Patent Publication Number: US-2023147090-A1

Title: Network node triggered mobility measurment reporting

Description:
TECHNICAL FIELD 
     Embodiments presented herein relate to a method, a network node, a computer program, and a computer program product for triggering mobility measurements. Embodiments presented herein further relate to a method, a User Equipment (UE), a computer program, and a computer program product for performing network node triggered mobility measurement reporting. 
     BACKGROUND 
     In communication networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed. 
     For example, densification via the deployment of more and more base stations (be them macro or micro base stations) is one of the mechanisms that can be employed to increase bandwidth/capacity in a communication network. Due to the current availability of more spectrum in the millimeter wave (mmw) frequency band, deploying small cells that operate in this frequency band is one deployment option for this purpose. However, deploying optical fiber links, or other types of cables, to the small cells, which is the usual way in which small cells are deployed, can end up being both expensive and impractical. Employing wireless links for connecting the small cells to the core network might be both cheaper and more practical. One such option is Integrated Access and Backhaul (IAB) networks, where part of the radio resources can be utilized for backhaul purposes (i.e., for communication between two IAB nodes). 
     However, there could be situations where issues arise when handover of a UE is needed from one network node to another network node. 
     It would be desirable to provide new ways to address one or more of the abovementioned issues. 
     SUMMARY 
     An object of embodiments herein is to address one or more of the issues noted above. 
     According to a first aspect there is presented a method for triggering mobility measurements. The method is performed by a network node. The method comprises obtaining information about backhaul link quality of a wireless backhaul link of the network node. The method comprises, as a result thereof, sending, to at least a subset of all UEs served by the network node in a cell, an indication for the subset of UEs to perform mobility measurements. The method comprises receiving mobility measurement reports from the subset of UEs. The method comprises determining a handover action for the subset of UEs based at least on the backhaul link quality and on the mobility measurement reports. 
     According to a second aspect there is presented a network node for triggering mobility measurements. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to obtain information about backhaul link quality of a wireless backhaul link of the network node. The processing circuitry is configured to cause the network node to, as a result thereof, send, to at least a subset of all UEs served by the network node in a cell, an indication for the subset of UEs to perform mobility measurements. The processing circuitry is configured to cause the network node to receive mobility measurement reports from the subset of UEs. The processing circuitry is configured to cause the network node to determine a handover action for the subset of UEs based at least on the backhaul link quality and on the mobility measurement reports. 
     According to a third aspect there is presented a network node for triggering mobility measurements. The network node comprises an obtain module configured to obtain information about backhaul link quality of a wireless backhaul link of the network node. The network node comprises a send module configured to, as a result thereof, send, to at least a subset of all user equipment, UEs, served by the network node in a cell, an indication for the subset of UEs to perform mobility measurements. The network node comprises a receive module configured to receive mobility measurement reports from the subset of UEs. The network node comprises a determine module configured to determine a handover action for the subset of UEs based at least on the backhaul link quality and on the mobility measurement reports. 
     According to a fourth aspect there is presented a computer program for triggering mobility measurements. The computer program comprises computer program code which, when run on processing circuitry of a network node, causes the network node to perform a method according to the first aspect. 
     According to a fifth aspect there is presented a method for performing network node triggered mobility measurement reporting. The method is performed by a UE. The method comprises receiving, from a network node serving the UE in a cell, an indication to perform network node triggered mobility measurements. The method comprises, in response thereto, performing mobility measurements on reference signals received from at least one other network node. The method comprises sending a mobility report of the mobility measurements to the network node serving the UE. 
     According to a sixth aspect there is presented a UE for performing network node triggered mobility measurement reporting. The UE comprises processing circuitry. The processing circuitry is configured to cause the UE to receive, from a network node serving the UE in a cell, an indication to perform network node triggered mobility measurements. The processing circuitry is configured to cause the UE to, in response thereto, perform mobility measurements on reference signals received from at least one other network node. The processing circuitry is configured to cause the UE to send a mobility report of the mobility measurements to the network node serving the UE. 
     According to a seventh aspect there is presented a UE for performing network node triggered mobility measurement reporting. The UE comprises a receive module configured to receive, from a network node serving the UE in a cell, an indication to perform network node triggered mobility measurements. The UE comprises a measure module configured to, in response thereto, perform mobility measurements on reference signals received from at least one other network node. The UE comprises a send module configured to send a mobility report of the mobility measurements to the network node serving the UE. 
     According to an eight aspect there is presented a computer program for performing network node triggered mobility measurement reporting, the computer program comprising computer program code which, when run on processing circuitry of a UE, causes the UE to perform a method according to the fifth aspect. 
     According to a ninth aspect there is presented a computer program product comprising a computer program according to at least one of the fourth aspect and the eight aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium. 
     Advantageously these methods, these network nodes, these UEs, and these computer programs enable a handover to be timely triggered before the UE experiences radio link failure. 
