WO2019024110A1

WO2019024110A1 - Methods and devices for beam recovery

Info

Publication number: WO2019024110A1
Application number: PCT/CN2017/096085
Authority: WO
Inventors: Fang Yuan; Gang Wang
Original assignee: Nec Corporation
Priority date: 2017-08-04
Filing date: 2017-08-04
Publication date: 2019-02-07

Abstract

Embodiments of the present disclosure relate to methods and devices for beam recovery. In example embodiments, a method implemented in a network device is provided. In the method, a first beam recovery request is received from a terminal device. A first potential candidate beam is selected from a set of predetermined potential candidate beams specific to the terminal device; indicating the first potential candidate beam to the terminal device. It is determined whether the first potential candidate beam has been identified by the terminal device. If it is determined that the first potential candidate beam has been identified, beam sweeping is initiated within a first beam range associated with the first potential candidate beam to determine a beam to be used for communications from the network device to the terminal device.

Description

METHODS AND DEVICES FOR BEAM RECOVERY

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of communications， and in particular， to methods and devices for beam recovery.

BACKGROUND

In a standardization work of the third Generation Partnership Project (3GPP) ， it has been agreed that a terminal device is able to transmit a beam recovery request to a network device for many times if the terminal device detects a beam failure. For example， the terminal device may use Random Access Channel (RACH) transmission occasions to transmit a plurality of beam recovery requests. These multiple transmissions of the beam recovery request may mitigate influences of channel fading and therefore increase probabilities of success in beam recovery.

The number of transmissions of the beam recovery requests is configurable in a network. Related configuration parameters include， for example， the maximum number of transmissions， the maximum time delay of transmissions， and a combination thereof. A plurality of beam recovery requests may be sent before at least one of configured limits is reached. In the case that the RACH transmission occasions is used for the transmission of the beam recovery requests， the maximum time delay of transmissions may be configured in associated with a Random Access Response (RAR) window. For example， the terminal device may transmit a plurality of beam recovery requests in a contention free manner in a plurality of message 1 (Msg1) on dedicated RACH transmission occasions before the end of the RAR window.

In the 3GPP， it is proposed that the network device transmits a beam recovery response on a Next Radio (NR) Physical Downlink Control Channel (PDCCH) . For example， the network device may transmit a Demodulation Reference Signal (DM-RS) on the PDCCH. The DMRS may be spatially Quasi-Co-Located with a reference signal (RS) of a candidate beam for future transmission. In order to receive the beam recovery response from the network device， the terminal device needs to monitor the PDCCH.

There are many conventional approaches for determining the candidate beam. In one of the conventional approaches， offline beam training is presented. For example， the network device may train a backup beam in an offline mode. If a current beam is failed， the network device will use the backup beam for transmission.

In another one of the conventional approaches， the network device may initiate beam sweeping upon reception of the beam recovery request from the terminal device. The beam recovery request may or may not include a potential candidate beam which has been identified by the terminal device. The potential candidate beam reported by the terminal device is typically coarse. In the context of the present disclosure， a coarser beam refers to a beam having a larger beam width.

In the conventional approaches of determining the candidate beam， multiple transmissions of the beam recovery request are not taken into account.

SUMMARY

In general， example embodiments of the present disclosure provide methods and devices for RS configuration.

In a first aspect， there is provided a method implemented in a network device. The method comprises： receiving a first beam recovery request from a terminal device； selecting a first potential candidate beam from a set of predetermined potential candidate beams specific to the terminal device； indicating the first potential candidate beam to the terminal device； determining whether the first potential candidate beam has been identified by the terminal device； and in response to determining that the first potential candidate beam has been identified， initiating beam sweeping within a first beam range associated with the first potential candidate beam to determine a beam to be used for communications from the network device to the terminal device.

In a second aspect， there is provided a method implemented in a terminal device. The method comprises： sending a first beam recovery request to a network device； detecting a first potential candidate beam selected by the network device from a set of predetermined potential candidate beams specific to the terminal device； and sending， to the network device， an indication that the first potential candidate beam has been identified by the terminal device， such that the network device initiates beam sweeping within a first beam range associated with the first potential candidate beam to determine a beam to be used for communications from the network device to the terminal device.

In a third aspect， there is provided a network device. The network device comprises a processor and a memory coupled to the processor. The memory stores instructions that when executed by the processor， cause the network device to perform the method according to the first aspect.

In a fourth aspect， there is provided a terminal device. The terminal device comprises a processor and a memory coupled to the processor. The memory stores instructions that when executed by the processor， cause the terminal device to perform the method according to the second aspect.

In a fifth aspect， there is provided a computer readable storage medium that tangibly stores instructions. The instructions， when executed on at least one processor， cause the at least one processor to perform the method according to the first or second aspect.

Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some 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：

Fig. 1 shows an example procedure of multiple transmissions of the Msgl as the beam recovery requests；

Fig. 2 shows an example communication network in which embodiments of the present disclosure can be implemented；

Fig. 3 shows example operations and communications in a network according to some embodiments of the present disclosure；

Fig. 4 shows example beam sweeping based on a beam tree according to some embodiments of the present disclosure；

Figs. 5-8 show example processes of the beam sweeping according to some embodiments of the present disclosure；

Fig. 9 shows an example method according to some embodiments of the present disclosure；

Fig. 10 shows an example method according to some other embodiments of the present disclosure；

Fig. 11 shows an example method according to some embodiments of the present disclosure；

Fig. 12 shows an example method according to some other embodiments of the present disclosure；

Fig. 13 shows a block diagram of an apparatus in accordance with some embodiments of the present disclosure；

Fig. 14 shows a block diagram of an apparatus in accordance with some other embodiments of the present disclosure； and

Fig. 15 is a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure.

Throughout the drawings， the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure， without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims， unless defined otherwise， all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein， the term “network device” or “base station” (BS) refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include， but not limited to， a Node B (NodeB or NB) ， an Evolved NodeB (eNodeB or eNB) ， a next generation NodeB (gNB) ， a Transmission Reception Point (TRP) ， an access point (AP) ， an access node， a Remote Radio Unit (RRU) ， a radio head (RH) ， a remote radio head (RRH) ， a low power node such as a femto node， a pico node， and the like.

As used herein， the term “terminal device” refers to a device having wireless or wired communication capabilities for communicating with a network device or a further terminal device in a wireless communication network. Examples of the terminal device include， but not limited to， user equipment (UE) ， personal computers， desktops， mobile phones， cellular phones， smart phones， personal digital assistants (PDAs) ， portable computers， image capture devices such as digital cameras， gaming devices， music storage and playback appliances， or Internet appliances enabling wireless or wired Internet access and browsing and the like.

As used herein， the term “beam sweeping” refers to a procedure of sweeping beams one by one to find a target beam for future communications. The swept beams may have different beam widths and different beam ranges. In the context of the present disclosure， the beam range refers to a range of beam angle.

As used herein， the singular forms “a” ， “an” and “the” are intended to include the plural forms as well， unless the context clearly indicates otherwise. The term “includes” and its variants are to be read as open terms that mean “includes， but is not limited to” . The term “based on” is to be read as “at least in part based on” . The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment” . The term “another embodiment” is to be read as “at least one other embodiment” . The terms “first” ， “second” ， and the like may refer to different or same objects. Other definitions， explicit and implicit， may be included below.

As described above， if the terminal device detects a beam failure， the terminal device may transmit a plurality of beam recovery requests. The beam recovery requests may be sent on a Physical Random Access Channel (PRACH) . For example， the terminal device may transmit multiple Msgl as the beam recovery requests on the PRACH.

Fig. 1 shows an example procedure of transmitting the multiple Msgl as the beam recovery requests. As shown， a RAR window 105 is configured as a time limit of the transmissions. Before the end of the RAR window 105， there are many RACH transmission occasions 110-1， 110-2， ... ， 110-N. The terminal device may use two of the RACH transmission occasions 110-1 and 110-2 to transmit two Msgl. It is to be understood that the terminal device may use other numbers of RACH transmission occasions for the transmissions of the Msg. The specific number of used RACH transmission occasions is configurable in a network， as described above.

