Recovery from beam failure

The present invention generally relates to wireless communication, more particularly, relates to recovery from beam failure in a wireless access network where beamforming technique is used in communication between network elements. According to one aspect of the present invention, there is provided a method for recovery from beam failure in a wireless access network accessed by a user equipment (UE). The method comprises: at the wireless access network, determining whether the beam failure occurs on the basis of presence of a response from the UE during communicating between the wireless access network and the UE via a first beam; and if it is determined that the beam failure occurs, communicating with the UE via an available beam selected from the first beam and one or more second beams.

TECHNICAL FIELD

The present invention generally relates to wireless communication, more particularly, relates to recovery from beam failure in a wireless access network where beamforming technique is used in communication between network elements.

BACKGROUND

The ultimate goal of mobile broadband should be the ubiquitous and sustainable provision of non-limiting data rates to everyone and everything at every time. Along this path, Ultra-Dense Network (UDN) is an important next step following the successful introduction of LTE for wide-area and local-area access.

Ultra-dense network (UDN) is envisioned to provide ubiquitous mobile broadband with access-node densities considerably higher than the current densest cellular networks. UDN can be deployed in areas with high traffic consumption. Through overprovision and related low average loads in an access network, UDN creates ubiquitous access opportunities which—even under realistic assumptions on user density and traffic—provide users with the desired data rates.

Overprovisioning is achieved by an extremely dense grid of access nodes; inter-access-node distances in the order of tens of meters and below are envisioned. For in-indoor deployments, one or even multiple access nodes are conceivable in each room. Additionally, in order to increase network capacity, densification—via reduced transmit powers—also offers access to vast spectrum holdings in the millimeter-wave bands and thus higher data rates.

Beamforming for concentrating transmitted energy on an intended receiver plays a critical role for UDN. However, using more narrow transmission beams also makes a wireless system more susceptible to sudden coverage loss due to beam failure. In light of the above, an efficient and reliable recovery from the beam failure constitutes an urgent issue to be addressed.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a method for recovery from beam failure in a wireless access network accessed by a user equipment (UE). The method comprises: at the wireless access network, determining whether the beam failure occurs on the basis of presence of a response from the UE during communication between the wireless access network and the UE via a first beam; and if it is determined that the beam failure occurs, communicating with the UE via an available beam selected from the first beam and one or more second beams.

According to the above aspect of the present invention, the beam failure can be effectively detected by a feedback-based determination without always-on reference signal. This is especially advantageous for a UE specific beam-based system such as UDN.

In an embodiment according to the present invention, the response is one selected from a group consisting of: an acknowledgement (ACK) message or a negative acknowledgement (NACK) message responding to a data message transmitted from an AN of the wireless access network on a downlink associated with the first beam, and a data message responding to a grant message transmitted from an AN of the wireless access network on a downlink associated with the first beam.

In an embodiment according to the present invention, the selection of the available beam is on the basis of radio link quality for downlinks associated with the first beam and the one or more second beams.

In an embodiment according to the present invention, the step of communicating with the UE via the available beam comprises: upon determining that the beam failure occurs, transmitting to the UE a message from one or more ANs of the wireless access network via the first beam and the one or more second beams; receiving information on the selection of the available beam from the UE; and using the selected available beam during communication with the UE.

In an embodiment according to the present invention, the step of communicating with the UE via the available beam comprises: upon determining that the beam failure occurs, transmitting to the UE a message from a first AN and a second AN of the wireless access network, wherein the message from the first AN is transmitted via the first beam and the message from the second AN is transmitted via the one or more second beams; receiving information on the selection of the available beam from the UE; and using the selected available beam during communication with the UE.

In an embodiment according to the present invention, the step of communicating with the UE via the available beam comprises: upon determining that the beam failure occurs, transmitting a message from a first AN and second AN of the wireless access network, wherein the message from the first AN is transmitted via the first beam and at least one of the second beams and the message from the second AN is transmitted via the other of the second beams; receiving information on the selection of the available beam from the UE; and using the selected available beam during communication with the UE.

