Technical Field

The invention relates to a client device and a network access node for handling beam failures. Furthermore, the invention also relates to corresponding methods and a computer program.

Background

The 5G cellular system, New Radio (NR), is currently being standardized and is targeting radio spectrum from below 1 GHz up to and above 60 GHz. To allow for such diverse radio environments, NR will support both different system bandwidths and different numerologies, i.e. different sub-carrier-spacings, from 15 kHz up to 120 or even 240 kHz. Furthermore, for 10+ GHz carriers, multiple antennas and beamforming are assumed to be used to combat the higher path loss at such high radio frequencies.

When beamforming is used, a next generation nodeB (gNB) comprising multiple antennas may transmit data in several directions in different transmit beams. The user equipment (UE) therefore has to tune its own receive antennas in different receive beam directions to communicate with the gNB. In order for the UE to be able to detect and track the transmit beams of the gNB, the UE performs beam monitoring. Hence, the gNB transmits known pilot signals in serving and adjacent beams, which the UE receives and uses to detect possible transmit beams, so called candidate beams, to switch to in case of changes in the radio environment.

Each possible connection between the UE and the gNB is called a beam pair link (BPL), where a BPL consists of a transmit beam associated to the transmitter and a receive beam associated to the receiver. Hence, a BPL can be seen as a spatial direction of a radio transmission, where the transmit beam corresponds to a certain spatial transmission direction and the receive beam corresponds to a certain spatial receiver direction. Furthermore, the spatial directions are further generated in the transmitter and receiver by different spatial transmission and reception parameters tuning the respective antenna transmit and receive panel in the respective spatial direction. The gNB will configure a set of BPLs for the UE to monitor. The configured set of monitored BPLs may be based on which BPL the UE has detected. This set can for example comprise all the BPLs associated with control channels and data channels between the gNB and the UE. The gNB will also configure a set of serving BPLs which will be used to transmit associated control information to the UE. The set of serving BPLs is a subset or equal to the set of monitored BPLs. The UE monitors the quality of the set of monitored BPLs and reports the quality in beam measurement report to the gNB. When the quality of the received signal in a BPL is below a threshold indicating unreliable detection, the BPL is in failure. If all serving BPLs for a UE are in failure, a beam failure is declared and the UE performs a beam recovery procedure.

The aim of the beam recovery procedure is to find a suitable candidate beam quickly and recover the radio link before the higher layer radio link monitoring procedure indicates a radio link failure. To re-establish the failed radio link as quickly as possible becomes especially important in case of low-latency services, such as e.g. ultra-reliable low-latency communications (URLLC) services.

Summary

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a client device for a wireless communication system, the client device being configured to

be connected to a first network access node over a first radio link and further at the same time be connected to at least one second network access node over a second radio link, upon detecting a beam failure on the first radio link, initiate a random access procedure to the first network access node over the first radio link, wherein the random access procedure is associated with the beam failure on the first radio link; and

transmit a first control message to the second network access node over the second radio link, wherein the first control message comprises information associated with the beam failure on the first radio link.

The first radio link can be a radio link comprising one or more beam pair links, such as e.g. a NR radio link. A beam pair link may in this context correspond to a spatial transmission direction for the first network access node in combination with a spatial reception direction for the client device. The second radio link can be a radio link which may or may not comprise one or more beam pair links, i.e. the second radio link can be a NR radio link, a LTE radio link, or another type of radio link. In this disclosure a beam failure on a radio link can correspond to an instance where the signal quality of all the beam pair links associated with one or more control channels of the radio link fall below a signal quality threshold.

An advantage of the client device according to the first aspect is that the client device can inform the first network access node about a beam failure on the first radio link via both the first radio link and the second radio link, i.e. via two separate radio links. Thereby, the reliability of beam failure recovery is increased and the latency associated with beam failure recovery can be decreased in some cases.

In an implementation form of a client device according to the first aspect, initiate the random access procedure comprises

transmit a random access preamble in a random access resource to the first network access node over the first radio link.

In an implementation form of a client device according to the first aspect, the first control message comprises information associated with at least one of

a random access preamble used in the random access procedure,

a random access resource used in the random access procedure, and

one or more candidate beams for beam failure recovery with the first network access node.

An advantage with this implementation form is that the first control message comprises information allowing the beam failure on the first radio link to be identified and a beam failure recovery for the first radio link to be initiated.

