Technical Field

The invention relates to a processing device and a client device comprising such a processing device. Furthermore, the invention also relates to 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.

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 operate in a discontinuous reception mode, wherein the processing device is further configured to

determine a first beam variation associated with one or more downlink beams during a first time period;

track the one or more downlink beams during off-durations of the discontinuous reception mode based on the first beam variation.

The discontinuous reception mode comprises on-durations in which the processing device is configured to monitor a physical downlink channel and off-durations in which the processing device is configured to not monitor a physical downlink channel. Each discontinuous reception mode cycle comprises one on-duration and one off-duration, where the on-duration and the off-duration defines both the duration and the location in the discontinuous reception mode cycle of the on state and the off state, respectively.

In this disclosure the terms downlink beam and uplink beam are used for describing the direction of reception of signals and direction of transmission of signals, respectively, for a processing device and/or an associated 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.

The first beam variation provides information related to how the one or more downlink beams change during the first time period, which e.g. gives an indication of the movement behaviour of the processing device.

Furthermore, to track a beam can in this disclosure be understood to mean to track/monitor reference signals in the beam, i.e. quasi-co-located with the beam, to determine the quality of the beam, where the quality of the beam may correspond to a reliability of reception of a control channel transmitted in the beam. The reference signals may be quasi co-located with the control channel. That a reference signal is quasi-co-located with a control channel can be interpreted to mean that the reference signal and the control channel are transmitted and/or received in the same direction (and using therefore the same propagation path), such as in the same downlink beam and/or in the same uplink beam.

An advantage of the processing device according to the first aspect of the invention is that the tracking of the one or more downlink beams can be adapted to the current movement behaviour of the processing device. Thereby, the power consumption of the processing device can be optimized.

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

determine a first beam tracking configuration based on the first beam variation, wherein the first beam tracking configuration comprises a first beam tracking pattern and at least one associated first wake-up duration for tracking the one or more downlink beams during the off- durations of the discontinuous reception mode;

track the one or more downlink beams according to the first beam tracking configuration. In this disclosure, a first beam tracking pattern can be understood to define how often the processing device should wake-up and track the one or more downlink beams, while the associated first wake-up duration can be understood to define the duration of a wake-up instance. The first beam tracking pattern can be periodic or non-periodic.

An advantage with this implementation form is that the wake-up time can be adapted to the current movement behaviour of the processing device or its associated client device. Thereby, the power consumption of the processing device can be optimized.

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

track at least one of a synchronization signal block, a channel state information reference-signal, and a tracking reference signal, wherein the synchronization signal block, the channel state information reference-signal, and the tracking reference signal have a quasi- collocated association to the one or more downlink beams.

An advantage with this implementation form is that the processing device has known reference signals to perform measurements on, thereby making the beam tracking simpler.

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

select at least one downlink beam among the one or more downlink beams based on the tracking of the one or more downlink beams during the off-durations of the discontinuous reception mode;

monitor a physical downlink channel e.g. physical downlink control channel PDCCH or physical downlink shared channel PDSCH associated with the selected downlink beam during on-durations of the discontinuous reception mode. The selected downlink beam may for example form a serving downlink beam for the processing device.

An advantage with this implementation form is that the processing device can select a high quality downlink beam for control channel monitoring and data information detection, thereby improving the reception performance.

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

determine the first beam variation based on a variation of the number of selected downlink beams during the first time period. An advantage with this implementation form is that by investigating the number of selected downlink beams a good measure of the client device movement is achieved. Thereby, optimized trade-off between beam tracking and power consumption is achieved.

In an implementation form of a processing device according to the first aspect, the variation of the number of selected downlink beams during the first time period is at least one of:

a number of selected downlink beams;

a fraction time of the first time period for the most selected downlink beam;

a variance metric associated with the number of selected downlink beams; and a rate of change of selected downlink beams.

An advantage with this implementation form is that above variation measures give a good measure of the client device movement. Thereby, optimized trade-off between beam tracking and power consumption is achieved.

