WO2018228697A1

WO2018228697A1 - Beam selection

Info

Publication number: WO2018228697A1
Application number: PCT/EP2017/064697
Authority: WO
Inventors: Joakim Axmon; Thomas Chapman; Torbjörn ELFSTRÖM; Esther SIENKIEWICZ
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2017-06-15
Filing date: 2017-06-15
Publication date: 2018-12-20
Anticipated expiration: 2019-12-15

Abstract

A beam selection method is disclosed of a network node adapted to use one or more of a plurality of transmission beams to accommodate communication with a plurality of wireless communication devices. Each transmission beam comprises a main lobe and one or more of the transmission beams further comprises one or more auxiliary lobes. The plurality of wireless communication devices comprises a first wireless communication device and one or more second wireless communication devices. The method comprises determining (110) an indication of a position of the first wireless communication device and selecting (131), from the plurality of transmission beams, one or more candidate beams for use in communication with the first wireless communication device based on the determined indication. The method also comprises, for beams used to communicate with the one or more second wireless communication devices, identifying (132) auxiliary lobes causing interference to the main lobe of any of the one or more candidate beams. The method comprises selecting (130, 137) a beam to be used in communication with the first wireless communication device based on the one or more candidate beams and the identified auxiliary lobes. Corresponding arrangement, network node and computer program product are also disclosed.

Description

BEAM SELECTION

TECHNICAL FIELD

The present disclosure relates generally to the field of wireless communication. More particularly, it relates to selection of beams in a network node adapted to use one or more of a plurality of transmission beams to accommodate communication with a plurality of wireless communication devices.

BACKGROUND

Multi-antenna techniques, such as Multi User Multiple Input Multiple Output (MU-MIMO), are well known and used in many wireless communication systems. In multi-path environments such multiple access schemes provide approaches for performance enhancing scheduling strategies. Typically, the channel response is measured by the wireless communication device and the scheduler of the network node utilizes measurement information reported by the wireless communication device to intelligently assign resources to users. Active (or Adaptive) Antenna Systems (AAS) is a generic term that is often used to describe network nodes (e.g. radio base stations) that incorporate a large number of separate transmitters that can be used for various MIMO techniques and/or beamforming, and which integrate active transmitter components and radiating elements. As wireless communication evolves to be able to reside at high frequencies and/or large bandwidths (compared to conventional wireless communication systems) larger antenna arrays and AAS will typically be beneficial, e.g. to achieve desired link budgets.

As frequency increases, propagation losses will also increase. Since the transmit power of both network nodes and wireless communication devices is typically limited by physical constraints as well as by considerations such as Electro-Magnetic Fields (EMF) for network nodes and Specific Absorption Rate (SAR) for wireless communication devices, it is typically not possible to compensate the increased penetration losses and provide sufficient signal-to-interference- and-noise ratio (SINR) when wide bandwidths are used simply by increasing the transmit power. I n order to achieve link budgets required for high data rates, beamforming will typically be seen as a solution.

Advantages of using integrated AAS implementations also include (in addition to accommodation of higher frequency and/or larger bandwidth) that the integrated design reduces loss factors and can reduce overall power consumption, and that there is some potential for site simplification. Typically, AAS network nodes may offer beamforming functionality: cell-specific beamforming (such as cell splitting, cell shaping with variable down tilt) and user specific beamforming.

Reference signals (e.g. Channel State I nformation Reference Signals, CSI-RS, or DeModulation Reference Signals, DM-RS) may typically be used for measurements (e.g. channel estimation) by the wireless communication device to determine a metric (e.g. Channel State I nformation, CSI, or Channel Quality I ndicator, CQJ) for report to the network. Such reference signaling, as well as corresponding measurements and reporting, is well known in the art, both for non- beamforming systems and beamforming systems, and will not be elaborated on further herein.

With AAS and FD-M I MO (Full Dimension M I MO) there is a dramatic increase in complexity and beamforming weight options as the number of transceivers, rank and hybrid beamforming options increase. With the huge amount of options regarding which beamforming set-up to use, the measurement task for the wireless communication device becomes extremely complex which may entail extreme time consumption, extreme hardware requirements and/or extreme power consumption. An increase of latency, until suitable beams have been identified, may have an adverse impact on the system performance, which may be measured in power consumption, system throughput and/or user experience.

Therefore, there is a need for a more efficient approach to beam selection. SUMMARY

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It is an object of some embodiments to solve or mitigate, alleviate, or eliminate at least some of the above or other disadvantages.

According to a first aspect, this is achieved by a beam selection method of a network node adapted to use one or more of a plurality of transmission beams to accommodate communication with a plurality of wireless communication devices. Each transmission beam comprises a main lobe and one or more of the transmission beams further comprises one or more auxiliary lobes. The plurality of wireless communication devices comprises a first wireless communication device and one or more second wireless communication devices.