According to another aspect of the present invention, there is provided a method for recovery from beam failure for a user equipment (UE) accessing a wireless access network. The method comprises: at the UE, determining whether the beam failure occurs on the basis of presence of a response from the wireless access network during communication between the wireless access network and the UE via a first beam; and if it is determined that the beam failure occurs, communicating with the wireless access network via an available beam selected from the first beam and one or more second beams.

In an embodiment according to the present invention, the response is one selected from a group consisting of: a grant message responding to a service request transmitted from the UE on an uplink associated with the first beam and a random access response message responding to a random access request transmitted from the UE on an uplink associated with the first beam.

In an embodiment according to the present invention, the selection of the available beam is on the basis of radio link quality for uplinks associated with the first beam and the one or more second beams.

In an embodiment according to the present invention, the step of communicating with the wireless access network via the available beam comprises: upon determining that the beam failure occurs, transmitting to one or more ANs of the wireless access network a message from the UE via the first beam and the one or more second beams; receiving information on the selection of the available beam from the one or more ANs of the wireless access network; and using the selected available beam during communication with the wireless access network.

According to another aspect of the present invention, there is provided an access node (AN) capable of communicating with a user equipment (UE). The AN is configured to: determine whether beam failure occurs on the basis of presence of a response from the UE during communication between the AN and the UE via a first beam; and if it is determined that the beam failure occurs, communicate with the UE via an available beam selected from the first beam and one or more second beams, or transfer to another AN communication with the UE, the communication being made via the available beam.

According to another aspect of the present invention, there is provided a user equipment (UE) capable of communicating with a wireless access network. The UE is configured to: determine whether the beam failure occurs on the basis of presence of a response from the wireless access network during communication between the wireless access network and the UE via a first beam; and if it is determined that the beam failure occurs, communicate with the wireless access network via an available beam selected from the first beam and one or more second beams.

According to another aspect of the present invention, there is provided a user equipment (UE) capable of interacting with a wireless access network. The UE comprises: a determining unit configured to determine whether the beam failure occurs on the basis of presence of a response from the wireless access network during communication between the wireless access network and the UE via a first beam; and a transceiver configured to communicate with the wireless access network via an available beam selected from the first beam and one or more second beams if the determining unit determines that the beam failure occurs.

In an embodiment according to the present invention, for communicating with the wireless access network via the available beam, the transceiver is configured to: transmit to one or more ANs of the wireless access network a message from the UE via the first beam and the one or more second beams if the determining unit determines that the beam failure occurs; receive information on the selection of the available beam from the one or more ANs of the wireless access network; and use the selected available beam to communicate with the wireless access network.

According to another aspect of the present invention, there is provided an access node (AN) capable of communicating with a user equipment (UE). The AN comprises: a determining unit configured to determine whether beam failure occurs on the basis of presence of a response from the UE during communication between the AN and the UE via a first beam; and a transceiver configured to, if the determining unit determines that the beam failure occurs, communicate with the UE via an available beam selected from the first beam and one or more second beams, or transfer to another AN communication with the UE, the communication being made via the available beam.

DETAILED DESCRIPTION

All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The discussion above and below in respect of any of the aspects of the present disclosure is also in applicable parts relevant to any other aspect of the present disclosure.

Generally, all terms used in the claims and the description are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. For example, the term “user equipment (UE)” may refer to any suitable terminal capable of wireless communication, such as a mobile phone or a portable computer. Likewise, the term “access node (AN)” may refer to any suitable intermediary devices providing wireless communication, such as a relay node, a router, an access point, a base station or a base site, which is capable of connecting a user equipment to another wireless access node or connecting a user equipment to a core network. The term “wireless link” or “radio link” may refer to a radio channel connecting wireless communication devices such as UEs and ANs with each other, and thus may refer to anyone of an uplink (UL), a downlink (DL), a forward link (FL) and a reverse link (RL).