In an implementation form of a client device according to the first aspect, the client device is further configured to

receive a third control message from at least one of the first network access node and the second network access node, wherein the third control message comprises configuration information associated with the transmission of the first control message;

transmit the first control message according to the configuration information.

An advantage with this implementation form is that the transmission of the first control message by the client device can be configured by any one of the network access nodes. Thereby, a flexible configuration of the transmission of the first control message is achieved. In an implementation form of a client device according to the first aspect, the first control message is a radio resource control message.

An advantage with this implementation form is that the radio resource entity in the second access network node can easily identify the intended recipient network access node and forward the message without any modifications. Another advantage is that the radio resource control entity in the first network access node, when being the main radio resource control entity for providing or handling configuration of the client device, can facilitate processing of the received radio resource control message. Furthermore, the radio resource control entity in the first network access node can forward the contents of the received radio resource control message to the entity, within the first network access node, handling beam failure recovery procedure.

In an implementation form of a client device according to the first aspect, the first control message is a packet data convergence protocol control packet data unit.

An advantage with this implementation form is that signaling of the first control message can be faster compared to the case when the first control message is a radio resource control message. A further advantage is that the packet data convergence protocol entity in the first network access node, when being the main packet data convergence protocol entity handling data transmission or data reception to or from the client device, can facilitate the processing of the received packet data convergence protocol control message. Furthermore, the packet data convergence protocol entity in the first network access node can forward the contents of the received packet data convergence protocol control message to the entity, within the first network access node, handling beam failure recovery procedure.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a first network access node for a wireless communication system, the first network access node being configured to

be connected to a client device over a first radio link;

receive a second control message from a second network access node, wherein the second control message comprises information associated with a beam failure on the first radio link;

perform beam failure recovery for the first radio link based on the second control message if no random access preamble associated with the beam failure on the first radio link has been received from the client device. The second control message can e.g. be received over a backhaul link between the first network access node and the second network access node.

That no random access preamble associated with the beam failure on the first radio link has been received from the client device can be understood to mean that no random access preamble associated with the beam failure on the first radio link has been previously received from the client device, i.e. before the second control message is received. In other words, the first network access node has not detected any random access preamble associated with the beam failure on the first radio link from the client device when the second control message is received.

An advantage of a first network access node according to the second aspect is that the first network access node can be informed about a beam failure on the first radio link by the second network access node. In this way, the first network access node can perform beam failure recovery for the first radio link even when the first network access node has not received, e.g. has not been able to detect, any random access preamble associated with the beam failure on the first radio link from the client device. Thereby, the reliability of beam failure recovery is increased and the latency associated with beam failure recovery can be decreased in some cases.

In an implementation form of a first network access node according to the second aspect, the first network access node is further configured to

perform the beam failure recovery for the first radio link if no random access preamble associated with the beam failure on the first radio link has been received from the client device during a pre-defined time after the reception of the second control message.

An advantage with this implementation form is that it provides flexibility to the first network access node. The first network node can e.g. utilize the received information associated with the beam failure on the first radio link to optimize beam failure recovery, by searching only for the specific random access preamble at the specific random access occasions increasing the likelihood to detect and confirm the beam failure. The first network access node may further use the received information to avoid scheduling data to the client device on the first radio link.

In an implementation form of a first network access node according to the second aspect, the first network access node is further configured to if a random access preamble associated with the beam failure on the first radio link has been received from the client device, perform the beam failure recovery for the first radio link based on the received random access preamble.

In an implementation form of a first network access node according to the second aspect, the second control message comprises information associated with at least one of

a random access preamble used by the client device in a random access procedure associated with the beam failure on the first radio link,

a random access resource used by the client device in a random access procedure associated with the beam failure on the first radio link, and

one or more candidate beams identified by the client device for beam failure recovery with the first network access.

An advantage with this implementation form is that the second control message comprises information allowing the first network access node to identify that a beam failure has been detected on the first radio link and to initiate beam failure recovery for the first radio link.

In an implementation form of a first network access node according to the second aspect, perform the beam failure recovery for the first radio link comprises at least one of

transmit a random access response to the client device,

transmit reference signals in one or more candidate beams to the client device, search for a random access preamble used by the client device in a random access procedure associated with the beam failure on the first radio link.

An advantage with this implementation form is that by performing one or more of the above mentioned actions or steps, the first network access node can facilitate recovery from the beam failure on the first radio link, and thereby transmit or receive data to or from the client device.

