Passive Intermodulation Sensing Beamforming

Abstract

The present subject matter relates to an apparatus for a communication system. The apparatus is configured to: for each beam direction in a set of beam directions of an antenna array of the communication system, determine a level of a passive intermodulation (PIM) signal at a receiver of the communication system, the PIM signal being caused by a set of signals transmitted by the antenna array in the beam direction, identify beam directions in the set of beam directions for which the PIM level is higher than a predefined threshold, and adjust beamforming of signals on at least a portion of the identified beam directions to mitigate the PIM level at the receiver.

Description

Technical Field

[0001] Various example embodiments relate to computer networking and, more particularly, to passive intermodulation aware beamforming. Background Art

[0002] When two or more signals at different frequencies are transmitted along a signal path that includes components having non-linear transmission characteristics, intermodulation products may be generated in a wireless system; these products are different in frequency from the signals from which they are generated and may potentially cause interference to other signals. Summary of the Invention

[0003] Example embodiments provide an apparatus for a communication system. The apparatus is configured to: for each beam direction in a set of beam directions of an antenna array of the communication system, determine a level of a passive intermodulation (PIM) signal at a receiver of the communication system, the PIM signal being caused by a set of signals transmitted by the antenna array in the beam direction, identify one or more beam directions in the set of beam directions for which the determined PIM level is higher than a predefined threshold, and adjust beamforming of signals on at least a portion of the identified beam directions to mitigate the PIM level at the receiver.

[0004] According to further example embodiments, a method for a communication system is provided. The method includes: for each beam direction in a set of beam directions of an antenna array of the communication system, determine a level of a passive intermodulation (PIM) signal at a receiver of the communication system, the PIM signal being caused by a set of signals transmitted by the antenna array in the beam direction, identify one or more beam directions in the set of beam directions for which the determined PIM level (or received PIM signal level) is higher than a predefined threshold, and adjust beamforming of signals on at least a portion of the identified beam directions to mitigate the PIM level at the receiver.

[0005] According to further example embodiments, a computer program includes instructions stored thereon for at least performing the following operations: for each beam direction in a set of beam directions of an antenna array of the communication system, determine a level of a passive intermodulation (PIM) signal at a receiver of the communication system, the PIM signal being caused by a set of signals transmitted by the antenna array in the beam direction, identify one or more beam directions in the set of beam directions for which the determined PIM level is higher than a predefined threshold, and adjust beamforming of signals on at least a portion of the identified beam directions to mitigate the PIM level at the receiver.

[0006] According to a further example embodiment, a system includes an antenna array, a transmitter, a receiver, and a device. The antenna array includes a receiving antenna element of the receiver and a transmitting antenna element of the transmitter. The device is configured to: for each beam direction in a set of beam directions of the antenna array of a communication system, determine a level of a passive intermodulation (PIM) signal at the receiver of the communication system, the PIM signal being caused by a set of signals transmitted by the antenna array in the beam direction; identify one or more beam directions in the set of beam directions for which the determined PIM level is higher than a predefined threshold, and adjust beamforming of the signals on at least a portion of the identified beam directions to mitigate the PIM level at the receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The drawings are included to provide a further understanding of the examples and are incorporated in and constitute a part of this specification. In the drawings:

[0008] Figure 1 A schematic diagram of a communication system is depicted;

[0009] Figure 2 A schematic diagram of a communication system according to an example of the present subject matter is depicted;

[0010] Figure 3 is a flowchart of a method for processing intermodulation products according to an example of the present subject matter;

[0011] Figure 4 A diagram depicting the impact of a PIM source on beamforming is depicted;

[0012] Figure 5 is a flowchart of a method for determining a PIM signal according to an example of the present subject matter;

[0013] Figure 6A is a flowchart of a method for configuring beamforming of an antenna array according to an example of the present subject matter;

[0014] Figure 6B A diagram depicting beamforming according to an example of the present subject matter is depicted;

[0015] Figure 7A is a flowchart of a method for configuring beamforming of an antenna array according to an example of the present subject matter;

[0016] Figure 7B A diagram depicting beamforming according to an example of the present subject matter is depicted;

[0017] Figure 8 is a block diagram showing an example for PIM avoidance;

[0018] Figure 9 is a block diagram showing an example for PIM avoidance;

[0019] Figure 10 It is a block diagram showing an example of a device showing an example according to the present subject matter. Detailed implementation

[0020] In the following description, for purposes of explanation and not limitation, specific details such as specific architectures, interfaces, technologies, etc. are set forth in order to provide a thorough understanding of the examples. However, it will be apparent to those skilled in the art that the disclosed subject matter may be practiced in other illustrative examples different from these specific details. In some cases, detailed descriptions of well-known devices and / or methods are omitted so as not to obscure the description with unnecessary details.