Beamforming is a signal processing technique used for directional signal transmission or reception. Beamforming can be used at both transmitting and receiving sides in order to achieve spatial selectivity. In a typical beamforming configuration, a transmitter with an antenna array amplifies a signal by different “weights” at the respective antennas, and thus the signal experiences constructive interference at particular directions or sectors and destructive interference at other directions or sectors. As a result, it can have a desired sensitivity pattern where a main lobe, serving as a beam for transmitting the signal to a receiver, is produced together with nulls and side lobes. By adjusting the main lobe width and the side lobe levels, the position of a null can be controlled. This is useful to ignore noise or jammers in one particular direction, while listening for events in other directions. A similar result can be obtained on reception. The details on beamforming are described in, e.g., IEEE 802.11ad, which is incorporated herein by reference in its entirety.

Beam failure, as discussed throughout the present disclosure, refers to such a situation where a beam currently being used for communication between a transceiver and a receiver becomes unavailable due to e.g., deteriorative radio link quality. A variety of events such as UE mobility, appearance of obstacle and orientation change for a UE may deteriorate the radio link quality.

FIG. 1is a schematic diagram depicting an Ultra-dense network (UDN) architecture. Referring toFIG. 1, a wireless network, e.g., UDN110herein, comprises ANs111A-111G, which are configured to provide UEs112A-112B with wireless access within their respective coverages by beamforming technique. For illustrative purpose, UEs112A and112B are communicatively coupled to ANs111E and111G, respectively. On the other hand, ANs111A-111G are communicatively coupled with each other. In particular, as shown inFIG. 1, ANs111A and111C are connected together via a fixed backhaul link, and other ANs111B,111D-111G are connected to AN111A or111C via wireless links. As a result, ANs111A-111G are either directly connected to fixed transport backhaul or wirelessly backhauled by other ANs. Moreover, these ANs are coupled to a transport aggregation node113, over which they can communicate with an operator core network120or an external data network130, e.g., internet.

As stated above, it has a correlation between the beam failure and the deteriorated radio link quality. Therefore, one can determine whether the beam failure occurs on the basis of the radio link quality. However, this heavily relies on an always-on common reference signal on uplinks or downlinks and thus is not attainable for a typical UDN radio access configuration where beamforming is used widely to compensate the limited link budget in high-frequency spectrum and thus transmission is UE specific rather than UE common, i.e., reference signals are transmitted only when a UE is expected to receive them.

According to one aspect of the present invention, a transmitter utilizes a feedback or response from a receiver to determine the occurrence of the beam failure. For example, in the UDN as shownFIG. 1, assuming that AN111E and UE112A communicate with each other via beam E1. In a session, AN111E transmits, to UE112A, a data message via beam E1and then waits for an acknowledgement (ACK) message or a negative acknowledgement (NACK) message from UE112A. If AN111E receives neither the ACK message nor the NACK message via beam E1within a predetermined time interval, it will determine the occurrence of the beam failure for beam E1. As another example, UE112A transmits a service request to AN111E via beam E1and then waits for a grant message from AN111E. If UE112A fails to receive the grant message via beam E1within a predetermined time interval, it will determine the occurrence of the beam failure for beam E1.

It shall be noted that the feedback-based determination as described above is also applicable to other message types. For example, at AN side, the determination may be established on a data message responding to a grant message transmitted from AN111E; and at UE side, one can make the determination on the basis of a random access response message responding to a random access request transmitted from UE112A.

With the feedback-based determination, the always-on reference signal is not necessary and thus the beam failure can be effectively detected in a UE specific beam-based system such as UDN.

Typically, for communication between a UE and a wireless access network, two or more beams are available and one of them may be selected for serving the communication. For example, in the UDN as shown inFIG. 1, UE112A and AN111E can communicate with each other via beams E1, E2, and E4. These beams are collectively referred to be “candidate beam” hereinafter. Among the candidate beams, one currently serving the communication or interaction is referred to as “serving beam” or “first beam” hereinafter; and other candidate beam(s) are referred to as “backup beam” or “second beam” hereinafter. One way to recover from beam failure is to use one of the backup beams to take over the coverage in case of the sudden beam loss of the serving beam. Note that the candidate beams are unnecessarily limited to only a pair of a UE and a specific AN. As described below, for the candidate beams, some of them may belong to the UE and one AN and the others may belong to the UE and another AN.

