WO2013112082A1

WO2013112082A1 - A network node, a low power radio base station and methods therein for controlling resource distribution

Info

Publication number: WO2013112082A1
Application number: PCT/SE2012/050075
Authority: WO
Inventors: Lars Klockar; Fredric Kronestedt
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2012-01-26
Filing date: 2012-01-26
Publication date: 2013-08-01

Abstract

A network node (400), a low power radio base station, RBS (500), and respective methods therein for controlling resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs are provided. By collecting measurement reports from UEs being located within the area, clusters of low power RBS(s) and macro RBS(s) are created. A traffic load or traffic distribution within the clusters when testing different offsets affecting cell borders of the low power RBS(s) are estimated. Then offset(s) are selected for the low power RBS(s) in the clusters so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s); and the cell borders of the low power RBS(s) are adjusted by the selected offsets.

Description

A NETWORK NODE, A LOW POWER RADIO BASE STATION AND METHODS THEREIN FOR CONTROLLING RESOURCE DISTRIBUTION

Technical field

[0001 ] The present disclosure relates to traffic distribution control and in particular to controlling resource distribution between macro radio base stations and low power radio base stations.

Background

[0002] A radio access network of a wireless or cellular communication network comprises a plurality of radio base stations, RBSs, distributed over an area. The area may be a region, a city, a country or several countries. Generally, each RBS is associated with a coverage area which is commonly referred to as a cell.

[0003] In a wireless or cellular communication network, users having user equipments may move around causing the traffic load in each cell or RBS to vary over time. As a result, some RBSs may experience very heavy traffic loads at certain times.

[0004] The geography of a wireless or cellular communication network may vary from cell to cell and also within a cell. For example, in a city there may be building of different heights and sizes, there may be roads or streets of different sizes and constitutions from cell to cell and also within a single cell.

[0005] Due to the variations in traffic loads over time, there may be certain areas, e.g. within a cell, which suffer from either a traffic load exceeding the capacity of the RBS of that cell, e.g. due to a large number of users at these certain areas. Due to the variations in geography, there may be certain areas, e.g. within a cell, which suffer from poor coverage, e.g. due to radio shadow caused by a building or the like.

[0006] One way to cope with these problems and to be able to provide services to users to the largest extent possible, low power RBSs are employed. A low power RBS is a RBS which has substantially lower transmit power than a regular RBS. A regular RBS is also referred to as a macro RBS. A low power RBS has a much smaller coverage area, or cell, than a macro RBS due to its reduced transmit power. The cell of a macro RBS is also referred to as a macro cell and the cell of a low power RBS is also referred to as a low power cell. A low power RBS are also referred to as a micro, pico, femto RBS depending on its transmit power. The plurality of macro RBSs and the low power RBSs may have whole or partly overlapping coverage areas. Often, a low power RBS may be placed within the coverage area of a macro RBS. The deployment of macro RBSs and low power RBSs are also called Heterogeneous network deployment or HetNet.

[0007] The HetNet deployment may also be used to handle a large traffic growth wherein low power RBS are added to increase capacity of the radio access network of the wireless or cellular communication network. The HetNet

deployment may also be used to extend network coverage to areas with no macro coverage. The output power from the small cells is typically several times smaller compared to the macro cells and this difference creates an imbalance between the uplink and downlink. A network with a large difference in output power among the cells will have different optimum cell borders for uplink and downlink as indicated in Figure 1 . Figure 1 is a schematic illustration of a macro radio base station and a low power radio base station.

[0008] Figure 1 illustrates a low power RBS 102 having a coverage area, or cell, indicated by a dotted oval. The coverage area, or cell border is determined by the received power of reference signals measured by user equipments, UEs, being located within or in proximity to the coverage area of the low power RBS. By applying an offset to the measured received power in the UEs, it is possible to extend the coverage area of the low power RBS as is illustrated in figure 1 by the whole oval encompassing the low power RBS 102. This is also known as cell expansion. A UE does not select to connect to the macro RBS until the difference in the received power of the reference signal between the macro RBS and the low power RBS is greater than the selected offset. Figure 1 also illustrates a macro RBS 101 which has a coverage area which is not illustrated in figure 1 but it is assumed that the macro cell encompasses the low power cell. [0009] Quite simplified, without cell expansion, it can be said that UEs being located within the low power cell will be provided with service from the low power RBS 102 and the UEs located outside the low power cell but within the macro cell will be provided with service from the macro RBS 101. By cell expansion, UEs located within the area between the dotted oval and the whole oval in figure will be provided with service from the low power RBS 102. This will result in a reduced load of the macro RBS 101 as compared to not employing cell expansion. The area between the dotted oval and the whole oval in figure 1 is also referred to as a extended region.

[00010] When coverage is extended with offsets for low power cells, it will create downlink areas with very poor performance, UEs in the extended region will no longer be connected to the strongest server in downlink. This poor downlink performance will also limit the uplink performance if the performance for the downlink control channels gets too bad. One way to combat this downlink degradation is to coordinate the resource usage between the small cells and the overlapping macro cell. This can either be done with a traditional frequency reuse pattern or by using more advanced 3GPP features as evolved Inter Cell

Interference Cancellation, elCIC. However, all these schemes will reduce the downlink capacity for the macro cell and if a major part of the traffic is allocated to the macro RBS it means that the total system capacity will be reduced in downlink.

Summary

[0001 1 ] The object is to obviate at least some of the problems outlined above. In particular, it is an object to provide a network node, a low power RBS and a respective method performed therein for controlling resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs, wherein offset(s) are selected for the low power RBS(s) so that the traffic load of the macro RBS(s) is reduced without overloading the low power RBS(s). These objects and others may be obtained by providing a network node and a low power RBS as well as a method in a network node and a method in a low power RBS according to the independent claims attached below.

[00012] According to an aspect a method in a network node in a wireless communication network for controlling resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs is provided. The method comprises collecting measurement reports from UEs being located within the area. The method further comprises creating clusters of low power RBS(s) and macro RBS(s) based on the collected measurement reports, wherein each cluster comprises one macro RBS and at least one low power RBS; and estimating a traffic load or traffic distribution within the clusters for the macro RBS and the low power RBS(s) when testing different offsets affecting cell borders of the low power RBS(s) based on the collected measurement reports. The method further comprises selecting offset(s) from the tested offsets for the low power RBS(s) in the clusters based on the estimated traffic load or traffic distribution within the clusters, which offsets are selected so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s); and adjusting the cell borders of the low power RBS(s) by the selected offsets.