In an implementation form of a first network access node according to the second aspect, the first network access node is further configured to

transmit a third control message to the client device, wherein the third control message comprises configuration information associated with transmission of a first control message from the client device to the second network access node over a second radio link, wherein the first control message comprises information associated with a beam failure on the first radio link. An advantage with this implementation form is that the first network access node can configure the transmission of the first control message by the client device. Thereby, a flexible configuration of the transmission of the first control message is achieved.

According to a third aspect of the invention, the above mentioned and other objectives are achieved with a second network access node for a wireless communication system, the second network access node being configured to

be connected to a client device over a second radio link;

receive a first control message from the client device over the second radio link, wherein the first control message comprises information associated with a beam failure on a first radio link between the client device and a first network access node;

transmit a second control message to the first network access node, wherein the second control message comprises the information associated with the beam failure on the first radio link.

The second control message can e.g. be transmitted over a backhaul link between the first network access node and the second network access node.

An advantage of a second network access node according to the third aspect is that the second network access node can inform the first network access node about a beam failure on a first radio link between the client device and the first network access node. Thereby, the reliability of beam failure recovery is increased and the latency associated with beam failure recovery can be decreased in some cases.

In an implementation form of a second network access node according to the third aspect, the first control message and the second control message comprises information associated with at least one of

a random access preamble used by the client device in a random access procedure associated with the beam failure on the first radio link,

a random access resource used by the client device in a random access procedure associated with the beam failure on the first radio link, and

one or more candidate beams identified by the client device for beam failure recovery with the first network access.

An advantage with this implementation form is that the information comprised in the first control message is forwarded in the second control message. Furthermore, the first control message and the second control message comprise information allowing the beam failure on the first radio link to be identified and a beam failure recovery for the first radio link to be initiated.

In an implementation form of a second network access node according to the third aspect, the second network access node is further configured to

transmit a third control message to the client device, wherein the third control message comprises configuration information associated with the transmission of the first control message.

An advantage with this implementation form is that the second network access node can configure the transmission of the first control message by the client device. Thereby, a flexible configuration of the transmission of the first control message is achieved.

According to a fourth aspect of the invention, the above mentioned and other objectives are achieved with a method for a client device being connected to a first network access node over a first radio link and further at the same time being connected to at least one second network access node over a second radio link, the method comprises

upon detecting a beam failure on the first radio link, initiating a random access procedure to the first network access node over the first radio link, wherein the random access procedure is associated with the beam failure on the first radio link; and

transmitting a first control message to the second network access node over the second radio link, wherein the first control message comprises information associated with the beam failure on the first radio link.

The method according to the fourth aspect can be extended into implementation forms corresponding to the implementation forms of the client device according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the client device.

The advantages of the methods according to the fourth aspect are the same as those for the corresponding implementation forms of the client device according to the first aspect.

According to a fifth aspect of the invention, the above mentioned and other objectives are achieved with a method for a first network access node being connected to a client device over a first radio link, the method comprises receiving a second control message from a second network access node, wherein the second control message comprises information associated with a beam failure on the first radio link;

performing beam failure recovery for the first radio link based on the second control message if no random access preamble associated with the beam failure on the first radio link has been received from the client device.

The method according to the fifth aspect can be extended into implementation forms corresponding to the implementation forms of the first network access node according to the second aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the first network access node.

The advantages of the methods according to the fifth aspect are the same as those for the corresponding implementation forms of the first network access node according to the second aspect.

According to a sixth aspect of the invention, the above mentioned and other objectives are achieved with a method for a second network access node being connected to a client device over a second radio link, the method comprises

receiving a first control message from the client device over the second radio link, wherein the first control message comprises information associated with a beam failure on a first radio link between the client device and a first network access node;

transmitting a second control message to the first network access node, wherein the second control message comprises the information associated with the beam failure on the first radio link.

The method according to the sixth aspect can be extended into implementation forms corresponding to the implementation forms of the second network access node according to the third aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the second network access node.

The advantages of the methods according to the sixth aspect are the same as those for the corresponding implementation forms of the second network access node according to the third aspect.

The invention also relates to a computer program, characterized in program code, which when run by at least one processor causes said at least one processor to execute any method according to embodiments of the invention. Further, the invention also relates to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

Further applications and advantages of the embodiments of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different embodiments of the invention, in which:

- Fig. 1 shows a client device according to an embodiment of the invention;

- Fig. 2 shows a method according to an embodiment of the invention;

- Fig. 3 shows a network access node according to an embodiment of the invention;

- Figs. 4a-b show methods according to an embodiment of the invention;

- Fig. 5 shows a wireless communication system according to an embodiment of the invention;

- Fig. 6 shows signalling initiated by detection of a beam failure according to an embodiment of the invention;

- Fig. 7 shows configuration information signalling according to an embodiment of the invention.

