A method implemented in a radio device of a network node communicating with a wireless device, and the radio device

Abstract

A method and radio device for passive intermodulation (PIM) downlink subspace acquisition in a network node. According to one aspect, the method includes determining a downlink projection matrix formed using downlink beamforming weights and determining a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexing (OFDM) symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that depends on passive intermodulation (PIM) power generated in one or more uplink channels.

Description

Technical Field

[0001] The present disclosure relates to wireless communications, and in particular, to passive intermodulation (PIM) downlink subspace acquisition. Background Art

[0002] Nonlinear interference is generated at the transceiver of a base station in a wireless communication system when at least one corrupted signal is affected by some nonlinear behavior. This nonlinear behavior can be experienced anywhere a corrupted signal is present. The nonlinear behavior can occur in the radio, signal transmission line network, antenna system, or in the RF environment in which the corrupted signal is transmitted. The corrupted signal is typically a downlink signal that interferes with the desired uplink signal due to the creation of nonlinear intermodulation terms.

[0003] One of the problems associated with nonlinear interference is when the interference couples into the receiver and overlaps with the assigned frequency channel for the receiver. The interference will degrade the quality of the received signal in the receiver, thereby reducing performance.

[0004] In network nodes such as cellular base stations, this nonlinear behavior can be attributed to passive devices exhibiting passive intermodulation (PIM). PIM sources can occur in many places. Some examples are in the radio's filters, connectors, and cable assemblies from the radio to the antenna; in the multiplexer if multiple radios are multiplexed onto the same cable or antenna; in the antenna; or in the environment outside the antenna.

[0005] Nonlinear interference generates interference at multiple frequencies. This interference can be problematic when some of the generated frequencies fall into the base station's assigned receive channel. The interference can desensitize the receiver, thereby degrading receiver performance.

[0006] Figure 1 A block diagram of a frequency division duplex (FDD) massive multiple-input multiple-output (MIMO) system with PIM interference is shown in FIG, where the following system parameters are referenced:

[0007] M downlink MIMO layers;

[0008] K uplink MIMO layers;

[0009] N downlink and uplink base station antennas;

[0010] ω_DL is the downlink channel frequency;

[0011] ω_UL is the uplink channel frequency;

[0012] I_s is the channel dimension affected by PIM - it may correspond to the total number of interferers such as PIM sources; and

[0013] N_L is the nonlinear order of the PIM source.

[0014] Figure 1 The system variables of the system are described below:

[0015] b is the Mx1 vector of DL control and service signaling in the layer domain;

[0016] a is the Nx1 vector of precoded DL control and traffic signaling in the antenna domain;

[0017] s is the Kx1 vector of UL control and traffic signaling in the layer domain at the WD;

[0018] r is the Nx1 vector of UL received control and traffic signaling in the antenna domain at the base station;

[0019] ·H DL_UE 12 is an MxN matrix of channel responses from the base station to the WD for each of the downlink subcarriers;

[0020] ·H UL_UE 14 is an NxK matrix of channel response from the WD to the base station for each of the uplink subcarriers;

[0021] ·H DL_IF 16 is the I of the channel response from the base station to the PIM source for each of the downlink subcarriers s xN matrix;

[0022] ·H UL_IF 18 is the N×I of the channel response from the PIM source to the base station for each of the uplink subcarriers s matrix;

[0023] ·h NL 20 are some nonlinear time domain models of PIM sources;

[0024] ·P DL 22 is an NxM matrix of beamforming weights for each of the DL subcarriers (PRB granularity may be used to reduce implementation cost); and

[0025] ·P UL 24 is a KxN matrix of beamforming weights for each of the UL subcarriers (PRB granularity may be used to reduce implementation cost).

