WO2021063487A1

WO2021063487A1 - Enhanced radio link failure detection for wireless networks

Info

Publication number: WO2021063487A1
Application number: PCT/EP2019/076536
Authority: WO
Inventors: Mikko SÄILY; Ahmad AWADA; Elena Virtej; Sofonias HAILU; Ingo Viering
Original assignee: Nokia Technologies Oy
Priority date: 2019-10-01
Filing date: 2019-10-01
Publication date: 2021-04-08

Abstract

According to an example embodiment, a method may include measuring, by a user device, at least one signal parameter of signals received from a plurality of cells; determining, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; initiating, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.

Description

ENHANCED RADIO LINK FAILURE DETECTION FOR WIRELESS NETWORKS

TECHNICAL FIELD

[0001] This description relates to wireless communications.

BACKGROUND

[0002] A communication system may be a facility that enables communication between two or more nodes or devices, such as fixed or mobile communication devices. Signals can be carried on wired or wireless carriers.

[0003] An example of a cellular communication system is an architecture that is being standardized by the 3^rd Generation Partnership Project (3 GPP). A recent development in this field is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. E- UTRA (evolved UMTS Terrestrial Radio Access) is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. In LTE, base stations or access points (APs), which are referred to as enhanced Node AP (eNBs), provide wireless access within a coverage area or cell. In LTE, mobile devices, or mobile stations are referred to as user equipments (UE). LTE has included a number of improvements or developments. Aspects of LTE are also continuing to improve.

[0004] 5G New Radio (NR) development is part of a continued mobile broadband evolution process to meet the requirements of 5G, similar to earlier evolution of 3G & 4G wireless networks. 5G is also targeted at the new emerging use cases in addition to mobile broadband. A goal of 5 G is to provide significant improvement in wireless performance, which may include new levels of data rate, latency, reliability, and security. 5G NR may also scale to efficiently connect the massive Internet of Things (IoT) and may offer new types of mission-critical services. For example, ultra-reliable and low- latency communications (URLLC) devices may require high reliability and very low latency. SUMMARY

[0005] According to an example embodiment, a method may include measuring, by a user device, at least one signal parameter of signals received from a plurality of cells; determining, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and, initiating, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.

[0006] According to an example embodiment, an apparatus may include means for measuring, by a user device, at least one signal parameter of signals received from a plurality of cells; means for determining, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and, means for initiating, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.

[0007] According to an example embodiment, an apparatus may include: at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: measure, by a user device, at least one signal parameter of signals received from a plurality of cells; determine, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and, initiate, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.

[0008] According to an example embodiment, a non-transitory computer-readable storage medium comprising instructions stored thereon that, when executed by at least one processor, are configured to cause a computing system to perform a method of: measuring, by a user device, at least one signal parameter of signals received from a plurality of cells; determining, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and, initiating, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.

[0009] The details of one or more examples of embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a block diagram of a wireless network according to an example embodiment.

[0011] FIG. 2 is a diagram of a user device (or UE) according to an example embodiment.

[0012] FIG. 3 is a flow chart illustrating operation of a user device or UE according to an example embodiment.

[0013] FIG. 4 is a diagram illustrating two conditions that may be used to describe operation of the UE according to an example embodiment.

[0014] FIG. 5 is a flow chart illustrating operation of a user equipment according to an example embodiment. [0015] FIG. 6 is a block diagram of a wireless station (e.g., AP, BS, RAN node, UE or user device, or other network node) according to an example embodiment.

DETAILED DESCRIPTION

[0016] FIG. 1 is a block diagram of a wireless network 130 according to an example embodiment. In the wireless network 130 of FIG. 1 , user devices 131, 132, 133 and 135, which may also be referred to as mobile stations (MSs) or user equipment (UEs), may be connected (and in communication) with a base station (BS) 134, which may also be referred to as an access point (AP), an enhanced Node B (eNB), a BS, next generation Node B (gNB), a next generation enhanced Node B (ng-eNB), or a network node. The terms user device and user equipment (UE) may be used interchangeably. A BS may also include or may be referred to as a RAN (radio access network) node, and may include a portion of a BS or a portion of a RAN node, such as (e.g., such as a centralized unit (CU) and/or a distributed unit (DU) in the case of a split BS). At least part of the functionalities of a BS (e.g., access point (AP), base station (BS) or (e)Node B (eNB), BS, RAN node) may also be carried out by any node, server or host which may be operably coupled to a transceiver, such as a remote radio head. BS (or AP) 134 provides wireless coverage within a cell 136, including to user devices (or UEs) 131, 132, 133 and 135. Although only four user devices (or UEs) are shown as being connected or attached to BS 134, any number of user devices may be provided. BS 134 is also connected to a core network 150 via a SI interface or NG interface 151. This is merely one simple example of a wireless network, and others may be used.

[0017] A base station (e.g., such as BS 134) is an example of a radio access network (RAN) node within a wireless network. A BS (or a RAN node) may be or may include (or may alternatively be referred to as), e.g., an access point (AP), a gNB, an eNB, or portion thereof (such as a centralized unit (CU) and/or a distributed unit (DU) in the case of a split BS or split gNB), or other network node.

[0018] According to an illustrative example, a BS node (e.g., BS, eNB, gNB, CU/DU, ...) or a radio access network (RAN) may be part of a mobile telecommunication system. A RAN (radio access network) may include one or more BSs or RAN nodes that implement a radio access technology, e.g., to allow one or more UEs to have access to a network or core network. Thus, for example, the RAN (RAN nodes, such as BSs or gNBs) may reside between one or more user devices or UEs and a core network. According to an example embodiment, each RAN node (e.g., BS, eNB, gNB, CU/DU, ...) or BS may provide one or more wireless communication services for one or more UEs or user devices, e.g., to allow the UEs to have wireless access to a network, via the RAN node. Each RAN node or BS may perform or provide wireless communication services, e.g., such as allowing UEs or user devices to establish a wireless connection to the RAN node, and sending data to and/or receiving data from one or more of the UEs. For example, after establishing a connection to a UE, a RAN node (e.g., BS, eNB, gNB, CU/DU, ...) may forward data to the UE that is received from a network or the core network, and/or forward data received from the UE to the network or core network.

RAN nodes (e.g., BS, eNB, gNB, CU/DU, ...) may perform a wide variety of other wireless functions or services, e.g., such as broadcasting control information (e.g., such as system information) to UEs, paging UEs when there is data to be delivered to the UE, assisting in handover of a UE between cells, scheduling of resources for uplink data transmission from the UE(s) and downlink data transmission to UE(s), sending control information to configure one or more UEs, and the like. These are a few examples of one or more functions that a RAN node or BS may perform. A base station may also be DU (Distributed Unit) part of IAB (Integrated Access and Backhaul) node (a.k.a. a relay node). DU facilitates the access link connection(s) for an IAB node.

[0019] A user device (user terminal, user equipment (UE), mobile terminal, handheld wireless device, etc.) may refer to a portable computing device that includes wireless mobile communication devices operating either with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (MS), a mobile phone, a cell phone, a smartphone, a personal digital assistant (PDA), a handset, a device using a wireless modem (alarm or measurement device, etc.), a laptop and/or touch screen computer, a tablet, a phablet, a game console, a notebook, a vehicle, a sensor, and a multimedia device, as examples, or any other wireless device. It should be appreciated that a user device may also be (or may include) a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A user device may be also MT (Mobile Termination) part of IAB (Integrated Access and Backhaul) node (a.k.a. a relay node).

MT facilitates the backhaul connection for an IAB node.

