WO2016080872A1

WO2016080872A1 - Method and arrangement for downlink comp scheduling and interference mitigation

Info

Publication number: WO2016080872A1
Application number: PCT/SE2014/051366
Authority: WO
Inventors: Ying Sun
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-11-18
Filing date: 2014-11-18
Publication date: 2016-05-26

Abstract

The present invention relates to an arrangement of a wireless communication network and to a method for coordinating scheduling of transmissions to wireless devices within a cluster of transmission points. The method is performed in the arrangement applying coordinated multipoint transmission in the cluster. The method comprises identifying (410) a transmission point in the cluster dominantly interfering transmissions to a wireless device from a serving transmission point in the cluster. The wireless device is capable of applying interference rejection combining. The identifying is based on CSI measurement reports received from the wireless device. The CSI measurement reports are associated with a CSI process configuration in the arrangement and in the wireless device. The method also comprises disregarding (420) the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device.

Description

METHOD AND ARRANGEMENT FOR DOWNLINK COMP SCHEDULING AND

INTERFERENCE MITIGATION

TECHNICAL FIELD

The disclosure relates to downlink Coordinated Multipoint (CoMP) scheduling in a wireless communication network, and more specifically to a method and arrangement for coordinating scheduling of transmissions to wireless devices within a cluster of transmission points, wherein the arrangement applies CoMP transmission in the cluster.

BACKGROUND

Long Term Evolution (LTE) is the fourth-generation mobile communication technologies standard developed within the 3^rd Generation Partnership Project (3GPP) to improve the Universal Mobile Telecommunication System (UMTS) standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. The Universal Terrestrial Radio Access Network (UTRAN) is the Radio Access Network (RAN) of a UMTS and Evolved UTRAN (E-UTRAN) is the RAN of an LTE system. In an E- UTRAN, a wireless device also referred to as a User Equipment (UE) is wirelessly connected to a Radio Base Station (RBS) commonly referred to as an evolved NodeB (eNodeB or eNB) in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to a wireless device and receiving signals transmitted by a wireless device.

Figure 1 illustrates a conventional RAN in an LTE system. An eNodeB 101 serves a UE 103 located within the eNodeB's geographical area of service also called coverage area or cell. The eNodeB 101 manages the radio resources in its cell and is directly connected to a Core Network (CN) node 105. As a major enhancement of LTE, LTE-Advanced (LTE-A) is currently being standardized by the 3GPP. LTE-A aims to fulfil the higher requirements for 4G systems. One of the goals with LTE-A is to support higher downlink cell average and cell edge throughput. CoMP is one of the promising techniques to improve both the cell average and cell edge throughput. CoMP

CoMP transmission and reception refers to a system where the transmission and/or reception at multiple, geographically separated antenna sites is coordinated in order to improve system performance. In the subsequent discussion we refer to an antenna covering a certain geographical area in a certain manner as a point, or more specifically as a transmission point (TP). A point will thus be referred to as a transmission point even if the transmission point will also be configured for reception in an uplink context. A transmission point might correspond to one of the sectors at a site, but it may also correspond to a site having one or more antennas all intending to cover a similar geographical area. Often, different points represent different sites. Antennas correspond to different points when they are sufficiently geographically separated and/or have antenna diagrams pointing in sufficiently different directions.

The CoMP coordination of transmission points in a so called cluster can either be distributed by means of direct communication between the different transmission points, or centralized by means of a central coordinating entity controlling the transmission at all the transmission points.

Techniques for CoMP introduce dependencies in the scheduling or transmission/reception among different points, in contrast to conventional cellular systems where a point from a scheduling point of view is operated more or less independently from the other points. Downlink CoMP operations may include, e.g., serving a certain UE from multiple points, either at different time instances or for a given subframe, on overlapping or not overlapping parts of the spectrum. There are many different CoMP transmission schemes, such as: · Dynamic Point Blanking, where multiple transmission points coordinates the transmission so that neighboring transmission points may mute the transmissions on the time-frequency resource elements (TFREs) that are allocated to UEs that experience significant interference.

• Dynamic Point Selection, where the data transmission to a UE may switch dynamically (in time and frequency) between different transmission points, so that the transmission points are fully utilized.

• Coordinated Beamforming, where the transmission points coordinate their transmissions in the spatial domain by beamforming the transmission power in such a way that the interference to UEs served by neighboring transmission points is suppressed.

• Joint Transmission, where the signal to a UE is simultaneously transmitted from multiple transmission points on the same time/frequency resource. The aim of joint transmission is to increase the received signal power and/or reduce the received interference.

Downlink CoMP is categorized into two classes: Joint Processing and Coordinated Scheduling (CS)/Coordinated Beamforming (CB). In the class of Joint Processing, data to one UE is available at multiple cells to increase the desired signal quality. CoMP Joint Processing can be further categorized into Joint Transmission and Dynamic Point Selection. In the class of Joint Transmission, multiple points will transmit data using the same Resource Blocks (RB) to the UE simultaneously. Some previous studies show that when Joint Transmission is applied, more system resources are allocated to a particular UE leading to fewer resources that can be assigned to other UEs. In the class of Dynamic Point Selection, only one transmission point transmits data to the UE in each Transmission Time Interval (TTI), while other transmission points can allocate the RB to other UEs.

In the class of CS/CB, data to one UE always needs to be transmitted by the serving cell. The scheduling and the beamforming decisions are made for coordination among multiple cells corresponding to a given measurement set. In such a case, interference generated within a measurement set can be well controlled thus resulting in performance improvement in both cell average and cell edge throughput.

In order to further improve the cell edge user throughput, Dynamic Point Blanking (DPB) is applied to the strongest interferer of the coordinated points. DPB can be used together with CS, wherein the serving cell transmits data to the UE and a coordinated cell configures zero power for the same RB. DPB can also be used together with Dynamic Point Selection wherein one cell in a CoMP cluster transmits data to the UE and other cells configure zero power for the same RB. Channel State Information (CSI)

In LTE, the format of the channel quality or CSI report is specified in detail and comprises CSI estimates in the form of Channel-Quality Indicator(s) (CQI), Rank Indicator (Rl), and Precoding Matrix Indicator (PMI). The quality and reliability of the CSI estimates such as CQI, Rl and PMI are crucial for the radio base station in order to make the best possible scheduling decisions for the upcoming downlink transmissions. The radio base station estimates the channel quality based on the content of the CSI report.