[0026] The expression of the downlink interference covariance matrix is as follows:

[0027]

[0028] in:

[0029] U is composed of N eigenvectors [u0,...,u N-1 ]The NxN matrix formed by:

[0030] The signal subspace of the channel covariance matrix of the interference source - the interference subspace - corresponds to I s Main eigenvectors as well as

[0031] The noise subspace of the uplink covariance matrix corresponds to the remaining eigenvectors

[0032] ∑ is the covariance matrix of the uplink interference channel with the eigenvalues λ0,...,λ set to N N-1 The first element λ is an NxN diagonal matrix with diagonal elements of i (i=0,...,I s -1) is the interference eigenvalue, and the remaining term λ i (i=I s ,...,N-1) is the noise eigenvalue;

[0033] ·(·) H The operator represents the Hermitian transpose (i.e., complex conjugation);

[0034] · Non-conjugate transpose operator (·) T Implementing uplink to downlink channel switching; and

[0035] · The operator represents the conjugation of a matrix without the transpose.

[0036] Those skilled in the art will appreciate that, as shown in the following equation, The downlink interference covariance matrix estimate may additionally require electronic transformation to compensate for the different inter-element antenna spacing between the uplink and downlink frequency bands:

[0037]

[0038] Where T λ (·) is an electrical transformation based on either multidimensional discrete Fourier transform (DFT) or other methods.

[0039] However, in frequency division duplex (FDD) systems with wide duplex gaps, some additional impairments caused by mutual coupling and other antenna imperfections can produce significant antenna response variations between the uplink and downlink bands. Figure 2 As shown, some analog black boxes 25 are introduced into the antenna model to capture frequency-dependent impairments from the subarray. Figure 2 As shown, the unknown response varies from one subarray and / or antenna to the next. Thus, for a system with N antennas, there are N different black boxes. The black box response is a function of three input parameters: frequency ω, elevation angle θ, and azimuth angle φ.

[0040] Furthermore, since the nulls are narrower than the beams, null steering is more sensitive to estimation errors than beam steering. Therefore, it is necessary to capture the effects of these simulated impairments to perform PIM downlink null steering in FDD systems with wide duplex gaps. Summary of the Invention

[0041] Some embodiments advantageously provide methods and systems for passive intermodulation (PIM) downlink subspace acquisition.

[0042] Some embodiments exploit the natural "PIM feedback loop" to generate an estimate of the downlink interference covariance matrix Some advantages of some of the embodiments described below may include one or more of the following:

[0043] Some embodiments operate independently of FDD uplink to downlink frequency separation;

[0044] Some embodiments work even in situations where significant sub-array response impairments do exist; and / or

[0045] PIM subspace is estimated during normal product operation; no special modes are required.

[0046] According to one aspect, a method implemented in a first radio device of a network node is provided. The method includes determining, by processing circuitry, a downlink projection matrix based at least in part on downlink beamforming weights. The method also includes determining a first downlink interference covariance matrix estimate for a current downlink Orthogonal Frequency Division Multiplexing (OFDM) symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that depends on passive intermodulation (PIM) power generated in one or more uplink channels.

[0047] According to this aspect, in some embodiments, the scaling factor is based at least in part on the power of the current downlink OFDM symbol, a constant used to compensate for differences in uplink and downlink power, and the received uplink PIM power. In some embodiments, the method further comprises: determining, by a PIM DL covariance matrix determiner, an additional downlink interference covariance matrix estimate, one additional downlink interference covariance matrix estimate for each of a plurality of OFDM symbols; and averaging the first downlink covariance matrix and the additional downlink covariance matrix for the plurality of OFDM symbols to determine an average downlink interference covariance matrix. In some embodiments, the averaging is performed during a time period selected to capture a plurality of downlink precoding weights with equal probability of occurrence. In some embodiments, the averaging is performed separately for each of a plurality of polarizations. In some embodiments, the averaging is performed jointly across multiple antennas of the network node. In some embodiments, the averaging is a wideband averaging. In some embodiments, the averaging excludes downlink interference covariance matrix estimates for which the received uplink passive intermodulation power is below a threshold. In some embodiments, the method further comprises sequentially determining a downlink interference covariance matrix for each downlink codebook in the plurality of downlink codebooks.In some embodiments, the received uplink PIM power is based at least in part on a measurement of PIM power, the measurement being received from the second radio of the network node.