In addition to the RACH transmission occasions， periodical scheduling request (SR) transmission occasions on a Physical Uplink Control Channel (PUCCH) may be used for the transmissions of the beam recovery request. For example， the terminal device may periodically transmit multiple beam recovery requests in multiple SR transmission occasions on the PUCCH.

After the network device receives a beam recovery request from the terminal device， the network device typically transmits a beam recovery response to the terminal device. In this response， the network device may indicate a candidate beam to the terminal device. As described above， in one of the conventional approaches for determining the candidate beam， a backup beam is obtained through the offline beam training. For example， the network device may train a backup beam independent of on ongoing communications with the terminal device. If a beam failure occurs， the network device may notify the terminal device of the backup beam for future use. However， such offline training of the backup beam may not accurately reflect current radio channel conditions.

Another one of the conventional approaches requires the network device to perform the beam sweeping upon the reception of the beam recovery request which may or may not indicate a potential candidate beam identified by the terminal device. If no identified potential candidate beam is indicated， the beam sweeping may be performed in an entire beam range. If an identified potential candidate beam is indicated， the beam sweeping may be performed within a beam range associated with the identified potential candidate beam. As described above， the identified potential candidate beam is conventionally coarser， which may include， for example， a beam used for a synchronization signal (SS) block. As a result， the conventional beam sweeping may be tedious and time-consuming.

In order to solve the problems above and one or more of other potential problems， embodiments of the present disclosure provides a new mechanism of beam sweeping in beam recovery. According to embodiments of the present disclosure， after the network node receives a beam recovery request from the terminal device， the network device selects a potential candidate beam from a set of predetermined potential candidate beams specific to the terminal device. These predetermined potential candidate beams are specified or determined prior to receiving the beam recovery request. Only for the purpose of discussion， the received beam recovery request will be referred to a first beam recovery request， and the selected potential candidate beam will be referred to as a first potential candidate beam.

Once the first potential candidate beam is selected， the network device indicates the first potential candidate beam to the terminal device. Then， the network device determines whether the first potential candidate beam has been identified by the terminal device. If the first potential candidate beam has been identified， the network node initiates beam sweeping within a beam range (referred to as a “first beam range” ) associated with the first potential candidate beam to determine a beam to be used for communications from the network device to the terminal device. In the context of the present disclosure， the first beam range may be any suitable beam range associated with the identified beam. For example， the first beam range may include a beam range covering or overlapping with a beam range of the first potential candidate beam. In some embodiments， the first beam range may be the same as the beam range of the first potential candidate beam.

Accordingly， at a terminal device side， after the first beam recovery request is sent， the terminal device detects the first potential candidate beam， which is selected by the network device from the set of predetermined potential candidate beams. If the first potential candidate beam is detected， the terminal device sends to the network device an indication that the first potential candidate beam has been identified by the terminal device.

In this way， the beam sweeping may be initiated by the network device within the first beam range associated with the first potential candidate beam. Thus， the probability of successfully finding a new beam and further efficiency of the beam sweeping may be increased.

Fig. 2 shows an example communication network 200 in which embodiments of the present disclosure can be implemented. The network 200 includes a network device 210 and a terminal device 220. It is to be understood that the numbers of network devices and terminal devices in Fig. 2 are only for the purpose of illustration， without suggestion of any limitation. The network 200 may include any suitable number of terminal devices and network devices.

The terminal device 220 may communicate with the network device 210， or with a further terminal device (not shown) via the network device 210. Communications in the network 200 may conform to any suitable standards including， but not limited to， New Radio Access， Long Term Evolution (LTE) ， LTE-Evolution， LTE-Advanced (LTE-A) ， Wideband Code Division Multiple Access (WCDMA) ， Code Division Multiple Access (CDMA) ， Global System for Mobile Communications (GSM) ， Orthogonal Frequency Division Multiplexing (OFDM) ， and the like. Furthermore， the communications may be implemented 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 (1G) ， the second generation (2G) ， 2.5G， 2.75G， the third generation (3G) ， the fourth generation (4G) ， 4.5G， the fifth generation (5G) communication protocols.

In the network 200， the network device 210 uses a beams to transmit data or signaling to the terminal device 220， and vice versa. When the terminal device 220 detects that a current beam in downlink is failed， the terminal device 220 sends a beam recovery request to the network device 210. According to embodiments of the present disclosure， the network device 210 performs the beam sweeping within a beam range of a potential candidate beam from a set of predetermined potential candidate beams specific to the terminal device 220. In this way， a new beam to be used for communications from the network device 210 to the terminal device 220 may be determined effectively and efficiently. Principles and implementations of the present disclosure will be described in detail below with reference to Figs. 3-8.

Fig. 3 shows example operations and communications in the network 200 according to some embodiments of the present disclosure. As shown， after the terminal device 220 detects (305) that a downlink beam 310 is failed， the terminal device 220 sends (315) the first beam recovery request to the network device 210. The first beam recovery request may be sent in any suitable approach already known or developed in the future. The scope of the present disclosure will not be limited in this regard. According to embodiments of the present disclosure， the first beam recovery request may be any of multiple beam recovery requests sent by the terminal device 220 upon the detection of the failed beam. Specifically， the first beam recovery request may or may not be the beam recovery request sent by the terminal device for the first time right after detecting the failed beam.

In some embodiments， the first beam recovery request may indicate a beam which has been identified by the terminal device 220. The network device 210 will proceed with the subsequent operations and acts， accordingly. Detailed embodiments in this regard will be discussed in the following paragraphs.

After the network device 210 receives the first beam recovery request， the network device 210 selects the first potential candidate beam 320 from the set of predetermined potential candidate beams specific to the terminal device 220. These predetermined potential candidate beams are determined by the network device 210 in advance. The determination may be implemented in any suitable approaches.

In some embodiments， the network device 210 may receive channel measurements from the terminal device 220. Based on the received channel measurements， the network device 210 may predict one or more potential candidate beams. For example， the network device 210 may determine a beam with better channel measurements as a potential candidate beam. In some other embodiments， the network device 210 may determine the potential candidate beams based on statistics of channels associated with the terminal device 220. For example， the network device 210 may perform statistics on fingerprint of the channels associated with the terminal device 220， and then determine the potential candidate beams based on the statistics. It is to be understood that the set of predetermined potential candidate beams may include any suitable number of predetermined potential candidate beams.

The selection of the first potential candidate beam 320 from the set of predetermined potential candidate beams may be implemented by the network device 210 in any suitable way. In some embodiments， the network device 210 may select one of the predetermined potential candidate beams adjacent to the failed beam 310 as the first potential candidate beam 320， for example， in low angle spread channels.

In the embodiments where the first beam recovery request indicates a beam identified by the terminal device 220， the network device 210 may select the first potential candidate beam based on the identified beam. For example， the first beam recovery request may include an identification of the identified beam. Then， the network device 210 may select one of the predetermined potential candidate beams within a beam range (referred to as a “second beam range” ) associated with the identified beam as the first potential candidate beam 320. The second beam range may be any suitable beam range associated with the identified beam， including， for example， a beam range covering or overlapping with a beam range of the identified beam.

If none of the predetermined potential candidate beam exists within the second beam range， the network device 210 may select another one of the predetermined potential candidate beams. For example， the network device 210 may select one of the predetermined potential candidate beams adjacent to the identified beam as the first potential candidate beam 320.

The identified beam may include any suitable beam. As an example， the identified beam may include a beam for the SS block. As another example， the identified beam may include a spurious beam detected by the terminal device 220.

It is to be understood that the identification of the identified beam included in the first beam recovery request is only illustrative， but not limited. The terminal device 220 may send the identification in any suitable message. The scope of the present disclosure will not be limited in this regard.

It is also to be understood that the selection of only the first potential candidate beam is only illustrative， but not limited. In some embodiments， the network device 210 may select more than one of the predetermined potential candidate beams upon the reception of the first beam recovery request. Further， all of these selected potential candidate beams may be indicated to the terminal device 220. Embodiments in this regard will be discussed in the following paragraphs.

