Patent Description:
In advanced antenna systems (AAS), one or more downlink communication layers tuned to the same or different frequencies may experience one or more wireless channels between an antenna array of a radio node and one or more passive intermodulation (PIM) sources located in the vicinity of a cellular site. The one or more signals in the wireless channel may excite the PIM sources which in turn may generate intermodulation signals centered around one or more PIM frequencies.

For example, PIM may occur when one or multiple signals in one or multiple frequencies interact in a non-linear manner with a structure in a propagation environment such as the cellular site. This interaction may generate at least one interfering signal, at a possibly different frequency from the transmitted frequency(ies), which may radiate out of the PIM source. This process may be referred to as the "rusty bolt" effect due to junctions of different materials/metals such as the un-rusted bolt portion and the rusted bolt portion that may cause PIM. In other words, in some examples, the mechanical components of the wireless communication system itself, such as rusty bolts, may become PIM sources, although other structures in the propagation environment may also become PIM sources. These PIM sources may generate interfering signal(s) that may interfere with reception of an intended wireless signal at a receiver such as a radio node receiver.

Some existing PIM mitigation/cancellation techniques have been implemented in existing systems in the situation where some of the PIM signals overlap with some of the uplink (UL) channels and have a non-negligible power at the antenna array. One such technique involves sending a technician to the cellular site to replace structural components causing PIM, such as replacing rusty bolts with new bolts. One problem with sending a technician to the cellular site is that the cost combined with the results of the site visit may be too high as the PIM issue may not always be solved. Further, large antenna gain may under some circumstances be dictated by the beamforming weights, thereby exciting PIM sources that may not be removable from the environment such as a lamp post and/or a metallic handrail.

Another technique involves time-domain PIM cancellation. However, time-domain PIM cancellation techniques may not be a feasible option for AAS systems. For example, one problem with time-domain PIM cancellation techniques is that the large number of non-linear terms that may be generated for the time-domain PIM cancellation techniques may depend on one or more of the parameters listed below:.

The number of non-linear terms that are generated increases exponentially for some of the parameter combinations. In addition, these non-linear terms may be generated at a larger sampling rate to avoid aliasing, which may result in a very large implementation cost that may prohibit the use of this technique for antenna arrays. <CIT> describes a method to adaptively cancel an external interference. <CIT> describes a method for determining a precoder to reduce interference to a wireless device in a neighboring cell.

Further, embodiments of the invention are defined by the claims. Moreover, examples, embodiments and descriptions, which are not covered by the claims are presented not as embodiments of the invention, but as background art or examples useful for understanding the invention. Some embodiments advantageously provide a method and system for modification of a radiation pattern in at least one communication direction of at least one interference source.

One or more embodiments of the disclosure relate to creating or configuring one or more beamforming nulls that point or are directed to the one or more interference sources such as PIM sources. In the downlink, one or more transmit nulls or very lower power signals can be generated in the communication direction(s) of the interference source(s) so that these interference sources such as PIM sources are not excited or minimally excited, thereby helping reduce the interference level. Further, one or more receive nulls may be formed or configured in the uplink towards the one or more interference source(s) such as PIM source(s) to help reduce the interference level.

According to one aspect of the disclosure, a first radio node comprising processing circuitry is configured to configure the first radio node to: obtain a first interference subspace, obtain beamforming weights based on the first interference subspace where the beamforming weights configured to modify a radiation pattern in at least one communication direction of at least one interference source, and perform wireless communications based on the beamforming weights.

According to one embodiment of this aspect, the first interference subspace is an uplink interference subspace; and the modified radiation pattern being in a downlink interference subspace. According to one embodiment of this aspect, the processing circuitry is further configured to configure the first radio node to: obtain an estimate of the downlink interference subspace based on the uplink interference subspace where the obtaining of the beamforming weights being based on the estimate of the downlink interference subspace. According to one embodiment of this aspect, the uplink interference subspace corresponds to an uplink set of eigenvectors.

According to one embodiment of this aspect, the modified radiation pattern in at least one communication direction of at least one interference source is configured to reduce the downlink transmission radiation pattern in at least one communication direction of the at least one interference source. According to one embodiment of this aspect, the at least one interference source is at least one passive intermodulation, PIM, source. According to one embodiment of this aspect, the first interference subspace is an uplink subspace where the modified radiation pattern being in an uplink interference subspace.

According to one embodiment of this aspect, the uplink interference subspace corresponds to a plurality of dominant eigenvectors. According to one embodiment of this aspect, the modified radiation pattern in at least one communication direction of at least one interference source is configured to reduce the uplink receive radiation pattern in at least one communication direction of the at least one interference source. According to one embodiment of this aspect, the uplink interference subspace is determined by: determining a signal subspace corresponding to a plurality of communication directions of a plurality of interference sources including the at least one interference source where the signal subspace corresponding to a first plurality of eigenvectors, generating a second radio node signal subspace based on predetermined second radio nodes where the second radio node signal subspace corresponding to a second plurality of eigenvectors, generating a vector of a plurality of correlation coefficients based on the signal subspace and second radio node signal subspace, and removing eigenvectors from the signal subspace corresponding to the signal correlation coefficients that meet a predefined threshold. The remaining eigenvectors from the signal subspace correspond to the uplink interference subspace.