[0048] According to another aspect, a first radio device of a network node includes processing circuitry configured to determine a downlink projection matrix based at least in part on downlink beamforming weights. The processing circuitry is further configured to determine a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexing (OFDM) symbol based at least in part on multiplying the downlink projection matrix by a scaling factor dependent on passive intermodulation (PIM) power generated in one or more uplink channels.

[0049] According to this aspect, in some embodiments, the scaling factor is based at least in part on the power of the current downlink OFDM symbol, a constant used to compensate for differences in uplink and downlink power, and the received uplink PIM power. In some embodiments, the processing circuitry is further configured to determine an additional downlink interference covariance matrix estimate, one additional downlink interference covariance matrix estimate for each of the plurality of OFDM symbols. The processing circuitry is further configured to average the first downlink interference covariance matrix estimate and the additional downlink interference covariance matrix estimates for the plurality of OFDM symbols to determine an average downlink interference covariance matrix estimate. In some embodiments, the averaging is performed during a time period selected to capture a plurality of downlink precoding weights with equal probability of occurrence. In some embodiments, the averaging is performed separately for each of a plurality of polarizations. In some embodiments, the averaging is performed jointly across multiple antennas of the network node. In some embodiments, the averaging is a wideband averaging. In some embodiments, the averaging excludes downlink interference covariance matrix estimates for which the received uplink passive intermodulation power is below a threshold. In some embodiments, the processing circuit is further configured to sequentially determine a downlink interference covariance matrix estimate for each downlink codebook in the plurality of downlink codebooks.In some embodiments, the received uplink PIM power is based at least in part on a measurement of PIM power, the measurement being received from the second radio device of the network node. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] A more complete understanding of the present embodiments and its attendant advantages and features will be more readily appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0051] Figure 1 is a block diagram of a frequency division duplex (FDD) massive multiple-input multiple-output (MIMO) system with PIM interference;

[0052] Figure 2 illustrating independent channel functions for communicating with different antennas, said channel functions representing subarray frequency-dependent impairments;

[0053] Figure 3 is a block diagram of an FDD massive MIMO system with a wide duplex gap;

[0054] Figure 4 is a block diagram of a network node having at least two radio devices, at least one of the at least two radio devices capable of null point control and another of the at least two radio devices capable of PIM measurement, and at least one of the at least two radio devices capable of PIM DL covariance matrix determination based on PIM measurements;

[0055] Figure 5 is a flow chart of an example process for determining a PIM DL covariance matrix estimate; and

[0056] Figure 6 is a flow chart of an alternative process for determining a PIM DL covariance matrix estimate. DETAILED DESCRIPTION

[0057] Before describing the exemplary embodiments in detail, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to passive intermodulation (PIM) downlink subspace acquisition. Accordingly, components have been represented in the figures by conventional symbols where appropriate, and the figures show only those specific details that are relevant to an understanding of the embodiments so as not to obscure the disclosure with details that will be readily apparent to one of ordinary skill in the art having the benefit of the description herein.

[0058] As used herein, relational terms such as "first" and "second," "top" and "bottom," and the like may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements.

[0059] The term "network node" as used herein may be any type of network node included in a radio network, and the network node may further include any of the following: a base station (BS), a radio base station, a base transceiver station (BTS), a base station controller (BSC), a radio network controller (RNC), a gNode B (gNB), an evolved Node B (eNB or eNodeB), a Node B, a multi-standard radio (MSR) radio node such as an MSR BS, a multi-cell / multicast coordination entity (MCE), an integrated access and backhaul (IAB) node, a relay node, a donor node that controls a relay, a radio access point (AP), a transmission point, a transmission node, a remote radio unit (RRU), a remote radio head (RRH), a core network node (e.g., a mobility management entity (MME), a self-organizing network (SON) node, a coordination node, a positioning node, an MDT node, etc.), an external node (e.g., a third-party node, a node outside the current network), a node in a distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also include test equipment. The term "radio node" as used herein may also be used to refer to a WD or a radio network node.

