. While a plurality of UEs491,492are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station412.

Communication system500further includes base station520provided in a telecommunication system and comprising hardware525enabling it to communicate with host computer510and with UE530. Hardware525may include communication interface526for setting up and maintaining a wired or wireless connection with an interface of a different communication device of communication system500, as well as radio interface527for setting up and maintaining at least wireless connection570with UE530located in a coverage area (not shown inFIG.27) served by base station520. Communication interface526may be configured to facilitate connection560to host computer510. Connection560may be direct or it may pass through a core network (not shown inFIG.27) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, hardware525of base station520further includes processing circuitry528, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. Base station520further has software521stored internally or accessible via an external connection.

It is noted that host computer510, base station520and UE530illustrated inFIG.27may be similar or identical to host computer430, one of base stations412a,412b,412cand one of UEs491,492ofFIG.26, respectively. This is to say, the inner workings of these entities may be as shown inFIG.27and independently, the surrounding network topology may be that ofFIG.26.

Wireless connection570between UE530and base station520is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to UE530using OTT connection550, in which wireless connection570forms the last segment.

In some embodiments a computer program, computer program product or computer readable storage medium comprises instructions which when executed on a computer perform any of the embodiments disclosed herein. In further examples the instructions are carried on a signal or carrier and which are executable on a computer wherein when executed perform any of the embodiments disclosed herein.

EMBODIMENTS

Group A Embodiments

1. A method performed by a wireless device, the method comprising:generating assistance information for mobility robustness operation;sending, to a network node, the generated assistance information for mobility robustness operation.2. The method of embodiment 1, wherein the assistance information comprises a radio link failure report.3. The method of embodiment 1, wherein the assistance information comprises a handover report.4. The method of any of embodiments 1-3, wherein the network node is a Centralized Unit.5. The method of any of embodiments 1-3, wherein the network node is a Distributed Unit.6. The method of any of the previous embodiments, further comprising:providing user data; andforwarding the user data to a host computer via the transmission to the base station.

Group B Embodiments

7. A method performed by a network node for mobility robustness optimization, the network node comprising a first Centralized Unit, the method comprising:receiving, from a wireless device, assistance information for mobility robustness optimization;determining a failure cause based on the received assistance information;determining a location where the failure originated;forwarding one or more of the assistance information and configuration changes related to mobility robustness optimization to one or more of:i. a Centralized Unit of the network node;ii. an associated Distributed Unit;iii. another Centralized Unit;iv. a Distributed Unit associated with another Centralized Unit.8. The method of embodiment 7, wherein the assistance information comprises a radio link failure report.9. The method of embodiment 7, wherein the assistance information comprises a handover report.10. The method of any of embodiments 7-9, wherein the location of the failure is determined based on one or more of:the failure cause; andlocation information provided in the assistance information.11. The method of any of embodiments 7-10, wherein the one or more of the assistance information and the configuration changes are forwarded to the location where the failure originated.12. A method performed by a network node for mobility robustness optimization, the network node comprising a second Centralized Unit, the method comprising:receiving assistance information for mobility robustness optimization, the assistance information indicating that a failure may have originated in a cell of a Distributed Unit associated with the second Centralized Unit; andforwarding one or more of the received assistance information and configuration changes related to mobility robustness optimization to the Distributed Unit where the failure may have originated.13. The method of embodiment 12, wherein the assistance information comprises a radio link failure report.14. The method of any of embodiments 12-13, further comprising determining a mapping between a cell identifier and the Distributed Unit.15. A method performed by a network node for mobility robustness optimization, the network node comprising a Distributed Unit, the method comprising:receiving assistance information for mobility robustness optimization, the assistance information indicating that a failure may have originated in a cell of the Distributed Unit;performing one or more parameter changes in one or more functions handled by the Distributed Unit; andindicating to the Distributed Unit any parameter changes performed in the one or more functions handled by the Distributed Unit.16. The method of embodiment 15, wherein the assistance information is received from a Centralized Unit.17. The method of any of embodiments 15-16, wherein the assistance information comprises a radio link failure report.18. The method of any of embodiments 15-17, wherein the one or more functions may comprise one or more of:random access;beam failure detection;beam failure recovery;radio link monitoring;cell quality derivation;beam management; andone or more other functions affected by beamforming parameters.19. The method of any of the previous embodiments, further comprising:obtaining user data; andforwarding the user data to a host computer or a wireless device.