The method comprises determining an indication of a position of the first wireless communication device and selecting, from the plurality of transmission beams, one or more candidate beams for use in communication with the first wireless communication device based on the determined indication.

The method also comprises, for beams used to communicate with the one or more second wireless communication devices, identifying auxiliary lobes causing interference to the main lobe of any of the one or more candidate beams.

The method comprises selecting a beam to be used in communication with the first wireless communication device based on the one or more candidate beams and the identified auxiliary lobes.

In some embodiments, selecting the one or more candidate beams may comprise acquiring beam coverage statistics in relation to the position of the first wireless communication device based on the indication, and selecting the one or more candidate beams based on the acquired beam coverage statistics. The candidate beams may be selected as beams for which the acquired beam coverage statistics indicate a coverage value above a coverage threshold.

The acquired beam coverage statistics may be based on previously performed coverage statistics measurements in relation to the plurality of transmission beams according to some embodiments. The method may, in some embodiments, further comprise causing the first wireless communication device to perform coverage statistics measurements in relation to one or more of the plurality of transmission beams, receiving a coverage statistics measurement report from the first wireless communication device, wherein the coverage statistics measurement report is indicative of a result of the performed coverage statistics measurements, and updating the beam coverage statistics in relation to the position of the first wireless communication device based on the result of the performed coverage statistics measurements.

In some embodiments, selecting the beam to be used in communication with the first wireless communication device may comprise causing the first wireless communication device to perform candidate coverage measurements in relation to the one or more candidate beams, receiving a candidate measurement report from the first wireless communication device, wherein the candidate measurement report is indicative of a result of the performed candidate coverage measurements, and selecting the beam to be used in communication with the first wireless communication device based on the result of the performed candidate coverage measurements and the identified auxiliary lobes.

According to some embodiments, selecting the beam to be used in communication with the first wireless communication device may comprise determining, for a prospect beam of the one or more candidate beams, whether the interference of the identified auxiliary lobes exceeds an interference threshold, and when the interference of the identified auxiliary lobes does not exceed the interference threshold, selecting the prospect beam as the beam to be used in communication with the first wireless communication device.

The method may further comprise, when the interference of the identified auxiliary lobes exceeds the interference threshold, performing one or more of: - selecting the prospect beam and reducing the interference caused by the identified auxiliary lobes by adjusting beam-forming weights of one or more of the beams used to communicate with the one or more second wireless communication devices, selecting the prospect beam and reducing the interference caused by the identified auxiliary lobes by reducing a transmission power of one or more of the beams used to communicate with the one or more second wireless communication devices, selecting the prospect beam and adjusting its beam-forming weights, and selecting a beam of the one or more candidate beams other than the prospect beam.

A second aspect is a computer program product comprising a computer readable medium, having thereon a computer program comprising program instructions. The computer program is loadable into a data processing unit and configured to cause execution of the method according to the first aspect when the computer program is run by the data processing unit.

A third aspect is a beam selection arrangement for a network node adapted to use one or more of a plurality of transmission beams to accommodate communication with a plurality of wireless communication devices, wherein each transmission beam comprises a main lobe and one or more of the transmission beams further comprises one or more auxiliary lobes, and wherein the plurality of wireless communication devices comprises a first wireless communication device and one or more second wireless communication devices.

The arrangement comprising a controller configured to cause determination of an indication of a position of the first wireless communication device, selection (from the plurality of transmission beams) of one or more candidate beams for use in communication with the first wireless communication device based on the determined indication, identification of auxiliary lobes (for beams used to communicate with the one or more second wireless communication devices) causing interference to the main lobe of any of the one or more candidate beams, and selection of a beam to be used in communication with the first wireless communication device based on the one or more candidate beams and the identified auxiliary lobes.

A fourth aspect is a network node comprising the arrangement of the third aspect.

In some embodiments, any of the above aspects may additionally have features identical with or corresponding to any of the various features as explained above for any of the other aspects. An advantage of some embodiments is that an efficient approach to beam selection is provided. Typically, the wireless communication device can reduce its measurements efforts when some embodiments are applied. Other possible effects include reduced latency of beam selection. Another advantage of some embodiments is that, since beams can be excluded from the candidate set that will be adversely affected by auxiliary lobes of other beams currently in use, no measurement efforts are wasted on those beams.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features and advantages will appear from the following detailed description of embodiments, with reference being made to the accompanying drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the example embodiments.

Figure 1 is a flowchart illustrating example method steps according to some embodiments; Figure 2 is a flowchart illustrating example method steps according to some embodiments;

Figure 3 is a flowchart illustrating example method steps according to some embodiments;

Figure 4 is a schematic drawing illustrating a top view (a) and a side view (b) of a network node with example beam directions according to some embodiments;

Figure 5 is a schematic drawing illustrating beam coverage statistics according to some embodiments;

Figure 6 is a schematic drawing illustrating top views (a) and (b) of beam radiation patterns according to some embodiments;

Figure 7 is a schematic block diagram illustrating an example arrangement according to some embodiments; Figure 8 is a schematic block diagram illustrating an example arrangement according to some embodiments; and

Figure 9 is a schematic drawing illustrating an example computer readable medium according to some embodiments.

