WO2019096395A1

WO2019096395A1 - Processing device and methods thereof

Info

Publication number: WO2019096395A1
Application number: PCT/EP2017/079493
Authority: WO
Inventors: Bengt Lindoff; Chaitanya TUMULA; Neng Wang
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2017-11-16
Filing date: 2017-11-16
Publication date: 2019-05-23
Also published as: CN111357210A; CN111357210B

Abstract

The invention relates to a processing device (100) for a client device (300), the processing device (100) determines a need for performing a Random Access, RA, procedure when being in a connected mode with a network access node (400) using a serving downlink beam (502). The processing device (100) further obtains RA parameters for the RA procedure, wherein the RA parameters indicate at least one RA resource and at least one RA preamble. The processing device (100) further selects an uplink beam (512) for the RA procedure based on a quasi co-located association with a reference signal resource received in a downlink beam from the network access node (400), and sends the RA preamble in the RA resource towards the network access node (400) using the selected uplink beam (512) so as to initiate the RA procedure. Furthermore, the invention also relates to a client device (300), corresponding methods, and a computer program product.

Description

PROCESSING DEVICE AND METHODS THEREOF

Technical Field

The invention relates to a processing device. Furthermore, the invention also relates to a client device comprising the processing device, corresponding methods and a computer program.

Background

The 5G cellular system, also called new radio (NR), is currently being standardized. NR is targeting radio spectrum from below 1 GHz up to and above 60 GHz. To allow for such diverse radio environments not only different system bandwidths will be supported, but also different numerologies, such as different sub-carrier-spacings (SCS). Furthermore, for carriers over 10 GHz multiple antennas and beamforming will be needed to combat the higher path loss at such high radio frequencies.

When beamforming is used, a next generation nodeB (gNB) transmits 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 need to perform beam monitoring. Hence, the gNB transmits known pilot signals in adjacent beams, which the UE receives and uses to detect possible transmit beams to switch to in case of changes in the radio environment. The principles behind beam monitoring can be compared to the cell search in legacy long term evolution (LTE), wideband code division multiple access (WCDMA) and high speed packet access (HSPA) systems. In such systems, the UE on a regular basis need to scan neighbouring cells for possible handover candidates.

Each possible connection between the UE and the gNB is called a beam pair link (BPL), where a BPL consists of the best match between a transmit beam and a receive beam. 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 a monitored BPL beam becomes stronger than the current serving BPL a beam switch could be initiated. The exact procedure for the beam switching is not yet defined in the NR standard. One approach could be that the UE triggers a beam measurement report comprising the event that a target BPL is stronger than the current serving BPL. Another scenario would be that the gNB determines, e.g. using uplink management procedures, that a target BPL has become a suitable serving BPL. The gNB could then order a beam switch to the target BPL.

In scenarios where the UE drops the serving BPL, due to e.g. rotation or blocking of the UE, and the quality of all serving downlink BPLs become worse than a pre-determined quality, the UE should declare beam failure and start a beam recovery procedure. The UE performs the beam recovery procedure to try to recover from the beam failure. In order to monitor the quality of the serving BPLs as well as candidate BPLs the UE could be configured to monitor either synchronization signal blocks (SSB) or CSI-RS that can be assumed to be quasi-co-located with the control channel on the respective BPL.

In NR, the beam recovery procedure involves a random access (RA) procedure. The main purpose of the RA procedure is to achieve uplink synchronization between the UE and network access node. The RA procedure is also used in other scenarios where the UE has no synchronization with the network such as e.g. at initial access. The standardization of the RA procedure in NR is not yet completed and details related to how the RA procedure should be performed in different scenarios is currently being discussed in NR standardization groups.

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 present 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 processing device for a client device, the processing device being configured to

determine a need for performing a Random Access, RA, procedure when being in a connected mode with a network access node using a serving downlink beam;

obtain RA parameters for the RA procedure, wherein the RA parameters indicate at least one RA resource and at least one RA preamble;

select an uplink beam for the RA procedure based on a quasi co-located association with a reference signal resource received in a downlink beam from the network access node; send the RA preamble in the RA resource towards the network access node using the selected uplink beam so as to initiate the RA procedure.

A need for performing a RA procedure can mean that the processing device currently cannot receive responses from the network access node upon uplink transmissions, and the processing device determines a need for performing other ways to perform uplink communication, such as performing a RA procedure as stated herein.