According to one embodiment of this aspect, the uplink interference subspace is determined by: generating a second radio node uplink signal subspace based on predetermined second radio nodes, generating a total uplink signal subspace where the uplink interference subspace being based on the second radio node uplink signal subspace and the total uplink signal subspace, generating a vector of correlation coefficients based on the second radio node uplink signal subspace and the total uplink signal subspace where the uplink interference subspace corresponds to a portion of the total uplink signal subspace associated with correlation coefficients having values below a predefined threshold. According to one embodiment of this aspect, the uplink interference subspace is obtained by: generating a second radio node uplink signal subspace based on predetermined second radio nodes, a contribution of the predetermined second radio nodes to a total received signal corresponds to a projection of a total received signal onto the second radio node uplink signal subspace, generating a residual quantity by subtracting the contribution of the predetermined second radio nodes from the total received signal where the residual quantity corresponding to an uplink vector of uplink noise plus interference, and where the uplink interference subspace being based on the residual quantity.

According to one embodiment of this aspect, the uplink interference subspace is obtained by: generating a residual quantity by subtracting a contribution of predetermined second radio nodes from a total received signal of pilot resource elements where the residual quantity corresponds to an uplink vector of an uplink noise plus interference, and the uplink interference subspace being generated based on the residual quantity. According to one embodiment of this aspect, the second radio node signal subspace corresponds to a set of uplink codebooks. According to one embodiment of this aspect, the radiation pattern is modified in the at least one communication direction of at least one interference source by removing a signal contribution that lies in an estimated downlink interference subspace by performing a projection. According to one embodiment of this aspect, the first interference subspace is used to modify the radiation pattern in the at least one communication direction of at least one interference source in more than one radio communication channel located in the same or in different radio frequency communication bands. According to one embodiment of this aspect, the wireless communications based on the beamforming weights are configured to be of similar power and <NUM> degrees out of phase with other wireless communications at the at least one interference source.

According to another aspect of the disclosure, a method for a first radio node is provided. A first interference subspace is obtained. Beamforming weights are obtained based on the first interference subspace, the beamforming weights configured to modify a radiation pattern in at least one communication direction of at least one interference source. Wireless communications are performed based on the beamforming weights.

According to one embodiment of this aspect, the first interference subspace is an uplink interference subspace, and the modified radiation pattern being in a downlink interference subspace. According to one embodiment of this aspect, an estimate of the downlink interference subspace is obtained based on the uplink interference subspace where the obtaining of the beamforming weights being based on the estimate of the downlink interference subspace. According to one embodiment of this aspect, the uplink interference subspace corresponds to an uplink set of eigenvectors.

According to one embodiment of this aspect, the modified radiation pattern in at least one communication direction of at least one interference source is configured to reduce the downlink transmission radiation pattern in at least one communication direction of the at least one PIM source. According to one embodiment of this aspect, the at least one interference source is at least one passive intermodulation, PIM, source. According to one embodiment of this aspect, the first interference subspace is an uplink subspace where the modified radiation pattern being in an uplink interference subspace.

According to one embodiment of this aspect, the uplink interference subspace corresponds to a plurality of dominant eigenvectors. According to one embodiment of this aspect, the modified radiation pattern in at least one communication direction of at least one interference source is configured to reduce the uplink receive radiation pattern in at least one communication direction of the at least one interference source. According to one embodiment of this aspect, the uplink interference subspace is determined by: determining a signal subspace corresponding to a plurality of communication directions of a plurality of interference sources including the at least one interference source where the signal subspace corresponding to a first plurality of eigenvectors, generating a second radio node signal subspace based on predetermined second radio nodes where the second radio node signal subspace corresponding to a second plurality of eigenvectors, generating a vector of a plurality of correlation coefficients based on the signal subspace and second radio node signal subspace, removing eigenvectors from the signal subspace corresponding to the signal correlation coefficients that meet a predefined threshold where the remaining eigenvectors from the signal subspace corresponding to the uplink interference subspace.

According to one embodiment of this aspect, the uplink interference subspace is determined by: generating a second radio node uplink signal subspace based on predetermined second radio nodes, generating a total uplink signal subspace, where the uplink interference subspace being based on the second radio node uplink signal subspace and the total uplink signal subspace, generating a vector of correlation coefficients based on the second radio node uplink signal subspace and the total uplink signal subspace where the uplink interference subspace corresponds to a portion of the total uplink signal subspace associated with correlation coefficients having values below a predefined threshold.

According to one embodiment of this aspect, the uplink interference subspace is obtained by: generating a second radio node uplink signal subspace based on predetermined second radio nodes where a contribution of the predetermined second radio nodes to a total received signal corresponds to a projection of a total received signal onto the second radio node uplink signal subspace, generating a residual quantity by subtracting the contribution of the predetermined second radio nodes from the total received signal where the residual quantity corresponding to an uplink vector of uplink noise plus interference, and the uplink interference subspace being based on the residual quantity. According to one embodiment of this aspect, the uplink interference subspace is obtained by: generating a residual quantity by subtracting a contribution of predetermined second radio nodes from a total received signal of pilot resource elements where the residual quantity corresponding to an uplink vector of an uplink noise plus interference. The uplink interference subspace is generated based on the residual quantity. According to one embodiment of this aspect, the second radio node signal subspace corresponds to a set of uplink codebooks.

According to one embodiment of this aspect, the radiation pattern is modified in the at least one communication direction of at least one interference source by removing a signal contribution that lies in an estimated downlink interference subspace by performing a projection. According to one embodiment of this aspect, the first interference subspace is used to modify the radiation pattern in the at least one communication direction of at least one interference source in more than one radio communication channel located in the same or in different radio frequency communication bands. According to one embodiment of this aspect, the wireless communications based on the beamforming weights are configured to be of similar power and <NUM> degrees out of phase with other wireless communications at the at least one interference source.