[0060] Referring again to the drawings, wherein like elements have like reference numerals, Figure 3 A block diagram of an example embodiment for determining the PIM DL covariance matrix is shown in FIG. Figure 1 The mark is "HDL_IF "The box Figure 3 Outside the box marked "black box", Figure 3 The examples and components in Figure 1 Therefore, the DL PIM channel response is replaced by the black box 26, because according to the disclosure, the uplink PIM covariance matrix cannot be directly used to estimate the DL PIM subspace in FDD systems with wide duplex gap.

[0061] exist Figure 4 In the example of FIG, the PIM downlink covariance matrix determiner 38 may estimate the PIM downlink covariance matrix as follows:

[0062]

[0063] in

[0064] ·E[·] is the expectation operator;

[0065] · corresponding to received uplink (UL) PIM power measured in real time using, for example, a method that is or becomes known;

[0066] · The power corresponding to the current downlink (DL) orthogonal frequency division multiplexing (OFDM) symbol; and

[0067] • α is an arbitrary constant used to compensate for UL to DL power differences.

[0068] A scaling factor is defined for each OFDM symbol. The scaling factor corresponds to the PIM power generated in the uplink. Plus an adjusted version of the DL OFDM symbol power The factor α is used to compensate for the UL to DL power difference. In other words, the scaling factor can be given by:

[0069]

[0070] This can be calculated by the PIM DL covariance matrix determiner 38. Then, the DL precoding weights P DL is used to form a downlink projection matrix, which is multiplied by a scaling factor and averaged with the results from other OFDM symbols. The multiplication may be performed by the PIM DL covariance matrix determiner 38. The averaging period may be long enough to capture all possible DL precoding weights with equal probability of occurrence. The averaging for each of the DL polarizations may be performed separately. The averaging process of the equation for can be performed over all antennas combined. The averaging process can be broadband or it can be performed with a finer frequency granularity.

[0071] Processing circuitry 34 may include circuitry for assisting The processing circuit 34 may include a processor and a memory. In particular, the processing circuit 34 may include, in addition to or in place of a processor such as a central processing unit and a memory, one or more processors and / or processor cores and / or an FPGA (field programmable gate array) and / or an ASIC (application-specific integrated circuit) adapted to execute instructions for processing and / or control. Such a processor may be configured to access (e.g., write to and / or read from) a memory, which may include, for example, a cache memory and / or a buffer memory and / or a RAM (random access memory) and / or a ROM (read-only memory) and / or an optical memory and / or an EPROM (erasable programmable read-only memory) of any kind of volatile and / or non-volatile memory.

[0072] For example, depending on the PIM uplink (UL) power If the power exceeds a predetermined threshold, some conditional statements can be used to discard or retain the result of each OFDM symbol. For example, when the PIM UL power is less than a predetermined threshold, the OFDM symbol can be discarded. The result of the calculation.

[0073] The PIM subspace acquisition method disclosed herein functions during normal product operation.In an alternative embodiment, there may be a PIM subspace acquisition mode where all possible DL codebooks are scanned continuously.

[0074] The feedback-assisted PIM subspace acquisition method described herein may be implemented in whole or in part in the cloud (ie, at multiple locations or at some central location connected to the network node 30 via the Internet).

[0075] The feedback-assisted PIM subspace acquisition method described in this paper exploits the natural PIM feedback loop to weight the PIM contributions of different DL precoding weights. The weighted contributions are averaged during the time interval to produce the downlink interference covariance matrix Estimates.

[0076] Figure 4A block diagram of two radios A and B (32-A, 32-B) in the same network node 30, collectively referred to as radios 32, is shown. In this example, radio 32-A transmits a DL signal that illuminates a PIM source in the environment, which in turn interferes with one or more uplink channels in radio 32-B, from which radio 32-B measures PIM. This measured PIM may be referred to as received uplink PIM power, from which a downlink interference covariance matrix is determined.

[0077] The PIM measurement unit 36-B may measure the PIM power of each of the plurality of DL precoding weights transmitted by the radio device 32-A. Based on the equations set forth above and repeated here, the PIM DL covariance matrix determiner 38-A may determine the PIM DL covariance matrix

[0078]

[0079] Thus, each radio 32 may have processing circuitry (34-A, 34-B), a PIM measurement unit (36-A, 36-B), a PIM DL covariance matrix determiner (38-A, 38-B), and a transceiver (40-A, 40-B). Each unit in radio 32-A operates similarly to each corresponding similarly numbered unit in radio 32-B.