DETAILED DESCRIPTION It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Embodiments of the present disclosure will be described and exemplified more fully hereinafter with reference to the accompanying drawings. The solutions disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the embodiments set forth herein.

A trend towards antennas with an increasing number of antenna elements may be seen in the field of wireless communication. The increased number of antenna elements caters for an increased number of simultaneous beams being available for serving wireless communication devices (WCD:s) within the coverage area. An increased number of beams leads to increased measurement complexity and/or increased latency for identifying suitable beams or combinations thereof with which to serve the WCD:s. Increased complexity also implies increased bill of material and/or increased power consumption. In order to capitalize on the investment in larger antenna arrays, an approach for reducing the measurement complexity as well as the latency would be beneficial, such that the system can be operated in as close to optimum state as possible with respect to multi-user reuse of physical resources.

A subset of a pre-coding code book is available as an option to achieve reduced latency (time to find an appropriate pre-coding). According to some embodiments presented herein knowledge of the beam radiation patterns (fingerprinting) is used, additionally or alternatively, to reduce the latency. The already known approach of using pre-coding matrix indicator (PMI) subsets may, thus, be combined with some embodiments presented herein to enable configuring. In the following, embodiments will be described where beam selection is made efficient by use of knowledge regarding auxiliary lobes of beams used by the network node. Such knowledge may be pre-calculated by the network node, e.g. based on beam-forming weights of each beam alternative. This knowledge may be beneficial to determine to what extent the main lobe of a particular candidate beam for communication with a wireless communication device experience interference caused by the auxiliary lobes. Alternatively or additionally to the pre-calculation of the auxiliary lobes, statistics from previous measurements performed by wireless communication devices may be kept by the network node (or another node associated with the network node). Such statistics may include interference metric values for different combinations of beam. Hence, the statistics may be informative regarding the extent of interference that can be expected for the main lobe of a particular candidate beam when certain other beams are simultaneously active. If it is determined (based on pre-calculation and/or statistics) that the expected interference from auxiliary lobes is severe for a candidate beam, the wireless communication device is typically not instructed to perform measurements for that candidate beam according to some embodiments, since that would be a waste of time and resources.

Figure 1 illustrates an example method 100 according to some embodiments. The example method is a beam selection method of a network node, and the network node is adapted to use one or more of a plurality of transmission beams to accommodate communication with a plurality of wireless communication devices comprising a first wireless communication device (for which a beam is to be selected by the method) and one or more second wireless communication devices. Each transmission beam of the plurality comprises a main lobe, and one or more of the transmission beams further comprises one or more auxiliary lobes. Auxiliary lobes may, for example, be side lobes and/or grating lobes. Generally, an auxiliary lobe of a beam may refer to any non-main lobe potentially causing interference to a main lobe of another beam.

The example method 100 starts in step 110, where an indication of a position of the first wireless communication device (WCD) is determined. The position may, for example, be a geographical position or another position related to the location of the first WCD. The indication may be determined by application of any suitable approach such as, for example, by using a global navigation satellite system (GNSS). In some embodiments, beam coverage statistics is used for the selection. Beam coverage statistics may include statistics regarding how strong a beam signal is in relation to a particular location and/or how strong interference is experienced in relation to a particular location (associated with the scenario of other beams currently used). Metrics (coverage values) comprised in the statistics may include, for example, signal strength and/or signal-to- interference ratio (SIR). In some embodiments, the beam coverage statistics is binary in relation to each particular location (indicating if a signal strength or SIR is below some threshold value or not). In optional step 120, the beam coverage statistics is acquired in relation to the position of the first wireless communication device based on the indication determined in step 110.

The example method 100 proceeds to step 130 where a beam is selected to be used in communication with the first wireless communication device. The selection is based on the determined indication as illustrated by sub-steps 131, 132 and 137.

In sub-step 131, one or more candidate beams are selected from the plurality of transmission beams based on the determined indication (and on the acquired statistics if applicable).

Typically, but not necessarily, the candidate beams may be beams with their main lobes directed at an angle (vertically, horizontally and/or omni-directionally) which deviate less than some threshold value from a direction corresponding to the position indicated by the determined indication. Alternatively or additionally, the candidate beams may be selected as beams having more than a certain level of its overall power directed towards the position indicated by the determined indication.

Candidate beams may, for example, be selected as beams for which the acquired beam coverage statistics indicate a coverage value above a coverage threshold. The coverage threshold may be static or dynamic. For example, it may be set such that a certain number of candidate beams are selected.