     Advantageously these methods, these network nodes, these UEs, and these computer programs enable efficient load balancing between network nodes 
     It is to be noted that any feature of the first, second, third, fourth, fifth, sixth seventh, eight, and ninth aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, fourth, fifth, sixth, seventh, eight, and/or ninth aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, module, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which: 
         FIGS.  1  and  2    are schematic diagrams illustrating a communication network according to embodiments; 
         FIGS.  3 ,  4 ,  5 ,  6 ,  7 , and  8    are flowcharts of methods according to embodiments; 
         FIG.  9    is a schematic diagram showing functional units of a network node according to an embodiment; 
         FIG.  10    is a schematic diagram showing functional modules of a network node according to an embodiment; 
         FIG.  11    is a schematic diagram showing functional units of a UE according to an embodiment; 
         FIG.  12    is a schematic diagram showing functional modules of a UE according to an embodiment; and 
         FIG.  13    shows one example of a computer program product comprising computer readable means according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional. 
       FIG.  1    is a schematic diagram illustrating a communication network  100   a  where embodiments presented herein can be applied. The communication network  100   a  comprises network nodes  200   a ,  200   b ,  400   a  that are operatively connected to a core network  110 . Further, network node  200   b  is operatively connected to the core network  110  via network node  200   a  which in turn is operatively connected to the core network  110  via network node  400   a . Further, whereas network node  400   a  has a wired connection to the core network  110 , the communication between network node  400   a  and network node  200   a  as well as between network node  200   a  and network node  200   b  is over wireless backhaul links  120   a ,  120   b.    
     In some aspects, the communication network  100   a  represents an IAB deployment where network node  400   a  acts as a donor node and network nodes  200   a  and  200   b  act as IAB relay nodes or IAB nodes. Further, since network node  200   a  is further upstream (i.e., operatively closer to the core network  110 ) than network node  200   b , network node  200   a  might be regarded as a parent network node to network node  200   b  and network node  200   b  might be regarded as a child network node to network node  200   a.    
     Further, each network node  200   a ,  200   b ,  400   a  provide network access to UEs  300   a ,  300   b ,  300   c ,  300   d  over wireless access links  130   a ,  130   b ,  130   c ,  130   d . The UEs  300   a : 300   c  are thereby enabled to access services and exchange data with a service network (not shown) operatively connected to the core network  110 . Each network node  200   a ,  200   b ,  400   a  could be any of: radio access network node, base station (BS), radio base station (RBS), base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR), radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), integrated access and backhaul (JAB) node, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH). 
     As disclosed above, there could be situations where issues arise when handover of a UE is needed from one network node to another network node. 
     In further detail, currently, all network nodes of the communication network  100   a  are assumed to be static, i.e., to be configured for operation at a fixed geographical location. It is envisioned that a network node might be moved from one location to another. One example of this would be if the network node is mounted on a network providing vehicle, such as a network connected Unmanned Aerial Vehicle (UAV) or the like. This would allow for both flexible and dynamic deployments of communication networks in the sense that the deployment could follow the user distribution, so that if a new hot spot of UEs would appear, the communication network could adjust its deployment in an optimal fashion. 
     When network nodes thus become moving network nodes, existing frameworks for handover would become insufficient due to lacking mobility support. In addition, the existing UE mobility mechanisms for handover and cell re-selection might not be directly applicable for a moving network node. Further on, existing mechanisms for handover are not designed for moving network nodes. 
     One issue is that it is not only the quality of the wireless access link  130   a  between the UE  300   a  and network node  200   a  that should be considered but also the wireless backhaul links  120   a ,  120   b . This is illustrated in  FIG.  2   .  FIG.  2 ( a )  is a schematic diagram illustrating a communication network  100   b  similar to communication network  100   a  but where there are two cells  500   a ,  500   b  with two network nodes in each cell; network nodes  200   a ,  400   a  are in cell  500   a  and network nodes  200   c ,  400   b  are in cell  500   b . Assume that UE  300   a  is served by network node  200   a  over wireless access link  130   a  and that network node  200   a  is to be moved along the direction indicated by arrow  150   a . Assume further that after movement, network node  200   a  will be located as in the communication network  100   c  of  FIG.  2 ( b ) . Since the distance between network node  200   a  and UE  300   a  has changed only very little from  FIG.  2 ( a )  to  FIG.  2 ( b )  it can be assumed that the access link quality of wireless access link  130   a  has not changed. However, the move has caused the distance between network node  200   a  and network node  400   a  to increase, which might cause the backhaul link quality of wireless backhaul link  120   a  to deteriorate. In this respect, the UE  300   a  could use legacy mobility measurements for quality evaluation of its wireless access link(s), including wireless access link(s) of both the serving cell and any neighbouring cells. For example, the UE  300   a  could be supplied with a measurement configuration (e.g., time to trigger, hysteresis setting for handover triggering, etc.). But since the UE  300   a  is only capable of measuring the access link quality of the wireless access links  130   a  and  130   e , the UE  300   a  would not notice deterioration of a backhaul link  120   a  from these configurations and measurements. Eventually, network node  200   a  might discover another network node (not shown) to which it establishes a new wireless backhaul link. But if not handled correctly, this might result in that UE  300   a  experiences a radio link failure (RLF) even though its access link quality has not been affected. The UE  300   a  might be eventually informed of the failure and perform RLF recovery to re-establish a wireless access link. But in cases where the network node  200   a  is moving, it would be too late for the UE  300   a  to be informed via RLF procedure, and data transmission would be interrupted. This could be the case in a network topology adaptation procedure for a migrating IAB node. More details of signalling in such a procedure are described in 3GPP TS 38.401 “NG-RAN; Architecture description”, version 16.0.0, Section 8.2.1.1. If possible, such RLF should be avoided. If the situation is handled timely, the UE  300   a  can perform actions (for example, handover action) before an RLF failure is triggered. 
