Patent Description:
New radio access system, which is also called NR system or NR network, is the next generation communication system. It has been agreed that carrier aggregation (CA) which is used in Long Term Evolution (LTE) -Advanced to increase the bandwidth will be supported in the NR system. When CA is used, there are a number of serving cells. Generally, a primary cell (PCell) and at least one secondary cell (SCell) are provided. A beam failure may occur when the quality of beam pair(s) of a serving cell falls low enough (for example, comparison with a threshold or time-out of an associated timer).

A beam failure recovery procedure is a mechanism for recovering beams when all or part of beams serving user equipment (UE) has failed. Beam recovery may be also referred to as link reconfiguration. Aim of the beam recovery is to detect when one or multiple physical downlink control channels (PDCCH) links are considered to be in failure conditions and recover the link. To recover the link, UE initiates signaling toward network to indicate failure and new potential link (beam) called candidate link (beam). As a response to beam failure recovery request (BFRR) received from the UE, the network may configure UE with a new PDCCH link. Currently the beam failure recovery has been defined for one serving cell, which in practice covers beam failure recovery for PCell only. Thus, there still remain questions regarding the beam failure recovery for SCell.

Through the more detailed description of some example embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein:.

As used herein, the term "communication network" refers to a network that follows any suitable communication standards or protocols such as long term evolution (LTE), LTE-Advanced (LTE-A) and <NUM> NR, and employs any suitable communication technologies, including, for example, Multiple-Input Multiple-Output (MIMO), OFDM, time division multiplexing (TDM), frequency division multiplexing (FDM), code division multiplexing (CDM), Bluetooth, ZigBee, machine type communication (MTC), eMBB, mMTC and uRLLC technologies. For the purpose of discussion, in some embodiments, the LTE network, the LTE-A network, the <NUM> NR network or any combination thereof is taken as an example of the communication network.

As used herein, the term "network device" refers to any suitable device at a network side of a communication network. The network device may include any suitable device in an access network of the communication network, for example, including a base station (BS), a relay, an access point (AP), a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a gigabit NodeB (gNB), a Remote Radio Module (RRU), a radio header (RH), a remote radio head (RRH), a low power node such as a femto, a pico, and the like. For the purpose of discussion, in some embodiments, the eNB is taken as an example of the network device.

The network device may also include any suitable device in a core network, for example, including multi-standard radio (MSR) radio equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), Multi-cell/multicast Coordination Entities (MCEs), Mobile Switching Centers (MSCs) and MMEs, Operation and Management (O&M) nodes, Operation Support System (OSS) nodes, Self-Organization Network (SON) nodes, positioning nodes, such as Enhanced Serving Mobile Location Centers (E-SMLCs), and/or Mobile Data Terminals (MDTs).

As used herein, the tenn "terminal device" refers to a device capable of, configured for, arranged for, and/or operable for communications with a network device or a further terminal device in a communication network. The communications may involve transmitting and/or receiving wireless signals using electromagnetic signals, radio waves, infrared signals, and/or other types of signals suitable for conveying information over air. In some embodiments, the terminal device may be configured to transmit and/or receive information without direct human interaction. For example, the terminal device may transmit information to the network device on predetermined schedules, when triggered by an internal or external event, or in response to requests from the network side.

Examples of the terminal device include, but are not limited to, user equipment (UE) such as smart phones, wireless-enabled tablet computers, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), and/or wireless customer-premises equipment (CPE). For the purpose of discussion, in the following, some embodiments will be described with reference to UEs as examples of the terminal devices, and the terms "terminal device" and "user equipment" (UE) may be used interchangeably in the context of the present disclosure.

As used herein, the term "cell" refers to an area covered by radio signals transmitted by a network device. The terminal device within the cell may be served by the network device and access the communication network via the network device.

<FIG> shows an example communication network <NUM> in which embodiments of the present disclosure can be implemented. The network <NUM> includes a network device <NUM> and a terminal device <NUM> served by the network device <NUM>. The network <NUM> may provide one or more serving cells <NUM>, <NUM> to serve the terminal device <NUM>. It is to be understood that the number of network devices, terminal devices and serving cells is only for the purpose of illustration without suggesting any limitations. The network <NUM> may include any suitable number of network devices, terminal devices and serving cells adapted for implementing embodiments of the present disclosure. It is to be noted that the term "cell" and "serving cell" can be used interchangeably herein.

In the communication network <NUM>, the network device <NUM> can communicate data and control information to the terminal device <NUM> and the terminal device <NUM> can also communication data and control information to the network device <NUM>. A link from the network device <NUM> to the terminal device <NUM> is referred to as a downlink (DL) or a forward link, while a link from the terminal device <NUM> to the network device <NUM> is referred to as an uplink (UL) or a reverse link.

The communications in the network <NUM> may conform to any suitable standards including, but not limited to, Long Term Evolution (LTE), LTE-Evolution, LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM) and the like. Furthermore, the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (<NUM>), the second generation (<NUM>), <NUM>, <NUM>, the third generation (<NUM>), the fourth generation (<NUM>), <NUM>, the fifth generation (<NUM>) communication protocols.

CA can be supported in the network <NUM>, in which two or more component carriers (CCs) are aggregated in order to support a broader bandwidth. In CA, the network device <NUM> may provide to the terminal device <NUM> a plurality of serving cells including one PCell <NUM> and at least one SCell <NUM>. Although only one SCell <NUM> is shown in <FIG>, the network device <NUM> may provide a plurality of SCells. It is also to be understood that the configuration of PCell <NUM> and SCell <NUM> shown in <FIG> is only for the purpose of illustration without suggesting any limitations. PCell <NUM> and SCell <NUM> may be in other configuration than that shown in <FIG>.

In embodiments, the network device <NUM> is configured to implement beamforming technique and transmit signals to the terminal device <NUM> via a plurality of beams. The terminal device <NUM> is configured to receive the signals transmitted by the network device <NUM> via the plurality of beams. There may be different beams configured for the PCell <NUM> and the SCell <NUM>. As shown in <FIG>, a DL beam <NUM> is configured for the SCell <NUM>. It is to be understood that the SCell <NUM> may have more beams associated therewith. Although not shown, the PCell <NUM> may also have beams associated therewith.