In LTE Release 10, the support for CSI-RS, Channel State Information Reference Signal, is introduced. The CSI-RSs are used by release 10 and 10+ UEs to determine CSI. Specifically, in release 10 it is used for transmission mode 9 (TM9) and in release 1 1 for transmission mode 10 (TM10). The reason to introduce CSI- RS is to improve channel estimation for coherent demodulation even with the most extreme channel conditions including very fast channel variations in both the time and frequency domain without introducing much overhead. Furthermore, it is found that introducing a new type of reference signal only targeting CSI is flexible and requires in general lower time/frequency density and therefore lower overhead per reference signal.

The CSI-RS resources are specifically configured for each wireless device by using Radio Resource Control (RRC) signaling. The RRC signaling may occur periodically, see e.g. 3GPP TS 36.213 V1 1 .4.0, 2013-09, Sections 7.2.5-7.2.6. For example, an RRC configuration message may be transmitted periodically every 5 ms, i.e. every 5th subframe. Alternatively, the RRC configuration message may be sent in an aperiodic manner, or may be triggered in a control message from the radio base station to a wireless device. A CSI-RS resource is a group of resource elements in a certain subframe that occurs periodically, for instance every 20th subframe. The CSI-RS utilizes an orthogonal cover code of length two to overlay two antenna ports on two consecutive time frequency resource elements (TFREs). Many different CSI-RS patterns are available. For the case of two CSI-RS antenna there are 20 different TFRE pair possibilities within a subframe. The corresponding number of patterns is 10 for four CSI-RS antenna ports, and 5 for eight CSI-RS antenna ports. The term CSI-RS resource corresponds to a particular pattern present in a particular subframe. Thus two different CSI-RS patterns in the same subframe constitute two separate CSI-RS resources, as well as the same CSI-RS pattern in two different subframes. Within the sub-frame the PDSCH TRFEs are mapped around the CSI- RS resources, so it is important that both the network and the UE are assuming the same CSI-RS resource configuration for the UE to be able to decode the PDSCH. There is a possibility to configure both Non-Zero Power (NZP) also referred to as non-muted CSI-RS resources and Zero Power (ZP) also referred to as muted CSI- RS resources. A ZP CSI-RS resource is simply an unused radio resource that can be matched to a NZP CSI-RS resource in an adjacent radio base station. A ZP CSI-RS may be used to improve the Signal to Interference plus Noise Ratio (SINR) for the CSI-RS measurements in the cell of the adjacent radio base station. However, the ZP CSI-RS resources may also be referred to or used as CSI- Interference Management (CSI-IM) resources. CSI-IM resources are defined in the same physical locations of the time/frequency grid as the CSI-RS, but with zero power. These are intended to give a wireless device the possibility to measure the power of interfering signals without having it overlaid on top of a CSI-RS signal, which is usually much stronger than any surrounding interference.

For the purpose of improved interference measurements new functionality was introduced in LTE Release 1 1 , where the network is able to configure a UE to measure interference on the CSI-IM resource. The network can control the interference seen on a CSI-IM, by for example muting all transmission points within a CoMP coordination cluster on the CSI-IM, in which case the UE will effectively measure the inter-cluster interference. Moreover, it is essential that an eNodeB can accurately evaluate the performance of a UE given different CoMP transmission hypotheses; otherwise the dynamic coordination becomes meaningless. Thus the system needs to be able to track or estimate also different intra-cluster interference levels corresponding to different transmission and blanking hypotheses. By configuring resources that a UE is mandated to use for measuring interference plus noise, e.g. a CSI-IM defined for LTE, a UE can assume that no transmission points of interest are transmitting on this resource, and the received power can therefore be used as a measure of the interference plus noise.

In uncoordinated systems the UE can effectively measure the interference observed from all other cells or transmission points, and this will be the relevant interference level in an upcoming data transmission. In coordinated systems such as CoMP, the network can to a large extent control which transmission points that interfere a UE. Hence, there will be multiple interference hypotheses depending on which transmission points that are transmitting. Additionally, the network can choose to transmit interference from specific transmission points for the sole purpose of testing how that particular interference hypothesis affects the UE (seen e.g. via the CSI feedback). The network can try to make an assessment of what hypothesis that is most likely to occur for upcoming transmission time intervals. For UEs that are on the boundaries of a coordination cluster of transmission points, the dominant interferers may not be found within the cluster but from outside the cluster. Such inter-cluster interference cannot be controlled and will impact the CSI reports in an unknown way. In LTE Release 1 1 , CSI processes are defined. Each CSI process is associated with a CSI-RS resource configuration which may comprise both CSI-RS and CSI- IM resources. A UE in TM10 can be configured with one to four CSI processes by higher layers and a CSI reported by the UE is associated to a certain CSI process. Since up to four CSI processes can be used for measurements and reported by the UEs spanning maximally three different CSI-IMs, the network can test different interference realizations simultaneously on the UE. Based on the effect fed back to the network through the CSI reports associated with the different CSI processes, the network may adapt its transmission scheme. A CSI report may also be referred to as a channel quality report.

If only one CSI process is used, it is common for the network to let the CSI-IM reflect the interference from all other radio base stations, i.e. the cell of the serving radio base station uses a ZP CSI-RS that overlaps with the CSI-IM, but in other adjacent radio base stations, there is no ZP CSI-RS on these resources. In this way, the wireless device may measure the interference from adjacent cells using measurements in the CSI-IM resource. If more than one CSI process is configured for the wireless device, it is possible for the network to also configure a ZP CSI-RS in the adjacent radio base station that overlaps with a CSI-IM for the CSI process configured for the wireless device. In this way, the wireless device may feedback accurate CSI estimates also for the case when this adjacent cell is not transmitting. Hence, measurements to support coordinated scheduling between radio base stations is enabled with the use of multiple CSI processes. One CSI process feeds back CSI estimates for the full interference case and the other CSI process feeds back CSI estimates for the case when an adjacent cell, preferably a strong interfering cell, is muted. As mentioned above, up to four CSI processes may be configured for a wireless device, thereby enabling feedback of four different transmission hypotheses.

