Downlink interference mitigation in wireless communication

Abstract

Embodiments include methods for a network node (NN) in a radio access network (RAN) providing service to terminal devices. Such methods include configuring a served UE about a CSI report on resources of DL RSs from the NN and a neighboring NN. Such methods include, the NN receives CSI report from the served UE and sends information about the CSI report to the neighboring NN. Then, it obtains an interference covariance matrix for spatial DL interference mitigation. Those methods provide a robust way to do interference rejection in the downlink without the need of requiring any reciprocity assumptions.

Description

[0001] P110411W001

[0002] DOWNLINK INTERFERENCE MITIGATION IN WIRELESS COMMUNICATION

[0003] TECHNICAL FIELD

[0004] The present disclosure relates generally to wireless networks, and more specifically to downlink interference mitigation in wireless communication.

[0005] BACKGROUND

[0006] The ever-increasing end-user demands are a significant challenge to the operators in telecommunications. Separating users spatially by means of precoding and / or beamforming is one way to improve the performance of a wireless system. The coherent transmission typically not only aims at maximizing the received signal power at the desired receiver, but also at reducing interference to all non-desired receivers.

[0007] Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) are the two dominating duplexing techniques to coordinate the uplink (UL) and downlink (DL) transmissions in 4G / 5G wireless communication.

[0008] In FDD, data transmissions in UL and DL occur on two nonoverlapping carriers or frequency bands, which may happen simultaneously in time.

[0009] In single carrier TDD system, a same carrier frequency band is used for both UL and DL transmissions. To avoid collisions between the transmissions in UL and DL, which otherwise would cause problems with interference between UL and DL, the UL and DL are transmissions in nonoverlapping time slots.

[0010] In the case of multi-carrier transmission, in 3GPP LTE / NR referred to as Carrier Aggregation (CA), there may exist several DL carriers and UL carriers. It is a common occurrence that not all the TDD carriers may have uplink time slots and will therefore carry no UL and only DL data.

[0011] A wireless cellular network typically consists of many cells. A user equipment (UE) is typically served by one cell which is the serving cell. A DL transmission from a radio node to a UE in a cell may be interfered by a simultaneous transmission in DL from another radio node towards a UE in a neighboring cell. This is what is referred to as DL inter-cell interference. A similar situation may also occur in the UL direction. A data transmission in UL from a UE to a radio node in one cell can be interfered by a simultaneous transmission in UL from another UE towards a radio node in a neighboring cell.

[0012] Reciprocity Assisted Interference-Aware Transmission (RAIT) was introduced as an interference mitigation technique for suppressing inter-cell interference in DL for reciprocal radio channel TDD systems. One of the key features of RAIT is the automatic interference P110411W001 handling based on sounding information. The idea behind is to estimate the inter-cell spatial interference covariance matrix in the uplink, based on sounding information. Assuming that the spatial distribution of the uplink inter-cell interferers is representative of the UE spatial properties, the DL transmission should be made with the UE spatial awareness to avoid sending interference in this "direction". For example, by means of precoding and / or beamforming nulls towards the dominating spatial directions, the inter-cell interfered UEs in the downlink can get less effected by the interference source.

[0013] Figure 1 illustrates an exemplary RAIT signaling exchange process in an operating telecommunication system including several radio access nodes (101a, 101b and 101c), respectively providing a cell as the serving cell for a corresponding UE (102a, 102b and 102c). For a first UE 102a served by a first cell provided by a first radio node 101a, starting from obtaining a scheduling of sounding reference signal (SRS) from the first radio node 101a, then, it transmits SRSs based on the UL scheduling. For a radio node 101b providing a neighboring cell to the first cell, it can also receive those SRSs sent from the UE 102a and then estimates the sounding channel interference based on the received SRSs and computes an interference covariance matrix.

[0014] Due to the assumption of channel reciprocity which means quality of the channel for UL SRS can be considered as the quality of the DL channel (since in TDD uplink and downlink transmission are on same frequency points), the matrix is then added to a precoder in which downlink precoding weights of the transceiver antennas of the radio node 101b are determined according to the uplink interference awareness. When there’s a severe interference from one spatial direction, the precoder generates nulls towards that direction to mitigate the DL interference. Note that it is feasible due to the prerequisite of channel reciprocity in TDD system, and channel conditions usually won’t tremendously change in such a short period within two consecutive UL and DL transmissions.

[0015] SUMMARY

[0016] An object of embodiments of the present disclosure is to provide approaches for downlink interference rejection unnecessarily with a reciprocal scenario in a radio access network (RAN). For example, under an FDD scheme, a network node can obtain interference information about its own downlink signals and then adjust its spatial downlink transmission to mitigate its interference to terminal devices served by other cell(s). Those downlink signals to be measured are signals which the network is scheduled to send, meaning that no new downlink signals are added for interference rejection. P110411W001

[0017] Embodiments include methods (e.g., procedures) for a network node configured for providing telecommunication services for terminal devices in a RAN and performing downlink interference rejection during its service.

[0018] Some of these exemplary methods include configuring a first terminal device served by a first cell which is provided by the network node, about a measurement report on resources of downlink signals from a neighboring cell which is a non-serving cell of the first terminal device. These exemplary methods also include receiving measurement report from the first terminal device, regarding interference information associate with the resources of those downlink signals.

[0019] The network node derives and collects interference information associate with those resources from CSI reports from all its active terminal devices served by the first cell, and send an interference covariance matrix per subband to the neighboring cell, so that the neighboring cell can form its own interference covariance matrix based on those matrices from its neighboring cells and perform interference rejection.