Being in a connected mode with a network access node using a serving downlink beam can in this disclosure mean that the processing device or a client device comprising the processing device is in a mode in which it can communicate with the network access node over the serving downlink beam. The connected mode may e.g. be a RRC connected mode, or another connected mode, where the network access node is aware of a client device encompassing the processing device.

That the uplink beam for the RA procedure is selected based on a quasi co-located association with a reference signal resource received in a downlink beam from the network access node can in this disclosure be understood to mean that an uplink beam which is directed in the same direction as the downlink beam transmitting the reference signal resource may be selected. Hence, the viewing direction of the selected uplink beam will be the same as the viewing direction of the downlink beam transmitting the reference signal resource as seen from the client device. Furthermore, that a reference signal is quasi-co-located with a control channel can be interpreted as that the reference signal and the control channel are transmitted and/or received in the same direction, such as the same uplink beam and/or the same downlink beam. Furthermore, the downlink beam transmitting the reference signal resource may be the serving downlink beam or a non-serving downlink beam.

In this disclosure the terms uplink beam and downlink beam are used for describing the direction of transmission of signals and direction of reception of signals, respectively, for a client device. Hence a specific beam can be interpreted as a certain spatial parameter setting or spatial filtering determined in the processing device. These settings or parameters may for instance be outputted from the processing device and used in the client device radio transceiver configuration for directing the transmission of signals or reception of signals in a certain direction.

Furthermore, the term beam failure can be interpreted as an indication made in the processing device based on radio link quality assessments in order to initiate a beam recovery procedure, or in more general terms, used for initiating a (radio) link reconfiguration, wherein a radio link here means a radio communication link between a client device including the processing device and a network access node.

An advantage of the processing device is that the processing device knows which RA parameters and which uplink beam to use upon a need to perform a RA procedure. Thereby, a client device comprising the processing device is aligned with the network access node and re-synchronization with the network access node can be achieved faster compared to known procedures in the art.

In an implementation form of a processing device according to the first aspect, the reference signal resource is a channel state information reference signal, CSI-RS, resource configured for the communication device.

An advantage with this implementation form is that the processing device can determine based on quasi co-located associations with CSI-RS resources which uplink beams are possible to use for performing the RA procedure. Thereby faster re-synchronization is achieved.

In an implementation form of a processing device according to the first aspect, the CSI-RS resource is received in the serving downlink beam.

This means that the processing device in this implementation may select the uplink serving beam which is directed in the same direction as the downlink serving beam transmitting the reference signal resource. Therefore, the quasi co-located association can be used due to the correspondence between the transmit beam and the receive beam. In other worlds, the viewing direction of the uplink serving beam is the same as the viewing direction of the downlink serving beam seen from the client device.

An advantage with this implementation form is that that the serving uplink beam will be selected. When using the serving uplink beam for performing the RA procedure, the RA detector in the network access node requires shorter search time for the RA, and hence a faster recovery is achieved.

In an implementation form of a processing device according to the first aspect, the reference signal resource is a synchronization signal block, SSB, resource. An advantage with this implementation form is that the processing device can determine based on quasi co-located associations with SSB resources which uplink beams are possible to use for performing the RA procedure.

In an implementation form of a processing device according to the first aspect, the SSB resource is received in the serving downlink beam.

An advantage with this implementation form is that the serving uplink beam will be selected. When using the serving uplink beam for performing the RA procedure, the RA detector in the network access node requires shorter search time for the RA, and hence a faster recovery is achieved.

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

obtain a threshold value corresponding to a channel quality metric;

determine a channel quality for each reference signal resource among a plurality of reference signal resources received on a plurality of corresponding downlink beams;

select the reference signal resource among the plurality of reference signal resources based on the threshold value and the channel qualities for the plurality of reference signal resources.

The selected reference signal resource is the same reference signal resource as for the processing device according to the first aspect.

An advantage with this implementation form is that the processing device selects an uplink beam for the RA procedure with sufficient channel quality. Thereby, the RA detection in the network access node becomes more reliable.

In an implementation form of a processing device according to the first aspect, the processing device is further configured to determine the need for performing the RA procedure based on an event triggered by an uplink transmission procedure.

