Patent Description:
Examples of mobile or wireless telecommunication systems may include the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E-UTRAN), LTE-Advanced (LTE-A), MulteFire, LTE-A Pro, and/or fifth generation (<NUM>) radio access technology or new radio (NR) access technology. Fifth generation (<NUM>) wireless systems refer to the next generation (NG) of radio systems and network architecture. <NUM> is mostly built on a new radio (NR), but the <NUM> (or NG) network can also build on E-UTRA radio. It is estimated that NR will provide bitrates on the order of <NUM>-<NUM> Gbit/s or higher, and will support at least enhanced mobile broadband (eMBB) and ultra-reliable low-latency-communication (URLLC) as well as massive machine type communication (mMTC). NR is expected to deliver extreme broadband and ultra-robust, low latency connectivity and massive networking to support the Internet of Things (IoT). With IoT and machine-to-machine (M2M) communication becoming more widespread, there will be a growing need for networks that meet the needs of lower power, low data rate, and long battery life. It is noted that, in <NUM>, the nodes that can provide radio access functionality to a user equipment (i.e., similar to Node B in UTRAN or eNB in LTE) may be named gNB when built on NR radio and may be named NG-eNB when built on E-UTRA radio.

The invention is directed to an apparatus according to appended independent claim <NUM>, a method according to appended independent claim <NUM> and a system according to appended independent claim <NUM>. Advantageous features are set out in the appended dependent claims <NUM>-<NUM> and <NUM>-<NUM>.

For proper understanding reference should be made to the accompanying drawings, wherein:.

According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims.

It will be readily understood that the components of certain example embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of some example embodiments of systems, methods, apparatuses, and computer program products for failure indication of master cell group (MCG), is not intended to limit the scope of certain embodiments but is representative of selected example embodiments.

Additionally, if desired, the different functions or steps discussed below may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the described functions or steps may be optional or may be combined. As such, the following description should be considered as merely illustrative of the principles and teachings of certain example embodiments, and not in limitation thereof.

Some example embodiments may relate to dual connectivity (DC) and/or carrier aggregation (CA) enhancements. For example, certain embodiments may relate to fast master cell group (MCG) link recovery that can support fast recovery of MCG link, e.g., by utilizing the secondary cell group (SCG) link and split signaling radio bearers (SRBs) for recovery during MCG failure while operating under DC or multi-radio DC (MR-DC).

3GPP technical specification TS <NUM> currently specifies, for SCG/MCG failure handling, that radio link failure (RLF) is declared separately for the MCG and for the SCG. If radio link failure is detected for MCG, the UE initiates the radio resource control (RRC) connection re-establishment procedure. In E-UTRA - NR DC (EN-DC) and NG-RAN - E-UTRA DC (NGEN-DC), the following SCG failure cases are supported: SCG RLF; secondary node (SN) change failure; SCG configuration failure (only for messages on SRB3); and/or SCG RRC integrity check failure (on SRB3). In some cases, SRB3 may refer to a signalling radio bearer between the UE and a secondary node. In dual connectivity, Signaling Radio Bearer <NUM> (SRB3) refers to a direct signaling radio bearer between the UE and the dual-connectivity Secondary Node.

In EN-DC and NGEN-DC, upon SCG failure the UE suspends SCG transmissions for all radio bearers and reports the SCG failure information, for example SCG Failure Information, to the master node (MN), instead of triggering re-establishment. The MN handles the SCG Failure Information message and may decide to keep, change, or release the SN/SCG. In all the cases, the measurement results according to the SN configuration and the SCG failure type may be forwarded to the old SN and/or to the new SN.

According to the current approach, upon detecting radio link failure for MCG, the UE initiates RRC connection re-establishment, which entails suspending all radio bearers and releasing its dual-connectivity configuration. This may be excessive if the UE's SCG is still up and running.

An embodiment provides an improved handling of MCG RLF detected by a UE configured in dual connectivity or in multiple cells. In certain embodiments, if the UE is configured with at least one of SRB3 terminated at the UE's secondary node, for example Secondary Node, and/or a split SRB terminated at the UE's master node, for example Master Node, and SCG transmissions are not suspended, MCG transmissions for radio bearers, in some cases for all radio bearers, may be suspended, a RRC indication of MCG failure information, for example "MCG Failure Information", may be reported over at least one of SRB3 and/or the SCG leg of the split SRB, and a timer, for example referred as "MCGFailTimer" or named differently, may be started. For example, the SCG transmission may have been suspended due to a prior detection of SCG failure. The split SRB comprises SRBs served by both the MN and the SN. Furthermore, the MN may be a DC MN; and, the SN may be a DC SN.