In an implementation form of a processing device according to the first aspect, each downlink beam of the one or more downlink beams comprises a receive beam and a transmit beam; and wherein the processing device is configured to at least one of

determine the first beam variation based on a variation of the number of receive beams of the selected downlink beams; and

determine the first beam variation based on a variation of the number of transmit beams of the selected downlink beams.

An advantage with this implementation form is that by looking at the variation of the number of receive beams and transmit beams separately the processing device can determine the type of client device movement and optimize the beam tracking configuration accordingly. Thereby, the power consumption of the processing device can be optimized.

In an implementation form of a processing device according to the first aspect, the variation of the number of receive beams or transmit beams during the first time period is at least one of: a number of transmit beams;

a fraction time of the first time period for the most selected transmit beam;

a variance metric associated with the number of transmit beams;

a rate of change of transmit beams;

a number of receive beams;

a fraction time of the first time period for the most selected receive beam; a variance metric associated with the number of receive beams; and

a rate of change of receive beams.

An advantage with this implementation form is that above variation measures give a good measure of the client device movement, thereby optimized trade-off between beam tracking and power consumption is achieved.

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

obtain one or more sensor signals from one or more motion sensors;

determine the first beam variation further based on the one or more sensor signals.

An advantage with this implementation form is that motion sensors give an additional indication of client device movement, thereby optimized trade-off between beam tracking and power consumption is achieved.

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

determine the first beam tracking configuration further based on transmission instances of reference signals in the one or more downlink beams.

An advantage with this implementation form is that the processing device only needs to wake- up during reference signal transmission which reduces the total wake-up time and thereby the power consumption can be reduced.

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

determine the first beam tracking configuration further based on a configuration of the discontinuous reception mode.

An advantage with this implementation form is that by taking the discontinuous reception configuration into account optimized wake-up time can be achieved.

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

determine a second beam variation associated with the one or more downlink beams during a second time period subsequent to the first time period; determine a second beam tracking configuration based on the second beam variation, wherein the second beam tracking configuration comprises a second beam tracking pattern and at least one associated second wake-up duration for tracking the one or more downlink beams during the off-durations of the discontinuous reception mode;

track the one or more downlink beams according to the second beam tracking configuration.

An advantage with this implementation form is that the processing device can adapt the wake- up time if the client device movement changes and hence adapt the beam tracking configuration to the current movement behaviour of the client device. Thereby, improving the overall power consumption.

In an implementation form of a processing device according to the first aspect, an accumulated time period of the second wake-up durations is longer than an accumulated time of the first wake-up durations if the second beam variation is larger than the first beam variation.

An advantage with this implementation form is that the processing device can increase the wake-up time if the client device movement increases, thereby adapting the beam tracking configuration for optimized receiver performance.

In an implementation form of a processing device according to the first aspect, an accumulated time period of the second wake-up durations is shorter than an accumulated time of the first wake-up durations if the second beam variation is smaller than the first beam variation.

An advantage with this implementation form is that the processing device can reduce the wake- up time if the client device movement reduces, thereby adapting the beam tracking configuration for optimized power consumption.

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

the first beam variation is determined based on the variation of the number of receive beams and transmit beams of selected downlink beams;

the second beam variation is determined based only on the variation of the number of receive beams of selected downlink beams.

An advantage with this implementation form is that the processing device can discriminate between rotational movement and other movements of the client device and thereby adapt the wake-up time for optimized power consumption. 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 proceeding claims.

An advantage of the client device according to the second aspect of the invention is that the tracking of the one or more downlink beams can be adapted to the current movement behaviour of the client device. Thereby, the power consumption of the client device can be optimized.

In an implementation form of a client device according to the second aspect, the client device further comprising one or more motion sensors configured to

provide one or more sensor signals to the processing device.

An advantage with this implementation form is that the processing device can use sensors for movement detection and thereby optimize the beam tracking configuration for optimized power consumption.

