Patent Description:
The present disclosure relates to beam failure recovery in a cellular communications system.

Carrier aggregation implies that the User Equipment (UE) is assigned more than one carrier, and that data communication may be performed over more than one carrier. The carriers are at least to some extent operated independently. Furthermore, the link quality of the carriers is in many cases independent. The different carriers are sometimes called Component Carriers (CCs).

In the Third Generation Partnership Project (3GPP) specification, the different CCs are known as different serving cells. A UE configured for carrier aggregation has one Primary Cell (PCell) and one or more Secondary Cells (SCells). Although the data is transmitted over all the serving cells, many procedures only rely on the PCell.

In 3GPP New Radio (NR) Release <NUM>, a procedure called beam recovery has been defined for the PCell. In beam recovery, an RRC_CONNECTED UE performs measurements associated to the quality of the serving link and, if that quality goes below a given threshold, the UE performs beam recovery. The procedure aims to solve the situation where the transmit (TX) and receive (RX) beams of the NR base station (called a gNodeB or gNB) and the UE have become misaligned, but where there are additional beams that could be used to maintain the connection between the gNB and the UE.

The beam failure recovery procedure includes the following aspects:.

Note that after declaring beam failure in step <NUM>, the UE considers the connection with the network to be lost and acts to restore the link.

Note that during all discussions in 3GPP, the term "beam recovery" is used, but in the specification (3GPP Technical Specification (TS) <NUM>), the term "link recovery" is used. As such, these terms are used interchangeably herein (i.e., have the same meaning herein).

For Release <NUM>, beam recovery for an SCell is being defined. Here, the first two steps described in in the Beam Recovery section above are reused. In particular, if configured, the UE still performs beam failure detection by monitoring a periodic reference signal and searches for new beams. However, the remainder of the SCell beam recovery procedure is different compared to the PCell beam recovery. It is assumed that the PCell is still operational, and the UE can communicate over the PCell.

For SCell beam recovery, it has been agreed that after beam failure detection, the UE sends a scheduling request to inform the network that at least one of the SCells has failed. If the UE already has a grant to transmit UL data, this step may be unnecessary. When receiving this scheduling request, the network grants the UE UL resources to transmit a Medium Access Control (MAC) Control Element (CE) message that contains information about which SCell failed and information about a new suitable beam where the communication can be reestablished. For future reference, this message will be denoted the beam failure recovery information message or BFRI message.

One way to convey control information between the network and the UE in NR is to use MAC CEs. This special MAC structure is implemented as a special bit string in the Logical Channel Identifier (ID) (LCID) field of the MAC header. The MAC CEs are transmitted over the Downlink or Uplink Shared Channel (UL-SCH or DL-SCH) and are thus protected by Hybrid Automatic Repeat Request (HARQ).

NR relies on HARQ to improve performance of physical channels. With HARQ, the receiver requests a retransmission of a packet if it is unable to decode it correctly. Each transmission is associated with a Cyclic Redundancy Check (CRC) to facilitate such error detection. In most cases, the receiver sends an Acknowledgement (ACK) or a Negative ACK (NACK) to the transmitter to inform the transmitter about the status of a transmission.

For the PUSCH in NR, the receiver (i.e., the base station) performs error detection using such a CRC. However, unlike Long Term Evolution (LTE), there is no explicit ACK/NACK transmitted. Instead, the base station schedules each retransmission explicitly. Each UL grant includes information about which HARQ process should be used for the corresponding transmission and if the transmission should include a retransmission of the previous transmission, or if it should include "new data" - there is a specific bit in the scheduling Downlink Control Information (DCI) called "new data. " If that bit indicates "new data," the UE transmits new data, otherwise it retransmits the previous packet.

There currently exist certain challenge(s). In particular, beam failure recovery for SCells in NR is new and results in new issues that need to be addressed.

Systems and methods for beam failure recovery are disclosed. A method performed by a wireless device for beam failure recovery is provided according to appended claim <NUM>.

A wireless device for beam failure recovery is provided according to appended claim <NUM>.

A method performed by a base station for beam failure recovery is provided according to appended claim <NUM>.

A base station for beam failure recovery is provided according to appended claim <NUM>.

Radio Access Node: As used herein, a "radio access node" or "radio network node" is any node in a Radio Access Network (RAN) of a cellular communications network that operates to wirelessly transmit and/or receive signals.

