WO2019101287A1

WO2019101287A1 - Method and devices for fast handover in a wireless network

Info

Publication number: WO2019101287A1
Application number: PCT/EP2017/079842
Authority: WO
Inventors: Tao Cai; Kari Juhani Leppanen
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2017-11-21
Filing date: 2017-11-21
Publication date: 2019-05-31

Abstract

A client device is configured to produce beam-specific values of one or more beam locking parameters through beam training with two or more network nodes of a wireless network for locking beams to said two or more network nodes. The client device is configured to update stored values of said beam locking parameters in response to a trigger that comprises a detected movement of the client device and/or a detected rotation of the client device. This is to maintain readiness of beam locking to a target network node among said two or more network nodes. The client device is configured to utilize the updated stored values of beam locking parameters that were stored for beam locking to said target network node to set up a communications connection with said target network node.

Description

METHOD AND DEVICES FOR FAST HANDOVER IN A WIRELESS NETWORK

TECHNICAL FIELD

[0001 ] The invention relates to the field of wireless network communications, and particularly to the utilization of beam locking for a client device towards a network node, which may be a serving network node or a target 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, gNodeB, may be controlling several transmission or reception points, TRPs. Each gNodeB 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 gNodeBs and TRPs may also be called network nodes, fixed 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] Also the UEs are expected to have the capability of directional transmission and reception, i.e. beam forming. The UE forms its beams by using sophisticated hardware and advanced signal processing, for example by tuning the relative phasing of signals going through different antenna elements. When the UE moves and rotates it may become difficult to maintain the best possible connection, because corresponding changes should be made in the signal processing in real time, in order to keep the active beam directed towards the serving network node.

[0004] A method called“beam locking” can be used to mitigate the effect of user node movement and rotation, with the help of internal sensors such as a gyroscope sensor that is capable of sensing rotation. Other sensors that can be involved include but are not limited to a compasses/magnetic sensors, accelerometers, gravity sensors and positioning sensors such as a GPS (Global Positioning System) receiver. In addition to or instead of measurements made with internal sensors the user node can follow the changes in its own orientation through measurements of external signals, e.g. the measurements on the angle of arrival of signals from the network nodes. Prior art describes beam locking as the operation of a calculator: it determines a beamforming parameter for aligning a beam direction with another apparatus by compensating for the change of a beam direction that resulted from movement and rotation of the device.

SUMMARY

[0005] It is an object of the invention to provide a client device and a network node that are capable of performing a fast handover of a communications connection from a source network node to a target network node when the client device has beam locking capability. It is also an object of the invention to provide methods for execution of the client device and network nodes that are in the role of a target or source network node for the client device.

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

[0007] According to a first aspect, a client device is provided. The client device is configured to produce beam- specific values of one or more beam locking parameters through beam training with two or more network nodes of a wireless network for locking beams to said two or more network nodes. The client device is also configured to update stored values of said beam locking parameters in response to a trigger that comprises at least one of: a detected movement of the client device, and a detected rotation of the client device, to maintain readiness of beam locking to a target network node among said two or more network nodes. The client device is also configured to utilize the updated stored values of beam locking parameters that were stored for beam locking to said target network node to set up a communications connection with said target network node.

[0008] In a first possible implementation form of the client device according to the first aspect the client device is configured to measure amounts of at least one of: detected movement of the client device, detected rotation of the client device; and configured to update stored values of said beam locking parameters as a response to the measured amount of at least one of detected movement or detected rotation of the client device exceeding a predetermined threshold. This involves the advantage that client device may utilize for example built-in sensors that are available in the client device, so that little or no changes are required to the detection hardware of the client device.

[0009] In a further implementation form of the first aspect, the client device is configured to perform said beam training with said target network node while maintaining a communications connection with another of said two or more network nodes. This involves the advantage that maintaining the virtual beam locking does not cause disruptions to the ongoing communications.

[001 0] In a further implementation form of the first aspect, the client device is configured to perform said beam training simultaneously with maintaining said communications connection through use of a multiple beam capability of the client device. This involves the advantage that no delays are caused to the ongoing communications.

[001 1 ] In a further implementation form of the first aspect, the client device is configured to perform said beam training interleaved in time with said communications connection. This involves the advantage that maintaining the virtual beam locking can be made even with relative simple devices.

[001 2] In a further implementation form of the first aspect, the client device is configured to perform said beam training according to a beam training command or schedule that the client device received from one of said two or more network nodes. This involves the advantage that the network has control over the actions that the client device performs with respect to beam training.

[001 3] In a further implementation form of the first aspect, the client device is configured to send to one of said two or more network nodes information descriptive of said stored values of beam locking parameters. This involves the advantage that the network nodes may utilize information created by the client device and store it for further use.

[001 4] In a further implementation form of the first aspect, the client device comprises a position detector configured to detect movements of the client device for performing said updating of said stored values of said beam locking parameters to maintain readiness of beam locking to said target network node. In particular, the client device may be configured to utilize position readings produced by said position detector and to detect changes in the position readings that take place over time in order to detect movements of the client device. This involves the advantage that the full capability of the client device regarding position detection, which may serve other purposes in the operation of the client device, is also available for virtual beam locking.