According to another aspect of the present invention, a UE (UE side) and a wireless access network (network side) reach pre-agreement on which beams qualify as the backup beams for a serving beam. The pre-agreement may be periodically carried out between these participators, or carried out at the beginning of establishing connection between them. In one embodiment, the UE side or the network side as a transmitter side (Tx side), transmits to the network side or the UE side as a receiver side (Rx side) a reference signal in different directions or via different beams associated with uplinks or downlinks. The receiver side reports the beam(s) via which the reference signal is received, preferably along with radio link quality associated with them. Therefore, for each beam being as a serving beam, one or more backup beams are identified by the participators. For example, assuming the Tx side transmits the reference signal to the Rx side via beams X1, . . . Xn, wherein n represents the number of the transmitting beams. If the Rx side receives the reference signal via beams X1, X3and Xi, beams X3and Xi are identified as the backup beams for beam X1, beams X1and Xi are identified as the backup beams for beam X3, and beams X1and X3are identified as the backup beams for beam Xi.

Preferably, in case of a plurality of backup beams for a serving beam, one is designated as a primary backup beam, which will be firstly selected as a new serving beam if the beam failure occurs. More preferably, the designation is made at the receiver side and is based on the radio link quality of the forward links associated with the backup beams. The radio link quality may be obtained from RSRP or SINR measurements at the receiver side. More preferably, the primary backup beam corresponds to one forward link having the best radio link quality.

In case of the network or AN side being as the transmitter side, the designation is made at the UE side. Since the network side does not dominate the designation of the primary backup beam associated with the downlink, it takes a risk that no radio resources are available when the beam failure occurs or the utilization of radio resources is not optimum. In one embodiment, the designation is always dominated at the network side so as to avoid the above defects. Particularly, the network side designates the primary backup beam based on, e.g., the radio link quality measurement made by the UE side and the current load distribution around the UE side. In one embodiment, the network side indicates the primary backup beam in each downlink transmission, e.g., as additional information in a Scheduling Assignment (SA) or as a MAC Control Element (MAC CE) in a MAC Protocol Data Unit (MAC PDU) carrying data. Alternatively, the network side may send a separate indicator on the primary backup beams by using a MAC CE, e.g., in a MAC PDU without higher layer data, or Radio Resources Control (RRC) signaling. In another embodiment, the primary backup beam is determined in a hybrid mode. As described above, the pre-agreement is periodically carried out between a UE side and a network side. At the beginning of the current pre-agreement cycle, the UE side, being as a receiver side, designates the backup beam corresponding to one forward link having the best radio link quality as the primary backup beam. However, the designation is changeable by the network side during the current pre-agreement cycle. For example, the network side may send a command for changing the primary backup beam in a downlink transmission, either in conjunction with data transmission or as a separate signaling message. Alternatively, the changed primary backup beam is valid until the next sending of the command. In other words, whatever measurements for radio link quality vary from one cycle to another cycle, the primary backup beam will be kept unchanged until the network side sends the command again.

According to another aspect of the present invention, the identified backup beams are mapped into specific downlink and uplink resources. The specific uplink resources may be UL PHY resources, e.g., random access channel resources or scheduling request resources, and the specific downlink resources may be DL PHY resources, e.g., downlink control channel resources according to a Discontinuous Reception (DRX) pattern.

As a result, a transmitter side (e.g., network or AN side in case of DL and UE side in case of UL) will notify the occurrence of beam failure for a serving beam via both of the current serving beam and the backup beam(s), or only via the backup beam(s), and a receiver side (e.g., network side in case of UL and UE side in case of DL) will recognize the beam failure by monitoring the mapped radio link resources. For UL, the AN side is ready for uplink reception on the mapped resources associated with the backup beams. If the AN side receives a request for transmission resources through a Scheduling Request (SR), e.g., on Physical Downlink Control Channel (PDCCH) resources or through a random access procedure initiated on a Random Access Channel (RACH) mapped to the resources associated with one of the backup beams, it recognizes that this backup beam is in use for the reselection of the serving beam. On the other hand, for DL, the UE side is ready for downlink reception on the mapped resources associated with the backup beams. If the UE receives SA on PDCCH of the mapped downlink resources associated with one of the backup beam, it recognizes that this backup beam is in use for the reselection of the serving beam.