[0020] In LTE (as an illustrative example), core network 150 may be referred to as Evolved Packet Core (EPC), which may include a mobility management entity (MME) which may handle or assist with mobility/handover of user devices between BSs, one or more gateways that may forward data and control signals between the BSs and packet data networks or the Internet, and other control functions or blocks. Other types of wireless networks, such as 5G (which may be referred to as New Radio (NR)) may also include a core network.

[0021 ] In addition, by way of illustrative example, the various example embodiments or techniques described herein may be applied to various types of user devices or data service types, or may apply to user devices that may have multiple applications running thereon that may be of different data service types. New Radio (5G) development may support a number of different applications or a number of different data service types, such as for example: machine type communications (MTC), enhanced machine type communication (eMTC), Internet of Things (IoT), and/or narrowband IoT user devices, enhanced mobile broadband (eMBB), and ultra-reliable and low-latency communications (URLLC). Many of these new 5G (NR) - related applications may require generally higher performance than previous wireless networks.

[0022] IoT may refer to an ever-growing group of objects that may have Internet or network connectivity, so that these objects may send information to and receive information from other network devices. For example, many sensor type applications or devices may monitor a physical condition or a status, and may send a report to a server or other network device, e.g., when an event occurs. Machine Type Communications (MTC, or Machine to Machine communications) may, for example, be characterized by fully automatic data generation, exchange, processing and actuation among intelligent machines, with or without intervention of humans. Enhanced mobile broadband (eMBB) may support much higher data rates than currently available in LTE.

[0023] Ultra-reliable and low-latency communications (URLLC) is a new data service type, or new usage scenario, which may be supported for New Radio (5G) systems. This enables emerging new applications and services, such as industrial automations, autonomous driving, vehicular safety, e-health services, and so on. 3GPP targets in providing connectivity with reliability corresponding to block error rate (BLER) of 10⁵ and up to 1 ms U-Plane (user/data plane) latency, by way of illustrative example. Thus, for example, URLLC user devices/UEs may require a significantly lower block error rate than other types of user devices/UEs as well as low latency (with or without requirement for simultaneous high reliability). Thus, for example, a URLLC UE (or URLLC application on a UE) may require much shorter latency, as compared to a eMBB UE (or an eMBB application running on a UE).

[0024] The various example embodiments may be applied to a wide variety of wireless technologies or wireless networks, such as LTE, LTE-A, 5G (New Radio (NR)), cmWave, and/or mmWave band networks, IoT, MTC, eMTC, eMBB, URLLC, etc., or any other wireless network or wireless technology. These example networks, technologies or data service types are provided only as illustrative examples.

[0025] In LTE (as an example), core network 150 may be referred to as Evolved Packet Core (EPC), which may include a mobility management entity (MME) which may handle or assist with mobility/handover of user devices between BSs, one or more gateways that may forward data and control signals between the BSs and packet data networks or the Internet, and other control functions or blocks.

[0026] According to an example implementation, a layer 1 protocol layer may include a physical layer (PHY) for measuring signals, and/or measuring synchronization conditions, such as detecting in-synchronization or In-Synchronization (IS) conditions (e.g., where the user device is synchronized to a transmission from the gNB/BS) and/or out-of-synchronization or out-of-sync (OOS) conditions (e.g., where the UE detects that it is not synchronized to a transmission from the gNB or BS) at the PHY protocol layer.

A layer 2 protocol layer may include, e.g., a media access control (MAC) layer, and/or a radio link control (RLC) layer, a radio link management (RLM) layer, and/or other protocol layer. A layer 3 layer may include, for example, a radio resource control (RRC) layer, for example. Each of these protocol layers may be, for example, implemented as a software protocol stack, running on a user device/UE, a BS or other network device.

[0027] Radio link monitoring (RLM) may include a process by which a UE or user device may monitor a radio link between the UE and a serving gNB or serving cell, in order to detect or declare a Radio Link Failure under certain circumstances. For example, according to an example implementation, in order to support user device (UE) mobility and to decrease service interruptions, UEs may perform radio link monitoring (RLM). For example, as part of RLM, a connected UE (e.g., connected to a serving cell/ gNB) may monitor a downlink radio link quality of the serving cell by measuring a link quality parameter(s) of a received signal of the downlink radio link. Thus, as part of RLM, a user device may monitor a downlink radio link quality by measuring a signal-to- noise ratio (SNR), or other signal parameter of the cell-specific reference signals received from a serving celEBS. The user device may compare the SNR (or other measured signal parameter) of the downlink radio link to a lower threshold (Qout) and/or to an upper threshold (Qin) for the purpose of monitoring downlink radio link quality of the serving cell/BS.

[0028] According to an example implementation, the lower threshold Qout may be defined as a level at which the downlink radio link cannot be reliably received and may, for example, correspond to a 10% block error rate (BLER) of a hypothetical PDCCH (physical downlink control channel) transmission, for example. The upper threshold Qin may be defined as the level at which the downlink radio link quality may be significantly more reliably received than at Qout and may, for example, correspond to 2% BLER of a hypothetical PDCCH transmission, as an illustrative example.

[0029] According to an example implementation, as part of RLM, a UE may frequently or even periodically measure a signal parameter or link quality (e.g., SNR) of a downlink radio link, and then compare the link quality (e.g., SNR) of the downlink radio link to a lower threshold (Qout) and/or to an upper threshold (Qin) to determine whether it is in out-of-synchronization (OOS) status or in in-synchronization (IS) status. While SNR is used as an example link quality in one or more illustrative example implementations described herein, a variety of different link parameters or link qualities may be used for measuring or determining a downlink radio link quality, e.g., such as signal-to-interference plus noise ratio (SINR), reference signal received power (RSRP), reference signal received quality (RSRQ), error rate (e.g., block error rate (BLER)), or other signal parameter or link quality.

[0030] According to an example implementation, there may be various rules that a UE may follow when comparing a SNR of the downlink radio link quality (e.g., SNR) to the lower threshold (Qout) and/or to the upper threshold (Qin). According to an example implementation, while a UE is connected (e.g., user device is in radio resource control (RRC) connected state) with a serving BS (or gNB)/cell, then the UE may periodically measure SNR of reference signals received from the serving cell/BS. If the downlink radio link quality, e.g., SNR (e.g., over a last period of time period of 200 ms or other time period, which may be shorter in beam based systems that require beamforming) is less than Qout, then a physical (PHY) layer (or layer 1) of the user device may send an out-of-synchronization (OOS) indication to higher layer(s) at the user device. Similarly, when the SNR of the downlink radio link (e.g., over a last time period of 100ms or other time period) is greater than Qin, then a PHY (or layer 1) of the user device/UE sends an in-synchronization (IS) indication to upper layers of the user device. If the SNR is in-between Qin and Qout, then neither a IS indication nor a OOS indication is sent by the PHY (LI) to upper layers of the UE.

[0031] An upper layer (e.g., radio resource control/RRC layer) of the UE may increment an OOS counter each time it receives an OOS indication. If a threshold number (e.g., 1 , 2, 3, 4, ...) of (e.g., consecutive) OOS indications are received by the upper layers of the UE without receiving an (or a threshold number of) in synchronization (IS) indication from the PHY (or lower layer) of the UE (e.g., OOS counter reaches a threshold number (e.g., N310 number) of OOS indications, meaning that an OOS condition exists for the UE with respect to the serving cell), then a recovery (e.g., T310) timer is started. If the recovery timer expires before a threshold number (e.g. N311) of IS indications is received from the UE PHY (e.g., before a SNR is measured for the downlink radio link that is greater than Qin), then the UE declares a radio link failure (RLF) for the radio link or connection between the UE and the serving cell or serving BS/gNB. On the other hand, if, before expiration of the OOS timer, a SNR measurement is received for the UE that is greater than Qin, then the IS counter is incremented for the user device, and the recovery timer is stopped when the IS counter reaches a threshold number, and OOS counter may be reset to zero, which prevents the UE from declaring a RLF. A SNR that is in-between Qin and Qout will not cause an OOS to be indicated to upper layers, and such an in-between SNR will not generate an IS that will stop a RLF from being triggered. Thus, once a recovery timer is started (based on one or more received OOS indications), only an IS indication (based on SNR greater than Qin) will prevent a radio link failure (RLF) for the UE/user device, for example.