[001 5] In a further implementation form of the first aspect, the client device comprises a rotation detector configured to detect rotations of the client device for performing said updating of said stored values of said beam locking parameters to maintain readiness of beam locking to said target network node. In particular, the client device may be configured to utilize rotation readings produced by said rotation detector and to detect rotation readings that deviate sufficiently from zero in order to detect movements of the client device. This involves the advantage that the full capability of the client device regarding rotation detection, which may serve other purposes in the operation of the client device, is also available for virtual beam locking.

[001 6] In a further implementation form of the first aspect, the client device comprises a detector of at least one of: phases, strengths, angles of arrival of received signals; and configured to utilize readings given by said detector to detect at least one of: movements of the client device, rotations of the client device for performing said updating of said stored values of said beam locking parameters to maintain readiness of beam locking to said target network node. This involves the advantage that virtual beam locking can be done even without dedicated sensors, and/or that the accuracy of detecting movements and/or rotations can be enhanced over what could be achieved with dedicated sensors alone.

[001 7] According to a second aspect, a network device is provided and configured to act in the role of a target network node. The network device is configured to produce, through beam training with such a client device of a wireless network for which the network device is currently a target network node, values of one or more beam forming parameters. The network device is also configured to update said stored values of beam forming parameters in preparation of a subsequent change to being a serving network node for said client device. The network device is also configured to utilize the updated stored values of beam forming parameters that were stored with respect to said client device, to set up a communications connection with said client device.

[001 8] In a first possible implementation form of the network device according to the second aspect the network device is configured to perform said beam training with said client device again after a predetermined time interval while the network device is still a target network node for said client device. This involves the advantage that a state of readiness can be maintained in the target network node.

[001 9] In a further implementation form the network device is configured to receive from said client device information descriptive of values of beam locking parameters that the client device stored, and to formulate said initial values of said beam forming parameters at least partly on the basis of such received information. This involves the advantage that the accuracy of formulating the beam forming parameters is improved.

[0020] In a further implementation form the network device is configured to receive from the wireless network copies of payload data that another network device is to transmit to said client device and to transmit said copies of payload data to the client device in preparation for said subsequent change to being a serving network node for said client device. This involves the advantage that a more versatile way can be utilized for preparing a handover.

[0021 ] According to a third aspect, a network device is provided and configured to act in the role of a source network node. The network device is configured to receive, from a client device for which the network device is currently a serving network node, information descriptive of values of beam locking parameters that the client device stored for beam locking to an other network device that is currently a target network node for said client device, and to send to said client device and to said other network device a command to set up a communications connection with each other, based on said received information.

[0022] According to a fourth aspect, there is provided method that a client device can execute. The method comprises producing in a client device beam- specific values of one or more beam locking parameters through beam training with two or more network nodes of a wireless network for locking beams to said two or more network nodes. The method comprises also updating stored values of said beam locking parameters in response to a trigger that comprises at least one of: a detected movement of the client device, and a detected rotation of the client device, thus maintaining readiness of beam locking to a target network node among said two or more network nodes. The method comprises also utilizing the updated stored values of beam locking parameters that were stored for beam locking to said target network node to set up a communications connection with said target network node.

[0023] According to a fifth aspect, there is provided a method that a target network device

- or a combination of network devices that constitute the target of a handover - can execute. The method comprises producing in a network device, through beam training with such a client device of a wireless network for which the network device is currently a target network node, values of one or more beam forming parameters. The method comprises also updating said stored values of beam forming parameters in preparation of a subsequent change to being a serving network node for said client device. The method comprises also utilizing the updated stored values of beam forming parameters that were stored with respect to said client device, to set up a communications connection with said client device.

[0024] According to a sixth aspect, there is provided a method that a source network device

- or a combination of network devices that constitute a source network node - can execute. The method comprises receiving in a network device, from a client device for which the network device is currently a serving network node, information descriptive of values of beam locking parameters that the client device stored for beam locking to an other network device that is currently a target network node for said client device. The method comprises also sending to said client device and to said other network device a command to set up a communications connection with each other, based on said received information.

[0025] According to a seventh aspect, there is provided a computer program comprising one or more series of one or more computer executable instructions that, when executed by one or more processors, are configured to cause the performing of at least one method of the kind described above. 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.

[0026] These and other aspects of the invention will be apparent from the enclosed figures and the embodiments described below.

BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 illustrates storing, updating, and utilizing values.

[0028] Figure 2 illustrates a client device and two network nodes.

[0029] Figure 3 illustrates a client device and two network nodes.

[0030] Figure 4 illustrates a client device and two network nodes.

[0031 ] Figure 5 illustrates a temporal order of beam training and communications.

[0032] Figure 6 illustrates a temporal order of beam training and communications.

[0033] Figure 7 illustrates an embodiment of handover.

[0034] Figure 8 illustrates an embodiment of handover.