According to a third aspect of the invention, the above mentioned and other objectives are achieved with a method for a processing device being configured to operate in a discontinuous reception mode, the method comprises

determine a first beam variation associated with one or more downlink beams during a first time period;

track the one or more downlink beams during off-durations of the discontinuous reception mode based on the first beam variation.

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 program code, which when run by at least one processor causes said at least one processor to execute any method according to embodiments of the 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 embodiments 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 method for tracking downlink beams during off-durations according to embodiments of the invention;

- Fig. 6 shows an examples of beam tracking during off-durations;

- Fig. 7 shows an examples of beam tracking during off-durations; and

- Fig. 8 shows an examples of beam tracking during off-durations.

Detailed Description

Before the embodiments of the invention will be described in detail some general details on beam pair quality measurements shall be explained.

When beamforming is used, a next generation nodeB (gNB) transmits data in several directions in different transmit beams. The user equipment (UE) therefore tunes 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 needs 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 needs to scan neighbouring cells for possible handover candidates.

Each possible downlink connection between the UE and the gNB consists of a gNB transmit beam and a UE receive beam Hence a downlink beam consist of a beam pair link (BPL). The gNB will configure a set of downlink beams for the UE to monitor. The configured set of monitored downlink beams may be based on which downlink beams the UE has detected. This set can for example comprise all the downlink beams associated with control channels and data channels between the gNB and the UE. The gNB will also configure a set of serving downlink beams which will be used to transmit associated control information to the UE. The set of serving downlink beams is a subset or equal to the set of monitored downlink beams. The UE monitors the quality of the set of monitored downlink beams and reports the quality in beam measurement report to the gNB. When a monitored downlink beam becomes stronger than the current serving downlink beam 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 downlink beam is stronger than the current serving downlink beam. Another scenario would be that the gNB determines, e.g. using uplink management procedures, that a target uplink beam has become a suitable serving uplink beam. The gNB could then order a beam switch to the corresponding target downlink beam.

Discontinuous reception in connected mode (C-discontinuous reception mode) is a key feature to reduce UE power consumption. When operating in C-discontinuous reception mode a UE is only required to listen to control channels at certain points in time, in the so-called on-durations. Outside the on-durations, the UE may switch off a significant part of its radio receiver to save power. C-discontinuous reception mode therefore allows the UE to reduce its power consumption.

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 100 may further comprise a plurality of processor cores 102. The memory 104 may store program code that, when being executed, causes the processor core(s) 102 of the processing device 100 to performing the functions and actions described herein. 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 functions or actions can in this disclosure be understood to mean that the processing device 100 comprises suitable means, such as e.g. the processor core(s) 102, configured to perform said functions or actions. The processing device 100 may for example be a baseband processor for use in a client device for a wireless communication system.

The processing device 100 in Fig.1 may be configured to operate in a discontinuous reception mode comprising on-durations in which the processing device 100 is configured to monitor a physical downlink channel and off-durations in which the processing device 100 is configured to not monitor a physical downlink channel. The processing device 100 is further configured to determine a first beam variation associated with one or more downlink beams 502a, 502b,..., 502n (shown in Fig. 4) during a first time period T 1 , and track the one or more downlink beams 502a, 502b,..., 502n during off-durations of the discontinuous reception mode based on the first beam variation.

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 processing device 100 is configured to operate in a discontinuous reception mode. The method 200 comprises determining 202 a first beam variation associated with one or more downlink beams 502a, 502b,..., 502n during a first time period T1 (see Fig. 5), and tracking 204 the one or more downlink beams 502a, 502b,..., 502n during off-durations of the discontinuous reception mode based on the first beam variation.