An advantage with this implementation form is that the processing device has determined that the uplink transmission procedure has failed and that a RA procedure is needed for further communication with the network access node. Thereby, a faster recovery of the communication link is achieved.

In an implementation form of a processing device according to the first aspect, the event triggered by the uplink transmission procedure is at least one of: a scheduling request has been transmitted for a maximum amount of times; a time alignment timer has expired; and a medium access control reset procedure.

An advantage with this implementation form is that the processing device has determined the type of uplink transmission procedure that has failed and that a RA procedure is needed for further communication with the network access node. Thereby, a faster recovery of the communication link is achieved.

In an implementation form of a processing device according to the first aspect, at least one of the RA resource and RA preamble is associated with the reference signal resource received in the downlink beam.

An advantage with this implementation form is that the one-to-one mapping between RA parameters used and the uplink beam used to transmit the preamble, will make the RA detection less complex in the network access node.

determine, prior to transmitting the RA preamble in the RA resource, a beam failure state for the serving downlink beam.

An advantage with this implementation form is that the processing device becomes aware of the beam failure state. Thereby, faster re-synchronization with the network access node can be achieved.

In an implementation form of a processing device according to the first aspect, the processing device is further configured to suspend the RA procedure if the determined beam failure state for the serving downlink beam is a failed state;

initiate a beam failure recovery procedure if the determined beam failure state for the serving downlink beam is the failed state.

An advantage with this implementation form is that the processing device knows which access procedure to use for re-establishing the connection to the network access node. Thereby, the re-connection of the link becomes fast, improving the user experience.

determine the beam failure state for the serving downlink beam according to a predefined beam monitoring procedure.

An advantage with this implementation form is that the processing device knows how to monitor beam failure, which means that the processing device can detect the beam failure state faster. Thereby, achieving a faster re-synchronization with the network access node.

determine the beam failure state for the serving downlink beam according to the predefined beam monitoring procedure based on a hypothetical error rate associated with a control channel, wherein the control channel is quasi co-located with the reference signal resource transmitted in the downlink beam.

An advantage with this implementation form is that the processing device uses a well-defined beam monitoring process, and hence determines possible beam failure states in a consistent way. Thereby, improving the overall reliability of the wireless communication system.

perform the RA procedure while in connected discontinuous reception, DRX, mode.

An advantage with this implementation form is that the processing device can operate in power saving modes in connected mode and still perform RA preamble transmission with low latency. According to a second aspect of the invention, the above mentioned and other objectives are achieved with a client device for a wireless communication system, the client device comprising a processing device according to any of the implementation forms of a processing device according to the first aspect.

An advantage of the client device is that the client device is aligned with the network access node and re-synchronization with the network access node can be achieved faster compared to known procedures in the art.

According to a third aspect of the invention, the above mentioned and other objectives are achieved with a method for a processing device, the method comprises

determining a need for performing a Random Access, RA, procedure when being in a connected mode with a network access node using a serving downlink beam;

obtaining RA parameters for the RA procedure, wherein the RA parameters indicate at least one RA resource and at least one RA preamble;

selecting an uplink beam for the RA procedure based on a quasi co-located association with a reference signal resource received in a downlink beam from the network access node; sending the RA preamble in the RA resource towards the network access node using the selected uplink beam so as to initiate the RA procedure.

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

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

The invention also relates to a computer program, characterized in code means, which when run by processing means causes said processing means to execute any method according to the present 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 present 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 present invention, in which:

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

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

- Fig. 3 shows a client device according to an embodiment of the invention;

- Fig. 4 shows a wireless communication system according to an embodiment of the invention;

- Fig. 5 shows a flow chart of a method according to an embodiment of the invention;

- Fig. 6 shows determination of beam failure state according to an embodiment of the invention.

Detailed Description

Fig. 1 shows a processing device 100 according to an embodiment of the invention. In the embodiment shown in Fig. 1 , the processing device 100 comprises at least one processor core 102 which can be coupled to an internal or external memory 104 with coupling/communication means 106 known in the art. The processing device may further comprise a plurality of processor cores 102. The memory 104 may store program code for performing the actions as described herein by the processor core(s) 102 of the processing device 100. The processing device 100 further comprises input means 108 and output means 1 10, which are both coupled to the processor core 102 with coupling/communication means 106 known in the art.