According to another aspect of the present invention, if, at the transmitter side, e.g., at the network or UE side, it determines that the beam failure for the current serving beam occurs, a new serving beam needs to be reselected from the candidate beams, including the current serving beam and the backup beam(s), or only from the backup beam(s). Note that at this time, it has no knowledge on which link (forward link, reverse link, or both) causes the beam failure. Therefore, a transmitter will notify a receiver of the occurrence of the beam failure via the current serving beam and the backup beam(s), or only via the backup beam(s). The notification may be transmitted in a forward link transmission, either in conjunction with data transmission or as a separate signaling message. Note that the explicit notification is unnecessary and the receiver side can recognize the beam failure only from the event that the data transmission is performed via the backup beam(s). At the receiver side, e.g., the network side or UE side, it monitors the forward links associated with the candidate beams. Upon receiving the notification or the data transmission via the backup beams, the receiver side utilizes an available beam as a new serving beam to communicate with the transmitter side. The available beam is selected from the serving beam and the backup beam(s), or only from the backup beam(s).

In one embodiment, the selection is made on the basis of the radio link quality. For example, assuming the transmitter side transmits the notification or the data transmission via beams X1, X2, X3and X4, and at the receiver side, the notification or the data transmission is received via beams X1, X2and X3. If the forward link associated with beam X2has the highest link quality, beam X2is selected as the new serving beam.

Alternatively, in case of the receiver side being the UE side, the new serving beam is selected by the network side. Particularly, upon receiving the notification or the data transmission via beams X1, X2and X3, the receiver reports the radio link quality for the forward links. Then, at the transmitter, the new serving beam is selected on the basis of the radio link quality measurement made by the UE side and the current load distribution around the UE side.

Preferably, upon receiving the notification or the data transmission via beams X1, X2and X3, the receiver reports to the transmitter the receipt of the notification or the data transmission via beams X1, X2and X3. Then, in response to the report from the receiver, the transmitter selects the new serving beam on the basis of the radio link quality for the reverse links associated with beams X1, X2and X3, and optionally along with the current load distribution around the UE side. In another embodiment, the new serving beam may be the primary backup beam designated in the manner as described above.

As a result, the communication continues between the transmitter side and the receiver side via the new serving beam. The new serving beam may be the serving beam previously in use or a backup beam.

FIG. 2is a process flow diagram of a method for reaching pre-agreement on backup beam(s) according to one exemplary embodiment of the present invention. For illustrative purpose, the following depiction is made in the context of the above architecture as shown inFIG. 1. However, one skilled artisan in the art would recognize that the present invention is applicable to other architectures. Moreover, one skilled artisan will recognize that all of the aspects of the present invention as described above are applicable to the present exemplary embodiment.

With reference toFIG. 2, at step S210, it determines whether a routine for reaching pre-agreement on backup beams for the current serving beams shall be initiated. Note that the routine may be triggered periodically or by the occurrence of a predefined event, e.g., establishment of connection between UE112A and AN111E. If the routine shall be initiated, the process proceeds to step S220; otherwise, the process continues to determine whether the routine shall be initiated at step S210.

At step S220, the routine for reaching pre-agreement on backup beams for the current serving beam is initiated. The initiator for the routine may be either UE112A or AN111E. For example, as an initiator, AN111E initiates the routine by transmitting, to UE112A, a reference signal via beams E1, E2, E3, and E4associated with downlinks.

Assuming UE112A receives the reference signal via downlinks associated with beams E1, E2and E4. Thus, at step S230, UE112A will respond to AN111E via uplinks associated with beams E1, E2and E4. Preferably, the response to AN111E may include radio link quality for the downlinks associated with these beams. As a result, the participants will identify backup beams for each beam. In particular, beams E2and E4are identified as the backup beams for beam E1, beams E1and E4as the backup beams for beam E2, and beams E1and E2as the backup beams for beam E4. The identified backup beams are mapped into specific downlink and uplink resources and thus the receiver side can recognize the beam failure by monitoring the mapped specific radio link resources.