[0020] Some of these exemplary methods include configuring a first terminal device served by a first cell which is provided by the network node, about a measurement report on resources of downlink signals from a neighboring cell which is a non-serving cell of the first terminal device. These exemplary methods also include sending information about a CSI report to the neighboring cell.

[0021] In some embodiments, the information can be information about an uplink grant which is to trigger the terminal device to measure and send out the CSI report it its serving cell.

[0022] In some further embodiments, the information is sent via a backhaul link between those two cells prior to the uplink grant is sent, so that the second cell can adjust its schedule for receiving the CSI report directly via the resource indicated by the uplink grant.

[0023] In some other further embodiments, the information is sent via air interface on a downlink channel of the first cell. The second cell works in a full band so that it is feasible to receive the information as a behavior of a terminal device.

[0024] In some embodiments, the second cell receives the same uplink grant as the terminal device does. As an exemplary method, when the first cell sends a DCI message to the terminal device, the second cell receives the DCI pretending as another terminal device.

[0025] Therefore, the second cell can receive the CSI report and directly get to know spatial interference information associate with the resources of its own downlink signals since it is knowledgeable of the uplink resource of the CSI report.

[0026] In some embodiments, a terminal device may include an interference covariance matrix in its CSI report, according to CSI measurement and reporting configuration. As an exemplary method, the second cell who receives those relevant CSI reports from a plurality of non-served P110411W001 terminal devices can derive directly and combine those relevant interference covariance matrices into a single interference covariance matrix per subband.

[0027] Some other embodiments include apparatus (e.g., structure) for a RAN node configured to providing service for terminal devices while mitigating DL interference towards other non-serving terminal devices. Some other embodiments include apparatus (e.g., structure) for aterminal device configured for providing interference measurement to its serving cell, assisting downlink interference rejection especially in a non-reciprocal channel condition.

[0028] These and other objects, features, and advantages of embodiments of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figures 1 illustrates an exemplary RAIT scheme in a TDD communication scheme according to the prior art.

[0031] Figure 2 is a block diagram illustrating a generalized method embodiment implemented in a network node according to the disclosure.

[0032] Figure 3 shows an exemplary communication between network nodes, and communication between network nodes and terminal devices, for obtaining DL inter-cell interference result according to some embodiments of the disclosure.

[0033] Figure 4-6 are some exemplary signaling diagrams illustrating actions and interactions among network nodes and terminal device(s) according to some embodiments of the disclosure.

[0034] Figure 7 shows an exemplary communication between network nodes via air interface, and communication between network nodes and terminal devices, for obtaining DL inter-cell interference result according to some embodiments of the disclosure.

[0035] Figure 8 shows an illustrating structure of a network node according to various embodiments of the present disclosure.

[0036] Figure 9 shows an illustrating structure of a terminal device according to various embodiments of the present disclosure.

[0037] DETAILED DESCRIPTION

[0038] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided as examples to convey the scope of the subject matter to those skilled in the art. P110411W001

[0039] In general, all terms used herein are to be interpreted according to their ordinary meaning to a person of ordinary skill in the relevant technical field, unless a different meaning is expressly defined and / or implied from the context of use. All references to a / an / the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise or clearly implied from the context of use. The operations of any methods and / or procedures disclosed herein do not have to be performed in the exact order disclosed, unless an operation is explicitly described as following or preceding another operation and / or where it is implicit that an operation must follow or precede another operation. Any feature of any embodiment disclosed herein can apply to any other disclosed embodiment, as appropriate. Likewise, any advantage of any embodiment described herein can apply to any other disclosed embodiment, as appropriate.

[0040] Furthermore, the following terms are used throughout the description given below:

[0041] • Network Node: As used hereinafter, a “network node” (or equivalently “radio network node,” “radio access network node,” “radio access node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., gNB in a 3 GPP 5G / NR network), base station distributed components (e.g., CU and DU), a high-power or macro base station, a low-power base station (e.g., micro, pico, femto, or home base station, or the like), an integrated access backhaul (IAB) node, a transmission point (TP), a transmission reception point (TRP), a remote radio unit (RRU or RRH), and a relay node.

[0042] • Terminal Device: As used hereinafter, a “terminal device” (or “wireless device”) is any type of device that is capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other wireless devices. Communicating wirelessly can involve transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information through air. Unless otherwise noted, the term “wireless device” is used interchangeably herein with the term “user equipment” (or “UE” for short), with both of these terms having a different meaning than the term “network node”.

[0043] • Radio Node: As used hereinafter, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0044] • Node: As used hereinafter, the term “node” (without prefix) can be any type of node that can in or with a wireless network (including RAN and / or core network), including a radio access node (or equivalent term), core network node, or wireless device. However, the P110411W001 term “node” may be limited to a particular type (e.g., radio access node) based on its specific characteristics in any given context.

[0045] • Interference measurements: As used hereinafter, “interference measurements” are mainly for measurements by a terminal device on downlink inter-cell interference from a (neighboring) non-serving cell. Network configuration includes the resources to be measured by the terminal device and what the terminal device needs to report regarding inter-cell interference.

[0046] The above definitions are not meant to be exclusive. In other words, various ones of the above terms may be explained and / or described elsewhere in the present disclosure using the same or similar terminology. Nevertheless, to the extent that such other explanations and / or descriptions conflict with the above definitions, the above definitions should control.

[0047] Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system.