That the processing device 100 is configured to perform certain actions should in this disclosure be understood to mean that the processing device 100 comprises suitable means, such as e.g. the processor core 102, configured to perform said actions. The processing device 100 may for example be a base band processor with a memory 104 for use in a client device for a mobile communication network.

The processing device 100 is configured to determine a need for performing a Random Access (RA) procedure when being in a connected mode with a network access node 400 using a serving downlink beam 502 (shown in Fig. 4). The processing device 100 is further configured to obtain RA parameters for the RA procedure. The RA parameters indicate at least one RA resource and at least one RA preamble. The processing device 100 is further configured to select an uplink beam 512 (shown in Fig. 4) for the RA procedure based on a quasi co-located association with a reference signal resource received in a downlink beam from the network access node 400. Furthermore, the processing device 100 is configured to send the RA preamble in the RA resource towards the network access node 400 using the selected uplink beam 512 so as to initiate (start) the RA procedure.

Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a processing device 100, such as the one shown in Fig. 1 . The method 200 comprises determining 202 a need for performing a RA procedure when being in a connected mode with a network access node 400 using a serving downlink beam 502. The method 200 further comprises obtaining 204 RA parameters for the RA procedure. The RA parameters indicate at least one RA resource and at least one RA preamble. The method 200 further comprises selecting 206 an uplink beam 512 for the RA procedure based on a quasi co-located association with a reference signal resource received in a downlink beam from the network access node 400. Furthermore, the method 200 comprises sending 208 the RA preamble in the RA resource towards the network access node 400 using the selected uplink beam 512 so as to initiate the RA procedure.

The processing device 100 may be comprised e.g. as a base band processor in a client device, such as the client device 300 shown in Fig. 3. In the embodiment shown in Fig. 3, the client device 300 comprises the processing device 100 and a transceiver/modem 302. The processing device 100 is coupled to the transceiver 302 by communication means 304 known in the art. The client device 300 further comprises an antenna or an antenna array 306 coupled to the transceiver 302, which means that the client device 300 is configured for wireless communications in a wireless communication system.

Fig. 4 shows a wireless communication system 500 according to an implementation. The wireless communication system 500 comprises a client device 300 and a network access node 400, both configured to operate in the wireless communication system 500. The client device 300 comprises a processing device 100. For simplicity, the wireless communication system 500 shown in Fig. 4 only comprises one client device 300 and one network access node 400. However, the wireless communication system 500 may comprise any number of client devices 300 and any number of network access nodes 400 without deviating from the scope of the invention.

In the wireless communication system 500, beamforming is used such that data is transmitted in several directions in different downlink beams and uplink beams between the client device 300 and the network access node 400. In Fig. 4, three downlink beams 502, 504, 506 and two uplink beams 512, 514 are shown. However, any number of uplink and/or downlink beams may exist between the client device 300 and the network access node 400 without deviation from the scope of the invention. In Fig. 4, the client device 300 is in a connected mode with the network access node 400 using the downlink beam 502 as a serving downlink beam and the uplink beam 512 as a serving uplink beam. In addition, the client device 300 may receive reference signal resources from the network access node 400 in the downlink beams 502, 504, 506. The received reference signal resources may be used by the client device 300 to evaluate the quality of the downlink beams 502, 504, 506 and to select a suitable serving downlink beam. In embodiments of the invention, the reference signal resource may be a channel state information reference signal (CSI-RS) resource configured for the client device 300 by the network access node 400. The CSI-RS resource may be received in the serving downlink beam 502. Alternatively, the reference signal resource may be a synchronization signal block (SSB) resource. In this case, the SSB resource may be received in the serving downlink beam 502. As previously described, the client device 300 may use the received reference signal resources to select an uplink beam for a RA procedure.

According to embodiments of the invention the determination of a need for performing a RA procedure may be triggered by an indication from an uplink transmission procedure. The uplink transmission procedure may be a scheduling request (SR) procedure, or a procedure where uplink transmission can be performed without an uplink grant, e.g. configured semi-persistent scheduling. Fig. 5 shows a flow chart of a method 600 for determining of a need for performing a RA procedure and performing the RA procedure according to embodiments of the invention. The method 600 shown in Fig. 5 may be performed by a processing device 100. In embodiments, the processing device 100 is comprised in a client device 300. The processing device 100 or the client device 300 is assumed to be in connected mode with a network access node 400 using a serving downlink beam 502. The method 600 is initiated in step 602 where the processing device 100 determines a need for performing a RA procedure. The processing device 100 may determine the need for performing the RA procedure based on an event triggered by an uplink transmission procedure. The event triggered by the uplink transmission procedure may be at least one of: a scheduling request has been transmitted for a maximum amount of times; a time alignment timer has expired; and a medium access control (MAC) reset procedure.