In one example, the MCG failure information indication may carry information, such as the cause of failure and/or latest measurement results. According to an embodiment, the timer may be a newly defined timer with a duration configured to the UE by the network by RRC or by the UE itself.

According to some embodiments, if the MCG-failure information is reported over SRB3, in some cases over SRB3 only, some or all the information in it may be relayed by the UE's secondary node (terminating SRB3) to the UE's master node, e.g., over a signaling protocol used between the MN and the SN, for example X2AP/XnAP. It is noted that over the split SRB this will occur naturally.

The UE stops the timer, for example referred as MCGFailTimer, upon one or more of the following events: successful reconfiguration or configuration of the UE's primary serving cell, and/or reception of a command to leave RRC_Connected state. According to one embodiment, the UE may trigger RRC connection re-establishment at least upon one or more of the following events: while the timer is running, the UE detects SCG failure or integrity-verification failure on a split SRB for a PDCP PDU received over SCG; and/or the timer expires. This could happen, for example, if the UE's master node has shut down completely.

<FIG> illustrates one example flow diagram of a method for failure indication of MCG with fall-back to RRC re-establishment, according to an embodiment. In some embodiments, the method of <FIG> may be performed by a node or element in a communications network or associated with such a network, such as a UE, mobile equipment (ME), mobile station, mobile device, mobile-termination module within an Integrated Access and Backhaul (IAB) node, stationary device, IoT device, or other device. As described herein, UE may alternatively be referred to as, for example, a mobile station, mobile equipment, mobile unit, mobile device, mobile termination, user device, subscriber station, wireless terminal, tablet, smart phone, IoT device or NB-IoT device, or the like. According to one example, the UE performing the method of <FIG> may be a UE that is configured in DC or in connection with multiple cells.

The method of <FIG> includes, at <NUM>, detecting MCG RLF. According to an embodiment, the method may include determining if the UE is configured with a signaling radio bearer between the UE and the SN and/or a split SRB and if SCG transmissions are suspended. The signaling radio bearer may be a direct signaling radio bearer between the UE and the SN. The SN may be a DC SN. In an embodiment, the signaling radio bearer may be a SRB3. When the UE is configured with the signaling radio bearer and/or a split SRB and SCG transmissions are not suspended, the method includes, at <NUM>, suspending MCG transmissions for radio bearers, transmitting or reporting a RRC indication over the signaling radio bearer (e.g., SRB3) and/or a SCG leg of the split SRB at <NUM>, and starting a timer at <NUM>. In an embodiment, the RRC indication may be a MCG failure information message that includes information on the cause of failure and/or the latest measurement results. According to one embodiment, the timer may be referred to as a "MCGFailTimer" or a different term, and the duration of the timer may be configured to the UE by the network by RRC.

In an embodiment, when the MCG failure information is reported over an SRB terminating at the UE's SN, some or all of the information in the MCG failure information may be relayed by the UE's SN to the UE's MN, e.g., over a signaling protocol used between the MN and the SN, such as X2AP/XnAP. The method also includes, at <NUM>, stopping the timer, for example MCGFailTimer, upon successful reconfiguration or configuration of the UE's primary serving cell and/or upon reception of a command to leave RRC connected state. In some embodiments, the method may include, at <NUM>, triggering RRC connection re-establishment upon the occurrence of at least one or more of triggering events. According to certain embodiments, the triggering events may include at least one of: while the timer is running, detecting SCG failure or integrity-verification failure on a split SRB for a PDCP PDU received over SCG; and/or when the timer expires, for example because the UE's MN has shut down completely.

<FIG> illustrates one example flow diagram of a method for failure indication of MCG with fall-back to RRC re-establishment, according to an embodiment. In some embodiments, the method of <FIG> may be performed by a node or element in a communications network or associated with such a network, such as a base station, access node, eNB, or gNB. In one example, the method of <FIG> may be performed by a DC master node.