As mentioned above, a beam failure may occur on any of the PCell <NUM> and the SCell <NUM>. Now a brief introduction to the beam failure detection (BFD) and beam failure recovery (BFR) will be described.

A network device configures a terminal device with a set of reference signals (RSs) for monitoring the quality of the link. This set of RSs may be referred as Q0 or beam failure detection RS or BFD-RS. Typically, BFD-RS(s) are configured to be spatially QCL'd (short for 'QCL-TypeD', see below) with PDCCH demodulation reference signal (DMRS). That is, these RSs correspond to downlink beams used to transmit PDCCH. Downlink beams are identified by RS, either synchronization signal (SS)/ physical broadcast channel (PBCH) block index (time location index) or channel state information-reference signal (CSI-RS) resource (set) index. The network device may configure the BFD-RS list using Radio Resource Control (RRC) signaling or it may be possible to use combined RRC and medium access control (MAC) control element (CE) signaling.

When two different signals share the same QCL type, they share the same indicated properties. As an example, the QCL properties may be e.g. delay spread, average delay, Doppler spread, Doppler shift, spatial RX. QCL type A means Doppler spread, Doppler shift, delay spread, and/or average delay, and QCL type D means spatial RX. Currently, QCL types are defined as following:.

As a further example, if a CSI-RS and a SSB have the type D QCL assumption between each other, it means that a network device (UE) may utilize the same RX spatial filter (beam) to receive these signals.

When the terminal device is not explicitly configured with BFD-RS list, it determines the BFD-RS resources implicitly based on the configured/indicated/activated PDCCH-Transmission Configuration Indication (TCI) states per control resource set (CORESET) i.e. the downlink reference signals (CSI-RS, SS/PBCH block or SSB) that are spatially QCL'd with PDCCH DMRS, or in other words, PDCCH beams. SS/PBCH block may be included in the BFD-RS set (Q0) either directly or indirectly. That is, SSB may be configured as TRS (tracking reference signal) and the TRS may be configured as BFD-RS by activation of TCI state for PDCCH for a CORESET. SSB may also be implicitly or explicitly configured as BFD-RS.

Physical layer assesses the quality of the radio link (based on BFD-RS in set of Q0) periodically. Assessment is done per BFD-RS and when the radio link condition of each BFD-RS in the beam failure detection set is considered to be in failure condition i.e. the hypothetical PDCCH Block Error Rate (BLER) estimated using the RS is above the configured threshold, a beam failure instance (BFI) indication is provided to higher layer (MAC). One example of BLER threshold value may be the out of sync threshold used for radio link monitoring OOS/Qout = <NUM>%. Evaluation and indication is done periodically. In the case where the at least one BFD-RS is not in failure condition, no indication is provided to higher layer.

MAC layer implements a counter to count the BFI indications from the physical layer and if the BFI counter reaches a maximum value (configured by the network device), a beam failure is declared. This counter can be configured to be supervised by a timer: each time MAC receives a BFI indication from lower layer a timer is started. Once the timer expires, the BFI counter is reset (counter value is set to zero).

The network device may provide the terminal device with a list of candidate RSs for recovery that can be indicated using dedicated signal. Candidate beam L1-Reference Signal Receiving Power (RSRP) measurements may be provided to MAC layer which performs the selection of new candidate beam and determines the uplink resources to indicate the new candidate beam to the network device. The network device may configure the terminal device with dedicated signaling resources, such as contention free random access (CFRA) resources that are candidate beam specific i.e. the terminal device can indicate new candidate by sending a preamble.

Beam failure recovery procedure is initiated if the terminal device has declared a beam failure and the terminal device has detected a new candidate beam or beams based on L1 measurements (e.g. L1-RSRP). A dedicated signal can be configured (e.g. from the PRACH pool) for beam failure recovery purposes that can be used to indicate a candidate beam or in other words a beam identified by the downlink RS (reference signal, SSB or CSI-RS). This dedicated signal, can be referred to as BFR resource or CFRA resource, and it has to be noted that beam recovery procedure using CFRA signals differs slightly from Random Access (RA) procedure when it comes to gNB response to preamble reception. A dedicated preamble may be configured for each candidate RS in the Candidate-Beam-RS-List. A specific threshold may be configured so that if any of the new candidate beams (based on L1-RSRP measurements) are above the threshold, they can be indicated using the dedicated signal (set of resources in set Q1 or candidate beam list). The terminal device first selects a candidate beam from that set and in the case where there are no beams above the configured threshold, the terminal device utilizes contention based signaling to indicate new candidate beam. Contention based random access (CBRA) preamble resources are mapped to specific downlink RS (SSB or CSI-RS).

The terminal device monitors the network response to BFRR (or BFRQ) during the beam recovery response window (similar to RAR window) using the same beam alignment (i.e. same beam direction that was used for TX is used for RX) used for transmitting the recovery signal; it expects the network device to provide response using a beam that is spatially QCL'd with the indicated downlink reference signal. A case where this correspondence does not hold is not yet defined.

In case of contention free signaling used for beam recovery purposes, the terminal device expects the network device to respond to the UE using Cell-Radio Network Temporary Identifier (C-RNTI) instead of Radom Access (RA-RNTI) when CFRA procedure is used. In case CBRA resources are used, the terminal device expects response as normally in RA procedure.

Currently the beam failure recovery (BFR) or link reconfiguration procedure does not differentiate between PCell and SCell (carrier aggregation case) and can be applied to a serving cell. This applies to a case where the SCell has also a corresponding uplink carrier. If the terminal device has a corresponding UL carrier with Contention Based RACH configuration, the current BFR/link reconfiguration procedures may be applied directly.

