TECHNICAL FIELD

[0001 ] The present invention relates to the field of wireless network communications, and particularly to beam recovery for a client device and a network node. Furthermore the invention relates to corresponding methods and a computer program.

BACKGROUND

[0002] In advanced wireless radio communications, such as the fifth generation, 5G, system, one central base station, gNB, may be controlling several transmission or reception points, TRPs. Each gNB or TRP may form several spatial beams which are used for transmitting or receiving data to or from several user equipments, UEs, simultaneously using a certain time, frequency and code. The UEs can also be called client devices, user nodes, user devices, mobile terminals, mobile devices, or mobile nodes. The gNBs and TRPs may also be called network nodes or network devices. The term network node or network device also includes but is not limited to a base station, a Node-B or eNode-B, an access node (ANd), a base station controller, an aggregation point or any other type of interfacing device in a communication environment.

[0003] A beam failure occurs when a beam currently being used for communication between a transceiver and a receiver becomes unavailable. Possible reasons for beam failure include but are not limited to movements of the UE, the appearance of an obstacle between the UE and the network node, and a change in the orientation of the UE.

[0004] Prior art suggests a procedure for beam recovery after a detected beam failure. The suggested procedure comprises identifying so-called backup beams and selecting one of them for continued communications with the UE. Drawbacks of known methods for beam recovery involve relative slowness and inefficient use of radio frequency bandwidth. SUMMARY

[0005] It is an object of the invention to provide a method and devices for performing beam recovery in a quick and effective manner.

[0006] The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms and advantages are apparent from the depending claims, the description and the figures.

[0007] According to a first aspect, a client device for a wireless network is provided. The client device is configured to receive reference signals, and detect a beam failure in a communications connection with a network node of said wireless network, said communications connection having involved reception of reference signals through a current beam. The client device is also configured to select a candidate beam for beam recovery based on measurement of beam specific reference signals, and determine a propagation delay information PDI, the PDI being indicative of a difference between a first propagation delay specific to said current beam and a second propagation delay specific to said candidate beam. The client device is further configured to select among at least two alternative mechanisms of beam recovery depending on said propagation delay information.

[0008] In a first possible implementation form of the client device according to the first aspect, the client device is configured to, as a part of said selecting among at least two alternative mechanisms of beam recovery, select a channel to be used for requesting said beam recovery depending on said propagation delay information. Making the selection of channel dependent on the propagation delay information involves the advantage that a more efficient channel, such as an uplink control channel, can be selected instead of a less efficient channel, such as a random access channel.

[0009] In a further implementation form of the first aspect, the client device is configured to select a random access channel for requesting said beam recovery in case the client device finds said propagation delay information to be insufficient according to a predefined criterion of sufficiency. This selection involves the advantage of robust uplink transmission in situations where the propagation delay information was found to be insufficient. [001 0] In a further implementation form of the first aspect, the client device is configured to select a random access channel for requesting said beam recovery in case the client device finds said propagation delay information to be unreliable according to a predefined criterion of reliability. This selection involves the advantage of robust uplink transmission in situations where the propagation delay information was found to be unreliable.

[001 1 ] In a further implementation form of the first aspect, the client device is configured to select an uplink control channel for requesting said beam recovery in case the client device finds said propagation information to fulfil said predefined criteria of sufficiency and reliability, and configured to determine a difference between said first and second propagation delays. Making this selection involves the advantage of enabling very fast beam recovery with minimal additional use of physical radio resources.

[001 2] In a further implementation form of the first aspect, the client device is configured to utilize a timing advance matching said first propagation delay also for communications through said candidate beam in case said difference between the first and second propagation delays is smaller than a predetermined first threshold. This involves the advantage of saving time and calculation resources in the client device.