Other selection criteria, as well as combination of the above selection criteria, are also possible as will be realized by the skilled person.

For example, among beams that would be selected as candidate beams based on the determined indication, sub-step 131 may comprise selecting the beams that have highest signal strength (or SIR) according to the beam coverage statistics, or may select only beams that have signal strength (or SIR) above some threshold value according to the beam coverage statistics.

If a single candidate beam is selected in sub-step 131, the remaining sub-steps may aim for suitably adjusting the beam-forming weights of the candidate beam for communication with the first WCD. If more than one candidate beam are selected in sub-step 131, the remaining sub-steps may aim for suitably selecting one of them for communication with the first WCD (and possibly also suitably adjusting its beam-forming weights).

In sub-step 132, auxiliary lobes are identified for beams used to communicate with the one or more second wireless communication devices and which cause interference to the main lobe of any of the one or more candidate beams. As mentioned above, such identification may be based on pre-calculated radiation patterns of each possible beam and/or on interference statistics of previously performed measurements.

Optionally, the network node may cause the first wireless communication device to perform candidate coverage measurements in relation to the one or more candidate beams as illustrated by sub-step 134 and receive a measurement report indicative of a result of the performed candidate coverage measurements from the first wireless communication device as illustrated by sub-step 135. Sub-step 134 may, for example, be accomplished by transmitting an instruction or other control signaling to the first WCD. Metrics (coverage values) acquired in the coverage measurements may include, for example, signal strength and/or SIR.

Then, sub-step 137 comprises selecting the beam to be used in communication with the first wireless communication device based on the one or more candidate beams, the identified auxiliary lobes, and (if applicable) the result of the performed candidate coverage measurements. For example, the candidate beam experiencing least interference from auxiliary lobes of beams used to communicate with the one or more second WCD:s may be selected. The interference may be as measured (e.g. in terms of SIR) and/or as pre-calculated.

In some embodiments, sub-step 137 may comprise determining, for a prospect beam of the one or more candidate beams, whether the interference of the identified auxiliary lobes exceeds an interference threshold. The interference threshold may be static or dynamic. For example, it may be based on a signal-to-interference ratio (SIR) requirement of the communication with the first WCD.

The prospect beam may be selected as the beam to be used in communication with the first wireless communication device when the interference of the identified auxiliary lobes does not exceed the interference threshold.

Even if the interference of the identified auxiliary lobes exceeds the interference threshold, the prospect beam may be selected as the beam to be used in communication with the first wireless communication device in some embodiments as exemplified below. Such a possibility may be particularly beneficial in cases when all of the candidate beams have interference from auxiliary lobes that exceeds the interference threshold.

The prospect beam may be selected when the interference of the identified auxiliary lobes exceeds the interference threshold if beam-forming weights of one or more of the beams used to communicate with the one or more second wireless communication devices are adjusted to reduce the interference caused by the identified auxiliary lobes.

The prospect beam may be selected when the interference of the identified auxiliary lobes exceeds the interference threshold if a transmission power of one or more of the beams used to communicate with the one or more second wireless communication devices is reduced to reduce the interference caused by the identified auxiliary lobes. A variant of this comprises completely stop using one or more of the beams used to communicate with the one or more second wireless communication devices.

The prospect beam may be selected when the interference of the identified auxiliary lobes exceeds the interference threshold if its beam-forming weights and/or transmission power are adjusted to adapt the prospect beam such that its SIR is increased at the position of the first WCD.

When the interference of the identified auxiliary lobes exceeds the interference threshold, a possibility may also include selecting a beam of the one or more candidate beams other than the prospect beam for communication with the first WCD. According to some embodiments, a null in the beam radiation pattern of an interfering beam may be steered into the direction of the prospect beam to reduce interference.

In a typical scenario, measurements are only caused in step 134 for candidate beams having interference of the identified auxiliary lobes that does not exceed the interference threshold, and the selection of sub-step 137 is based on the measurement reports. Then, sub-step 137 may comprise selecting the beam to be used in communication with the first wireless communication device based on the performed candidate coverage measurements (which are performed for the one or more candidate beams having interference of the identified auxiliary lobes that does not exceed the interference threshold). Typically, the acquired beam coverage statistics may be based on previously performed coverage statistics measurements in relation to the plurality of transmission beams. For example, the acquired beam coverage statistics may be the most recently performed coverage statistics measurements for the position indicated by the determined indication. Alternatively, the acquired beam coverage statistics may comprise a filtered (or averaged) value of previously performed coverage statistics measurements for the position indicated by the determined indication.

The previously performed coverage statistics measurements may comprise measurements performed and reported in relation to steps 134 and 135. Alternatively or additionally, the example method 100 may also comprise causing performance of coverage statistics measurements specifically for updating of the statistics. Such measurements may, for example, be caused periodically and/or triggered by some event.