[0021] When steering a beam to a moving receiving device or switching a beam to a different receiving device, the beam of the antenna array may encounter a PIM obstacle. The PIM obstacle may be a metallic object. A metallic object near the radiating antenna array may cause PIM distortion, the frequency of which is similar to that of the uplink channel. For example, the energy density (such as the effective isotropic radiated power (EIRP)) generated where the beam is directed may be so high that even metallic objects of a more distant communication system may cause the TX carrier to mix in the air (the higher the beam energy density, the more distant PIM objects may cause problems). Thus, the PIM obstacle may cause a decrease in uplink (UL) sensitivity, depending on the uplink and downlink beam directions of the beam. The present subject matter can address this problem by changing beamforming at the transmitter and / or receiver for example for a beam direction coinciding with the PIM obstacle. Thus, the received signal power or the signal-to-noise ratio (SNR) at the intended receiver can be increased. This may be particularly advantageous in a multi-user massive multiple-input multiple-output (MIMO) 4G / 5G beamforming frequency-division duplex (FDD) system (for example, the system may be a system using MIMO and FDD technologies), in which the PIM effect can be mainly observed. The receiver may be, for example, part of a device. The device, the transmitter, and the antenna array may be part of a communication system. The receiver may be configured to process multiple signals received at multiple receive antenna elements of the antenna array. The PIM signals caused by the set of signals transmitted by the antenna array may fall within the receive band of the receiver.

[0022] Two directions are coincident directions if the difference between them meets a predefined coincidence criterion. For example, the difference can be the distance or angular distance between the two directions. For example, the coincidence criterion can require the distance to be less than or equal to a coincidence threshold. If the distance is higher than the coincidence threshold, the two directions do not coincide. For example, a direction can be defined by an azimuth angle φ and / or an elevation angle θ relative to an antenna array. The azimuth angle φ and the elevation angle θ can be defined in a predefined coordinate system, for example, the x-y plane is parallel to the ground and the z-axis is perpendicular to the ground upward. For example, the azimuth angle can vary between -30° and 30°, while the elevation angle can vary between -10° and 10°.

[0023] Beamforming can involve a spatial filtering mechanism that can be used for the transmit antenna elements and / or receive antenna elements of an antenna array to improve one or more properties, such as the received signal power or SNR at an intended receiver. Beamforming can be used for directional signal transmission and / or reception. The beam direction can be defined by an azimuth angle φ and / or an elevation angle θ relative to the antenna array.

[0024] Each antenna element of the antenna array can be separately fed with a signal to be transmitted or received. A beamforming setup can be used to perform beamforming. For example, the beamforming setup can include weights of amplitude and / or phase. Beamforming can be performed to obtain the maximum signal intensity in the beam direction of the radiation pattern of the antenna array. The beam direction can be the direction of the beam, where the beam can be the main lobe of the radiation pattern. Beamforming can include manipulating the phase and amplitude of each signal (according to the beamforming setup) such that the signals concentrate the energy into a narrow beam with the beam direction. In one example, the beamforming setup can be determined by an on-the-fly device for performing the adjustment steps of the present subject matter. In another example, the manipulation of the phase and amplitude can be performed according to a predefined and stored beamforming setup to perform the adjustment steps of the present subject matter. For example, different stored beamforming setups can be associated with different configurations, where the configuration can indicate the direction of the PIM source and the direction of the receiving and / or transmitting device.

[0025] For example, based on the current direction (φ0, θ0) of the receiving device, beamforming can be performed by controlling the beamforming setup of the transmit antenna elements of the antenna array to generate a directional beam pointing to a given direction (φ2, θ2) such that the receiving device can receive data via the directional beam. If the current direction of the receiving device does not coincide with the identified beam direction, the given direction can be the current direction, i.e., (φ2, θ2) = (φ0, θ0). However, if the current direction (φ0, θ0) corresponds to one or more identified beam directions, the given direction can be determined using the current direction according to the present subject matter, i.e., (φ2, θ2) is different from (φ0, θ0).

[0026] In one example, the set of beam directions may include the directions of candidate PIM sources of a communication system. By using only the directions of candidate PIM sources known to the user, the processing resources required to scan the entire range of directions (e.g., if the user does not know the location of the PIM source) can be saved. In one example, the set of beam directions may include the directions in which an antenna array can transmit signals, e.g., within the range of azimuth angles from -30° to 30°. By scanning all possible reachable directions, an accurate determination of all PIM levels can be achieved. This can enable an improvement in the signal reception quality in the communication system. In one example, the set of beam directions may include user-defined directions.

[0027] The PIM signal can be determined using a measurement method. The measurement method may include: measuring a first noise power level at a receiver when the signal transmission by a transmitter is turned off or disabled, radiating a signal causing PIM from the transmitter in a specific direction, measuring a second noise power level at the receiver after the radiation, comparing the first power level and the second power level, and determining the PIM level for the specific direction based on the difference between the first power level and the second power level. For example, if the difference between the first power level and the second power level is higher than a threshold, there may be an indication of a PIM source, and the difference can be used as the PIM level.

[0028] According to an example, the signal includes a downlink signal to a receiving device. The receiving device has a direction that coincides with one of the identified beam directions. The component is configured to perform an adjustment, including generating one or more beam directions that are closest to the direction of the receiving device and do not coincide with one of the identified beam directions, and adjusting the beamforming settings of the transmission antenna elements of the antenna array according to the generated directions. At least part of the identified beam directions is the one of the identified beam directions.

[0029] The identified set of beam directions can be named where i ranges between 1 and the total number of identified beam directions. The direction of the receiving device can be named DIR rec , and can coincide with the one of the identified beam directions, e.g., it is direction DIR rec coincides with the direction , e.g., if the angular distance between the two directions (represented as for simplicity of description) is less than or equal to a coincidence threshold T coinc . For example, if the angular distance is higher than T coinc , the two directions do not coincide.