In an embodiment, the method of <FIG> may include, at <NUM>, receiving, by a MN, an indication of failure of a MCG configured to a UE. According to one embodiment, the UE may be served by the MN. In one example, the MN may be a DC MN. In response to receiving the indication, the method may further include, at <NUM>, sending to the UE a command to reconfigure or configure a primary serving cell of the UE. In an embodiment, the indication may be received over an interface between the MN and a SN. In one example, the indication may indicate the cause of the failure. According to certain embodiments, the indication may indicate results of radio measurements performed by the UE. In some embodiments, the command to reconfigure the primary serving cell may be based at least in part on the measurement results. In one example, the command may be sent via the SN. In one example, the SN may be a DC SN.

<FIG> illustrates an example of an apparatus <NUM> according to an embodiment. In an embodiment, apparatus <NUM> may be a node, host, or server in a communications network or serving such a network. For example, apparatus <NUM> may be a satellite, base station, a Node B, an evolved Node B (eNB), <NUM> Node B or access point, next generation Node B (NG-NB or gNB), and/or WLAN access point, associated with a radio access network, such as a LTE network, <NUM> or NR. In example embodiments, apparatus <NUM> may be an eNB in LTE or gNB in <NUM>. In other example embodiments, apparatus <NUM> may be a dual-connectivity master node.

In some embodiments, apparatus <NUM> may also include or be coupled to one or more antennas <NUM> for transmitting and receiving signals and/or data to and from apparatus <NUM>. Apparatus <NUM> may further include or be coupled to a transceiver <NUM> configured to transmit and receive information. The transceiver <NUM> may include, for example, a plurality of radio interfaces that may be coupled to the antenna(s) <NUM>. The radio interfaces may correspond to a plurality of radio access technologies including one or more of GSM, NB-IoT, LTE, <NUM>, WLAN, Bluetooth, BT-LE, NFC, radio frequency identifier (RFID), ultrawideband (UWB), MulteFire, and the like. The radio interface may include components, such as filters, converters (for example, digital-to-analog converters and the like), mappers, a Fast Fourier Transform (FFT) module, and the like, to generate symbols for a transmission via one or more downlinks and to receive symbols (for example, via an uplink).

As introduced above, in certain embodiments, apparatus <NUM> may be a network node or RAN node, such as a base station, access point, Node B, eNB, gNB, WLAN access point, or the like. In one example, apparatus <NUM> may be a master node or dual-connectivity master node (DC MN). According to certain embodiments, apparatus <NUM> may be controlled by memory <NUM> and processor <NUM> to perform the functions associated with any of the embodiments described herein, such as the flow or signaling diagrams illustrated in <FIG>. In some embodiments, apparatus <NUM> may be configured to perform a procedure for failure indication of MCG, for example.

For instance, in one embodiment, apparatus <NUM> may be controlled by memory <NUM> and processor <NUM> to receive an indication of failure of a MCG of a UE. The UE may be served by the apparatus <NUM>. In response to receiving the indication, apparatus <NUM> may be controlled by memory <NUM> and processor <NUM> to send to the UE a command to reconfigure or configure a primary serving cell of the UE. In an embodiment, the indication may be received over an interface between the apparatus <NUM> and a SN. In one embodiment, the indication may indicate the cause of the failure. According to certain embodiments, the indication may indicate results of radio measurements performed by the UE. In some embodiments, the command to reconfigure the primary serving cell may be based at least in part on the measurement results. In one example, the command may be sent via the SN. In one example, the SN may be a DC SN.

<FIG> illustrates an example of an apparatus <NUM> according to another embodiment. In an embodiment, apparatus <NUM> may be a node or element in a communications network or associated with such a network, such as a UE, mobile equipment (ME), mobile station, mobile device, mobile termination, stationary device, IoT device, or other device. As described herein, UE may alternatively be referred to as, for example, a mobile station, mobile equipment, mobile unit, mobile device, user device, subscriber station, wireless terminal, tablet, smart phone, IoT device, sensor or NB-IoT device, or the like. As one example, apparatus <NUM> may be implemented in, for instance, a wireless handheld device, a wireless plug-in accessory, or the like.