[00013] According to an aspect, a method in a low power RBS in a wireless communication network for controlling resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs is provided. The method comprises collecting measurement reports from UEs currently being connected to the low power RBS, and forwarding the collected measurement reports to a network node in the wireless communication network.

[00014] According to an aspect, a network node in a wireless communication network adapted to control resource distribution within an area comprising at least one macro Radio Base Station, RBS, and a plurality of low power RBSs is provided. The network node comprises a collecting unit adapted to collect measurement reports from UEs being located within the area. The network node also comprises a creating unit adapted to create clusters of low power RBS(s) and macro RBS(s) based on the collected measurement reports, wherein each cluster comprises one macro RBS and at least one low power RBS. Further, the network node comprises an estimating unit adapted to estimate a traffic load or traffic distribution within the clusters for the macro RBS and the low power RBS(s) when testing different offsets affecting cell borders of the low power RBS(s) based on the collected measurement reports. The network node further comprises a selecting unit adapted to select offset(s) from the tested offsets for the low power RBS(s) in the clusters based on the estimated traffic load within the clusters, which offsets are selected so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s), and an adjusting unit adapted to adjust the cell borders of the low power RBS(s) by the selected offsets.

[00015] According to an aspect, a low power RBS in a wireless communication network adapted to control resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs is provided. The low power RBS comprises a collecting unit adapted to collect measurement reports from UEs currently being connected to the low power RBS; and a forwarding unit adapted to forward the collected measurement reports to a network node in the wireless communication network.

[00016] The network node, the low power radio base station and the respective method therein have several advantages. One advantage is that the service (bitrate) coverage and capacity may be optimized and maximized to take network characteristics, such as propagation effects and traffic distributions, into account in a scenario where macro cells are complemented with small cells. The downlink capacity of the macro RBS may not be reduced. Since the traffic load of the macro RBS is minimised, the total system capacity will be maximised in downlink.

Brief description of drawings

[00017] Embodiments will now be described in more detail in relation to the accompanying drawings, in which:

[00018] Figure 1 is a schematic illustration of a macro radio base station and a low power radio base station. [00019] Figure 2 is a flowchart of a method in a network node in a wireless communication network for controlling resource distribution according to an exemplifying embodiment.

[00020] Figure 3 is a flowchart of a method in a low power radio base station for controlling resource distribution according to an exemplifying embodiment.

[00021 ] Figure 4 is a block diagram of a network node adapted to control resource distribution according to an exemplifying embodiment.

[00022] Figure 5 is a block diagram of a low power radio base station adapted to control resource distribution according to an exemplifying embodiment.

[00023] Figure 6 is an exemplifying overview of a plurality of low power RBSs and macro RBSs and the interference situation between them.

[00024] Figure 7 is an example of clustering of macro radio base satiations and low power radio base stations.

[00025] Figure 8 is an example of a potential traffic off load from a macro radio base station to low power radio base stations for different offsets.

[00026] Figure 9 is a schematic illustration of an exemplifying network

architecture.

[00027] Figure 10 is a schematic illustration of an exemplifying network architecture.

Detailed description

[00028] Briefly described, exemplifying embodiments of a method in a network node, a method in a low power RBS as well as a network node and a low power RBS are provided for controlling resource distribution within an area comprising at least one macro Radio Base Station, RBS, and a plurality of low power RBSs. In short, clusters of low power RBS(s) and macro RBS(s) are created based on collected measurement reports from UEs; and offset(s) are tested and selected for the low power RBS(s) in the clusters based on estimated traffic load within the clusters. The offsets are selected so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s).

[00029] An exemplifying embodiment of a method in a network node in a wireless communication network for controlling resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs will now be described with reference to figure 2.

[00030] The method comprising collecting 210 measurement reports from UEs being located within the area. The method further comprises creating 220 clusters of low power RBS(s) and macro RBS(s) based on the collected measurement reports, wherein each cluster comprises one macro RBS and at least one low power RBS; and estimating 230 a traffic load or traffic distribution within the clusters for the macro RBS and the low power RBS(s) when testing different offsets affecting cell borders of the low power RBS(s) based on the collected measurement reports. The method further comprises selecting 240 offset(s) from the tested offsets for the low power RBS(s) in the clusters based on the estimated traffic load or traffic distribution within the clusters, which offsets are selected so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s); and adjusting 250 the cell borders of the low power RBS(s) by the selected offsets.

[00031 ] In the above exemplifying embodiment of the method, an area comprises at least one macro RBS and a plurality of low power RBSs. The low power RBSs may by any of a micro, pico, femto, or relay RBS and any mixture between the different types of low power RBSs. Further, in this area, a plurality of UEs are located and each individual UE is connected to one of the at least one macro RBS and the plurality of the low power RBSs. When a UE is connected to an RBS, the UE may be provided with services from the wireless or cellular communication network. There may be UEs present in the area which are not connected to any RBS meaning that they are not making use of any service from the network.

[00032] The connected UEs will receive signalling of some sort from the RBSs to which they are connected and each UE will perform at least one measurement regarding the received strength or quality of the received signalling and report the measurement(s) to the RBS which they are connected to.

[00033] A UE may also receive signalling from neighbouring RBSs to which they are not connected, perform measurements regarding the received strength or quality of the received signalling from those RBSs from which they receive the signalling and send measurement reports to those RBSs too, in addition to the RBS to which each individual UE is connected as is described directly above.

[00034] The method in the network node comprises collecting all these measurement reports from the UEs present in the area in which resource distribution is to be controlled.

[00035] Once the network node has collected all these measurement reports from the UEs, the method comprises creating clusters of low power RBS(s) and macro RBS(s) based on the collected measurement reports. Each cluster will comprise one macro RBS and at least one low power RBS. Generally, there will about be the same amount of clusters as there are number of macro RBSs in the area in which resource distribution is to be controlled. However, there may be macro RBSs which will not be clustered together with any low power RBS, hence there may be fewer clusters than there are macro RBSs.

[00036] The method then comprises estimating a traffic load within the clusters for the macro RBS and the low power RBS(s) when testing different offsets affecting cell borders of the low power RBS(s) based on the collected

measurement reports. This means that for each cluster, different offsets are tested for each low power RBS in that cluster. For each cluster and for each different offset and for each low power RBS, a traffic load or traffic distribution is estimated within the cluster. The traffic load may be measured with regard to the macro RBS for the different offsets for each low power RBS in the cluster.