The processing device 100 may be comprised in a client device, such as e.g. the client device 300 shown in Fig. 3. The processing device 100 may hence be a functional module, e.g. a communication module such as a base band processor, configured to operate in the client device 300. 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. Furthermore, the client device 300 may comprise one or more motion sensors 122a, 122b,..., 122n configured to provide one or more sensor signals to the processing device 100. The purpose of the motion sensors 122a, 122b,..., 122n and the use of the sensor signals will be explained below with reference to step 602 in Fig. 5. Fig. 4 shows a wireless communication system 500 according to an embodiment of the invention. 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 between the client device 300 and the network access node 400. In the embodiment shown in Fig. 4, several downlink beams 502a, 502b,..., 502n exist between the client device 300 and the network access node 400. Each downlink beam 502a, 502b,..., 502n comprises a transmit beam associated with the network access node 400 and a receive beam associated with the client device 300. Hence the downlink beam can be seen as a beam pair link BPL. Hence, as shown in Fig. 4, the downlink beam 502a comprises a transmit beam 502a TX and a receive beam 502a RX, the downlink beam 502b comprises a transmit beam 502b TX and a receive beam 502b RX, and the downlink beam 502n comprises a transmit beam 502n TX and a receive beam 502n RX. The client device 300 is assumed to be operating in a discontinuous reception mode, and hence operates in on- durations and off-durations of the discontinuous reception mode. To determine which of the received downlink beams 502a, 502b,..., 502n the client device 300 should monitor during on- durations, the client device 300 tracks the three downlink beams 502a, 502b,..., 502n during off-durations according to embodiments of the invention. Thus, based on the tracking of the three downlink beams 502a, 502b,..., 502n during an off-duration, the client device may select at least one downlink beam among the three downlink beams 502a, 502b,..., 502n to monitor during the next on-duration. According to embodiments of the invention the client device 300 may determine how the tracking during off-durations should be performed based on a determined beam variation or according to a determined beam tracking configuration, as will now be described with reference to Fig. 5.

Fig. 5 shows a flow chart of a method 600 for tracking downlink beams during off-durations according to embodiments of the invention. The method 600 shown in Fig. 5 may be performed by a processing device 100, which in embodiments of the invention may be comprised in a client device 300. The processing device 100 or the client device 300 is assumed to operate in a discontinuous reception mode comprising on-durations and off-durations as previously described. The method 600 is initiated in step 602 where the processing device 100 determines a first beam variation associated with one or more downlink beams 502a, 502b,..., 502n during a first time period T 1 . The first time period T 1 may comprise one or more on-durations and off- durations in discontinuous reception mode. In addition, the first time period T1 may comprise time periods where the processing device 100 is operating in continuous reception mode. Thus, during the first time period T1 the processing device 100 may be operating in discontinuous reception mode only, in continuous reception mode only, or partly in discontinuous connection mode and partly in continuous connection mode.

The first beam variation during the first time period T1 is determined to indicate a current movement behaviour of the processing device 100. Input to the determining of the first beam variation in step 602 may be sensor signals and/or downlink beam variation information. In embodiments where the first beam variation is determined based on sensor signals, the processing device 100 obtains one or more sensor signals from one or more motion sensors 122a, 122b,..., 122n. Based on the one or more sensor signals the processing device 100 determines the first beam variation. The one or more motion sensors 122a, 122b,..., 122n may be any type of sensor that can be used to determine different kind of movement or rotation of the client device 300. Examples of such motion sensors are gyroscopes, accelerometers, magnetometers, and GPSs. As described with reference to Fig. 3, the one or more motion sensors 122a, 122b,..., 122n may be comprised in the client device 300. In this case, the one or more motion sensors 122a, 122b,..., 122n comprised in the client device 300 provide the one or more sensor signals to the processing device 100.

In embodiments where the first beam variation is determined based on downlink beam variations, the processing device 100 may determine the first beam variation based on a variation of a number of selected downlink beams during the first time period T1 . These selected downlink beams can for example be serving downlink beams of the client device 300. Hence, the processing device determines how for the first time period T 1 the serving downlink beam or beams vary. A selected downlink beam is herein at least one downlink beam among the one or more downlink beams 502a, 502b,..., 502n selected by the processing device 100 based on the tracking of the one or more downlink beams 502a, 502b,..., 502n during the off- durations of the discontinuous reception mode. To determine the variation of the number of selected downlink beams, during the first time period T1 , the processing device 100 may consider at least one of:

• a number of selected downlink beams, i.e. the number of different downlink beams that have been a selected downlink beam during the first time period T1 , where a selected downlink beam may be selected based on channel quality measurements such as e.g. reference signal received power (RSRP), signal-to-interference-plus-noise ratio (SINR), or reference signal received quality (RSRQ);

• a fraction time of the first time period T 1 for the most selected downlink beam, i.e. the time period the most selected downlink beam has been the selected downlink beam during the first time period T 1 ;

• a variance metric associated with the number of selected downlink beams; and

• a rate of change of selected downlink beams, i.e. how many times the selected downlink beams have changed per time unit.

As previously described with reference to Fig. 4 each downlink beam 502a, 502b,..., 502n may comprise a receive beam associated with the client device 300 and a transmit beam associated with the network access node 400. Hence, the processing device 100 may further determine the variation of a receive beam and a transmit beam separately. This allows the processing device 100 to further determine the type of movement, as a variation of a receive beam typically indicates a rotational movement while a variation of both a receive beam and a transmit beam typically indicates mobility. The processing device 100 may therefore be configured to determine the first beam variation based on a variation of the number of receive beams of the selected downlink beams and/or determine the first beam variation based on a variation of the number of transmit beams of the selected downlink beams. To determine the variation of the number of receive beams or transmit beams, during the first time period T1 , the processing device 100 may therefore consider at least one of:

• a number of transmit beams;

• a fraction time of the first time period T 1 for the most selected transmit beam;

• a variance metric associated with the number of transmit beams;

• a rate of change of transmit beams;

• a number of receive beams;

• a fraction time of the first time period T 1 for the most selected receive beam;

• a variance metric associated with the number of receive beams; and

• a rate of change of receive beams.

In an optional step 604, the processing device 100 may determine a first beam tracking configuration based on the first beam variation determined in step 602. The first beam tracking configuration indicates how the beam tracking should be performed by the processing device 100. The first beam tracking configuration may therefore comprise a first beam tracking pattern and at least one associated first wake-up duration for tracking the one or more downlink beams 502a, 502b,..., 502n during the off-durations of the discontinuous reception mode. The first beam tracking pattern may define how many times the processing device 100 should wake-up and track the one or more downlink beams 502a, 502b,..., 502n during the off-duration, while the associated first wake-up duration may define the duration of a wake-up instance, i.e. the time period available to the processing device 100 for tracking the one or more downlink beams 502a, 502b,..., 502n in one wake-up instance.

If the first beam variation determined in step 602 is high this indicates that the processing device 100 or its associated client device 300 is moving and that there is a high risk that the currently selected downlink beam(s) used during the previous on-duration cannot be the best downlink beam during the next on-duration. Hence, the processing device 100 may in this case determine the first beam tracking pattern in step 604 to comprise several first wake-up durations to allow enough time to track more downlink beams than the currently selected downlink beam(s). On the other hand, if the first beam variation determined in step 602 is low, the processing device 100 may in this case determine the first beam tracking pattern in step 604 to comprise only one first wake-up duration. A low first beam variation indicates that the processing device 100 is not moving and hence that it is likely that the current selected downlink beam(s) can be used also during the next on-duration. The meaning of high and low beam variation, respectively, may depend on application and/or on the system configuration of related reference signals or synchronization signals. However, in general a high beam variation indicates a movement (rotational movement or a spatial movement) which will have effect on the selection of downlink beam(s). For example, a high beam variation may mean that the number of selected transmit beams in the selected downlink beam is larger than one, or that the number of selected receive beams in the selected downlink beam is larger than 4 during the first time period T1. On the other hand, a low beam variation may mean that the number of selected transmit beams in the selected downlink beam is equal to one, or that the number of selected receive beams in the selected downlink beam is below 4 during the first time period T1 .