[0032] In some cases, after declaring RLF, the user device (or UE) may no longer be connected, but may now be disconnected from the network, which may also be referred to as idle state or RRC idle state. For example, after RLF occurs or is declared for the UE, the UE stays in RRC (radio resource control) connected mode and may initiate or request a connection re-establishment (with the previously connected cell, or a different cell). Thus, after RLF, the UE is detached from the serving cell, but it remains connected to the network. For example, if connection re-establishment fails, the UE transitions to RRC idle state (and becomes disconnected from the network). If connection re-establishment (to the same or different cell) is successful, the connection continues (no idle state was involved for the UE).

[0033] Therefore, if a signal quality of a downlink radio link falls below a threshold Qout, the user device may be expected to declare it is in out-of-synchronization (OOS) status, and then user device may eventually trigger or declare a Radio Link Failure (RLF) for the connection. For a user device already in out-of-synchronization (OOS) status, the user device may be expected to declare it comes back to in-synchronization (IS) status, if the downlink signal quality exceeds another predefined threshold Qin to avoid unnecessarily triggering RLF.

[0034] According to an example embodiment, after declaring a RLF. the UE may try to find and then establish a connection to the same or a different cell or BS, e.g., through a connection re-establishment including a random access procedure. According to an example implementation, after declaring RLF, a UE may initiate a connection re establishment, by sending a connection re-establishment request to a suitable cell (either the previous serving cell, or another cell). Alternatively, the UE may perform cell search and measurement, which may include, for example, a UE monitoring one or more signals, e.g., including searching for, synchronizing to, and estimating the received signal quality from one or more neighbor cells. Measurement may include, e.g., the UE tuning its wireless transceiver (transmitter/receiver) to a frequency to receive synchronization signals (e.g., primary synchronization signals and secondary synchronization signals) from a cell, acquiring frequency and symbol synchronization and frame synchronization to the neighbor cell, determining a physical cell identity or cell ID of the neighbor cell, and measuring a signal quality (e.g., reference signal received power/RSRP or SNR of reference signals) of signals received from the cell. If a suitable cell has been found based on the received signal quality or link quality, then the UE may send a random access (e.g., RACH) preamble to the cell/BS for connection establishment, as part of a random access procedure. If the suitable cell receives the random access request and the connection re-establishment request, and if the suitable cell has a security (e.g., AS) context for this UE, the UE may become connected to the suitable cell, and the UE may resume performing RLM for the new serving celFBS. Otherwise the connection re establishment procedure fails and the UE transitions to RRC idle state.

[0035] Also, according to an example embodiment, UE may be configured to perform measurement reporting, for one or more measurement events. For example, the UE may be configured by the serving cell/gNB to measure certain signal parameters from one or more cells, and then send a measurement report if a configured measurement event is detected. For example, the UE may be configured to trigger or cause transmission of a measurement report to the serving cell if an A3 event is detected (e.g.., neighbour cell has a signal parameter (e.g., RSRP) that is an offset better than the measured signal parameter of the serving cell) for a predefined period of time (e.g. time to trigger). The UE may perform signal measurements (e.g., measure RSRP or other signal parameter) of the serving cell and one or more neighbor cells, and then trigger (or cause transmission of) a measurement report if the configured measurement event is detected. The measurement report may, for example, identify the cell that triggered the transmission of the measurement report, along with other information.

[0036] Also, according to an example embodiment, a RAN node (e.g., BS or gNB), when receiving a measurement report (from a UE) triggered by a measurement event, may initiate a handover (HO) procedure for the UE. As a consequence, if the measurement report is not received at the RAN node (e.g., due to bad radio conditions), or when the handover procedure is not successful (e.g., the HO instructions sent from RAN node (BS/gNB) to the UE fail (or are not received by UE) due to bad radio conditions), a required handover may not be completed by the UE and the UE may typically experience interference of the cell that has triggered the measurement report. Thus, in some cases, if a HO instruction is not received in time by the UE, this may cause the UE to experience a RLF, a loss of connection, and/or other performance degradation.

[0037] Thus, as noted above, in an illustrative example, the T310 timer (or radio link recovery timer) may typically start when a threshold (e.g., N310) number of OOS indications have been detected by the UE. However, in some cases, relying on the T310 timer may result in a late (or delayed) detection of a RLF, since the T310 timer may start only when the threshold number of OOS indications have been detected.

[0038] Furthermore, in some cases, an additional timer, e.g., a T312 timer, which may be referred to as an early detection timer (or early RLF detection timer) may be used as well, such as to allow a UE to perform an earlier detection of a RLF, e.g., at least in some cases even before expiration of the T310 timer. For example, the T312 (or early RLF detection) timer may, at least in some cases, be started upon triggering or causing (by the UE) of a transmission of a measurement report by the UE, if the T310 timer is already running at the time of the triggering of the measurement report. Thus, in such case, upon triggering of a measurement report to the serving cell, the UE may first confirm that the T310 timer is already running (e.g., timer T310 may start running when an OOS condition exists for the UE, such as based on the UE detecting N310 (or a threshold number) of consecutive OOS indications by the UE). If the measurement report has been triggered, and the timer T310 (or recovery timer) is running at the time the transmission of the measurement report was triggered, then the UE may typically start the T312 timer. The T312 timer may have a smaller (or shorter in time) value as compared to the T310 value, for example. The UE may declare a RLF if the T312 timer expires. Also, for example, the T312 timer may stop whenever a handover command or a conditional handover command is received by the UE from the serving BS/gNB or serving cell, or if timer T310 is stopped (e.g., based on a threshold number of IS indications being detected by the UE before expiration of the T310 timer), or if a RLF is declared for any other reason.

[0039] Therefore, an early RLF detection (or T312) timer may be used in order to reduce the UE outage time and speed up the recovery from RLF. For example, a T312 timer may be used to shorten the time a UE may wait to send a connection re establishment request to a cell, if the measurement report was triggered while the T310 timer was running. However, as noted above, the T312 timer may typically start only if the measurement report is triggered while T310 timer is (already) running. Therefore, under such an operation, the earlier RLF detection offered by the early RLF detection (e.g., T312) timer is not provided to the UE in a case where recovery (e.g., T310) timer is started running (e.g., threshold number of consecutive number of OOS indications are detected by UE) only after triggering at the UE of the measurement report. That is, the current T312 timer does not cover the case where a target cell is detected and reported in a triggered measurement report before an out-of-synchronization condition (e.g., causing timer T310 to start) of the UE occurs towards the serving cell.

[0040] Therefore, according to an example embodiment, an enhanced early RLF detection (or T312) timer operation may provide early RLF detection, even in a case where the UE detects the OOS condition exists for the UE with respect to the serving cell (e.g., timer T310 has been started) only after the measurement report was triggered at the UE. According to an example embodiment, the UE may initiate a connection re establishment (e.g., send a connection re-establishment request) with a cell after a threshold period of time has elapsed since the measurement report has been triggered (e.g., timer 312 has expired), regardless whether timer T310 was running (or an OOS condition existed for the UE) at the time that the measurement report was triggered.