Problems with Existing Solutions

When using Dynamic Point Blanking for downlink CoMP, the resource usage is degraded since a frequency reuse of one is not maintained and radio resources such as RB and transmission power may not be fully used. The average cell throughput gain is thus not obvious, and in a worst case it may even be degraded. Furthermore, CSI process configurations used for a Dynamic Point Blanking transmission scheme does not take full advantage of whether there is a possible Interference Rejection Combining (IRC) gain using an IRC receiver in the UE. Muting the strongest interferer may not give the best performance for the UE that supports IRC in its receiver as the UE can cancel the dominant interferer. SUMMARY

It is an object to address some of the problems outlined above, and to provide a solution allowing a higher overall throughput when applying downlink CoMP. This object and others are achieved by the method and the apparatus according to the independent claims, and by the embodiments according to the dependent claims.

In accordance with a first aspect, a method for coordinating scheduling of transmissions to wireless devices within a cluster of transmission points is provided. The method is performed in an arrangement of a wireless communication network applying coordinated multipoint transmission in the cluster. The method comprises identifying a transmission point in the cluster dominantly interfering transmissions to a wireless device from a serving transmission point in the cluster. The wireless device is capable of applying interference rejection combining. The identifying is based on CSI measurement reports received from the wireless device. The CSI measurement reports are associated with a CSI process configuration in the arrangement and in the wireless device. The method also comprises disregarding the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device.

In accordance with a second aspect, an arrangement of a wireless communication network for coordinating scheduling of transmissions to wireless devices within a cluster of transmission points is provided. The arrangement is applying coordinated multipoint transmission in the cluster. The arrangement is configured to identify a transmission point in the cluster dominantly interfering transmissions to a wireless device from a serving transmission point in the cluster. The wireless device is capable of applying interference rejection combining. The identifying is based on CSI measurement reports received from the wireless device. The CSI measurement reports are associated with a CSI process configuration in the arrangement and in the wireless device. The arrangement is also configured to disregard the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device. An advantage of embodiments is that the IRC gain can be taken into account when making coordinated scheduling decisions. This will in turn enable a higher performance gain for downlink CoMP.

Other objects, advantages and features of embodiments will be explained in the following detailed description when considered in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration of an LTE RAN according to prior art.

Figure 2 is a schematic illustration of an example scenario of a downlink CoMP deployment.

Figure 3 is a diagram where SINR is given as a function of frequency illustrating one example according to embodiments.

Figures 4a-c are flow charts schematically illustrating the method performed by the arrangement according to embodiments. Figures 5a-c are block diagrams schematically illustrating the arrangement according to embodiments.

DETAILED DESCRIPTION

In the following, different aspects will be described in more detail with references to certain embodiments and to accompanying drawings. For purposes of explanation and not limitation, specific details are set forth, such as particular scenarios and techniques, in order to provide a thorough understanding of the different embodiments. However, other embodiments that depart from these specific details may also exist.

Embodiments are described in a non-limiting general context in relation to an example scenario in an E-UTRAN illustrated in Figure 2 with an eNodeB 101 applying downlink CoMP transmission to a UE 103 over three transmission points TP1 , TP2, TP3 in a coordination cluster 200. One transmission point TP1 is the serving transmission point and the other two transmission points TP2, TP3 are interfering transmission points. Although the embodiments are described in the LTE environment, they could be applied for other wireless communication systems supporting CoMP transmission in the downlink, and the UE may be any kind of wireless device. Furthermore, although the embodiments are described for a centralized solution where one eNodeB 101 controls the transmission from all transmission points TP1 , TP2, and TP3, they could also be applied for a distributed solution with more than one eNodeB controlling the transmission from multiple transmission points, where the eNodeBs have direct and fast communication with each other to enable the coordinated transmission. In the example scenario of Figure 2 used for describing the embodiments, a transmission point is equivalent to a sector or a cell. However, embodiments of the invention may as well be applied for multi-sector cells or combined cells.

For UEs of Transmission Mode 10 (TM10) in a scenario such as the one described in Figure 2, DPB may not be a big problem since the point muting decision is based on interference hypothesizes computed from the CSI measurements where the interference measured on CSI IM is taking the interference cancellation gain into account. However, there is still a problem related to the inefficient CSI configuration scheme which does not consider the IRC gain. For example, in 3GPP the default CSI configuration scheme for a three sector coordination cluster is as given in Table 1 below.

Table 1 : CSI configuration for three sector DPB scheme assuming that the UE is served by the transmit point TP1.

The signal quality is measured for three CSI processes on CSI-RS configuration 3,4 and the transmission point TP1 is transmitting CSI-RS according to the configuration 3,4. The interference hypothesis is measured for CSI process 1 at 5,6 where the transmission point TP2 is muted but TP3 is transmitting. The interference hypothesis of CSI process 2 is measured at 7,8 where the transmission point TP2 is transmitting and transmission point TP3 is muted. The interference hypothesis of CSI process 3 is measured at 9, 10 where both transmission points, TP2 and TP3, are transmitting. This configuration enables to derive a channel quality based on measurements containing three interference hypothesizes: (1 ) muting transmission point TP2; (2) muting transmission point TP3; (3) both transmission points TP2 and TP3 are transmitting. The idea is to select the TPB based on the measurement results.