As discussed above, some existing PIM mitigation/cancellation techniques suffer from one or more problems. The teachings of the disclosure solve at least in part one problem with these one or more existing PIM mitigation/cancellation techniques. In particular, one or more embodiments of the disclosure relate to a layer-domain interference mitigation technique. Unlike some existing PIM mitigation/cancellation techniques, the layer-domain interference mitigation technique described herein provides one or more of the following advantages:.

In one or more embodiments, the layer-domain interference mitigation technique is based on subspace tracking, i.e., one or more subspace tracking algorithms. In general, subspace tracking algorithms play a role in a variety of adaptive subspace processes. In one or more embodiments described herein, one or more subspace tracking algorithms may be implemented. One or more of these subspace tracking algorithms may be used implemented to acquire/obtain and/or track one or more subspaces described herein such as obtaining and/or tracking dominant eigenvectors that may correspond to an interference subspace described herein. Some examples of subspace tracking algorithms may include one or more principle subspace trackers (PST) such as projection approximation subspace tracking using deflation (PASTD), Subspace Projection (SP) algorithm, etc. that may be configured for obtaining and/or tracking a subspace. One advantage of using the subspace tracking algorithms as described herein is that it makes the concept of determining a subspace such as the interference subspace practical by significantly reducing the implementation cost, e.g., requires less processing resources.

Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to the modification of a radiation pattern in at least one communication direction of at least one interference source. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

The term "first radio node" used herein can be any kind of radio node comprised in a radio network which may further comprise any of network node, radio base station, base station, base transceiver station (BTS), first radio node controller (BSC), radio network controller (RNC), gNB, evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The first radio node may also comprise test equipment. The term "radio node" used herein may be used to also denote a user equipment (UE)/wireless device or a radio network node.

In some embodiments, the "second radio node" herein can be any type of radio node capable of communicating with a first radio node or another user equipment (UE) or wireless device over radio signals. The second radio node may also be a radio communication device, user equipment, target device, device to device (D2D) radio node, wireless device, machine type radio node or radio node capable of machine to machine communication (M2M), low-cost and/or low-complexity radio node, a sensor equipped with UE, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device, etc. Similarly, functions and descriptions attributed to the "first" radio node can be performed by the "second" radio node, and vice versa. In other words, in some embodiments, the "first" radio node can be the "second" radio node, and the "second" radio node can be the "first" radio node.

Note that although terminology from one particular wireless system, such as, for example, 3GPP Long Term Evolution (LTE) and/or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system.

Note further, that functions described herein as being performed by a second radio node such as a user equipment or a first radio node such as a network node may be distributed over a plurality of second radio nodes and/or first radio nodes. In other words, it is contemplated that the functions of the first radio node and second radio node described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices.

An indication generally may explicitly and/or implicitly indicate the information it represents and/or indicates. Implicit indication may for example be based on position and/or resource used for transmission. Explicit indication may for example be based on a parametrization with one or more parameters, and/or one or more index or indices, and/or one or more bit patterns representing the information. It may in particular be considered that control signaling as described herein, based on the utilized resource sequence, implicitly indicates the control signaling type.

A channel may generally be a logical or physical channel. A channel may comprise and/or be arranged on one or more carriers, in particular a plurality of subcarriers. A wireless communication network may comprise at least one first radio node, in particular a first radio node as described herein. A second radio node connected or communicating with a network may be considered to be connected or communicating with at least one first radio node, in particular any one of the first radio nodes described herein.

A cell may be generally a communication cell, e.g., of a cellular or mobile communication network, provided by a radio node. A serving cell may be a cell on or via which a first radio node (the node providing or associated to the cell, e.g., base station, gNB or eNodeB) transmits and/or may transmit data (which may be data other than broadcast data) to a second radio node, in particular control and/or user or payload data, and/or via or on which a second radio node transmits and/or may transmit data to the radio node; a serving cell may be a cell for or on which the second radio node is configured and/or to which it is synchronized and/or has performed an access procedure, e.g., a random access procedure, and/or in relation to which it is in a RRC_connected or RRC_idle state, e.g., in case the node and/or user equipment and/or network follow LTE based standard or NR based standards. One or more carriers (e.g., uplink and/or downlink carrier/s and/or a carrier for both uplink and downlink) may be associated to a cell.

It may be considered for cellular communication there is provided at least one uplink (UL) connection and/or channel and/or carrier and at least one downlink (DL) connection and/or channel and/or carrier, e.g., via and/or defining a cell, which may be provided by a second radio node, in particular a base station, gNB or eNodeB. An uplink direction may refer to a data transfer direction from a second radio node to a first radio node, e.g., base station, gNB and/or relay station. A downlink direction may refer to a data transfer direction from a first radio node, e.g., base station, gNB and/or relay node, to a second radio node. UL and DL may be associated to different frequency resources, e.g., carriers and/or spectral bands. A cell may comprise at least one uplink carrier and at least one downlink carrier, which may have different frequency bands. A second radio node, e.g., a base station, gNB or eNodeB, may be adapted to provide and/or define and/or control one or more cells, e.g., a PCell and/or a LA cell.

Configuring a second radio node may involve instructing and/or causing the second radio node to change its configuration, e.g., at least one setting and/or register entry and/or operational mode. A second radio node may be adapted to configure itself, e.g., according to information or data in a memory of the second radio node. Configuring a second radio node by another device or node or a network may refer to and/or comprise transmitting information and/or data and/or instructions to the second radio node by the other device or node or the network, e.g., allocation data (which may also be and/or comprise configuration data) and/or scheduling data and/or scheduling grants. Configuring a second radio node may include sending allocation/configuration data to the second radio node indicating which modulation and/or encoding to use. A second radio node may be configured with and/or for scheduling data and/or to use, e.g., for transmission, scheduled and/or allocated uplink resources, and/or, e.g., for reception, scheduled and/or allocated downlink resources. Uplink resources and/or downlink resources may be scheduled and/or provided with allocation or configuration data.