Thus, in this way, the UE may receive the early RLF detection benefits of the T312 timer, even if the T310 timer was not running at the time that the UE measurement report transmission is triggered.

[0041] Thus, for example, a method may include: measuring, by a UE, at least one signal parameter (e.g., SNR) of signals received from a plurality of cells (e.g., measure SNR or other signal parameters of signals received by UE from the serving cell and one or more neighbour cells); determining, by the UE, that a transmission of a measurement report from the user device to the serving cell has been triggered at the UE based on the measuring (e.g., UE detects that an A3 measurement event (or other configured measurement event) has been satisfied, which triggers or causes the UE to transmit a measurement report to the serving cell); detecting, by the UE, that the out-of- synchronization condition exists (e.g., based on detecting a threshold number of OOS indications at the UE, causing the T310) for the user device with respect to the serving cell after the measurement report was triggered; and, initiating, by the UE, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered (e.g., after expiration of the T312 timer), regardless whether an out-of-synchronization condition existed for the UE with respect to the serving cell at the time that transmission of the measurement report was triggered. In other words, the UE may initiate connection re-establishment with a cell after expiration of the T312 timer (e.g., which was started when measurement report was triggered) as long as the T310 timer was started (or OOS condition existed for the UE) with respect to the serving cell after the measurement report was triggered, regardless whether timer T310 was running at the time of triggering the measurement report. Thus, this may allow the UE to receive the benefit of the early RLF detection (e.g., T312) timer, even in a case where the T310 timer was not running at the time that the UE measurement report transmission is triggered.

[0042] FIG. 2 is a diagram of a user device (or UE) according to an example embodiment. UE 132 includes a UE lower protocol layer 210, e.g., which may include a physical (or PHY) protocol layer. The lower protocol layer 210 may detect IS and/or OOS indications, and may report the IS and/or OOS indications 212 to radio link monitoring (RLM) function 214 provided at an upper protocol layer(s). RLM function 214 may perform radio link monitoring, including radio link failure (RLF) detection and/or RLF recovery. One or more threshold counter values 216 may be provided or stored at UE 132, e.g., including N310 (e.g., a threshold number of OOS indications for an OOS condition to exist at the UE, or required to start timer T310), and/or N311 (e.g., a threshold number of IS indications required to stop T310 timer, once it has started running). In addition, UE 132 may also include one or more timers, such as a radio link recovery timer (or T310 timer) 220, and/or an early RLF detection timer (or T312 timer) 218.

[0043] In an illustrative example, the UE or user device may monitor the radio link towards the current serving cell for example by detecting the loss of synchronization (OOS indications) of the physical layer. In case of out of synchronization from lower layers (e.g., a threshold number of OOS indications have been detected by UE), the upper protocol layer is indicated of the radio problem (e.g., UE upper radio protocol is notified of threshold number of OOS indications). The indication of the physical radio link problem (OOS condition of UE, based on threshold number of OOS indications being detected by UE) can be stopped (and timer T310 can be stopped) when the synchronization with the lower layers is recovered (e.g., an IS condition has been detected for the UE) or if the UE is triggered with a handover procedure to a target cell or the current link is re-established. When the radio link monitoring indicates that the connectivity towards the serving cell has been lost and could not be recovered, for example by detection of a physical layer problem at the serving cell (e.g., when an OOS condition for the UE has been detected based on a threshold number of out-of-sync indications reaches a threshold), a radio link failure is declared and connection is re established.

[0044] However, as noted above, the existing RLF detection mechanism has significant limitations. Presently, the T312 timer may typically start only if the measurement report is triggered while T310 is (already) running. Therefore, the early RFL detection provided by the early RFF detection (e.g., T312) timer is not provided to the UE in a case where recovery (e.g., T310) timer is started running (e.g., threshold number of consecutive number of OOS indications are detected by UE) only after triggering of the measurement report.

[0045] Thus, according to an example embodiment, the early RLF detection provided by the early RLF detection (e.g., T312) timer will not be provided or offered to the UE in a case where recovery (e.g., T310) timer was started running (e.g., threshold number of consecutive number of OOS indications are detected by UE) only after triggering of the measurement report. In this manner, a faster and more robust recovery of a RLF due to mobility (or other cause) can be achieved when the UE or device identifies a triggering of a measurement reporting trigger. Sending a measurement report starts a radio link monitoring function (at the UE) associated with the measurement identity where the evaluation of a radio link quality (OOS condition) was already on going. The monitoring function may be started upon triggering a measurement report for the associated measurement identity when the radio link monitoring is not indicating out- of-synch condition (e.g., the monitoring function, or starting to T312 timer, may begin upon triggering at the UE of transmission of measurement report, even when the OOS condition does not yet exist or starting of timer T310 has not started at the time of the measurement report triggering). The monitoring function, e.g., expiration of the T312 timer, may trigger the radio resource control to start the re-establishment or execution of a conditional handover in the case radio link monitoring has indicated the out of synchronization (00 S) condition from lower layers and tries to recover the radio link. In other words, the UE may initiate a connection re-establishment upon expiration of the T312 timer (e.g., after a threshold period of time has elapsed since triggering of the measurement report), e.g., if the OOS condition exists (G310 timer started) after the measurement report was triggered.

[0046] According to an example embodiment, the solution may enable the monitoring function (e.g., timer T312) to start before a radio link problem towards the source cell is detected (e.g., timer T312 may be started in response to measurement report triggering and before the OOS condition at the UE was detected (or before starting of timer T310 has begun).

[0047] Radio link monitoring, e.g., based on expiration of the T312 timer, can start the re-establishment or execution of a conditional handover earlier in the situation where measurement event has been triggered.

[0048] The UE can resume data transmission earlier towards a new cell, e.g. upon the expiry of monitoring function (e.g., upon expiration of the T312 timer).

[0049] According to an example embodiment: A Threshold for out-of synchronization (OOS) indications may be N310; A Threshold for in-synchronization (IS) indications may be N311; Monitoring function associated to measurement identity may be timer T312; and Radio link monitoring with RLF declaration may be timer T310.

[0050] According to an example embodiment, the proposed implementation of the algorithm introduces radio link monitoring function where the timer T312 is started upon triggering a measurement report for a measurement identity associated with T312 even if timer T310 is not running, unlike in the existing solutions. Upon the expiry of T312 timer, connection re-establishment is initiated if T310 is running. Otherwise, for example, no action is necessarily taken by the UE. This procedure is summarized in pseudocode below:

[0051] o (1) IF an event condition with use T312 flag set to TRUE has triggered (e.g., if a configured measurement event associated with a T312 timer has triggered transmission of a measurement report) ^■ (2) Start T312 timer if it is not already started

^■ (3) IF T312 timer expires

• (4) IF T310 timer is running, e.g., DL radio link monitoring indicates a potential problem (e.g., there is a threshold number of consecutive OOS indications detected by UE) o (5) Initiate connection re-establishment procedure, e.g., towards the target cell that triggered the transmission of the measurement report

• (6) ELSE o Do nothing

[0052] The above solution can be further extended (unlike in the existing T312 enhancement solutions), where upon the expiry of T312, the UE executes HO towards a prepared cell, e.g., UE may execute a conditional handover (CHO) to a prepared cell.