Thus, the network node may cause the first wireless communication device (and/or any of the other wireless communication devices of the plurality) to perform coverage statistics measurements in relation to one or more of the plurality of transmission beams as illustrated by optional step 140. Typically, step 140 may generally correspond to step 134. However, the selection of beams for the measurements caused in step 140 may be different than the selection of the candidate beams in step 131. This is because the aim is to collect statistics as needed rather than to find an acceptable beam for communication. In optional step 150, a coverage statistics measurement report is received from the first (or other) wireless communication device, wherein the coverage statistics measurement report is indicative of a result of the performed coverage statistics measurements (compare with step 135). The beam coverage statistics in relation to the position of the first (or other) wireless communication device is then updated in step 160 based on the result of the performed coverage statistics measurements. The updating may, for example, comprise replacing previous measurement data with data provided by the new measurement, or combining the data provided by the new measurement with previous measurement data (e.g. via filtering or averaging).

Examples of approaches that may be applied in relation to the collection and updating of beam coverage statistics may be found in US 9445339 B2 and US 8892103 B2.

In Figure 1, optional steps 140, 150 and 160 may be performed in parallel with steps 120 and 130, as indicated by the parallelization of the transition from step 110 to steps 120 and 140. Alternatively or additionally, optional steps 140, 150 and 160 may be performed before or after steps 120 and 130 according to some embodiments.

Figure 2 illustrates an example method 200, which may be seen as a variation of the method described in connection to Figure 1. The method starts in step 210 with determining a location of a WCD (compare with step 110 of Figure 1). In step 220, beam coverage statistics are retrieved for the location (compare with step 120 of Figure 1), and conflicting auxiliary lobes are identified based on the beam coverage statistics in step 230 (compare with step 132 of Figure 1). In step 240, beam forming weights (of a selected beam and/or of beams causing the interference) may be modified as exemplified above in connection with step 137 of Figure 1. Then, in step 250, the WCD is scheduled on a selected beam. Figure 3 illustrates an example method 300, which may also be seen as a variation of the method described in connection to Figure 1. The method starts in step 310 with determining a location of a WCD (compare with step 110 of Figure 1). Then, beam coverage statistics is evaluated via measurements for the determined location in step 330 (compare with steps 140 and 150 of Figure 1), and the beam coverage statistics is updated accordingly in step 330 (compare with step 160 of Figure 1).

Figure 4 is a schematic drawing of a top view (a) and a side view (b) of a network node 400 with example beam directions to illustrate two different parameters of a transmission beam 401. In the top view, it is illustrated by 402 that the beam may vary in angle in a horizontal dimension and, in the side view, it is illustrated by 403 that the beam may vary in angle in a vertical dimension.

Figure 5 schematically illustrates example beam coverage statistics 500 according to some embodiments. The example beam coverage statistics 500 relates to three different beams having respective statistics 520, 530, 540.

In this example, the beam coverage statistics comprises binary metric values and areas of location are indicated as either having coverage 521, 522 or not having coverage 523. The binary metric values may, for example, comprise an indication of whether or not a signal strength value or a SIR value is above some threshold value. In the example of Figure 5, it can be seen that, for a position 510, coverage may be achieved for the beam corresponding to the statistics 520 (see area 521 which may correspond to a main lobe), while the beam corresponding to the statistics 530 provides no coverage and the beam corresponding to the statistics 540 may cause interference (see area 542 which may correspond to a side lobe). Of course, beam coverage statistics is typically represented by population of a data base and it should be understood that Figure 5 is merely meant to visualize the concept.

Figure 6 schematically illustrates top views of beam radiation patterns according to some embodiments. Part (a) illustrates a beam radiation pattern of a transmission beam comprising a main lobe 610 and two auxiliary lobes; a side lobe 620 and a grating lobe 630. Part (b) illustrates the beam radiation pattern (solid line) of the same transmission beam (first transmission beam) overlaid with beam radiation patterns (dashed and dotted lines, respectively) of two other transmission beams (second and third transmission beams). If the first transmission beam is a candidate to be used for communication with a first WCD, its main lobe 610 may be interfered by a grating lobe 640 of the second transmission beam and by a side lobe 650 of the third transmission beam when the second and third transmission beams are used for communication with other WCD:s.

Typically, the beam radiation pattern depends on the beam-forming weights used. Beam- forming weights may be generated from a standardized codebook or in a proprietary manner by the network node. The pre-coding (beam-forming) weights correspond to different radiation patterns, where the main beam pointing direction is different. In beamforming, besides the desirable main beam, side lobes and sometimes grating lobes arise. There are typically a set of standardized weights available and even though the main lobe may be best suited to serve a WCD the energy is also spread by side lobes and grating lobes. A large grating lobe or side lobe can be a large interferer for a main lobe of another beam.