<FIG> is a schematic diagram <NUM> illustrating a BFD-RS configuration where spatial QCL is assumed across the carries and <FIG> is a schematic diagram <NUM> illustrating a BFD-RS configuration where there is no spatial QCL assumption across the carries. The RSs shown in <FIG> are SS/PBCH block and CSI-RS. For example, for the PCell <NUM>, a beam <NUM> is configured for the SS/PBCH block and beams <NUM> and <NUM> are configured for the CSI-RS. For SCell 21N shown in <FIG>, a beam <NUM> is configured for the SS/PBCH block and beams <NUM> and <NUM> are configured for the CSI-RS. In general, <FIG> illustrates a case where a group of cells may be considered to be in failure condition simultaneously i.e. if one cell is in beam failure condition it may be considered that all the cells in the group are in failure condition. Thus, in some cases it may be possible to define only one cell for beam failure detection purposes.

In the case as shown in <FIG>, the cross carrier spatial QCL is valid for PCell <NUM> and SCells <NUM>-20N. A beam failure can be detected on BFD-RS resources (CSI-RS, SS/PBCH block) of PCell <NUM> and it implicitly means that all the SCells <NUM>-20N are in the beam failure condition due to spatial QCL assumption of the reference signals used for assessing the link quality.

On the other hand, in the case as shown in <FIG>, the spatial QCL assumption for BFD-RS does not hold across all carriers. The PCell <NUM> and SCells <NUM>-21N belong to a group of cells or in a beam management group <NUM>, and the Scells <NUM>, <NUM>-22N belong to a group of SCells or another beam management group <NUM>. There is no spatial QCL assumption between cells in the beam management groups <NUM> and <NUM>. In the case where none of the SCells are spatially QCL with each other, the terminal device needs to be able to detect beam failure and perform recovery for each serving cell separately. In general, <FIG> illustrates that when one group of cells can be considered to be in beam failure condition, another group of cells may or may not be considered to be in failure condition.

The scenario shown in <FIG> may occur e.g. when the Pcell <NUM> is located in Frequency Range <NUM>(FR1 i.e. below <NUM> "low frequency") and the SCells is configured on FR2 (e.g. above <NUM> or "high frequency"). Alternatively, both the PCell and Scells may operate on same FR, but due to the PDCCH TCI configuration (which is cell specific) the BFD-RS detection resources may be different i.e. there may not be correspondence between the Pcell and SCell failure. The latter may happen in particular in case a cell with multiple Transmission/Reception Points (TRPs) is deployed. In yet alternative case, there may not be correspondence between the failure of one group of SCells (or more generally group of serving cells) and another group of SCells (or serving cells). A group of serving cells may comprise zero, one or more SCells and PCell may be included in the group of serving cells. It is to be noted that although the term "a group of SCell" is used in the description below, a group of SCell herein may also include a PCell.

However, the current beam failure recovery considers only one cell. For the case of SCell failure recovery, additional mechanisms are needed to make the recovery procedure and related signaling efficient. When BFD is performed on multiple SCells, some cells may fail concurrently, e.g., in the case where a same obstacle is preventing the communication to the current serving beams. Thus, a mechanism for reporting the beam failure of multiple SCells concurrently is also needed.

According to embodiments of the present disclosure, there is proposed a solution for beam failure recovery for a serving cell, and in particularly for beam failure recovery for an SCell (SCell BFR). In the present disclosure, a MAC CE format for indicating SCell BFR (which is also referred to as SCell BFR MAC CE) is proposed. To indicate the beam failure on an SCell, the SCell BFR MAC CE comprises at least one field. If a beam failure is detected on an SCell, the field associated with the SCell is set to be a predefined value to indicate the beam failure. The solution for beam failure recovery in accordance with embodiments of the present disclosure can be adapted to the beam failure occurring in the SCell. Moreover, embodiments of the present disclosure enable more efficient beam failure recovery than the conventional beam recovery schemes.

Principle and implementations of the present disclosure will be described in detail below with reference to <FIG> shows a flowchart of an example method <NUM> for BFR according to some example embodiments of the present disclosure. The method <NUM> can be implemented at the terminal device <NUM> as shown in <FIG>. For the purpose of discussion, the method <NUM> will be described with reference to <FIG>.

At <NUM>, the terminal device <NUM> detects a beam failure on a serving cell of the terminal device <NUM>. The serving cell comprises at least one of the PCell <NUM> and the SCell <NUM>. For example, the terminal device <NUM> may detect a beam failure on the SCell <NUM>. At <NUM>, the terminal device determines whether the beam failure is detected on the serving cell (e.g. the SCell <NUM>). If the beam failure is detected on the serving cell, the process proceeds to block <NUM>. At <NUM>, the terminal device <NUM> generates an MAC CE, which is also called an SCell BFR MAC CE herein. The SCell BFR MAC CE comprises a field associated with the serving cell and the field associated with the serving cell is set to be a predefined value indicating the beam failure. It is to be noted that although the MAC CE described herein is called "SCell BFR MAC CE", the SCell BFR MAC CE can be used to indicate the beam failure on the PCell <NUM>, or on the SCell <NUM>, or on both of the PCell <NUM> and SCell <NUM>.

In some embodiments, the serving cell may be the SCell <NUM> and the SCell BFR MAC CE may comprise a bitmap including a plurality of fields and the field associated with the SCell <NUM> may be included in the bitmap. The format of the SCell BFR MAC CE is now described in detail with reference to <FIG> shows the SCell BFR MAC CE <NUM> in accordance with some embodiments of the present disclosure.

As shown in <FIG>, the SCell BFR MAC CE <NUM> comprise a bitmap <NUM> and each of the Ci (i=<NUM>-<NUM>) fields <NUM>-<NUM> corresponds to an SCell or a group of SCells. For example, the group of SCells may be a beam management group (e.g. the beam management group shown in <FIG>) comprising SCells that share a common beam failure criterion. In other words, when one of the SCells in the group of SCells is in beam failure condition, the other SCells in the same group are also in beam failure condition. Although <FIG> shows seven Ci fields, the bitmap length in <FIG> should be considered as a non-limiting example and various values of 'i' can be used.