     The embodiments disclosed herein thus relate to mechanisms for triggering mobility measurements and network node triggered mobility measurement reporting. In order to obtain such mechanisms there is provided a network node  200   a , a method performed by the network node  200   a , a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the network node  200   a , causes the network node  200   a  to perform the method. In order to obtain such mechanisms there is further provided a UE  300   a , a method performed by the UE  300   a , and a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the UE  300   a , causes the UE  300   a  to perform the method. 
     Reference is now made to  FIG.  3    illustrating a method for triggering mobility measurements as performed by the network node  200   a  according to an embodiment. 
     S 102 : The network node  200   a  obtains information about backhaul link quality of a wireless backhaul link of the network node  200   a.    
     S 108 : The network node  200   a , as a result of having obtained the information, sends, to at least a subset of all UEs  300   a  served by the network node  200   a  in a cell  500   a , an indication for the subset of UEs  300   a  to perform mobility measurements. 
     S 110 : The network node  200   a  receives mobility measurement reports from the subset of UEs  300   a.    
     S 112 : The network node  200   a  determines a handover action for the subset of UEs  300   a  based at least on the backhaul link quality and on the mobility measurement reports. 
     Embodiments relating to further details of triggering mobility measurements as performed by the network node  200   a  will now be disclosed. 
     There could be different examples of quality parameters according to which the backhaul link quality is measured. In some examples, the backhaul link quality pertains to at least one of: reference signal received power (RSRP), signal to interference plus noise ratio (SINR), reference signal received quality (RSRQ), received signal strength indicator (RSSI), etc. 
     There could be different wireless backhaul links of the network node  200   a  that information about backhaul link quality is obtained. Different embodiments relating thereto will now be described in turn. 
     In some aspects, the wireless backhaul link is between the network node  200   a  itself and its parent network node. That is, in some embodiments, the network node  200   a  is operatively connected to a parent network node, and the wireless backhaul link is between the network node  200   a  and the parent network node. 
     In some aspects, the wireless backhaul link is further upstream from the network node  200   a . That is, in some embodiments, the network node  200   a  is operatively connected to a parent network node, and the wireless backhaul link is upstream the parent network node (and hence further closer to the wired connection to the core network). 
     There could be different types of information about the backhaul link quality that the network node  200   a  obtains in S 102 . 
     In some aspects, the information pertains to that the backhaul link quality of the wireless backhaul link is deteriorating. Particularly, in some embodiments, the wireless backhaul link is towards a donor node  400   a  of the network node  200   a , and the information about the backhaul link quality pertains to that backhaul link quality of the wireless backhaul link towards the donor node  400   a  is deteriorating. 
     The information that the backhaul link quality is deteriorating might then pertain to at least one of: the backhaul link quality of the wireless backhaul link is below threshold link quality value, the bitrate of the wireless backhaul link is below a threshold bitrate value, the transmission delay of the wireless backhaul link is above a threshold transmission delay value. 
     Further, in this respect, there might be different ways to determine that the backhaul link quality of the wireless backhaul link towards the donor node  400   a  is deteriorating. In some embodiments, the backhaul link quality might be determined to be deteriorating by being worse than a threshold value, by being worse than the backhaul link quality of another wireless backhaul link towards the donor node  400   a , or by being worse than the backhaul link quality of another wireless backhaul link towards another donor node  400   b.    
     In further examples, the backhaul link quality of the wireless backhaul link is determined to be deteriorating when the backhaul link quality has decreased below a configured threshold quality value. The configured threshold quality value might be absolute or relative to a filtered average over a certain time period. In further examples, the backhaul link quality of the wireless backhaul link is determined to be deteriorating when the achieved bitrate on the wireless backhaul link has decreased below a configured threshold bitrate value. The configured threshold bitrate value might be absolute or relative to a filtered average over a certain time period. It might also be relative to the achieved bitrate of wireless backhaul links to any child network nodes or the access interface to the UE  300   a , thereby ensuring that it is the backhaul link quality that is the bottleneck. In further examples, the backhaul link quality of the wireless backhaul link is determined to be deteriorating when the achieved transmission delay on the wireless backhaul link has increased above a configured threshold delay value. The configured threshold delay value might be absolute or relative to a filtered average over a certain time period. 
     There could be different ways for the network node  200   a  to determine to which UEs  300   a  the indication in S 108  should be sent. In some aspect, the decision regarding which of all UEs  300   a  served by the network node  200   a  the indication is sent is based on prior information that the network node  200   a  has access to. For example, to which of all UEs  300   a  served by the network node  200   a  the indication is sent might depend on at least one of: degree of deterioration of the wireless backhaul link, previous measurement reports received from the UEs  300   a  (i.e., measurement reports received before S 108  is performed, such as an ordinary mobility measurement report or a previously trigged mobility measurement report), Quality of Service (QoS) requirements for the UEs  300   a , locations of the UEs  300   a , and UE capability information. 