At UE112A, one of beams E2and E4may be designated as a primary backup beam based on the radio link quality of the downlinks associated with these backup beams. Alternatively, the designation is performed by AN111E on the basis of the radio link quality and the current load distribution around UE112A.

After step S230, the process proceeds to step S210.

FIG. 3is a process flow diagram of a method for recovery from beam failure in a wireless access network according to another exemplary embodiment of the present invention. For illustrative purpose, the following depiction is made in the context of the above architecture as shown inFIG. 1. However, one skilled artisan in the art would recognize that the present invention is applicable to other architectures. Moreover, one skilled artisan will recognize that all of the aspects of the present invention as described above are applicable to the present exemplary embodiment.

For illustrative purpose, in the present exemplary embodiment, it assumes that UE112A accesses to UDN110through AN111E via beam E1, which is taken as the current serving beam at the beginning of the process, and under pre-agreement, beams E2and E4are taken as the backup beams for beam E1.

At step S310, UE112A or AN111E determines whether beam failure for the current serving beam, i.e., beam E1, occurs. The determination may be the feedback-based determination as described above. In particular, UE112A or AN111E may utilize a feedback or response from a receiver to determine the occurrence of the beam failure. If it determines the beam failure occurs, the process proceeds to step S320; otherwise, the process continues to determine whether the beam failure occurs at step S310.

For illustrative purpose, it assumes that the beam failure is determined at AN111E. Then at step S320, AN111E transmits notification of the occurrence of the beam failure to UE112A via the current serving beam E1and the backup beams E2and E4. Alternatively, the notification may be transmitted only via the backup beams E2and E4. Likewise, the notification may be transmitted either in conjunction with data transmission or as a separate signaling message.

As described above, upon receiving the notification or the data transmission via the backup beams, the receiver side utilizes an available beam as a new serving beam to communicate with the transmitter side. The available beam is selected from the serving beam and the backup beams, or only from the backup beams. Therefore, at step S330, AN111E receives from UE112A information on the selection of the available beam or the new serving beam. For illustrative purpose, assuming beam E4is selected as the new serving beam.

Alternatively, instead of selecting a new serving beam, the receiver side may send to the transmitter side a report on the beams via which the notification or the data transmission is received. For example, it assumes that the notification or the data transmission is received via beams E1and E4at the receiver side. Thus, it will be reported that the notification or the data transmission is received via beams E1and E4. Accordingly, at step S330, upon receiving the report from the receiver side, the transmitter side selects a new serving beam based on the radio link quality for the forward links associated with the reported beams, i.e., beams E1and E4. For illustrative purpose, assuming that the forward link associated with beam E4has the best radio link quality, as a result, beam E4is selected as the new serving beam at the transmitter side.

At step S340, AN111E continues the interaction or communication with UE112A via beam E4and then returns to step S310.

In case the beam failure is determined at UE112A, UE112A transmits notification of the occurrence of the beam failure to AN111E via beams E1, E2, and E4or only via beams E2and E4at step S320. Then at step S330, UE112A receives from AN111E information on the selection of the available beam or the new serving beam. The process proceeds to step S340, where UE112A continues the communication with AN111E via beam E4and then returns to step S310.

In the above embodiments, it assumes that the backup beams belong to the same AN. However, this assumption is not necessary and the present invention may be extended to such a scenario where, for a serving beam, some or all of the backup beams belong to an AN different from the AN of the serving beam. For example, as shown inFIG. 1, UE112B can access to AN111G via beams G1or G2, or to AN111F via beam F2. Therefore, for serving beam G1(G2), besides backup beam G2(G1) in AN111G, beam F2in AN111F can be also used as a backup beam; likewise, for serving beam F2, beams G1and G2can be used as backup beams. The above configuration enhances recovery capability from beam failure, especially when all of the beams within an AN are unavailable.

In case the backup beams involve with multiple ANs, it is advantageous to introduce inter-AN coordination between the involved ANs in the pre-agreement on the backup beams and the selection of the new serving beam. Preferably, the inter-AN coordination is performed via an intermediate node, e.g., a control node acting as a cluster head for controlling a cluster comprising the involved ANs. Alternatively, the inter-AN coordination may be performed directly between the involved ANs.