Further information may also be considered when determining the first beam tracking configuration in step 604. In embodiments, the processing device 100 may e.g. consider the timing of reference signals transmitted in the one or more downlink beams 502a, 502b,..., 502n, i.e. timing of reference signals that are quasi-co-located with the respective one or more downlink beams 502a, 502b,..., 502n. These reference signals may be used to track the one or more downlink beams 502a, 502b,..., 502n and hence the processing device 100 may configure first wake-up durations to coincide with the transmission of reference signals in the one or more downlink beams 502a, 502b,..., 502n. Thus, the processing device 100 may in embodiments determine the first beam tracking configuration further based on transmission instances of reference signals in the one or more downlink beams 502a, 502b,..., 502n.

Moreover, the processing device 100 may take parameters related to the discontinuous reception mode into account when determining the first beam tracking configuration in step 604. Hence, the processing device 100 may in embodiments determine the first beam tracking configuration further based on a configuration of the discontinuous reception mode. The configuration of the discontinuous reception mode may comprise parameters, such as e.g. configured discontinuous reception mode cycle length, on-duration, and inactivity timers. For example, if the discontinuous reception mode cycle length is short, typically 20-40 ms, the first beam tracking pattern may only consist of one wake-up instance in discontinuous reception mode even if the first beam variation is high. However, if the discontinuous reception mode cycle length is large, typically 100-2000 ms, the number of wake-up instances when the first beam variation is high may be significantly larger than when the first beam variation is low. Furthermore, if the on-duration is long relative to the discontinuous reception mode cycle length, a large amount of periodic and aperiodic channel state information reference-signals (CSI-RS) may be configured for the processing device 100 to measure the quality of a downlink beam. Hence, the processing device 100 may not need to perform tracking of the downlink beam outside the on-duration. On the other hand, if few CSI-RSs are configured and/or the on-duration is short, the processing device 100 may need extra wake-up instances to track and estimate the downlink beams.

In embodiments, the first beam tracking configuration may be pre-determined and stored as information in a look-up table. In such cases the determination in step 604 may comprise determining the first beam tracking configuration based on the look-up table. The look-up table may e.g. give a specific first beam tracking configuration as output using the discontinuous reception length and on-duration as input.

In step 606 in Fig. 5, the processing device 100 tracks the one or more downlink beams 502a, 502b,..., 502n during off-durations of the discontinuous reception mode. Depending on if the optional step 604 has been performed or not, the processing device 100 may track the one or more downlink beams 502a, 502b,..., 502n based on the first beam variation determined in step 602 or according to the first beam tracking configuration determined in step 604. When the tracking is performed based on the first beam variation, the processing device 100 may track the one or more downlink beams 502a, 502b,..., 502n during a number of wake-up durations, where the number of wake-up durations and the length of the wake-up durations are dependent on the first beam variation. When the tracking is performed according to the first beam tracking configuration, the processing device 100 may track the one or more downlink beams 502a, 502b,..., 502n according to the first beam tracking pattern during the at least one associated first wake-up duration. The tracking of the one or more downlink beams 502a, 502b,..., 502n in step 606 may involve the processing device 100 tracking at least one of a synchronization signal block (SSB), a CSI-RS, and a tracking reference signal. The SSB, the CSI-RS, and the tracking reference signal have a quasi-collocated association to the one or more downlink transmit beams 502a TX, 502b TX,..., 502n TX. Based on the SSB, the CSI- RS, or the tracking reference signal received during the tracking, the processing device 100 may determine a radio signal quality metric, e.g. RSRP, SINR, or RSRQ, for each of the one or more downlink beams 502a, 502b,..., 502n. The information gathered during the tracking of the one or more downlink beams 502a, 502b,..., 502n in step 606 may be used to select one or more downlink beams to monitor during the next on-duration, as will be described below with reference to step 608 and 610. In addition, the information gathered during the tracking of the one or more downlink beams 502a, 502b,..., 502n in step 606 may be used to determine an updated beam variation. In this case, the at least one first wake-up duration may be part of a second time period T2 during which a second beam variation is determined, as will be described below.