     Depending on the degree of deterioration of the wireless backhaul link, the indication in S 108  could be sent to different subsets of UEs  300   a . In one extreme case, for example when the performance of the wireless backhaul link is really low, e.g. 10% of its maximum performance, the indication in S 108  could be sent to all UEs  300   a  which have data transported on this wireless backhaul link. In case the performance of the wireless backhaul is only slightly degraded, the indication in S 108  could be sent only to a small subset of the UEs  300   a.    
     There could be different ways for the network node  200   a  to send the indication in S 108 . In some examples, the indication is sent as a single bit, where the value “o” indicates that no mobility measurements are to be performed whereas the value “1” indicates that mobility measurements are to be performed. In some examples, the indication is sent as a flag, where when the flag is set, this indicates that mobility measurements are to be performed and else no mobility measurements are to be performed. In some examples, the indication is sent using more than one bit. The indication might be sent using broadcast signalling to all UEs  300   a  or using dedicated signalling to individual UEs  300   a . In some examples, the indication is sent in any of: a reference signal, a system information block (SIB), a master information block (MIB), radio resource control (RRC) signalling, downlink control information (DCI), a medium access control (MAC) control element, a paging-message. 
     There could be further pieces of information that is sent with the indication in S 108 . In some embodiments, the indication is accompanied by any of: measurement configuration based on which the subset of UEs  300   a  are to perform mobility measurements, identification of the UEs  300   a  in the subset of UEs  300   a , identification of cells and/or carriers/frequencies on which the subset of UEs  300   a  are to perform mobility measurements. 
     In some aspects, the network node  200   a  forwards information as obtained in S 102  to its child network nodes. That is, in some embodiments, where the network node  200   a  is operatively connected to at least one child network node  200   c , the network node  200   a  is configured to perform (optional) step S 104 : 
     S 104 : The network node  200   a  forwards the information (as obtained in S 102 ) towards the at least one child network node  200   c.    
     In some aspects, the network node  200  is made aware of the backhaul link qualities of neighbouring network nodes in the same cell  500   a  or in another cell  500   b . This can be requested and received via the X2 interface or via a donor network node. That is, in some embodiments, the network node  200   a  is configured to perform (optional) step S 106 : 
     S 106 : The network node  200   a  obtains backhaul link quality information of another wireless backhaul link in another cell  500   b  than the cell  500   a  of the network node  200   a.    
     The UEs  300   a  might then be instructed not to measure on neighbouring cell  500   b  with poor backhaul link quality. That is, in some embodiments, when the backhaul link quality information of this another wireless backhaul link indicates that this another wireless backhaul link suffers from deterioration, the indication sent to the subset of UEs  300   a  instructs the subset of UEs  300   a  to refrain from performing mobility measurements on the cell  500   b  of this another wireless backhaul link. 
     In some examples, the network node  200   a  could also obtain backhaul link quality information of another wireless backhaul link of another network node in the same cell  500   a  as the network node  200   a . If the backhaul link quality of the network node  200   a  is worse than the backhaul link quality of this another network node, an indication might be sent by the network node  200   a  for triggering UEs to perform mobility measurements. That is, as a result of having obtained the information, the network node  200   a  might send to at least a subset of all UEs  300   a  served by the network node  200   a  in a cell  500   a , an indication for the subset of UEs  300   a  to perform mobility measurements. 
     There could be different handover actions that are determined in S 112 . Different embodiments relating thereto will now be described in turn. 
     In some embodiments, the handover action involves the subset of UEs  300   a  to be handed over to any cell  500   b  as indicated in the mobility measurement reports providing higher access link quality than a threshold access link quality value. Further details thereof will be disclosed with reference to the flowchart of  FIG.  6   . 
     In some embodiments, the handover action involves the subset of UEs  300   a  to be handed over to any cell  500   b  as indicated in the mobility measurement reports providing combined higher access link quality and higher backhaul link quality than the cell  500   a  of the IAB node  200   a . Further details thereof will be disclosed with reference to the flowchart of  FIG.  7   . 
     In some embodiments, the handover action involves the subset of UEs  300   a  to be handed over to any cell  500   b  as indicated in the mobility measurement reports where minimum of access link quality and backhaul link quality is higher than in the cell  500   a  of the IAB node  200   a . Further details thereof will be disclosed with reference to the flowchart of  FIG.  8   . 
     In some embodiments, the handover action involves the subset of UEs  300   a  to be handed over to any cell  500   b  as indicated in the mobility measurement reports providing combined higher access link quality, higher backhaul link quality, higher bitrate than the cell  500   a  of the network node  200   a . Further details thereof will be disclosed with reference to the flowchart of  FIG.  9   . 
     Once having determined the handover action, the handover action might be provided to at least some of the UEs  300   a  served by the network node  200   a . That is, in some embodiments, the network node  200   a  is configured to perform (optional) step S 114 : 
     S 114 : The network node  200   a  sends a handover command in accordance with the handover action. 