[0048] As mentioned above, it is prerequisite to the TDD system for the RAIT approach for DL interference mitigation. And interference rejection / mitigation in DL comes at a cost in form of a loss of beamforming gain towards the UE who is served by the cell / sector. This loss in beamforming gain is overcome by the accumulated interference rejection effect from several cells / sectors which provides a net gain on system level. For the gain on system level, it is crucial that the interference rejection in downlink is only performed when there are active DL data transmission being interfered in the neighbouring cells / sectors. In other words, interference suppression / rej ection must only be enabled towards those victim users that are receiving data transmission in the neighbouring cells / sectors. It is therefore important to share the resource allocation of active users per slot between the scheduler of neighbouring cells / sectors.

[0049] Therefore, the current DL interference suppression based on UL SRS need a tight coupling between an active UL SRS channel and an ongoing DL data transfer. Due to periodic UL SRS might have long interval, a flexible way to create a tight coupling is aperiodic SRS triggered by DCIl l (which can be enabled and disabled quickly) on a per slot basis. However, it needs extra aperiodic SRSs (UL resources) and extra signalings, and still bases on a channel reciprocity assumption. In a nutshell, there need a way for DL interference suppression especially under FDD system or an FDD+TDD CA scenario.

[0050] This disclosure provides solutions to how DL interference mitigation is done for nonreciprocal scenarios such as an FDD system where there is no frequency overlapping DL and UL carriers and also on an FDD carrier of a FDD+TDD Carrier Aggregation (CA) configuration for a UE. P110411W001

[0051] A method is provided with the interference awareness being measured based on downlink signals instead of sounding reference signals. Figure 2 as a block diagram illustrates main steps of an embodiment of the method, which can provide a robust way to do interference rejection in the downlink without the need of requiring any reciprocity assumptions.

[0052] A method implemented in a first network node (NN) serving a first terminal device in a radio access network (RAN) is provided. The method comprising: transmitting (210), configuration information to the first terminal device about a measurement report on resources of downlink signals received from a second neighboring NN and downlink reference signals received from the first NN; receiving (220) a channel state information, CSI, report comprising interference measurement on the downlink signals transmitted on the resources; sending (230) information about the CSI report to the second neighboring NN; obtaining (250) an interference covariance matrix for spatial DL interference mitigation.

[0053] There is shown in Figure 3 a schematic diagram of a communication system 20, according to an embodiment of the above-mentioned method, such as a 3 GPP-type cellular network that supports standards such as NR (5G) on or above release 8 or future generation, which comprises an access network, such as a radio access network, and a core network (omitted in the figure). The access network comprises a plurality of NNs 201a, 201b, 201c, such as NBs, gNBs or other types of wireless access points, each defining its corresponding coverage area. A first network node 201a and a third network node 201c (hereinafter “NB” according to the embodiment) are both connected to a second NB 201b via backhaul interface, such as X2, E5 or similar interface. NBs 201a and 201c may also connect to each other via backhaul interface, directly or indirectly connected by a core NN according to network deployment, which is not shown in the figure.

[0054] A first terminal device 202a (hereinafter “UE” according to the embodiment) is configured to wirelessly connect to, or be paged by, the corresponding NB 201a which is then serving the first UE 202a. It may also locate close to (even within) the coverage area of a neighboring NB 201b, which means signals from the neighboring NB 201b are possibly detectable by the first UE 202a and may cause downlink interference to the communication between NB 201a and the first UE 202a. Note that the first UE might also connected to NB 201c which is within a same Coordinated Multi Point, CoMP, cluster with the NB 201a, the connection not being shown in the figure for simplicity. Similar to the first UE, a second UE 202b is served by the second NB 201b, and a third UE 202c is served by the third NB 201c. Note that although only three UEs correspondingly served by those three NBs are shown for convenience, the communication system may include many more terminal devices and NNs. P110411W001

[0055] Note that in another embodiment, the NBs shown in the figure could be exchanged to transmission points (TRPs). For example, a first TRP 201a is in a cell serving a first UE 202a, and a second TRP 202a is in a neighboring cell currently not serving the first UE 202a but serving a second UE 202b. The second TRP 202a might have dominating interference effect to the first UE 202a, when the second UE 202b moves to another location, shown in Figure 3 as UE 202b’, in which the second TRP’s signaling towards the second UE 202b’ are in similar direction as it towards the first UE 202a.

[0056] In a further embodiment, the first NN may not only send information about the CSI report to the second neighboring NN. Based on a same scheme, it could also receive (S240) information about a CSI report from its neighboring NNs, for example, the second neighboring NN and / or another neighboring NN. The CSI report indicates spatial interference information on CSI-RS resource associated to the first NN.

[0057] In a further embodiment, interference covariance matrix obtained by the first NN corresponding to one of its operating subbands. The first NN obtains interference covariance matrix for each of its operating band for spatial DL interference mitigation. After the first NN obtains interference covariance matrix for each of its operating subbands, it can schedule a PDSCH transmission to its serving UE(s) and use a precoder that takes into account the interference covariance matrix per subband.

[0058] For example, an interference suppressing precoder such as Minimum Mean Square Error (MMSE) precoder can make generate nulls or reduced transmission power towards dominating spatial direction(s) of the interference covariance matrix. These nulls provide interference rejection towards those UEs in the neighboring cells, such as the third neighboring cell, that have interference components included in the interference covariance matrix. In those spatial directions, interference brought by the first NN will be mitigated.

[0059] Taking the first NB (or TRP) 201 a as an example of the first NN, three main embodiments are hereinafter provided.