After the first potential candidate beam is selected， the network device 210 indicates (325) the first potential candidate beam to the terminal device 220. The indicating may be implemented in any suitable way. In some embodiments， the network device 210 may indicate the first potential candidate beam to the terminal device 220 at least in part on a PDCCH. The PDCCH may be a common PDCCH or a dedicated PDCCH for the terminal device 220.

By way of example， the network device 210 may send a DMRS beamformed with the first potential candidate beam 320 on the PDCCH. In some embodiments， the DMRS may indicate an identification of the first potential candidate beam 320. For example， an index or a scrambling code of the DMRS may be associated with the identification of the first potential candidate beam 320. Accordingly， the terminal device 220 may obtain the identification and further report it to the network device 210. The operations of the terminal device 220 will be described in details below with reference to Figs. 11 and 12.

As another example， the network device 210 may indicate resources for a channel state information-reference signal (CSI-RS) on the PDCCH. The CSI-RS is beamformed with the first potential candidate beam 320 and sent in the indicated resources. The PDCCH may also be beamformed. In this case， the beam used for the PDCCH may have a larger beam width such that the terminal device 220 is able to detect the PDCCH and obtain the resources for the CSI-RS. Similar to the DMRS， the CSI-RS may indicate the identification of the first potential candidate beam 320， for example， with an index or a scrambling code of the CSI-RS.

Since the network device 210 indicates (325) the first potential candidate beam 320 to the terminal device 220， the terminal device 220 detects the first potential candidate beam 320， accordingly. For example， in the embodiments where the DMRS on the PDCCH is beamformed with the first potential candidate beam 320， the terminal device 220 may detect the DMRS. If the DMRS is detected， the terminal device 220 may determine that the first potential candidate beam 320 is identified. If the DMRS indicates the identification of the first potential candidate beam 320， the terminal device 220 may obtain the identification from the detected DMRS.

In the embodiments where the CSI-RS is beamformed with the first potential candidate beam 320 and the resources for the CSI-RS is indicated on the PDCCH， the terminal device 220 may receive an indication of the resources for the CSI-RS on the PDCCH， and then detect the CSI-RS in the indicated resources. If the CSI-RS is detected， the terminal device 220 may determine that the first potential candidate beam 320 is identified. If the CSI-RS indicates the identification of the first potential candidate beam 320， the terminal device 220 may obtain the identification from the detected CSI-RS.

If the terminal device 220 identifies the first potential candidate beam 320， the terminal device 220 sends (330) to the network device 210 an indication that the first potential candidate beam 320 has been identified. The indication may be implemented in any suitable form. In some embodiments， the indication may include an acknowledgement (ACK) that the first potential candidate beam 320 has been identified by the terminal device. Alternatively or in addition， if the terminal device 220 has obtained the identification of the first potential candidate beam 320， the indication may include the identification of the first potential candidate beam 320.

The indication may be sent by the terminal device 220 using any suitable uplink resource. In some embodiments， the network device 210 may allocate a PUCCH for the transmission of the indication. Accordingly， the terminal device 220 may send the ACK and/or the identification of the first potential candidate beam 320 on the allocated PUCCH.

In some embodiments， considering that the identification of the first potential candidate beam 320 requires more bits to be transmitted， the network device 210 may allocate a physical uplink shared channel (PUSCH) for the transmission of the identification. The terminal device 220 may then send the identification on the allocated PUSCH. In some embodiments， in order to ensure that the network device 210 successfully receives the identification on the PUSCH， a part of resources on the PUSCH used by the terminal device 220 for sending the identification of the first potential candidate beam 320 may be separated from a part of the resources for uplink data transmission. In this case， the identification of the first potential candidate beam 320 may not be rate mapped， which will be detailed below with reference to Fig. 8.

If the terminal device 220 is allowed to send a plurality of beam recovery requests， the terminal device 220 may use a transmission occasion of the beam recovery request to send the indication that the first potential candidate beam 320 has been identified. For example， the terminal device 220 may include the indication into a further beam recovery request (referred to as a “second beam recovery request” ) . Similar to the first beam recovery request， the second beam recovery request may be any of the plurality of beam recovery requests sent by the terminal device 220 subsequent to the first beam recovery request.

In the case that the indication is included in the second beam recovery request， in some embodiments， the terminal device 220 may maintain a count number associated with the first beam recovery request without increment of the count number. Alternatively or in addition， the terminal device 220 may extend a time period for detecting a beam recovery response to the first beam recovery request from the network device 210. If no beam recovery response is received from the network device 210 after the extended time period， the terminal device 220 may determine that the beam recovery is failed. Detailed operations and acts of the terminal device 220 in this regard will be discussed in detail below with reference to Figs. 5-8.

If the network device 210 receives from the terminal device 220 the indication that the first potential candidate beam 320 has been identified， the network device 210 determines that the first potential candidate beam 320 has been identified by the terminal device 220. The transmission and reception of the indication may be associated with a predetermine time period， which will be detailed below with reference to Figs. 5-8.

Then， the network device 210 initiates (340) the beam sweeping within the first beam range associated with the first potential candidate beam 320 to determine a beam to be used for communications from the network device 210 to the terminal device 220. As shown， in this example， the beam sweeping is performed based on three sub-level potential candidate beams 340-1， 340-2， and 340-3 within the beam range of the first potential candidate beam 320.

In this way， the beam sweeping may be initiated based on the predetermined potential candidate beam. As a result， a new beam may be found more rapidly and accurately. Therefore， the efficiency of the beam sweeping may be increased significantly.

Fig. 4 shows example beam sweeping based on a beam tree according to some embodiments of the present disclosure. As shown， the beam sweeping involves three beam levels including a first beam level 405-1， a second beam level 405-2， and a third beam level 405-3. From the beam level 405-3 to the first beam level 405-1， the beams gradually narrow down. In the context， a narrower beam has a smaller beam width， and a wider beam has a larger beam width.

In this example， a failed beam 410 is detected at the first beam level 405-1. The network device 210 selects two potential candidate beams from the set of predetermined potential candidate beams， including a potential candidate beam 415-1 at the third beam level 405-3 and a potential candidate beam 415-2 at the second beam level 405-2. A SS block related beam 420 is coarser than the potential candidate beam 415-1 at the third beam level 405-3. The a potential candidate beam 415-1 at the third beam level 405-3 and the potential candidate beam 415-2 at the second beam level 405-2 may be indicated to the terminal device 220 using a periodic CSI (P-CSI) and an aperiodic CSI (AP-CSI) ， respectively.

If one of the two potential candidate beams 415-1 and 415-2 is identified by the terminal device 220， the network device 210 initiates the beam sweeping within a corresponding beam range of the identified potential candidate beam 415-1 or 415-2. By the beam sweeping， a new beam 425 is found at the first beam level 405-1. Embodiments of the present disclosure provide a shortcut in the beam sweeping， thereby improving the efficiency of the beam sweeping.

For the purpose of discussion， the beam sweeping based on the predetermined potential candidate beams is referred to as a backoff mode herein. Embodiments of the present disclosure also provide a fallback mode of beam sweeping to increase the probability that a new beam is found through the beam sweeping. In the fallback mode， if no new beam is found， the network device 210 may initiate default beam sweeping based on a coarser beam， such as the SS block related beam.

Four example processes of the beam sweeping according to some embodiments of the present disclosure will be discussed below with reference to Figs. 5-8. Fig. 5 shows an example process 500 of the beam sweeping where no resource on PUCCH/PUSCH is allocated by the network device 210 for beam reporting. As shown， upon the detection of a failed beam， the terminal device 220 sends (505) the first beam recovery request to the network device 210. After the network device 210 selects the first potential candidate beam from the set of predetermined potential candidate beams， the network device 210 sends (510) the DMRS on the PDCCH where the DMRS is beamformed with the first potential candidate beam. The PDCCH may contain a tag (as the identification) of the first potential candidate beam， for example， at a timing advance field.