[001 3] In a further implementation form of the first aspect, the client device is configured to - in case the difference between said first and second propagation delays is larger than a predetermined first threshold but smaller than a predetermined second threshold, wherein the predetermined second threshold is larger than said first predetermined threshold - use the difference to calculate a new timing advance for use in communications through said candidate beam, and send said new timing advance to a network node of said wireless network. Said second threshold may be optional or defined as a very large or infinite value, so that the client device is configured to use the difference to calculate a new timing advance for use in communications through said candidate beam and send said new timing advance to a network node of said wireless network when the difference is larger than said first threshold. This involves the advantage of enabling relatively fast beam recovery with little additional use of physical radio resources, and certainly less than if the use of random access channel would be used for sending the beam recovery request.

[001 4] In a further implementation form of the first aspect, the client device is configured to send said new timing advance in a beam recovery request message transmitted to the network node. This involves the advantage that the new timing advance will become known to the network as early as possible.

[001 5] In a further implementation form of the first aspect, the client device is configured to send said new timing advance in a signaling message transmitted to the network node separately from a beam recovery request message. This involves the advantage that the beam recovery request message can be kept as short and compact as possible.

[001 6] In a further implementation form of the first aspect, the client device is configured to transmit said signaling message in the same uplink control channel as said beam recovery request message. This involves the advantage of streamlined execution of processes in the communicating devices, because no additional uplink channels need to be involved.

[001 7] In a further implementation form of the first aspect, the client device is configured to transmit said signaling message on a shared uplink channel of said wireless network. This may involve the advantage of optimizing the use of channels.

[001 8] In a further implementation form of the first aspect, the client device is configured to obtain said propagation delay information in the form of timing advance values received from said wireless network. This involves the advantage of optimizing control possibilities of the wireless network.

[001 9] In a further implementation form of the first aspect, the client device is configured to obtain said propagation delay information through a propagation delay measurement of said current and candidate beams. This involves the advantage of allowing the client devices to schedule their measurements and distributing the processing load evenly in the network.

[0020] According to a second aspect, a network node of a wireless network is provided. The network node is configured to receive from a client device of said wireless network a beam recovery request on an uplink control channel, said beam recovery request indicating a candidate beam for beam recovery. The network node is further configured to receive from said client device a new timing advance to be used in the requested beam recovery, and store said new timing advance as a value specific to said client device.

[0021 ] In a further implementation form of the second aspect, the network node is configured to receive said new timing advance in a same message as said beam recovery request. This involves the advantage that the new timing advance will become known to the network as early as possible.

[0022] In a further implementation form of the second aspect, the network node is configured to receive said new timing advance in a different message than said beam recovery request. This involves the advantage that the beam recovery request message can be kept as short and compact as possible.

[0023] According to a third aspect, a method is provided. The method comprises receiving reference signals, detecting a beam failure in a communications connection with a network node of a wireless network, said communications connection having involved reception of reference signals through a current beam, selecting a candidate beam for beam recovery based on measurement of beam specific reference signals, determining a propagation delay information PDI, the PDI being indicative of a difference between a first propagation delay specific to said current beam and a second propagation delay specific to said candidate beam, and selecting among at least two alternative mechanisms of beam recovery depending on said propagation delay information.

[0024] According to a fourth aspect, a method is provided, the method comprises receiving from a client device of a wireless network a beam recovery request on an uplink control channel, said beam recovery request indicating a candidate beam for beam recovery, receiving from said client device a new timing advance to be used in the requested beam recovery, and storing said new timing advance as a value specific to said client device.

[0025] According to a fifth aspect, a computer program is provided. The computer program comprises program code configured to perform a method according to any of the third or fourth aspects when the computer program is executed on a computer. The computer program can be stored or embodied on a volatile or non-volatile computer-readable non-transitory record medium in the form of program code.

BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 illustrates communications using beams.

[0027] Figure 2 illustrates an example of beam recovery.

[0028] Figure 3 illustrates an example of beam recovery.

[0029] Figure 4 illustrates an example of beam recovery.

[0030] Figure 5 illustrates a method for a client device.