[00037] The method further comprises selecting offset(s) from the tested offsets for the low power RBS(s) in each respective cluster based on the estimated traffic load or traffic distribution within the clusters. The offsets are selected so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s).

[00038] This means that when an offset is used for a low power RBS, the coverage area or the cell of that low power RBS is increased, in some proportion to the size of the offset, resulting in that potentially more UEs will become served by or connected to that low power RBS. This will result in a reduced traffic load in the macro RBS since those UEs which are located in the extended region, as described in relation to figure 1 , will become served by or connected to the low power RBS instead of the macro RBS.

[00039] The method further comprises adjusting the cell borders of the low power RBS(s) by the selected offsets. This means that the selected offsets are communicated to the low power RBSs. More precisely, for each low power RBS in each of the cluster(s), a selected offset is communicated to that low power RBS.

[00040] Thereby, it is also possible to determine the difference between a current traffic load in the macro RBS and the new reduced traffic load obtained by applying the selected offset(s). This difference may also be determined in percentage which means that it is possible to determine how much of the resources in the macro RBS that may be blanked, i.e. no transmission or transmission with reduced power.

[00041 ] It shall be pointed out that a corresponding negative offset may be applied to the macro RBS, i.e. an offset of the same size but with a negative value for the macro RBS.

[00042] The method described above has several advantages. One advantage is that the service (bitrate) coverage and capacity may be optimized and maximized to take network characteristics, such as propagation effects and traffic

distributions, into account in a scenario where macro cells are complemented with small cells. The downlink capacity of the macro RBS may not be reduced. Since the traffic load of the macro RBS is minimised, the total system capacity will be maximised in downlink. [00043] According to an embodiment, the measurement reports comprise any of Reference Signal Received Power, RSRP, for Long Term Evolution, LTE, wireless communication networks, Received Signal Code Power, RSCP, for Code Division Multiple Access, CDMA, wireless communication networks, or Received Signal Level, RxLev, for Time Division Multiple Access, TDMA, wireless communication networks.

[00044] Different Radio Access Technologies, RATs, employ different types for the UEs to measure the signal strength or signal quality. The signal strength or signal quality is most often measured using pilot signals which are sent from the macro and the low power RBSs to the UEs. Depending on the RAT, the signal strength or signal quality may be measured in different ways. When the RAT employs LTE, the measurement reports from the UEs may comprise RSRP. When the RAT employs CDMA, RSCP may be used to measure the signal strength or signal quality and hence, the measurement reports from the UEs may comprise RSCP. When the RAT employs TDMA, one example of measuring the signal strength or signal quality is RxLev. One example of a RAT employing TDMA is the Global System for Mobile communication, GSM.

[00045] According to still an embodiment, the method further comprises receiving 215, from the low power RBS(s), an indication of their respective capacity usage level, wherein the selection of offsets for the low power RBS(s) in the clusters is based on the indicated capacity usage levels.

[00046] It may be important to ensure that any of the low power RBSs in each cluster is not overloaded, meaning that it gets more UEs connected to it than it can handle due to the cell expansion. It may happen that a low power RBS in a cluster already has almost as many UEs as it can handle, from a capacity point of view, connected to it. In other words the traffic load in the low power cell is close to a maximum of that the low power RBS is design to handle. In case the low power cell is expanded, additional UEs may become connected to the low power RBS which will cause a traffic overload in the low power RBS. Alternatively, the low power RBS may be able to handle a relatively small cell expansion but a larger cell expansion may cause a traffic overload situation in the low power RBS. [00047] By receiving an indication from each of the low power RBSs indicating a current capacity usage level for each respective low power RBS, it is possible for the network node to avoid selecting an offset that would reduce the traffic load from the macro RBS but that would also result in a traffic overload situation in one or more low power RBSs in a cluster comprising the macro RBS. In this manner an optimal distribution may be achieved with regard to minimising the traffic load of the macro RBS without overloading any of the low power RBSs.

[00048] According to yet an embodiment, the network node is a macro RBS.

[00049] In this embodiment, the network node and the macro RBS of each of the clusters are one and the same.

[00050] According to still an embodiment, collecting measurement reports from UEs being located within the area comprises receiving measurement reports from UEs being connected to the macro RBS and receiving measurement reports from UEs being connected to those low power RBS(s) which experience the highest interference from the macro RBS.

[00051 ] In case the macro RBS is the network node in which the method is performed, the macro RBS will collect or receive measurement reports from UEs being connected to the macro RBS. Further, the macro RBS, i.e. the network node, receives measurement reports from UEs being connected to those low power RBS(s) which experience the highest interference from the macro RBS. This means that the low power RBSs in the area in which resource distribution is to be controlled, identify which one macro RBS is causing the highest interference for the respective low power RBSs. The low power RBSs then forward the measurement reports they have received from UEs to the respective macro RBS which causes the highest interference to the respective low power RBSs. In this manner, the macro RBS, i.e. the network node, receives measurement reports from UEs being connected to the macro RBS and the macro RBS receives measurement reports from UEs being connected to those low power RBS(s) which experience the highest interference from the macro RBS. [00052] This further means that the macro RBS, i.e. the network node, creates a cluster comprising itself and those low power RBS(s) which experience the highest interference from the macro RBS. In this manner, for the area in which resource distribution is to be controlled, clusters are created by the macro radio base station, i.e. the network node, the clusters comprising at least one low power RBS and a macro RBS based on the collected measurement reports.

[00053] Thereafter, the macro radio base stations, i.e. the network nodes, in the area in which traffic distribution is to be controlled, estimate a traffic load or traffic distribution within the respective clusters for the respective macro RBS and the low power RBS(s) when testing different offsets affecting cell borders of the low power RBS(s) based on the collected measurement reports. Further, the macro radio base stations, i.e. the network nodes, selects offset(s) from the tested offsets for the low power RBS(s) in the respective clusters based on the estimated traffic load within the respective clusters, which offsets are selected so that the traffic load of the respective macro RBS is reduced without overloading the low power RBS(s). The macro radio base stations, i.e. the network nodes, then adjust the cell borders of the low power RBS(s) by the selected offsets.

[00054] According to an embodiment, the network node is a Radio Network Controller, RNC, or a Base Station Controller, BSC.

[00055] According to still an embodiment, wherein the network node is an

Operation, Maintenance and Administration, OAM, node.

[00056] According to yet an embodiment, collecting measurement reports from UEs being located within the area comprises receiving measurement reports forwarded by the at least one macro RBS and the plurality of low power RBSs.