If the PDCCH is detected by the terminal device 220， the terminal device 220 determines that the first potential candidate beam has been identified by itself. Accordingly， the terminal device 220 sends an indication to the network device 210. Since no resource on the PUCCH and/or PUSCH is allocated for the beam reporting， the terminal device 220 uses the second beam recovery request to carry the indication.

As described above， the transmission and reception of the indication is associated with the predetermined time period. In this example， as shown， the terminal device 220 waits a time period T1 for a next transmission occasion of the beam recovery request. Then， the terminal device 220 sends (515) to the network device 210 the second beam recovery request including the indication that the first potential candidate beam has been identified. Transmission beams and/or powers for the first and second beam recovery requests may or may not be the same. As described above， the indication may include the ACK and/or the identification of the first potential candidate beam if any. Accordingly， the network device 210 detects the indication in the time period T1.

If the terminal device 220 does not detect the PDCCH， the terminal device 220 determines that no beam recovery response has been received from the network device 210. In this case， the terminal device 220 also sends (515) the second beam recovery request， but the second beam recovery request includes no indication. According to embodiments of the present disclosure， the terminal device 220 may or may not know that the backoff mode have been activated by the network device 210. If the terminal device 220 knows that the backoff mode is activated， the terminal device 220 may include a non-acknowledgement (NAK) in the second beam recovery request ton indicate that the terminal device 220 fails to identify the first potential candidate beam.

After receiving the second beam recovery request from terminal device 220， the network device 210 initiates (520) the beam sweeping. If the second beam recovery request indicates that the first potential candidate beam has been identified， the beam sweeping is performed within the first range of the first potential candidate beam. If the second beam recovery request includes no indication， the network device 210 initiates (520) the default beam sweeping within a wider beam width. The beam sweeping may continue before the end of the RAR window 525 unless a new beam is found. In this example， the RAR window is configured as the time limit of the beam sweeping.

Fig. 6 shows an example process 600 of the beam sweeping according to some other embodiments of the present disclosure. As shown， after the terminal device 220 sends (605) the first beam recovery request to the network device 210， the network device 210 sends (610) a beam recovery response on the PDCCH. The DMRS on the PDCCH is beamformed with the first potential candidate beam.

In this example， the PUCCH has been allocated by the network device 210 for the beam reporting. The allocation of the PUCCH may be indicated in the PDCCH. Upon the detection of the PDCCH， the terminal device 220 may obtains resources of the PUCCH and then sends (615) the beam reporting on the PUCCH after a specific time period T2. The time period T2 is related to timing of the allocated PUCCH.

In the beam reporting， the terminal device 220 may send the ACK and/or the identification of the potential candidate beam to indicate that the first potential candidate beam has been identified by. Upon the reception of the reporting， the network device 210 initiates (620) the beam sweeping within the first beam range associated with the first potential candidate beam.

In addition to the use of the PDCCH， in some embodiments， downlink control information (DCI) may be used by the network device 210 to schedule resource allocation of the PUCCH， trigger the beam reporting， and notify a tag (as an identification) of an ongoing potential candidate beam such as a receiving potential candidate beam associated with the first potential candidate beam.

As described above， the identification of the first potential candidate beam may need more bits to be transmitted. Thus， more uplink resources are required to transmit the identification compared with the ACK. In particular， if a plurality of potential candidate beams needs to be indicated to the network device 210， the required uplink resources are even more. Thus， in this example， as shown， the terminal device 220 may send (625) the second beam recovery request to carry the identification， for example， if the allocated resources on the PUCCH are insufficient. Accordingly， the network device 210 may wait for the next transmission occasion of the beam recovery request (for example， the time period T1 as shown in Fig. 5) to determine whether the potential candidate beam has been identified by the terminal device 220.

Similar to the process of beam sweeping as shown in Fig. 5， if the terminal device 220 fails to detect the beam recovery response from the network device 210， the terminal device 220 may send (625) the second beam recovery request with the NAK or with no indication. Then， the network device 210 may perform the default beam sweeping before the end of the RAR window 630. For example， the network device 210 may immediately trigger the default beam sweeping upon the reception of the second beam recovery request with the NAK or with no indication.

Fig. 7 shows another example process 700 of the beam sweeping according to some embodiments of the present disclosure. In this example， after the terminal device 220 sends (705) the first beam recovery request， the network device 210 sends (710) the PDCCH as well as the CSI-RS. The PDCCH is beamformed with a coarser beam， such as the SS block related beam and indicates the resources for the CSI-RS. The CSI-RS is beamformed using the first potential beam candidate. After the terminal device 220 detects the PDCCH， the terminal device 220 may be aware of the resources of the CSI-RS. Then， the terminal device 220 uses the indicated resources to detect the CSI-RS.

If the CSI-RS is detected， the terminal device 220 indicates， to the network device 210 on the PUCCH or PUSCH allocated by the network device 210， that the first potential candidate beam has been identified. As described above， the allocation of the PUCCH or PUSCH may be indicated on the PDCCH or the DCI. In this example， as shown， the terminal device 220 sends (710) the ACK as the indication on PUCCH/PUSCH. The ACK is sent after a specific time period T3 based on the timing of the PUCCH or PUSCH subsequent to the detection of the PDCCH. Accordingly， the network device 210 may detect the indication in the time period T3 and then performs the beam sweeping in the back mode.

If the terminal device 220 fails to detect the CSI-RS， the terminal device 220 may send (710) the NAK in the beam reporting on the PUCCH/PUSCH. Upon reception of the NAK， the network device 210 initiates (720) the default beam sweeping.

In this example， the allocated resources on the PUCCH/PUSCH are not enough to transmit the identification of the first potential candidate beam. Thus， the terminal device 220 sends (725) the second beam recovery request to carry the identification. Accordingly， the network device 210 waits for the next transmission occasion of the beam recovery request to initiate (730) the beam sweeping in the backoffmode. As described above， the beam sweeping continues before the end of the RAR window 735.

The waiting before the transmission occasion of the second beam recovery request is optional but not necessary. In some embodiments， after receiving the ACK on the PUCCH/PUSCH， the network device 210 may initiate the beam sweeping in the backoff mode rather waiting for the second beam recovery request.

Fig. 8 shows an example process 800 of the beam sweeping according to some other embodiments of the present disclosure. Similar to the example as shown in Fig. 7， after the terminal device 220 sends (805) the first beam recovery request， the network device 210 sends the PDCCH beamformed with a coarser beam as well as the CSI-RS beamformed with the first potential candidate beam. In this example， the PUCCH and/or PUSCH may be triggered in a specific time period T4 for the beam reporting. Similar to the time period T3 as shown in Fig. 7， the time period T4 is associated with the timing of the PUCCH or PUSCH. In the beam reporting on the PUCCH/PUSCH， the terminal device 220 may send the ACK/NAK and/or the identification of the first potential candidate beam as the indication that the first potential candidate beam has been identified.

In the case that the PUSCH has been allocated for the beam reporting， the indication may be carried in uplink control information (UCI) . Unlike data transmission on the PUSCH， such UCI is transmitted without rate mapping， such as interleaving， channel encoding， modulation and coding schemes， and the like. Furthermore， a part (referred to as a “first part” ) of the resources for the UCI is separated from a part (referred to as a “second part” ) of the resources for the data transmission.

If the network device 210 determines， by detecting the indication on the PUCCH/PUSCH， that the first potential candidate beam has been identified by the terminal device 220， the network device 210 initiates (820) the beam sweeping in the backoff mode. If the NAK is received， the network device 210 determines that the first potential candidate beam has not been identified and then initiates (820) the default beam sweeping.

As alternative example， after the network device 210 receives the ACK and/or the identification of the first potential candidate beam， the network device 210 may not immediately initiate the beam sweeping. Instead， the network device 210 may wait for the transmission occasion of the second beam recovery request to make a second confirmation. If the second beam recovery request indicates the same as the PUCCH/PUSCH， the network device 210 will initiate the corresponding beam sweeping. The beam sweeping likewise continues before the end of the RAR window 830.