[0035] Figure 9 illustrates a client device.

[0036] Figure 10 illustrates a transceiver.

DETAIFED DESCRIPTION

[0037] In this text, network devices may be referred to as a serving network nodes, source network nodes, and target network nodes. These designations refer to the roles of the respective network devices with respect to the communications they have with a particular client device. A serving network node is a network device with which the client device has currently an active communications connection, irrespective of whether a handover is actual or not. The concepts of source and target network nodes refer to a handover situation, in which the network device called the source network node is the serving network node before the handover. The network device called the target network node becomes the serving network node after the handover. [0038] Figure 1 is a schematic illustration of producing, updating and utilizing values of one or more beam locking parameters, and can be interpreted as a kind of state machine. A state machine representation is a way of describing, how a programmable device is configured to operate. A state machine representation is typically a simplification of the actual way in which the device operates, because the state machine is assumed to be capable of being in exactly one of a finite number of states at any given time, and to perform sharp transitions between such states. Many programmable devices, particularly devices equipped for multitasking, can be said to actually perform tasks related to two or more states simultaneously, and to make transitions between states to a varying extent. Despite its simplicity the state machine representation is nevertheless a practical way of explaining some features of interest in the operation of the device.

[0039] In this case the programmable device may be a client device of a wireless network, and in particular a client device that has beam forming capability. In other words, the client device is capable of using one or more antenna elements and the associated signal processing means to direct wireless communications in one or more well-defined spatial directions called beams, and also capable of changing the direction(s) of said beam(s) in the local coordinate system defined by the physical structure of the client device. The client device can determine the relation between the local coordinate system and an external coordinate system (defined by the physical structure of the fixed network nodes), through measuring the downlink reference signals transmitted by the network nodes; or through receiving information sent from the network node to the client device about the network nodes’ measurements on the uplink reference signals transmitted by the client device. The external coordinate system may be called a global coordinate system.

[0040] State 101 corresponds to storing beam- specific values of one or more beam locking parameters for locking beams to two or more network nodes of a wireless network. The beam locking parameters may comprise for example the gain and/or phasing to be applied in a number of signal processing branches coupled to a number of antenna elements in order to direct a beam into a particular direction in the local coordinate system. Additionally or alternatively the beam locking parameters may comprise some parameters from which such gain and phasing to be applied in a number of signal processing branches can be derived or calculated.

[0041 ] State 102 corresponds to updating stored values of beam locking parameters of the kind explained above. Updating in accordance with state 102 may take place in response to a trigger 103, which in the state machine representation of Figure 1 causes a transition from state 101 to state 102. The trigger 103 may comprise for example a detected movement of the client device and/or a detected rotation of the client device.

[0042] Exactly how much movement and/or rotation must be detected in order to create a trigger 103 may be defined by programming the client device. One possibility is to trigger a transition to state 102 each and every time when any movement or rotation, no matter how little, was detected. Such an alternative involves the advantage of making the updating procedure as sensitive and accurate as possible. Another possibility is to configure the client device to measure amounts of detected movement and/or rotation of the client device, and to update the stored values of beam locking parameters as a response to the measured amount of detected movement and/or rotation of the client device exceeding a predetermined first threshold. Such an alternative involves the advantage of enabling the optimization of the use of calculating resources in the client device, as well as enabling dynamic changes in sensitivity simply by changing the value of said first threshold.

[0043] The purpose of updating the stored values of beam locking parameters in accordance with state 102 is to maintain readiness of beam locking to a target network node among the two or more network nodes mentioned above. A target network node is one that is not currently a serving network node of the client device but might become one in a near future. In other words, the client device does not have an active communications connection with the target network node, because the active communications between the client device and the wireless network take place between the client device and its current serving network node. However, it may happen that the communications connection with the current serving network node is not the best possible any more, or that for some other reasons it will be considered more advantageous to take one of those network nodes that are currently just target network nodes, and make such a taken network node the new serving network node.

[0044] Maintaining readiness of beam locking to a target network node can be called virtual beam locking. Contrary to the actual beam locking that can be performed for a beam that actually exists and is utilized in the currently active communications connection with the serving network node, virtual beam locking does not result (yet) in actually forming any beam. The client device just maintains up-to-date knowledge of what kind of values the beam locking parameters should have, if an actual beam should really be set up for communications with the network node that for the time being is only a target network node. Completing the updating operation at state 102, meaning that the updated values for the beam locking parameters have been calculated, causes a transition 104 back to state 101 in the state machine representation of Figure 1.

[0045] State 105, which can be actual simultaneously with state 101, represents utilizing the updated stored values of beam locking parameters for beam locking to a network node. As long as there are no changes to the serving network node, state 105 represents utilizing the values of beam locking parameters to locking the actual beam to the serving network node. However, if a handover to a target network node becomes actual, state 103 represents utilizing the updated stored values of beam locking parameters that were stored for beam locking to the target network node to set up a communications connection with the target network node. In other words, at that moment the previously maintained virtual beam locking is converted into actual beam locking.