[00057] In an example, the macro RBSs in the area in which traffic distribution is to be controlled, receive measurement reports from UEs and possibly also from low power RBSs. The macro RBSs forwards the received measurement reports to the RNC or the BSC. Further, the low power RBSs receives measurement reports from UEs which the low power RBSs either forwards a macro RBS, to the RNC or the BSC, or both. In this manner, the RNC or the BSC collects measurement reports from UEs being located within the area in which traffic distribution is to be controlled. Thereafter, the RNC or the BSC creates clusters as having been described above and estimates a traffic load or traffic distribution within the clusters for different offsets, selects offsets and adjust cell borders accordingly as having been described in detail above.

[00058] In an example, measurement reports from UEs are collected in the same manner as measurement reports from UEs are collected by the RNC or the BSC described above. Also in this embodiment, the macro RBSs in the area in which traffic distribution is to be controlled, receive measurement reports from UEs and possibly also from low power RBSs. The macro RBSs forwards the received measurement reports to the OAM node. Further, the low power RBSs receives measurement reports from UEs which the low power RBSs either forwards a macro RBS, to the OAM node, or both. In this manner, the OAM node collects measurement reports from UEs being located within the area in which traffic distribution is to be controlled. Thereafter, the OAM node creates clusters as having been described above and estimates a traffic load or traffic distribution within the clusters for different offsets, selects offsets and adjust cell borders accordingly as having been described in detail above.

[00059] According to an embodiment, the creating of clusters of low power RBS(s) and macro RBS(s) comprises identifying, for each low power RBS, the one macro RBS which causes the most interference for the low power RBS and clustering each respective macro RBS with those low power RBS(s) which are most adversely interfered by the respective macro RBS.

[00060] In case the network node is a macro RBS, the low power RBSs send their received measurement reports from UEs to that specific macro RBS which most adversely interfere with the respective low power RBS. In case the network node is a BSC, RNC or an OAM node, the BSC, RNC or OAM node analyses the collected measurement reports and based on this analysis, identifies for each low power RBS, which specific macro RBS most adversely interferes with the low power RBS. Thereafter, the BSC, RNC or OAM node may create clusters accordingly. Alternatively, the low power RBSs indicate to the BSC, RNC or an OAM node which macro RBS most adversely interfere with the respective low power RBS so that the BSC, RNC or the OAM node may make use of this information when identifying, for each low power RBS, the one macro RBS which causes the most interference for the low power RBS and clustering each respective macro RBS with those low power RBS(s) which are most adversely interfered by the respective macro RBS.

[00061 ] According to an embodiment, the offset(s) for the low power RBS(s), within each cluster, are selected such that the traffic load of the low power RBS(s) are maximised, thereby reducing the traffic load of the macro RBS.

[00062] The network node strives to reduce the traffic load of the macro RBSs in the area in which traffic distribution is to be controlled. In order to reduce the traffic load of the macro RBSs as much as possible, as much traffic as possible should be handled by the low power RBSs, of course without overloading any of the low power RBSs. By selecting the offsets for the low power RBSs after having estimated the a traffic load or traffic distribution within the clusters for the macro RBS and the low power RBS(s) when testing different offsets, the network node is able to select those offsets which will maximize the traffic load of the low power RBS(s), thereby reducing the traffic load of the macro RBS within each cluster.

[00063] Embodiments herein also relate to a method in a low power RBS in a wireless communication network for controlling resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs. Such embodiments will now be described with reference to figure 3, which is is a flowchart of a method in a low power RBS for controlling resource distribution according to an exemplifying embodiment.

[00064] Figure 3 illustrates the method comprising collecting 310 measurement reports from UEs currently being connected to the low power RBS, and forwarding 320 the collected measurement reports to a network node in the wireless communication network.

[00065] The low power RBS receives measurement reports from the UEs which are being connected to the low power RBS. The UEs measure signal strength or signal quality e.g. by receiving pilot signals from the low power RBS. The UEs send measurement reports to the low power RBS providing the low power RBS with the results of the measurements. When the low power RBS receives a measurement report from a UE being connected to the low power RBS, the low power RBS forwards the measurement report to a network node in the wireless communication network. If the network node is a macro RBS, the low power RBS identifies which macro RBS most adversely interfere with the low power RBS and sends the measurement report to that macro RBS. In case the network node is a BSC, RNC or an OAM node, the low power RBS forwards the received

measurement report, or reports, to the BSC, RNC or the OAM node whichever is the network node. Optionally, when the network node is a BSC, RNC or an OAM node, the low power RBS identifies which macro RBS most adversely interfere with the low power RBS and sends an indication to the network node indicating which macro RBS most adversely interfere with the low power RBS.

[00066] This has several advantages. One advantage is that the service (bitrate) coverage and capacity may be optimized and maximized to take network characteristics, such as propagation effects and traffic distributions, into account in a scenario where macro cells are complemented with small cells. The downlink capacity of the macro RBS may not be reduced. Since the traffic load of the macro RBS is minimised, the total system capacity will be maximised in downlink.

[00067] According to an embodiment, the measurement reports comprise any of Reference Signal Received Power, RSRP, for Long Term Evolution, LTE, wireless communication networks, Received Signal Code Power, RSCP, for Code Division Multiple Access, CDMA, wireless communication networks, or Received Signal Level, RxLev, for Time Division Multiple Access, TDMA, wireless communication networks. [00068] Different Radio Access Technologies, RATs, employ different types for the UEs to measure the signal strength or signal quality. The signal strength or signal quality is most often measured using pilot signals which are sent from the macro and low power RBSs to the UEs. Depending on the RAT, the signal strength or signal quality may be measured in different ways. When the RAT employs LTE, the measurement reports from the UEs may comprise RSRP. When the RAT employs CDMA, RSCP may be used to measure the signal strength or signal quality and hence, the measurement reports from the UEs may comprise RSCP. When the RAT employs TDMA, one example of measuring the signal strength or signal quality is RxLev.

[00069] According to still an embodiment, the method further comprises indicating 330 to the network node a capacity usage level in the low power RBS.

[00070] As described above, the low power RBS shall not be overloaded by traffic due to the network node selecting an offset which will expand the coverage area of the low power RBS in such a way that the low power RBS will have to serve more UEs than it can handle. In other words, the coverage area of the low power RBS may not be expanded too much causing a traffic overload situation in the low power RBS due to too many UEs being connected to the low power RBS. In order to enable the network node to select an offset for the low power RBS which will not cause a traffic overload situation in the low power RBS, the low power RBS indicates to the network node a current capacity usage level in the low power RBS.