Based on the tracking of the one or more downlink beams 502a, 502b,..., 502n during the off- durations of the discontinuous reception mode, the processing device 100 selects at least one downlink beam among the one or more downlink beams 502a, 502b,..., 502n in step 608. The selected downlink beam may e.g. be the downlink beam among the one or more downlink beams 502a, 502b,..., 502n with the highest radio signal quality, or one of the downlink beams with a radio signal quality above a preconfigured threshold which indicates a sufficient beam quality. In embodiments where a radio signal quality metric is determined for each of the one or more downlink beams 502a, 502b,..., 502n in step 606, the selection in step 608 may be based on these radio signal quality metrics. However, the invention is not limited to this approach, instead any known method to select a downlink beam based on information gathered during the tracking of downlink beams may be used.

The downlink beam selected in step 608 may be used by the processing device 100 in the next on-duration as serving downlink beam. Hence, the processing device 100 may in step 610 monitor a physical downlink channel associated with the selected serving downlink beam during on-durations of the discontinuous reception mode.

As the movement of the processing device 100 may change with time, the method 600 may be repeated e.g. based on a second time period T2 subsequent to the first time period T1. In such cases, the processing device 100 determines in step 602 a second beam variation associated with the one or more downlink beams 502a, 502b, ..., 502n during a second time period T2 subsequent to the first time period T1 . In a similar way as for the first time period, the second time period T2 may comprise one or more on-durations and off-duration in discontinuous reception mode, as well as time periods where the processing device 100 is operating in continuous reception mode. The second time period T2 may further comprise the first wake-up durations determined in step 604 based on the first beam variation during the first time period T1 .

Furthermore, the second beam variation during the second time period T2 may be determined in a similar way as the first beam variation during the first time period T1 was determined. The second beam variation may hence be based on a variation of a number of selected downlink beams during the second time period T2. As previously described with reference to the determining of the first beam variation in step 602, the first beam variation may be determined based on a variation of the number of receive beams of the selected downlink beams and/or based on a variation of the number of transmit beams of the selected downlink beams. In embodiments where the first beam variation is determined based on the variation of the number of receive beams and transmit beams of selected downlink beams, the processing device 100 may determine the second beam variation in step 602 based only on the variation of the number of receive beams of selected downlink beams.

In step 604, the processing device 100 determines a second beam tracking configuration based on the second beam variation, wherein the second beam tracking configuration comprises a second beam tracking pattern and at least one associated second wake-up duration for tracking the one or more downlink beams 502a, 502b,..., 502n during the off- durations of the discontinuous reception mode. The second beam tracking configuration may be determined in relation to the first beam tracking configuration. For example, if the second beam variation is larger than the first beam variation, an accumulated time period of the second wake-up durations is determined to be longer than the accumulated time of the first wake-up durations. On the other hand, if the second beam variation is smaller than the first beam variation the accumulated time period of the second wake-up durations is determined to be shorter than the accumulated time of the first wake-up durations.

The processing device 100 tracks the one or more downlink beams 502a, 502b,..., 502n according to the second beam tracking configuration in step 606. Based on the tracking in step 606, the processing device 100 further selects at least one downlink beam among the one or more downlink beams 502a, 502b,..., 502n in step 608 e.g. as serving downlink beam, and monitors a physical downlink channel associated with the selected serving downlink beam during on-durations of the discontinuous reception mode in step 610, as previously described.