Core Network Node: As used herein, a "core network node" is any type of node in a core network or any node that implements a core network function. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a Packet Data Network Gateway (P-GW), a Service Capability Exposure Function (SCEF), a Home Subscriber Server (HSS), or the like. Some other examples of a core network node include a node implementing a Access and Mobility Management Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Exposure Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), or the like.

Note that, in the description herein, reference may be made to the term "cell;" however, particularly with respect to <NUM> NR concepts, beams may be used instead of cells and, as such, it is important to note that the concepts described herein are equally applicable to both cells and beams.

There currently exist certain challenge(s) with respect to beam failure recovery. In particular, if the network does not receive the first transmission of the beam failure recovery information message, the network will at some point in time schedule a retransmission of the message. However, there is no way for the UE to know that the beam failure recovery message has been received by the network, since the uplink (UL) Hybrid Automatic Repeat Request (HARQ) transmission is not explicitly acknowledged. Therefore, the UE is not aware that the beam failure recovery procedure is successfully completed, and therefore cannot apply the correct procedures.

Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. Systems and methods for beam failure recovery are described herein. These systems and methods are particularly beneficial for beam failure recovery in 3GPP NR; however, they are not limited thereto (e.g., they may be used in other types of wireless networks or cellular communications networks that perform beam failure recovery). As described below, in embodiments of the present disclosure, the beam failure recovery procedure is completed when the UE receives a UL grant for the HARQ process that was used to transmit the beam failure recovery information message, and where the UL grant indicates "new data. " In other words, during beam failure recovery, the UE transmits a beam failure recovery information message using a particular HARQ process. Upon successfully receiving the beam failure recovery information message, the base station (e.g., gNB) responds with a UL grant comprising a "new data" indicator. At the UE, the UE receives the UL grant and interprets the "new data" indicator as an Acknowledgement (ACK) for the beam failure recovery information message. Based on this ACK, the UE performs one or more actions associated with successful completion of beam failure recovery (e.g., the UE discards measurements used for beam failure recovery).

Certain embodiments may provide one or more of the following technical advantage(s). By using embodiments of the solution described herein, the UE knows when the beam failure recovery procedure is completed.

<FIG> illustrates one example of a cellular communications system <NUM> in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system <NUM> is preferably a <NUM> System (5GS) including a NR RAN, but is not limited thereto. In this example, the RAN includes base stations <NUM>-<NUM> and <NUM>-<NUM>, which in <NUM> NR are referred to as gNBs, controlling corresponding (macro) cells <NUM>-<NUM> and <NUM>-<NUM>. The base stations <NUM>-<NUM> and <NUM>-<NUM> are generally referred to herein collectively as base stations <NUM> and individually as base station <NUM>. Likewise, the (macro) cells <NUM>-<NUM> and <NUM>-<NUM> are generally referred to herein collectively as (macro) cells <NUM> and individually as (macro) cell <NUM>. The RAN may also include a number of low power nodes <NUM>-<NUM> through <NUM>-<NUM> controlling corresponding small cells <NUM>-<NUM> through <NUM>-<NUM>. The low power nodes <NUM>-<NUM> through <NUM>-<NUM> can be small base stations (such as pico or femto base stations) or Remote Radio Heads (RRHs), or the like. Notably, while not illustrated, one or more of the small cells <NUM>-<NUM> through <NUM>-<NUM> may alternatively be provided by the base stations <NUM>. The low power nodes <NUM>-<NUM> through <NUM>-<NUM> are generally referred to herein collectively as low power nodes <NUM> and individually as low power node <NUM>. Likewise, the small cells <NUM>-<NUM> through <NUM>-<NUM> are generally referred to herein collectively as small cells <NUM> and individually as small cell <NUM>. The cellular communications system <NUM> also includes a core network <NUM>, which in the 5GS is referred to as the <NUM> Core (5GC). The base stations <NUM> (and optionally the low power nodes <NUM>) are connected to the core network <NUM>.

Now, a discussion of some example embodiments of the present disclosure will be provided. In one embodiment, a UE (e.g., UE <NUM>) performs a beam failure recovery procedure in which the UE considers the beam failure recovery procedure complete when the UE receives a new UL grant for the HARQ process used for transmission of the beam failure recovery information message, and the UL grant indicates "new data. " In some embodiments, the new UL grant indicating "new data" contains a UL grant of a minimum size larger than zero bits. In yet another embodiment, the new UL grant indicating "new data" contains a UL grant of size zero bits.