FIG. 4is a process flow diagram of a method for recovery from beam failure in a wireless access network according to another exemplary embodiment of the present invention. For illustrative purpose, the following depiction is made in the context of the above architecture as shown inFIG. 1. However, one skilled artisan in the art would recognize that the present invention is applicable to other architectures. Moreover, one skilled artisan will recognize that all of the aspects of the present invention as described above are applicable to the present exemplary embodiment.

For illustrative purpose, in the present exemplary embodiment, it assumes that UE112B access to UDN110through AN111G (referred to be “serving node” hereinafter) via beam G1, which is taken as the current serving beam at the beginning of the process, and between AN111G, AN111F (referring to as “neighboring node” hereinafter) and UE112B, it reaches pre-agreement that beams G2and F2are backup beams for beam G1. As described above, an intermediate node such as a cluster head, e.g., transport aggregation node113as shown inFIG. 1, coordinates the pre-agreement on the backup beams. Likewise, the pre-agreement may be updated periodically or by the occurrence of a predefined event, e.g., establishment of connection between UE112B and AN111G. The identified backup beams G2and F2are mapped into specific downlink and uplink resources and thus the receiver side can recognize the beam failure by monitoring the mapped specific radio link resources.

With reference toFIG. 4, at step S410, UE112B determines that beam failure for the current serving beam, i.e., beam G1, occurs. Likewise, the determination may be the feedback-based determination as described above. For example, if UE112B fails to receive a follow-up DL signaling after an UL transmission, e.g., an ACK/NACK feedback, it determines the beam failure for beam G1occurs.

Then at step S420, UE112B initiates multiple transmission e.g., by sending a backup beam activation command via uplinks associated with both of the serving and backup beams, i.e., beams G2and F2. The backup beam activation command may be in the form of a SR.

The serving and neighboring nodes, i.e., AN111G and AN111F, keep on monitoring the mapped specific uplink resources, e.g., the SR resources. Assuming that beam F2is designated as a primary backup beam for beam G1, or the radio link quality for beam F2is superior to G2, or beams failure for beam G2also occurs. Thus, with the inter-AN coordination by the cluster head, beam F2is selected as the new serving beam. As a result, at step S430, the neighboring node returns a UL grant to UE112B to confirm the activation of the backup beam, i.e., beam F2. Then at step S440, AN111F and UE112B start to communicate with each other.

At step S450, with the inter-AN coordination by the cluster head, the serving node notifies the neighboring node of the deactivation of beam G1, which was previously taken as the serving beam. Afterwards, at step S460, the neighboring node transmits DL signaling, e.g., a beam deactivation command to UE112B to confirm the deactivation of previous serving beam G1.

In the above embodiment, a third node such as a cluster head participates in the inter-AN coordination. As described above, however, the inter-AN coordination may be performed directly between the serving node and the neighboring node.

FIG. 5is a block diagram illustrating a user equipment (UE) having recovery capability from beam failure according to another exemplary embodiment of the present invention. For illustrative purpose, the present embodiment is described in the context of the UDN architecture as discussed with reference toFIG. 1. However, one skilled artisan in the art would recognize that the present invention is applicable to other wireless access networks. Moreover, one skilled artisan will recognize that the aspects of the present invention as described above are applicable to the present exemplary embodiment.

With reference toFIG. 5, in the present embodiment, a UE500comprises a transceiver510and a determining unit520coupled to each other.

The transceiver510is configured to interact with one or more ANs in a wireless access network, e.g., ANs111A-111G in UDN110as shown inFIG. 1. For example, the transceiver510is able to communicate or interact with AN111E via beams E1, E2and E4. Assuming beam E1is selected as a current serving beam and beams E2and E4are selected as backup beams. As an example, the transceiver510transmits a service request or a random access request on an uplink associated with beam E1and waits for a response responding to the service request or the random access request on a downlink associated with beam E1. Meanwhile, the transceiver510monitors the mapped specific radio link resources associated with beams E2and E4.