Referring now to the drawing figures in which like elements are referred to by like reference numerals, there is shown in <FIG> a schematic diagram of a communication system <NUM>, according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (<NUM>), which comprises an access network <NUM>, such as a radio access network, and a core network <NUM>. The access network <NUM> comprises a plurality of first radio nodes 16a, 16b, 16c (referred to collectively as first radio nodes <NUM>, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas <NUM>). Each first radio node 16a, 16b, 16c is connectable to the core network <NUM> over a wired or wireless connection <NUM>. A second radio node 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding first radio node 16c. A second radio node 22b in coverage area 18b is wirelessly connectable to the corresponding first radio node 16a. While a plurality of second radio nodes 22a, 22b (collectively referred to as second radio nodes <NUM>) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole second radio node is in the coverage area or where a sole second radio node is connecting to the corresponding first radio node <NUM>. Note that although only two second radio nodes <NUM> and three first radio nodes <NUM> are shown for convenience, the communication system may include many more second radio nodes <NUM> and first radio nodes <NUM>.

Also, it is contemplated that a second radio node <NUM> can be in simultaneous communication and/or configured to separately communicate with more than one first radio node <NUM> and more than one type of first radio node <NUM>. For example, a second radio node <NUM> can have dual connectivity with a first radio node <NUM> that supports LTE and the same or a different first radio node <NUM> that supports NR. As an example, second radio node <NUM> can be in communication with an eNB for LTE/E-UTRAN and a gNB for New radio (NR)/Next Generation Radio Access Network (NG-RAN).

The communication system of <FIG> as a whole enables connectivity between one of the connected second radio nodes 22a, 22b and the host computer <NUM>. The host computer <NUM> and the connected second radio nodes 22a, 22b are configured to communicate data and/or signaling via the OTT connection, using the access network <NUM>, the core network <NUM>, any intermediate network <NUM> and possible further infrastructure (not shown) as intermediaries. For example, a first radio node <NUM> may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer <NUM> to be forwarded (e.g., handed over) to a connected second radio node 22a. Similarly, the first radio node <NUM> need not be aware of the future routing of an outgoing uplink communication originating from the second radio node 22a towards the host computer <NUM>.

A first radio node <NUM> is configured to include a beamforming unit <NUM> which is configured to modify a radiation pattern in at least one communication direction of at least one interference source, as described herein. A second radio node <NUM> may be configured to include a one or more units which are configured to perform one or more second radio node functions as described herein.

Example implementations, in accordance with an embodiment, of the second radio node <NUM>, first radio node <NUM> and host computer <NUM> discussed in the preceding paragraphs will now be described with reference to <FIG>.

The host application <NUM> may be operable to provide a service to a remote user, such as a second radio node <NUM> connecting via an OTT connection <NUM> terminating at the second radio node <NUM> and the host computer <NUM>. The "user data" may be data and information described herein as implementing the described functionality. In one embodiment, the host computer <NUM> may be configured for providing control and functionality to a service provider and may be operated by the service provider or on behalf of the service provider. The processing circuitry <NUM> of the host computer <NUM> may enable the host computer <NUM> to observe, monitor, control, transmit to and/or receive from the first radio node <NUM> and or the second radio node <NUM>. The processing circuitry <NUM> of the host computer <NUM> may include an information unit <NUM> configured to enable the service provider to at least partially determine and/or provide information related to the modification of a radiation pattern in at least one communication direction of at least one interference source.

The communication system <NUM> further includes a first radio node <NUM> provided in a communication system <NUM> and comprising hardware <NUM> enabling it to communicate with the host computer <NUM> and with the second radio node <NUM>. The hardware <NUM> may include a communication interface <NUM> for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system <NUM>, as well as a radio interface <NUM> for setting up and maintaining at least a wireless connection <NUM> with a second radio node <NUM> located in a coverage area <NUM> served by the first radio node <NUM>.

In the embodiment shown, the hardware <NUM> of the first radio node <NUM> further includes processing circuitry <NUM>.

Thus, the first radio node <NUM> further has software <NUM> stored internally in, for example, memory <NUM>, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the first radio node <NUM> via an external connection. The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by first radio node <NUM>. Processor <NUM> corresponds to one or more processors <NUM> for performing first radio node <NUM> functions described herein. The memory <NUM> is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software <NUM> may include instructions that, when executed by the processor <NUM> and/or processing circuitry <NUM>, causes the processor <NUM> and/or processing circuitry <NUM> to perform the processes described herein with respect to first radio node <NUM>. For example, processing circuitry <NUM> of the first radio node <NUM> may include beamforming unit <NUM> configured to modify a radiation pattern in at least one communication direction of at least one interference source.

The communication system <NUM> further includes the second radio node <NUM> already referred to. The second radio node <NUM> may have hardware <NUM> that may include a radio interface <NUM> configured to set up and maintain a wireless connection <NUM> with a first radio node <NUM> serving a coverage area <NUM> in which the second radio node <NUM> is currently located.

The hardware <NUM> of the second radio node <NUM> further includes processing circuitry <NUM>.

Thus, the second radio node <NUM> may further comprise software <NUM>, which is stored in, for example, memory <NUM> at the second radio node <NUM>, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the second radio node <NUM>. The client application <NUM> may be operable to provide a service to a human or non-human user via the second radio node <NUM>, with the support of the host computer <NUM>. In the host computer <NUM>, an executing host application <NUM> may communicate with the executing client application <NUM> via the OTT connection <NUM> terminating at the second radio node <NUM> and the host computer <NUM>.