Grating lobes arise when the antenna separation becomes large. For codebook based pre- coding, if there is a mismatch between the antenna element distance and the distance assumed in the fixed set of pre-coding weights used for beam-forming, then distortions of the radiation pattern may arise. Typically, a good design of the antenna array will trade off beam width, grating lobe size and side lobe suppression to maximize beam directivity whilst minimizing inter-beam interference.

An example of circumstances under which beams might cause interference to one another include two beams (beam 1 and beam 2) being transmitted to different users in different directions. In the main lobe of beam 1, a side lobe may create interference. If a transmission applying 64-Q.AM (quadrature amplitude modulation) would be transmitted in beam 1, then an EVM (Error Vector Magnitude) of at least 8% is needed, which corresponds to a signal-to- interference-and-noise ratio (SINR) of around -22dB. Thus, in order to avoid compromising the transmission in beam 1, the received power of interference from beam 2 side lobes must be at least 22dB lower than the power in beam 1. If this is not the case, the well-known technique of applying tapering to beam 2 (which would widen the main lobe but suppress the side lobes) could be applied. Tapering is one example of adjusting the beam-forming weights.

Figure 7 is a schematic block diagram illustrating an example arrangement 700 according to some embodiments. The arrangement 700 may, for example, be comprised in a network node and may be adapted to perform (or cause performance of) method steps as described in connection with any of Figures 1 through 3.

Hence, the arrangement 700 is beam selection arrangement for a network node adapted to use one or more of a plurality of transmission beams to accommodate communication with a plurality of wireless communication devices, wherein each transmission beam comprises a main lobe and one or more of the transmission beams further comprises one or more auxiliary lobes, and wherein the plurality of wireless communication devices comprises a first wireless communication device and one or more second wireless communication devices.

The arrangement 700 comprises a controller (CNTR) 710 and may also comprise, or be otherwise associated with one or more of: transceiving circuitry (e.g. a transceiver, RX/TX) 770, one or more data bases (DB) 750, 760, and scheduling circuitry (e.g. a scheduler, SCH) 720 for scheduling of WCD:s to transmission beams.

The controller 710 is configured to cause determination (compare with step 110 of Figure 1) of an indication of a position of the first wireless communication device and selection (compare with step 131 of Figure 1), from the plurality of transmission beams, of one or more candidate beams for use in communication with the first wireless communication device based on the determined indication.

It is also configured to cause, for beams used to communicate with the one or more second wireless communication devices, identification (compare with step 132 of Figure 1) of auxiliary lobes causing interference to the main lobe of any of the one or more candidate beams and selection (compare with step 137 of Figure 1) of a beam to be used in communication with the first wireless communication device based on the one or more candidate beams and the identified auxiliary lobes.

The determination may, for example, be made by the transceiver being adapted to receive the indicating from the first WCD where it may have been determined by GNSS circuitry, for example.

The identification may, for example, be made by a lobe identifier (LID) 723 based on statistics and/or pre-calculated lobe correlations acquired from the data base(s) 750, 750. The selection of candidate beams may be performed by candidate selection circuitry (e.g. a candidate selector, CAND) 721 and the selection of the beam to be used may be performed by beam selection circuitry (e.g. a beam selector, SEL) 722. The candidate selection circuitry may be comprised in, or otherwise associated with, the beam selection circuitry according to some embodiments.

In various embodiments, the arrangement may further comprise circuitry configured to cause one or more of the other method steps previously described.

A method for the first wireless communication device is also disclosed, wherein the first wireless communication device is adapted to communicate with a network node adapted to perform the method of the first aspect described earlier.

The method comprises determining a position of the first wireless communication device and transmitting an indication of the position to the network node. Furthermore, the method may comprise performing candidate coverage measurements in relation to the one or more candidate beams as instructed by the network node and transmitting a candidate measurement report from the first wireless communication device, wherein the candidate measurement report is indicative of a result of the performed candidate coverage measurements. The method may comprise performing coverage statistics measurements in relation to one or more of the plurality of transmission beams as instructed by the network node and transmitting a coverage statistics measurement report from the first wireless communication device, wherein the coverage statistics measurement report is indicative of a result of the performed coverage statistics measurements. The first wireless communication device may have specified modes for performance of the measurements.

Thus, some embodiments relate to a methodology to determine in which parts of the coverage area certain combinations of beams are suitable. The set of beams may be priorly known. One or more WCD:s get configured by the network node to carry out channel quality measurements and interference measurements, and the network node determines the position of each WCD and collects statistics on suitable beam combinations at the positions where the WCD:s are. After having acquired sufficient statistics, the network node will have prior information on suitable beam combinations in different areas of the coverage area, and hence can reduce the efforts in determining the best combination of beams by which to serve future WCD:s.