In other words, in one embodiment, a UE (e.g., UE <NUM>) performs a beam failure recovery procedure in which the UE considers the beam failure recovery procedure complete when the UE receives a new UL grant for the HARQ process used for transmission of the beam failure recovery information message, and the UL grant comprises information that implicitly indicates that the beam failure recovery information message was successfully received by the base station (e.g., a base station <NUM> such as, e.g., a gNB). In some preferred embodiments, the information comprised in the UL grant that indicates that the beam failure recovery information message was successfully received by the base station is a "new data" indicator (e.g., one or more bits that explicitly indicate that the UL grant is for new data to be transmitted for the HARQ process rather than for a retransmission for the HARQ process). In some embodiments, the UL grant additionally or alternatively includes information that indicates that the UL grant is of a minimum size larger than zero bits. In some other embodiments, the UL grant additionally or alternatively includes information that indicates that the UL grant is a UL grant of size zero bits.

In this regard, <FIG> illustrates the operation of a UE (e.g., a UE <NUM>) and a network node (e.g., a base station <NUM> such as, e.g., a gNB) to perform a Secondary Cell (SCell) beam failure recovery procedure in accordance with some embodiments of the present disclosure. In this example, the UE does not have a UL grant, so the UE starts the beam failure recovery procedure by transmitting a Scheduling Request (SR) to the network node to get UL transmission resources (step <NUM>). In response, the network node transmits and the UE receives a UL grant for a particular HARQ process (step <NUM>). In this example, the HARQ process is a HARQ process having a HARQ Identifier (ID) = <NUM>. Also, a New Data Indicator (NDI) in the UL grant indicates that new data can be transmitted. This may be achieved by setting NDI to TRUE, or that the value of NDI is toggled, i.e. its value is different compared to when it was previously received. In the illustrated example, the NDI is set to TRUE to indicate that new data can be transmitted and set to FALSE to indicate that a retransmission is needed. However, as mentioned above, the NDI can alternatively be used to indicate that new data can be transmitted by toggling the value of the NDI as compared to its previous value. Using the UL grant, the UE transmits a Beam Failure Recovery Information (BFRI) message to the network node (step <NUM>). As explained above, the BFRI message may be a MAC CE message that contains information about which SCell failed and information about a new suitable beam where the communication can be reestablished (e.g., information indicating the cell of the beam failure and a new beam suitable for reestablishing the communication). However, this initial transmission of the BFRI message fails, so the network node schedules a retransmission of the BFRI message (step <NUM>). The network node schedules the retransmission of the BFRI message by sending a UL grant for the same HARQ process with the NDI indicating that new data should not be transmitted, which in this example is done by setting the NDI to FALSE.

In response to the UL grant of step <NUM>, the UE transmits a retransmission of the BFRI message (step <NUM>). In this example, the retransmission of the BFRI message successfully reaches the network node, so the network node acknowledges the reception by requesting new data for the corresponding HARQ process. In other words, the network node acknowledges reception of the retransmission of the BFRI message by sending a UL grant to the UE for the same HARQ process with the NDI indicating that new data can be transmitted, which in this example is done by setting the NDI to TRUE (step <NUM>). At the UE, the UE receives the UL grant of step <NUM> and interprets the UL grant as an ACK for the retransmission of the BFRI message (step <NUM>). The UE thus determines that a beam failure recovery procedure related to the BFRI is complete based on the NDI in the UL grant. Optionally, the UE transmits (e.g., "dummy") data to the network node in response to the UL grant of step <NUM> (step <NUM>). In addition, the UE performs one or more actions associated with successful completion of the beam failure recovery procedure (step <NUM>). For example, the UE may delete measurements associated with the beam failure recovery procedure.