In the case where the each of the Ci fields <NUM>-<NUM> corresponds to an SCell, Ci may refer to an SCell index. When the corresponding field (bit in this example) is set to be the predefined value (e.g. "<NUM>"), it indicates that a beam failure has occurred on the corresponding SCell; when the corresponding field (bit in this example) is set to be another predefined value (e.g. "<NUM>"), it indicates that a beam failure has not detected on the corresponding SCell. As an example, the field corresponding to the SCell <NUM> is the C<NUM> field <NUM>. Then, the terminal device <NUM> at <NUM> may set the value of the C<NUM> field <NUM> to be "<NUM>" to indicate the beam failure on the SCell <NUM>.

In the case where the each of the Ci fields <NUM>-<NUM> corresponds to a group of SCells, the indexing of the bitmap <NUM> is logical. In this case, the Ci fields <NUM>-<NUM> are not directly mapped to the indices of the SCells but to the groups. In other words, the bitmap <NUM> indicates the SCells in logical order for where the failure has been detected. When the corresponding field (bit in this example) is set to be the predefined value (e.g. "<NUM>"), it indicates that beam failures has occurred on the SCells in the group; when the corresponding field is set to be another predefined value (e.g. "<NUM>"), it indicates that a beam failure has not detected on the SCells in the group.

As an example, the network device <NUM> may configure the terminal device <NUM> with SCell#<NUM>, <NUM>, <NUM>, <NUM> but the BFD is only performed for SCell#<NUM> and SCell#<NUM> in a manner that detecting a beam failure on SCell#<NUM> determines also a beam failure on SCell#<NUM>, which means that SCell#<NUM> and SCell#<NUM> belong to a same group of SCells, e.g., SCell group <NUM>. Accordingly, detecting a beam failure on SCell#<NUM> determines also a beam failure on SCell#<NUM>, which means that SCell#<NUM> and SCell#<NUM> belong to a same group of SCells, e.g., SCell group <NUM>. Thus, the bitmap <NUM> in the MAC CE <NUM> can be used to indicate beam failure(s) for group(s) of SCells that can be determined to be in failure based on failure of one of the SCells in the group. With two groups as in this example, only two bits would be used in the MAC CE <NUM>.

As another example, the SCell <NUM> may belong to a group of SCells, to which the the C<NUM> field corresponds and the SCell <NUM> may be configured to determine beam failures on SCells in that group. Then, at <NUM>, the terminal device <NUM> may set the value of the C<NUM> field <NUM> to be "<NUM>" to indicate the beam failures on that group of SCells. Additionally, if the terminal device <NUM> determines that a beam failure occurs on another SCell, the field associated with that SCell may also be set to the predefined value.

The MAC CE <NUM> may further comprise a Logical Channel ID, LCID, field <NUM> to identify that the MAC CE <NUM> is used for indicating the beam failure. In the embodiments where the bitmap <NUM> is associate with groups of SCells, the MAC CE <NUM> may include another LCID field (not shown) to indicate that bits in the bitmap <NUM> correspond to groups of SCells.

It is to be understood that although seven Ci fields are shown in <FIG>, the SCell BFR MAC CE may include more or less fields to indicate the beam failure. When less than <NUM> SCells or groups of SCells are involved, some of the Ci field <NUM>-<NUM> may be reserved and when more than <NUM> SCells or groups of SCells are involved, the SCell BFR MAC CE may be extended to include additional bits.

In some embodiments, the bitmap may include a further field associated with the PCell serving the terminal device, for example, the PCell <NUM> serving the terminal device <NUM> shown in <FIG>. In the example MAC CE shown in <FIG>, the R field <NUM> is reserved. <FIG> shows another SCell BFR MAC CE <NUM> in accordance with some embodiments of the present disclosure.

The MAC CE <NUM> comprises LCID field <NUM> and a bitmap <NUM> including Ci fields <NUM>-<NUM> and a P field <NUM>. The LCID field <NUM> and Ci fields <NUM>-<NUM> are similar as the LCID field <NUM> and Ci fields <NUM>-<NUM> as described with reference to <FIG>. The P field <NUM> is included to indicate whether a beam failure has been detected on the PCell <NUM>.

When the P field <NUM> (in this example, a bit) is set to be e.g. '<NUM>', it indicates the network device <NUM> that the PCell <NUM> is not in failure. This allows the use of CBRA procedure beams that are not currently configured as active TCI states for PDCCH and prevents the network device <NUM> to falsely determine the beam failure of the PCell <NUM>. When the P field <NUM> is set to e.g. '<NUM>', it indicates the network device <NUM> that the PCell <NUM> is also in beam failure condition and the selected DL RS (SSB/CSI-RS) indicates a new candidate beam for the PCell <NUM> and the bitmap <NUM> indicates the failed SCell indexes/group indexes.

According to the invention, the MAC CE described herein with P field <NUM> is also used to indicate only beam failure on the PCell <NUM> (also referred to as PCell failure). This MAC CE may be transmitted in msg-<NUM> in a RACH procedure (e.g. contention based RACH procedure) to indicate the network device <NUM> that beam failure on the PCell <NUM> has occurred and RACH procedure has been initiated for beam failure recovery. The network device <NUM> may determine the new candidate beam. The MAC CE may be transmitted to indicate PCell failure regardless of the configuration for carrier aggregation i.e. the terminal device <NUM> may not have any SCells configured but the same MAC CE described herein could be used. Also in carrier aggregation cases (when the terminal device <NUM> has been configured with SCell or SCells), a beam failure occurring only on the PCell (PCell-only failure) can be indicated using the MAC CE. In some cases, the network device <NUM> may not configure the terminal device <NUM> to perform failure detection on the SCell <NUM> and the terminal device <NUM> may consider only PCell failure. The MAC CE described herein may be used to indicate PCell-only failure. In some additional embodiments, when carrier aggregation is not configured, the terminal device <NUM> may transmit the MAC CE with LCID only to indicate PCell failure. This mechanism can reduce the size of the MAC CE.

When a MAC CE in such a format, such as the MAC CE <NUM>, is used, the method <NUM> may include additional steps or processes. The terminal device <NUM> may detect a beam failure on the PCell <NUM>. If the beam failure on the PCell <NUM> is detected, the terminal device <NUM> may set P field <NUM> to be the predefined value (e.g. "<NUM>") to indicate the beam failure on the PCell <NUM>.