[0080] In some embodiments, the PIM DL covariance matrix determiner 38 may be implemented as software instructions stored in a memory and executable by a microprocessor. Such software may be stored in a memory. As described above, a memory and a microprocessor may be included in the processing circuit 34.

[0081] Figure 5 1 is a flow chart of an example process for determining a PIM DL covariance matrix in a radio device, such as the radio device 32 of the network node 30. The process includes determining, by the processing circuit 34, a scaling factor based at least in part on the power of the current downlink OFDM symbol, a constant used to compensate for differences in uplink power and downlink power, and received uplink passive intermodulation (PIM) power (block S10). The process also includes determining a downlink projection matrix based at least in part on the downlink beamforming weights for the current OFDM symbol (block S12). The process also includes multiplying the downlink projection matrix by the scaling factor for the current OFDM symbol (block S14). The process further includes averaging the multiplication results over multiple OFDM symbols to produce an estimate of the downlink interference covariance matrix (block S16).

[0082] Figure 6 1 is a flow chart of an alternative process for determining a downlink interference covariance matrix estimate in a radio device, such as radio device 32, of a network node 30. The process includes determining a downlink projection matrix based at least in part on downlink beamforming weights (block S18). The process further includes determining a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexing (OFDM) symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that depends on passive intermodulation (PIM) power generated in one or more uplink channels (block S20).

[0083] Thus, according to one aspect, a method is provided for implementation in a first radio device of a network node 30. The method includes determining, by processing circuitry 34, a downlink projection matrix based at least in part on downlink beamforming weights. The method also includes determining a first downlink interference covariance matrix estimate for a current downlink Orthogonal Frequency Division Multiplexing (OFDM) symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that depends on passive intermodulation (PIM) power generated in one or more uplink channels.

[0084] According to this aspect, in some embodiments, the scaling factor is based at least in part on the power of the current downlink OFDM symbol, a constant used to compensate for differences in uplink and downlink power, and the received uplink PIM power. In some embodiments, the method further includes determining, via a PIM DL covariance matrix determiner 38, an additional downlink interference covariance matrix estimate, one for each of a plurality of OFDM symbols; and averaging the first downlink covariance matrix and the additional downlink covariance matrix for the plurality of OFDM symbols to determine an average downlink interference covariance matrix estimate. In some embodiments, the averaging is performed during a time period selected to capture a plurality of downlink precoding weights with equal probability of occurrence. In some embodiments, the averaging is performed separately for each of a plurality of polarizations. In some embodiments, the averaging is performed jointly across a plurality of antenna polarizations. In some embodiments, the averaging is a wideband averaging. In some embodiments, the averaging excludes downlink interference covariance matrix estimates for which the received uplink passive intermodulation power is below a threshold. In some embodiments, the method further comprises sequentially determining a downlink interference covariance matrix for each downlink codebook in the plurality of downlink codebooks.In some embodiments, the received uplink PIM power is based at least in part on a measurement of PIM power, the measurement being received from the second radio of the network node.

[0085] According to another aspect, the first radio device of the network node 30 includes a processing circuit 34 configured to determine a downlink projection matrix based at least in part on the downlink beamforming weights. The processing circuit 34 is further configured to determine a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexing (OFDM) symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that depends on a passive intermodulation (PIM) power generated in one or more uplink channels.