However, since the IRC gain is not considered when configuring the CSI processes, the configuration is not efficient for its purpose when the UE is capable of applying IRC. Assuming that the dominant interferer comes from the coordinated cluster, the dominant interferer in hypothesis (1 ) is TP3 which may be cancelled with an IRC receiver in the UE. In hypothesis (2), the dominant interferer is TP2 which may also be cancelled with the IRC receiver. Therefore the measurement results related to the CSI process 1 and 2 effectively equal to the same thing: SINR=P1/n where P1 is the received signal power from transmission point TP1 and n is the uncoordinated noise. For hypothesis measurement related to CSI process 3, the eNodeB cannot know how much IRC gain that has been applied for any of the transmission points. Embodiments of the invention tackle the abovementioned problems with a coordination scheme that takes the IRC interference cancellation gain into account. In embodiments of the invention the CSI processes comprising the CSI resources are configured such that the identification of a dominantly interfering transmission point is facilitated. If the UE is IRC capable, the dominantly interfering transmission point can be cancelled by the IRC receiver in the UE. The muting of the dominantly interfering transmission point as done e.g. with DPB - which results in a lower resource usage and lower overall throughput - is in such a case unnecessary. Therefore, the dominantly interfering transmission point may be disregarded when coordinating the scheduling of transmissions from the transmission points of the cluster. Furthermore, by controlling the transmission power of other transmission points in the coordination cluster the network may achieve the best coordination gain. By e.g. reducing the transmit power of the second highest interferer, the channel quality of the UE may be further improved without sacrificing resource utilization. In scenarios when no transmission point is dominantly interfering, the eNodeB can reduce the transmit power of one of the transmission points in order to create a dominant interferer. Interference from a dominant interferer can be cancelled by the IRC receiver in the UE and the created dominantly interfering transmission point can therefore be disregarded when coordinating scheduling of transmissions in the cluster. One way to identify whether a served UE is capable of applying IRC is to determine whether a number of layers used by the UE is smaller than a number of reception antennas at the UE. The number of reception antennas used by the UE may be determined from capability information received by the eNodeB from the UE. Furthermore, the number of layers used by the UE may be determined based on a Rank Indicator (Rl) that may be received from the UE in the CSI measurement reports. According to current standard the UE is configured to send CSI reports comprising among other things the Rl where the Rl is an indication of the numbers of layers preferred by the UE. If the UE has four antennas although it reports a Rl of two, it is possible to deduce that the UE will have the capability to perform IRC using one or more of the antennas not used for the two layer transmission.

Another possibility to "identify" the UE as IRC capable is to use the feature in the network to select another rank or number of layers than that indicated by the Rl received from the UE. This feature is often referred to as rank-override. The eNodeB may thus select a lower rank than that indicated by the UE for the purpose of leaving receiving capacity in the UE for applying IRC of a strong or dominant interferes

Two main parts of embodiments of the invention will be described in the following two sections:

1 . The CSI process configuration; and 2. The coordination of scheduling and transmit power control within the cluster.

1 . CSI process configuration

In embodiments of the invention, CSI processes are configured in the eNodeB 101 as well as in the served UE 103 such that the dominantly interfering transmission point can be identified. The example scenario focuses on TM10 UEs which may support maximally four CSI processes, and maximally three different CSI-RS and CSI-IM resources. For the UE 103 with the transmission point TP1 as the serving sector, the CSI configuration scheme is described in Table 2 below.

Table 2: A proposed CSI configuration scheme enabling identification of dominantly interfering transmission points

In the proposal in Table 2, the three transmission points (TP1 , TP2 and TP3) of the coordination cluster transmit CSI-RSs in three different CSI-RS resources configured for three different CSI processes (CSI process 2-4) of the UE 103. The UE 103 has transmission point TP1 as the serving transmission point. The CSI-IM configuration for the three CSI processes 2-4 are the same. All transmission points within the cluster are muted at the configured CSI-IM resource, resulting in that only uncoordinated noise n is measured. The uncoordinated noise comprises the interference from the transmission points not belonging to the coordinated cluster plus the thermal noise. The channel quality deduced from the CSI measurement reports received from the UE 103 and related to the CSI processes 2-4 will be the quantized value of P1/n, P2/n and P3/n, where P1, P2 and P3 are the power levels of the transmission points TP1 , TP2 and TP3 respectively as received at the UE 103.

The CSI process 1 is configured according to the most probable transmission scheme, where the transmit power of transmission point TP2 Ptx, 2' is:

Ptx,2'=xPtx where x is a factor used for transmit power control, and Ptx is a reference transmit power which is the same for all transmission points. The received power at the UE 103 from transmission point TP2 will be:

P2'=xPtxG2 = xP2 where G2 is the path gain from transmission point TP2 to the UE. Similarly, the received power from TP3 is equal to:

P3' = yP3 where y is a factor used to control transmission power of transmission point TP3. The CSI measurement report related to the CSI process 1 (CSI_report1 ), which is the transmission scheme which takes into account the power control of the coordinated transmission points, results in the following measurement:

CSI_report1 = P1/(xP2+yP3+n) as already stated in Table 2. x=0 means that the transmission point TP2 is muted, and y=0 means that the transmission point TP3 is muted. To avoid the inaccuracy that may be caused by the UE's CSI measurement filtering, the first value is measured for a transmission where x=y=0, which gives a same CSI measurement report result related to CSI process 1 and to CSI process 2: CSI_report1= CSI_Report2=P1/n

After the first transmission is performed, and based on the feedback of CSI reports from all the measurements, the dominantly interfering transmission point may be identified, and coordination scheduling and power control may be performed as described in the next section 2 - Coordinated scheduling and power control, where the factors x and y used to control the transmit power of the coordinated interfering transmission points TP2 and TP3 are determined.

2. Coordinated scheduling and power control

By looking at the CSI measurement reports related to CSI process 3 and CSI process 4, with a reported value CSI_Report3=P2/n and CSI_Report4=P3/n respectively, the relative relation of received power from the potentially interfering transmission points TP2 and TP3 can be obtained. Furthermore, it may be assumed that the interference from the transmit points within the coordinated cluster is always larger than the interference from transmission points not belonging to the cluster, i.e., CSI_Report3=P2/n>1 and CSI_Report4=P3/n>1. When performing coordinated scheduling within the cluster, a threshold TH_IRC is used to identify a dominant interferer among the transmission points TP2 and TP3. In one example embodiment TH_IRC may be equal to 3 dB. The following criterion may be used in embodiments of the coordinated scheduling and power control scheme:

CSI_Report3/CSI_Report4 = P2/P3 > THJRC

If the above criterion is fulfilled, transmission point TP2 is the dominantly interfering transmission point. Since the dominantly interfering transmission point can be cancelled by the UE using IRC, the eNodeB does not need to apply any coordination scheme for transmission point TP2 which may thus be disregarded when performing the coordination of scheduling.