Fig. 9 shows an example method 900 according to some embodiments of the present disclosure. The method 900 can be implemented in the network device 210 as shown in Fig. 2. For the purpose of discussion， the method 900 will be described with reference to Fig. 2.

As shown， at block 905， the network device 210 receives a first beam recovery request from the terminal device 220. At block 910， the network device 210 selects a first potential candidate beam from a set of predetermined potential candidate beams specific to the terminal device 220. At block 915， the network device 210 indicates the first potential candidate beam to the terminal device 220. At block 920， the network device 210 determines whether the first potential candidate beam has been identified by the terminal device 220. At block 925， in response to determining that the first potential candidate beam has been identified， the network device 210 initiates beam sweeping within a first beam range associated with the first potential candidate beam to determine a beam to be used for communications from the network device 210 to the terminal device 220.

In some embodiments， the network device 210 may determine the set of predetermined potential candidate beams prior to selecting the first potential candidate beam from the set of predetermined potential candidate beams. The network device 210 may determine the set of predetermined potential candidate beams in any suitable way. In some embodiments， the network device 210 may receive channel measurements from the terminal device 220. Then， the network device 210 may predict the set of predetermined potential candidate beams based on the received channel measurements， In some other embodiments， the network device 210 may determine the set of predetermined potential candidate beams based on statistics of channels associated with the terminal device 220.

The network device 210 may select the first potential candidate beam from the set of predetermined potential candidate beams in any suitable way. In some embodiments， if the first beam recovery request is sent by the terminal device upon detection of a failed beam， the network device 210 may select one of predetermined potential candidate beams adjacent to the failed beam as the first potential candidate beam.

In some embodiments， if the network device 210 receives an identification of a beam identified by the terminal device 220， the network device 210 may select the first potential candidate beam from the set of predetermined potential candidate beams based on the identified beam. For example， the network device 210 may select one of the predetermined potential candidate beams within a second beam range associated with the identified beam as the first potential candidate beam.

According to embodiments of the present disclosure， the network device 210 may indicate the first potential candidate beam to the terminal device in any suitable way. In some embodiments， the network device 210 may indicate the first potential candidate beam to the terminal device at least in part on a PDCCH. For example， the network device 210 may send a DMRS on the PDCCH where the DMRS is beamformed with the first potential candidate beam. In some embodiments， an identification of the first potential candidate beam is indicated by the DMRS.

In some embodiments， the network device 210 may indicate resources for a CSI-RS on the PDCCH， and send the CSI-RS in the indicated resources. The CSI-RS is beamformed with the first potential candidate beam. In some embodiments， an identification of the first potential candidate beam is indicated by the CSI-RS.

Any suitable approach may be used by the network device 210 to determine whether the first potential candidate beam has been identified by the terminal device 220. In some embodiments， the network device 210 may determine whether an indication has been received from the terminal device 220， the indication indicating that the first potential candidate beam has been identified by the terminal device 220. If the indication has been received， the network device 210 may determine that the first potential candidate beam has been identified by the terminal device 220. If no indication has been received (or any indication has not been received) ， the network device 210 may determine that the first potential candidate beam has not been identified by the terminal device 220.

The indication may include an acknowledgement (referred to as a “first acknowledgement” ) that the first potential candidate beam has been identified by the terminal device 220. Accordingly， the network device 210 may determine whether the indication has been received from the terminal device 220 by determining whether the first acknowledgement has been received.

In some embodiments， the network device 210 may allocate a PUCCH (referred to as a “first PUCCH” ) to the terminal device 220 for transmission of the first acknowledgement. Accordingly， the network device 210 may determine whether the first acknowledgement has been received from the terminal device 220 on the first physical uplink control channel. Any suitable resource on the first PUCCH may be used for the transmission of the first acknowledgement. In some embodiments， the transmission of the first acknowledgement may reuse resources predefined for transmission of an acknowledgement (referred to as a “second acknowledgement” ) for downlink data. For example， the network device 210 may allocate the predefined resources on the first PUCCH to the terminal device 220 for the transmission of the first acknowledgement.

In some embodiments， the indication may further include an identification of the first potential candidate beam. In some embodiments， after determining that the first acknowledgement has been received on the first PUCCH， the network device 210 may further determine whether the identification of the first potential candidate beam has been received from the terminal device 220.

In some embodiments， after determining that the first acknowledgement has been received， the network device 210 may allocate a further PUCCH (referred to as a “second PUCCH” ) or a PUSCH for transmission of the identification of the first potential candidate beam from the terminal device 220. The second PUCCH is different from the first PUCCH. Accordingly， the network device 210 may determine whether the identification of the first potential candidate beam has been received from the terminal device 220 on the second PUCCH or the PUSCH.

In some embodiments， the network device 210 may determine whether the identification of the first potential candidate beam has been received by determining whether the identification has been received in a second beam recovery request from the terminal device 220.

In some embodiments， in response to determining that the first potential candidate beam has not been identified by the terminal device， the network device 210 may initiate the beam sweeping within a further beam range (referred to as a “third beam range” ) . The third beam range is different from the first beam range and equal to or larger than the first beam range.

Fig. 10 shows an example method 1000 according to some other embodiments of the present disclosure. The method 1000 can be implemented in the network device 210 as shown in Fig. 2. For the purpose of discussion， the method will be described with reference to Fig. 2.

As shown， at block 1005， the network device 210 receives a first beam recovery request. At block 1010， the network device 210 determines whether the backoff mode is entered. If yes， the method 1000 proceeds to block 1015 where the network device 210 sends a beam recovery response and potential candidate beams to be tested. At block 1020， the network device 210 determines whether one of the potential candidate beams is identified by the terminal device 220. If yes， the network device 210 starts the beam sweeping in the backoff mode at block 1025. If no， the method 1000 returns to block 1010.

If the network device 210 determines that the backoff mode is not entered at block， the method proceeds to block 1030 where network device 210 sends the beam recovery response and triggers the beam sweeping in the fallback mode.

Fig. 11 shows an example method 1100 according to some embodiments of the present disclosure. The method 1100 can be implemented in the terminal device 220 as shown in Fig. 2. For the purpose of discussion， the method 1100 will be described with reference to Fig. 2.

As shown， at block 1105， the terminal device 220 sends a first beam recovery request to the network device 210. At block 1110， the terminal device 220 detects a first potential candidate beam selected by the network device 210 from a set of predetermined potential candidate beams specific to the terminal device 220. At block 1115， the terminal device 220 sends， to the network device 210， an indication that the first potential candidate beam has been identified by the terminal device 220， such that the network device 210 initiates beam sweeping within a first beam range of the first potential candidate beam to determine a beam to be used for communications from the network device 210 to the terminal device 220.

In some embodiments， the terminal device 220 may send channel measurements to the network device 210 for use by the network device 210 in determining the set of predetermined potential candidate beams.

In some embodiments， the terminal device 220 may send， to the network device 210， an identification of a beam identified by the terminal device for use by the network device 210 in selecting the first potential candidate beam from the set of predetermined potential candidate beam.

According to embodiments of the present disclosure， the terminal device 220 may detect the first potential candidate beam in any suitable way. In some embodiments， the terminal device 220 may detect a DMRS on a PDCCH where the DMRS is beamformed with the first potential candidate beam. In some embodiments， the terminal device 220 may obtain an identification of the first potential candidate beam from the detected DMRS.

In some embodiments， the terminal device 220 may receive an indication of resources for a CSI-RS on a PDCCH where the CSI-RS is beamformed with the first potential candidate beam. Then， the terminal device 220 may detect the CSI-RS in the resources. In some embodiments， the terminal device 220 may obtain an identification of the first potential candidate beam from the detected CSI-RS.

In some embodiments， the indication sent (at block 1115) by the terminal device 220 may include a first acknowledgement that the first potential candidate beam has been identified by the terminal device 220. Accordingly， the terminal device 220 may send the first acknowledgement to the network device 210 on a PUCCH. In some embodiments， the sending of the first acknowledgement may reuse resources predefined for transmission of a second acknowledgement for downlink data on the first PUCCH. In some embodiments， the terminal device 220 may receive， from the network device 210， an indication that the PUCCH has been allocated for transmission of the acknowledgement.