[0086] According to this aspect, in some embodiments, the scaling factor is based at least in part on the power of the current downlink OFDM symbol, a constant used to compensate for differences in uplink and downlink power, and the received uplink PIM power. In some embodiments, the processing circuitry 34 is further configured to determine an additional downlink interference covariance matrix estimate, one for each of the plurality of OFDM symbols. The processing circuitry 34 is further configured to average the first downlink interference covariance matrix estimate and the additional downlink interference covariance matrix estimate for the plurality of OFDM symbols to determine an average downlink interference covariance matrix estimate. In some embodiments, the averaging is performed during a time period selected to capture a plurality of downlink precoding weights with equal probability of occurrence. In some embodiments, the averaging is performed separately for each of a plurality of polarizations. In some embodiments, the averaging is performed jointly across multiple antennas of the network node. In some embodiments, the averaging is a wideband averaging. In some embodiments, the averaging excludes downlink interference covariance matrix estimates for which the received uplink passive intermodulation power is below a threshold. In some embodiments, the processing circuit 34 is further configured to sequentially determine a downlink interference covariance matrix for each downlink codebook in the plurality of downlink codebooks. In some embodiments, the received uplink PIM power is based at least in part on a measurement of PIM power, the measurement being received from the second radio device of the network node.

[0087] As will be appreciated by those skilled in the art, the concepts described herein may be embodied as methods, data processing systems, and / or computer program products. Thus, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining all software and hardware aspects generally referred to herein as "circuits" or "modules." Furthermore, the disclosure may take the form of a computer program product on a tangible computer-usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer-readable medium may be utilized, including a hard disk, a CD-ROM, an electronic storage device, an optical storage device, or a magnetic storage device.

[0088] Some embodiments are described herein with reference to flowchart illustrations and / or block diagrams of methods, systems, and computer program products. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device to produce a machine, such that the instructions, executed by the processor of the computer or other programmable data processing device, create components for implementing the functions / actions specified in the flowchart and / or block diagram block or blocks.

[0089] These computer program instructions that can direct a computer or other programmable data processing device to operate in a specific manner may also be stored in a computer-readable memory or storage medium, so that the instructions stored in the computer-readable memory produce an article of manufacture including instruction components that implement the functions / actions specified in the flowchart and / or block diagram block or multiple flowcharts and / or block diagram blocks.

[0090] Computer program instructions can also be loaded onto computer or other programmable data processing equipment, to impel a series of operating steps to be performed on computer or other programmable equipment, thereby produce the process of computer implementation, make the instruction carried out on computer or other programmable equipment provide for realizing the step of the function / action specified in flow chart and / or block diagram frame or a plurality of flow charts and / or block diagram frame.It is to be understood that the function / action of annotation in the frame can not occur in the order of annotation in the operating instructions.For example, depending on the functionality / action involved, in fact can carry out two frames shown continuously simultaneously, or can sometimes carry out described frame in opposite order.Although some figures among the figure comprise the arrow on the communication path to illustrate the main direction of communication, it is to be understood that communication can occur in the direction opposite to the arrow of depiction.

[0091] You can use In one embodiment, the computer program code for performing the operation of the concept described herein can be written in an object-oriented programming language such as C or C++. However, the computer program code for performing the disclosed operation can also be written in a conventional procedural programming language such as the "C" programming language. The program code can be executed completely on the user's computer, partially on the user's computer, executed as an independent software package, partially on the user's computer and partially on a remote computer, or executed completely on the remote computer. In the latter scenario, the remote computer can be connected to the user's computer by a local area network (LAN) or a wide area network (WAN), or (for example, using an Internet service provider to pass through the Internet) can be made to be connected to an external computer.

[0092] Many different embodiments have been disclosed herein in conjunction with the above description and figures. It will be understood that literally describing and illustrating every combination and subcombination of these embodiments would be unduly repetitive and obscure. Therefore, all embodiments may be combined in any manner and / or combination, and this specification, including the figures, should be construed as constituting a complete written description of all combinations and subcombinations of the embodiments described herein, as well as the manner and process of making and using them, and this specification, including the figures, should support claims to any such combination or subcombination.

[0093] Some abbreviations that may be used in this article are as follows:

[0094] Abbreviation Explanation

[0095] DL Downlink

[0096] FDD Frequency Division Duplex

[0097] MIMO Multiple Input Multiple Output

[0098] OFDM Orthogonal Frequency Division Duplex

[0099] PIM Passive Intermodulation

[0100] UL Uplink

[0101] Those skilled in the art will appreciate that the embodiments described herein are not limited to what has been particularly shown and described hereinabove. In addition, unless otherwise stated above, it should be noted that none of the figures in the accompanying drawings are drawn to scale. Various modifications and variations are possible in accordance with the above teachings without departing from the scope of the following claims.