However, it is further possible to decide the coordination scheme for transmission point TP3. The following describe two possible embodiments for the coordination of scheduling for transmission point TP3 which is interfering although not dominantly:

Embodiment A: if CSI_Report 4/CSI_Report2>THmute, the geometry of the UE between transmission points TP3 and TP1 is very poor, and transmission point TP3 may thus quite severely interfere transmissions from transmission point TP1 to the UE. In embodiments, the transmission point TP3 may therefore be muted by setting y=0, or the transmission power of transmission point TP3 may be reduced e.g. by setting y = ½ or any other value between 0 and 1 . THmute may correspond to a fixed value, for example 2dB. However, it may alternatively be a variable value depending on the SINR value of CSI_report 2, where the variable value indicates how much gain that may be obtained in number of bits. An example of a predefined mapping table can be used to determine the value of THmute, as illustrated in Table 3 below.

Table 3: Table mapping value of CSI_report 2 to THmute.

Embodiment B: A more elaborated coordination hypothesis with different transmit power hypothesis for all the UEs served in the coordinated cluster may be used according to the following. Compared to the previous embodiment A, all UEs of the cluster are taken into account and not only one of them. The SINR value of UE m and hypothesis H is given by:

The hypothesis of different transmission power of transmission point TP3 for all the UEs in the coordinated cluster is avoided and fewer hypotheses may be evaluated, which results in less processing complexity. In analogy with the above described example scenario where transmission point TP2 is identified as the dominantly interfering transmission point, transmission point TP3 may be identified as the dominantly interfering transmission point if the following criterion is fulfilled: CSI_Report4/ CSI_Report3 = P3/P2 > THJRC

The eNodeB may thus disregard transmission point TP3 when coordinating the scheduling, and does not need to apply any coordination scheme for transmission point TP3. The coordination of scheduling for other transmission points of the cluster is analogous to the above described scenario, and will therefore not be repeated here.

As already mentioned above, scenarios when no transmission point is dominantly interfering may exist. According to embodiments, the eNodeB may in such a case reduce the transmit power of one of the transmission points in order to create a dominant interferer, which can subsequently be cancelled by the IRC receiver in the UE and therefore disregarded when coordinating scheduling of transmissions in the cluster.

Therefore, the following criterion is checked:

CSI_Report4/CSI_Report3= P3/P2 > THJRC

If fulfilled this means that neither transmission point TP2 nor transmission point TP3 is dominantly interfering. According to embodiments, the interfering transmission point TPx that reports the smallest power value in its CSI measurement report may be selected. However, other basis than a CSI measurement report value may be used for selecting a transmission point. The selection may e.g. be based on one or more of CSI measurement reports, a channel quality measurement received from the wireless device such as a Reference Signal Received Power (RSRP) measurement, and a load situation for the transmission points in the cluster. In the above described example scenario, CSI_Report 4=P3/n corresponding to transmission point TP3 may e.g. be smaller than CSI_Report 3= P2/n corresponding to transmission point TP2. By reducing the transmit power of transmission point TP3 in this example by a factor of TP3, y, where y=CSI_Report3/CSI_Report4/TH_IRC, transmission point TP2 becomes a dominant interferes Transmission point TP2 may thus be cancelled by the IRC receiver in the UE and may therefore be disregarded when coordinating scheduling of transmissions in the cluster. Making the same considerations as above, transmission point TP3 may be muted, or the transmit power of transmission point TP3 may be reduced.

Frequency selective scheduling in the coordinated non-serving cells

As described above, the serving transmission point scheduler may compute a required power of the coordinated transmission points based on e.g. geometry information of a UE. The required power or a factor of power change, together with the UE allocation in frequency and time e.g. in terms of Physical Resource Blocks (PRBs), may then be sent to the coordinated transmission points. The scheduler of the coordinated transmission points may modify the channel quality value of the corresponding PRB or PRB group based on the received power input for all scheduled UEs. A PRB weight may also be updated. With frequency selective scheduling, the PRB group/PRB with reduced transmit power will have lower priority. When the PRB/PRB group is selected, the transmit power of the eNodeB may be updated and the link adaptation may be performed accordingly. In the above described example scenario, the selected power factors, x and y, together with an indication of the resource blocks RBi in which the UE is allocated, is sent to the scheduler of transmission points TP2 and TP3 respectively. The SINR value of resource block RBi in the scheduler of transmission point TP2 is reduced by a factor x for all the scheduling UE candidates with a serving transmission point TP2, and the SINR value of resource block RBi in the scheduler of transmission point TP3 is reduced by a factor y for all the scheduling UE candidates with serving transmission point TP3.

Figure 3 is a diagram where SINR is given as a function of frequency illustrating one example. The dashed line is the SINR per PRB without power reduction in the interfering transmission point TP2. The solid line is SINR value per PRB for the UE after power reduction of 10log10(x) dB.

The transmit power of the scheduling UE candidate in TP2 with an allocation of RBi will be reduced with a factor x. The transmit power for the scheduling candidate in TP3 which is allocated with RBi will be reduced with a factor y. The transmit power of the scheduling candidates which are not allocated in RBi will not be affected.

Strictly following the transmit power requirement received from a serving transmission point may not always be efficient. Therefore, it may also be possible for the coordinated cell to override the power control decision by applying another transmit power than the serving transmission point required. In this situation, a signaling is needed to the serving cell to inform about what the actually used transmit power is. The coordinated link adaptation may then be performed in the serving cell accordingly.

Embodiments of method in arrangement Figure 4a is a flowchart illustrating one embodiment of a method for coordinating scheduling of transmissions to wireless devices within a cluster of transmission points. The method is performed in an arrangement 500 of a wireless communication network applying coordinated multipoint transmission in the cluster. In the example scenario described above illustrating a centralized embodiment, the arrangement comprises an eNodeB controlling the transmission performed by the three transmission points TP1 , TP2 and TP3 forming a coordination cluster. The transmission points may be remote radio units or antennas covering different sectors of the eNodeB's coverage area. In a distributed embodiment, the arrangement may comprise more than one network node or eNodeB. Each network node may control the transmission performed by at least one of the transmission points. The wireless devices may be UEs, as described in the example scenario. The method comprises:

- 410: Identifying a transmission point in the cluster dominantly interfering transmissions to a wireless device from a serving transmission point in the cluster. The wireless device is capable of applying IRC. The identifying is based on CSI measurement reports received from the wireless device, where the CSI measurement reports are associated with a CSI process configuration in the arrangement and in the wireless device. The arrangement and the wireless device are thus both configured with a CSI process associated with a CSI-RS resource configuration. The CSI-RS resource configuration may in embodiments comprise a CSI-IM resource configuration.