[00071 ] According to an embodiment, the network node is a macro RBS, the method comprising identifying which macro RBS that causes the highest interference for the low power RBS and sending the collected measurement reports to the identified macro RBS.

[00072] In this scenario, the low power RBS receives measurement reports from the UEs which are connected to the low power RBS. The low power RBS identifies which macro RBS causes the highest interference for the low power RBS. The low power RBS may be subjected to interference from more than one macro RBS and the low power RBS analyses the received measurement reports which it has received from the UEs and from this analysis, the low power RBS identifies which of the macro RBSs that causes the highest interference for the low power RBS. Thereafter, the low power RBS sends or forwards the measurement reports to that identified macro RBS. In this manner, the identified macro RBS being the network node is enabled to create a cluster comprising itself and all those low power RBSs which have identified the macro RBS to be the one which causes the highest interference and has consequently sent all their measurement reports to the identified macro RBS.

[00073] According to still an embodiment, the method comprising identifying which macro RBS causes the highest interference for the low power RBS and indicating, to the network node, the identified macro RBS.

[00074] In this scenario, the network node is a BSC, RNC or an OAM node. In the same manner as described above, the low power RBS receives measurement reports from the UEs which are connected to the low power RBS and the low power RBS identifies which macro RBS causes the highest interference for the low power RBS by analysing the received measurement reports. Thereafter, the low power RBS indicates to the network node which is a BSC, RNC or an OAM node, the identified macro RBS. In this manner, the network node is enabled to create clusters comprising one macro RBS and those low power RBSs which suffer the highest interference from that one macro RBS. In an alternative solution in which the low power RBS does not identify which macro RBS causes the highest interference for the low power RBS, the network node will analyse the received measurement reports and from that analysis deriving, for each of the low power RBS, which of the macro RBS causes the highest interference for each respective low power RBS. Thereafter, the network node may create clusters as having been described above.

[00075] Embodiments herein also relate to a network node and a low power RBS. The network node and the low power RBS have the same objects, technical features and advantages as the respective method performed therein. Consequently, the network node and the low power RBS will only be described in brief in order to avoid unnecessary repetition.

[00076] Figure 4 is a block diagram of a network node adapted to control resource distribution according to an exemplifying embodiment.

[00077] According to an embodiment, the network node in a wireless

communication network is adapted to control resource distribution within an area comprising at least one macro Radio Base Station, RBS, and a plurality of low power RBSs. Figure 4 illustrates the network node comprising a collecting unit 421 adapted to collect measurement reports from UEs being located within the area. The network node also comprises a creating unit 422 adapted to create clusters of low power RBS(s) and macro RBS(s) based on the collected measurement reports, wherein each cluster comprises one macro RBS and at least one low power RBS. Further, the network node comprises an estimating unit 423 adapted to estimate a traffic load or traffic distribution within the clusters for the macro RBS and the low power RBS(s) when testing different offsets affecting cell borders of the low power RBS(s) based on the collected measurement reports. Figure 4 further illustrates the network node comprising a selecting unit 424 adapted to select offset(s) from the tested offsets for the low power RBS(s) in the clusters based on the estimated traffic load within the clusters, which offsets are selected so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s), and an adjusting unit 425 adapted to adjust the cell borders of the low power RBS(s) by the selected offsets.

[00078] This has several advantages. One advantage is that the service (bitrate) coverage and capacity may be optimized and maximized to take network characteristics, such as propagation effects and traffic distributions, into account in a scenario where macro cells are complemented with small cells. The downlink capacity of the macro RBS may not be reduced. Since the traffic load of the macro RBS is minimised, the total system capacity will be maximised in downlink.

[00079] In figure 4, the network node is also illustrated comprising a receiving unit 41 1 and a transmitting unit 412. Through these two units, the network node is adapted to communicate with other entities in the wireless communication network. The receiving unit 41 1 may comprise more than one receiving

arrangement. For example, the receiving unit may be connected to both a wire and an antenna, by means of which the network node is enabled to communicate with other nodes and/or entities in the wireless communication network. Similarly, the transmitting unit 412 may comprise more than one transmitting arrangement, which in turn are connected to both a wire and an antenna, by means of which the network node is enabled to communicate with other nodes and/or entities in the wireless communication network. The network node further comprises a memory for storing data. Further, the network node is illustrated comprising a processing unit 420 which in turns comprises the different units 421-425. It shall be pointed out that this is merely an illustrative example and the network node may comprise more, less or other units or modules which execute the functions of the network node in the same manner as the units illustrated in figure 4.

[00080] According to an embodiment, the measurement reports comprise any of Reference Signal Received Power, RSRP, for Long Term Evolution, LTE, wireless communication networks, Received Signal Code Power, RSCP, for Code Division Multiple Access, CDMA, wireless communication networks, or Received Signal Level, RxLev, for Time Division Multiple Access, TDMA, wireless communication networks.

[00081 ] According to still an embodiment, the collection unit 421 further is adapted to receive, from the low power RBS(s), an indication of their respective capacity usage level, wherein the selection unit is adapted to select offsets for the low power RBS(s) in the clusters based on the indicated capacity usage levels.

[00082] According to yet an embodiment, the network node 400 is a macro RBS.

[00083] According to still an embodiment, the collection unit 421 further is adapted to receive measurement reports from UEs being connected to the macro RBS and to receive measurement reports from UEs being connected to those low power RBS(s) which experience the highest interference from the macro RBS. [00084] According to another embodiment, the network node 400 is a Radio Network Controller, RNC, or a Base Station Controller, BSC.

[00085] According to still another embodiment, the network node 400 is an Operation, Maintenance and Administration, OAM, node.

[00086] According to an embodiment, the collection unit 421 is adapted to receive measurement reports forwarded by the at least one macro RBS and the plurality of low power RBSs.

[00087] According to yet an embodiment, the creating unit 422 is adapted to identify, for each low power RBS, the one macro RBS which causes the most interference for the low power RBS and to cluster each respective macro RBS with those low power RBS(s) which are most adversely interfered by the respective macro RBS.

[00088] According to still an embodiment, the selecting unit 424 is adapted to select the offset(s) for the low power RBS(s), within each cluster, such that the traffic load of the low power RBS(s) are maximised, thereby reducing the traffic load of the macro RBS.

[00089] Figure 5 is a block diagram of a low power radio base station adapted to control resource distribution according to an exemplifying embodiment.