Claims

1. A method implemented in a first radio device of a network node communicating with a wireless device WD, the method comprising: determining a downlink projection matrix based at least in part on the downlink beamforming weights; as well as determining a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexing (OFDM) symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that is dependent on passive intermodulation (PIM) power generated in one or more uplink channels; The scaling factor is based at least in part on the power of the current downlink OFDM symbol, a constant used to compensate for a difference between uplink power and downlink power, and a received uplink PIM power.

2. The method of claim 1, further comprising: determining additional downlink interference covariance matrix estimates, one additional downlink interference covariance matrix estimate for each OFDM symbol in a plurality of OFDM symbols; and The first downlink interference covariance matrix estimate and the additional downlink interference covariance matrix estimates for the plurality of OFDM symbols are averaged to determine an average downlink interference covariance matrix estimate.

3. The method according to claim 2, wherein: The averaging is performed during a time period selected to capture a plurality of downlink precoding weights with equal probability of occurrence.

4. The method according to claim 2, wherein: The averaging is performed separately for each antenna polarization of the plurality of antenna polarizations.

5. The method according to claim 2, wherein: The averaging is performed jointly over multiple antenna polarizations.

6. The method of claim 2, wherein: The averaging is a broadband averaging.

7. The method of claim 2, wherein: The averaging is performed for each subcarrier or subcarrier group separately.

8. The method of claim 2, wherein: The averaging excludes downlink interference covariance matrix estimates for which the received uplink passive intermodulation power is below a threshold.

9. The method of claim 1, further comprising sequentially determining a downlink interference covariance matrix estimate for each downlink codebook in a plurality of downlink codebooks.

10. The method according to any one of claims 1 to 9, wherein: The received uplink PIM power is based at least in part on a measurement of PIM power, the measurement being received from a second radio of the network node.

11. A first radio device of a network node, comprising a processing circuit, the processing circuit being configured to: determining a downlink projection matrix based at least in part on the downlink beamforming weights; and determining a first downlink interference covariance matrix estimate for a current downlink orthogonal frequency division multiplexing (OFDM) symbol based at least in part on multiplying the downlink projection matrix by a scaling factor that is dependent on passive intermodulation (PIM) power generated in one or more uplink channels; in, The scaling factor is based at least in part on the power of the current downlink OFDM symbol, a constant used to compensate for differences in uplink power and downlink power, and a received uplink PIM power.

12. The first radio device according to claim 11, wherein The processing circuit (34) is further configured to: determining additional downlink covariance interference matrix estimates, one additional downlink interference covariance matrix estimate for each OFDM symbol in a plurality of OFDM symbols; and The first downlink interference covariance matrix estimate and the additional downlink interference covariance matrix estimates for the plurality of OFDM symbols are averaged to determine an average downlink interference covariance matrix estimate.

13. The first radio device according to claim 12, wherein The averaging is performed during a time period selected to capture a plurality of downlink precoding weights with equal probability of occurrence.

14. The first radio device according to claim 12, wherein The averaging is performed separately for each polarization of the plurality of polarizations.

15. The first radio device according to claim 12, wherein The averaging is performed jointly over multiple antenna polarizations.

16. The first radio device according to claim 12, wherein The averaging is a broadband averaging.

17. The first radio device according to claim 12, wherein: The averaging is performed for each subcarrier or subcarrier group separately.

18. The first radio device according to claim 12, wherein The averaging excludes downlink interference covariance matrix estimates for which the received uplink passive intermodulation power is below a threshold.

19. The first radio device according to claim 11, wherein The processing circuit (34) is further configured to sequentially determine a downlink interference covariance matrix estimate for each downlink codebook in a plurality of downlink codebooks.

20. The first radio device according to any one of claims 11 to 17, wherein The received uplink PIM power is based at least in part on a measurement of PIM power, the measurement being received from a second radio of the network node.

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