The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by second radio node <NUM>. The processor <NUM> corresponds to one or more processors <NUM> for performing second radio node <NUM> functions described herein. The second radio node <NUM> includes memory <NUM> that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software <NUM> and/or the client application <NUM> may include instructions that, when executed by the processor <NUM> and/or processing circuitry <NUM>, causes the processor <NUM> and/or processing circuitry <NUM> to perform the processes described herein with respect to second radio node <NUM>. For example, the processing circuitry <NUM> of the second radio node <NUM> may include one or more units that are configured to perform one or more second radio node <NUM> functions are described herein.

In some embodiments, the inner workings of the first radio node <NUM>, second radio node <NUM>, and host computer <NUM> may be as shown in <FIG> and independently, the surrounding network topology may be that of <FIG>.

In <FIG>, the OTT connection <NUM> has been drawn abstractly to illustrate the communication between the host computer <NUM> and the second radio node <NUM> via the first radio node <NUM>, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the second radio node <NUM> or from the service provider operating the host computer <NUM>, or both.

The wireless connection <NUM> between the second radio node <NUM> and the first radio node <NUM> is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the second radio node <NUM> using the OTT connection <NUM>, in which the wireless connection <NUM> may form the last segment.

There may further be an optional network functionality for reconfiguring the OTT connection <NUM> between the host computer <NUM> and second radio node <NUM>, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection <NUM> may be implemented in the software <NUM> of the host computer <NUM> or in the software <NUM> of the second radio node <NUM>, or both. The reconfiguring of the OTT connection <NUM> may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the first radio node <NUM>, and it may be unknown or imperceptible to the first radio node <NUM>. In certain embodiments, measurements may involve proprietary second radio node signaling facilitating the host computer's <NUM> measurements of throughput, propagation times, latency and the like.

Thus, in some embodiments, the host computer <NUM> includes processing circuitry <NUM> configured to provide user data and a communication interface <NUM> that is configured to forward the user data to a cellular network for transmission to the second radio node <NUM>. In some embodiments, the cellular network also includes the first radio node <NUM> with a radio interface <NUM>. In some embodiments, the first radio node <NUM> is configured to, and/or the first radio node's <NUM> processing circuitry <NUM> is configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the second radio node <NUM>, and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the second radio node <NUM>.

In some embodiments, the host computer <NUM> includes processing circuitry <NUM> and a communication interface <NUM> that is configured to a communication interface <NUM> configured to receive user data originating from a transmission from a second radio node <NUM> to a first radio node <NUM>. In some embodiments, the second radio node <NUM> is configured to, and/or comprises a radio interface <NUM> and/or processing circuitry <NUM> configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the first radio node <NUM>, and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the first radio node <NUM>.

Although <FIG> and <FIG> show various "units" such as beamforming unit <NUM> as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry.

Having generally described arrangements for modifying of a radiation pattern in at least one communication direction of at least one interference source to thereby mitigate the effects of interference such as PIM, details for these arrangements, functions and processes are provided as follows, and which may be implemented by the first radio node <NUM>, second radio node <NUM> and/or host computer <NUM>.

A mathematics-based approach to modification of the radiation pattern is described with reference to <FIG>. More specifically, <FIG> is a mathematical system model of an example massive-MIMO frequency-division duplex (FDD) system with interference such as PIM interference. The system parameters of the system model include:.

The system model variables are described as:.

PUL is a K × N matrix of the beamforming weights for each of the UL subcarriers (PRB granularity may be used to reduce the implementation cost).

In the downlink, some "transmit nulls" or very low power DL signals may be created at the PIM sources through beamforming so that the PIM sources may not be excited into generating PIM signals, thereby reducing PIM interference for the uplink MIMO layers.

Massive-MIMO systems may correspond to some underdetermined systems of equation that may have, in theory, an infinite number of solutions. The teachings of the disclosure introduce the treatment of the DL beamforming problem as constrained optimization between a PIM requirement and a Multi-User Interference (MUI) requirement.

To satisfy the two conditions, the downlink beamforming solution a must minimize the following cost function: <MAT>.

The first line of the PDL cost function helps ensure that the downlink signal energy is minimized at the PIM sources while the second line states that the downlink communication layers are transmitted to the intended second radio nodes <NUM> without any cross-layer interference (MUI condition). The optimization problem of equation (<NUM>) can be solved using Lagrangian multipliers and is referred to as the Constrained Least Norm (CLEAN) beamforming algorithm: <MAT>.

Where λ is a M × <NUM> vector of Lagrange multipliers and (·)T is a vector transpose operation. Setting to zero the two partial derivatives of the Lagrange function (<NUM>) with respect to the a and λ variables produces: <MAT> <MAT>.

Where the (·)H operator denotes the matrix Hermitian (i.e., complex conjugate) transpose.

Substituting (<NUM>) into (<NUM>) to find λ: <MAT>.

Substituting (<NUM>) back into (<NUM>): <MAT>.

To simplify the notation, the downlink PIM channel covariance matrix is written as: <MAT>.

Finally, substituting (<NUM>) into (<NUM>) leads to: <MAT>.

The downlink channel matrix HDL_IF between the second radio node <NUM> and the PIM sources is unknown. However, equation (<NUM>) does not require the knowledge of the PIM channel but only of its covariance matrix RDL_IF, which can also be written in terms of its eigenvectors: <MAT> Where:.