[0046] Because the client device maintained also the virtual beam locking in states 101 and 102, setting up an actual beam that points accurately towards the selected target network node at state 105 is fast. The client device and the target network node do not need to perform any separate beam training procedure at this moment in order to make the client device capable of accurately setting up the appropriate beam, which saves time and radio resources and thus enhances the user experience of the user of the client device, while simultaneously helping to optimize the network performance as a whole.

[0047] State 106 in Figure 1 represents producing beam- specific values of one or more beam locking parameters through beam training. Such producing of values is advantageous every time when, for some reason or another, the client device does not yet have any values for the beam locking parameters, as illustrated by condition 107. Producing beam- specific values of beam locking parameters in accordance with state 106 is also advantageous if, for some reason or another, just updating previously stored values in accordance with state 102 is not possible anymore and/or does not produce updated values that would be reliable enough.

[0048] The transition 108 from state 101 to state 106 is indicated in Figure 1 as taking place in response to a timeout. Indeed, one reason for considering it impossible or at least not advantageous to just update previously stored values as in state 102 may be that a predetermined maximum time has expired since the last round of beam training. If, for example, the updating at state 102 has been based on detected movements and/or detected rotations of the client device, it can be assumed that some random error may have accumulated in the updated values over time because the movements or rotations cannot be detected at 100% accuracy. In addition to or in place of a timeout, the transition from state 101 to state 106 may also take place because of some other reason. For example, updating the stored values of beam locking parameters at state 102 may have failed because a random error occurred in the execution of an algorithm. Yet another reason may be that the amount of detected movement and/or rotation may have exceeded a predetermined second threshold that is higher than the (possibly used) first threshold mentioned earlier.

[0049] As illustrated by state 106 of Figure 1, the beam training is performed with two or more network nodes of the wireless network, for locking beams to said two or more network nodes. One of these two or more network nodes may be the serving network node, while at least one other is a target network node so that the beam training performed with it results in just virtually locking one or more beams to such a target network node. The client device may form an actual beam towards such a target network node for the duration of a beam training period. Such a formed actual beam does not, however, make that network node change roles from a target network node to a serving network node, because the formed actual beam is only used for beam training purposes and not for data communications purposes. When the beam training is complete, a transition 109 to state 101 takes place.

[0050] Typically the loop consisting of states and transitions 101, 103, 102, and 104 is circulated more often than the loop consisting of states and transitions 101, 108, 106, and 109 in Figure 1. This means that the client device is capable of maintaining relatively reliable values of beam locking parameters, for both actual and virtual beam locking, through updating in accordance with state 102 for relatively long periods before it must perform a new round of beam training in accordance with state 106.

[0051 ] Figures 2, 3, and 4 illustrate in more detail the difference between actual beam locking and virtual beam locking. In Figure 2 the client device 200 utilizes a properly directed beam 201 for active communications with a first network node 202 of a wireless network. The first network node 202 is thus currently the serving network node. In order to establish and properly direct the beam 201 the client device 200 has previously performed beam training with the first network node 202, thus producing a first set 203 of beam- specific values for one or more beam locking parameters. As an illustrative example, it may be assumed that the direction of the beam 201 is towards direction (xl, yl, zl) in a local (Cartesian) coordinate system of the client device. Here xl, yl, and zl are coefficients of a set of mutually orthogonal unit vectors defined in said local coordinate system of the client device. Thus a triplet like (xl, yl, zl) can be used to unambiguously indicate a direction in said local coordinate system. Directions in the local coordinate system can be expressed differently, in particular if some other kind of local coordinate system is used. For example in a polar coordinate system a tuplet like (theta 1, phil) can indicate a direction, so that the first value indicates an elevation angle and the second value indicates an azimuth angle. Angles are defined in relation to the corresponding reference directions of the coordinate system.

[0052] There is a second network node 204, which is currently a target network node. Thus the client device 200 does not currently have any active communications connection with the second network node 204. However, it has previously performed beam training also with the second network node 204, thus producing a second set 205 of beam- specific values for one or more beam locking parameters. These values would enable the client device 200 to set up a properly directed beam 206 for active communications with the second network node 204, if needed. However, the beam 206 in Figure 2 does not actually exist, it has been drawn only to show that the client device 200 would know how to set it up. The direction in which the beam 206 would point, if the beam would actually exist, would be (x2, y2, z2) in the local coordinate system of the client device, where x2, y2, and z2 are another set of coefficients for the mutually orthogonal unit vectors in said local coordinate system.

[0053] Between Figures 2 and 3 the client device 200 undergoes a rotation. It uses a rotation detector to detect the amount and direction of rotation. For the purpose of the present example it may be assumed that the detected rotation was +A degrees around an axis, the direction of which is (i, j, k) in said local coordinate system, where A is a real number and i, j, and k are a set of coefficients for the mutually orthogonal unit vectors in said local coordinate system.