[0060] In a first main embodiment to which Figure 4 is also referred, a first UE 202a is configured (S410) by its serving cell provided by a first NB 201a to measure a plurality of downlink signals and then report the measurement. A UE is typically configured e.g. via RRC message, with measurement configuration and measurement reporting configuration e.g. measurement gap pattern, carrier frequency information, types of measurements (e.g. RSRP etc.), higher layer filtering coefficient, time to trigger report, reporting mechanism (e.g. periodic, event triggered reporting, event triggered periodic reporting etc.) etc.

[0061] The downlink signals to be measured can be CSI reference signals, RSs. Those signals can be RSs from the first NB 201a. They can also be PDSCH transmission and / or RSs from a second P110411W001 cell provided by a second NB 201b, where the second cell is a neighbor cell of the first cell serving the first UE 202a. The first UE 202a might be interfered by one or more of its non-serving cells (e.g., the second cell). The first UE is knowledgeable on CSI-RS resources belonging to its serving cell(s) and downlink resources belong to one or more non-serving cell(s) according to the configuration.

[0062] In order to enable the first UE 202a to measure CSI-RS and / or PDSCH from a non-serving cell (e.g., the second cell), the first NB 201a sets CSI Interference Measurement (CSI-IM) resource elements coincide with zero power (ZP) CSI-RS resource. The CSI-IM resource can be used for measuring inter-cell interference from neighbor cells. ZP implies that no data or CSI-RS is sent from the first cell on the resource elements dedicated to CSI-IM. And then the non-zero power (NZP) CSI-RS and / or PDSCH sent by the second NB 202a carried on overlapping resource elements of the CSI-IM resource are then become clearly visible in the CSI-IM / ZP-CSI-RS resource elements by the first UE 202a. CSI-RS and / or PDSCH resource associated to or owned by the second cell hereinafter refers to NZP-CSI-RS resource of the second cell and in meanwhile overlaps with ZP-CSI-RS resource / CSI-IM resource of the first cell.

[0063] According to the current 3GPP standard, for example in 38.214 V8.11.0, CSI- ReportConflg is associated with a single downlink BWP given in the associated CSI- ResourceConflg for channel measurement and contains the parameter(s) for one CSI reporting band. The reportFreqConflguration indicates the reporting granularity in the frequency domain, including the CSI reporting band and the PMI / CQI reporting is sub-band. Although periodic or semi-persistent CSI-RS / CSI-IM can be used to measure channel / interference, aperiodic CSI-RS triggered by DCI would be much more flexible for this scheme. The CSI-ReportConflg can also include CodebookConflg, which contains configuration parameters for Type-I, Type II, Enhanced Type II CSI, or Further Enhanced Type II, since those embodiments may be considered as being codebook based.

[0064] The first NB 201a can indicate the second cell provided by the second 201b NB via parameter addtionalPCI. addtionalPCI in 3GPP standard 38.331 such as version V8.10.0 indicates physical cell ID (PCI) of SSB transmitted from a cell. The CSI-ReportConflg includes TCI-State in which addtionalPCI is comprised as below and when TCI-state is pointing to the second cell which is a non-serving cell, the first UE 202a will then measure and report CSI-RS from the second cell provided by the second NB 201b according to the CSI-ReportConflg.

[0065] TCI-State information element P110411W001

[0066] When the first NB 201a receives (S420) a CSI report from the first UE 202a, the CSI report includes CSI measurements of all the CSI-RS resources the first UE 202a is indicated, e.g., via addtionalPCI. Aperiodic CSI report can be triggered by DCI on PDCCH which we can also say that the configuration may include both RRC message and DCI.

[0067] The received CSI report may include Channel Quality Indicator (CQI), precoding matrix indicator (PMI), CSI-RS resource indicator (CRI), layer indicator (LI), rank indicator (RI), Layer 1 Reference Signal Receiving Power (Ll-RSRP), Layer 1- Signal to Interference plus Noise Ratio (Ll-SINR) or Capability Index. PMI, CQI, RI and Ll-SINR are typically indicating interference measurement result.

[0068] Practically, there could be multiple UEs served by the first cell, and NZP-CSI-RS or PDSCH resources of non-serving cells of those multiple UEs are indicated by the first NB201 with ZP / IM ports in the first cell via configuration. Therefore, the first NB201 may receive multiple CSI reports from those UEs, regarding its own NZP-CSI-RS resources and NZP-CSI-RS resources of its neighboring cells, e.g., the second cell. For simplicity, CSI-RSs from the nonserving neighboring cell(s) are detected and measured by a terminal device as basis for the CSI report to its serving cell. PDSCH data (or multiplexed with CSI-RS) from the non-serving neighboring cell(s) is also applied hereinafter as long as the configuration indicates by ZP / IM ports in the serving cell.

[0069] The first NB 201a would convert the CSI interference reports of each UEs served by the first cell into a corresponding interference covariance matrix per subband. As a further embodiment, only UEs in active state would be configured for this kind of CSI report. For each CSI-RS resource associated with its neighboring cells, the matrices for all those UEs that are active in DL on a subband are combined into one interference covariance matrix corresponding to the CSI-RS resource.

[0070] Then, the first NB 201a sends (S430) information about the CSI report(s) to the second NB 201b, via a backhaul link, e.g., a X2 or E5 link. The information is the interference covariance matrix corresponding to the CSI-RS resource associated with the second cell to the second NB 201b.