In a Frequency Division Duplex (FDD) system, the spatial behavior experienced by the antenna array of the first radio node <NUM> (i.e., directions of arrival and departure of communication signals) is similar in both the uplink and downlink. In other words, the dominant downlink interference eigenvectors - which correspond to the directions of departure at the antenna array - can be estimated using the uplink interference directions of arrival. The estimated downlink interference covariance matrix R̂DL_IF can be expressed in terms of the uplink interferers' subspace as follows: <MAT>.

The transpose operation on the first line of equation (<NUM>) implements the uplink-to-downlink channel conversion. The (·) operator in equation (<NUM>) represents the matrix conjugation without transpose.

The process for obtaining and tracking the uplink interferers' eigenvectors can be divided into two distinct scenarios:.

Note that, in one or more embodiments, this technique may not be best suited for identifying common eigenvectors UUE/interf between the scheduled second radio nodes <NUM> and the interferers. Indeed, in the situation where some of the interferers have uplink directions of arrival that are similar to those of the second radio nodes <NUM>, their contribution may also be projected - partly or in total - onto the second radio node <NUM> signal subspace. Thus, these sources of interference may have a high probability of going unnoticed during the verification step of section described in Scenario <NUM> (d).

The teachings described herein are compatible with codebook-based MIMO transmissions with some minor modifications. The algorithm steps for codebook-based precoding are described below:.

Where I is the N × N identity matrix and <MAT> is the matrix of the downlink codebook pre-coding weights.

The procedure of equation (<NUM>) may, in one or more embodiments, initially increase the noise and interference levels in the received layer-domain constellations at the second radio node(s) <NUM>. However, the codebook selection may be an adaptive process such that the second radio node(s) <NUM> may adapt to the spatial constraints over time.

In the uplink, some receive nulls or very low power signals may be generated through beamforming in the directions of the interference sources (e.g., PIM sources) to help reduce interference for the uplink MIMO communication layers.

The uplink cost function can be written as follows: <MAT>.

Where the matrix <MAT> corresponds to the uplink beamforming weights, ∥·∥Fro is the Frobenius norm and I is the K × K identity matrix.

The first line of the GUL cost function may ensure that the interferers' signal energy is minimized in the received layers while the second line removes the uplink cross-layer interferences between the scheduled second radio nodes <NUM> (MUI condition). The optimization problem of equation (<NUM>) can be solved using Lagrangian multipliers: <MAT>.

Where Λ is a K × K matrix of Lagrange multipliers. Setting to zero the two partial derivatives of the Lagrange function (<NUM>) with respect to the PUL and Λ variables produces: <MAT> <MAT>.

Isolating <MAT> in (<NUM>) yields: <MAT>.

Substituting (<NUM>) into (<NUM>) to find Λ: <MAT>.

Note that both Λ and ( <MAT>) are Hermitian matrices, signifying that they are equal to their own complex-conjugate transposes (e.g.: Λ = ΛH).

To simplify the notation, the uplink interference channel covariance matrix is written as: <MAT>.

Finally, substituting (<NUM>) into (<NUM>) we obtain: <MAT>.

The uplink interferers' channel covariance matrix RUL_IF is built from the interferers' subspace UUL_IF as per the right-hand side of equation (<NUM>). The interferers' subspace UUL_IF is in turn determined using any of the techniques described herein with respect to the Eigenvectors Acquisition and Tracking section.

In some cases, there may be instances where an antenna array may not be able to avoid transmitting in the direction of an interference source such as a PIM source. This may happen, for example, if second radio node <NUM> movement patterns in a given area pass by a PIM source in proximity of the array. In these situations, multi-array cooperation may be used where one or more secondary arrays create an auxiliary transmission directed at the PIM source in order to have two transmissions of similar amplitude that are out of phase by <NUM>° at the PIM source such that these two transmissions cancel or nearly cancel each other as illustrated in <FIG>. In one or more embodiments, "similar" amplitude or power may correspond to the amplitude/power of two or more transmissions being within a predefined amplitude/power quantity from each other.

Mathematically, eigenvectors of array <NUM> (illustrated in <FIG>) that correspond to the "unavoidable" PIM sources that may be regarded as eigenvectors that are common to both the second radio node <NUM> and the interference subspaces. These common eigenvectors are referred to as the common subspace UUE/interf. The total downlink covariance matrix for array <NUM> (illustrated in <FIG>) can be written as: <MAT>.

Since the secondary array <NUM> has a different location in the <NUM>-D space, it is likely that the secondary array <NUM> eigenvectors to these PIM sources are decorrelated from its second radio node signal subspace. In one or more embodiments, array <NUM> is associated with the first radio node 16a while the array <NUM> is associated with the first radio node 16b that is different from the first radio node 16a.

The auxiliary transmission from the secondary array <NUM> to the PIM source may be calibrated. It may be preferable to not have any traffic scheduled on array <NUM> during this calibration stage/process, although it may not be necessary:.

During operation, the portion of a transmitted signal of the array <NUM> that lies in the common UE/interference subspace may be identified using a projection onto that subspace as follows: <MAT>.

The aUE/interf vector may be forwarded to array <NUM> together with transmission scheduling information using a backhaul network connection. This signal is then transmitted by the array <NUM> with a <NUM>° phase offset, initially using the weights that have been identified during the calibration stage.

Given the unstable nature of radio frequency (RF) propagation environments, some directivity/delay/power adjustments may be needed in the operational stage in order to keep minimizing the total downlink power at the PIM source. These adjustments may be performed iteratively solving either a mathematical cost function, through an exhaustive search by sweeping the parameters or using a combination of the two techniques.