- 420: Disregarding the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device.

In embodiments of the invention, which is illustrated in the figure 4b, the method may further comprise:

- 430: Coordinating scheduling of transmissions from transmission points in the cluster other than the identified transmission point based on the CSI measurement reports received from the wireless device. Coordinating scheduling may in embodiments comprise adjusting either transmission power and/or beamforming of transmissions from transmission points in the cluster other than the identified transmission point. It is also illustrated in Figure 4b that the method may comprise the initial step of:

- 400: Identifying the wireless device as capable of applying IRC when a number of layers used by the wireless device is smaller than a number of reception antennas at the wireless device. Identifying the wireless device as capable of applying IRC may further comprise determining the number of reception antennas used by the wireless device based on a capability received from the wireless device, and determining the number of layers used by the wireless device based on a rank indicator received from the wireless device. Alternatively, identifying the wireless device as capable of applying IRC may further comprise receiving a Rl from the wireless device, and determining to use a number of layers which is smaller than the number of layers indicated by the received Rl for the communication with the wireless device. In this case the arrangement applies rank-override to allow the wireless device to be capable of applying IRC. Figure 4c is a flowchart illustrating another embodiment of the method performed by the arrangement. The method may comprise the steps 400-430 described above with reference to Figure 4c, wherein the step 410 of identifying the transmission point in the cluster dominantly interfering comprises:

- 41 1 : Selecting the transmission point from the cluster of transmission points. The transmission point may be selected based on one or more of the CSI measurement reports, a channel quality measurement received from the wireless device, and a load situation for the transmission points in the cluster.

- 412: Reducing transmission power for all transmission points in the cluster except the selected transmission point, such that the selected transmission point is identified as dominantly interfering.

As already mentioned above, scenarios when no transmission point is dominantly interfering may exist. However, according to embodiments, the arrangement may in such a case reduce the transmit power of one of the transmission points in order to create a dominant interferer, which interference can subsequently be cancelled by the IRC receiver in the UE and therefore disregarded when coordinating scheduling of transmissions in the cluster.

In any of the above described embodiments, the CSI process configuration may be configured such that the CSI measurement reports associated with the CSI process configuration enables determination of power received at the wireless device from each transmission point in the cluster.

Further, in any of the above described embodiments, the CSI process configuration may be configured such that the CSI measurement reports associated with the CSI process configuration enables determination of power received at the wireless device from the serving transmission point relative to power received at the wireless device from all non-serving transmission points in the cluster.

In one embodiment, corresponding to the example scenario described above using a CSI process configuration according to Table 2 above, the cluster may comprise a first and a second non-serving transmission point in addition to the serving transmission point. In the scenario described above, transmission point TP1 corresponds to the serving transmission point, and transmission points TP2 and TP3 correspond to the first and second non-serving transmission points. The CSI process configuration may comprise a first CSI process configured with a first CSI-RS resource for the first non-serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the first non-serving transmission point. The CSI process configuration may further comprise a second CSI process configured with a second CSI-RS resource for the second non-serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the second non-serving transmission point. The method may further comprise controlling transmission of CSI-RSs in accordance with the CSI process configuration. Identifying 410 the transmission point in the cluster dominantly interfering may comprise receiving a first and a second CSI measurement report associated with the first and second CSI processes respectively, and identifying one of the first and second non-serving transmission points as the dominantly interfering transmission point based on a comparison of the first and the second CSI measurement reports. This embodiment may correspond to the example embodiment described in section 2. Coordinated scheduling and power control above, in which the threshold TH_IRC is used to identify a dominant interferer among the transmission points TP2 and TP3. The following criterion may e.g. be used for the comparison of the CSI measurement reports: CSI_Report3/CSI_Report4 = P2/P3 > THJRC In another embodiment, and according to the example CSI process configuration given in Table 2 above, the CSI process configuration may further comprise a third CSI process configured with a third CSI-RS resource for the serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the serving transmission point. The method may further comprise when one of the first and second non-serving transmission points has been identified 410 as the dominantly interfering transmission point:

- Receiving a third CSI measurement report associated with the third CSI process.

- Comparing the second CSI measurement report with the third CSI measurement report when the first non-serving transmission point has been identified as the dominantly interfering transmission point.

- Comparing the first CSI measurement report with the third CSI measurement report when the second non-serving transmission point has been identified as the dominantly interfering transmission point.

The scheduling may be coordinated 430 based on the comparing with the third CSI measurement report.

Embodiments of arrangement An embodiment of an arrangement 500 of a wireless communication network for coordinating scheduling of transmissions to wireless devices within a cluster of transmission points TP1 , TP2, TP3, is schematically illustrated in the block diagram in Figures 5a and 5b. The arrangement 500 is applying coordinated multipoint transmission in the cluster. In Figure 5a corresponding to a centralized solution, the arrangement comprises a network node 500 such as an eNodeB controlling the transmission performed by the transmission points TP1 , TP2, TP3 of the cluster. In Figure 5b corresponding to a distributed solution, the arrangement 500 comprises more than one network node, 510, 520, each network node controlling the transmission performed by at least one of the transmission points TP1 , TP2, TP3.

The arrangement is in both the centralized and the distributed solution further configured to identify a transmission point in the cluster dominantly interfering transmissions to a wireless device 550 from a serving transmission point in the cluster. The wireless device 550 is capable of applying IRC. The identifying of the transmission point is based on CSI measurement reports received from the wireless device. The CSI measurement reports are associated with a CSI process configuration in the arrangement and in the wireless device. The arrangement is further configured to disregard the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device.

In embodiments, the arrangement 500 is further configured to coordinate scheduling of transmissions from transmission points in the cluster other than the identified transmission point based on the CSI measurement reports received from the wireless device. The arrangement 500 may be further configured to coordinate scheduling by adjusting at least one of transmission power and beamforming of transmissions from transmission points in the cluster other than the identified transmission point.

In embodiments, the arrangement 500 is further configured to identify the transmission point in the cluster dominantly interfering by selecting the transmission point from the cluster of transmission points, and reducing transmission power for all transmission points in the cluster except the selected transmission point. In this way the selected transmission point may be identified as dominantly interfering. The arrangement may be further configured to select the transmission point based on at least one of the CSI measurement reports, a channel quality measurement received from the wireless device, and a load situation for the transmission points in the cluster.