According to an example embodiment, apparatus <NUM> may optionally be configured to communicate with a network via a wireless or wired communications link <NUM> according to any radio access technology, such as NR.

As discussed above, according to some embodiments, apparatus <NUM> may be a UE, mobile device, mobile station, ME, IoT device and/or NB-IoT device, for example. In one embodiment, apparatus <NUM> may include a UE configured in DC.

According to certain embodiments, apparatus <NUM> may be controlled by memory <NUM> and processor <NUM> to perform the functions associated with example embodiments described herein. For example, in some embodiments, apparatus <NUM> may be configured to perform one or more of the processes depicted in any of the flow charts or signaling diagrams described herein, such as the flow diagrams illustrated in <FIG>. For example, in certain embodiments, apparatus <NUM> may be configured to perform a procedure for failure indication of MCG, for instance.

Apparatus <NUM> is controlled by memory <NUM> and processor <NUM> to detect MCG RLF. According to an embodiment, apparatus <NUM> may be controlled by memory <NUM> and processor <NUM> to determine if the apparatus <NUM> is configured with SRB3 and/or a split SRB and if SCG transmissions are suspended. When the apparatus <NUM> is configured with a signaling radio bearer between apparatus <NUM> and the SN and/or a split SRB, and SCG transmissions are not suspended, apparatus <NUM> is controlled by memory <NUM> and processor <NUM> to suspend MCG transmissions for radio bearers, to transmit or report a RRC indication over the signaling radio bearer and/or a SCG leg of the split SRB, and to start a timer. The signaling radio bearer comprises a direct signaling radio bearer between the apparatus <NUM> and the SN. The SN comprises a DC SN. According to one example, the direct signaling radio bearer may be SRB3. In an embodiment, the RRC indication may be a MCG failure information message that includes information on the cause of failure and/or the latest measurement results. According to one embodiment, the timer may be referred to as a "MCGFailTimer" and the duration of the timer may be configured to the UE by the network by RRC.

In an embodiment, when the MCG failure information is reported over an SRB terminating at the SN of apparatus <NUM>, some or all of the information in the MCG failure information may be relayed by the SN of apparatus <NUM> to the MN of apparatus <NUM>. For example, the information may be relayed to the MN over a signaling protocol used between the MN and the SN. In one example, the signaling protocol comprises X2AP/XnAP. Apparatus <NUM> is controlled by memory <NUM> and processor <NUM> to stop the timer, for example MCGFailTimer, upon successful reconfiguration or configuration of the primary serving cell of apparatus <NUM> and/or upon reception of a command to leave RRC connected state. In an embodiment, apparatus <NUM> may be controlled by memory <NUM> and processor <NUM> to trigger RRC connection re-establishment upon the occurrence of at least one or more of triggering events. According to certain embodiments, the triggering event may include, while the timer is running, detecting SCG failure or integrity-verification failure on a split SRB for a PDCP PDU received over SCG. Additionally or alternatively, in an embodiment, the triggering event may include the expiration of the timer (e.g., if the MN of apparatus <NUM> has shut down completely).

Therefore, certain example embodiments provide several technical improvements, enhancements, and/or advantages. For example, according to certain embodiments, RRC connection re-establishment and the time-consuming cell selection that comes with it, can be avoided whenever the UE can continue communication with its Master Node over the SCG, thereby serving the purpose of fast MCG recovery. Meanwhile, communication over any radio bearers utilizing the SCG is never interrupted at all. Additionally, certain embodiments provide RRC connection re-establishment as a fall-back to avoid UE remaining in a state without an operational Primary Cell. Accordingly, the use of certain example embodiments results in improved functioning of communications networks and their nodes.

In some example embodiments, the functionality of any of the methods, processes, signaling diagrams, algorithms or flow charts described herein may be implemented by software and/or computer program code or portions of code stored in memory or other computer readable or tangible media, and executed by a processor.

In some example embodiments, an apparatus may be included or be associated with at least one software application, module, unit or entity configured as arithmetic operation(s), or as a program or portions of it (including an added or updated software routine), executed by at least one operation processor. Programs, also called program products or computer programs, including software routines, applets and macros, may be stored in any apparatus-readable data storage medium and include program instructions to perform particular tasks.