<FIG> is a flowchart of an example process performed by beamforming unit <NUM> in a first radio node <NUM> for modifying a radiation pattern in at least one communication direction of at least one interference source, as described herein. The first radio node <NUM> such as via processing circuitry <NUM> is configured to obtain a first interference subspace, as described herein (block S <NUM>). The first radio node <NUM>, such as via processing circuitry <NUM>, is configured to obtain beamforming weights based on the first interference subspace where the beamforming weights are configured to modify a radiation pattern in at least one communication direction of at least one interference source, as described herein (block S <NUM>). The first radio node <NUM> such as via processing circuitry <NUM> is configured to perform wireless communications based on the beamforming weights, as described herein (block S104).

According to one or more embodiments, the first interference subspace is an uplink interference subspace where the modified radiation pattern is in a downlink interference subspace. According to one or more embodiments, the processing circuitry is further configured to configure the first radio node to: obtain an estimate of the downlink interference subspace based on the uplink interference subspace where the obtaining of the beamforming weights being based on the estimate of the downlink interference subspace. According to one or more embodiments, the uplink interference subspace corresponds to an uplink set of eigenvectors.

According to one or more embodiments, the modified radiation pattern in at least one communication direction of at least one interference source is configured to reduce the downlink transmission radiation pattern in at least one communication direction of the at least one interference source. According to one or more embodiments, the at least one interference source is at least one passive intermodulation, PIM, source. According to one or more embodiments, the first interference subspace is an uplink subspace where the modified radiation pattern being in an uplink interference subspace. According to one or more embodiments, the estimate of the downlink interference subspace is based on an estimate of a downlink interference covariance matrix.

According to one or more embodiments, the uplink interference subspace corresponds to a plurality of dominant eigenvectors. According to one or more embodiments, the modified radiation pattern in at least one communication direction of at least one interference source is configured to reduce the uplink receive radiation pattern in at least one communication direction of the at least one interference source.

According to one or more embodiments, the uplink interference subspace is determined by: determining a signal subspace corresponding to a plurality of communication directions of a plurality of interference sources including the at least one interference source where the signal subspace corresponding to a first plurality of eigenvectors, generating a second radio node signal subspace based on predetermined second radio nodes <NUM> where the second radio node signal subspace corresponding to a second plurality of eigenvectors, generating a vector of a plurality of correlation coefficients based on the signal subspace and second radio node signal subspace, and removing eigenvectors from the signal subspace corresponding to the signal correlation coefficients that meet a predefined threshold where the remaining eigenvectors from the signal subspace corresponding to the uplink interference subspace. According to one or more embodiments, the uplink interference subspace is determined by: generating a second radio node uplink signal subspace based on predetermined second radio nodes <NUM>, generating a total uplink signal subspace where the uplink interference subspace being based on the second radio node uplink signal subspace and the total uplink signal subspace, generating a vector of correlation coefficients based on the second radio node uplink signal subspace and the total uplink signal subspace where the uplink interference subspace corresponding to a portion of the total uplink signal subspace associated with correlation coefficients having values below a predefined threshold.

According to one or more embodiments, the uplink interference subspace is obtained by: generating a second radio node uplink signal subspace based on predetermined second radio nodes <NUM> where a contribution of the predetermined second radio nodes <NUM> to a total received signal corresponds to a projection of a total received signal onto the second radio node uplink signal subspace, and generating a residual quantity by subtracting the contribution of the predetermined second radio nodes <NUM> from the total received signal where the residual quantity corresponding to an uplink vector of uplink noise plus interference. The uplink interference subspace is based on the residual quantity.

According to one or more embodiments, the uplink interference subspace is obtained by: generating a residual quantity by subtracting a contribution of predetermined second radio nodes <NUM> from a total received signal of pilot resource elements where the residual quantity corresponding to an uplink vector of an uplink noise plus interference. The uplink interference subspace is generated based on the residual quantity. According to one or more embodiments, the second radio node signal subspace corresponds to a set of uplink codebooks. According to one or more embodiments, the radiation pattern is modified in the at least one communication direction of at least one interference source by removing a signal contribution that lies in an estimated downlink interference subspace by performing a projection.

According to one or more embodiments, the first interference subspace is used to modify the radiation pattern in the at least one communication direction of at least one interference source in more than one radio communication channel located in the same or in different radio frequency communication bands. According to one or more embodiments, the wireless communications based on the beamforming weights are configured to be of similar power and <NUM> degrees out of phase with other wireless communications at the at least one interference source.

<FIG> is a flowchart of another example process of beamforming unit <NUM> in a first radio node <NUM> for modifying a radiation pattern in at least one communication direction of at least one interference source, as described herein. In particular, this example is directed to toward downlink transmissions. The first radio node <NUM> such as via processing circuitry <NUM> is configured to obtain an indication of an uplink interference subspace, as described herein (block S <NUM>). The first radio node <NUM> such as via processing circuitry <NUM> is configured to obtain an estimate of a downlink interference subspace based on the uplink interference subspace, as described herein (block S <NUM>). The first radio node <NUM> such as via processing circuitry <NUM> is configured to perform downlink transmission with a modified radiation pattern in a downlink interference subspace that is based on the estimated downlink interference subspace, as described herein (block S <NUM>).

In one or more embodiments, the modified radiation pattern corresponds to a reduction in wireless communication signal power in at least one communication direction of at least one passive intermodulation, PIM, source. In one or more embodiments, the estimate of the downlink interference subspace is based on an estimate of a downlink interference covariance matrix. In one or more embodiments, the estimate of the downlink interference subspace corresponds to a set of eigenvectors of the estimated downlink interference covariance matrix where a remaining set of eigenvectors of the estimated downlink interference covariance matrix corresponding to a noise subspace.