In embodiments, the arrangement 500 may be further configured to identify the wireless device as capable of applying IRC when a number of layers used by the wireless device is smaller than a number of reception antennas at the wireless device. The arrangement may be further configured to identify the wireless device as capable of applying IRC by determining the number of reception antennas used by the wireless device based on a capability received from the wireless device, and by determining the number of layers used by the wireless device based on a rank indicator received from the wireless device. Alternatively, the arrangement may be configured to identify the wireless device as capable of applying IRC by receiving a Rl from the wireless device, and determining to use a number of layers which is smaller than the number of layers indicated by the received Rl for the communication with the wireless device. In embodiments, the CSI process configuration may be configured such that the CSI measurement reports associated with the CSI process configuration enables determination of power received at the wireless device from each transmission point in the cluster. The CSI process configuration may be configured such that the CSI measurement reports associated with the CSI process configuration enables determination of power received at the wireless device from the serving transmission point relative to power received at the wireless device from all non- serving transmission points in the cluster.

In embodiments, the cluster may comprise a first and a second non-serving transmission point in addition to the serving transmission point. The CSI process configuration may comprise a first CSI process configured with a first CSI-RS resource for the first non-serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the first non-serving transmission point. The CSI process configuration may further comprise a second CSI process configured with a second CSI-RS resource for the second non-serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the second non-serving transmission point. The arrangement may be configured to control transmission of CSI-RSs in accordance with the CSI process configuration. The arrangement may be further configured to identify the transmission point in the cluster dominantly interfering by receiving a first and a second CSI measurement report associated with the first and second CSI processes respectively, and identifying one of the first and second non-serving transmission points as the dominantly interfering transmission point based on a comparison of the first and the second CSI measurement reports. Furthermore, the CSI process configuration may further comprise a third CSI process configured with a third CSI-RS resource for the serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the serving transmission point. The arrangement may be further configured to, when one of the first and the second non-serving transmission point has been identified as the dominantly interfering transmission point:

- receive a third CSI measurement report associated with the third CSI process;

- compare the second CSI measurement report with the third CSI measurement report when the first non-serving transmission point has been identified as the dominantly interfering transmission point;

- compare the first CSI measurement report with the third CSI measurement report when the second non-serving transmission point has been identified as the dominantly interfering transmission point; and - coordinate the scheduling based on the comparing with the third CSI measurement report.

In embodiments of the invention, the arrangement or the network nodes 500, 510, 520, of the arrangement may comprise a processing circuit 501 , 51 1 , 521 , configured to control the transmission over the transmission points TP1 , TP2, TP3 of the cluster and a memory 502, 512, 522, storing instructions that, when executed by the respective processing circuit, cause the arrangement to identify a transmission point in the cluster dominantly interfering transmissions to a wireless device 550 from a serving transmission point in the cluster, and disregard the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device. Furthermore, in the embodiment illustrated in Figure 5b, the network nodes 510, 520 may comprise a communication interface each 514, 524, allowing the communication between the two network nodes 510, 520. The processing circuits described above may comprise a Central Processing Unit (CPU) which may be a single unit or a plurality of units. Furthermore, the memory may be a non-volatile memory, e.g. an EEPROM (Electrically Erasable Programmable Read-Only Memory), a flash memory or a disk drive. The memory may correspond to a computer program product (CPP) comprising a computer program. The computer program comprises code means which when run on the arrangement causes the CPU to perform steps of the methods described earlier with reference to Figures 4a-4c.

In an alternative way to describe the embodiment in Figure 5a, illustrated in Figure 5c, the arrangement 500 comprises a means for identifying a transmission point in the cluster dominantly interfering transmissions to a wireless device 550 from a serving transmission point in the cluster, and a means for disregarding the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device. The means described above are functional means which may be implemented in hardware, software, firmware or any combination thereof. In one embodiment, the means are implemented as a computer program running on a processor.

The above mentioned and described embodiments are only given as examples and should not be limiting. Other solutions, uses, objectives, and functions within the scope of the accompanying patent claims may be possible.

Claims

A method for coordinating scheduling of transmissions to wireless devices within a cluster of transmission points (TP1 , TP2, TP3), the method being performed in an arrangement (500) of a wireless communication network applying coordinated multipoint transmission in the cluster, the method comprising:

- identifying (410) a transmission point in the cluster dominantly interfering transmissions to a wireless device (550) from a serving transmission point in the cluster, the wireless device being capable of applying interference rejection combining, wherein the identifying is based on Channel State Information, CSI, measurement reports received from the wireless device, the CSI measurement reports being associated with a CSI process configuration in the arrangement and in the wireless device, and

- disregarding (420) the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device.

The method according to claim 1 , further comprising:

- coordinating (430) scheduling of transmissions from transmission points in the cluster other than the identified transmission point based on the CSI measurement reports received from the wireless device.

The method according to claim 2, wherein coordinating (430) scheduling comprises adjusting at least one of transmission power and beamforming of transmissions from transmission points in the cluster other than the identified transmission point.

The method according to any of the preceding claims, wherein identifying (410) the transmission point in the cluster dominantly interfering comprises:

- selecting (41 1 ) the transmission point from the cluster of transmission points, and - reducing (412) transmission power for all transmission points in the cluster except the selected transmission point, such that the selected transmission point is identified as dominantly interfering. 5. The method according to claim 4, wherein the transmission point is selected based on at least one of the CSI measurement reports, a channel quality measurement received from the wireless device, and a load situation for the transmission points in the cluster. 6. The method according to any of the preceding claims, further comprising:

- identifying (400) the wireless device as capable of applying interference rejection combining when a number of layers used by the wireless device is smaller than a number of reception antennas at the wireless device. 7. The method according to claim 6, wherein identifying (400) the wireless device as capable of applying interference rejection combining further comprises:

- determining the number of reception antennas used by the wireless device based on a capability received from the wireless device,

- determining the number of layers used by the wireless device based on a rank indicator received from the wireless device.

The method according to claim 6, wherein identifying (400) the wireless device as capable of applying interference rejection combining further comprises:

- receiving a rank indicator from the wireless device, and

- determining to use a number of layers which is smaller than the number of layers indicated by the received rank indicator for the communication with the wireless device.