Detailed Description

The dual connectivity concept allows a client device to be simultaneously connected to two network access nodes. One network access node is the master node and the other network access node is the secondary node. The master node and the secondary node are connected via a network interface, such as a backhaul link, and at least the master node is further connected to the core network.

Dual connectivity can be used in intra-radio access technology (RAT) scenarios, where the master node and the secondary node supports the same RAT, as well as in inter-RAT scenarios where the master node and the secondary node supports different RATs. When the master node and/or the secondary node is a NR network access node, a so-called next generation nodeB (gNB), beamforming can be used between the gNB and the client device. In this case, beam management is performed for the radio link between the gNB and the client device, and beam failure recovery is initiated if all serving beam pair links of the radio link fails. To increase the reliability of beam failure recovery in a dual connectivity scenario, a client device according to embodiments of the invention can transmit information associated with the beam failure to both the master node and the secondary node.

Fig. 1 shows a client device 100 according to an embodiment of the invention. In the embodiment shown in Fig. 1 , the client device 100 comprises a processor 102, a transceiver 104 and a memory 106. The processor 102 is coupled to the transceiver 104 and the memory 106 by communication means 108 known in the art. The client device 100 further comprises an antenna or an antenna array 1 10 coupled to the transceiver 104, which means that the client device 100 is configured for wireless communications in a wireless communication system.

That the client device 100 is configured to perform certain actions can in this disclosure be understood to mean that the client device 100 comprises suitable means, such as e.g. the processor 102 and the transceiver 104, configured to perform said actions.

According to embodiments of the invention the client device 100 is configured to be connected to a first network access node 300 (e.g. above mentioned master or secondary node) over a first radio link 512 and further at the same time configured to be connected to at least one second network access node 320 (e.g. above mentioned secondary or master node) over a second radio link 514. The client device 100 may e.g. be configured to operate in a dual connectivity mode, as will be further described below with reference to Fig. 5. Upon detecting a beam failure on the first radio link 512, the client device 100 is configured to initiate a random access procedure to the first network access node 300 over the first radio link 512. The random access procedure is associated with the beam failure on the first radio link 512 and initiated by the client device 100 to trigger a beam failure recovery for the first radio link 512. The client device 100 is further configured to transmit a first control message 502 to the second network access node 320 over the second radio link 514. The first control message 502 comprises information associated with the beam failure on the first radio link 512 and hence informs the second network access node 320 that a beam failure has been detected on the first radio link 512.

Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a client device 100, such as the one shown in Fig. 1 . The method 200 may be performed when the client device 100 is connected to a first network access node 300 over a first radio link 512 and to at least one second network access node 320 over a second radio link 514. The method 200 comprises, upon detecting a beam failure on the first radio link 512, initiating 202 a random access procedure to the first network access node 300 over the first radio link 512, wherein the random access procedure is associated with the beam failure on the first radio link 512. The method 200 further comprises transmitting 204 a first control message 502 to the second network access node 320 over the second radio link 514, wherein the first control message 502 comprises information associated with the beam failure on the first radio link 512.

Fig. 3 shows a network access node 300; 320 according to an embodiment of the invention. In the embodiment shown in Fig. 3, the network access node 300; 320 comprises a processor 302, a transceiver 304 and a memory 306. The processor 302 is coupled to the transceiver 304 and the memory 306 by communication means 308 known in the art. The network access node 300; 320 may be configured for both wireless and wired communications in wireless and wired communication systems, respectively. The wireless communication capability is provided with an antenna or an antenna array 310 coupled to the transceiver 304, while the wired communication capability is provided with a wired communication interface 312 coupled to the transceiver 304.

That the network access node 300; 320 is configured to perform certain actions can in this disclosure be understood to mean that the network access node 300; 320 comprises suitable means, such as e.g. the processor 302 and the transceiver 304, configured to perform said actions.