[0031 ] Figure 6 illustrates a method for a network node.

[0032] Figure 7 illustrates a client device.

DETAILED DESCRIPTION

[0033] Figure 1 illustrates a situation where a client device 101 of a wireless network has a communications connection with a network node 102 of the wireless network. The client device 101 is assumed to be a mobile device, although this is not a necessary requirement. Examples of client devices include but are not limited to smartphones, portable computers, tablets, cameras, personal digital assistants, navigator devices, vehicle-mounted communications devices, wearable communications devices, and the like.

[0034] Both the client device 101 and the network node 102 are configured to use beams for transmission. The use of a beam for transmission means that the device in question is capable of, and makes use of, directed reception and transmission of wireless signals. Sophisticated hardware and software are involved in forming and utilizing beams. For example, signals components going through spatially distinct antenna elements can be processed in different ways with respect to their phase and amplitude, and the resulting processed signal components can be combined and sampled in various ways. A major advantage of using beams is the improved signal to noise ratio, which allows using higher transmission rates than with omnidirectional antennas for the same overall power consumption.

[0035] In figure 1 it is assumed that the client device 101 and the network node 102 used to communicate using a so-called current beam 103 of the network node 102. Also the client device 101 is assumed to have beamforming capability in figure 1, so a corresponding beam 104 of the client device 101 is also shown in figure 1. The adjective "current" is used in the sense of being actual, i.e. currently in use.

[0036] The client device 101 has moved, for example because its user was walking, so that an obstacle 105 appeared between the client device 101 and the network node 102. The signal path 106 of signals that are transmitted and received through beams 103 and 104 is relatively long, and not straight. At some point a beam failure may occur, meaning that communications through beams 103 and 104 are lost or at least the communications quality deteriorates below a certain threshold of acceptability.

[0037] After a beam failure a candidate beam should be selected for beam recovery. In some cases, particularly if the disturbance in communications through the current beam was only temporary, the current beam may be available as a candidate beam. However, in many cases - and also in the example case of figure 1 - there are one or more other beams available for selection as candidate beams. Beam 107 is schematically shown as an example in figure 1. The corresponding beam at the client device 101 is shown as beam 108.

[0038] The other beam 107 may give better communications quality than the current beam 103 in the situation of figure 1, because it offers line-of-sight communications. Additionally the distance along the communications path is shorter using beams 107 and 108 than using beams 103 and 104. The difference in distance will cause a difference in propagation delay of the wireless signals.

[0039] A propagation delay on a transmission path between a client device and a network node of a wireless network can be compensated for by using so-called timing advance. A timing advance is the amount of time by which a client device advances its wireless transmission in relation to a time reference in order to make said wireless transmission arrive at the network node in appropriate alignment with the frame schedule or other transmission timing arrangement applied by the network node. In third generation wireless networks the client device sends a so-called random access preamble to the network node, which uses the known characteristics of the random access preamble to measure the propagation delay. The network node then converts the measured propagation delay into a timing advance value, which it transmits to the client device. Having received a timing advance value from the network node, the client device takes it into use and advances its subsequent transmissions accordingly. If the propagation delay changes in 3G systems, the network node transmits an updated timing advance value to the client device, which uses it to replace the previous timing advance value.

[0040] Uplink signaling channels of a wireless network can be categorized into two categories based on whether the transmitting client device is able to use a valid timing advance value or not. A client device that does not know a valid timing advance value is expected to make an uplink transmission on a so-called random access channel, the timing of which is defined loosely enough so that uplink transmissions that arrive at the network node slightly misaligned in time do not cause interference to each other. Another category of uplink signaling channels are uplink control channels. They are more strictly regulated concerning time: a client device is expected to have and utilize a valid timing advance value when it makes a transmission on an uplink control channel. The timing of uplink control channels may be based on so-called cyclic prefixes, so that an uplink transmission from a client device must arrive at the network node within the appropriate cyclic prefix in order not to cause interference to other simultaneous communications connections. During the time when the client device is connected to the network the network monitors changes in propagation delay. The network node orders the client device to tune its uplink timing advance, UL TA, if needed, using dedicated timing advance commands.