[00090] The low power RBS in a wireless communication network for allowing control of resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs . Figure 5 illustrates the low power RBS 500 comprising a collecting unit 521 adapted to collect measurement reports from UEs currently being connected to the low power RBS; and a forwarding unit 524 adapted to forward the collected measurement reports to a network node in the wireless communication network.

[00091 ] This has several advantages. One advantage is that the service (bitrate) coverage and capacity may be optimized and maximized to take network characteristics, such as propagation effects and traffic distributions, into account in a scenario where macro cells are complemented with small cells. The downlink capacity of the macro RBS may not be reduced. Since the traffic load of the macro RBS is minimised, the total system capacity will be maximised in downlink.

[00092] In figure 5, the low power RBS is also illustrated comprising a receiving unit 51 1 and a transmitting unit 512. Through these two units, the low power RBS is adapted to communicate with other nodes and/or entities in the wireless communication network. The receiving unit 51 1 may comprise more than one receiving arrangement. For example, the receiving unit may be connected to both a wire and an antenna, by means of which the low power RBS is enabled to communicate with other nodes and/or entities in the wireless communication network. Similarly, the transmitting unit 512 may comprise more than one transmitting arrangement, which in turn are connected to both a wire and an antenna, by means of which the low power RBS is enabled to communicate with other nodes and/or entities in the wireless communication network. The low power RBS further comprises a memory 530 for storing data. Further, the low power RBS is illustrated comprising a processing unit 520 which in turns comprises the different units 521 -524. It shall be pointed out that this is merely an illustrative example and the low power RBS may comprise more, less or other units or modules which execute the functions of the low power RBS in the same manner as the units illustrated in figure 5.

[00093] According to an embodiment, the measurement reports comprise any of Reference Signal Received Power, RSRP, for Long Term Evolution, LTE, wireless communication networks, Received Signal Code Power, RSCP, for Code Division Multiple Access, CDMA, wireless communication networks, or Received Signal Level, RxLev, for Time Division Multiple Access, TDMA, wireless communication networks.

[00094] According to still an embodiment, the low power RBS further comprises an indicating unit 522 adapted to indicate, to the network node, a capacity usage level in the low power RBS. [00095] According to yet an embodiment, the network node is a macro RBS, the low power RBS comprises and identifying unit 523 adapted to identify which macro RBS that causes the highest interference for the low power RBS, wherein the forwarding unit 524 is adapted to forward the collected measurement reports to the identified macro RBS.

[00096] According to another embodiment, the low power RBS comprises an identifying unit 523 adapted to identify which macro RBS that causes the highest interference for the low power RBS, wherein the low power RBS further comprises an indicating unit 522 adapted to indicate, to the network node, the identified macro RBS.

[00097] In an example, the methods as described above in both the network node and in the low power RBS are executed when a new low power RBS is added, started or activated; and/or when an existing low power RBS is removed, switched off or deactivated within the area in which resource distribution is to be controlled. The area may be the whole wireless communication network or a part thereof.

[00098] When a new low power RBS is added, started or activated it will not be allocated any offset. Consequently, the coverage area of the low power RBS can be said to be of an initial size depending on the power of the low power RBS and the environment in which the low power RBS is situated. After the methods have been executed, the new RBS may have an expanded coverage area due to the allocation of an offset from the network node. In case the new low power RBS is heavily loaded already at start-up, its coverage area may remain unchanged or unexpanded.

[00099] In another example, the methods as described above in both the network node and in the low power RBS are executed regularly or on demand. In case the methods are executed regularly, possible times of executions may be derived from statistics, the statistics showing different points in time where the traffic load is high or low in different areas, or in other words, when in time there is likely to be a change in traffic load from high to low and from low to high in different areas of the wireless communication network.

[000100] When the methods are executed, the area in which resource distribution is to be controlled is defined. Once the area is defined, the number of macro RBSs may be derived. Once the methods have been executed, all or most of the low power RBSs have been clustered together with the macro RBSs in the area. When the clusters are to be created, for each of the low power RBSs, the one macro RBS which most adversely interferes with the respective low power RBS is identified. Several macro RBSs may cause interference to a low power RBS. The macro RBS which has the highest percentage of being identified as the strongest neighbour, i.e. causes the highest interference, for a specific low power RBS among the reported UE measurements will be clustered together with the low power RBS.

[000101 ] Figure 6 is an exemplifying overview of a plurality of low power RBSs and macro RBSs and the interference situation between them. In case the area in which resource distribution is to be controlled is a city or a part of a city, most likey the area will comprise a plurality of different building of varying size and heights and a plurality of roads or streets of varying width and directions. This may result in that the macro RBS which causes the highest interference to a low power RBS may possible not be the macro RBS which are geographically closest to the low power RBS. Figure 4 illustrates by the dotted lines which macro RBS most adversely affect a low power RBS, i.e. causes the highest interference to the low power RBS.

[000102] In the case that there is no single macro RBS which causes highest interference to a certain low power RBS, this low power RBS may possibly not be clustered to any macro RBS and hence will not be allocated any offset. This might happen e.g. if a low power RBS is located or situated on or close to a cell border of two, or more, macro RBSs. Another example of when such a scenario occurs is when the low power RBS is located indoors. [000103] Figure 7 is an example of clustering of macro RBSs and low power RBSs.

[000104] In figure 7, an interference situation between five macro RBS, A-E, and five pico, i.e. low power RBSs, A-E, are indicated. The five macro RBSs or cells are represented in the rows of the diagram and the five pico RBSs or cells are represented in the columns of the diagram. For pico RBS A, the macro RBS which causes most interference is macro RBS A with 20%. For pico RBS B, macro RBS D is identified as causing the highest interference with 36%. Figure 7 also illustrates that pico RBS E, no dominant macro RBS can be identified as no macro RBS interfere to the pico RBS E. In this example, three clusters will be created, the first cluster comprising macro RBS A together with pico RBSs A and D. The second cluster comprises macro RBS D together with pico RBS B and the third cluster comprises macro RBS E together with pico RBS C. It shall be noted that e.g. the highest interference percentage value for macro RBS A may be derived by the number of measurement reports where macro RBS A is reported as the "strongest" neighbour divided by the total number of measurement reports in the pico RBS A.

[000105] When the cell clusters have been created the next step is to estimate the traffic offload from macro to pico given different offsets. The estimation of the potential traffic offload is based on the UE measurements reports. Typically, the UEs perform measurements regularly, but alternatively a request to perform a measurement is issued. In this part of the algorithm only UE measurements from the macro cell is used. In figure 8 is an example illustrated for how large percentage of traffic that can be distributed from macro to pico given different offsets. In figure 8, five pico RBSs A-E are illustrated all being clustered together with a macro RBS A.