The method according to any of the preceding claims, wherein the CSI process configuration is configured such that the CSI measurement reports associated with the CSI process configuration enables determination of power received at the wireless device from each transmission point in the cluster.

10. The method according to any of the preceding claims, wherein the CSI process configuration is configured such that the CSI measurement reports associated with the CSI process configuration enables determination of power received at the wireless device from the serving transmission point relative to power received at the wireless device from all non-serving transmission points in the cluster.

1 1 . The method according to any of the preceding claims, wherein the cluster comprises a first and a second non-serving transmission point in addition to the serving transmission point, and wherein the CSI process configuration comprises a first CSI process configured with a first CSI-RS resource for the first non-serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the first non-serving transmission point, the CSI process configuration further comprising a second CSI process configured with a second CSI-RS resource for the second non-serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the second non-serving transmission point, the method further comprising:

- controlling transmission of CSI-RSs in accordance with the CSI process configuration,

and wherein identifying (410) the transmission point in the cluster dominantly interfering comprises:

- receiving a first and a second CSI measurement report associated with the first and second CSI processes respectively,

- identifying one of the first and second non-serving transmission points as the dominantly interfering transmission point based on a comparison of the first and the second CSI measurement reports.

12. The method according to claim 1 1 when dependent on claim 2, wherein the CSI process configuration further comprises a third CSI process configured with a third CSI-RS resource for the serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the serving transmission point, the method further comprising when one of the first and second non-serving transmission points has been identified (410) as the dominantly interfering transmission point:

- receiving a third CSI measurement report associated with the third CSI process,

- comparing the second CSI measurement report with the third CSI measurement report when the first non-serving transmission point has been identified as the dominantly interfering transmission point,

- comparing the first CSI measurement report with the third CSI measurement report when the second non-serving transmission point has been identified as the dominantly interfering transmission point,

and wherein the scheduling is coordinated (430) based on the comparing with the third CSI measurement report.

13. An arrangement (500) of a wireless communication network for coordinating scheduling of transmissions to wireless devices within a cluster of transmission points (TP1 , TP2, TP3), wherein the arrangement (500) is applying coordinated multipoint transmission in the cluster, the arrangement being configured to:

- identify a transmission point in the cluster dominantly interfering transmissions to a wireless device (550) from a serving transmission point in the cluster, the wireless device being capable of applying interference rejection combining, wherein the identifying is based on Channel State Information, CSI, measurement reports received from the wireless device, the CSI measurement reports being associated with a CSI process configuration in the arrangement and in the wireless device, and

- disregard the identified transmission point when coordinating scheduling of transmissions from transmissions points in the cluster for reducing interference at the wireless device.

14. The arrangement (500) according to claim 13, further configured to:

- coordinate scheduling of transmissions from transmission points in the cluster other than the identified transmission point based on the CSI measurement reports received from the wireless device.

15. The arrangement (500) according to claim 14, further configured to coordinate scheduling by adjusting at least one of transmission power and beamforming of transmissions from transmission points in the cluster other than the identified transmission point.

16. The arrangement (500) according to any of claims 13-15, further configured to identify the transmission point in the cluster dominantly interfering by:

- selecting the transmission point from the cluster of transmission points, and

- reducing transmission power for all transmission points in the cluster except the selected transmission point, such that the selected transmission point is identified as dominantly interfering.

17. The arrangement (500) according to claim 16, further configured to select the transmission point based on at least one of the CSI measurement reports, a channel quality measurement received from the wireless device, and a load situation for the transmission points in the cluster.

18. The arrangement (500) according to any of claims 13-17, further configured to:

- identify the wireless device as capable of applying interference rejection combining when a number of layers used by the wireless device is smaller than a number of reception antennas at the wireless device.

19. The arrangement (500) according to claim 18, further configured to identify the wireless device as capable of applying interference rejection combining by: - determining the number of reception antennas used by the wireless device based on a capability received from the wireless device, - determining the number of layers used by the wireless device based on a rank indicator received from the wireless device.

20. The arrangement (500) according to claim 18, further configured to identify the wireless device as capable of applying interference rejection combining by:

- receiving a Rl from the wireless device, and

- determining to use a number of layers which is smaller than the number of layers indicated by the received Rl for the communication with the wireless device.

21 . The arrangement (500) according to any of claims 13-20, wherein the CSI process configuration is configured such that the CSI measurement reports associated with the CSI process configuration enables determination of power received at the wireless device from each transmission point in the cluster.

22. The arrangement (500) according to any of claims 13-21 , wherein the CSI process configuration is configured such that the CSI measurement reports associated with the CSI process configuration enables determination of power received at the wireless device from the serving transmission point relative to power received at the wireless device from all non-serving transmission points in the cluster.

23. The arrangement (500) according to any of claims 13-22, wherein the cluster comprises a first and a second non-serving transmission point in addition to the serving transmission point, and wherein the CSI process configuration comprises a first CSI process configured with a first CSI-RS resource for the first non-serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the first non-serving transmission point, the CSI process configuration further comprising a second CSI process configured with a second CSI-RS resource for the second non-serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the second non-serving transmission point, the arrangement being configured to:

- control transmission of CSI-RSs in accordance with the CSI process configuration, and

- identify the transmission point in the cluster dominantly interfering by:

• receiving a first and a second CSI measurement report associated with the first and second CSI processes respectively, and

• identifying one of the first and second non-serving transmission points as the dominantly interfering transmission point based on a comparison of the first and the second CSI measurement reports.

24. The arrangement (500) according to claim 23 when depending on claim 13, wherein the CSI process configuration further comprises a third CSI process configured with a third CSI-RS resource for the serving transmission point and with CSI-IM resources such that all other transmission points in the cluster are muted during transmission of the CSI-RS by the serving transmission point, the arrangement being further configured, when one of the first and second non- serving transmission points has been identified as the dominantly interfering transmission point, to:

- receive a third CSI measurement report associated with the third CSI process,

- compare the second CSI measurement report with the third CSI measurement report when the first non-serving transmission point has been identified as the dominantly interfering transmission point,

- compare the first CSI measurement report with the third CSI measurement report when the second non-serving transmission point has been identified as the dominantly interfering transmission point, and

coordinate the scheduling based on the comparing with the third CSI measurement report.