<FIG> illustrates the operation of a UE (e.g., a UE <NUM>) and a network node (e.g., a base station <NUM> such as, e.g., a gNB) to perform an SCell beam failure recovery procedure in accordance with some embodiments of the present disclosure. In the illustrated example, the NDI is set to TRUE to indicate that new data can be transmitted and set to FALSE to indicate that a retransmission is needed. However, as mentioned above, the NDI can alternatively be used to indicate that new data can be transmitted by toggling the value of the NDI as compared to its previous value. In this example, the UE has an ongoing data transmission and hence a UL grant, so the UE directly sends the BFRI message (e.g., the Medium Access Control (MAC) Control Element (CE) containing the BFRI) (step <NUM>). The UE multiplexes the BFRI with other data from its ongoing data transmission. In this example, the initial transmission of the BFRI message is multiplexed with an ongoing data transmission for a HARQ process having HARQ ID = <NUM>. The initial transmission of the BFRI message fails, so the network node schedules a retransmission of the message (step <NUM>). The network node schedules the retransmission of the BFRI message by sending a UL grant for the same HARQ process (HARQ process with HARQ ID = <NUM> in this example) with the NDI indicating that new data should not be transmitted, which in this example is done by setting the NDI to FALSE.

In response to the UL grant of step <NUM>, the UE transmits a retransmission of the data and the BFRI message (step <NUM>). In this example, the retransmission successfully reaches the network node, so the network node acknowledges the reception by requesting new data for the corresponding HARQ process. In other words, the network node acknowledges reception of the retransmission of the BFRI message by sending a UL grant to the UE for the same HARQ process (HARQ ID = <NUM>) with the NDI indicating that new data should be transmitted, which in this example is done by setting the NDI to TRUE (step <NUM>). At the UE, the UE receives the UL grant of step <NUM> and interprets the UL grant as an ACK for the retransmission of the BFRI message (step <NUM>). The UE transmits data to the network node in response to the UL grant of step <NUM> (step <NUM>). Optionally, the UE performs one or more actions associated with successful completion of the beam failure recovery procedure (step <NUM>). For example, the UE may delete measurements associated with the beam failure recovery procedure.

Note that, in the example of <FIG>, between the initial transmission of the BFRI and data by the UE in step <NUM> and transmission of the UL grant for the retransmission of the BFRI and data in step <NUM>, the network sends UL grants associated with other HARQ processes (e.g., HARQ ID = <NUM> and HARQ ID=<NUM>, in this example) and the UE responds with appropriate transmissions/retransmissions (steps <NUM> through <NUM>). Note that steps <NUM> through <NUM> are optional.

<FIG> is a schematic block diagram of a base station <NUM> according to some embodiments of the present disclosure. The base station <NUM> may be, for example, a base station <NUM> or <NUM>. As illustrated, the base station <NUM> includes a control system <NUM> that includes one or more processors <NUM> (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like), memory <NUM>, and a network interface <NUM>. The one or more processors <NUM> are also referred to herein as processing circuitry. In addition, the base station <NUM> includes one or more radio units <NUM> that each includes one or more transmitters <NUM> and one or more receivers <NUM> coupled to one or more antennas <NUM>. The radio units <NUM> may be referred to or be part of radio interface circuitry. In some embodiments, the radio unit(s) <NUM> is external to the control system <NUM> and connected to the control system <NUM> via, e.g., a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) <NUM> and potentially the antenna(s) <NUM> are integrated together with the control system <NUM>. The one or more processors <NUM> operate to provide one or more functions of a base station <NUM> as described herein (e.g., one or more functions of the base station/gNB/network node described above, e.g., with respect to <FIG> and <FIG>). In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory <NUM> and executed by the one or more processors <NUM>.

<FIG> is a schematic block diagram that illustrates a virtualized embodiment of the base station <NUM> according to some embodiments of the present disclosure.

As used herein, a "virtualized" base station is an implementation of the base station <NUM> in which at least a portion of the functionality of the base station <NUM> is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the base station <NUM> includes the control system <NUM> that includes the one or more processors <NUM> (e.g., CPUs, ASICs, FPGAs, and/or the like), the memory <NUM>, and the network interface <NUM> and the one or more radio units <NUM> that each includes the one or more transmitters <NUM> and the one or more receivers <NUM> coupled to the one or more antennas <NUM>, as described above. The control system <NUM> is connected to the radio unit(s) <NUM> via, for example, an optical cable or the like. The control system <NUM> is connected to one or more processing nodes <NUM> coupled to or included as part of a network(s) <NUM> via the network interface <NUM>. Each processing node <NUM> includes one or more processors <NUM> (e.g., CPUs, ASICs, FPGAs, and/or the like), memory <NUM>, and a network interface <NUM>.