[000106] In figure 8, the percentage may be calculated in the following way for different offsets 2 dB, 4dB, 6 dB, 8 dB and 10 dB: ¾-i.-X = Number of measurement reports where pico cell L is reported as a neighbour with signal strength that is X dB below that of serving macro cell A. L is for example A, B ,C or D in the example of figure 7 or 8.

¾toi = Total number of measurement reports in e.g. macro cell A exemplified in figure 8.

_ ^A-L-X

¹ of load — ^~f

^Atot is the total offload of traffic load in percent from the macro

RBS to the low power RBS(s) that can be obtained when expanding the low power cell or cells. As can be seen in figure 8, macro RBS A can offload 10% of traffic load to pico cell A, or pico RBS A, 14% to pico cell B, 10% to pico cell C, 10% to pico cell D and 4% to pico cell C. This adds up to a total traffic offload of 48%. This illustrates that a substantial offload of traffic can be achieved by selecting the offset for the low power RBSs in accordance with the embodiments described above. In other words, it is possible to find the optimum cell selection offset for each pico cell and also how much of the total macro resources that should be shared with the pico layer. Before the macro cell or RBS can apply the wanted resource sharing strategy it is important to check the current load situation in the low power cells to not cause congestion in the low power cells. After checking the current load situation in the low power cells the percentage in figure 8 might need to be updated for some low power cells or pico cells in this example. For instance if the traffic load in pico cell B already is at 95% then it is not possible to offload additional 14% from the macro. In this case pico cell B cannot have any offset at all and the optimum resource sharing between macro and pico is therefore decreased to 34%.

[000107] The sharing of resources is in one example a frequency reuse where macro users only can use 34% of the available bandwidth and pico users use the other 34% of the resources. In another example the sharing of resources may be used together with e-ICIC to decide how large part of the available resources that should be allocated for Almost-Blank Subframes (ABS).

[000108] Figure 9 is a schematic illustration of an exemplifying network

architecture. [000109] In figure 9, one macro RBS 810 is illustrated and two low power RBSs 830 and 840. The macro RBS has some UEs 851 connected to it, low power RBS 830 has some UEs 852 connected to it and low power RBS 840 has one UE 853 connected to it. It is illustrated in figure 9 that the UEs 851 , 852 and 853 send measurement reports to the respective RBS to which respective UE is connected. It is also illustrated in figure 9 that the low power RBSs 830 and 840 each forwards the received measurement reports to the macro RBS 810. Further, in figure 9, the macro RBS 810 is the network node which has been described above and the macro RBS 810 estimates traffic load for different offsets, selects offsets and then indicates the selected offsets to the low power RBSs 830 and 840.

[0001 10] Figure 10 is a schematic illustration of another exemplifying network architecture.

[0001 1 1 ] In this example, one OAM node 900 is illustrated together with two macro RBSs 910 and 920. Further two low power RBSs 930 and 940 are illustrated as well as a plurality of UEs 951 , 952, 953 and 954 connected to the different RBSs 910-940. In this example, the OAM node 900 is the network node which has been described above. The OAM node 900 collects measurement reports from the UEs 951 , 952, 953 and 954, either via the macro RBSs 910 and 920 or directly from the low power RBS 930. As can be seen in figure 10, low power RBS 940 forwards it received measurement reports to the macro RBS 920, which then forwards those measurement reports as well as the measurement reports which it has received from the USs 954 directly connected to the macro RBS 920. This means that the OAM node 900 collects measurement reports, estimates traffic load for different offsets, selects offsets and then indicates the selected offsets to the macro RBSs 910 and 920 as well as the low power RBS 930. Since the low power RBS 940 is connected to, or reports via macro RBS 920, the offset for low power RBS 940 is sent to the macro RBS 920 which forwards the offset to low power RBS 940.

[0001 12] It should be noted that figures 4-5 merely illustrates various functional units in the network node and the low power RBS in a logical sense. The functions in practice may be implemented using any suitable software and hardware means/circuits etc. Thus, the embodiments are generally not limited to the shown structures of the network node and the low power RBS and the functional units. Hence, the previously described exemplary embodiments may be realised in many ways. For example, one respective embodiment for the network node and the low power RBS includes a computer-readable medium having instructions stored thereon that are executable by the respective processing unit for executing the method steps as described above. The instructions executable by the computing system and stored on the computer-readable medium perform the method steps of the present invention as set forth in the claims.

[0001 13] While the embodiments have been described in terms of several embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent upon reading of the specifications and study of the drawings. It is therefore intended that the following appended claims include such alternatives, modifications, permutations and equivalents as fall within the scope of the embodiments and defined by the pending claims.

Claims

1 . A method (200) in a network node in a wireless communication network for controlling resource distribution within an area comprising at least one macro Radio Base Station, RBS, and a plurality of low power RBSs, the method comprising:

collecting (210) measurement reports from user equipments being located within the area,

creating (220) clusters of low power RBS(s) and macro RBS(s) based on the collected measurement reports, wherein each cluster comprises one macro RBS and at least one low power RBS,

estimating (230) a traffic load or traffic distribution within the clusters for the macro RBS and the low power RBS(s) when testing different offsets affecting cell borders of the low power RBS(s) based on the collected measurement reports,

selecting (240) offset(s) from the tested offsets for the low power RBS(s) in the clusters based on the estimated traffic load or traffic distribution within the clusters, which offsets are selected so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s), and

adjusting (250) the cell borders of the low power RBS(s) by the selected offsets.

2. A method (200) according to claim 1 , wherein the measurement reports comprise any of Reference Signal Received Power, RSRP, for Long Term

Evolution, LTE, wireless communication networks, Received Signal Code Power, RSCP, for Code Division Multiple Access, CDMA, wireless communication networks, or Received Signal Level, RxLev, for Time Division Multiple Access, TDMA, wireless communication networks.

3. A method (200) according to claim 1 or 2, further comprising receiving (215), from the low power RBS(s), an indication of their respective capacity usage level, wherein the selection of offsets for the low power RBS(s) in the clusters is based on the indicated capacity usage levels.

4. A method (200) according to any of claims 1 -3, wherein the network node is a macro RBS.

5. A method (200) according to claim 4, wherein collecting measurement reports from user equipments being located within the area comprises receiving measurement reports from user equipments being connected to the macro RBS and receiving measurement reports from user equipments being connected to those low power RBS(s) which experience the highest interference from the macro RBS.