[0053] Therefore, as shown in the pseudocode above, an enhanced early RLF detection (or T312) timer operation may be provided in order to provide improved or earlier RLF detection and recovery. At operation (1) and (2), the UE starts a timer T312 in response to the triggering at the UE of a measurement report associated with the T312 timer. Note that timer T312 is started, regardless whether timer T310 is running (e.g., timer T312 is started even if timer T310 is not running/OOS condition does not exist at the UE at the time the measurement report is triggered). At operations (3), (4) and (5), in response to detecting that timer T312 has expired (e.g., a threshold period of time has elapsed since triggering transmission of the measurement report at UE), the UE at operation (5) initiates a connection re-establishment to a cell (e.g., to the target cell that triggered the measurement report) if at operation (4), the timer T310 is running (e.g.,

OOS condition exists at the UE, and/or timer T310 is running at the time the timer T312 expires). Otherwise, at operation (6), the UE does not initiate a connection re establishment. Thus, in this manner, the UE may receive the early RLF detection benefits of the T312 timer, even if the T310 timer was not running at the time that the UE measurement report transmission is triggered. Also, for example, the RLF may be declared by the UE, and the connection re-establishment initiated by the UE, upon expiration of the T312 timer, if the timer T310 is running (and/or a threshold number of consecutive OOS indications were detected by UE) at a time when the timer T312 expired. Thus, this solution may allow the UE to receive the benefit of the early RLF detection (e.g., T312) timer, even where the T310 timer was not started (or a threshold number of OOS indications were detected) until after triggering of the measurement report.

[0054] FIG. 3 is a flow chart illustrating operation of a user device or UE according to an example embodiment. As shown in the example of FIG. 3, the procedure begins at operation 1). At operation 2), the UE may evaluate a measurement event (e.g., compare measured signal parameters of signals received from cells to each other, and/or to a threshold, or other evaluation) for which a T312 timer has been configured. At operation 3, the UE determines whether the measurement event (for which the T312 timer has been configured) is satisfied. If the measurement event is satisfied, this triggers the transmission of the measurement report from the UE to the serving cell. If the measurement event is satisfied, then flow proceeds to operation 4). At operation 4), in response to the triggering of the measurement report (the measurement event being satisfied), the UE starts timer T312 if it is not already running. Note that at operation 4), the starting of timer T312 is performed regardless if timer T310 is running or not. At operation 5), the UE determines whether the T312 timer has expired. If the T312 timer expires, flow proceeds to operation 6). At operation 6), the UE determines if the T310 timer is running (e.g., determines if a threshold number of OOS indications has been detected by the lower layer 210 of the UE and reported to the RLM function 214 (FIG.

2). At operation 6), if the T310 timer is running (at the time of the expiration of the T312 timer), then a connection re-establishment is performed at operation 7), e.g., towards the cell that satisfied the measurement event or triggered the measurement report. At operation 8, the procedure ends.

[0055] In another exemplary embodiment, instead of initiating a connection re establishment at operation 7), the UE may perform an early HO execution, unlike in the current solutions where it is used to declared RLF, and thus initiate recovery procedure early. Thus, in this alternative embodiment, the UE may perform a handover or condition handover to a prepared cell, for example, instead of initiating connection re establishment.

[0056] FIG. 4 is a diagram illustrating two conditions that may be used to describe operation of the UE according to an example embodiment.

[0057] Condition 1 : At time T2, the radio link to the source cell is poor (OOS condition exists at UE). Thus, for example, a timer T310 may be started when this condition atT2 is fulfilled, e.g., radio link problem is detected towards the source cell.

[0058] Condition 2: At time T1 , there is a neighbor cell with good signal quality (e.g., satisfying measurement event, and triggering measurement report from UE). Thus, for example, a measurement report may be triggered for a measurement identity for which T312 has been configured when this condition is fulfilled, causing timer T312 to start.

[0059] According to an example embodiment, improved RLF detection and recovery may be provided, e.g., where the monitoring function (T312 timer) is started immediately (or within a threshold period of time, or in response to triggering of measurement report) when the condition 2 at time T1 (where T1 < T2, or time T1 is before time T2) holds (or occurs), regardless whether condition 2 will occur in the future (at T2) or not (T2 = infinity). In other words, in an example embodiment, timer T312 may be started upon triggering of the measurement report, even though timer T310 may not be running.

[0060] This may lead to following benefit: Timer T312 is started at T1 when condition 2 is fulfilled at time T1 (regardless whether timer T310 is running when measurement report is triggered). This may allow the RLF recovery process to be initiated or started earlier than other methods by [T310-T312 + T2-T1], since T312 is typically shorter than T310, and T312 is started earlier (at T1 instead of T2).

[0061] Some Example Features:

[0062] The solution improves radio link monitoring, e.g., including improving radio link failure detection and/or recovery.

[0063] The solution enables the start of T312 timer before a radio link problem towards the source cell is detected.

[0064] The solution enables the initiation of the RLF recovery process earlier, e.g., by up to T312 timer length earlier in some cases.

[0065] With this approach, in the situation where measurement event has been triggered before the radio link problem (OOS condition for UE detected based on threshold number of OOS indications from PHY) has started, radio link failure/recovery can be initiated much earlier than with current proposals. More specifically, timer T312 may be started earlier than with current solutions assuming. Expiration of T312 may cause RLF recovery, assuming timer T310 is running at the expiration ofT312.

[0066] The UE can execute handover towards a prepared cell upon the expiry of T312, which is currently used for accelerated RLF declaration and thus starting the re establishment procedure earlier.

[0067] According to an example embodiment, receiving may mean (or may include) preparing a message or, in the case the apparatus comprises radio parts (e.g., wireless transceiver) or is coupled to them, receiving via a radio path (e.g., antenna and wireless transceiver) as well. Controlling transmitting may mean or may include preparing a message (e.g., a group of bits, or a packet) for transmission, and then transmitting the message via a wireless transceiver or other apparatus, as an illustrative example. Thus, controlling transmitting may include transmitting.

[0068] Example 1. FIG. 5 is a flow chart illustrating operation of a user device

(or UE) according to an example embodiment. Operation 510 includes measuring, by a user device, at least one signal parameter of signals received from a plurality of cells. For example, a UE 132 (FIGs. 1 , 2) may measure at least one signal parameter, such as a reference signal received power (RSRP), a signal to noise ratio (SNR), or other signal parameter, of signals received from a serving cell, and from one or more neighbor cells. See operation 2) of FIG. 3.

[0069] Operation 520 of FIG. 5 includes determining, by the user device (e.g., UE 132, FIGs. 1-2), that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring. UE 132 may be configured to measure a signal parameter(s) of signals received from one or more cells, and send a measurement report when one or more measurement events are satisfied. For example, the UE may be configured to trigger or cause transmission of a measurement report to the serving cell if an A3 event is detected (e.g., neighbor cell has a signal parameter (e.g., RSRP) that is an offset better than the measured signal parameter of the serving cell) for a predefined period of time (e.g. time to trigger). The UE may perform signal measurements (e.g., measure RSRP or other signal parameter) of the serving cell and one or more neighbor cells, and then trigger (or cause transmission of) a measurement report if the configured measurement event (e.g., A3 measurement event) is detected. The measurement report may, for example, identify the cell that triggered the transmission of the measurement report, along with other information. See operations 2)- 3) of flow chart of FIG. 3.