According to embodiments of the invention a first network access node 300 is configured to be connected to a client device 100 over a first radio link 512. The first network access node 300 is configured to receive a second control message 504 from a second network access node 320 e.g. over a backhaul link 522 (shown in Fig. 5), wherein the second control message 504 comprises information associated with a beam failure on the first radio link 512. The first network access node 300 is further configured to perform beam failure recovery for the first radio link 512 based on the second control message 504, if no random access preamble associated with the beam failure on the first radio link 512 has been previously received from the client device 100. Of course the first network access node 300 may have previously received random access preambles associated with other (earlier) beam failures on the first radio link 512. But here this mentioned random access preamble is specific to (associated with) the currently ongoing and not yet treated beam failure for which information was just received in the second control message 504. Fig. 4a shows a flow chart of a corresponding method 400 which may be executed in a first network access node 300, such as the one shown in Fig. 3. The method 400 may be performed when the first network access node 300 is connected to a client device 100 over a first radio link 512. The method 400 comprises receiving 402 a second control message 504 from a second network access node 320, e.g. over a backhaul link 522, wherein the second control message 504 comprises information associated with a beam failure on the first radio link 512. The method 400 further comprises performing 404 beam failure recovery for the first radio link 512 based on the second control message 504, if no random access preamble associated with the beam failure on the first radio link 512 has been previously received from the client device 100.

According to embodiments of the invention a second network access node 320 is configured to be connected to a client device 100 over a second radio link 514. The second network access node 320 is configured to receive a first control message 502 from the client device 100 over the second radio link 514, wherein the first control message 502 comprises information associated with a beam failure on a first radio link 512 between the client device 100 and a first network access node 300. The second network access node 320 is further configured to transmit a second control message 504 to the first network access node 300, e.g. over a backhaul link 522, wherein the second control message 504 comprises the information associated with the beam failure on the first radio link 512.

Fig. 4b shows a flow chart of a corresponding method 420 which may be executed in a second network access node 320, such as the one shown in Fig. 3. The method 420 may be performed when the second network access node 320 is connected to a client device 100 over a second radio link 514. The method 420 comprises receiving 422 a first control message 502 from the client device 100 over the second radio link 514, wherein the first control message 502 comprises information associated with a beam failure on a first radio link 512 between the client device 100 and a first network access node 300. The method 400 further comprises transmitting 424 a second control message 504 to the first network access node 300, e.g. over a backhaul link 522, wherein the second control message 504 comprises the information associated with the beam failure on the first radio link 512.

Fig. 5 shows a wireless communication system 500 according to an embodiment of the invention. The wireless communication system 500 comprises a client device 100, a first network access node 300, and a second network access node 320 configured to operate in the wireless communication system 500. For simplicity, the wireless communication system 500 shown in Fig. 5 only comprises one client device 100, one first network access node 300, and one second network access node 320. However, the wireless communication system 500 may comprise any number of client devices 100, first network access nodes 300, and second network access nodes 320 without deviating from the scope of the invention.

The client device 100 can be simultaneously connected to both the first network access node 300 and the second network access node 320, e.g. when operating in a dual connectivity mode. In the embodiment shown in Fig. 5, the client device 100 is connected to the first network access node 300 over a first radio link 512 and connected to the second network access node 320 over a second radio link 514. Note, although not shown in Fig. 5, the client device 100 may further at the same time be connected to additional second network access nodes 320, i.e. a multi connectivity scenario, without deviating from the scope of the invention. Furthermore, the first network access node 300 and the second network access node 320 are connected to each other over a backhaul link 522. The first network access node 300 is in this embodiment assumed to be a network access node supporting beamforming, such as e.g. a NR network access node, a so called next generation nodeB (gNB). This means that beamforming can be used between the first network access node 300 and the client device 100. Hence, the first radio link 512 can comprise one or more beam pair links. A beam pair link may in this context correspond to a spatial transmission direction for the first network access node 300 in combination with a spatial reception direction for the client device 100.

The second network access node 320 may either be an evolved nodeB (eNB) or a gNB. Depending on the type of core network used and whether the first network access node 300 or the second network access node 320 is the master node, the backhaul link 522 between the first network access node 300 and the second network access node 320 can be a X2- interface or a Xn-interface. Table 1 gives non-limiting examples of different dual connectivity configurations and information about the network interface used between the master node and the secondary node in different dual connectivity configurations.

Table 1

In the embodiment shown in Fig. 5, the client device 100 monitors the quality of the one or more beam pair links of the first radio link 512. If the quality of received signals over all beam pair links is poor, e.g. below a configured signal quality threshold value, the first radio link 512 is deemed to be in failure and a beam failure instance may be determined. After a configurable number of consecutive beam failure instances, the client device 100 declares a beam failure. Upon detecting a beam failure on the first radio link 512, the client device 100 initiates a beam recovery procedure towards the first network access node 300 and transmits a first control message 502 to the second network access node 320, as will now be described with reference to Fig. 6.