In such embodiments, indicating whether the PCell is in failure can prevent the network device <NUM> to detect PCell failure when the terminal device <NUM> utilizes RACH procedure and also enable the terminal device <NUM> to indicate PCell failure using scheduling request (SR) procedure if SR is triggered and UL grant is received. This may be possible since the failure condition is <NUM>% hypothetical PDCCH BLER for DL RS, or in the case where the uplink direction still works while the DL direction is in failure condition, the terminal device <NUM> is able to trigger SR on working uplink. Besides, even with RA procedure, indicating beam failure for PCell is useful information for the network device <NUM> to know the RA being triggered by BFR other than other cases, e.g. SR failure.

In some embodiments, when the PCell <NUM> is in failure condition and at least one SCell can be used to transmit on uplink, the terminal device <NUM> may utilize the MAC CE <NUM> to transmit the indication of the beam failure on the PCell <NUM>.

In some embodiments, the SCell BFR MAC CE, for example the MAC CE <NUM> or <NUM>, may have only the LCID field (<NUM> or <NUM>) to indicate the beam failure. Such a format may be triggered when there is only one SCell serving the terminal device <NUM>. Alternatively, this format may be used when one SCell is used for determining the beam failure for a set/group of SCells. Alternatively, when this format is used and at least one of the SCells is in failure condition, the terminal device <NUM> may trigger transmission of the SCell BFR MAC CE to indicate the beam failure.

Still refer to <FIG>. In some cases, the SCell BFR MAC CE may be triggered by some predefined conditions. In some embodiments, the SCell BFR MAC CE may be triggered in a condition when CFRA is not configured for recovery of the serving cell (e.g. SCell <NUM>) or CFRA signaling cannot be used, for example when no SCell or SCells with candidate beam or beams with CFRA resource are available or the resources are not suitable from signal quality point of view i.e. the quality metric is below candidate beam threshold. In such embodiments, at <NUM>, the terminal device <NUM> may further determine CFRA resource configured for the beam failure on the SCell <NUM>. If there is no CFRA resource configured for the recovery of the SCell <NUM> or if the configured CFRA resource is not available, the terminal device <NUM> may generate the SCell BFR MAC CE, for example, the MAC CE <NUM> or <NUM>. It is to be noted that the above acts may also be performed by the terminal device <NUM> at other stage of the method <NUM>.

In some embodiments, the SCell BFR MAC CE may be triggered, when at least two SCells or two groups of SCells are in failure condition and more than one RA procedures would be triggered. In this case, the SCell MAC CE may be generated and transmitted regardless of the CFRA availability. Optionally the terminal device <NUM> may continue with one of the already triggered RA procedures to transmit the MAC CE.

In such embodiments, at <NUM>, the terminal device <NUM> may further determine a further beam failure on a further SCell serving the terminal device <NUM>. The further beam failure may be detected before the detection at <NUM> and may have triggered a RA procedure. In this case, the terminal device <NUM> will generate the SCell BFR MAC CE regardless of the CFRA availability. The generated SCell BFR MAC CE may comprise a further field associated with the further SCell and the further field is set to be the predefined value, e.g., "<NUM>". For example, the further field may be the C<NUM> field <NUM> shown in <FIG>.

In the case where the SCells are organized into groups of SCell, the further secondary cell and the SCell <NUM> may belong to different groups of SCells. In other words, when at least two groups of SCells are in failure condition, the terminal device <NUM> may generate the SCell BFR MAC CE. As another example, PCell failure may also be indicated as part of the SCell group without explicit indication of using 'P' field in the MAC CE. That is, if a first group of SCell or SCells includes also the PCell, to indicate PCell failure in addition to SCell group failure, it is necessary to indicate only the group identifier for the beam failure.

In some embodiments, before the detection of the beam failure on the SCell <NUM>, the terminal device <NUM> may have detected a beam failure and initiated a recovery procedure on a first/one SCell in a first group of SCells using CFRA. While the recovery procedure for the first SCell is still on-going (RACH procedure for beam failure recovery has been initiated), the beam failure recovery is triggered for the SCell <NUM> which belongs to a different group of SCells than the first group of SCells (i.e. the two groups are exclusive groups). In this case, the terminal device <NUM> may cancel the on-going recovery procedures (the random access procedure for beam failure recovery) on the first SCell and generate the SCell BFR MAC CE and initiate RACH/SR procedure on the PCell <NUM>. In this way, the signaling of beam failures on the at least two cells can be more efficient. Alternatively, the terminal device <NUM> may continue the random access procedure for beam failure recovery on the first SCell and generate the SCell BFR MAC CE and initiate a RACH/SR procedure on the PCell <NUM>.

At <NUM>, the terminal device <NUM> transmits the MAC CE to a network device associated with the serving cell. For example, the terminal device <NUM> transmits the SCell BFR MAC CE to the network device <NUM>. In general, the SCell BFR MAC CE is sent only on the cells that are not in the beam management groups where the beam failure was detected, unless the UL grant is given during the random access procedure.

In some embodiments, the terminal device <NUM> may apply implicitly mapping restrictions for the generated SCell BFR MAC CE for transmission. For example, the terminal device <NUM> may restrict the mapping of the SCell BFR MAC CE to granted uplink resources on the failed SCells or group of SCells. In other words, the MAC entity of the terminal device <NUM> does not multiplex the SCell BFR MAC CE for any uplink resource that has been allocated for SCells or group of SCells where beam failure has been detected. The terminal device <NUM> may instead map the generated SCell BFR MAC CE to a granted uplink resource on the PCell <NUM> or any SCell or group of SCells where no beam failure has been detected. Such uplink resource may be considered as a valid uplink resource for the SCell BFR MAC CE, for instance.