The determining unit520is configured to determine whether beam failure for the current serving beam, i.e., beam E1, occurs. The determination may be the feedback-based determination as described above. If the determining unit520determines that the beam failure occurs, the determining unit520instructs the transceiver510to transmit notification of the occurrence of the beam failure to AN111E via uplinks associated with the current serving beam E1and the backup beams E2and E4. Alternatively, the notification may be transmitted only via uplinks associated with the backup beams E2and E4.

When the transceiver510receives from AN111E information on the selection of the available beam or the new serving beam, e.g., beam E2, the determining unit520will instruct the transceiver510to continue the communication or interaction with AN111E via the new serving beam. Note that the information may be sent via downlinks associated with the new serving beam only, or associated with all of the beams linked to the mapped specific radio link resources.

Note that in case the backup beams involve with multiple ANs, the determining unit520is further configured to instruct the transceiver510to transmit the notification to all involved ANs, and the transceiver510is configured to communicate or interact with the wireless access network via the new serving beam selected with an inter-AN coordination.

FIG. 6is a block diagram illustrating an access node (AN) having recovery capability from beam failure according to another exemplary embodiment of the present invention. For illustrative purpose, the present embodiment is described in the context of the UDN architecture as discussed with reference toFIG. 1. However, one skilled artisan in the art would recognize that the present invention is applicable to other wireless access networks. Moreover, one skilled artisan will recognize that the aspects of the present invention as described above are applicable to the present exemplary embodiment.

With reference toFIG. 6, in the present embodiment, an AN600, e.g., anyone of ANs111A-111G as shown inFIG. 1, comprises a transceiver610and a determining unit620coupled to each other.

The transceiver610is configured to interact with a UE, e.g., UE112A or112B as shown inFIG. 1, and other ANs in a wireless access network, e.g., UDN110as shown inFIG. 1. For example, the transceiver610, e.g., in AN111G, is able to interact with UE112B via beams G1and G2, and is connected to AN111F directly or via a third node(s). Assuming beam G1is selected as a current serving beam and beams G2and F2are selected as backup beams. As an example, the transceiver610, e.g., in AN111G transmits a data message or a grant message on a downlink associated with beam G1, and then waits for an acknowledgement (ACK) message or a negative acknowledgement (NACK) message to the data message, or a data message to the grant message on a downlink associated with beam G1. Meanwhile, with a pre-agreement, the transceivers610, e.g., in AN111G and AN111F monitor the mapped specific radio link resources associated with beams G2and F2, respectively.

The determining unit620, e.g., in AN111G is configured to determine whether beam failure for the current serving beam, i.e., beam G1, occurs. The determination may also be also the feedback-based determination as described above. If the determining unit620determines that the beam failure occurs, in AN111G, the determining unit620instructs the transceiver610to transmit notification of the occurrence of the beam failure to UE112B via uplinks associated with the current serving beam G1and the backup beam G2. Moreover, with an inter-AN coordination, the transceiver610in AN111F transmits the notification to UE112B via an uplink associated with beam F2. Alternatively, the notification may be transmitted only via uplinks associated with the backup beams G2and F2.

Assuming beam F2is the primary backup beam as designated or is selected as a new serving beam by UE112B. Thus, UE112B will send information on the new serving beam, e.g., beam F2. At AN111F, if the transceiver610receives the information from UE112B, the determining unit620will instruct the transceiver610to communicate or interact with UE112B via the new serving beam.

In the exemplary embodiment described with reference toFIGS. 5 and 6, the determining unit can be implemented as a processor or part of the processor to perform various tasks as discussed above. The processor can include a microprocessor, microcontroller, processor module or subsystem, programmable integrated circuit, programmable gate array, or another control or computing device.

It should be noted that the aforesaid embodiments are illustrative of this invention instead of restricting this invention, substitute embodiments may be designed by those skilled in the art without departing from the scope of the claims enclosed. The wordings such as “include”, “including”, “comprise” and “comprising” do not exclude elements or steps which are present but not listed in the description and the claims. It also shall be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. This invention can be achieved by means of hardware including several different elements or by means of a suitably programmed computer. In the unit claims that list several means, several ones among these means can be specifically embodied in the same hardware item. The use of such words as first, second, third does not represent any order, which can be simply explained as names.