[0030] One or more generated directions may be named where j≥1. The directions generated according to this embodiment are the directions closest to DIR rec and do not coincide with the identified beam direction in this one beam direction, that is are the directions closest to DIR rec and satisfy

[0031] Adjusting the beamforming settings of the antenna array according to the generated directions can, for example, enable the beam to be directed towards one or more of the generated beam directions. For example, instead of forming a beam towards the direction DIR rec to transmit data to the receiving device, the adjusted beamforming settings are used to direct the beam towards one or more of the generated beam directions

[0032] One or more generated directions may include two directions. For example, these two directions may be symmetrically distributed around the identified beam direction such as and This can further increase the received signal power or SNR at the intended receiver.

[0033] In one example, for each identified beam direction in at least a portion of the identified beam directions, the component is configured to determine two beam directions around the identified beam direction and adjust the beamforming settings of the antenna array such that the antenna array redirects the beam destined for the receiving device to a receiving device having a direction that coincides with the identified beam direction, and the redirection is performed for the two determined beam directions. The surrounding directions can be defined, for example, by and to define.

[0034] According to the example, the signal includes a downlink signal to the receiving device. The component is configured to perform an adjustment that includes adjusting the beamforming settings of the transmission antenna elements of the antenna array to notch the beam in each direction of at least a portion of the identified beam directions. The beam can be formed so that the receiving device can receive the signal. Notching the beam in a particular direction can include manipulating the phase and amplitude of each signal of the downlink signal such that the antenna array radiates little radio power in the particular direction, for example, the radio power in the particular direction is less than a power threshold. The particular direction can be null.

[0035] According to an example, at least some of the identified beam directions can be directions that coincide with the direction of the receiving device.

[0036] According to an example, at least some of the identified beam directions can be directions that do not coincide with the direction of the receiving device (e.g., ), and are one of the following directions: the direction closest to the direction of the receiving device, or the direction with the highest determined PIM level. In this example, the direction of the receiving device does not coincide with any of the identified beam directions.

[0037] For example, if there are more than one identified beam directions, the direction can be the identified direction closest to the direction DIR rec of the receiving device. The direction among the identified directions closest to the direction DIR rec of the receiving device may not coincide with the receiving device, e.g., This embodiment can adjust beamforming when the receiving device is close to a PIM source.

[0038] According to an example, the component is configured to select at least some of the identified beam directions based on the PIM level. This can save processing resources that would otherwise be required to adjust beamforming for each of the identified beam directions. For example, nulling the beam towards the selected beam direction can be performed by recalculating the phase and amplitude values for the receive antenna elements and / or transmit antenna elements of the antenna array to adjust the beamforming of the antenna array accordingly.

[0039] According to an example, for each of the identified beam directions among at least some of the identified beam directions, the component is configured to configure the beamforming of the antenna array by adjusting the weights of the amplitude and / or phase associated with the identified beam direction. For example, the configuration of the beamforming can be performed to null the beam in the identified beam direction, or by generating two (redirected) beam directions for the identified beam direction.

[0040] According to an example, the antenna array includes a number of transmit and receive antenna elements that is higher than a predefined minimum number of antenna elements. For example, the antenna array includes at least 8x8 transmit antenna elements and 8x8 receive antenna elements. According to the present subject matter, this can further improve the beamforming accuracy. For example, this may be advantageous in the case of adjusting beamforming according to more than one generated beam direction.

[0041] According to an example, the signal includes an uplink signal from a transmission device. The component is configured to perform an adjustment that includes adjusting the beamforming settings of the receiving antenna elements of the antenna array for a direction among the identified beam directions that does not coincide with the direction DIR of the transmission device trs in one of the identified beam directions that does not coincide (e.g., ) to notch the beam. Notching the beam in a particular direction can include manipulating the phase and amplitude of each signal of the uplink signal such that the antenna array receives little radio power in the particular direction, e.g., the radio power in the particular direction is less than a power threshold.

[0042] According to an example, at least part of the beam directions of the identified beam directions can be directions that do not coincide with the direction of the transmission device and are one of the following: the direction closest to the direction of the transmission device, the direction with the highest determined PIM level.

[0043] According to an example, the signal further includes a downlink signal to the transmission device. The component is configured to perform an adjustment that includes adjusting the beamforming settings of the transmission antenna elements of the antenna array to notch the beam in each direction of at least part of the beam directions of the identified beam directions.

[0044] For example, if there are more than one identified beam directions, the direction can be the closest identified direction to the direction DIR of the transmission device. The direction among the identified directions that is closest to the direction DIR trs of the transmission device trs may not coincide with the direction of the transmission device, e.g.:

[0045] According to an example, one or more generated beam directions are the beam directions of a first beam towards a subset of signals of a receiving device. These signals may cause PIM at the receiver. The component is configured to perform an adjustment that further includes adjusting the beamforming settings of the transmission antenna elements of the antenna array to form a second beam for another subset of signals towards another receiving device. The second beam has a direction DIR b2 different from the (multiple) generated directions. For example, the direction DIR b2 of the second beam The angular distance between each of them is higher than a predefined inter-beam distance threshold. Two signal subsets (TX1, TX2) of two beams can have different transmission frequency bands or different carriers in the same frequency band. For example, in a multi-beam system, the transmission signals TX1 and TX2 that cause PIM are scheduled onto different TX beams, beam 1 and beam 2, where beam 1 and beam 2 are scheduled in such a way that they do not look at the same PIM direction simultaneously. This can enable serving two receiving devices simultaneously. For example, these two beams can be associated with downlink signals towards the corresponding receiving devices.