Moreover, the need for measurements is reduced by taking into account grating lobes and side lobes, all of which can be calculated beforehand with knowledge of the beamforming weights, the carrier frequency, and the physical array geometry. Since all three are known, it can be deduced that e.g. a grating lobe for one beam would overlap a main lobe for an adjacent main beam, and it can be concluded that WCD:s served by those two beams cannot share physical resources (time and frequency allocations). Alternatively or additionally, the beamforming weights for the beam causing the overlapping may be modified such that the grating lobe is steered away from the main lobe of the other beam.

In addition, building statistics over time allows the network node to be aware of the static reflectors surrounding the network node site, and the impact they have on the radio propagation and hence on the suitable beam combinations.

Occasionally the network node may configure one or more WCD:s to carry out a full set of measurements (e.g., on all possible beams) in order to update the statistics to follow e.g. seasonal variations cause e.g. by foliage. The number of permutations for suitable beam combinations for serving a large set of WCD:s becomes even larger with different optimization parameters (e.g. which WCD to prioritize or which metric to use; based upon UE application such as streaming data, SMS, voice, etc.) The position referred to herein may, for example, be determined by the network node via a combination of timing advance and angle-of-arrival, via radio frequency (RF) finger printing, via reception of GPS coordinates from the WCD, via reciprocity based on antenna array signature of received uplink signals, or via any other suitable approach.

In some embodiments, reduced complexity is achieved for both the network node and the WCD when determining suitable beam combinations, by using statistics that reflects the constraints on the radio propagation as imposed by the surroundings of the network node transceiver site. Finding a suitable combination sooner leads to improved system throughput both by reduced radio resource control (RRC) signaling for channel state information (CSI) measurement purposes and by more optimum reuse of physical resources (MU-MIMO). Some particular example implementations and variations will now be described to further illustrate various applications according to some embodiments.

In one example, the following components may be used: an interference impact evaluation unit,

- a beam adjustment unit, and

a beam coverage statistics unit, each of which are described further below.

A typical functional architecture for an AAS network node is shown in Figure 8. The architecture comprises: - an array of antennas (AA) 880,

a radio distribution network (RDN) 875 that distributes signals from transceiver units to the antennas,

an array of transmitter/receiver units (RDU) 870a, 870b, 870c, and

beam-forming control functionality in a scheduling unit (SCH) 820. Typically, the array of RDU:s, the RDN and the antenna array may be integrated into a single unit, and the beamforming control functionality may also be contained in the single unit or may be implemented elsewhere. The AAS base station architecture of Figure 8 further comprises interference impact evaluation units (INT EVAL) 823, beam adjustment control (BAC) 830, and beam coverage statistics which may be comprised in the interference impact evaluation unit and/or in a separated data base 860.

The interference impact evaluation unit 823, which may be realized in hardware, software, or a combination thereof, takes into account received channel state reports from WCD:s and evaluates combinations of beams between which there is significant interference. The interference evaluation unit contains knowledge of the antenna array geometry and be able to predict further beam combinations.

The beam adjustment control unit 830, which may be realized in hardware, software, or a combination thereof, contains specific knowledge of the antenna array geometry. The beamforming adjustment unit is able to use its knowledge of the antenna array geometry in order to adjust beamforming weights to mitigate inter-beam interference.

The beam coverage statistics unit, which may be realized in hardware, software, or a combination thereof, is maintaining statistics on the coverage by each of the downlink beams in the coverage area of the base station.

In a first example, the interference impact evaluation unit carries out analyses on how different beam combinations interfere with each other in different parts of the coverage area. The analyses may be based on various kinds of CSI measurements, and the results are processed by the beam coverage statistics unit, which for instance may quantify the average achievable signal quality for a beam in a certain part of the coverage area.

Steps 310, 320, 330 of Figure 3 may be one example that illustrates the operation of the interference impact evaluation unit when acquiring information on beam coverage.

The network node determines a proxy for the WCD location within the coverage area (310). This may be based on either or a combination of the non-limiting examples: - angle of arrival measurements,

distance measurements (timing advance, signal attenuation, etc.)

reported position according to e.g. LTE (Long Term Evolution) positioning protocol

(LPP),

uplink beam space signature,

- downlink RF fingerprint via measurement reporting, and

current beam(s) serving the WCD.

The network node carries out CSI measurements by transmitting corresponding reference signals (e.g. CSI-RS) and configuring the WCD to carry out CSI measurements (320). When deciding which beam combinations to investigate, the network node may for instance base the decision on: current beam coverage statistics, and

determination of grating lobes and side lobes. In the former case, the network node may identify coverage areas where the information on certain beam combinations might be outdated, e.g. due to seasonal variations as foliage. In the latter case, the network node may identify that a grating lobe (or side lobe) associated with one beam will overlap e.g. a main lobe (or side lobe or grating lobe) of another beam, for which it may: avoid the beam combination since it is already known that a grating lobe of the first beam will cause interference to the main lobe of the second beam, or

investigate the beam combination as it may be desirable to see e.g. how much interference a side lobe of the first beam will cause to a main lobe of the second beam, and to assess whether different WCD:s still can share physical resources when served by each respective main lobe.