     The handover command might be sent to all, or only some, UEs  300   a  served by the network node  200   a . That is, in some embodiments, the handover command is sent only to a subset of the subset of UEs  300   a.    
     The subset of the subset of UEs  300   a  might be those UEs  300   a  with the worst wireless access links, those UEs  300   a  with worst combined links, and/or those UEs  300   a  requiring, or using, the highest bitrates. 
     Reference is now made to  FIG.  4    illustrating a method for network node triggered mobility measurement reporting as performed by the UE  300   a  according to an embodiment. 
     As disclosed below, the network node  200   a  in S 108  sends an indication for the UE  300   a  to perform mobility measurements. It is assumed that the UE  300   a  receives the indication and thus is configured to perform step S 202 : 
     S 202 : The UE  300   a  receives, from a network node  200   a  serving the UE  300   a  in a cell  500   a , an indication to perform network node triggered mobility measurements. 
     The UE  300   a  then performs mobility measurements accordingly and is thus configured to perform step S 206 : 
     S 206 : The UE  300   a , in response to having received the indication in S 202 , performs mobility measurements on reference signals received from at least one other network node  200   b ,  200   c.    
     In some examples, the mobility measurements could be performed on reference signals such as Synchronization Signal Block (SSB) or Channel State Information Reference signal (CSI-RS). The mobility measurement could relate to quality that pertains to at least one of: reference signal received power (RSRP), signal to interference plus noise ratio (SINR), reference signal received quality (RSRQ), received signal strength indicator (RSSI), etc. As an example, the obtained mobility measurement relates to quality of one or more wireless access links of the UE  300   a , such as quality of the wireless access link  130   a  from the UE  300   a  to the serving network node  200   a , quality of the wireless access link  130   b  from the UE  300   a  to the network node  200   b , and/or quality of the wireless access link  130   e  from the UE  300   a  to the network node  200   c.    
     Upon having performed the mobility measurements, the mobility measurements are reported to the network node  200   a . That is, the UE  300   a  is configured to perform step S 208 : 
     S 208 : The UE  300   a  sends a mobility report of the mobility measurements to the network node  200   a  serving the UE  300   a.    
     Embodiments relating to further details of network node triggered mobility measurement reporting as performed by the UE  300   a  will now be disclosed. 
     In some aspects, the UE  300   a  receives an indication from another cell  500   b  than the cell  500   a  served by the network node  200   a  of backhaul link quality in this other cell  500   b . In particular, in some embodiments, the UE  300   a  is configured to perform (optional) step S 204 : 
     S 204 : The UE  300   a  receives, from a network node  200   d  of another cell  500   b , information of deteriorating backhaul link quality of a wireless backhaul link in this another cell  500   b.    
     The UE  300   a  then in S 206  refrains from performing mobility measurements on reference signals (such as SSB or CSI-RS) received from any network nodes  200   d  of this another cell  500   b.    
     As disclosed above, in some embodiments the network node  200   a  sends a handover command in accordance with a determined handover action. As further disclosed above, the handover command might be sent to all, or only some, UEs  300   a  served by the network node  200   a . In some aspects, it is thus assumed that the UE  300   a  receives the handover command. That is, in some embodiments, the UE  300   a  is configured to perform (optional) step S 210 : 
     S 210 : The UE  300   a  receives a handover command from the network node  200   a  serving the UE. The handover command is dependent on backhaul link quality of a wireless backhaul link in the cell  500   a  and on the mobility measurement report. 
     The UE  300   a  might then act according to the received handover command. That is, in some embodiments, the UE  300   a  is configured to perform (optional) step S 212 : 
     S 212 : The UE  300   a  performs a handover according to the handover command. 
     Non-limiting examples of handover of the UE  300   a  will now be disclosed. 
     In one case, for a UE  300  in RRC IDLE mode or RRC INACTIVE mode, the cell selection, or cell reselection, procedure might be improved so that the UE  300   a  selects, or reselects, a cell with best wireless access link and best wireless backhaul links. 
     In another case, the UE might improve its RRC connection reestablishment procedure. During an RRC connection reestablishment procedure, the UE  300   a  might select a cell with best wireless access link and best wireless backhaul links to reestablish its RRC connection. 
     In yet another case, a condition handover (CHO) procedure is example. The serving network node  200   a  might configure the UE  300   a  with multiple CHO candidates. 
     Each such CHO candidate is then associated with certain trigger conditions. One or multiple trigger conditions related to wireless backhaul links could be configured for each CHO candidate. 
     In yet another case, for a UE  300   a  configured with multiple wireless access links, data split, or data flow mapping, might be performed based on the information as received in S 202 . The data or flows on the wireless access links with the indication could be remapped to other wireless access links without the indication. 
     For any above case, a joint consideration of both wireless backhaul links and wireless access link could be configured for the UE  300   a.    
     Further examples of handover actions according to which the handover is to be performed have been disclosed below and apply equally here. 