[0070] And, operation 530 of FIG. 5 includes initiating, by the user device, a connection re-establishment (see operation 7) of FIG. 3) with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization (OOS) condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered. According to an example embodiment, the threshold period of time may be measured or indicated by the initiating a connection re-establishment with a cell may include transmitting a connection re-establishment request to a cell (e.g., either the previously serving cell, or a different cell). For example, an early RLF (radio link failure) detection timer (T312 timer 218) may be started (started running) when the transmission of the measurement report is triggered at the UE (e.g., see operation 4) of FIG. 3). In an example embodiment, initiation of the connection re-establishment may be performed when a threshold period of time has elapsed since the transmission of the measurement report has been triggered (e.g., initiation of the connection re-establishment may be performed upon expiration of the T312 timer 218 of the UE, FIGs. 1-2), regardless whether an out-of-synchronization (OOS) condition existed for the UE at the time the transmission of the measurement report is triggered. For example, the OOS condition for the UE 132 may include UE 132 detecting of a threshold (e.g., N310) number of consecutive OOS indications with respect to the serving cell (e.g., which may cause timer T310220 to start running). Thus, initiation of connection re-establishment may be performed by UE 132 upon expiration of the T312 timer 218, even in a case where the OOS condition did not exist (and/or timer T310 was not running) at a time when the transmission of the measurement report was triggered.

[0071] Example 2. The method of example 1 , wherein the determining, by the user device, that a transmission of the measurement report from the user device to the serving cell has been triggered comprises: determining, by the user device based on the measuring, that a measurement event has been satisfied, causing the user device to initiate transmission of the measurement report. For example, the UE 132 (FIGs. 1-2) may be configured to trigger or cause transmission of a measurement report to the serving cell if an A3 (as an illustrative example event) measurement event is detected (e.g., a neighbor cell has a signal parameter (e.g., RSRP) that is an offset better than the measured signal parameter of the serving cell) for a predefined period of time (e.g., time to trigger). Thus, after measuring a signal parameter(s) for signals received from a plurality of cells, the UE 132 may determine whether the configured measurement event has been satisfied, e.g., whether a RSRP of a signal received by the UE from a neighbor cell is an offset better (greater) than RSRP of a signal received by the UE from the serving cell. If this measurement event (as an illustrative example) is satisfied, this will trigger (or cause) the UE 132 to transmit a measurement report to the serving cell, for example.

[0072] Example 3. The method of any of examples 1 -2, wherein the out-of- synchronization condition for the user device comprises: at least a threshold number of consecutive out-of-synchronization indications for the user device with respect to the serving cell. For example, the OOS condition for the UE 132 may include RLM function 214 of UE 132 detecting of a threshold (e.g., N310, see threshold counter values 216,

FIG. 2) number of consecutive OOS indications with respect to the serving cell (e.g., which may cause T310 timer 220 to start running). For example, OOS indications may be reported by a UE lower protocol layer (e.g., PHY layer) 210 to a RLM function 214 (which may be provided at a higher protocol layer) of the UE 132, FIG. 2. An OOS condition may exist at the UE 132, for example, after a threshold (e.g., N310) number of consecutive OOS indications have been reported by lower protocol layer 210 to the RLM function 214 ofUE 132 (see FIG. 2).

[0073] Example 4. The method of any of examples 1-3, further comprising: detecting, by the user device, that the out-of-synchronization condition exists for the user device with respect to the serving cell after the measurement report was triggered. According to an example embodiment, the UE 132 (e.g., see FIGs. 1-2) may detect that an OOS condition exists for the UE with respect to the serving cell after the measurement report was triggered. The OOS condition may cause T310 timer 220 to start running (FIG. 2).

[0074] Example 5. The method of example 4, wherein the initiating comprises: initiating, by the user device, a connection re-establishment with a cell after the threshold period of time has elapsed since the transmission of the measurement report has been triggered and in response to the detecting that the out-of-synchronization condition existed for the user device with respect to the serving cell after the measurement report was triggered, and regardless whether the out-of-synchronization condition existed for the user device at a time that the transmission of the measurement report was triggered. See, e.g., operations 3) - 7), of FIG. 3. For example, the initiating of the connection re establishment by the UE 132 (e.g., operation 7) of FIG. 3) may be performed based on (or in response to) both the expiration of the T312 timer 218 and the OOS condition existing (or timer 310 running) at the time of expiration of T312 timer, and regardless whether the OOS condition may have existed (or whether timer T310220 was running) at a time when the measurement report was triggered (or when timer T312 was started). Thus, for example, timer T312 may be started in response to the measurement report being triggered, even in a case where the OOS condition does not exist (or timer T310 is not running) at the time of the triggering of the transmission of the measurement report. See, e.g., operations 5), 6) and 7) of example flow chart of FIG. 3, where it can be seen in this example that the connection re-establishment may be initiated by UE 132 upon expiration of the T312 timer 218 if the timer T310220 is running at the time of the T312 expiration, according to an example embodiment. This initiating of the connection establishment may be performed at operation 7) (FIG. 3), for example, even if the OOS condition did not exist at the time when the measurement report was triggered.

[0075] Example 6. The method of any of examples 1-5, wherein the initiating a connection re-establishment comprises: sending, by the user device to a suitable cell, a connection re-establishment message to request re-establishment of a connection between the user device (or UE) and the suitable cell, wherein the suitable cell is selected by predefined criteria. According to an example embodiment, UE 132 (e.g., see FIGs. 1-2) may initiate the connection re-establishment with the serving (or previously serving) cell or a different cell, which may be selected based on some predefined criteria. For example, the cell to which the connection re-establishment request will be sent may be the cell that caused the triggering of the measurement report, e.g., the cell that sent signals that were measured by the UE to have a RSRP that is an offset better than RSRP of the signals received from the serving cell. This cell (e.g., target cell) that caused or triggered the UE to transmit the measurement report may be selected by the UE as a suitable cell to which the connection re-establishment request may be sent, according to an illustrative example.

[0076] Example 7. The method of any of examples 1-6, wherein the initiating comprises: starting running a first timer (e.g., starting T312 timer 218, shown as operation 4) of FIG. 3) in response to the transmission of the measurement report being triggered; determining that the first timer (e.g., T312 timer 218) has expired (e.g., operation 5) of FIG. 3 shows detecting when T312 timer has expired); determining, by the user device (or UE 132) at a time of expiration of the first timer, whether a second timer (e.g., timer T310220) is running (e.g., UE 132 detecting whether T310 timer 220 is running at operation 6) of FIG. 3, at a time that the T312 timer 218 expired), wherein the second timer will be started running if an out-of-synchronization condition exists for the user device with respect to the serving cell (e.g., T310 timer 220 will start running if an OOS condition exists or is detected at the UE, e.g., which may include determining that a threshold number of consecutive OOS indications have been detected by UE 132); and initiating, by the user device (by UE 132), a connection re-establishment with a cell, in response to determining that the first timer has expired and only if the second timer is running at the time of expiration of the first timer. For example, at operation 7) of FIG.

3, the UE 132 may initiate a connection re-establishment in response to the T312 timer 218 has expired and only if the T310 timer 220 is running at the time that timer T312 expired.

[0077] Example 8. The method of any of examples 1-7, wherein the initiating comprises: starting running a first timer (e.g., starting T312 timer 218, shown as operation 4) of FIG. 3) in response to the transmission of the measurement report being triggered; determining that the first timer (e.g., T312 timer 218, FIG. 2) has expired (e.g., see operation 5) of FIG. 3); determining, by the user device (e.g. UE 132, FIGs. 1-2), that a second timer (e.g., T310 timer 220) is running at the time that the first timer (timer T312) expired (e.g., UE 132 determining that T310 timer 220 is running at operation 6) of FIG. 3, at the time that T312 timer 218 expired), wherein the second timer will be started running if an out-of-synchronization condition exists for the user device with respect to the serving cell (e.g., T310 timer 220 will start running if an OOS condition exists or is detected at the UE, e.g., which may include determining that a threshold (e.g., N310) number of consecutive OOS indications have been detected by UE 132); and initiating, by the user device, a connection re-establishment with a cell, in response to both the determining that the first timer has expired and the determining that the second timer is running at the time that the first timer expired. For example, at operation 7) of FIG. 3, the UE 132 initiates a connection re-establishment in response to the T312 timer 218 expiring and only if the T310 timer 220 is running at the time that timer T312 expired.