In some embodiments, the network device <NUM> may configure the terminal device <NUM> with a specific uplink signaling resource to indicate a beam failure on an SCell (e.g. SCell <NUM>) or group of SCells. Such uplink signaling resource may be individually configured for each SCell/SCell group or may be applied commonly to all SCells/SCell groups which have been configured for the terminal device <NUM>. Such signaling resource may be configured on the PCell <NUM> of the terminal device <NUM>. Such signaling may be called an SCell beam failure indication, for instance. The specific uplink signaling resource may be any of the Scheduling Request (SR) resource, Physical Random Access Channel preamble (PRACH preamble), or a configured grant resource. The specific uplink signaling resource may be configured on, e.g., PUCCH (Physical Uplink Control Channel), PRACH, or PUSCH (Physical Uplink Shared Channel).

In some embodiments, if the terminal device <NUM> has no valid uplink resource (such as that defined above) for the SCell BFR MAC CE, the transmission of the SCell beam failure indication may be enforced. The network device <NUM> may determine, based on the received SCell beam failure indication from the terminal device <NUM>, that beam failure has been detected on at least one SCell/SCell group. The network device <NUM> may therefore allocate a valid uplink resource, for instance an uplink grant, for the terminal device <NUM> to transmit the SCell BFR MAC CE. For instance, the valid uplink resource could be provided on the PCell <NUM> or on an SCell where beam failure has not been detected. In the case where the terminal device <NUM> is not configured with the specific uplink signaling resource to perform the SCell beam failure indication, it may trigger and perform random access procedure on the PCell <NUM>.

In some embodiments, the terminal device <NUM> may transmit the SCell BFR MAC CE on a cell that does not belong to the beam management groups where the beam failure has been detected, for example, does not belong to the group of SCells including the SCell <NUM>. In this case, at <NUM>, the terminal device <NUM> may further determine a cell from the PCell <NUM>, the SCell <NUM> and a further SCell serving the terminal device <NUM>. The determined cell is different from the serving cell where the beam failure has been detected. As an example, if the beam failure has been detected on the SCell <NUM>, the determined cell may be the PCell <NUM> or another SCell which belongs to a different group of SCells with the SCell <NUM>. Then, the terminal device <NUM> may transmit the MAC CE on the determined cell.

In some embodiments, the terminal device <NUM> may transmit, during the random access procedure, the SCell BFR MAC CE. For ease of discussion, it is assumed that the beam failure on the SCell <NUM> occurs on a first beam of the SCell <NUM>. In this case, at <NUM>, the terminal device <NUM> may transmit a random access preamble to the network device <NUM>. Upon receiving the random access preamble, the network device <NUM> may determine a second beam being different from the first beam and transmit an uplink grant for the second beam of the SCell <NUM>. Upon receiving the uplink grant for the second beam of the SCell <NUM>, the terminal device <NUM> may transmit the SCell BFR MAC CE via the second beam of the SCell <NUM>.

As mentioned above, upon the detection of the beam failure on e.g. the SCell <NUM>, the terminal device <NUM> may determine a new beam for the SCell <NUM>. For example, the terminal device <NUM> may select a candidate beam from a list of candidate reference signals based on measurements on the candidate reference signals (for example, L1-RSRP measurements) and transmit information of the selected candidate beam to the network device <NUM> for further communication between the network device <NUM> and the terminal device <NUM>. The information of the selected candidate beam may be included in the SCell BFR MAC CE. Alternatively or in addition, the information of the selected candidate beam may be transmitted using another MAC CE or an uplink control channel report (such as PUCCH or PUSCH beam reporting, candidate beam reporting).

In some embodiments, for each of the serving cells or groups of cells as indicated in failure condition, the SCell BFR MAC CE may further include information of a new candidate RS/beam (SSB or CSI-RS). The terminal device <NUM> may include the information of the selected candidate beam into the SCell BFR MAC CE and transmit, at <NUM>, the SCell BFR MAC CE to the network device <NUM>. The information of the selected candidate beam for each of the serving cells or groups of cells as indicated in failure condition may be included in the fields following the bitmap <NUM> or <NUM> shown in <FIG>.

Optionally, the information of the selected candidate beam may include an indication whether SSB or CSI-RS is reported. There may also be an indication that no new candidate beam exists for the indicated serving cells(s)/group(s) of cells.

In the case where the UL grant for transmitting the SCell BFR MAC CE cannot accommodate the reporting of candidate beams to all failed cells, the reported cells may be in one of increasing/decreasing order of the index(es) of SCell(s)/group(s) of SCells; order configured by the network device <NUM>; based on the number of cells associated to a group of SCells; or any combination thereof.

In some other embodiments, the terminal device <NUM> may transmit the information of the selected candidate beam using another specific MAC CE or an uplink control channel report. The terminal device <NUM> may receive, from the network device <NUM>, a request for a candidate beam report. Then the terminal device <NUM> may generate a further MAC CE or an uplink control channel report including the information of the selected candidate beam and transmit the further MAC CE or the uplink control channel report to the network device <NUM>.

As an example, when the terminal device <NUM> has successfully transmitted the SCell BFR MAC CE, it may generate a MAC CE for reporting candidate beam(s) for each cell as indicated in failure condition. Optionally, this candidate beam report may be request by the network device <NUM> using specific MAC CE. After successful transmission of the SCell BFR MAC CE, the terminal device <NUM> may initiate a timer. If the network device <NUM> does not request the terminal device <NUM> to report any new candidate beam before the timer expires, the terminal device <NUM> may deactivate the failed cell (for example, the SCell <NUM>).

As another example, the network device <NUM> may trigger aperiodic PUCCH or MAC CE reporting for the cell(s) for which the terminal device <NUM> reports a beam failure. If the network device <NUM> triggers aperiodic PUCCH report for the recently indicated failed SCell, the terminal device <NUM> reports up to N best candidate beams in the PUCCH report. In this aperiodic PUCCH report, the terminal device <NUM> may report any DL RS that has not been configured for e.g. periodic beam reporting. Optionally, the reported candidate beams may be SSB beams, CSI-RS beams or CSI-RS and SSB beams.

If the network device <NUM> triggers candidate beam reporting via MAC CE, the terminal device <NUM> may generate SCell specific report, or include all the failed SCell with candidate beams in the report.