[0041 ] In the situation of figure 1 the client device 101 should request beam recovery from the network node 102 by sending a beam recovery request. If the client device 101 sends the beam recovery request on a random access channel, there follows a procedure in which the network node 102 measures the propagation delay, converts the measured propagation delay into a timing advance value, and transmits the obtained timing advance value to the client device 101. Only after it received the timing advance value from the network node 102 and stored it for use, the client device 101 may send its next uplink transmission. This procedure is relatively slow, and it may be said to consume relatively much the available physical radio resources.

[0042] The network node 102 is configured to transmit so-called downlink reference signals, known by the acronym DL RS. The reference signals are beam specific, meaning that a client device that is configured to receive the reference signals can tell, which received reference signals were specific to which beam of the network node 102. The beam specific reference signals can also be called synchronization signals or beam identification reference signals. The client device 101 may be capable of measuring the beam specific reference signals; more particularly, the client device 101 may be capable of using measurements of the beam specific reference signals both to select a candidate beam for beam recovery, and to determine a propagation delay information, PDI. The PDI is indicative of a difference between a first propagation delay specific to the current beam 103 and a second propagation delay specific to the candidate beam 107. The client device may be configured to select among at least two alternative mechanisms of beam recovery based on said determined propagation delay information.

[0043] Here a mechanism of beam recovery is a generic term that may involve aspects such as selecting a particular channel to be used for requesting beam recovery, and selecting the kind of message that will be used for requesting beam recovery. A mechanism of beam recovery may also involve other aspects, like whether to use one or more transmitted messages for beam recovery, and what kind of timing is to be used in requesting the beam recovery.

[0044] Figure 2 illustrates an example of how a client device may be configured to act. Figure 2 illustrates schematically a client device 101 and a network node 102 that have a communications connection in a wireless network. The network node 102 is configured to transmit DL RS, and the client device 101 is configured to receive these as reference signals, as illustrated by step 201.

[0045] The client device 101 is configured to detect a beam failure in the communications connection with the network node 102 of the wireless network, as illustrated by block 202 in Figure 2. The communications connection in which the beam failure is detected is the one that involved the reception of the wireless signals 201 through the current beam. The exact mechanism through which the client device 101 detects the beam failure is not important; in general, the client device 101 may detect that the network is no longer able to reach the client device 101 with a (downlink) control channel due to incorrect adjustment of beams. For example, the client device 101 may estimate the quality of a hypothetical PDCCH (Physical Downlink Control CHannel) reception transmitted over a beam that the network would use to reach the client device 101. In beam failure detection the client device 101 estimates the quality of a hypothetical PDCCH reception from reference signals.

[0046] The reception of reference signals 201 may continue at the client device 101 even after the beam failure was detected at 202. In particular, the client device 101 may receive reference signals 201 transmitted through multiple beams by the network node 102, or reference signals transmitted through multiple beams by two or more network nodes, and measure the beam specific reference signals. The client device 101 is configured to select a candidate beam for beam recovery based on the measurement of the beam specific reference signals, as illustrated by block 203 in Figure 2. In general, selecting the candidate beam for beam recovery at 203 should mean selecting that beam, the measured reference signals of which would give the highest estimate of quality of a hypothetical PDCCH reception.

[0047] The client device 101 is configured to determine a propagation delay information, PDI, as illustrated by block 204 in Figure 2. The PDI is indicative of a difference between a first propagation delay specific to the current beam (corresponding to which the beam failure was detected at 202) and a second propagation delay specific to the candidate beam selected at 203. Determining the PDI at 204 may be implemented according to various embodiments that may be alternative to each other and that are described in more detail in the following.