The event that a scheduling request has been transmitted for a maximum amount of times may e.g. be triggered in scenarios where the network access node 400 is heavy loaded in the uplink and hence has no resources available for uplink transmission for the client device 300, or the client device 300 has dropped uplink or downlink connection to the network access node 400. The event that a time alignment timer has expired is related to timing advance and means that uplink transmission timing may no longer be correct, and hence the client device may have lost uplink synchronization. Moreover, the event that a MAC reset procedure has occurred may e.g. be triggered by semi persistent scheduling resources being revoked.

If the processing device 100 determines a need for performing a RA procedure in step 602, the processing device 100 moves on to step 604. In step 604, the processing device 100 obtains RA parameters for performing the RA procedure. The RA parameters indicate at least one RA resource, such as e.g. a time and/or a frequency resource, and at least one RA preamble, such as e.g. a preamble signature. Furthermore, in embodiments of the invention at least one of the RA resource and RA preamble may be associated with a reference signal resource received in a downlink beam. Hence, different downlink beams associated with different reference signal resources may have different sets of RA parameters. In an example where the reference signal resource is a SSB resource, this means that a first SSB resource transmitted in a first downlink beam may be associated with first RA parameters, while a second SSB resource transmitted in a second downlink beam may be associated with second RA parameters, and so on. Hence, if an uplink beam has been selected in step 606, as will be described below, based on the first SSB resource received in the first downlink beam, the processing device 100 obtains the first RA parameters based on the association between the first SSB resource and the first RA parameters.

In addition to obtaining RA parameters, the processing device 100 selects an uplink beam for the RA procedure in step 606. In Fig. 5 step 606 is shown to be performed after step 604. However, step 606 may instead be performed before step 604 or at least partially in parallel with step 604. The selection of the uplink beam for the RA procedure is based on a quasi co located association with a reference signal resource received in a downlink beam from the network access node 400. This means that the processing device 100 may select the uplink beam which is directed in the same direction as the downlink beam with/on which the reference signal resource was received by the processing device 100. As an example the spatial filtering applied for the RA procedure in the uplink may be the same as the spatial filtering applied for receiving the reference signal resource. As previously described the reference signal resource may e.g. be a CSI-RS resource or a SSB resource. Hence, the quasi co-located association may be with a CSI-RS resource configured for the client device 300 or with a SSB resource. The quasi co-located association may be used due to the correspondence between the transmit beam and the receive beam. When the client device 300 determines one downlink beam based on an association with e.g. a CSI-RS transmission, the client device 300 knows which specific transmit beam the network access node 400 uses and which specific receive beam to use in downlink. Hence, the client device 300 can use the specific receive beam as the transmit beam and be sure that the network access node 400 will receive the information. In other worlds, the viewing direction of the uplink beam is the same as the viewing direction of the downlink beam seen from the client device 300.

The selection of the uplink beam in step 606 in Fig. 5 may further be based on a channel quality for each received reference signal resource. In such cases, the processing device 100 may obtain a threshold value corresponding to a channel quality metric, and may determine a channel quality for each reference signal resource among a plurality of reference signal resources received on a plurality of corresponding downlink beams. The processing device 100 further selects the reference signal resource to use in step 606 among the plurality of reference signal resources based on the threshold value and the channel qualities for the plurality of reference signal resources. With this approach an uplink beam with good channel quality may be selected, which increases the chances of a successful RA procedure.