[0071] The first NB 201a obtains (S440) an interference covariance matrix for each of its operating subband, which is also called interference awareness. The interference parameters can be obtained from the multiple CSI reports transmitted by its serving UEs. In a further vice versa embodiment, interference parameters can be further obtained from its neighboring cells, as shown in block S240 in Figure 2. For example, it can be obtained from a third neighboring cell provided by a third NB 201c (not shown in Figure 3), and part of the interference parameters is P110411W001 received from a third UE 202c served by the third cell. In this situation, the first cell is a nonserving cell of the third UE 202c, other than the first NB 201a and the third NB 201c being a CoMP cluster for the third UE 202c. As such, the interference awareness is obtained by combining the interference information and is used to mitigate the first cell’s DL interference to the neighboring UEs not served by itself, e.g., the third UE 202c.

[0072] Note that from the first NB 20 la’s angle, there’s no limited step sequence between sending interference covariance matrix corresponding to the second cell’s CSI-RS resource and obtaining interference covariance matrix corresponding to the first cell’s CSI-RS resource. While if interference covariance matrix of the first cell’s CSI-RS resource is going to be sent by the second NB 201b, the obtaining interference covariance matrix corresponding to the first cell’s CSI-RS resource might be performed after the first NB20 la receives interference information from the second NB 201b via backhaul link.

[0073] Therefore, from a viewing angle of the second cell which is an interfering cell to the first UE 202a, the second NB 201b providing the second cell receives (S430) an interference covariance matrix corresponding to CSI-RS resource associated to the second cell from the first NB 201a. It may also receive another interference covariance matrix corresponding to CSI-RS resource associated to the second cell from a third neighboring cell provided by a third NB 201c. And then, it combines (S440) the received interference covariance matrices into a single matrix per subband. Further, the second NB 201b adds the interference covariance matrix (per subband) to its MMSE precoder. The precoder generates null towards the direction to the first UE 202a. in this way, the first UE’s spatial DL inter-cell interference from the second cell can be mitigated, in regardless of whether channel reciprocity is a prerequisite or not.

[0074] A variant embodiment can be that a first UE 201b is capable of generating an interference covariance matrix as a new interference report type in the CSI report to be sent to its serving cell. One possible way is to set up several CSI-IM ports, e.g., 32 CSI-IM ports in a same OFDM symbol. And then the first UE 201b registers base band samples on each CSI-IM port. For example, the complex samples per OFDM symbol would be a matrix, e(port, subcarrier).

[0075] An interference covariance matrix for a subband spanning N subcarriers (starting at subcarrier index Nstart) is computed as:

[0076] Q(i,j) = sum(e(i,sc)*conj(e(j,sc)), wherein SC=Nstart. . . Nstart+N-1

[0077] The Q matrix describes the spatial properties of the interference and is sent (S220) via a CSI report from the first UE 201b. The first NB 201a providing the first cell serving the first UE 201b collects the Q matrices from the served UEs active in the first cell. For each CSI-RS resource P110411W001 associated with the second cell, the first NB 201a combines relevant interference covariance matrices and send (S230) to the second NB 202a.

[0078] In a second main embodiment to which Figure 5 is also referred, a first UE 202a is configured (S510) by the first NB 201a in a similar way as is described in the first main embodiment. A similar assumption is hold that the first UE 202a is severely interfered by a second cell’s DL signal. Sending (S230) information about a CSI report to the second neighboring network node comprises that the first NB 201a providing a first cell serving the first UE 202a sends (S520) a message to a second NB 202a providing the second cell, including uplink grant information to be sent to the first UE 202a. After an uplink grant with same corresponding information has been sent to the first UE 202a to trigger a measurement and report from the first UE 202a, the second NB 202a can also receive (S550) and decode a CSI report from the first UE 202a, which is intentionally sent (S540) to the first NB 201a according to the CSI report configuration.

[0079] For an aperiodic CSI report, it is normally transmitted on a PUSCH, and can be multiplexed with uplink data. CSI reporting on PUSCH support both Type 1 and Type 2 CSI report. The second NB 201b capable of receiving and decoding the CSI report from the first UE 202a should be knowledgeable of the scheduling information and other necessary information, such as DMRS sequences and PUSCH scrambling sequences, and needs to schedule its uplink resource in advance to the UL grant being sent. From the angle of the first NB 201a, considering possible transmission delay in backhaul link, the scheduling information and other necessary information should be conveyed (S520) to one or more interfering NBs via the backhaul link prior to said scheduling is sent (S530).

[0080] The scheduling of UL resource can be sent (S530) in DCI format 0 1 or DCI format0_2 via PDCCH to trigger aperiodic CSI trigger state. When the first UE 202a successfully decodes the DCI, CSI-RS from both its serving cell and the interfering cells (which can be seen in Figure 5), such as the second cell, can be measured and measurement report is sent out according to the CSI report configuration.

[0081] From the first NB 201a’s angle, CSI reports from multiple UEs from neighboring cells are received (corresponding to S220 in Figure 2 however not shown in Figure 5) and interference information regarding the CSI-RS resource associated with the first cell is collected. For example, a CSI report from a third UE 202c served by a third cell is received by the first NB 201a, due to an earlier knowledge of a UL grant which is to be sent by a third NB 203 a. The third NB 203 a can be a same or different node with the second NB 202a. Then the first NB 201a combined (S560) into a corresponding interference covariance matrix per subband. The matrix can be added to a MMSE precoder which will make the precoder generate nulls towards the dominating spatial P110411W001 directions of the interference covariance, so that spatial DL interference to UEs in the neighboring cell(s) can be mitigated.