[0054] In Figure 3 the first network node 202 is still the serving network node, with which the client device 200 maintains an active communications connection. In order to keep the corresponding beam directed towards the first network node 202, the client device has updated the first set of beam-specific values of the one or more beam locking parameters. The updated first set of beam-specific values is shown with the reference designator 303 to emphasize that they are not (necessarily) the same values as before the updating. The updated first set 303 of beam-specific values defines a beam direction (cG, yl’, zl’) which was obtained from the direction (xl, yl, zl) by rotating it by -A degrees around the axis direction (i, j, k) in said local coordinate system. Thus the amount and direction by which the beam that is locked to the first network node 202 was rotated exactly compensates the detected rotation of the client device itself. Different (i.e. updated) values of the beam locking parameters are used for the beam than in Figure 2, and in the local coordinate system of the client device it points to a different direction, so a reference designator 301 is used for the beam in Figure 3.

[0055] In Figure 3 the second network node 204 is still the target network node, with which the client device does not maintain an active communications connection. In order to maintain virtual beam locking, i.e. to maintain readiness of beam locking to the target network node, also the second set of beam-specific values of one or more beam locking parameters is updated. The updated second set 305 of beam-specific values defines a beam direction (x2’, y2’, z2’) which was obtained from the direction (x2, y2, z2) by rotating it by -A degrees around the axis direction (i, j, k) in said local coordinate system. Thus the amount and direction by which the beam that is virtually locked to the second network node 204 was rotated exactly compensates the detected rotation of the client device itself.

[0056] Between Figures 3 and 4 it is found that routing the active communications between the client device 200 and the wireless network through the second network node 204 would be more beneficial. The client device 200 utilizes the updated second set 305 of beam-specific values for the one or more beam locking parameters to actually set up the beam 306. It also stops using the previously used beam 301 for active communications: it is not needed anymore because the active communications connection is now with the second network node 204. It is possible that a handover back to the first network node 202 becomes actual in the near future, so it may be advantageous to maintain the first network node 202 as a possible target network node. In such a case the client device could maintain virtual beam locking with the first network node 202, as illustrated by the beam 301 and first set 303 of beam- specific values of the beam locking parameters in Figure 4.

[0057] In general, the client device may be configured to perform the beam training with the target network node while maintaining a communications connection with another (i.e. serving) network node. An advantage of such an arrangement is that the user of the client device can experience continuous service even if he or she is using the communications connection for a real-time service.

[0058] The expression“while maintaining” may cover at least two slightly different embodiments. Figure 5 illustrates schematically an embodiment in which the client device is configured to perform the beam training 501 interleaved in time with those intervals 502 of actual communications during which it maintains the beam locking. The beam training 501 may take such a short time each time that the user does not actually notice any interruption even in a real time service. An advantage of a time interleaved arrangement like that of Figure 5 is that the client device does not need to have multiple beam capability, so a simpler client device with lower manufacturing costs may suffice.

[0059] Figure 6 illustrates an embodiment in which the client device is configured to perform the beam training 601 truly simultaneously with maintaining an active communications connection with a (serving) network node. This can be accomplished through the use of a multiple beam capability of the client device. One or more of the beams that the client device is capable of maintaining may be completely dedicated to beam training operations, while the other beams are used for continued communications with a serving network node. Alternatively all beams may be used for communications as a default, and one or more of them may be just intermittently reserved for beam training. An advantage of such a truly simultaneous arrangement is that the user of the client device can certainly experience uninterrupted service even in the most demanding applications of communications.

[0060] In any of the cases explained above the client device may be configured to perform the beam training according to a beam training command or schedule that the client device received from one of the two or more network nodes mentioned earlier. In such an embodiment the network can optimally schedule the moments of beam training with client devices so that the beam training causes as little interference to the actual communications as possible. It may also be advantageous to configure the client device to send to either the serving network node or to the target network node information descriptive of the stored values of the beam locking parameters. This way the network may keep track of how good results the beam training has produced in each client device. The network may use such information for e.g. deciding the target network node to which the client device will be commanded to do a handover.

[0061 ] Figure 7 illustrates some communications between and some actions within a client device 200 and two network devices 202 and 204, one of which is a source network node while the other is a target network node. These designations refer in particular to the roles that the network devices have in the beginning of the procedure shown in Figure 7.

[0062] The client device exchanges payload data transmissions with the serving network node through an active communications connection as illustrated by step 701. Step 702 is an example of a case in which the client device receives a beam training command or schedule from one of the network nodes; here from the serving network node. The client device may be configured to perform the subsequent instances of beam training according to the beam training command or schedule that it receives at step 702.

[0063] At step 703 the source network node 202 transmits downlink reference signals, and at step 704 the target network node 204 transmits downlink reference signals. The client device receives at least some of these reference signals and uses them to perform beam training at step 705. The beam training at step 705 results in values of beam locking parameters for at least one actual beam towards the source network node, as well as for at least one virtual beam towards the target network node.