[0048] According to a first embodiment of determining the PDI at 204, the client device 101 may already have one or more valid TA (Timing Advance) values for different beams. This may be the case for example if the client device 101 has multi- beam capability, and has been receiving reference signals specific to said different beams (and made measurements of said reference signals) already before the beam failure was detected at 202. Another possibility is that there has been a recent change of beams from another beam to the current beam in which the beam failure was detected at 202, and said other beam is now available again as a candidate beam. According to this first embodiment, the determined PDI comprises the TA values that the client device already has. [0049] According to a second embodiment of determining the PDI at 204, the client device 101 may measure the propagation delay difference between the current beam and the candidate beam from the reference signals specific to these beams that the client device received at 201. If such a measurement is successful and if the client device 101 has a valid timing advance that it used in the communications through the current beam before the beam failure was detected, the client device 101 is capable of calculating a timing advance also for the candidate beam.

[0050] According to a third embodiment of determining the PDI at 204, the client device 101 may find out that it does not have sufficient information about the propagation delay specific to the candidate beam selected at 203. This may be the case for example if the client device 101 did not succeed in making the measurements of the reference signals 201 that were described above. What is considered sufficient depends on e.g. the accuracy at which uplink transmissions are required to be timed in that particular wireless network. It may be assumed that the standards of the wireless network define a predefined criterion of sufficiency, i.e. how much and what kind of propagation delay information a client device must have in order to produce acceptable uplink transmissions on a particular channel. According to this third embodiment of determining the PDI the client device finds the propagation delay information to be insufficient according to said predefined criterion of sufficiency.

[0051 ] According to a fourth embodiment of determining the PDI at 204, the client device 101 may find out that even if it has some propagation delay information, that propagation delay information is unreliable according to a predefined criterion of reliability. As an example, it may be defined that for each determined timing advance there is an expiry time, measured from the moment of determining said timing advance, after which the timing advance is so old that it is not reliable any more. As another example, the predetermined criterion of reliability may be simply a largest allowable difference to the timing advance that was used for communications through the current beam: a difference that is larger than a predefined threshold may be interpreted as making the propagation delay information unreliable.

[0052] As another example, the client device 101 may be configured to compare a calculated timing advance to previous timing advances it has used in the near past. Previous timing advances may be considered to constitute a kind of probability distribution, the mean value of which tells the most typical timing advance that has been used recently. Additionally or alternatively there may be noted a trend in previous timing advances: how the timing advances have developed recently (from which it can be e.g. told, whether the client device has recently moved closer to or farther from the network node). The predefined criterion of reliability may be interpreted so that if the propagation delay information determined at 204 seems to fit very poorly to a distribution and/or trend in previous timing advances, it is not reliable.

[0053] The client device 101 is configured to select among at least two alternative mechanisms of beam recovery depending on the propagation delay information determined at 204. Selecting a mechanism of beam recovery may, in turn, involve embodiments that may be alternative to each other and that are described in more detail in the following. Making the selection of mechanism dependent on the propagation delay information involves the advantage that an optimal mechanism can be selected in each case, resulting in optimal use of physical radio resources as well as a very short delay in communications, particularly if one of the fastest mechanisms can be chosen.

[0054] According to a first embodiment of selecting a mechanism of beam recovery, the client device may be configured to select a channel to be used for requesting the beam recovery depending on the propagation delay information. In general, if the client device has accurate and reliable information about the timing to be used in communications through the selected candidate beam, it may use an uplink control channel for requesting the beam recovery. If the client device has insufficient and/or unreliable information about the timing to be used in communications through the selected candidate beam, it may use a random access channel for requesting the beam recovery. Making the selection of channel dependent on the propagation delay information involves the advantage that a more efficient channel, such as an uplink control channel, can be selected instead of a less efficient channel, such as a random access channel. [0055] According to a second embodiment of selecting a mechanism of beam recovery, the client device may be configured to select the way in which it signals to the network any information related to the recovered communications. As an example we may consider that the client device may have determined, in one way or another, a new timing advance for use in communications through the selected candidate beam. If the new timing advance is not yet known to the network, the client device may send the new timing advance to a network node of the wireless network. It may be configured to send the new timing advance in a beam recovery request message transmitted to the network node. Such a selection involves the advantage that the new timing advance will become known to the network as early as possible. Alternatively or additionally the client device may be configured to send the new timing advance in a signaling message transmitted to the network node separately from a beam recovery request message. Such a selection involves the advantage that the beam recovery request message can be kept as short and compact as possible.