[0082] Comparing with the first main embodiment, the first NB 201a sends a message regarding information of an UL grant to a neighboring second NB 202a prior to the CSI report is generated, instead of sending a message regarding interference information associated with the second NB 202a after the CSI report is generated and transmitted. Therefore, in this embodiment, the step of receiving (S220) a CSI report on resource associated with its neighboring cells is performed later than the step of sending (S230) information about the CSI report to its neighboring cells.

[0083] The direct over the air coordination (OTA) communication between the first UE 201b and the neighboring second NB 202a eliminates the need for backhaul communication of the spatial interference information. The UL grant information needed to decode the CSI is expected to be smaller than the amount of information contained in a spatial interference information report.

[0084] From the second NB 202a’ s angle, CSI reports from multiple UEs from neighboring cells are received (S550) and interference information regarding the CSI-RS resource associated with the second cell is collected, and then combined (S560) into a corresponding interference covariance matrix per subband. The matrix can be added to a MMSE precoder which will make the precoder generate nulls towards the dominating spatial directions of the interference covariance, so that spatial DL interference to the first UE 202a can be mitigated.

[0085] Similar to the variant embodiment of the first main embodiment, the first UE 201b is capable of generating an interference covariance matrix as a new interference report type in the CSI report to be sent (S540) to its serving cell. And the second NB 202a also receives (S550) the interference covariance matrix comprised in the CSI report. Less calculation is performed at the receiving node since it can simply collect interference information regarding the resource associated with itself.

[0086] In a third main embodiment to which both Figure 6 and Figure 7 are referred, a first UE 202a is configured (S610) in a similar way as is described in the first main embodiment. A similar assumption is hold that the first UE 202a is severely interfered by a second cell’s DL signal. A first NB 201a providing a first cell serving the first UE 202a sends (S620) an UL grant scheduling to the first UE 202a. It can be a DCI format 0 1 or DCI format0_2 via PDCCH as a trigger for the first UE 202a to measure CSI-RSs from both the first NB 201a and the second NB 201b and send out CSI report based on the CSI report configuration. A second NB 201b providing the second cell, including uplink grant information to be sent to the first UE 202a.

[0087] An uplink grant (i.e., the scheduling of UL resource) is sent (S620) in DCI format 0 1 or DCI format0_2 via PDCCH to trigger aperiodic CSI trigger state. The second NB 201b is configured to eavesdrop on the PDCCH. The UL grant intended for the first UE 202a which is in P110411W001 a neighboring cell of the second cell is received (S620) by the second NB 201b, as is also shown in Figure 7 by the arrow from NB 201a to NB 201b. Alternatively, information of the UL grant can be provided to the second NB 202a by the first NB 201a in advance to the scheduling (similar to the sequence of S530 and S520 in Figure 5), so that there is still time for the second NB 202a to adjust its uplink scheduling in order to receive the CSI report from the first UE 201b.

[0088] After receiving an uplink grant sent by the first NB 201a with the intention to trigger the first UE 202a to measure and send a CSI report back to its serving node, the second NB 202a, acting as a UE, can also receive (S640) and decode a CSI report from the first UE 202a, which is intentionally sent (S630) to the first NB 201a according to the CSI report configuration. Note that in Figure 6, the first NB 201a and the second NB 202a respectively receiving the CSI report from the first UE 201b through the same PDSCH in different arrows doesn’t mean they are independent steps. The receiving of the CSI report by the second NB 202a might be later than the receiving of the CSI report by the first NB 201a due to location distance or transmission path(s). Theoretically, the order can be adverse for example when the first UE is on the edge of the first cell and is closer to the second NB 202a providing the second cell.

[0089] Comparing to the second main embodiment, OTA delivery of the CSI report does not require a fast backhaul. Where the CSI report transmission is scheduled / configured by the serving cell (e.g., the first NB 201a) and where this scheduling information (and other information necessary to receive the CSI report such as DMRS sequences and PUSCH scrambling sequences) is conveyed to the one or more interfering NBs / TRPs (e.g., the second NB 202a) using OTA signaling prior to or in meanwhile with said scheduling so that these additional interfering NBs / TRPs can receive the CSI report transmission from the UE.

[0090] In the OTA signaling phase, the interfering NB / TRP (e.g., the second NB 202a) will act as a terminal device according to its configuration, to eavesdrop to a PDCCH that holds the UL grant information, or the PDCCH that holds the UL grant intended to trigger the UE to generate a CSI report. The radio condition in the interfering NB / TRP must therefore be capable of receive and decode signals on the part of the DL bandwidth where the DL PDCCH will be scheduled. Therefore, the receiving bandwidth of an FDD or CA TDD radio should cover the bandwidth of both the UL carrier but also the bandwidth for all the DL carriers.

[0091] As is shown in figure 7, the second NB 201b might also eavesdrop on a PDCCH for UL grant intended for a third UE 202c in a third cell provided by a third NB 201c. It might also receive and decode a CSI report from the third UE 202c, which is intentionally sent to the third NB 201c who triggers the CSI report. In both CSI reports respectively from the first UE 202a and the third UE 202c, interference report, including for example PMI, CQI and RI regarding the CSI-RS resource associated with the second NB 201b are decoded. The second NB 201b combines (S650) P110411W001 that interference information into a corresponding interference covariance matrix per sub band. Vice versa, the first NB 201a may receive CSI reports from multiple UEs in the neighboring cells, and then, combine and obtain an interference covariance matrix per sub band.