Alternatively, the candidate beam reporting may be SINR based i.e. hypothetical PDCCH BLER based reporting.

In some embodiments, the terminal device <NUM> may further monitor a response to the transmitted SCell BFR MAC CE from the network device <NUM>. If no response is received in a predetermined period of time, the terminal device <NUM> may deactivate the SCell where beam failure has been detected, e.g. the SCell <NUM>. For example, when the terminal device <NUM> has triggered the report and successfully transmitted the SCell BFR MAC CE, it may initiate the deactivation timer. If the network device <NUM> does not configure reporting or new TCI state for at least the indicated SCell <NUM>, the terminal device <NUM> may deactivate it. Alternatively, the terminal device <NUM> may deactivate the SCells indicated as beam failure if it does not receive report request/new TCI state for PDCCH for those cells.

<FIG> shows a flowchart of an example method <NUM> for BFR according to some example embodiments of the present disclosure. The method <NUM> can be implemented at the network device <NUM> as shown in <FIG>. For the purpose of discussion, the method <NUM> will be described with reference to <FIG>.

At <NUM>, the network device <NUM> receives, from a terminal device <NUM>, a MAC CE, the MAC CE (e.g. the SCell BFR MAC CE <NUM> or <NUM>) comprising a field associated with a serving cell of the terminal device <NUM>, the serving cell comprising at least one of the PCell <NUM> and the SCell <NUM> serving the terminal device <NUM>, wherein the field is set to be a predefined value indicating a beam failure.

In some embodiments, the serving cell comprises the SCell <NUM> and the field associated with the serving cell may be included in a bitmap, such as the bitmap <NUM> or <NUM>. The bitmap includes a plurality of fields, each of which is associated with an SCell or a group of SCells.

In some embodiments, the bitmap may include a further field associated with a PCell, e.g. the PCell <NUM>. The network device <NUM> may further determine, based on the further field in the bitmap, a beam failure on the PCell <NUM>.

In some embodiments, the field associated with the serving cell comprises Logical Channel ID, LCID, set to be the predefined value.

In some embodiments, the network device <NUM> may receive the MAC CE on a cell being different from the serving cell, and the cell is determined by the terminal device <NUM> from the PCell <NUM>, the SCell 102and a further SCell serving the terminal device <NUM>.

In some embodiments, the beam failure may occur on a first beam of serving cell (e.g. the SCell <NUM>). The network device <NUM> may receive a random access preamble from the terminal device <NUM> and transmit an uplink grant for a second beam of the serving cell, the second beam being different from the first beam in response to the reception of the random access preamble. The network device <NUM> may then receive the MAC CE via the second beam of the serving cell.

At <NUM>, the network device <NUM> determines, based on the field in the MAC CE, the beam failure on the serving cell (e.g. the SCell <NUM>).

In some embodiments, the network device <NUM> may further receive information of a candidate beam from the terminal device <NUM>. The candidate beam may be selected by the terminal device from a list of candidate reference signals based on measurements on the candidate reference signals. The network device <NUM> may then communicate with the terminal device <NUM> via the selected candidate beam.

In some embodiments, the information of the candidate beam may be included in the SCell BFR MAC CE. The network device <NUM> may receive the MAC CE from the terminal device <NUM> and determine, from the MAC CE, the information of the candidate beam.

In some embodiments, the network device <NUM> may transmit to the terminal device <NUM> a request for a candidate beam report, and may receive, from the terminal device <NUM>, a further MAC CE or an uplink control channel report including the information of the candidate beam.

In some embodiments, the serving cell may comprise the secondary cell and if at <NUM> the MAC CE is received from the terminal device <NUM>, the network device <NUM> may transmit to the terminal device <NUM> a response to the received MAC CE.

In some embodiments, an apparatus capable of performing the method <NUM> (for example, the terminal device <NUM>) may comprise means for performing the respective steps of the method <NUM>. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some embodiments, the apparatus comprises: means for detecting a beam failure on a serving cell of the terminal device, the serving cell comprising at least one of a primary cell and a secondary cell serving the terminal device; means for in response to detecting the beam failure on the serving cell, generating a medium access control, MAC, control element, CE, the MAC CE comprising a field associated with the serving cell, wherein the field is set to be a predefined value indicating the beam failure; and means for transmitting the MAC CE to a network device associated with the serving cell.

In some embodiments, the serving cell comprises the secondary cell and the field associated with the serving cell is included in a bitmap, the bitmap including a plurality of fields, each of the plurality of fields associated with a secondary cell or a group of secondary cells.

In some embodiments, the bitmap includes a further field associated with the primary cell and the apparatus further comprises means for detecting a beam failure on the primary cell; and means for in response to detecting the beam failure on the primary cell, setting the further field associated with the primary cell to be the predefined value to indicate the beam failure on the primary cell.

In some embodiments, the means for in response to detecting the beam failure on the secondary cell generating the MAC CE may comprise means for in response to detecting the beam failure on the serving cell, determining a contention free random access, CFRA, resource configured for the beam failure on the serving cell; and means for generating the MAC CE in response to absence of the CFRA resource or the CFRA resource being unavailable.

In some embodiments, the serving cell comprises the secondary cell and the means for in response to detecting the beam failure on the secondary cell generating the MAC CE may comprise means for determining a further beam failure on a further secondary cell serving the terminal device; and means for in response to the further beam failure on the further secondary cell being determined, generating the MAC CE, the MAC CE comprising a further field associated with the further secondary cell, wherein the further field is set to be the predefined value.

In some embodiments, the further secondary cell and the secondary cell belong to different groups of secondary cells.

In some embodiments, means for transmitting the MAC CE may comprise means for determining a cell from the primary cell, the secondary cell and a further secondary cell serving the terminal device, the determined cell being different from the serving cell; and means for transmitting the MAC CE on the determined cell.

In some embodiments, the beam failure occurs on a first beam of the serving cell and means for transmitting the MAC CE may comprise means for transmitting a random access preamble to the network device; and means for in response to receiving an uplink grant for a second beam of the serving cell, transmitting the MAC CE via the second beam of the serving cell, the second beam being different from the first beam.