[0064] At step 706 the client device sends, to one of the network nodes, information descriptive of the stored values of beam locking parameters. In Figure 7 this transmission goes to the source network node 202, and it may contain information descriptive of values of beam locking parameters that the client device stored for beam locking to an other network device that is currently a target network node 204 for the client device 200. The transmission is called an uplink report in Figure 7, and it may contain also other kinds of information that the client device is obliged to report to the wireless network. The client device may make similar transmissions also to other network nodes. Additionally or alternatively the client device may transmit so-called pilot signals or uplink reference signals to network nodes that are not currently serving network nodes of the client device. An example of such a transmission is shown at step 707 in Figure 7.

[0065] Step 708 represents a period of time during which the source network node 202 is still the serving network node, but the client device 200 maintains virtual beam locking also for a virtual beam that would be directed towards the target network node 204. Thus step 708 may comprise updating the stored values of the beam locking parameters in response to any trigger that occurs while the client device still has an active communications connection with the source network node 202. Such updating is performed to maintain readiness of beam locking to at least the target network node 204, but the client device 200 may maintain virtual beam locking to also other possible target nodes. To emphasize that the source network node 202 is still the serving network node at this stage, Figure 7 illustrates a further step of exchanging payload data transmissions with the source network node at step 709.

[0066] Although the practice of virtual beam locking has been explained above primarily as a feature of a client device, also network nodes may be capable of similar operations. Since network devices do not typically move or rotate, the term virtual beam forming is used instead of virtual beam locking. In Figure 7 the target network node 204 has such capability. It is configured to produce, through beam training with such a device of a wireless network for which the network device is currently a target network node, values of one or more beam forming parameters. Such beam forming parameters may be produced for example on the basis of the uplink reference signals or other transmissions that the target network node 204 received from the client device at step 707. The step of producing the values of the beam forming parameters is shown as step 710 in Figure 7.

[0067] The transmission from the client device 200 to the target network node 204 at step 707 may contain also information descriptive of values that the client device stored. In such a case the target network node 204 may be configured to formulate the initial values of its beam forming parameters at least partly on the basis of such received information.

[0068] Multiple rounds of receiving uplink reference signals or similar transmissions from a client device for which the target network node 204 is not currently a serving network node may take place. Thus steps 707 and 710 may be performed repeatedly. This way the target network device 204 is configured to update the stored values of beam forming parameters in preparation of a subsequent change to being a serving network node for the client device.

[0069] At step 711 the source network node transmits to the client device a command to perform a handover. An alternative definition of the command is a command to set up a communications connection with the target network device 204, and it may be based on the information that the source network node received in the uplink report transmission at step 706. The command at step 711 may contain information about the intended handover, such as for example an indication of the target network node that should become the new serving network node for the client device. In the embodiment of Figure 7 the source network node 202 transmits also to the target network node 204 a command to set up a communications connection with this particular client device. This transmission is shown as step 712 in Figure 7.

[0070] At step 713 a handover is performed, in which the target network node 204 becomes the new serving network node for the client device 200. At least the client device 200 utilizes the updated stored values of beam locking parameters that were stored for beam locking to the target network node 204 to set up a communications connection with the target network node 204. If, like in Figure 7, also the target node 204 stored and updated beam forming parameters with respect to the client device 200, it may use them in performing its part of setting up the communications connection with the client device 200. After the handover payload data can be exchanged in transmissions between the client device 200 and the target network node 204, which has thus now become the serving network node, as illustrates by step 714 in Figure 7.

[0071 ] In an embodiment the network devices may not practice beam forming towards arbitrary directions but only beam switching. This means that the network device maintains a number of beams constantly directed into fixed directions, and only selects - for each client device for which the network device is a serving network node - the beam that provides the best performance. This is mostly synonymous with selecting for each client device the beam that points most accurately towards the direction of the client device. In such a case the virtual beam forming step 710 of Figure 7 may mean virtually designating that client device as a user of a particular beam. Such a virtual designation does not use any physical radio resources, but represents a preparatory measure that may speed up the setting up of an actual communications connection if and when it becomes actual.

[0072] Figure 8 illustrates an embodiment in which some of the physical radio resources of the possible target network node(s) are reserved for transmitting copies of such payload data to the client device that primarily still go through the serving network node. Up to step

806 the steps in Figure 8 are similar to the correspondingly numbered steps in Figure 7. Figure 8 does not explicitly show the client device 200 transmitting uplink pilot signals or the like to the target network node 204 like in step 707 of Figure 7, but that - and the subsequent step of virtual beam forming at the target network node 204 - is not excluded in the embodiment of Figure 8. Maintaining readiness of beam locking to a (number of) target node(s) through updating the stored values of beam locking parameters takes place at step

807 of Figure 8, in the same way as in step 708 of Figure 7.

[0073] Step 808 in Figure 8 represents the continued exchanging of payload data transmissions between the client device 200 and the source network node 202, which at this stage is still the serving network node. However, the target network node 204 is configured to receive from the wireless network copies of payload data that the source network node is to transmit to the client device. It is also configured to transmit said copies of payload data to the client device in preparation for said subsequent change to being a serving network node for said client device. Such transmissions of copies of downlink payload data are represented by step 809 in Figure 8.