     As disclosed above, there could be different ways for the network node  200   a  to send the indication in S 108 . The UE  300   a  might thus receive the indication in s 102  in the corresponding ways. That is, in some examples, the indication is received in any of: a reference signal, a SIB, a MIB, RRC signalling, DCI, a MAC control element, a paging-message. 
     As disclosed above, there could be further pieces of information that is sent with the indication in S 108 . The UE  300   a  might thus receive the corresponding further pieces of information. That is, in some embodiments, the indication is accompanied by any of: measurement configuration based on which the UE  300   a  is to perform mobility measurements, identification of the UE  300   a , identification of cells and/or carriers/frequencies on which the UE  300   a  is to perform mobility measurements. 
     As disclosed above, the UE  300   a  might be instructed not to measure on neighbouring cell  500   b  with poor backhaul link quality. That is, in some embodiments, the indication instructs the UE  300   a  to refrain from performing mobility measurements on at least one other cell  500   b  than the cell  500   a  of the network node  200   a.    
     Four particular embodiments for triggering mobility measurements based on at least some of the above disclosed embodiments will now be disclosed. In general terms, when the backhaul link quality of a wireless backhaul link drops below a threshold quality value, an indication is sent to all or a subset of UEs for which this wireless backhaul link is utilized. Upon reception of the reports of mobility measurements from the UEs, the network node  200   a  checks if there are other network nodes with sufficient access link quality. The network node  200   a  may then send handover commands to all or a subset of the UEs to a ensure optimal performance. 
     A first particular embodiment for triggering mobility measurements based on at least some of the above disclosed embodiments will now be disclosed in detail with reference to the flowchart of  FIG.  5   . 
     In this embodiment, whether to perform handover or not is based on fixed thresholds. 
     S 301 : The network node  200   a  obtains information about backhaul (BH) link quality of a wireless backhaul link of the network node  200   a.    
     S 302 : The network node  200   a  checks if the backhaul link quality of the wireless backhaul link is below threshold link quality value. If yes, step S 303  is entered, and else step S 301  is entered again. 
     S 303 : The network node  200   a  sends to at least a subset of all UEs  300   a  served by the network node  200   a , an indication for the subset of UEs  300   a  to perform mobility measurements. 
     S 304 : The UEs  300   a  having received the indication perform mobility measurements on reference signals received from at least one other network IAB node  200   c  of a neighbouring cell “c”  500   b.    
     S 305 : The UEs  300   a  send a mobility report of the mobility measurements to the network node  200   a  serving the UEs  300   a.    
     S 306 : The network node  200   a , for each received mobility report and for each UE  300   a  having reported a mobility report, checks if the UE  300   a  has reported any neighbouring cell “c”  500   b  providing higher access link quality than a threshold access link quality value. If yes, step S 307  is entered, and else no further action is taken. 
     S 307 : The network node  200   a  determines to handover the UEs  300   a  to a network node of the neighbouring cell “c”  500   b  identified in S 306  and sends a corresponding handover command to the UEs  300   a.    
     A second particular embodiment for triggering mobility measurements based on at least some of the above disclosed embodiments will now be disclosed in detail with reference to the flowchart of  FIG.  6   . 
     In this embodiment, whether to perform handover or not is based on a combination of measurements of the wireless access link and the wireless backhaul link of the serving network node and any network nodes in a neighbouring cell  500   b.    
     S 401 : The network node  200   a  obtains information about backhaul link quality of a wireless backhaul link of the network node  200   a.    
     S 402 : The network node  200   a  checks if the backhaul link quality of the wireless backhaul link is below threshold link quality value. If yes, step S 303  is entered, and else step S 401  is entered again. 
     S 403 : The network node  200   a  sends to at least a subset of all UEs  300   a  served by the network node  200   a , an indication for the subset of UEs  300   a  to perform mobility measurements. 
     S 404 : The UEs  300   a  having received the indication perform mobility measurements on reference signals received from at least one other network IAB node  200   c  of a neighbouring cell  500   b.    
     S 405 : The UEs  300   a  send a mobility report of the mobility measurements to the network node  200   a  serving the UEs  300   a.    
     S 406 : The network node  200   a , for each received mobility report and for each UE  300   a  having reported a mobility report, checks if the UE  300   a  has reported any neighbouring cell  500   b  providing combined higher access link quality and higher backhaul link quality than the cell serving cell  500   a . If yes, step S 407  is entered, and else no further action is taken. 
     S 407 : The network node  200   a  determines to handover the UEs  300   a  to a network node of the neighbouring cell identified in S 406  and sends a corresponding handover command to the UEs  300   a.    
     The access link quality and backhaul link quality might be considered with respect to either available bitrate or maximum bitrate. 
     A third particular embodiment for triggering mobility measurements based on at least some of the above disclosed embodiments will now be disclosed in detail with reference to the flowchart of  FIG.  7   . 
     In this embodiment, whether to perform handover or not is based on checking if there are any neighbouring cell  500   b  that has a minimum of the backhaul link quality and the access link quality that is higher than for the serving cell  500   a.    
     S 501 : The network node  200   a  obtains information about backhaul link quality of a wireless backhaul link of the network node  200   a.    