[0056] If the client device is configured to send the new timing advance in a signaling message transmitted to the network node separately from a beam recovery request message, such a signaling message may be transmitted rather in the same uplink control channel as the beam recovery request message or on some other, shared uplink channel of the wireless network. Transmitting it in the same uplink control channel may involve the advantage of streamlined execution of processes in the communicating devices, because no additional uplink channels need to be involved. Transmitting it on some other, shared uplink channel of the wireless network may involve the advantage of otherwise optimizing the use of channels, for example so that a maximum number of possible beam recovery request messages can be accommodated because the same uplink channel is not used for transmitting also the new timing advances.

[0057] In the example illustration of Figure 2, determining the PDI at 204 gives either the result that the client device 101 finds the propagation delay information to be insufficient according to a predefined criterion of sufficiency, or the result that the client device finds said propagation delay information to be unreliable according to a predefined criterion of reliability. As a consequence the client device selects a random access channel for requesting the beam recovery, as illustrated by the step 205.

[0058] Figure 3 illustrates an alternative example, in which the actions of the devices follow the course explained above with reference to Figure 2 up to the determining of the PDI. In Figure 3 determining the PDI at step 301 gives the result that the client device 101 finds the propagation delay information to fulfil the predefined criteria of sufficiency and reliability mentioned above. Such a finding means that at 301 the client device 101 is also configured to determine a difference between the first and second propagation delays, i.e. the propagation delays specific to the current and candidate beams respectively. In figure 3 it is further assumed that said difference is smaller than a predetermined first threshold. As a result, the client device is configured to utilize a timing advance matching said first propagation delay also for communications through the candidate beam, as illustrated by block 302 in Figure 3. Knowing the valid timing advance enables the client device to select an uplink control channel for requesting the beam recovery, as illustrated by step 303 in Figure 3.

[0059] Figure 4 illustrates an alternative example, in which the actions of the device again follow the course explained above with reference to Figures 2 and 3 up to the determining of the PDI. In the Figure 4 determining the PDI at 401 gives the result that the difference between said first and second propagation delays is larger than a predetermined first threshold but smaller than a predetermined second threshold. The predetermined second threshold is larger than said first predetermined threshold. In other words, the client device 101 finds out that the propagation delay in communications through the candidate beam differ too much from that in communications through the current beam for the last-mentioned to be simply used also in communications through the candidate beam. As a result, the client device is configured to use the difference to calculate a new timing advance for use in communications through the candidate beam, as illustrated by block 402 in Figure 4. Knowing this new, calculated timing advance enables nevertheless the client device to select an uplink control channel for requesting the beam recovery, as illustrated by step 403 in Figure 4. The same request, or some other uplink signaling message as explained earlier, can be used to send the new timing advance to the network node 102 of the wireless network.

[0060] Figure 5 is a flow diagram that shows an example of how the client device may be configured to proceed in determining the PDI, which was illustrated earlier with reference designators 204, 301, and 401 in Figures 2, 3, and 4, as well as performing some of the subsequent actions. Figure 5 can also be an illustration of a method steps according to an embodiment of the client device.

[0061 ] The preceding steps 501 comprise receiving reference signals, and detecting a beam failure in a communications connection with a network node of a wireless network, said communications connection having involved reception of reference signals through a current beam. Step 502 comprises selecting a candidate beam for beam recovery based on measurement of beam specific reference signals, and thus corresponds to how the client device is configured to operate according to block 203 in Figures 2, 3, and 4.