[0074] The client device 200 may be configured to utilize the received copies of downlink payload data from the target network node 204 in various ways. For example, the client device 200 may use them as one input to the process of updating the stored values of beam locking parameters. Additionally the client device may use them to deduce, which of a possible multitude of target network nodes would be the best selection for the new serving network node. The client device 200 may send to the source network node 202 information descriptive of such findings, for use as inputs to an eventual handover decision on the network side.

[0075] Also the target network node 204 may attempt to receive uplink transmissions from the client device 200, even if the target network node 204 is not yet the serving network node. This may help the target network node 204 to update the values of beam forming parameters it has stored with respect of this particular client device.

[0076] In the embodiment of Figure 8 it may be sufficient that the source network node 202 transmits the handover command to only the client device 200, as illustrated by step 810 in Figure 8. This is because the possible target network node(s) are already transmitting copies of downlink payload data to the client device 200: the handover at step 811 will then mainly consist of the client device 200 choosing, which of those target network nodes it wants to select that had been transmitting said copies of downlink payload data. The choice may be left to the responsibility of the client device 200, or the choice may be dictated by the wireless network in the handover command at step 810. After the handover the target network node 204 becomes the new serving network node, as illustrated by the step 812 of exchanging payload data transmissions with the client device 200.

[0077] Figure 9 is a schematic block diagram of a client device 200 according to an embodiment. The operation of the client device is controlled by one or more processors 901 that execute machine-readable instructions stored in one or more memories 902 in the form of program code. Wireless communications between the client device and network nodes of the wireless network go through a connectivity block 903, 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 904 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.

[0078] A positioning block 905 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 906 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 907 gives the client device the capability of recording visual information, such as still images and video. A display block 908 gives the client device the capability of displaying visual information to its user. It may also include touch screen control functions that give the client device the capability of receiving touch commands from the user. A power block 909 comprises the components and functions that are necessary for providing operating power to the parts of the client device that need it.

[0079] Receiving signals transmitted by the network nodes of a wireless network, to which the client device should be able to lock its beams, takes place through the mobile wireless part 910 of the connectivity block 903. Producing beam-specific values of beam locking parameters, updating stored values of such beam locking parameters, and utilizing the updated stored values of beam locking parameters may involve operations of at least the processor(s) 901, the memory 902, and the connectivity block 903. 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 9, but also producing and storing in memory 902 the machine-readable instructions that the processor(s) 901 may execute and thus make the client device perform the operations described above.

[0080] The client device 200 may comprise a position detector configured to detect movements of the client device for performing the updating of stored values of beam locking parameters. In the schematic representation of Figure 9 the position detector may comprise, and/or involve at least parts of, the global positioning unit 911, the local (indoor) positioning unit 912, the acceleration sensor 913, and/or the proximity sensor 914.

[0081 ] The client device 200 may comprise a rotation detector configured to detect rotations of the client device for performing the updating of stored values of beam locking parameters. In the schematic representation of Figure 9 the rotation detector may comprise, and/or involve at least parts of, the gyroscopic sensor 915, the magnetic compass 916, and/or the acceleration sensor 913.

[0082] A position detector and a rotation detector were mentioned above as examples of detectors, the readings of which may help the client device to decide, how the stored beam- specific values of beam locking parameters should be updated. Also other kinds of detectors may be used for similar purposes. The client device may comprise for example a detector of phases, strengths, and/or angles of arrival of received signals. Detected changes in this kind of quantities may reveal, what kind of changes have taken place in the directions (as defined in the local coordinate system of the client device) between the client device and its nearest network nodes. The client device may be configured to utilize readings given by such detectors to detect movements and/or rotations of the client device, for performing the updating of the stored values of the (virtual) beam locking parameters to maintain readiness of beam locking to the target network node.

[0083] Figure 10 is a schematic illustration of some hardware parts of an example of a mobile wireless part 910 of a client device. A number of controllable switches, filters, and phasing elements 1001 couple an array of antenna elements 1002 to the reception and transmission branch amplifiers 1003 and 1004. A further array of controllable switches, mixers, and filters 1005 couple the amplifiers 1003 and 1004 to reception and transmission baseband blocks 1006 and 1007. These are further coupled to a connectivity processor 1008, from which there are further couplings to the applications processor(s) of the client device. The connectivity processor 1008 uses a reception branch controller 1009 to control the operation of the reception chain, and a corresponding transmission branch controller 1010 to control the operation of the transmission chain.

[0084] In the schematic approach shown in Figure 10 the values of beam locking parameters may be values stored in (or within the easy reach of) the connectivity processor 1008, which uses the stored values to control the phasing on the various signal propagation paths to and from different antenna elements in block 1001.

[0085] A network device according to an embodiment may have a wireless transmitting and receiving entity that resembles that of Figure 10, so that in an analogous manner the values of beam forming parameters may be values stored in (or within the easy reach of) a connectivity processor, which uses the stored values to control the phasing on the various signal propagation paths to and from different antenna elements of the network node.