In some embodiments， the indication further includes an identification of the first potential candidate beam. For example， in addition to the first acknowledgement， the terminal device 220 may send the identification of the first potential candidate beam to the network device 210.

In some embodiments， the terminal device 220 may send the identification of the first potential candidate beam on a second PUCCH or a PUSCH. The second PUCCH is different from the first PUCCH. In some embodiments， after the terminal device 220 sends the first acknowledgement on the first PUCCH， the terminal device 220 may receive， from the network device 210， an indication that the second PUCCH or the PUSCH has been allocated for transmission of the identification of the first potential candidate beam.

In the embodiments where the terminal device 220 sends the identification on the PUSCH， the terminal device 220 may send the identification of the first potential candidate beam in a first part of resources on the PUSCH， the first part of resources being separated from a second part of the resources for data transmission.

In addition to sending on the PUCCH/PUSCH the indication that the first potential candidate beam has been identified， in some embodiments， the terminal device 220 may send to the network device a second beam recovery request including the indication. If the second beam recovery request is used， the terminal device 220 may maintain a count number associated with the first beam recovery request. Alternatively or in addition， the terminal device 220 may extend a time period for detecting a beam recovery response to the first beam recovery request from the network device 210.

Fig. 12 shows an example method 1200 according to some embodiments of the present disclosure. The method 1200 can be implemented in the terminal device 220 as shown in Fig. 2. For the purpose of discussion， the method 1200 will be described with reference to Fig. 2.

As shown， at block 1205， the terminal device 220 detects a beam failure. At block 1210， the terminal device 220 sends the first beam recovery request. At block 1215， the terminal device 220 monitors the beam recovery response. At block 1220， the terminal device 220 determines whether the beam recovery response is received. If yes， the method 1200 proceeds to block 1225 where the terminal device 220 determines whether the beam recovery response is indicated by the backoff mode. If yes， the terminal device 220 monitors resources of the beam sweeping in the backoff mode and potential candidate beams at block 1230. At block 1235， the terminal device 220 determines whether a new beam has been identified. If yes， the terminal device 220 reports the new beam at block 1240.

If it is determined that the beam recovery response is not indicated by the backoff mode， the method 1200 proceeds to block 1245 where the terminal device 220 monitors resources of the default beam sweeping.

It is to be understood that all operations and features related to the network device 220 and the terminal device 210 described above with reference to Figs. 3-8 are likewise applicable to the methods 900-1200 and have similar effects. For the purpose of simplification， the details will be omitted.

Fig. 13 shows a block diagram of an apparatus 1300 in accordance with some embodiments of the present disclosure. The apparatus 1300 can be considered as an example implementation of the network device 210 as shown in Fig. 2.

As shown， the apparatus 1300 comprises a first receiving unit 1305 configured to receive a first beam recovery request from the terminal device 220； a first selecting unit 1310 configured to select a first potential candidate beam from a set of predetermined potential candidate beams specific to the terminal device 220； a first indicating unit 1315 configured to indicate the first potential candidate beam to the terminal device 220； a first determining unit 1320 configured to determine whether the first potential candidate beam has been identified by the terminal device 220； and a first initiating unit 1325 configured to， in response to determining that the first potential candidate beam has been identified， initiate beam sweeping within a first beam range of the first potential candidate beam to determine a beam to be used for communications from the network device 210 to the terminal device 220.

In some embodiments， the first selecting unit 1310 may comprise： a second determining unit configured to determine the set of predetermined potential candidate beams. In some embodiments， the second determining unit may comprise： a second receiving unit configured to receive channel measurements from the terminal device 220； and a predicting unit configured to predict the set of predetermined potential candidate beams based on the received channel measurements. In some other embodiments， the second determining unit may comprise： a third determining unit configured to determine the set of predetermined potential candidate beams based on statistics of channels associated with the terminal device 220.

In some embodiments， the first beam recovery request may be sent by the terminal device 220 upon detection of a failed beam. The first selecting unit 1310 may comprise： a second selecting unit configured to select one of predetermined potential candidate beams adjacent to the failed beam as the first potential candidate beam.

In some embodiments， the first selecting unit 1310 may comprise： a third receiving unit configured to receive an identification of a beam identified by the terminal device 220； and a third selecting unit configured to select the first potential candidate beam from the set of predetermined potential candidate beams based on the identified beam.

In some embodiments， the third selecting unit may comprise： a fourth selecting unit configured to select one of the predetermined potential candidate beams within a beam range of the identified beam as the first potential candidate beam.

In some embodiments， the first indicating unit 1315 may comprise： a second indicating unit configured to indicate the first potential candidate beam to the terminal device 220 at least in part on a PDCCH.

In some embodiments， the second indicating unit may comprise： a first sending unit configured to send a DMRS on the PDCCH， the DMRS being beamformed with the first potential candidate beam. In some embodiments， an identification of the first potential candidate beam may be indicated by the DMRS.

In some embodiments， the second indicating unit may comprise： a third indicating unit configured to indicate resources for a CSI-RS on the PDCCH； and a second sending unit configured to send the CSI-RS in the indicated resources， the CSI-RS being beamformed with the first potential candidate beam. In some embodiments， an identification of the first potential candidate beam is indicated by the CSI-RS.

In some embodiments， the first determining unit 1320 may comprise： a fourth determining unit configured to determine whether an indication has been received from the terminal device 220， the indication indicating that the first potential candidate beam has been identified by the terminal device 220； and a fifth determining unit configured to in response to determining that the indication has been received， determine that the first potential candidate beam has been identified by the terminal device. In some embodiments， the first determining unit 1320 may comprise： a sixth determining unit configured to in response to determining that no indication has been received， determine that the first potential candidate beam has not been identified by the terminal device.

In some embodiments， the indication may include a first acknowledgement that the first potential candidate beam has been identified by the terminal device 220. The first determining unit 1320 may comprise： a first allocating unit configured to allocate a first PUCCH for transmission of the acknowledgement from the terminal device 220； and a seventh determining unit configured to determine whether the first acknowledgement has been received from the terminal device 220 on the first PUCCH. In some embodiments， the first allocating unit may comprise： a second allocating unit configured to allocate resources predefined for transmission of a second acknowledgement for downlink data on the first PUCCH to the terminal device 220 for the transmission of the first acknowledgement.

In some embodiments， the indication may further include an identification of the first potential candidate beam. The first determining unit 1320 may further comprise： an eighth determining unit configured to in response to determining that the first acknowledgement has been received on the first PUCCH， determine whether the identification of the first potential candidate beam has been received from the terminal device 220.

In some embodiments， the eighth determining unit may comprise： a third allocating unit configured to allocate a second physical uplink control channel or a PUSCH for transmission of the identification of the first potential candidate beam， the second PUCCH being different from the first PUCCH； and a ninth determining unit configured to determine whether the identification of the first potential candidate beam has been received from the terminal device 220 on the second PUCCH or the PUSCH.

In some embodiments， the eighth determining unit may comprise： a tenth determining unit configured to determine whether the identification of the first potential candidate beam has been received in a second beam recovery request from the terminal device 220.

In some embodiments， the apparatus 1300 may further comprise： a second initiating unit (not shown) configured to in response to determining that the first potential candidate beam has not been identified by the terminal device 220， initiate the beam sweeping within a third beam range， the second beam range being different from the first beam range and equal to or larger than the first beam range.

Fig. 14 shows a block diagram of an apparatus 1400 in accordance with some embodiments of the present disclosure. The apparatus 1400 can be considered as an example implementation of the terminal device 220 as shown in Fig. 2.

As shown， the apparatus 1400 comprises： a first sending unit 1405 configured to send a first beam recovery request to a network device 210； a first detecting unit 1410 configured to detect a first potential candidate beam selected by the network device 210 from a set of predetermined potential candidate beams specific to the terminal device 220； and a second sending unit 1415 configured to send， to the network device 210， an indication that the first potential candidate beam has been identified by the terminal device 220， such that the network device 210 initiates beam sweeping within a first beam range associated with the first potential candidate beam to determine a beam to be used for communications from the network device 210 to the terminal device 220.