Further details related to the beam tracking configurations according to embodiments of the invention will now be described with reference to Figs. 6 - 8, which show receive beam tracking outside on-durations in three different scenarios. In all three scenarios, a client device 300 comprising a processing device 100 tracks one or more selected downlink beams in search for a receive beam for a given transmit beam associated with a selected downlink beam that gives the highest SINR or RSRP. To assist the client device 300 in the search for the receive beam with the highest SINR or RSRP, the network access node 400, transmitting the one or more selected downlink beams, transmits SSBs, CSI-RSs, and/or tracking reference signals in the one or more selected downlink beams. In the three scenarios shown in Figs. 6 - 8, the network access node 400 transmits periodic SSBs in SSB bursts. Each SSB burst may comprise a maximum of 64 SSBs. These 64 SSBs are transmitted within a 5 ms duration, and transmitted in different transmit beams. In case the network access node 400 has fewer than 64 transmit beams, the network access node 400 may transmit only a subset of the possible 64 SSBs in an SSB burst. The information about which of the SSBs that are transmitted is known to the client device 300. Each SSB may comprise one primary SS (PSS) symbol, one secondary SS (SSS) symbol and two physical broadcast channel (PBCH) symbols. Since cell ID as well as the selected transmit beam for the selected cell is known to the client device 300, PSS, SSS and at least the PBCH-demodulation reference signals (PBCH-DMRS) are known to the client device 300. Moreover, the client device 300 also knows the periodicity of the SSB and information about which SSB(s) in each SSB burst that are quasi-collocated with the selected transmit beam(s). It is possible that the network access node 400 may transmit SSBs outside the on-duration as shown in Figs. 6 - 8. The client device 300 can wake-up during one or more of such SSB transmissions and perform receive beam tracking. In Figs. 6 - 8, ON indicates that the client device 300 is awake and able to perform tracking, i.e. a radio receiver of the client device 300 is switched on, while OFF indicates the client device 300 is not awake, i.e. in a power saving mode with at least a significant part of its radio receiver switched off. The receive beam tracking can be performed using receive beam sweeping across one or more SSBs corresponding to the selected transmit beam(s). Since one SSB transmitted using one transmit beam, has four different symbols, the client device 300 can test up to four different receive beams per SSB. In the scenarios shown in Figs. 6 - 8 the client device 300 is assumed to have eight different receive beams.

In Fig. 6, it is assumed that the client device 300 has determined that the beam variation is low. The client device 300 has further determined that the beam variation is only associated with receive beams. This implies that the client device 300 is affected by a small rotational movement. Based on the determined low receive beam variation, the client device 300 may determine a beam tracking configuration comprising only one wake-up duration at a time instance where a SSB quasi-collocated with the selected transmit beam is transmitted. Typically, the time instance of the wake-up duration is selected to coincide with the transmission of the last SSB prior to the next on-duration, as shown in Fig. 6. During the wake- up duration the client device 300 has in this case time to check the selected receive beam, as well as three adjacent receive beams, to track the small rotational movement. It is noted that a maximum of four receive beams can be checked for each SSB in some communication systems. If the beam variation is determined to be very small or there is no beam variation, the beam tracking configuration may comprise a beam tracking pattern with no wake-up durations such that no tracking is performed by the client device 300 during off-durations. In this case, the client device 300 can instead rely on monitoring of e.g. the CSI-RS or other reference symbols such as tracking reference symbols or dedicated reference symbols (DMRS) transmitted during on-duration for beam tracking.

In Fig. 7, it is assumed that the client device 300 has determined that the beam variation is moderate. The client device 300 has further determined that the beam variation is only associated with receive beams. This implies that the client device 300 is affected by a moderate rotational movement. Based on the determined moderate receive beam variation, the client device 300 determines a beam tracking configuration comprising two wake-up durations at time instances where SSB quasi-collocated with the selected transmit beam is transmitted. Typically, the time instances of the wake-up durations are selected to coincide with the transmission of the last two SSB prior to the next on-duration, as shown in Fig. 7. During the wake-up durations the client device 300 has in this case time to check the selected receive beam, as well as all other seven receive beams, to track the moderate rotational movement.

In Fig. 8, it is assumed that the client device 300 has determined that the beam variation is high. The client device 300 has further determined that the beam variation is associated with both selected transmit beams and receive beams. This implies that the client device 300 is affected by mobility, i.e. moving. Based on the determined high receive beam variation, the client device 300 determines a beam tracking configuration comprising wake-up durations at each time instance where a SSB quasi-collocated with a transmit beam is transmitted, as shown in Fig. 8. During the wake-up durations the client device 300 has in this case time to check all transmit beams to track the high mobility. 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.