In one or more embodiments, the modified radiation pattern that reduces wireless communication signal power in at least one communication direction of at least one PIM source is configured to reduce the downlink transmission radiation pattern in at least one communication direction of the at least one PIM source. In one or more embodiments, the uplink interference subspace is obtained by: determining a signal subspace corresponding to a plurality of communication directions of a plurality of interference sources including the at least one PIM source, the signal subspace corresponding to a first plurality of eigenvectors, generating a second radio node signal subspace based on predetermined second radio nodes <NUM> where the second radio node signal subspace corresponding to a second plurality of eigenvectors, generating a vector of a plurality of correlation coefficients based on the signal subspace and second radio node signal subspace and removing eigenvectors from the signal subspace corresponding to the signal correlation coefficients that meet a predefined threshold. The remaining eigenvectors from the signal subspace correspond to the uplink interference subspace.

In one or more embodiments, the uplink interference subspace is obtain by: generating a second radio node uplink signal subspace based on predetermined second radio nodes <NUM> and generating a total uplink signal subspace where the uplink interference subspace is based on the second radio node uplink signal subspace and the total uplink signal subspace, and generating a vector of correlation coefficients based on the second radio node uplink signal subspace and the total uplink signal subspace. The uplink interference subspace corresponds to a portion of the total uplink signal subspace associated with correlation coefficients having values below a predefined threshold.

In one or more embodiments, the uplink interference subspace is obtained by: generating a second radio node uplink signal subspace based on predetermined second radio nodes <NUM> where a contribution of the predetermined second radio nodes <NUM> to a total received signal corresponds to a projection of a total received signal onto the second radio node uplink signal subspace, and generating a residual quantity by subtracting the contribution of the predetermined second radio nodes <NUM> from the total received signal where the residual quantity corresponding to an uplink vector of uplink noise plus interference. The uplink interference subspace being based on the residual quantity.

In one or more embodiments, the uplink interference subspace is obtained by: generating a residual quantity by subtracting a contribution of predetermined second radio nodes <NUM> from a total received signal of pilot resource elements, the residual quantity corresponding to an uplink vector of an uplink noise plus interference. The uplink interference subspace is generated based on the residual quantity. In one or more embodiments, the second radio node signal subspace corresponds to a set of uplink codebooks. In one or more embodiments, the radiation pattern is modified in the at least one communication direction of at least one interference source by removing a signal contribution that lies in an estimated downlink interference subspace by performing a projection.

In one or more embodiments, the first interference subspace is used to modify the radiation pattern in the at least one communication direction of at least one interference source in more than one radio communication channel located in the same or in different radio frequency communication bands. In one or more embodiments, the wireless communications based on the beamforming weights are configured to be of similar power and <NUM> degrees out of phase with other wireless communications at the at least one interference source.

<FIG> is a flowchart of another example process of beamforming unit <NUM> in a first radio node <NUM> for modifying a radiation pattern in at least one communication direction of at least one interference source, as described herein. In particular, this example is directed to uplink transmissions. The first radio node <NUM> such as via processing circuitry <NUM> is configured to obtain an indication of an uplink interference subspace (block S112). The first radio node <NUM> such as via processing circuitry <NUM> is configured to obtain a set of beamforming weights with a modified radiation pattern in the uplink interference subspace based on the uplink interference subspace (block S114). In one or more embodiments, the reduced radiation pattern corresponds to a reduction in wireless communication signal power in at least one communication direction of at least one passive intermodulation, PIM, source. The first radio node <NUM> such as via processing circuitry <NUM> is configured to perform wireless communications based on the beam forming weights (block S116).

In one or more embodiments, the modified radiation pattern that reduces wireless communication signal power in at least one communication direction of at least one PIM source is configured to reduce the uplink receive radiation pattern in at least one communication direction of the at least one PIM source. In one or more embodiments, the uplink interference subspace is obtained by: determining a signal subspace corresponding to a plurality of communication directions of a plurality of interference sources including the at least one PIM source where the signal subspace corresponds to a first plurality of eigenvectors, generating a second radio node signal subspace based on predetermined second radio nodes <NUM> where the second radio node signal subspace corresponding to a second plurality of eigenvectors, generating a vector of a plurality of correlation coefficients based on the signal subspace and second radio node signal subspace and removing eigenvectors from the signal subspace corresponding to the signal correlation coefficients that meet a predefined threshold. The remaining eigenvectors from the signal subspace correspond to the uplink interference subspace.

In one or more embodiments, the uplink interference subspace is obtained by: generating a second radio node uplink signal subspace based on predetermined second radio nodes <NUM>, generating a total uplink signal subspace where the uplink interference subspace is based on the second radio node uplink signal subspace and the total uplink signal subspace, and generating a vector of correlation coefficients based on the second radio node uplink signal subspace and the total uplink signal subspace. The uplink interference subspace corresponds to a portion of the total uplink signal subspace associated with correlation coefficients having values below a predefined threshold.

According to one or more embodiments, described herein, one or more interference sources may correspond to one or more inter-cell second radio nodes <NUM> that are interferers in the uplink and interfered in the downlink.

Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them.

Claim 1:
A first radio node (<NUM>) comprising processing circuitry (<NUM>) configured to configure the first radio node (<NUM>) to:
obtain (S100) a first interference subspace;
obtain (S102) beamforming weights based on the first interference subspace, the beamforming weights configured to modify a radiation pattern in at least one communication direction of at least one interference source, characterized in that the at least one interference source is at least one passive intermodulation, PIM, source; and
perform (<NUM>) wireless communications based on the beamforming weights, wherein the wireless communications based on the beamforming weights are configured to be of similar power and <NUM> degrees out of phase with other wireless communications at the at least one interference source.