[0092] In this embodiment, no time-critical backhaul coordination is required. And all time critical signaling and the measurement reporting coordination happen in OTA, which we call it dual-step-OTA. This approach eliminates the need of explicit exchange of UL grant information via X2 / E5 backhaul communication. A key functionality for the network node is its capability for signal reception over the full total system bandwidth so that the PDCCH of the UL grants can be detected when they are transmitted on a DL frequency band that falls in the frequency bands of the network node’s receiver.

[0093] According to another aspect of the disclosure, a method embodiment implemented by a terminal device is provided. The terminal device (202a, 202b, 202c) is configured by its serving cell for CSI measurement and reporting, where DL interference from a non-serving cell is to be reported. The non-serving cell is indicated by its PCI in the configuration and its NZP-CSI-RS or PDSCH resource overlaps with CSI-IM resource of the serving cell. A new interference report type is also configured so that the CSI report includes a Q matrix describing spatial properties of interference of neighboring cell(s).

[0094] After triggered by an UL grant, the terminal device performs CSI reporting to its serving cell. And the interfering neighboring cell(s) could receive the CSI report directly via air interface, e.g., PUSCH indicated by information of the UL grant, or receive spatial interference measurement result indirectly via backhaul link from the serving cell, according to different embodiments, while this is transparent to the terminal device. After calculation on interference covariance matrices, the interfering cell(s) will applies / apply the matrices (e.g, can be one matrix per subband) to an MMSE precoder to mitigate DL interference towards the terminal device.

[0095] In another aspect, embodiments of a network node and a terminal device are hereinafter provided.

[0096] Figure 8 shows a network node 800 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (e.g., radio access points), Transmission Points (TRPs) and base stations (e.g., radio base stations, Node Bs, eNBs, and gNBs).

[0097] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as P110411W001 centralized digital units and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0098] Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0099] Network node 800 includes processing circuitry 802, memory 804, communication interface 806, and power source 808. Network node 800 may be composed of multiple physically separate components (e.g., aNodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which network node 800 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, network node 800 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 804 for different RATs) and some components may be reused (e.g., a same antenna 810 may be shared by different RATs). Network node 800 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 800, for example LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 800.

[0100] Processing circuitry 802 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 800 components, such as memory 804, to provide network node 800 functionality.

[0101] In some embodiments, processing circuitry 802 includes a system on a chip (SOC). In some embodiments, processing circuitry 802 includes one or more of radio frequency (RF) P110411W001 transceiver circuitry 812 and baseband processing circuitry 814. In some embodiments, RF transceiver circuitry 812 and baseband processing circuitry 814 may be on separate chips (or sets of chips), boards, or units. For example, baseband processing circuitry 814 locates in digital units (DUs) when radio units (RUs) are separated from DUs. In alternative embodiments, part or all of RF transceiver circuitry 812 and baseband processing circuitry 814 may be on the same chip or set of chips, boards, or units.

[0102] Memory 804 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by processing circuitry 802. Memory 804 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions (collectively denoted computer program 804a, which may be a computer program product) capable of being executed by processing circuitry 802 and utilized by network node 800. Memory 804 may be used to store any calculations made by processing circuitry 802 and / or any data received via communication interface 806. In some embodiments, processing circuitry 802 and memory 804 is integrated.

[0103] Communication interface 806 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, communication interface 806 comprises port(s) / terminal(s) 816 to send and receive data, for example to and from another network node over a wired connection. Communication interface 806 also includes radio front-end circuitry 818 that may be coupled to, or in certain embodiments a part of, antenna 810. Radio front-end circuitry 818 comprises filters 820 and amplifiers 822. Radio front-end circuitry 818 may be connected to an antenna 810 and processing circuitry 802. The radio front-end circuitry may be configured to condition signals communicated between antenna 810 and processing circuitry 802. Radio front-end circuitry 818 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 818 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 820 and / or amplifiers 822. The radio signal may then be transmitted via antenna 810. Similarly, when receiving data, antenna 810 may collect radio signals which are then converted into digital data by radio front-end circuitry 818. The digital data may P110411W001 be passed to processing circuitry 802. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0104] In certain alternative embodiments, network node 800 does not include separate radio front-end circuitry 818, instead, processing circuitry 802 includes radio front-end circuitry and is connected to antenna 810. Similarly, in some embodiments, all or some of the RF transceiver circuitry 812 is part of communication interface 806. In still other embodiments, communication interface 806 includes one or more ports or terminals 816, radio front-end circuitry 818, and the RF transceiver circuitry 812, as part of a radio unit (not shown), and communication interface 806 communicates with the baseband processing circuitry 814, which is part of a digital unit (not shown).

[0105] Antenna 810 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 810 may be coupled to radio front-end circuitry 818 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 810 is separate from network node 800 and connectable to network node 800 through an interface or port.

[0106] Antenna 810, communication interface 806, and / or processing circuitry 802 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, antenna 810, communication interface 806, and / or processing circuitry 802 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0107] Power source 808 provides power to the various components of network node 800 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 808 may further comprise, or be coupled to, power management circuitry to supply the components of network node 800 with power for performing the functionality described herein. For example, network node 800 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of power source 808. As a further example, power source 808 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0108] Embodiments of network node 800 may include additional components beyond those shown in Figure 8 for providing certain aspects of the network node’s functionality, including any P110411W001 of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, network node 800 may include user interface equipment to allow input of information into network node 800 and to allow output of information from network node 800. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 800.