[0046] According to an example, the signal further includes an uplink signal from a transmission device. The component is configured to perform an adjustment that further includes adjusting the beamforming settings of the receiving antenna elements of the antenna array for forming a beam having a direction different from that one of the identified beam directions, for example This embodiment can enable serving multiple devices simultaneously. For example, if the transmission signal TX direction points to a PIM source, the RX beam may not point in the same direction but may point towards the transmission device.

[0047] Figure 1 A schematic diagram of a communication system 100 is depicted. The communication system 100 includes a transceiver system 101. The transceiver system 101 can be a base station for a cellular communication network, but is not limited thereto. The transceiver system 101 can be, for example, a multi-carrier or multi-band system (e.g., a system operating simultaneously in at least two different transmission frequency bands or at least two carriers in the same frequency band).

[0048] The transceiver system 101 is configured to transmit a set of signals via an antenna 102. For simplicity of description, only one antenna is shown, but it is not limited thereto. Although only a set of two signals, Tx1 and Tx2, is shown for this particular example, it should be understood that the set of signals can include more than two signals.

[0049] The set of signals Tx1 and Tx2 is transmitted at frequencies F1 and F2 accordingly. However, when the set of signals Tx1 and Tx2 is transmitted along a signal path including a PIM source, intermodulation products may be generated. The source of PIM may be external to the transceiver system for air-induced PIM. In another example, the source of PIM may also include a source inside the transceiver system that induces conducted PIM, equally affecting all signals in the same frequency band. Air-induced PIM may be caused by a source of PIM at a predefined distance from the transceiver system 101. For example, in the case of a transceiver system with a MIMO installation having multiple transmitted signals, the transmitted signals at the same frequency may cause a relatively high power spectral density and thus metal objects within 10 m or more from the transceiver system 101 cannot be ignored and may cause uplink (UL) insensitivity and throughput loss.

[0050] In Figure 1 In the example shown, the set of signals Tx1 and Tx2 impinges on the source of PIM 106. The source of PIM 106 may be, for example, a metal component including ferromagnetic material. Due to the non-linear response of the source of PIM 106, IM products 107 of the set of signals Tx1 and Tx2 are generated.

[0051] The set of signals Tx1 and Tx2 may generate, for example, third-order IM products at frequencies 2F1 - F2 and 2F2 - F1, fifth-order IM products at frequencies 3F1 - 2F2 and 3F2 - 2F1, and other products. This provides the relationship between the signal frequencies (e.g., F1 and F2), and the frequencies of the IM products generated from those frequencies. Figure 1 The IM products 107 of the set of signals Tx1 and Tx2 transmitted from the source of PIM 106 are shown. The transmission of the IM products 107 may be performed at the corresponding frequencies of the IM products 107.

[0052] The IM products 107 at least partially fall within the receiving channel at frequency F3 and appear as interference to the received signal Rx transmitted at radio frequency from, for example, a user equipment 109 communicating with the transceiver system 101.

[0053] Figure 2FIG. depicting a communication system 200 according to an example of the present subject matter. The communication system 200 can be, for example, a MIMO radio system. The communication system 200 includes a transceiver system 201. The transceiver system 201 includes a plurality of transmitters 203A - 203N and receivers 210 coupled to an antenna array 215 or an antenna having a plurality of antenna elements. The antenna array 215 includes receive antenna elements and transmit antenna elements. For example, each subset of the transmitters 203A - 203N can be coupled to a corresponding antenna element 215. Each subset of the transmitters can be configured to transmit data in a corresponding transmission frequency band (referred to as a TX band). The TX band can include, for example, Long Term Evolution (LTE) bands 14, 17, and 29. By isolating each data stream of the transmitters 203A - 203N, quality issues can be mitigated. The transmitters 203A - 203N and the receivers 210 can be coupled to the antenna array 215 via a duplexer 214. Signals captured by the receive antenna elements of the antenna array 215 can be received at the receivers 210 of the transceiver system 201.

[0054] Figure 2 Only one transceiver system is shown, but it is not limited thereto. For example, the communication system 200 can include multiple transceiver systems, such as the transceiver system 201.

[0055] Each of the transmitters 203A - 203N includes a digital - to - analog (D / A) converter 204A - 204N and a power amplifier (PA) 205A - 205N connected as shown. Each of the transmitters 203A - 203N operates to process a corresponding digital input signal Tx1 - Txn (which can be, for example, a digital baseband signal) to output a radio - frequency transmission signal. The processing of the digital input signal can include, for example, crest factor reduction (CFR) and digital pre - distortion processing. The radio - frequency transmission signal of each of the transmitters 203A - 203N reaches the corresponding transmit antenna element of the antenna array 215 through the duplexer 214, such that the radio - frequency transmission signal is transmitted by the transceiver system 201.

[0056] In Figure 2 the example of, a source of PIM 206 that generates air - induced PIM is depicted. The radio - frequency transmission signal passes through or affects the source of PIM 206 after output. Due to the non - linearity of the source of PIM, PIM may be introduced into the radio - frequency received signal received at the receivers 210 via the antenna array 215 (the PIM signal falls within the receive band of the receivers 210, for example, as Figure 1 shown). PIM can include IM products of the radio - frequency transmission signal. IM products include third - order IM products, fifth - order IM products, etc.

[0057] For example, the receiver 210 may include receiver components such as low-noise amplifiers (LNAs) 217A - 217M, filters, down-conversion circuitry, analog-to-digital converters 216A - 216M, etc. The receiver 210 operates to process (e.g., amplify, filter, down-convert, and analog-to-digital convert) radio frequency receive signals received via the duplexer 214 from the receive antenna elements of the antenna array 215 to output a digital output signal 220, referred to herein as the receiver output signal 220.