     S 502 : The network node  200   a  checks if the backhaul link quality of the wireless backhaul link is below threshold link quality value. If yes, step S 303  is entered, and else step S 501  is entered again. 
     S 503 : The network node  200   a  sends to at least a subset of all UEs  300   a  served by the network node  200   a , an indication for the subset of UEs  300   a  to perform mobility measurements. 
     S 504 : The UEs  300   a  having received the indication perform mobility measurements on reference signals received from at least one other network IAB node  200   c  of a neighbouring cell  500   b.    
     S 505 : The UEs  300   a  send a mobility report of the mobility measurements to the network node  200   a  serving the UEs  300   a.    
     S 506 : The network node  200   a , for each received mobility report and for each UE  300   a  having reported a mobility report, checks if the UE  300   a  has reported any neighbouring cell  500   b  where the minimum of access link quality and backhaul link quality is higher than in the serving cell  500   a . If yes, step S 507  is entered, and else no further action is taken. 
     S 507 : The network node  200   a  determines to handover the UEs  300   a  to a network node of the neighbouring cell identified in S 506  and sends a corresponding handover command to the UEs  300   a.    
     A fourth particular embodiment for triggering mobility measurements based on at least some of the above disclosed embodiments will now be disclosed in detail with reference to the flowchart of  FIG.  8   . 
     In this embodiment, whether to perform handover or not is based on maintaining a stable and efficient load on the different network nodes even when the backhaul link quality of one wireless backhaul link is deteriorating. Here, the network node  200   a  determine which network node each UE  300   a  should be connected to based on a comparison of backhaul link quality of network nodes in neighbouring cells  500   b , combined with the access link quality, and additionally, combined with the UEs used bitrate. This enables the network node  200   a  to perform load balancing by handing over of some UEs  300   a  to network nodes of neighbouring cells  500   a  where the UE  300   a  has acceptable access link quality and where the backhaul link quality is better than that of the network node  200   a.    
     S 601 : The network node  200   a  obtains information about backhaul link quality of a wireless backhaul link of the network node  200   a.    
     S 602 : The network node  200   a  checks if the backhaul link quality of the wireless backhaul link is below threshold link quality value. If yes, step S 303  is entered, and else step S 601  is entered again. 
     S 603 : The network node  200   a  sends to at least a subset of all UEs  300   a  served by the network node  200   a , an indication for the subset of UEs  300   a  to perform mobility measurements. 
     S 604 : The UEs  300   a  having received the indication perform mobility measurements on reference signals received from at least one other network IAB node  200   c  of a neighbouring cell  500   b.    
     S 605 : The UEs  300   a  send a mobility report of the mobility measurements to the network node  200   a  serving the UEs  300   a.    
     S 606 : The network node  200   a , for each received mobility report and for each UE  300   a  having reported a mobility report, checks if the UE  300   a  has reported any neighbouring any cell  500   b  providing higher access link quality than the serving cell  500   a . If yes, step S 607  is entered, and else no further action is taken. 
     S 607 : The network node  200   a , for each received mobility report and for each UE  300   a  having reported a mobility report, checks if the UE  300   a  has reported any neighbouring any cell  500   b  providing higher backhaul link quality than the serving cell  500   a . If yes, step S 608  is entered, and else no further action is taken. 
     S 608 : The network node  200   a  determines to handover the UEs  300   a  to a network node of the neighbouring cell identified in S 607  and sends a corresponding handover command to the UEs  300   a.    
       FIG.  9    schematically illustrates, in terms of a number of functional units, the components of a network node  200   a  according to an embodiment. Processing circuitry  210  is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product  1410   a  (as in  FIG.  13   ), e.g. in the form of a storage medium  230 . The processing circuitry  210  may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). 
     Particularly, the processing circuitry  210  is configured to cause the network node  200   a  to perform a set of operations, or steps, as disclosed above. For example, the storage medium  230  may store the set of operations, and the processing circuitry  210  may be configured to retrieve the set of operations from the storage medium  230  to cause the network node  200   a  to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry  210  is thereby arranged to execute methods as herein disclosed. 
     The storage medium  230  may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. 
     The network node  200   a  may further comprise a communications interface  220  for communications with other entities, functions, nodes and devices, as in  FIG.  1    and  FIG.  2   . As such the communications interface  220  may comprise one or more transmitters and receivers, comprising analogue and digital components. 
     The processing circuitry  210  controls the general operation of the network node  200   a  e.g. by sending data and control signals to the communications interface  220  and the storage medium  230 , by receiving data and reports from the communications interface  220 , and by retrieving data and instructions from the storage medium  230 . Other components, as well as the related functionality, of the network node  200   a  are omitted in order not to obscure the concepts presented herein. 
       FIG.  10    schematically illustrates, in terms of a number of functional modules, the components of a network node  200   a  according to an embodiment. The network node  200   a  of  FIG.  10    comprises a number of functional modules; an obtain module  210   a  configured to perform step S 102 , a send module  210   d  configured to perform step S 108 , a receive module  210   e  configured to perform step S 110 , and a determine module  210   f  configured to perform step S 112 . The network node  200   a  of  FIG.  10    may further comprise a number of optional functional modules, such as any of a forward module  210   b  configured to perform step S 104 , an obtain module  210   c  configured to perform step S 106 , and a send module  210   g  configured to perform step S 114 . 