[0086] The connectivity processor and the applications processor(s) of either a client device or a network node are programmable circuits. They operate by executing a computer program that consists of one or more sets of one or more machine-readable instructions. Such machine-readable instructions can be stored on a tangible memory medium that is a part of or provided within the reach of the corresponding processor. Computer program embodiments of the kind explained above a referred to the appended claims are such sets of machine-readable instructions that are stored on such tangible memory media. [0087] 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.

[0088] 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.

[0089] 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 present invention.

Claims

1. A client device, configured to:

produce beam- specific values of one or more beam locking parameters through beam training with two or more network nodes of a wireless network for locking beams to said two or more network nodes,

update stored values of said beam locking parameters in response to a trigger that comprises at least one of: a detected movement of the client device, and a detected rotation of the client device, to maintain readiness of beam locking to a target network node among said two or more network nodes, and

utilize the updated stored values of beam locking parameters that were stored for beam locking to said target network node to set up a communications connection with said target network node.

2. The client device of claim 1, configured to measure amounts of at least one of: detected movement of the client device, detected rotation of the client device; and configured to update stored values of said beam locking parameters as a response to the measured amount of at least one of detected movement or detected rotation of the client device exceeding a predetermined threshold.

3. The client device of claim 1 or 2, configured to perform said beam training with said target network node while maintaining a communications connection with another of said two or more network nodes.

4. The client device of claim 3, configured to perform said beam training simultaneously with maintaining said communications connection through use of a multiple beam capability of the client device.

5. The client device of claim 3 or 4, configured to perform said beam training interleaved in time with said communications connection.

6. The client device of any of claims 3 to 5, configured to perform said beam training according to a beam training command or schedule that the client device received from one of said two or more network nodes.

7. The client device of any of the preceding claims, configured to send to one of said two or more network nodes information descriptive of said stored values of beam locking parameters.

8. The client device of any of the preceding claims, comprising a position detector configured to detect movements of the client device for performing said updating of said stored values of said beam locking parameters to maintain readiness of beam locking to said target network node.

9. The client device of any of the preceding claims, comprising a rotation detector configured to detect rotations of the client device for performing said updating of said stored values of said beam locking parameters to maintain readiness of beam locking to said target network node.

10. The client device of any of the preceding claims, comprising a detector of at least one of: phases, strengths, angles of arrival of received signals; and configured to utilize readings given by said detector to detect at least one of: movements of the client device, rotations of the client device for performing said updating of said stored values of said beam locking parameters to maintain readiness of beam locking to said target network node.

11. A network device configured to operate as target network node, and configured to:

produce, through beam training with such a client device of a wireless network for which the network device is currently a target network node, values of one or more beam forming parameters,

update said stored values of beam forming parameters in preparation of a subsequent change to being a serving network node for said client device, and

utilize the updated stored values of beam forming parameters that were stored with respect to said client device, to set up a communications connection with said client device.

12. The network device of claim 11, configured to perform said beam training with said client device again after a predetermined time interval while the network device is still a target network node for said client device.

13. The network device of any of claims 11 or 12, configured to receive from said client device information descriptive of values of beam locking parameters that the client device stored, and to formulate said initial values of said beam forming parameters at least partly on the basis of such received information.

14. The network device of any of claims 11 to 13, configured to receive from the wireless network copies of payload data that another network device is to transmit to said client device and to transmit said copies of payload data to the client device in preparation for said subsequent change to being a serving network node for said client device.

15. A network device configured to operate as a serving network node, and configured to

receive, from a client device for which the network device is currently a serving network node, information descriptive of values of beam locking parameters that the client device stored for beam locking to an other network device that is currently a target network node for said client device, and

send to said client device and to said other network device a command to set up a communications connection with each other, based on said received information.

16. A method, comprising

producing in a client device beam- specific values of one or more beam locking parameters through beam training with two or more network nodes of a wireless network for locking beams to said two or more network nodes,

updating stored values of said beam locking parameters in response to a trigger that comprises at least one of: a detected movement of the client device, and a detected rotation of the client device, thus maintaining readiness of beam locking to a target network node among said two or more network nodes, and

utilizing the updated stored values of beam locking parameters that were stored for beam locking to said target network node to set up a communications connection with said target network node.

17. A method, comprising:

producing in a network device, through beam training with such a client device of a wireless network for which the network device is currently a target network node, values of one or more beam forming parameters,

updating said stored values of beam forming parameters in preparation of a subsequent change to being a serving network node for said client device, and utilizing the updated stored values of beam forming parameters that were stored with respect to said client device, to set up a communications connection with said client device.

18. A method, comprising

receiving in a network device, from a client device for which the network device is currently a serving network node, information descriptive of values of beam locking parameters that the client device stored for beam locking to an other network device that is currently a target network node for said client device, and

sending to said client device and to said other network device a command to set up a communications connection with each other, based on said received information.

19. A computer program comprising program code configured to perform a method according to any of claims 16, 17, or 18 when the computer program is executed on a computer.