[0058] PIM distortion in the receiver output signal 220 output by the receiver 210 is caused by IM products of radio frequency transmit signals generated by the source of PIM that fall within the passband of the receiver 210.

[0059] The PIM distortion of the digital signal, referred to herein as the PIM signal or interference signal, can be measured or determined. The PIM signal is determined by the device 230. The device 230 may be part of the transceiver system 201. For example, the device 230 may be integrated in the antenna system of the transceiver system 201. Being part of the transceiver system 201 may enable the device to be individually adjusted for different transceiver systems. In another example, the device 230 may not be part of the transceiver system 201. This may enable centralized control and thus consistent control of the PIM effects between different transceiver systems.

[0060] The device 230 is configured to receive the receiver output signal 220. The device 230 is configured to receive radio frequency transmit signals transmitted over the air by the transmitters of the transmitters 203A, 203N. The device 230 is configured to determine the PIM signal and its level. In the case of multiple transceiver systems, the device 230 may be configured to determine the PIM signal for the receiver of each of the transceiver systems.

[0061] Device 230 may control antenna array 215 to generate a directional beam 240 that is directed towards beam direction 242 for communication via a wireless access link, for example. Beamforming may be performed using beamforming settings associated with each beam direction. The beamforming settings may include, for example, weights of amplitudes and / or phases associated with the antenna elements of antenna array 215. Device 230 may be configured to control antenna array 215 to steer the directional beam 240 in beam direction 242, for example, between 0 and 90 degrees. Device 230 may control antenna array 215 to steer the directional beam 240 by configuring the beamforming settings of antenna array 215. For example, device 230 may configure the beamforming settings of antenna array 215 by adjusting the phase shifts to be applied to the antenna elements of antenna array 215. Adjusting the phase shifts may enable determination and / or control of the width, gain, and / or direction of directional beam 240. For example, the adjustment of the phase may be performed in the digital domain or via additional RF phase shifters.

[0062] Device 230 may re - adjust the beamforming settings of antenna array 215 according to the present subject matter, for example, based on the PIM level. For example, device 230 may control the steering of directional beam 240 to reach a given direction, such as the direction of a receiving device. Transceiver system 201 may be configured to track the movement of a mobile device and steer directional beam 240 based on the movement. Device 230 may be configured to control and steer directional beam 240 in azimuth and / or elevation angles relative to antenna array 215. For example, if the mobile device moves clockwise relative to transceiver system 201, the azimuth angle of directional beam 240 may be steered. For example, if the mobile device moves away from or towards transceiver system 201, the elevation angle of directional beam 240 may be steered. In another example, if the mobile device moves up or down and moves clockwise relative to transceiver system 201, both the elevation angle and the azimuth angle of directional beam 240 may be steered.

[0063] Figure 3 is a flow chart of a method for processing inter - modulation products in a communication system, such as 200. For illustrative purposes, the method may be implemented in the system shown above Figures 1 to 2 but is not limited to that implementation.

[0064] For each beam direction in the set of beam directions of the antenna array, such as 215 of communication system 200, the level of the PIM signal at the receiver 210 of communication system 200 can be determined in step 301. The PIM signal can be caused by a set of signals transmitted by the transmit antenna elements of the antenna array 215 in the beam direction. The device 230 can determine the PIM level of the set of beam directions, for example, by determining the PIM signal associated with the beam directions of the set of beam directions. In another example, the device 203 can be configured to access a database that stores information about the PIM levels at the receiver 210 for different beam directions. The PIM level can be determined by the device 230 using the database.

[0065] The beam direction can be defined by the azimuth angle and / or elevation angle relative to the antenna array 215. The set of beam directions can be the directions that can define the beamforming settings or the directions where the beamforming settings are available in the communication system. For example, for each pair of individual azimuth angle and elevation angle (φ, θ), the received power in the associated RX channel of the receiver 210 is measured and compared with the noise / interference reference level to determine the PIM level.

[0066] For example, step 301 can cause each direction in the set of beam directions to be associated with a corresponding value of the PIM level. The result can be provided in the form of a distribution map or a table. In another example, the result can be presented in a heat map, where the color coding indicates the directions with PIM noise problems or PIM levels higher than a predefined threshold. For example, as Figure 4 shown, the beam 410 destined for the first UE 401 may hit the PIM obstacle 406, thus inducing a PIM signal in the receiver 210 of the communication system. However, the beam 411 can reach the second UE 402 directly without hitting the PIM obstacle 406. Therefore, the PIM level in the beam direction of the second UE 402 may be less than the PIM level in the beam direction of the first UE 401. Therefore, the two UE directions may have different signal reception qualities, for example, when the beam direction is switched from the first UE to the second UE.

[0067] The determination of the PIM level can be performed after the radio / system deployment of the communication system. For example, step 301 can be performed in an offline calibration step. For example, the term "offline" may mean that there is no active service and no elevated RX noise level due to radiation.

[0068] The beam directions with PIM levels higher than a predefined threshold in the set of beam directions can be identified in step 303. In one example, the number of identified beam directions may not exceed a predefined maximum number, because processing a large number of PIM sources may consume resources. This is because, for example, additional nulling / notching may require additional complexity within the beamforming system. To this end, the PIM levels of the identified beam directions can be sorted, and the top N highest PIM levels can be selected. The number N can be user-defined, for example, N = 2. The beam directions associated with the selected PIM levels among the identified beam directions can be selected and provided.