In some embodiments， the apparatus 1400 may further comprise： a third sending unit (not shown) configured to send channel measurements to the network device 210 for use by the network device 210 in determining the set of predetermined potential candidate beams.

In some embodiments， the apparatus 1400 may further comprise： a fourth sending unit (not shown) configured to send， to the network device 210， an identification of a beam identified by the terminal device 220 for use by the network device 210 in selecting the first potential candidate beam from the set of predetermined potential candidate beam.

In some embodiments， the first detecting unit 1410 may comprise： a second detecting unit configured to detect a DMRS on a PDCCH， the DMRS being beamformed with the first potential candidate beam. In some embodiments， the first detecting unit 1410 may further comprise： a first obtaining unit configured to obtain an identification of the first potential candidate beam from the detected DMRS.

In some embodiments， the first detecting unit 1410 may comprise： a first receiving unit configured to receive an indication of resources for a CSI-RS on a PDCCH， the CSI-RS being beamformed with the first potential candidate beam； and a fifth detecting unit configured to detect the CSI-RS in the resources. In some embodiments， the first detecting unit 1410 may further comprise： a second obtaining unit configured to obtain an identification of the first potential candidate beam from the detected CSI-RS.

In some embodiments， the indication may include a first acknowledgement that the first potential candidate beam has been identified by the terminal device 220. The second sending unit 1415 may comprise： a fifth sending unit configured to send the first acknowledgement to the network device 210 on a first PUCCH. In some embodiments， the fifth sending unit may comprise： a sixth sending unit configured to send the first acknowledgement to the network device 210 in resources predefined for transmission of a second acknowledgement for downlink data on the first PUCCH. In some embodiments， the apparatus 1400 may further comprise： a second receiving unit (not shown) configured to receive， from the network device 210， an indication that the first PUCCH has been allocated for transmission of the first acknowledgement.

In some embodiments， the indication may further include an identification of the first potential candidate beam. In some embodiments， the second sending unit 1415 may comprise： a seventh sending unit configured to send the identification of the first potential candidate beam on a second PUCCH or a PUSCH， the second PUCCH being different from the first PUCCH. In some embodiments， the apparatus 1400 may further comprise： a third receiving unit (not shown) configured to receive， from the network device 210 subsequent to sending the first acknowledgement on the first PUCCH， an indication that the PUSCH has been allocated for transmission of the identification of the first potential candidate beam.

In some embodiments， the sixth sending unit may comprise： an eighth sending unit configured to send the identification of the first potential candidate beam in a first part of resources on the PUSCH， the first part of resources being separated from a second part of the resources for data transmission.

In some embodiments， the second sending unit 1415 may comprise： a ninth sending unit configured to send， to the network device 210， a second beam recovery request including the indication. In some embodiments， the apparatus 1400 may further comprise： a maintaining unit (not shown) configured to maintain a count number associated with the first beam recovery request. In some embodiments， the apparatus 1400 may further comprise： an extending unit (not shown) configured to extend a time period for detecting a beam recovery response to the first beam recovery request from the network device 210.

It is also to be noted that the

apparatuses

1300 and 1400 may be respectively implemented by any suitable technique either known at present or developed in the future. Further， a single device such as the network device 210 and the terminal device 220 as shown in Figs. 2-8 may be alternatively implemented in multiple component devices separately， and multiple separated devices may be implemented in a single device. The scope of the present disclosure is not limited in these regards.

It is noted that the

apparatuses

1300 and 1400 may be configured to implement functionalities as described with reference to Figs. 2-12. Therefore， the features discussed with respect to the methods 900-1200 may apply to the corresponding components of the

apparatuses

1300 and 1400. It is further noted that the components of the

apparatuses

1300 and 1400 may be embodied in hardware， software， firmware， and/or any combination thereof. For example， the components of the

apparatuses

1300 and 1400 may be respectively implemented by a circuit， a processor or any other appropriate device. Those skilled in the art will appreciate that the aforesaid examples are only for illustration not limitation.

In some embodiment of the present disclosure， the

apparatuses

1300 and 1400 may comprise at least one processor. The at least one processor suitable for use with embodiments of the present disclosure may include， by way of example， both general and special purpose processors already known or developed in the future. The

apparatuses

1300 and 1400 may further comprise at least one memory. The at least one memory may include， for example， semiconductor memory devices， e.g.， RAM， ROM， EPROM， EEPROM， and flash memory devices. The at least one memory may be used to store program of computer executable instructions. The program can be written in any high-level and/or low-level compliable or interpretable programming languages. In accordance with embodiments of the present disclosure， the computer executable instructions may be configured， with the at least one processor， to cause the apparatus 1300 to at least perform according to the

methods

900 and 1000 as discussed above and to cause the apparatus 1400 to at least perform according to the

methods

1100 and 1200 as discussed above.

Based on the above description， the skilled in the art would appreciate that the present disclosure may be embodied in an apparatus， a method， or a computer program product. In general， the various exemplary embodiments may be implemented in hardware or special purpose circuits， software， logic or any combination thereof. For example， some aspects may be implemented in hardware， while other aspects may be implemented in firmware or software which may be executed by a controller， microprocessor or other computing device， although the disclosure is not limited thereto. While various aspects of the exemplary embodiments of this disclosure may be illustrated and described as block diagrams， flowcharts， or using some other pictorial representation， it is well understood that these 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 various blocks shown in Figs. 13 and 14 may be viewed as method steps， and/or as operations that result from operation of computer program code， and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function (s) . At least some aspects of the exemplary embodiments of the disclosures may be practiced in various components such as integrated circuit chips and modules， and that the exemplary embodiments of this disclosure may be realized in an apparatus that is embodied as an integrated circuit， FPGA or ASIC that is configurable to operate in accordance with the exemplary embodiments of the present disclosure.

Fig. 15 is a simplified block diagram of a device 1500 that is suitable for implementing embodiments of the present disclosure. As shown， the device 1500 includes one or more processors 1510， one or more memories 1520 coupled to the processor (s) 1510， one or more transmitters and/or receivers (TX/RX) 1540 coupled to the processor 1510.

The processor 1510 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. The device 1500 may have multiple processors， such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 1520 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.

The memory 1520 stores at least a part of a program 1530. The TX/RX 1540 is for bidirectional communications. The TX/RX 1540 has at least one antenna to facilitate communication， though in practice a terminal device or a network device mentioned in this disclosure may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements.

The program 1530 is assumed to include program instructions that， when executed by the associated processor 1510， enable the device 1500 to operate in accordance with the embodiments of the present disclosure， as discussed herein with reference to Figs. 2-14. That is， embodiments of the present disclosure can be implemented by computer software executable by the processor 1510 of the device 1500， or by hardware， or by a combination of software and hardware.

While this specification contains many specific implementation details， these should not be construed as limitations on the scope of any disclosure or of what may be claimed， but rather as descriptions of features that may be specific to particular embodiments of particular disclosures. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely， various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover， although features may be described above as acting in certain combinations and even initially claimed as such， one or more features from a claimed combination can in some cases be excised from the combination， and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

Similarly， while operations are depicted in the drawings in a particular order， this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order， or that all illustrated operations be performed， to achieve desirable results. In certain circumstances， multitasking and parallel processing may be advantageous. Moreover， the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments， and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

Various modifications， adaptations to the foregoing exemplary embodiments of this disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description， when read in conjunction with the accompanying drawings. Any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this disclosure. Furthermore， other embodiments of the disclosures set forth herein will come to mind to one skilled in the art to which these embodiments of the disclosure pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.

Therefore， it is to be understood that the embodiments of the disclosure are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are used herein， they are used in a generic and descriptive sense only and not for purpose of limitation.