Some specific examples of how the processing device 100 may select the uplink beam for the RA procedure in step 606 in Fig. 5 when the processing device 100 is comprised in the client device 300 shown in Fig. 4 will now be given:

a) The processing device 100 may select the uplink beam by using a quasi co-located association with a CSI-RS configured for the client device 300, wherein the uplink beam may also be the serving uplink beam 512 associated with the serving downlink beam 502.

b) The processing device 100 may select the uplink beam by utilizing the knowledge of quasi co-located association with a SSB. Since there may be several downlink beams associated with different SSBs, the processing device 100 may select an uplink beam 512, 514 associated with the downlink beam 502, 504, 506 whose quality is above a threshold value.

c) The processing device 100 may select the uplink beam by utilizing the knowledge of quasi co-located association with a SSB, and further the selected uplink beam 512 is quasi co-located with the serving uplink beam 502. In this case, the client device 300 would select the uplink beam 512 that corresponds to the serving downlink beam 502 which is also a downlink beam used for a SSB.

d) The processing device 100 may select the uplink beam 512 that corresponds to the serving downlink beam 502 or select an uplink beam 514 that corresponds to a downlink beam 504 associated to SSB even if CSI-RS is configured to the serving downlink beam 502. In step 608 the processing device 100 initiates the RA procedure using the obtained RA parameters and the selected uplink beam. Hence, the processing device 100 sends the RA preamble in the RA resource towards the network access node 400 using the selected uplink beam. This includes e.g. sending the RA preamble to a lower layer for transmission over the radio link. According to embodiments of the invention the connected mode of the processing device 100 may be a connected discontinuous reception (DRX) mode. In such embodiments, the processing device 100 may hence initiate the RA procedure in step 608 while in connected DRX mode.

In some embodiments of the invention the client device 300 may determine a beam failure state for the serving downlink beam prior to performing the RA procedure, shown in Fig. 5 as optional step 610. In step 610, the processing device 100 determines, prior to transmitting the RA preamble in the RA resource, a beam failure state for the serving downlink beam 502, i.e. determines whether the serving downlink beam 502 is reliable or not. The determination of the beam failure state for the serving downlink beam 502 may be based on a beam monitoring procedure. For example, the processing device 100 may determine the beam failure state for the serving downlink beam 502 according to a predefined beam monitoring procedure. The predefined beam monitoring procedure may be based on measuring link quality on a reference signal resource transmitted in the serving downlink beam 502, the link quality corresponds to a hypothetical error rate associated with a control channel, wherein the control channel is quasi co-located with the reference signal resource transmitted in the serving downlink beam 502. If the link quality is below a configured threshold value, the serving downlink beam 502 is in a failed state, otherwise not.

If the determined beam failure state for the serving downlink beam 502 is a failed state, i.e. the outcome of the check in step 610 is YES, the processing device 100 may suspend the RA procedure and initiate a beam failure recovery procedure, shown as step 612 in Fig. 5. The beam failure recovery procedure can be performed according to beam recovery procedures well known in the art.

On the other hand, if the determined beam failure state for the serving downlink beam 502 is not a failed state, i.e. the outcome of the check in step 610 is NO, the processing device 100 will move to step 604 in Fig. 5 and perform step 604, step 606 and step 608 as previously described. Thereby, the processing device 100 will obtain RA parameters, select uplink beam and will further initiate the RA procedure based on the obtained RA parameters and the selected uplink beam. Embodiments where a beam failure state for the serving downlink beam is determined may e.g. be used when the client device 300 is in connected DRX mode. Fig. 6 shows an application of such an embodiment and illustrates occasions where a client device 300 in connected DRX mode can determine a beam failure state for a serving downlink beam 502. In the example shown in Fig. 6, reference signal resources are transmitted every 20 milliseconds in the serving downlink beam 502, as indicated by the black columns in Fig. 6. Furthermore, the client device 300 has its on-durations ON every 100 milliseconds. During the on-durations ONs the client device 300 performs a beam monitoring procedure, i.e. measures link quality on the reference signal resources transmitted in the serving downlink beam 502. Hence, in each on-duration ON the client device 300 may determine the beam failure state for the serving downlink beam 502. However, according to embodiments of the invention a beam monitoring procedure may additionally be performed during a scheduling request procedure or upon a scheduling request failure. Fig. 6 shows a scheduling request procedure SRP comprising four scheduling request SR attempts. During the scheduling request procedure SRP the client device 300 is on and may hence perform an additional beam monitoring procedure to determine the beam failure state for the serving downlink beam 502. Furthermore, if the scheduling request procedure SRP is unsuccessful, the client device 300 may perform an additional beam monitoring procedure directly after the scheduling request failure, instead of waiting until the next on- duration ON. The additional beam monitoring procedure may be performed during an additional on-duration ON_add occurring directly after the scheduling request procedure SRP, as shown in Fig. 6. In this way, the client device 300 may determine the beam failure state for the serving downlink beam 502 before the client device 300 needs to perform a RA procedure triggered by the scheduling request failure. Therefore, the client device 300 will only perform the RA procedure if the determined beam failure state for the serving downlink beam 502 is not a failed state, as previously described with reference to Fig. 5. Thereby, saving system resources and decreasing power consumption in the client device 300.