[0069] The beamforming of the signal can be adjusted in step 305 for at least some of the identified beam directions to reduce the PIM level at the receiver 210. For example, the signal can include an uplink signal from a transmitting device and / or a downlink signal to a receiving device, where the beamforming is adjusted by comparing the direction of the transmitting device and / or the receiving device with at least some of the identified beam directions.

[0070] In a first example, and in the case where the direction of the receiving device does not coincide with any of the directions of at least some of the identified beam directions, the nulling or notching of the beam can be performed towards a given identified direction of at least some of the identified directions. The given identified direction can be the direction closest to the receiving device. The nulling can be performed at the receiver and / or transmitter by correspondingly adjusting the beamforming settings of the receiving antenna elements and / or the transmitting antenna elements of the antenna array. In this first example, at least some of the identified beam directions can be the given identified direction.

[0071] In a second example, in the case where the direction of the receiving device coincides with a specific direction of at least some of the identified beam directions, the nulling or notching of the beam towards the specific direction of at least some of the identified directions can be performed. The nulling can be performed at the receiver and / or transmitter by correspondingly adjusting the beamforming settings of the receiving antenna elements and / or the transmitting antenna elements of the antenna array. In this second example, at least some of the identified beam directions can be the specific direction.

[0072] In another example, at least some of the identified beam directions can be selected beam directions. In the case where the direction of the receiving device does not coincide with any of the directions of at least some of the identified beam directions, the nulling or notching of the beam towards each of the directions of at least some of the identified directions can be performed.

[0073] In another example, at least a portion of the identified beam directions includes all of the identified beam directions of step 303. In the case where the direction of the receiving device does not coincide with any of the directions of at least a portion of the identified beam directions, nulling or notching of the beams in each direction of at least a portion of the identified directions can be performed.

[0074] Beamforming can be adjusted at the antenna array. For example, beamforming can be adjusted as described with reference to Figure 6A and 6B described.

[0075] Figure 5 is a flowchart of a method for determining the PIM level in a communication system such as 200. For illustrative purposes, the method can be implemented in the system shown above Figures 1 to 2 but is not limited to that implementation.

[0076] For example, the method can be performed using device 230. In step 501, a first noise power level can be measured at receiver 210 while the signal transmission of the communication system is turned off. In step 503, the PIM causing the signal can be transmitted by the transmitter in a specific direction. After step 503, a second power level can be measured at the receiver in step 505. The first power level and the second power level can be compared, and based on the difference between the first power level and the second power level, the PIM level can be determined for the specific direction in step 507. Steps 501 to 507 can be repeated for each direction in the set of beam directions.

[0077] Figure 6A is a flowchart of a method for configuring the beamforming of an antenna array (such as 215) according to an example of the present subject matter. Figure 6A The method of Figure 6B can be performed for a given beam direction (φ0, θ0) as shown in Figure 6B for example, the given beam direction can be the current direction of the receiving device 614 that is expected to receive signals from the antenna array 615.

[0078] The given beam direction (φ0, θ0) can be compared with each of the identified beam directions of step 303. For example, the angular distance between the pair of angles (φ0, θ0) and each pair of angles of the identified beam directions can be calculated. If the distance is less than the coincidence threshold, this indicates that the receiving device 614 coincides with the PIM source. In other words, this indicates that the given beam direction (φ0, θ0) coincides with one of the identified beam directions, for example (φ1, θ1).

[0079] In the case where a given beam direction (φ0, θ0) coincides with an identified beam direction (e.g., (φ1, θ1)) in (query step 601), two beam directions around the identified beam direction (φ1, θ1) can be generated in step 602. For example, as Figure 6B shown, two beam directions (φ2, θ2) and (φ3, θ3) can be obtained by offsetting at least one of the two angles (φ1, θ1) of the identified beam direction. For example, φ2 = φ1 + d12, θ2 = θ1 + d22, φ3 = φ1 - d12, and θ3 = θ1 - d22. For example, d12 and d22 can be user-defined offsets. The offset can be performed such that the distance between each of the generated beam directions (φ2, θ2) and (φ3, θ3) and the identified beam direction (φ1, θ1) (e.g., |(φ2, θ2) - (φ1, θ1)| and |(φ3, θ3) - (φ1, θ1)|) is greater than the coincidence threshold and still close to the direction (φ0, θ0). That is, (φ2, θ2) and (φ3, θ3) are the directions closest to (φ0, θ0) that do not coincide with (φ1, θ1).

[0080] The beamforming settings of the transmission antenna elements of the antenna array 215 can be adjusted in step 603 such that the antenna array can direct the beam destined for the given beam direction (φ0, θ0) to the two determined beam directions (φ2, θ2) and (φ3, θ3). For example, the device can control the transmission antenna elements of the antenna array 615 to perform beamforming in the two determined beam directions (φ2, θ2) and (φ3, θ3). This is shown, for example, in Figure 6B where two beams are directed to the beam directions (φ2, θ2) and (φ3, θ3).

[0081] For example, the device can provide a data structure, such as a table, that maps each beam direction in the identified beam directions (e.g., (φ1, θ1)) to a corresponding pair of determined directions, such as (φ2, θ2) and (φ3, θ3). When it is determined that the receiving device 614 is in the current direction (φ0, θ0) and (φ0, θ0) coincides with the identified beam direction (φ1, θ1), the device can use the data structure to determine that the direction (φ1, θ1) is associated with a pair of directions (φ2, θ2) and (φ3, θ3), and thus can use the pre-computed beamforming settings associated with the directions (φ2, θ2) and (φ3, θ3) to control the antenna array.