Fig. 6 shows signalling between the client device 100, the first network access node 300, and the second network access node 320 triggered by the detection of a beam failure on the first radio link 512. In step I in Fig. 6, a beam failure on the first radio link 512 is detected by the client device 100. The client device 100 can detect the beam failure on the first radio link 512 as previously described. Upon detecting the beam failure on the first radio link 512, the client device 100 initiates a beam recovery procedure towards the first network access node 300. The beam recovery procedure comprises the client device 100 initiating a random access RA procedure to the first network access node 300 over the first radio link 512, as shown in step II in Fig. 6. The random access procedure initiated by the client device 100 may comprise the client device 100 transmitting a random access preamble in a random access resource to the first network access node 300 over the first radio link 512.

The random access procedure may either be non-contention based or contention based. If a non-contention based random access procedure is used, the client device 100 may select the random access preamble from a set of random access preambles for beam failure recovery configured by the first network access node 300. For example, the client device 100 may have been configured by the first network access node 300 with a set of resource indexes to monitor to identify candidate beams, i.e. suitable beams to switch to in case a serving beam fails. The set of resource indexes may e.g. be channel state information reference symbol (CSI-RS) resource configuration indexes and/or synchronization signal (SS)/ physical broadcast channel (PBCH) block indexes. In addition, each resource index may be configured to be associated with a random access preamble and a random access resource for beam failure recovery. When a beam failure is detected, the client device 100 checks if any of the resource indexes in the set of monitored resource indexes satisfies a criterion for candidate beam selection. If at least one of the resource indexes fulfils the criterion for candidate beam selection, the client device 100 selects the random access preamble and the random access resource associated with that resource index. The client device 100 further transmits the random access preamble in the random access resource as a part of beam failure recovery procedure. In case no resource index among the monitored set of resource indexes satisfies the criterion of candidate beam selection, the client device 100 may use a contention-based random access procedure. Note that in this case, no explicit random access preamble sequences are configured for beam failure recovery procedure.

Upon detecting the beam failure on the first radio link 512 in step I in Fig. 6, the client device 100 further transmits a first control message 502. The first control message 502 is transmitted to the second network access node 320 over the second radio link 514 (which is not in failure), as shown in step III in Fig. 6. The first control message 502 comprises information associated with the beam failure on the first radio link 512 and is transmitted to inform the second network access node 320 that a beam failure has been detected on the first radio link 512. The first control message 502 may comprise information associated with the random access procedure initiated by the client device 100 over the first radio link 512. Hence, the first control message 502 may comprise information, such as e.g. which random access preamble and/or which random access resource was used in the random access procedure started with the first network node 300. Furthermore, the first control message 502 may comprise information associated with one or more candidate beams for beam failure recovery with the first network access node 300. The one or more candidate beams can herein be transmit beams of the first network access node 300 and identified by the client device 100 to be suitable beams to switch to in case of beam failure of a serving beam. Information associated with the one or more candidate beams may e.g. comprise information identifying the one or more candidate beams and information about the received signal quality associated with the one or more candidate beams. Hence, the information allows the first network access node 300 to select a suitable candidate beam to recover from beam failure on the first radio link 512.

In embodiments of the invention, the first control message 502 may be a radio resource control (RRC) message. In this case, the lower layers responsible for beam management such as the physical layer (PHY) layer and the medium access control (MAC) layer provide the information to be carried in the first control message 502 to the RRC layer. The RRC layer includes the information in a RRC message which is transmitted to the second network access node 320 over the second radio link 514. The first control message 502 may further be a packet data convergence protocol (PDCP) control packet data unit (PDU). In this case, the lower layers responsible for beam management, such as the PHY layer and the MAC layer, provide the information to be carried in the first control message 502 to the PDCP layer. The PDCP layer includes the information in a PDCP control PDU which is transmitted to the second network access node 320 over the second radio link 514. When the second network access node 320 receives the first control message 502, the second network access node 320 generates a second control message 504 based on the first control message 502 in step IV in Fig. 6. The second network access node 320 transmits the second control message 504 to the first network access node 300, as shown in step V in Fig. 6. When the first control message 502 is a RRC message a radio resource entity in the second access network node 320 may identify the first network access node 300 as the intended recipient and transmit the second control message 504 to the first network access node 300 as a RRC message. When the first control message 502 is a PDCP control PDU a radio link control protocol in the second access network node 320 may identify the first network access node 300 as the intended recipient and transmit the second control message 504 to the first network access node 300 as a PDCP control PDU.