Claims

A method implemented in a network device， comprising：

receiving a first beam recovery request from a terminal device；

selecting a first potential candidate beam from a set of predetermined potential candidate beams specific to the terminal device；

indicating the first potential candidate beam to the terminal device；

determining whether the first potential candidate beam has been identified by the terminal device； and

in response to determining that the first potential candidate beam has been identified， initiating beam sweeping within a first beam range associated with the first potential candidate beam to determine a beam to be used for communications from the network device to the terminal device.
The method of claim 1， wherein selecting a first potential candidate beam from a set of predetermined potential candidate beams comprises：

determining the set of predetermined potential candidate beams.
The method of claim 2， wherein determining the set of potential candidate beams comprises：

receiving channel measurements from the terminal device； and

predicting the set of pre determined potential candidate beams based on the received channel measurements.
The method of claim 2， wherein determining the set of predetermined potential candidate beams comprises：

determining the set of predetermined potential candidate beams based on statistics of channels associated with the terminal device.
The method of claim 1， wherein the first beam recovery request is sent by the terminal device upon detection of a failed beam， and selecting the first potential candidate beam comprises：

selecting one of predetermined potential candidate beams adjacent to the failed beam as the first potential candidate beam.
The method of claim 1， wherein selecting the first potential candidate beam comprises：

receiving an identification of a beam identified by the terminal device； and

selecting the first potential candidate beam from the set of predetermined potential candidate beams based on the identified beam.
The method of claim 6， wherein selecting the first potential candidate beam based on the identified beam comprises：

selecting one of the predetermined potential candidate beams within a second beam range associated with the identified beam as the first potential candidate beam.
The method of claim 1， wherein indicating the first potential candidate beam to the terminal device comprises：

indicating the first potential candidate beam to the terminal device at least in part on a physical downlink control channel.
The method of claim 8， wherein indicating the first potential candidate beam at least in part on the physical downlink control channel comprises：

sending a demodulation reference signal on the physical downlink control channel， the demodulation reference signal being beamformed with the first potential candidate beam.
The method of claim 9， wherein an identification of the first potential candidate beam is indicated by the demodulation reference signal.
The method of claim 8， wherein indicating the first potential candidate beam at least in part on the physical downlink control channel comprises：

indicating resources for a channel state information-reference signal on the physical downlink control channel； and

sending the channel state information-reference signal in the indicated resources， the channel state information-reference signal being beamformed with the first potential candidate beam.
The method of claim 11， wherein an identification of the first potential candidate beam is indicated by the channel state information-reference signal.
The method of claim 1， wherein determining whether the first potential candidate beam has been identified by the terminal device comprises：

determining whether an indication has been received from the terminal device， the indication indicating that the first potential candidate beam has been identified by the terminal device； and

in response to determining that the indication has been received， determining that the first potential candidate beam has been identified by the terminal device.
The method of claim 13， wherein determining whether the first potential candidate beam has been identified by the terminal device further comprises：

in response to determining that no indication has been received， determining that the first potential candidate beam has not been identified by the terminal device.
The method of claim 13， wherein the indication includes a first acknowledgement that the first potential candidate beam has been identified by the terminal device， and determining whether the indication has been received comprises：

allocating a first physical uplink control channel to the terminal device for transmission of the first acknowledgement； and

determining whether the first acknowledgement has been received from the terminal device on the first physical uplink control channel.
The method of claim 15， wherein allocating the first physical uplink control channel for the transmission of the first acknowledgement comprises：

allocating resources predefined for transmission of a second acknowledgement for downlink data on the first physical uplink control channel to the terminal device for the transmission of the first acknowledgement.
The method of claim 15， wherein the indication further includes an identification of the first potential candidate beam， and determining whether the indication has been received further comprises：

in response to determining that the first acknowledgement has been received on the first physical uplink control channel， determining whether the identification of the first potential candidate beam has been received from the terminal device.
The method of claim 17， wherein determining whether the identification of the first potential candidate beam has been received comprising：

allocating a second physical uplink control channel or a physical uplink shared channel to the terminal device for transmission of the identification of the first potential candidate beam， the second physical uplink control channel being different from the first physical uplink control channel； and

determining whether the identification of the first potential candidate beam has been received from the terminal device on the second physical uplink control channel or the physical uplink shared channel.
The method of claim 17， wherein determining whether the identification of the first potential candidate beam has been received comprising：

determining whether the identification of the first potential candidate beam has been received in a second beam recovery request from the terminal device.
The method of claim 1， further comprising：

in response to determining that the first potential candidate beam has not been identified by the terminal device， initiating the beam sweeping within a third beam range， the third beam range being different from the first beam range and equal to or larger than the first beam range.
A method implemented in a terminal device， comprising：

sending a first beam recovery request to a network device；

detecting a first potential candidate beam selected by the network device from a set of predetermined potential candidate beams specific to the terminal device； and

sending， to the network device， an indication that the first potential candidate beam has been identified by the terminal device， such that the network device initiates beam sweeping within a first beam range associated with the first potential candidate beam to determine a beam to be used for communications from the network device to the terminal device.
The method of claim 21， further comprising：

sending channel measurements to the network device for use by the network device in determining the set of predetermined potential candidate beams.
The method of claim 21， further comprising：

sending， to the network device， an identification of a beam identified by the terminal device for use by the network device in selecting the first potential candidate beam from the set of predetermined potential candidate beam.
The method of claim 21， wherein detecting the first potential candidate beam comprises：

detecting a demodulation reference signal on a physical downlink control channel， the demodulation reference signal being beamformed with the first potential candidate beam.
The method of claim 23， wherein detecting the first potential candidate beam further comprises：

obtaining an identification of the first potential candidate beam from the detected demodulation reference signal.
The method of claim 21， wherein detecting the first potential candidate beam comprises：

receiving an indication of resources for a channel state information-reference signal on a physical downlink control channel， the channel state information-reference signal being beamformed with the first potential candidate beam； and

detecting the channel state information-reference signal in the resources.
The method of claim 26， wherein detecting the first potential candidate beam further comprises：

obtaining an identification of the first potential candidate beam from the detected channel state information-reference signal.
The method of claim 21， wherein the indication includes a first acknowledgement that the first potential candidate beam has been identified by the terminal device， and sending the indication to the network device comprises：

sending the first acknowledgement to the network device on a first physical uplink control channel.
The method of claim 28， wherein sending the first acknowledgement on the first physical uplink control channel comprises：

sending the first acknowledgement to the network device in resources predefined for transmission of a second acknowledgement for downlink data on the first physical uplink control channel.
The method of claim 29， further comprising：

receiving， from the network device， an indication that the first physical uplink control channel has been allocated for transmission of the first acknowledgement.
The method of claim 29， wherein the indication further includes an identification of the first potential candidate beam.
The method of claim 31， wherein sending the indication to the network device further comprises：

sending the identification of the first potential candidate beam on a second physical uplink control channel or a physical uplink shared channel， the second physical uplink control channel being different from the first physical uplink control channel.
The method of claim 32， further comprising：

receiving， from the network device subsequent to sending the first acknowledgement on the first physical uplink control channel， an indication that the second physical uplink control channel or the physical uplink shared channel has been allocated for transmission of the identification of the first potential candidate beam.
The method of claim 32， wherein sending the identification of the first potential candidate beam on the physical uplink shared channel comprises：

sending the identification of the first potential candidate beam in a first part of resources on the physical uplink shared channel， the first part of resources being separated from a second part of the resources for data transmission.
The method of claim 21， wherein sending the indication to the network device comprises：

sending， to the network device， a second beam recovery request including the indication.
The method of claim 35， further comprising：

maintaining a count number associated with the first beam recovery request.
The method of claim 35， further comprising：

extending a time period for detecting a beam recovery response to the first beam recovery request from the network device.
A network device， comprising：

a processor； and

a memory coupled to the processor and storing instructions thereon， the instructions， when executed by the processor， causing the network device to perform the method according to any of claims 1-20.
A terminal device， comprising：

a processor； and

a memory coupled to the processor and storing instructions thereon， the instructions， when executed by the processor， causing the network device to perform the method according to any of claims 21-37.
A computer readable storage medium tangibly storing instructions which， when executed on at least one processor， cause the at least one processor to perform the method according to any of claims 1-37.