[0109] Figure 9 shows a terminal device 900 in accordance with some embodiments. As used herein, a terminal device refers to a device capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other terminal devices. It may support device- to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-every thing (V2X). In other examples, it may not necessarily have a user in the sense of a human user who owns and / or operates the relevant device. Instead, it may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, it may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

[0110] The terminal device 900 includes processing circuitry 902 that is operatively coupled via a bus 904 to an input / output interface 906, a power source 908, a memory 910, a communication interface 912, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 9. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0111] The processing circuitry 902 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in the memory 910. The processing circuitry 902 may include multiple central processing units (CPUs).

[0112] The input / output interface 906 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 900. Examples of an input device include a touch-sensitive or presencesensitive display, a camera, a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. P110411W001

[0113] The processing circuitry 902 may be configured to communicate with an access network or other network using the communication interface 912. The communication interface 912 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 922. The communication interface 912 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 918 and / or a receiver 920 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 918 and receiver 920 may be coupled to one or more antennas (e.g., antenna 922) and may share circuit components, software or firmware, or alternatively be implemented separately.

[0114] The memory 910 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 910 includes one or more application programs 914, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 916. The memory 910 may store, for use by the terminal device 900, any of a variety of various operating systems or combinations of operating systems.

[0115] In some embodiments, communication interface circuitry (912) of a terminal device (900) is configured to communicate with a radio network node to which it can get access and then served by a serving cell provided by the radio network node. The terminal device (900) receives measurement configuration and measurement report configuration via antenna (922) from its serving cell. It then detects CSI-RS from its serving cell and CSI-RS / PDSCH from a neighboring non-serving cell. Processing circuitry (902) measures channel information and interference information and generates a CSI report in memory (910). The CSI report may include a new interference report type, e.g., an interference covariance matrix per subband. Upon receiving an UL grant by communication interface (912), transmitter (918) transmits the CSI report via antenna (922) to the serving cell. And according to some embodiments in this disclosure, the neighboring non-serving cell might also receive the CSI report.

[0116] The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the spirit and scope of the P110411W001 disclosure. Various embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art.

[0117] The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and / or electronic devices and can include, for example, electrical and / or electronic circuitry, devices, modules, processors, memories, logic solid state and / or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and / or displaying functions, and so on, as such as those that are described herein.

[0118] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according to one or more embodiments of the present disclosure.

[0119] As described herein, device and / or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and / or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

[0120] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as P110411W001 having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0121] In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood, that although these terms (and / or other terms that can be synonymous to one another) can be used synonymously herein, there can be instances when such words can be intended to not be used synonymously.

Claims

P110411W001CLAIMS1. A method for a first network node, NN, configured for serving a first terminal device in a radio access network, RAN, the method comprising: transmitting (S210), configuration information to the first terminal device about a channel state information, CSI, report on resources of downlink signals received from a second neighboring NN and the first NN; receiving (S220) the CSI report comprising interference measurement on the downlink signals transmitted on the resources; sending (S230) information about the CSI report to the second neighboring second NN; and obtaining (S250) an interference covariance matrix for spatial downlink, DL, interference mitigation.

2. The method of claim 1, wherein receiving (S220) a CSI report comprises receiving the CSI report from the first terminal device; the method further comprising: receiving (S240), from a third neighboring NN, information about a CSI report on a downlink channel on which the first NN transmits its downlink signal; wherein the calculating comprises: combining the received interference covariance matrices into a single matrix per subband.

3. The method of claim 1, wherein sending (S230) information about the CSI report to the second neighboring NN comprises: sending a message comprising information of a first uplink grant indicating uplink resource on which the CSI report is to be transmitted; and wherein receiving (S220) a CSI report comprises: receiving the CSI report from the first terminal device on the uplink resource; the method further comprising: receiving information of a third uplink grant from the third neighboring NN; and receiving (S240) a CSI report from a third terminal device served by the third neighboring NN according to the information of the third uplink grant; wherein obtaining (S250) an interference covariance matrix is based on both CSI reports respectively from the first terminal device and the third terminal device.P110411W0014. The method of claim 3, wherein sending the information about the CSI report comprises: sending the information of the first uplink grant on a backhaul link between the first NN and the second neighboring NN.

5. The method of claim 3, wherein receiving information of a third uplink grant comprises: receiving the information of the third uplink grant on a physical downlink control channel, PDCCH, on which the third uplink grant is received by the third terminal device.

6. The method of any of claims 1 to 5, wherein the CSI report comprises one or more of: Precoding matrix indicator (PMI), Rank Indicator (RI), Layer Indicator (LI), Layer 1 Reference Signal Receiving Power (Ll-RSRP), Layer 1 -Signal to Interference plus Noise Ratio (Ll-SINR) about the downlink signal from the second neighboring NN.

7. The method of any of claims 1 to 6, wherein the configuration information comprises a physical cell ID (PCI) associated with the second cell.

8. The method of any of claims 1 to 7, wherein the configuration comprises an information element on resources for CSI interference measurement, CSI-IM, indicating the resources for downlink signals received from the second neighboring NN.

9. A network node (201a, 201b, 201c, 800), NN, configured to serve a first terminal device in a radio access network, RAN, the NN comprising: communication interface circuitry (806) configured to communicate with the first terminal device and with a second neighboring NN; memory (804) configured to store data and instruction therein, and processing circuitry (802) operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of claim 1.

10. The network node according to claim 9, wherein the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of claims 2 to 8.

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