[0082] Figure 7A is a flowchart of a method for configuring beamforming of an antenna array according to an example of the present subject matter. It can be performed for a given beam direction (φ0, θ0) as shown in Figure 7B and Figure 7AThe method, for example, the given beam direction can be the current direction of the receiving device 714 expected to receive signals from the antenna array 715. Figure 7B

[0083] The given beam direction (φ0, θ0) can be compared with each of the identified beam directions in step 303. For example, the distance between the angle pair (φ0, θ0) and each pair of angles of the identified beam directions can be calculated. If the distance is less than the coincidence threshold, this indicates that the receiving device 714 coincides with the PIM source. In other words, this indicates that the given beam direction (φ0, θ0) coincides with one of the identified beam directions, such as (φ1, θ1).

[0084] In the case where (query step 701) the given beam direction (φ0, θ0) coincides with one of the identified beam directions (such as (φ1, θ1)), the beamforming settings of the transmission antenna elements of the antenna array 715 can be adjusted in step 703 so that the beam (as Figure 7B shown) notches towards the identified beam direction (φ1, θ1).

[0085] Figure 8 is a block diagram showing an example of avoiding PIM via scheduling of beams according to multi-user beamforming techniques. In this example, the signals include uplink signals TX1 and TX2, and the received signals include downlink RX signals. The beamforming settings of both the receiving antenna elements and the transmission antenna elements are adjusted so that separate beams simultaneously serve user equipment UE1 and UE2. Since the direction of the TX beam points to the PIM obstacle, scheduling can be performed so that the RX beam points to different directions, so that different UEs can be served simultaneously. As Figure 8 shown, the TX beam with TX1 and TX2 signals serves user equipment UE1, while the RX beam serves user equipment UE2 simultaneously. The beamforming settings of the transmission antenna elements can be adjusted according to this subject to avoid PIM obstacles, for example, by notching or generating one or more offset beams.

[0086] Figure 9 is a block diagram showing an example of avoiding PIM via scheduling multi-user beamforming. In Figure 9 the example, the downlink signals TX1 and TX2 causing PIM can be scheduled according to the multi-beam method so that each set of the downlink signals TX1 and TX2 can be transmitted to the corresponding user equipment UE1 and UE2 in the corresponding beams TX beam 1 and TX beam 2. In this case, the beams TX beam 1 and TX beam 2 can be formed so that they do not look at the same PIM direction simultaneously, as Figure 9As shown. In addition, the receiver can be configured to receive two beams, RX beam 1 and RX beam 2, from user equipment UE1 and UE2 accordingly.

[0087] In Figure 10 a circuit block diagram showing the configuration of device 1070 is presented, and device 1070 is configured to implement at least a part of the present subject matter. It should be noted that Figure 10 device 1070 shown in

[0088] may include several additional elements or functions other than those described hereinbelow, and for simplicity, they are omitted herein as they are not necessary for understanding. In addition, the device may also be another device with similar functions, such as a chipset, a chip, a module, etc., which may also be part of the device or attached to the device as a separate element, etc. Device 1070 may include a processing function or a processor 1071, such as a CPU, etc., which executes instructions given by a program related to a flow control mechanism, etc. Processor 1071 may include one or more processing parts dedicated to specific processing as described below, or the processing may run in a single processor. For example, the part for performing such specific processing may also be provided as a discrete element or in one or more additional processors or processing parts, such as in one physical processor (such as a CPU) or several physical entities. Reference symbol 1072 represents a transceiver or an input / output (I / O) unit (interface) connected to processor 1071. I / O unit 1072 can be used to communicate with one or more other network elements, entities, terminals, etc. I / O unit 1072 may be a combined unit including communication devices facing several network elements, or may include a distributed structure having multiple different interfaces for different network elements. Reference symbol 1073 represents a memory, which can be used, for example, to store data and programs to be executed by processor 1071, and / or as a working storage of processor 1071. Processor 1071 is configured to perform processing related to the above-mentioned subject matter. In particular, device 1070 may be configured to perform at least a part of the methods described in conjunction with Figure 3 , 5 , 6A and 7A.

[0089] Processor 1071 is configured to determine the level of PIM signals at the receiver of a communication system, identify beam directions in a set of beam directions where the determined PIM level is higher than a predefined threshold, and adjust the beamforming of signals on at least a part of the identified beam directions to mitigate the PIM level at the receiver.

Claims

1. An apparatus for a communication system, the apparatus comprising components configured for: For each beam direction in a set of beam directions of an antenna array of the communication system, determining a level of a passive intermodulation (PIM) signal at a receiver of the communication system, the PIM signal being caused by a set of signals transmitted by the antenna array in the beam direction; Identifying one or more beam directions in the set of beam directions for which the determined PIM level is higher than a predefined threshold; Adjusting beamforming of signals on at least some of the identified beam directions to mitigate the PIM level at the receiver, wherein: The signals include downlink signals to a receiving device having a direction coinciding with one of the identified beam directions, and the adjustment includes: generating one or more beam directions that are the directions closest to the direction of the receiving device and do not coincide with the one of the identified beam directions.

2. The apparatus according to claim 1, wherein the signals include downlink signals to a receiving device having a direction coinciding with one of the identified beam directions, and the components are configured to perform the adjustment, and the adjustment further includes: Adjusting beamforming settings of transmission antenna elements of the antenna array according to the generated directions, where at least some of the identified beam directions are the one of the identified beam directions.