In some embodiments, the apparatus further comprises: means for in response to detecting the beam failure on the serving cell, selecting a candidate beam from a list of candidate reference signals based on measurements on the candidate reference signals; and means for transmitting information of the selected candidate beam to the network device for further communication between the network device and the terminal device.

In some embodiments, the means for transmitting information of the selected candidate beam may comprise means for including, into the MAC CE, the information of the selected candidate beam; and means for transmitting the MAC CE to the network device.

In some embodiments, the means for transmitting information of the selected candidate beam may comprise means for in response to receiving, from the network device, a request for a candidate beam report, generating a further MAC CE or an uplink control channel report including the information of the selected candidate beam; and means for transmitting the further MAC CE or the uplink control channel report to the network device.

In some embodiments, the serving cell comprises the secondary cell and the apparatus further comprises: means for monitoring a response to the transmitted MAC CE from the network device; and means for in response to absence of the response in a predetermined period of time, deactivating the secondary cell.

In some embodiments, an apparatus capable of performing the method <NUM> (for example, the network device <NUM>) may comprise means for performing the respective steps of the method <NUM>. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some embodiments, the apparatus comprises: means for receiving, from a terminal device, a medium access control, MAC, control element, CE, the MAC CE comprising a field associated with a serving cell of the terminal device, the serving cell comprising at least one of a primary cell and a secondary cell serving the terminal device, wherein the field is set to be a predefined value indicating a beam failure; and means for determining, based on the field in the MAC CE, the beam failure on the serving cell.

In some embodiments, the serving cell comprises the secondary cell and the field associated with the serving cell is included in a bitmap, the bitmap including a plurality of fields, each of the plurality of fields associated with a secondary cell or a group of secondary cells.

In some embodiments, the bitmap includes a further field associated with the primary cell and the apparatus may further comprise means for determining, based on the further field in the bitmap, a beam failure on the primary cell.

In some embodiments, the means for receiving the MAC CE may comprise means for receiving the MAC CE on a cell being different from the serving cell, the cell being determined by the terminal device from the primary cell, the secondary cell and a further secondary cell serving the terminal device.

In some embodiments, the beam failure occurs on a first beam of the serving cell, and the means for receiving the MAC CE may comprise means for receiving a random access preamble from the terminal device; means for transmitting an uplink grant for a second beam of the serving cell, the second beam being different from the first beam; and means for receiving the MAC CE via the second beam of the serving cell.

In some embodiments, the apparatus may further comprise means for receiving information of a candidate beam from the terminal device, the candidate beam being selected by the terminal device from a list of candidate reference signals based on measurements on the candidate reference signals; and means for communicating with the terminal device via the candidate beam.

In some embodiments, the means for receiving the information of the candidate beam may comprise means for receiving the MAC CE from the terminal device; and means for determining, from the MAC CE, the information of the candidate beam.

In some embodiments, the means for receiving the information of the candidate beam may comprise means for transmitting to the terminal device a request for a candidate beam report; and means for receiving, from the terminal device, a further MAC CE or an uplink control channel report including the information of the candidate beam.

In some embodiments, the serving cell comprises the secondary cell and the apparatus may further comprise means for in response to receiving the MAC CE from the terminal device, transmitting to the terminal device a response to the received MAC CE.

<FIG> is a simplified block diagram of a device <NUM> that is suitable for implementing example embodiments of the present disclosure. The device <NUM> can be considered as a further example implementation of a terminal device <NUM> as shown in <FIG>. Accordingly, the device <NUM> can be implemented at or as at least a part of the terminal device <NUM>.

As shown, the device <NUM> includes a processor <NUM>, a memory <NUM> coupled to the processor <NUM>, a suitable transmitter (TX) and receiver (RX) <NUM> coupled to the processor <NUM>, and a communication interface coupled to the TX/RX <NUM>. The memory <NUM> stores at least a part of a program <NUM>. The TX/RX <NUM> is for bidirectional communications. The TX/RX <NUM> has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2 interface for bidirectional communications between eNBs, S1 interface for communication between a Mobility Management Entity (MME)/Serving Gateway (S-GW) and the eNB, Un interface for communication between the eNB and a relay node (RN), or Uu interface for communication between the eNB and a terminal device.

The program <NUM> is assumed to include program instructions that, when executed by the associated processor <NUM>, enable the device <NUM> to operate in accordance with the example embodiments of the present disclosure, as discussed herein with reference to <FIG> and <FIG>. The example embodiments herein may be implemented by computer software executable by the processor <NUM> of the device <NUM>, or by hardware, or by a combination of software and hardware. The processor <NUM> may be configured to implement various example embodiments of the present disclosure. Furthermore, a combination of the processor <NUM> and memory <NUM> may form processing means <NUM> adapted to implement various example embodiments of the present disclosure.

The memory <NUM> may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory <NUM> is shown in the device <NUM>, there may be several physically distinct memory modules in the device <NUM>. The processor <NUM> may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples.

While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to any of <FIG> and <FIG>. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Examples of the carrier include a signal, computer readable media.

Claim 1:
A method implemented at a terminal device, comprising:
detecting a beam failure on a serving cell of the terminal device, the serving cell comprising at least one of a primary cell and a secondary cell serving the terminal device;
in response to detecting the beam failure on the serving cell, generating a medium access control, MAC, control element, CE, the MAC CE comprising a field associated with the serving cell, wherein the field is set to be a predefined value indicating the beam failure; and
transmitting the MAC CE to a network device associated with the serving cell, wherein the serving cell comprises the secondary cell and the field associated with the serving cell is included in a bitmap, the bitmap including a plurality of fields, each of the plurality of fields associated with a secondary cell or a group of secondary cells, and a further field associated only with the primary cell, the method further comprising:
detecting a beam failure on the primary cell;
in response to detecting the beam failure on the primary cell, setting the further field associated with the primary cell to be the predefined value to indicate the beam failure on the primary cell; and
transmitting the MAC CE to the network device to indicate that beam failure on the primary cell has occurred.