     In general terms, each functional module  210   a - 210   g  may be implemented in hardware or in software. Preferably, one or more or all functional modules  210   a - 210   g  may be implemented by the processing circuitry  210 , possibly in cooperation with the communications interface  220  and/or the storage medium  230 . The processing circuitry  210  may thus be arranged to from the storage medium  230  fetch instructions as provided by a functional module  210   a - 210   g  and to execute these instructions, thereby performing any steps of the network node  200   a  as disclosed herein. 
     The network node  200   a  may be provided as a standalone device or as a part of at least one further device. For example, the network node  200   a  may be provided in a node of the radio access network or in a node of the core network. Alternatively, functionality of the network node  200   a  may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as the radio access network or the core network) or may be spread between at least two such network parts. In general terms, instructions that are required to be performed in real time may be performed in a device, or node, operatively closer to the cell than instructions that are not required to be performed in real time. 
     Thus, a first portion of the instructions performed by the network node  200   a  may be executed in a first device, and a second portion of the instructions performed by the network node  200   a  may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the network node  200   a  may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a network node  200   a  residing in a cloud computational environment. Therefore, although a single processing circuitry  210  is illustrated in  FIG.  9    the processing circuitry  210  may be distributed among a plurality of devices, or nodes. The same applies to the functional modules  210   a - 210   g  of  FIG.  10    and the computer program  1420   a  of  FIG.  13   . 
       FIG.  11    schematically illustrates, in terms of a number of functional units, the components of a UE  300   a  according to an embodiment. Processing circuitry  310  is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product  1410   b  (as in  FIG.  13   ), e.g. in the form of a storage medium  330 . The processing circuitry  310  may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). 
     Particularly, the processing circuitry  310  is configured to cause the UE  300   a  to perform a set of operations, or steps, as disclosed above. For example, the storage medium  330  may store the set of operations, and the processing circuitry  310  may be configured to retrieve the set of operations from the storage medium  330  to cause the UE  300   a  to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry  310  is thereby arranged to execute methods as herein disclosed. 
     The storage medium  330  may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. 
     The UE  300   a  may further comprise a communications interface  320  for communications with other entities, functions, nodes and devices, as in  FIG.  1    and  FIG.  2   . As such the communications interface  320  may comprise one or more transmitters and receivers, comprising analogue and digital components. 
     The processing circuitry  310  controls the general operation of the UE  300   a  e.g. by sending data and control signals to the communications interface  320  and the storage medium  330 , by receiving data and reports from the communications interface  320 , and by retrieving data and instructions from the storage medium  330 . Other components, as well as the related functionality, of the UE  300   a  are omitted in order not to obscure the concepts presented herein. 
       FIG.  12    schematically illustrates, in terms of a number of functional modules, the components of a UE  300   a  according to an embodiment. The UE  300   a  of  FIG.  12    comprises a number of functional modules; a receive module  310   a  configured to perform step S 202 , a measure module  310   c  configured to perform step S 206 , and a send module  310   d  configured to perform step S 208 . The UE  300   a  of  FIG.  12    may further comprise a number of optional functional modules, such as any of a receive module  310   b  configured to perform step S 204 , a receive module  310   e  configured to perform step S 210 , and a handover (HO) module  310   f  configured to perform step S 112 . In general terms, each functional module  310   a - 310   f  may be implemented in hardware or in software. Preferably, one or more or all functional modules  310   a - 310   f  may be implemented by the processing circuitry  310 , possibly in cooperation with the communications interface  320  and/or the storage medium  330 . The processing circuitry  310  may thus be arranged to from the storage medium  330  fetch instructions as provided by a functional module  310   a - 310   f  and to execute these instructions, thereby performing any steps of the UE  300   a  as disclosed herein. 
       FIG.  13    shows one example of a computer program product  1410   a ,  1410   b  comprising computer readable means  1430 . On this computer readable means  1430 , a computer program  1420   a  can be stored, which computer program  1420   a  can cause the processing circuitry  210  and thereto operatively coupled entities and devices, such as the communications interface  220  and the storage medium  230 , to execute methods according to embodiments described herein. The computer program  1420   a  and/or computer program product  1410   a  may thus provide means for performing any steps of the network node  200   a  as herein disclosed. On this computer readable means  1430 , a computer program  1420   b  can be stored, which computer program  1420   b  can cause the processing circuitry  310  and thereto operatively coupled entities and devices, such as the communications interface  320  and the storage medium  330 , to execute methods according to embodiments described herein. The computer program  1420   b  and/or computer program product  1410   b  may thus provide means for performing any steps of the UE  300   a  as herein disclosed. 
     In the example of  FIG.  13   , the computer program product  1410   a ,  1410   b  is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product  1410   a ,  1410   b  could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program  1420   a ,  1420   b  is here schematically shown as a track on the depicted optical disk, the computer program  1420   a ,  1420   b  can be stored in any way which is suitable for the computer program product  1410   a ,  1410   b.    
     The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.