In this example, functions <NUM> of the base station <NUM> described herein (e.g., one or more functions of the base station/gNB/network node described above, e.g., with respect to <FIG> and <FIG>) are implemented at the one or more processing nodes <NUM> or distributed across the control system <NUM> and the one or more processing nodes <NUM> in any desired manner. In some particular embodiments, some or all of the functions <NUM> of the base station <NUM> described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) <NUM>. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) <NUM> and the control system <NUM> is used in order to carry out at least some of the desired functions <NUM>. Notably, in some embodiments, the control system <NUM> may not be included, in which case the radio unit(s) <NUM> communicate directly with the processing node(s) <NUM> via an appropriate network interface(s).

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of base station <NUM> (e.g., one or more functions of the base station/gNB/network node described above, e.g., with respect to <FIG> and <FIG>) or a node (e.g., a processing node <NUM>) implementing one or more of the functions <NUM> of the base station <NUM> in a virtual environment according to any of the embodiments described herein is provided.

<FIG> is a schematic block diagram of the base station <NUM> according to some other embodiments of the present disclosure. The base station <NUM> includes one or more modules <NUM>, each of which is implemented in software. The module(s) <NUM> provide the functionality of the base station <NUM> described herein (e.g., one or more functions of the base station/gNB/network node described above, e.g., with respect to <FIG> and <FIG>).

<FIG> is a schematic block diagram of a UE <NUM> according to some embodiments of the present disclosure. As illustrated, the UE <NUM> includes one or more processors <NUM> (e.g., CPUs, ASICs, FPGAs, and/or the like), memory <NUM>, and one or more transceivers <NUM> each including one or more transmitters <NUM> and one or more receivers <NUM> coupled to one or more antennas <NUM>. The transceiver(s) <NUM> includes radio-front end circuitry connected to the antenna(s) <NUM> that is configured to condition signals communicated between the antenna(s) <NUM> and the processor(s) <NUM>, as will be appreciated by on of ordinary skill in the art. The processors <NUM> are also referred to herein as processing circuitry. The transceivers <NUM> are also referred to herein as radio circuitry. In some embodiments, the functionality of the UE <NUM> described above (e.g., one or more functions of the UE described above, e.g., with respect to <FIG> and <FIG>) may be fully or partially implemented in software that is, e.g., stored in the memory <NUM> and executed by the processor(s) <NUM>. Note that the UE <NUM> may include additional components not illustrated in <FIG> such as, e.g., one or more user interface components (e.g., an input/output interface including a display, buttons, a touch screen, a microphone, a speaker(s), and/or the like and/or any other components for allowing input of information into the UE <NUM> and/or allowing output of information from the UE <NUM>), a power supply (e.g., a battery and associated power circuitry), etc..

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the UE <NUM> according to any of the embodiments described herein (e.g., one or more functions of the UE described above, e.g., with respect to <FIG> and <FIG>) is provided.

The module(s) <NUM> provide the functionality of the UE <NUM> described herein (e.g., one or more functions of the UE described above, e.g., with respect to <FIG> and <FIG>).

Claim 1:
A method performed by a wireless device (<NUM>; <NUM>) for beam failure recovery, the method comprising:
- transmitting (<NUM>) a scheduling request to a base station (<NUM>; <NUM>) after detecting a beam failure;
- receiving (<NUM>, <NUM>), from the base station, a first uplink grant for a particular Hybrid Automatic Repeat Request, HARQ, process, wherein the first uplink grant comprises a new data indicator, NDI;
- transmitting (<NUM>, <NUM>), using the first uplink grant, an uplink transmission to the base station, the uplink transmission comprising beam failure recovery information, the uplink transmission being associated with the particular HARQ process;
- receiving (<NUM>, <NUM>), from the base station, a second uplink grant for the particular HARQ process, wherein the second uplink grant comprises a NDI, wherein the NDI comprised in the second uplink grant is a bit in the second uplink grant, wherein a value of the bit is toggled compared to the NDI comprised in the first uplink grant, the NDI comprised in the second uplink grant thereby indicating that new data can be transmitted; and
- determining (<NUM>, <NUM>), based on the NDI comprised in the second uplink grant, that a beam failure recovery procedure related to the beam failure recovery information is complete.