[0062] In Figure 5 determining a propagation delay information PDI begins by the client device examining, according to step 503, whether it is capable of obtaining a timing advance for use in communications through the selected candidate beam through its own actions. If the client device is not capable of obtaining the propagation delay (or valid TA) difference between current and candidate beams, a transition to step 504 occurs. This means that selecting a mechanism of beam recovery involves this time the use of a random access channel for beam recovery. Although slower and more inefficient regarding physical radio resources, this selection nevertheless allows robust uplink transmission in situations where a current TA may not be suitable for compensating for the propagation delay in communications through the selected candidate beam.

[0063] A positive finding at step 503 means that the client device has at least some information indicative of the propagation delay difference between the current and candidate beams. Step 505 comprises evaluating the difference, i.e. comparing the timing advance that should be used for communications through the candidate beam to that used for communications through the current beam. Step 506 comprises evaluating the result of the comparison. If the comparison shows that the timing advance that should be used for communications through the candidate beam is almost equal to that used for communications through the current beam, a transition to step 507 occurs. The comparison may apply for example a (first) threshold, below which the difference between TA values must be in order for the method to branch to step 507. Such a threshold can be dependent on cyclic prefix length configuration or configured radio frame numerology, or it can be signaled to client devices with RRC (Radio Resource Controlling) signaling, for example.

[0064] At step 507 the client device selects an uplink control channel for transmitting the request for beam recovery. Since the TA for the candidate beam was found to be almost equal to that for the current beam, the client device does not need to send any new timing advance to the network at this stage. Making this selection involves the advantage of enabling very fast beam recovery with minimal additional use of physical radio resources.

[0065] A negative finding at step 506 means that the difference between TA values is too large for the method to branch to step 507. If the first threshold mentioned above was used in the comparison, a negative finding at step 506 means that the difference between TA values is not below the first threshold. A further evaluation step 508 follows, comprising finding out, whether the difference is excessively large, i.e. larger than a predetermined second threshold that is larger than the first predetermined threshold mentioned above. It yes, the determined propagation delay information must be considered unreliable according to the predefined criterion of reliability, and a transition to step 504 occurs with the consequences that were already described above.

[0066] A negative finding at step 508 means that the difference between TA values was larger than the first predetermined threshold but smaller than the second predetermined threshold. As a consequence there occurs a transition to step 509, which comprises using the difference to calculate a new timing advance for use in communications through the candidate beam. The client device selects an uplink control channel for requesting beam recovery at step 510. In order to keep the TA synchronized with the network, the client device sends the new timing advance to a network node of the wireless network. This selection involves the advantage of enabling relatively fast beam recovery with little additional use of physical radio resources, and certainly less than if the use of random access channel would be used for sending the beam recovery request.

[0067] The first and second predetermined thresholds mentioned above can have different values for different cyclic prefix length configurations or different radio frame numerology configurations. Such dependencies may be predefined and fixed, so that once the client device knows the cyclic prefix length configuration and/or radio frame numerology configuration to be used, it can read the predetermined thresholds from its memory. Alternatively the network may use downlink signaling to inform all client devices of the applicable first and/or second threshold values. In some cases the second threshold value may be defined very large or infinite, which essentially means that there is no meaningful second threshold value but the client device is expected to always use the difference between propagation delays to calculate a new timing advance for use in communications through the candidate beam, and send said new timing advance to a network node of said wireless network, when the difference is larger than the first threshold.

[0068] Figure 6 is a flow diagram that shows an example of how the network node may be configured to proceed in responding to a beam recovery request that it receives from a client device that operates according to one of the embodiments described above. Figure 6 can also be read as an illustration of a method according to an embodiment.