3. The apparatus according to claim 1, wherein the signals include downlink signals to a receiving device, and the components are configured to perform the adjustment, and the adjustment includes: Adjusting beamforming settings of transmission antenna elements of the antenna array to notch the beam in each direction of at least some of the identified beam directions.

4. The apparatus according to claim 3, wherein at least some of the identified beam directions coincide with the direction of the receiving device.

5. The apparatus according to claim 3, wherein at least some of the identified beam directions do not coincide with the direction of the receiving device and are directions of one of: the direction closest to the direction of the receiving device, or the direction having the highest determined PIM level.

6. The apparatus according to claim 1, wherein the signals include uplink signals from a transmission device having a direction not coinciding with at least some of the identified beam directions, and the components are configured to perform the adjustment, and the adjustment includes: Adjusting beamforming settings of receiving antenna elements of the antenna array to notch the beam in each direction of at least some of the identified beam directions.

7. The apparatus according to claim 6, wherein at least part of the beam directions of the identified beam directions are directions that do not coincide with the direction of the transmission device and are one of the following: the direction closest to the direction of the transmission device or the direction having the highest determined PIM level.

8. The apparatus according to claim 6, wherein the signal further includes a downlink signal to the transmission device, and the component is configured to perform the adjustment, the adjustment comprises: Adjusting the beamforming settings of the transmission antenna elements of the antenna array to notch the beam in each direction of at least part of the beam directions of the identified beam directions.

9. The apparatus according to claim 2, wherein one or more of the generated beam directions are the beam directions of a first beam that is a subset of the signals to the receiving device, and the component is configured to perform the adjustment, the adjustment further comprises: Adjusting the beamforming settings of the transmission antenna elements to form a second beam for another subset of the signals to another receiving device, the second beam having a direction different from the generated direction.

10. The apparatus according to claim 2, wherein the signal further includes an uplink signal from the transmission device, and the component is configured to perform the adjustment, the adjustment further comprises: Adjusting the beamforming settings of the receiving antenna elements of the antenna array to form a beam having a direction of the transmission device different from one of the identified beam directions.

11. The apparatus according to claim 3, wherein the signal further includes an uplink signal from the transmission device, and the component is configured to perform the adjustment, the adjustment further comprises: Adjusting the beamforming settings of the receiving antenna elements of the antenna array to form a beam having a direction of the transmission device different from at least part of the beam directions of the identified beam directions.

12. The apparatus according to claim 1, wherein the component is configured to select at least part of the beam directions of the identified beam directions based on the PIM level.

13. The apparatus according to claim 1, for each of the identified beam directions of at least part of the beam directions of the identified beam directions, the component is configured to perform the adjustment, the adjustment comprises: Adjusting the weights of the amplitude and / or phase associated with the identified beam direction.

14. The apparatus according to any one of the preceding claims, wherein the component includes at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured to cause the execution of the apparatus together with the at least one processor.

15. A communication system, comprising an antenna array, a receiver, a transmitter, and an apparatus, the apparatus being configured to: For each beam direction in the set of beam directions of the antenna array, determine the level of passive intermodulation (PIM) signals at the receiver, where the PIM signals are caused by the set of signals transmitted by the antenna array in the beam direction; Identify the beam directions in the set of beam directions where the PIM level is higher than a predefined threshold; Adjust the beamforming of the signals on at least some of the identified beam directions to reduce the PIM level at the receiver, where: The signals include downlink signals to a receiving device having a direction coinciding with one of the identified beam directions, and the adjustment includes: generating one or more beam directions that are the directions closest to the direction of the receiving device and do not coincide with the one of the identified beam directions.

16. The communication system according to claim 15, wherein the antenna array includes a number of antenna elements higher than a predefined minimum number of antenna elements.

17. A method for a communication system, comprising: For each beam direction in the set of beam directions of the antenna array of the communication system, determine the level of passive intermodulation (PIM) signals at the receiver of the communication system, where the PIM signals are caused by the set of signals transmitted by the antenna array in the beam direction; Identify the beam directions in the set of beam directions where the PIM level is higher than a predefined threshold; Adjust the beamforming of the signals on at least some of the identified beam directions to reduce the PIM level at the receiver, where: The signals include downlink signals to a receiving device having a direction coinciding with one of the identified beam directions, and the adjustment includes: generating one or more beam directions that are the directions closest to the direction of the receiving device and do not coincide with the one of the identified beam directions.

18. The method according to claim 17, wherein the determining of the PIM level and the identifying step are performed in an offline calibration step, and the adjustment step is performed during real-time operation of the communication system.

19. A computer-readable storage medium, including program instructions stored thereon, the program instructions for causing a device to at least perform the following operations: For each beam direction in the set of beam directions of the antenna array of a communication system, determine the level of passive intermodulation (PIM) signals at the receiver of the communication system, where the PIM signals are caused by the set of signals transmitted by the antenna array in the beam direction; Identify the beam directions in the set of beam directions where the PIM level is higher than a predefined threshold; Adjust the beamforming of the signals on at least some of the identified beam directions to reduce the PIM level at the receiver, where: The signal includes a downlink signal to a receiving device having a direction coinciding with one of the identified beam directions, and the adjustment includes: generating one or more beam directions that are the directions closest to the direction of the receiving device and do not coincide with the one of the identified beam directions.

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