A computer program product may comprise one or more computer-executable components which, when the program is run, are configured to carry out some example embodiments. The one or more computer-executable components may be at least one software code or portions of it. Modifications and configurations required for implementing functionality of an example embodiment may be performed as routine(s), which may be implemented as added or updated software routine(s). Software routine(s) may be downloaded into the apparatus.

As an example, software or a computer program code or portions of it may be in a 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 may include a record medium, computer memory, read-only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and software distribution package, for example. The computer readable medium or computer readable storage medium may be a non-transitory medium.

In other example embodiments, the functionality may be performed by hardware or circuitry included in an apparatus (e.g., apparatus <NUM>), for example through the use of an application specific integrated circuit (ASIC), a programmable gate array (PGA), a field programmable gate array (FPGA), or any other combination of hardware and software. In yet another example embodiment, the functionality may be implemented as a signal, a non-tangible means that can be carried by an electromagnetic signal downloaded from the Internet or other network.

According to an example embodiment, an apparatus, such as a node, device, or a corresponding component, may be configured as circuitry, a computer or a microprocessor, such as single-chip computer element, or as a chipset, including at least a memory for providing storage capacity used for arithmetic operation and an operation processor for executing the arithmetic operation.

A first method includes detecting MCG RLF. When the UE is configured with at least one of a signaling radio bearer between the UE and a SN or a split SRB, and SCG transmissions are not suspended, the method includes suspending MCG transmissions for radio bearers, transmitting or reporting a RRC indication over the at least one of the signaling radio bearer between the UE and the SN,or the SCG leg of the split SRB. The method further includes starting a timer. In one example, the signaling bearer between the UE and the SN may include SRB3. Furthermore, the signaling bearer may comprise a direct signaling bearer between the UE and the SN. The SN may comprise a DC SN.

In a variant, the RRC indication may be a MCG failure information message that includes at least one of information on the cause of failure or the latest measurement results. According to a variant, the timer may be referred to as a "MCGFailTimer". The duration of the timer may be configured at the UE from the network via RRC or the duration of the timer may be configured by the UE itself.

In a variant, he MCG failure information is reported over an SRB, wherein the SRB is terminated at the UE's SN. Some or all of the information in the MCG failure information may be relayed by the UE's SN to the UE's MN. The relaying may be performed over a signaling protocol used between the MN and the SN. In one example, the signaling protocol may include X2AP/XnAP.

In a variant, the method may also include stopping the timer upon successful configuration or reconfiguration of the UE's primary serving cell and/or upon reception of a command to leave RRC connected state.

In a variant, the method may also include triggering RRC connection re-establishment upon the occurrence of at least one or more of triggering events. According to certain embodiments, the triggering events may include at least one of: i) while the timer is running, detecting SCG failure or integrity-verification failure on a split SRB for a PDCP PDU received over SCG, or ii) when the timer expires.

A second method includes receiving, by a MN, an indication of a RLF of a MCG configured to a UE. In response to receiving the indication, the method may further include sending to the UE a command to configure or reconfigure a primary serving cell of the UE. The UE may be served by the MN. The MN may be a DC MN.

In a variant, the indication may be received over an interface between the MN and a SN. In another variant, the indication may indicate the cause of the failure. According to a variant, the indication may indicate result of radio measurements from the UE. In a variant, the command to reconfigure or configure the primary serving cell may be based at least in part on the measurement results. In one variant, the command may be sent via the SN. The SN may be a DC SN.

An apparatus may comprise means for performing the first method or the second method or any of their variants discussed above.

Claim 1:
An apparatus comprising means for performing:
detecting (<NUM>) a radio link failure of a master cell group;
suspending (<NUM>) master cell group transmission for radio bearers, based on the detecting;
transmitting or reporting (<NUM>) a radio resource control indication over at least one of a signaling radio bearer between the apparatus and a secondary node, or a secondary cell group leg of a split signaling radio bearer, wherein the radio resource control indication comprises a master cell group failure information message, the apparatus characterized by further comprising means for performing:
starting (<NUM>) a timer upon transmitting or reporting the radio resource control indication, wherein the timer comprises a master cell group failure timer; and
stopping (<NUM>) the timer upon at least one of successful configuration or reconfiguration of the apparatus's primary serving cell, or reception of a command to leave radio resource control connected state.