The second control message 504 is transmitted to inform the first network access node 300 about the beam failure on the first radio link 512 and may comprise the information received in the first control message 502. The second control message 504 may hence comprise information associated with the beam failure on the first radio link 512 such as e.g. which random access preamble and/or which random access resource was used by the client device 100 in a random access procedure associated with the beam failure on the first radio link 512, and one or more candidate beams identified by the client device 100 for beam failure recovery with the first network access 100. The second network access node 320 may transmit the second control message 504 to the first network access node 300 e.g. over a backhaul link such as the backhaul link 522 shown in Fig. 5. However, any available (wired or wireless) link between the second network access node 320 and the first network access node 300 may be used to transmit the second control message 504.

The first network access node 300 receives the second control message 504 from the second network access node 320. As described above, the second control message 504 may e.g. be received over the backhaul link 522. Furthermore, the second control message 504 comprises information associated with the beam failure on the first radio link 512. Hence, the second control message 504 informs the first network access node 300 that a beam failure has been detected on the first radio link 512 and provides the first network access node 300 with information associated with the beam failure on the first radio link 512. The information associated with the beam failure on the first radio link 512 comprised in the second control message 504 can be used by the first network access node 300 to perform beam failure recovery for the first radio link 512. However, before performing beam failure recovery for the first radio link 512 based on the second control message 504, the first network access node 300 may determine if a beam failure recovery procedure associated with the beam failure on the first radio link 512 has already been started or not. In the embodiment shown in Fig. 6, the first network access node 300 determines if a beam failure recovery procedure associated with the beam failure on the first radio link 512 has already been started or not in step VI, and further performs beam failure recovery for the first radio link 512 in step VII based on the outcome of the determination in step VI.

The determination in Step VI in Fig. 6 may be based on whether a random access preamble associated with the beam failure on the first radio link 512 has been received from the client device 100 or not. Thus, the first network access node 300 may determine that a beam failure recovery procedure associated with the beam failure on the first radio link 512 has been started, if a random access preamble associated with the beam failure on the first radio link 512 has been received from the client device 100. Furthermore, the first network access node 300 may determine that no beam failure recovery procedure associated with the beam failure on the first radio link 512 has been started, if no random access preamble associated with the beam failure on the first radio link 512 has been received from the client device 100. That the first network access node 300 receives a random access preamble from the client device 100 can herein be understood to mean that the first network access node 300 has detected a random access preamble transmitted from the client device 100.

If the first network access node 300 determines in step VI in Fig. 6 that a beam failure recovery procedure associated with the beam failure on the first radio link 512 has been started, the first network access node 300 may ignore the second control message 504 and continue the ongoing beam failure recovery procedure for the first radio link 512. In other words, if a random access preamble associated with the beam failure on the first radio link 512 has been received from the client device 100, the first network access node 300 performs beam failure recovery for the first radio link 512 in step VII in Fig. 6 based on the received random access preamble.

On the other hand, if no random access preamble associated with the beam failure on the first radio link 512 has been received from the client device 100, the first network access node 300 performs beam failure recovery for the first radio link 512 in step VII in Fig. 6 based on the second control message 504. Hence, the first network access node 300 may in this case use the information in the second control message 504 to perform beam failure recovery for the first radio link 512. As described above, the information in the second control message 504 may comprise information associated with the beam failure on the first radio link 512, such as a random access preamble and/or a random access resource used by the client device 100 in a random access procedure associated with the beam failure on the first radio link 512, and one or more candidate beams identified by the client device 100 for beam failure recovery with the first network access 100.

The beam failure recovery for the first radio link 512 may comprises at least one of transmit a random access response to the client device 100, transmit reference signals in one or more candidate beams to the client device 100, and search for a random access preamble used by the client device 100 in a random access procedure associated with the beam failure on the first radio link 512. For example, if the first network access node 300 obtains information associated with a random access preamble and/or random access resource from the second control message 504, the first network access node 300 may transmit a random access response RAR to the client device 100 based on the obtained information associated with the random access preamble and/or random access resource, as shown in step VIII in Fig. 6, even without having received the random access preamble over the first radio link 512. The first network access node 300 may further use the information associated with the random access preamble and the random access resource to efficiently search for the random access preamble transmitted from the client device 100 at the specific random access occasion given by the random access resource. In this way, the likelihood for detecting and confirming the random access preamble from the client device 100 is increased. Furthermore, if the first network access node 300 obtains information associated with one or more candidate beams from the second control message 504, the first network access node 300 may transmit reference signals in the one or more candidate beams to the client device 100. In this way, the client device 100 may perform further refinement of its receive beam for each of the candidate beams based on the reference signals transmitted using one or more candidate beams.