[0078] Example 9. An apparatus comprising means for performing the method of any of examples 1-8.

[0079] Example 10. Anon-transitory computer-readable storage medium (e.g., memory 1006, FIG. 6) comprising instructions stored thereon that, when executed by at least one processor, are configured to cause a computing system to perform the method of any of examples 1-8.

[0080] Example 11. An apparatus (e.g., 1000, FIG. 6, and/or UE 132 ofFIGs. 1- 2) comprising: at least one processor (controller 1008 and/or processor 1004, FIG. 6); and at least one memory (e.g., memory 1006, FIG. 6) including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform the method of any of examples 1-8.

[0081] Example 12. A computer program comprising instructions which, when the program is executed by an apparatus (e.g., apparatus 1000, processor 1004 and/or controller 1008), cause the apparatus (e.g., apparatus 1000, FIG. 6) to carry out the method of any of examples 1-8.

[0082] Example 13. An apparatus (e.g., 1000, FIG. 6, and/or UE 132 ofFIGs. 1- 2) comprising: at least one processor (e.g., controller 1008 and/or processor 1004, FIG.

6); and at least one memory (e.g., memory 1006, FIG. 6) including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: measure ( e.g., operation 510, FIG. 5), by a user device (e.g., UE 132, FIGs. 1-2, and/or apparatus 1000 of FIG. 6), at least one signal parameter of signals received from a plurality of cells; determine (e.g., operation 520), by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and initiate, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.

For Examples 13-20, see example embodiments described with respect to Examples 1-8, respectively.

[0083] Example 14. The apparatus (e.g., 1000, FIG. 6, and/or UE 132 ofFIGs. 1- 2) of example 13, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to determine comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: determine, by the user device based on the measuring, that a measurement event has been satisfied, causing the user device to initiate transmission of the measurement report.

[0084] Example 15. The apparatus (e.g., 1000, FIG. 6, and/or UE 132 ofFIGs. 1- 2) of any of examples 13-14, wherein the out-of-synchronization condition for the user device comprises: at least a threshold number of consecutive out-of-synchronization indications for the user device with respect to the serving cell.

[0085] Example 16. The apparatus (e.g., 1000, FIG. 6, and/or UE 132 ofFIGs. 1- 2) of any of examples 13-15, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus to: detect, by the user device, that the out-of-synchronization condition exists for the user device with respect to the serving cell after the measurement report was triggered.

[0086] Example 17. The apparatus (e.g., 1000, FIG. 6, and/or UE 132 ofFIGs. 1- 2) of example 16, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to initiate comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: initiate, by the user device, a connection re establishment with a cell after the threshold period of time has elapsed since the transmission of the measurement report has been triggered and in response to the detecting that the out-of-synchronization condition existed for the user device with respect to the serving cell after the measurement report was triggered, and regardless whether the out-of-synchronization condition existed for the user device at a time that the transmission of the measurement report was triggered.

[0087] Example 18. The apparatus (e.g., 1000, FIG. 6, and/or UE 132 ofFIGs. 1- 2) of any of claims 13-17, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to initiate comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: send, by the user device to a suitable cell, a connection re-establishment message to request re-establishment of a connection between the user device and the suitable cell, wherein the suitable cell is selected by predefined criteria.

[0088] Example 19. The apparatus (e.g., 1000, FIG. 6, and/or UE 132 of FIGs. 1- 2) of any of examples 13-18, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to initiate comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: start running a first timer in response to the transmission of the measurement report being triggered; determine that the first timer has expired; determine, by the user device at a time of expiration of the first timer, whether a second timer is running, wherein the second timer will be started running if an out-of-synchronization condition exists for the user device with respect to the serving cell; and initiate, by the user device, a connection re-establishment with a cell, in response to determining that the first timer has expired and only if the second timer is running at the time of expiration of the first timer.

[0089] Example 20. The apparatus (e.g., 1000, FIG. 6, and/or UE 132 of FIGs. 1- 2) of any of examples 13-19, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to initiate comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: start running a first timer in response to the transmission of the measurement report being triggered; determine that the first timer has expired; determine, by the user device, that a second timer is running at the time that the first timer expired, wherein the second timer will be started running if an out-of- synchronization condition exists for the user device with respect to the serving cell; and initiate, by the user device, a connection re-establishment with a cell, in response to both the determining that the first timer has expired and the determining that the second timer is running at the time that the first timer expired. As noted, for Examples 13-20, see example embodiments described above with respect to Examples 1-8, respectively. [0090] Example 21. An apparatus (e.g., 1000, FIG. 6, and/or UE 132 ofFIGs. 1- 2) comprising: means (e.g., controller 1008 and/or processor 1004, FIG. 6; and/or operation 510 of FIG. 5, and/or operation 2) of FIG. 3) for measuring, by a user device, at least one signal parameter of signals received from a plurality of cells; means (e.g., controller 1008 and/or processor 1004, FIG. 6, and/or operation 520, FIG. 5, and/or operation 3) of FIG. 3) for determining, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and means (e.g., controller 1008 and/or processor 1004, FIG. 6, and/or RFM function 214, FIG. 2, and/or operation 530 of FIG. 5, and/or operation 7) of FIG. 3) for initiating, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered. See Example embodiments described with reference to Example 1.

[0091] FIG. 6 is a block diagram of a wireless station (e.g., AP, BS or user device/UE, or other network node) 1000 according to an example embodiment. The wireless station 1000 may include, for example, one or more (e.g., two as shown in FIG. 6) RF (radio frequency) or wireless transceivers 1002A, 1002B, where each wireless transceiver includes a transmitter to transmit signals and a receiver to receive signals.

The wireless station also includes a processor or control unit/entity (controller) 1004 to execute instructions or software and control transmission and receptions of signals, and a memory 1006 to store data and/or instructions.

[0092] Processor 1004 may also make decisions or determinations, generate frames, packets or messages for transmission, decode received frames or messages for further processing, and other tasks or functions described herein. Processor 1004, which may be a baseband processor, for example, may generate messages, packets, frames or other signals for transmission via wireless transceiver 1002 (1002A or 1002B). Processor 1004 may control transmission of signals or messages over a wireless network, and may control the reception of signals or messages, etc., via a wireless network (e.g., after being down-converted by wireless transceiver 1002, for example). Processor 1004 may be programmable and capable of executing software or other instructions stored in memory or on other computer media to perform the various tasks and functions described above, such as one or more of the tasks or methods described above. Processor 1004 may be (or may include), for example, hardware, programmable logic, a programmable processor that executes software or firmware, and/or any combination of these. Using other terminology, processor 1004 and transceiver 1002 together may be considered as a wireless transmiter/receiver system, for example.

[0093] In addition, referring to FIG. 6, a controller (or processor) 1008 may execute software and instructions, and may provide overall control for the station 1000, and may provide control for other systems not shown in FIG. 6, such as controlling input/output devices (e.g., display, keypad), and/or may execute software for one or more applications that may be provided on wireless station 1000, such as, for example, an email program, audio/video applications, a word processor, a Voice over IP application, or other application or software.

[0094] In addition, a storage medium may be provided that includes stored instructions, which when executed by a controller or processor may result in the processor 1004, or other controller or processor, performing one or more of the functions or tasks described above.