[0069] The network node is configured to receive, from a client device of the wireless network, a beam recovery request as in step 601 of Figure 6. Since a known procedure can be followed if the beam recovery request came on a random access channel (evaluation at step 602 - random access procedure at step 603), the following description concentrates on how the network node is configured to act if it receives the beam recovery request on an uplink control channel.

[0070] In order for the method step to proceed from step 602 to step 604 the network node must be configured to receive beam recovery requests from client devices on an uplink control channel. Step 604 comprises examining, whether a new timing advance was received from the client device to be used in the requested beam recovery. If not, the client device has proceeded according to step 507 in Figure 5, and the network node may correspondingly execute step 605, which comprises continuing the beam recovery without any changes to the TA value that is stored specific to the client device that sent the request. A positive finding at step 604 means that the client device has proceeded according to steps 509 and 510 in Figure 5. Correspondingly the network node may execute step 606, which comprises following the beam recovery procedure initiated on an uplink control channel but storing the received new timing advance as a value specific to that client device.

[0071 ] Figure 7 is an illustration of a client device according to an embodiment. The operation of the client device is controlled by one or more processors 701 that execute machine-readable instructions stored in one or more memories 702 in the form of program code. Wireless communications between the client device and network nodes of the wireless network go through a connectivity block 703, which may comprise wireless communications modules for various technologies, such as mobile wireless; wireless LAN; short-distance radio; and/or short-distance optical communications. A sensors block 704 gives the client device the capability of making measurements and observations of its immediate environments and its own movements, including but not being limited to rotation, translational movement, direction of magnetic field, amount of ambient light, and proximity of external objects.

[0072] A positioning block 705 gives the client device the capability of finding and tracking its own position in a coordinate system, such as a global coordinate system or a local coordinate system within a building. An audio block 706 gives the client device the capability of emitting sounds, such as reproduced speech received during an audio call and/or signal sounds meant for alerting the user. A video block 707 gives the client device the capability of recording visual information, such as still images and video. A display block 708 gives the client device the capability of displaying visual information to its user. It may also include touchscreen control functions that give the client device the capability of receiving touch commands from the user. A power block 709 comprises the components and functions that are necessary for providing operating power to the parts of the client device that need it. [0073] Receiving reference signals, detecting beam failures, selecting candidate beams, determining PDI, selecting between mechanisms of beam recovery, and sending the appropriate transmissions may involve operations of at least the processor(s) 701, the memory 702, and the connectivity block 703. Configuring the client device to perform the operations described above involves not only equipping it with the appropriate hardware components, as illustrated schematically in Figure 7, but also producing and storing in memory 702 the machine-readable instructions that the processor(s) 701 may perform and thus make the client device perform the operations described above.

[0074] A network device may involve similar hardware parts as the processors 701 , memory 702, connectivity block 703, and power block 709 that in Figure 7 are shown as parts of the client device. Configuring the network device to perform the operations described above involves not only equipping it with the appropriate hardware components but also producing and storing in memory the machine-readable instructions that its processor(s) may perform and thus make the network device perform the operations described above.

[0075] The invention has been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the description and claims the word "comprising" does not exclude other elements and steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored and/or distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications system.

[0076] Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined in the appended claims.

[0077] Although the invention has been described with reference to specific features and embodiments thereof, it is evident that various modifications and combinations can be made thereto without departing from the spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded simply as an illustration of the invention as defined by the appended claims, and are contemplated to cover any and all modifications, combinations, or equivalents that fall within the scope of the invention.

[0078] The propagation delay information PDI can be defined as indicative of a difference between a first propagation delay specific to said current beam and a second propagation delay specific to said candidate beam. However, PDI can be defined also as uplink time alignment information including one or more client device's timing advance values and/or difference between timing advance values and/or validity of said timing advance values. Hence, selecting beam recovery mechanism and/or channel can be dependent on validity of client device's uplink beam time alignment values. Therefore the client device's uplink beam time alignment values can be used instead of the propagation delay information in all of the above embodiments mentioned earlier.