The client device 300 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 the present 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 network access node 400 herein may also be denoted as a radio network access node, an access network access node, an access point, or a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter,“eNB”,“eNodeB”,“NodeB” or“B node”, depending on the technology and terminology used. The radio network access nodes 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 network access node 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 network access node 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 300 and the network access node 400 comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the present 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 present solution.

Especially, the processor(s) of the client device 300 and the network access node 400 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.

Claims

1 . A processing device (100) for a client device (300), the processing device (100) being configured to

determine a need for performing a Random Access, RA, procedure when being in a connected mode with a network access node (400) using a serving downlink beam (502); obtain RA parameters for the RA procedure, wherein the RA parameters indicate at least one RA resource and at least one RA preamble;

select an uplink beam (512) for the RA procedure based on a quasi co-located association with a reference signal resource received in a downlink beam from the network access node (400);

send the RA preamble in the RA resource towards the network access node (400) using the selected uplink beam (512) so as to initiate the RA procedure.

2. The processing device (100) according to claim 1 , wherein the reference signal resource is a channel state information reference signal, CSI-RS, resource configured for the processing device (100).

3. The processing device (100) according to claim 2, wherein the CSI-RS resource is received in the serving downlink beam (502).

4. The processing device (100) according to any of the preceding claims, wherein the reference signal resource is a synchronization signal block, SSB, resource.

5. The processing device (100) according to claim 4, wherein the SSB resource is received in the serving downlink beam (502).

6. The processing device (100) according to any of the preceding claims, configured to obtain a threshold value corresponding to a channel quality metric;

7. The processing device (100) according to any of the preceding claims, configured to determine the need for performing the RA procedure based on an event triggered by an uplink transmission procedure.

8. The processing device (100) according to claim 7, wherein the event triggered by the uplink transmission procedure is at least one of: a scheduling request has been transmitted for a maximum amount of times; a time alignment timer has expired; and a medium access control reset procedure.

9. The processing device (100) according to any of the preceding claims, wherein at least one of the RA resource and RA preamble is associated with the reference signal resource received in the downlink beam.

10. The processing device (100) according to any of the preceding claims, configured to

determine, prior to transmitting the RA preamble in the RA resource, a beam failure state for the serving downlink beam (502).

1 1 . The processing device (100) according to claim 10, configured to

suspend the RA procedure if the determined beam failure state for the serving downlink beam (502) is a failed state;

initiate a beam failure recovery procedure if the determined beam failure state for the serving downlink beam (502) is the failed state.

12. The processing device (100) according to claim 10 or 1 1 , configured to

determine the beam failure state for the serving downlink beam (502) according to a predefined beam monitoring procedure.

13. The processing device (100) according to claim 12, configured to

determine the beam failure state for the serving downlink beam (502) according to the predefined beam monitoring procedure based on a hypothetical error rate associated with a control channel, wherein the control channel is quasi co-located with the reference signal resource transmitted in the serving downlink beam (502).

14. The processing device (100) according to any of the preceding claims, configured to

perform the RA procedure while in connected discontinuous reception, DRX, mode.

15. A client device (300) for a wireless communication system (500), the client device (300) comprising a processing device (100) according to any of the preceding claims.

16. A method for a processing device (100), the method (200) comprising

determining (202) a need for performing a Random Access, RA, procedure when being in a connected mode with a network access node (400) using a serving downlink beam (502); obtaining (204) RA parameters for the RA procedure, wherein the RA parameters indicate at least one RA resource and at least one RA preamble;

selecting (206) an uplink beam (512) for the RA procedure based on a quasi co-located association with a reference signal resource received in a downlink beam from the network access node (400);

sending (208) the RA preamble in the RA resource towards the network access node (400) using the selected uplink beam (512) so as to initiate the RA procedure.

17. Computer program with a program code for performing a method according to claim 16 when the computer program runs on a computer.