According to embodiments of the invention the first network access node 300 may further schedule data to the client device 100 based on the second control message 504. The second control message 504 may inform the first network access node 300 that a beam failure has been detected on the first radio link 512. Hence, the first network access node 300 may avoid scheduling data to the client device 100 on the first radio link 512 after receiving the second control message 504.

The beam failure recovery performed by the first network access node 300 based on the second control message 504 may in embodiments not be started directly upon reception of a second control message 504. The first network access node 300 may instead wait a pre defined time before starting a beam failure recovery for the first radio link 512 based on the second control message 504. During the predefined time, the first network access node 300 may monitor to see if any random access preamble associated with the beam failure on the first radio link 512 is received from the client device 100. The first network access node 300 may e.g. efficiently search for a random access preamble transmitted from the client device 100 at a specific random access occasion based on the random access preamble and the random access resource information obtained from the second control message 504, as previously described. If no random access preamble associated with the beam failure on the first radio link 512 has been received from the client device 100 during the pre-defined time after the reception of the second control message 504, the first network access node 300 performs the beam failure recovery for the first radio link 512 based on the second control message 504.

According to embodiments of the invention the client device 100 may be configured by the first network access node 300 or the second network access node 320 to transmit a first control message 502 to the second network access node 320 upon detecting a beam failure on the first radio link 512. Fig. 7 shows configuration information signalling according to such an embodiment. The client device 100 may receive the configuration information from the first network access node 300 or the second network access node 320 in a third control message 506. When the first network access node 300 configures the client device 100, the first network access node 300 transmits a third control message 506 to the client device 100, as shown in step la in Fig. 7. On the other hand, when the second network access node 320 configures the client device 100, the second network access node 320 transmits a third control message 506 to the client device 100, as shown in step lb in Fig. 7. The third control message 506 comprises configuration information associated with transmission of a first control message 502 from the client device 100 to the second network access node 320 over a second radio link 514, wherein the first control message 502 comprises information associated with a beam failure on a first radio link 512. The configuration information associated with transmission of the first control message 502 may e.g. comprise information determining scenarios and conditions for when the first control message 502 should be transmitted. For example, if the first control message 502 is to be transmitted upon each detected beam failure or only upon detecting a beam failure on a radio link used for e.g. low latency services. The first network access node 300 and/or the second network access node 320 may determine the configuration information based on factors such as e.g. capability of the client device 100, services currently configured for the client device 100, the load in the network and/or the network access node, the quality of the first radio link 512 and/or second radio link 514. The client device 100 receives the third control message 506 from the first network access node 300 in step la and/or the second network access node 320 in step lb. As previously described, the third control message 506 comprises configuration information associated with the transmission of the first control message 502. The client device 100 further transmits the first control message 502 according to the configuration information. Hence, when a beam failure is detected in a scenario and under conditions given by the configuration information received in the third control message 506, the client device 100 transmits a first control message 502, as shown in step II in Fig. 7.

The client device 100 herein, may be denoted as a user device, a User Equipment (UE), a mobile station, an internet of things (loT) device, a sensor device, a wireless terminal and/or a mobile terminal, is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in this context may be, for example, portable, pocket-storable, hand-held, computer- comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The UE may also be configured for communication in 3GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation wireless technologies, such as New Radio.

The first network access node 300 and the second network access node 320 herein may also be denoted as a radio client device, an access client device, an access point, or a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter, “gNB”,“gNodeB”,“eNB”,“eNodeB”,“NodeB” or“B node”, depending on the technology and terminology used. The radio client devices may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio client device can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The radio client device may also be a base station corresponding to the fifth generation (5G) wireless systems.

Furthermore, any method according to embodiments of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive. Moreover, it is realized by the skilled person that embodiments of the client device 100, the first network access node 300, and the second network access node 320 comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution.

Especially, the processor(s) of the client device 100, the first network access node 300 and the second network access node 320 may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like.

Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.