[0095] According to another example embodiment, RF or wireless transceiver(s) 1002A/1002B may receive signals or data and/or transmit or send signals or data. Processor 1004 (and possibly transceivers 1002 A/1002B) may control the RF or wireless transceiver 1002A or 1002B to receive, send, broadcast or transmit signals or data.

[0096] The embodiments are not, however, restricted to the system that is given as an example, but a person skilled in the art may apply the solution to other communication systems. Another example of a suitable communications system is the 5G system. It is assumed that network architecture in 5G will be quite similar to that of the LTE-advanced. 5G is likely to use multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates.

[0097] It should be appreciated that future networks will most probably utilise network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into “building blocks” or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations may be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

[0098] Embodiments of the various techniques described herein may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Embodiments may be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, a data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. Embodiments may also be provided on a computer readable medium or computer readable storage medium, which may be a non-transitory medium. Embodiments of the various techniques may also include embodiments provided via transitory signals or media, and/or programs and/or software embodiments that are downloadable via the Internet or other network(s), either wired networks and/or wireless networks. In addition, embodiments may be provided via machine type communications (MTC), and also via an Internet of Things (IOT).

[0099] The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

[00100] Furthermore, embodiments of the various techniques described herein may use a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the embodiment and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers,...) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals. The rise in popularity of smartphones has increased interest in the area of mobile cyber-physical systems. Therefore, various embodiments of techniques described herein may be provided via one or more of these technologies.

[00101] A computer program, such as the computer program(s) described above, can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit or part of it suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[00102] Method steps may be performed by one or more programmable processors executing a computer program or computer program portions to perform functions by operating on input data and generating output. Method steps also may be performed by, and an apparatus may be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[00103] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer, chip or chipset. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer may include at least one processor for executing instructions and one or more memory devices for storing instructions and data.

Generally, a computer also may include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory may be supplemented by, or incorporated in, special purpose logic circuitry.

[00104] To provide for interaction with a user, embodiments may be implemented on a computer having a display device, e.g., a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user and a user interface, such as a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[00105] Embodiments may be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an embodiment, or any combination of such back-end, middleware, or front-end components. Components may be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN) and a wide area network (WAN), e.g., the Internet.

[00106] While certain features of the described embodiments have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the various embodiments.

Claims

WHAT IS CLAIMED IS:

1. A method comprising: measuring, by a user device, at least one signal parameter of signals received from a plurality of cells; determining, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and initiating, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.

2. The method of claim 1 , wherein the determining, by the user device, that a transmission of the measurement report from the user device to the serving cell has been triggered comprises: determining, by the user device based on the measuring, that a measurement event has been satisfied, causing the user device to initiate transmission of the measurement report.

3. The method of any of claims 1 -2, wherein the out-of-synchronization condition for the user device comprises: at least a threshold number of consecutive out-of-synchronization indications for the user device with respect to the serving cell.

4. The method of any of claims 1 -3, further comprising: detecting, by the user device, that the out-of-synchronization condition exists for the user device with respect to the serving cell after the measurement report was triggered.

5. The method of claim 4, wherein the initiating comprises: initiating, by the user device, a connection re-establishment with a cell after the threshold period of time has elapsed since the transmission of the measurement report has been triggered and in response to the detecting that the out-of-synchronization condition existed for the user device with respect to the serving cell after the measurement report was triggered, and regardless whether the out-of-synchronization condition existed for the user device at a time that the transmission of the measurement report was triggered.

6. The method of any of claims 1 -5, wherein the initiating a connection re establishment comprises: sending, by the user device to a suitable cell, a connection re-establishment message to request re-establishment of a connection between the user device and the suitable cell, wherein the suitable cell is selected by predefined criteria.

7. The method of any of claims 1 -6, wherein the initiating comprises: starting running a first timer in response to the transmission of the measurement report being triggered; determining that the first timer has expired; determining, by the user device at a time of expiration of the first timer, whether a second timer is running, wherein the second timer will be started running if an out-of- synchronization condition exists for the user device with respect to the serving cell; and initiating, by the user device, a connection re-establishment with a cell, in response to determining that the first timer has expired and only if the second timer is running at the time of expiration of the first timer.

8. The method of any of claims 1 -7, wherein the initiating comprises: starting running a first timer in response to the transmission of the measurement report being triggered; determining that the first timer has expired; determining, by the user device, that a second timer is running at the time that the first timer expired, wherein the second timer will be started running if an out-of- synchronization condition exists for the user device with respect to the serving cell; and initiating, by the user device, a connection re-establishment with a cell, in response to both the determining that the first timer has expired and the determining that the second timer is running at the time that the first timer expired.

9. An apparatus comprising means for performing the method of any of claims 1-8.

10. A non-transitory computer-readable storage medium comprising instructions stored thereon that, when executed by at least one processor, are configured to cause a computing system to perform the method of any of claims 1-8.

11. An apparatus comprising: at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform the method of any of claims 1 -

8.

12. A computer program comprising instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the method of any of claims 1-8.

13. An apparatus comprising: at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: measure, by a user device, at least one signal parameter of signals received from a plurality of cells; determine, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and initiate, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.

14. The apparatus of claim 13, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to determine comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: determine, by the user device based on the measuring, that a measurement event has been satisfied, causing the user device to initiate transmission of the measurement report.

15. The apparatus of any of claims 13-14, wherein the out-of-synchronization condition for the user device comprises: at least a threshold number of consecutive out-of-synchronization indications for the user device with respect to the serving cell.

16. The apparatus of any of claims 13-15, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus to: detect, by the user device, that the out-of-synchronization condition exists for the user device with respect to the serving cell after the measurement report was triggered.

17. The apparatus of claim 16, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to initiate comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: initiate, by the user device, a connection re-establishment with a cell after the threshold period of time has elapsed since the transmission of the measurement report has been triggered and in response to the detecting that the out-of-synchronization condition existed for the user device with respect to the serving cell after the measurement report was triggered, and regardless whether the out-of-synchronization condition existed for the user device at a time that the transmission of the measurement report was triggered.

18. The apparatus of any of claims 13-17, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to initiate comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: send, by the user device to a suitable cell, a connection re-establishment message to request re-establishment of a connection between the user device and the suitable cell, wherein the suitable cell is selected by predefined criteria.

19. The apparatus of any of claims 13-18, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to initiate comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: start running a first timer in response to the transmission of the measurement report being triggered; determine that the first timer has expired; determine, by the user device at a time of expiration of the first timer, whether a second timer is running, wherein the second timer will be started running if an out-of- synchronization condition exists for the user device with respect to the serving cell; and initiate, by the user device, a connection re-establishment with a cell, in response to determining that the first timer has expired and only if the second timer is running at the time of expiration of the first timer.

20. The apparatus of any of claims 13-19, wherein the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to initiate comprises the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: start running a first timer in response to the transmission of the measurement report being triggered; determine that the first timer has expired; determine, by the user device, that a second timer is running at the time that the first timer expired, wherein the second timer will be started running if an out-of- synchronization condition exists for the user device with respect to the serving cell; and initiate, by the user device, a connection re-establishment with a cell, in response to both the determining that the first timer has expired and the determining that the second timer is running at the time that the first timer expired.

21. An apparatus comprising: means for measuring, by a user device, at least one signal parameter of signals received from a plurality of cells; means for determining, by the user device, that a transmission of a measurement report from the user device to the serving cell has been triggered at the user device based on the measuring; and means for initiating, by the user device, a connection re-establishment with a cell after a threshold period of time has elapsed since the measurement report has been triggered, regardless whether an out-of-synchronization condition existed for the user device with respect to the serving cell at the time that transmission of the measurement report was triggered.