Group C Embodiments

20. A wireless device, the wireless device comprising:processing circuitry configured to perform any of the steps of any of the Group A embodiments; andpower supply circuitry configured to supply power to the wireless device.21. A network node, the network node comprising:processing circuitry configured to perform any of the steps of any of the Group B embodiments;power supply circuitry configured to supply power to the network node.22. A user equipment (UE), the UE comprising:an antenna configured to send and receive wireless signals;radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry;the processing circuitry being configured to perform any of the steps of any of the Group A embodiments;an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry;an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; anda battery connected to the processing circuitry and configured to supply power to the UE.23. A computer program, the computer program comprising instructions which when executed on a computer perform any of the steps of any of the Group A embodiments.24. A computer program product comprising a computer program, the computer program comprising instructions which when executed on a computer perform any of the steps of any of the Group A embodiments.25. A non-transitory computer-readable storage medium or carrier comprising a computer program, the computer program comprising instructions which when executed on a computer perform any of the steps of any of the Group A embodiments.26. A computer program, the computer program comprising instructions which when executed on a computer perform any of the steps of any of the Group B embodiments.27. A computer program product comprising a computer program, the computer program comprising instructions which when executed on a computer perform any of the steps of any of the Group B embodiments.28. A non-transitory computer-readable storage medium or carrier comprising a computer program, the computer program comprising instructions which when executed on a computer perform any of the steps of any of the Group B embodiments.29. A communication system including a host computer comprising:processing circuitry configured to provide user data; anda communication interface configured to forward the user data to a cellular network for transmission to a user equipment (UE),wherein the cellular network comprises a network node having a radio interface and processing circuitry, the network node's processing circuitry configured to perform any of the steps of any of the Group B embodiments.30. The communication system of the pervious embodiment further including the network node.31. The communication system of the previous 2 embodiments, further including the UE, wherein the UE is configured to communicate with the network node.32. The communication system of the previous 3 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; andthe UE comprises processing circuitry configured to execute a client application associated with the host application.33. A method implemented in a communication system including a host computer, a network node and a user equipment (UE), the method comprising:at the host computer, providing user data; andat the host computer, initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the network node performs any of the steps of any of the Group B embodiments.34. The method of the previous embodiment, further comprising, at the network node, transmitting the user data.35. The method of the previous 2 embodiments, wherein the user data is provided at the host computer by executing a host application, the method further comprising, at the UE, executing a client application associated with the host application.36. A user equipment (UE) configured to communicate with a network node, the UE comprising a radio interface and processing circuitry configured to performs the of the previous 3 embodiments.37. A communication system including a host computer comprising:processing circuitry configured to provide user data; anda communication interface configured to forward user data to a cellular network for transmission to a user equipment (UE),wherein the UE comprises a radio interface and processing circuitry, the UE's components configured to perform any of the steps of any of the Group A embodiments.38. The communication system of the previous embodiment, wherein the cellular network further includes a network node configured to communicate with the UE.39. The communication system of the previous 2 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; andthe UE's processing circuitry is configured to execute a client application associated with the host application.40. A method implemented in a communication system including a host computer, a network node and a user equipment (UE), the method comprising:at the host computer, providing user data; andat the host computer, initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the UE performs any of the steps of any of the Group A embodiments.41. The method of the previous embodiment, further comprising at the UE, receiving the user data from the network node.42. A communication system including a host computer comprising:communication interface configured to receive user data originating from a transmission from a user equipment (UE) to a network node,wherein the UE comprises a radio interface and processing circuitry, the UE's processing circuitry configured to perform any of the steps of any of the Group A embodiments.43. The communication system of the previous embodiment, further including the UE.44. The communication system of the previous 2 embodiments, further including the network node, wherein the network node comprises a radio interface configured to communicate with the UE and a communication interface configured to forward to the host computer the user data carried by a transmission from the UE to the network node.45. The communication system of the previous 3 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application; andthe UE's processing circuitry is configured to execute a client application associated with the host application, thereby providing the user data.46. The communication system of the previous 4 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application, thereby providing request data; andthe UE's processing circuitry is configured to execute a client application associated with the host application, thereby providing the user data in response to the request data.47. A method implemented in a communication system including a host computer, a network node and a user equipment (UE), the method comprising:at the host computer, receiving user data transmitted to the network node from the UE, wherein the UE performs any of the steps of any of the Group A embodiments.48. The method of the previous embodiment, further comprising, at the UE, providing the user data to the network node.49. The method of the previous 2 embodiments, further comprising:at the UE, executing a client application, thereby providing the user data to be transmitted; andat the host computer, executing a host application associated with the client application.50. The method of the previous 3 embodiments, further comprising:at the UE, executing a client application; andat the UE, receiving 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,wherein the user data to be transmitted is provided by the client application in response to the input data.51. A communication system including a host computer comprising a communication interface configured to receive user data originating from a transmission from a user equipment (UE) to a network node, wherein the network node comprises a radio interface and processing circuitry, the network node's processing circuitry configured to perform any of the steps of any of the Group B embodiments.52. The communication system of the previous embodiment further including the network node.53. The communication system of the previous 2 embodiments, further including the UE, wherein the UE is configured to communicate with the network node.54. The communication system of the previous 3 embodiments, wherein:the 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 the user data to be received by the host computer.55. A method implemented in a communication system including a host computer, a network node and a user equipment (UE), the method comprising:at the host computer, receiving, from the network node, user data originating from a transmission which the network node has received from the UE, wherein the UE performs any of the steps of any of the Group A embodiments.56. The method of the previous embodiment, further comprising at the network node, receiving the user data from the UE.57. The method of the previous 2 embodiments, further comprising at the network node, initiating a transmission of the received user data to the host computer.

Although this disclosure has been described in terms of certain embodiments, alterations and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the scope of this disclosure, as defined by the following claims.