6. A method (200) according to any of claims 1 -3, wherein the network node is a Radio Network Controller, RNC, or a Base Station Controller, BSC.

7. A method (200) according to any of claims 1 -3, wherein the network node is an Operation, Maintenance and Administration, OAM, node.

8. A method (200) according to claim 6 or 7, wherein collecting

measurement reports from user equipments being located within the area comprises receiving measurement reports forwarded by the at least one macro RBS and the plurality of low power RBSs.

9. A method (200) according to any of claims 1 -8, wherein the creating of clusters of low power RBS(s) and macro RBS(s) comprises identifying, for each low power RBS, the one macro RBS which causes the most interference for the low power RBS and clustering each respective macro RBS with those low power RBS(s) which are most adversely interfered by the respective macro RBS.

10. A method according to any of the claims 1 -9, wherein the offset(s) for the low power RBS(s), within each cluster, are selected such that the traffic load of the low power RBS(s) are maximised, thereby reducing the traffic load of the macro RBS.

1 1 . A method (300) in a low power radio base station, RBS, in a wireless communication network for controlling resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs , the method comprising:

- collecting (310) measurement reports from user equipments currently being connected to the low power RBS, and

- forwarding (320) the collected measurement reports to a network node in the wireless communication network.

12. A method (300) according to claim 1 1 , wherein the measurement reports comprise any of Reference Signal Received Power, RSRP, for Long Term Evolution, LTE, wireless communication networks, Received Signal Code Power, RSCP, for Code Division Multiple Access, CDMA, wireless communication networks, or Received Signal Level, RxLev, for Time Division Multiple Access, TDMA, wireless communication networks.

13. A method (300) according to claim 1 1 or 12, further comprising indicating (330) to the network node a capacity usage level in the low power RBS.

14. A method (300) according to any of claims 1 1 -13, wherein the network node is a macro RBS, the method comprising identifying which macro RBS causes the highest interference for the low power RBS and sending the collected measurement reports to the identified macro RBS.

15. A method (300) according to any of claims 1 1 -13, the method comprising identifying which macro RBS causes the highest interference for the low power RBS and indicating, to the network node, the identified macro RBS.

16. A network node (400) in a wireless communication network adapted to control resource distribution within an area comprising at least one macro Radio Base Station, RBS, and a plurality of low power RBSs, the network node comprising:

a collecting unit (421 ) adapted to collect measurement reports from user equipments being located within the area, a creating unit (422) adapted to create clusters of low power RBS(s) and macro RBS(s) based on the collected measurement reports, wherein each cluster comprises one macro RBS and at least one low power RBS, an estimating unit (423) adapted to estimate a traffic load or traffic distribution within the clusters for the macro RBS and the low power RBS(s) when testing different offsets affecting cell borders of the low power RBS(s) based on the collected measurement reports,

a selecting unit (424) adapted to select offset(s) from the tested offsets for the low power RBS(s) in the clusters based on the estimated traffic load within the clusters, which offsets are selected so that the traffic load of the macro RBS is reduced without overloading the low power RBS(s), and - an adjusting unit (425) adapted to adjust the cell borders of the low power RBS(s) by the selected offsets.

17. A network node (400) according to claim 16, wherein the measurement reports comprise any of Reference Signal Received Power, RSRP, for Long Term Evolution, LTE, wireless communication networks, Received Signal Code Power, RSCP, for Code Division Multiple Access, CDMA, wireless communication networks, or Received Signal Level, RxLev, for Time Division Multiple Access, TDMA, wireless communication networks.

18. A network node (400) according to claim 16 or 17, wherein the collection unit further is adapted to receive, from the low power RBS(s), an indication of their respective capacity usage level, wherein the selection unit is adapted to select offsets for the low power RBS(s) in the clusters based on the indicated capacity usage levels.

19. A network node (400) according to any of claims 16-18, wherein the network node is a macro RBS.

20. A network node (400) according to claim 19, wherein the collection unit further is adapted to receive measurement reports from user equipments being connected to the macro RBS and to receive measurement reports from user equipments being connected to those low power RBS(s) which experience the highest interference from the macro RBS.

21 . A network node (400) according to any of claims 16-18, wherein the network node is a Radio Network Controller, RNC, or a Base Station Controller, BSC.

22. A network node (400) according to any of claims 16-18, wherein the network node is an Operation, Maintenance and Administration, OAM, node.

23. A network node according to claim 21 or 22, wherein the collection unit is adapted to receive measurement reports forwarded by the at least one macro RBS and the plurality of low power RBSs.

24. A network node (400) according to any of claims 16-23, wherein the creating unit is adapted to identify, for each low power RBS, the one macro RBS which causes the most interference for the low power RBS and to cluster each respective macro RBS with those low power RBS(s) which are most adversely interfered by the respective macro RBS.

25. A network node (400) according to any of claims 16-24, wherein the selecting unit is adapted to select the offset(s) for the low power RBS(s), within each cluster, such that the traffic load of the low power RBS(s) are maximised, thereby reducing the traffic load of the macro RBS.

26. A low power radio base station, RBS, (500) in a wireless communication network adapted to control resource distribution within an area comprising at least one macro RBS and a plurality of low power RBSs , the low power RBS comprising:

- a collecting unit (521 ) adapted to collect measurement reports from user equipments currently being connected to the low power RBS, and

- a forwarding unit (524) adapted to forward the collected measurement reports to a network node in the wireless communication network.

27. A low power RBS (500) according to claim 26, wherein the

measurement reports comprise any of Reference Signal Received Power, RSRP, for Long Term Evolution, LTE, wireless communication networks, Received Signal Code Power, RSCP, for Code Division Multiple Access, CDMA, wireless communication networks, or Received Signal Level, RxLev, for Time Division Multiple Access, TDMA, wireless communication networks.

28. A low power RBS (500) according to claim 26 or 27, further comprising an indicating unit (522) adapted to indicate, to the network node, a capacity usage level in the low power RBS.

29. A low power RBS according to any of claims 26-28, wherein the network node is a macro RBS, the low power RBS comprises and identifying unit (523) adapted to identify which macro RBS causes the highest interference for the low power RBS, wherein the forwarding unit (524) is adapted to forward the collected measurement reports to the identified macro RBS.

30. A low power RBS (500) according to any of claims 26-28, wherein the low power RBS comprises an identifying unit (523) adapted to identify which macro RBS causes the highest interference for the low power RBS, wherein the low power RBS further comprises an indicating unit (522) adapted to indicate, to the network node, the identified macro RBS.