After the network node has evaluated the beam coverage, it updates the beam coverage statistics (330) with information on the beam coverage at the determined WCD location.

Steps 210, 220 and 250 of Figure 2 may be one example that illustrates the operation of the scheduler which is utilizing beam coverage statistics to determine which beam combinations can be used for serving one or more WCD:s.

The network node determines a proxy for the WCD location within the coverage area (210). This may be based on either or a combination of the non-limiting examples: angle of arrival measurements,

- distance measurements (timing advance, signal attenuation, etc.)

reported position according to e.g. LTE (Long Term Evolution) positioning protocol (LPP),

uplink beam space signature,

downlink RF fingerprint via measurement reporting, and

- current beam(s) serving the WCD.

The network node retrieves the beam coverage statistics for the determined WCD location (220), by which it gets a candidate set of beams that can serve the WCD. This narrows down the search space compared to had there been no prior information on suitable beams. The network node uses the beam coverage statistics in the scheduling decisions (250), and may, in case of multiple WCD:s being served, determine whether physical resources can be reused when serving each respective WCD. Particularly, physical reuse (MU-MIMO) is possible when there is no overlapping coverage of main lobe and grating lobes between beams, or when there is such overlap but the signal from one beam is attenuated compared to the other beam due to reflections and differences in propagation paths.

In a second example, steps 210, 220, 230, 240 and 250 of Figure 2 may be one example that illustrates the alternative where a grating or a side lobe for one beam is overlapping the coverage provided by another beam's main lobe. After having determined the location of the WCD, and identified a suitable beam by which to serve the WCD, the network node uses knowledge about the antenna geometry, the sets of beamforming weights currently in use, and the carrier frequency, in order to determine whether any grating or side lobe associated with another beam would cause interference for the suitable beam to serve this WCD with (230). If so, the beam adjustment control unit may modify the weights of the beam causing the overlapping grating or side lobe, such that the interfering lobe is steered clear of the main lobe of the beam by which to serve this WCD (240).

In case there is no overlapping grating or side lobe, either by coincidence or since the beam adjustment control unit has been successful in finding a modified set of weights, the WCD:s served by the two beams can share physical resources (MU-MIMO). Otherwise, the WCD:s will be scheduled in non-overlapping physical resources.

According to some embodiments, a method is provided in a network node for reducing system complexity when determining suitable beams by which to provide coverage to a set of WCD:s (e.g. User Equipments, UE:s), thereby improving the system throughput and reducing the UE complexity and/or power consumption.

The method comprises:

Determining a representation of UE position (i.e. an apparent position not necessarily the same as a geographical coordinate),

Retrieving information about beam(s) with main lobe coverage at the UE position, Determining whether other active beam(s) cause interference, and

Mitigating the interference.

Representation of the UE position may be determined through any or a combination of: angle of arrival measurements,

- distance measurements (timing advance, signal attenuation, etc.)

reported position according to e.g. LTE positioning protocol (LPP),

uplink beam space signature,

downlink RF finger print via measurement reporting, and

current beam(s) serving the UE. Retrieving information about beam(s) with main lobe coverage at the UE location may comprise retrieving stored information.

Retrieving information about beam(s) with main lobe coverage at the UE location may comprise configuring the UE for CSI measurements, and storing the results for later retrieval.

Determining whether other active beam(s) causes interference may comprise calculating direction and strength of grating lobes and/or side lobes, and comparing it to the direction and strength of the main lobe, by using the following information:

Beam forming weights of the concerned beams,

Antenna geometry, and

Carrier frequency in use. Mitigating the interference may comprise any of:

Modifying beamforming weights in order to steer grating and side lobes clear of the main lobe, and scheduling the UE:s served by the concerned beams in overlapping physical resources (MU-MIMO), and

Scheduling UE:s in non-overlapping physical resources. The described embodiments and their equivalents may be realized in software or hardware or a combination thereof. The embodiments may be performed by general purpose circuitry. Examples of general purpose circuitry include digital signal processors (DSP), central processing units (CPU), co-processor units, field programmable gate arrays (FPGA) and other programmable hardware. Alternatively or additionally, the embodiments may be performed by specialized circuitry, such as application specific integrated circuits (ASIC). The general purpose circuitry and/or the specialized circuitry may, for example, be associated with or comprised in an apparatus such as a wireless communication device or a network node. Embodiments may appear within an electronic apparatus (such as a network node) comprising arrangements, circuitry, and/or logic according to any of the embodiments described herein. Alternatively or additionally, an electronic apparatus (such as a wireless communication device or a network node) may be configured to perform methods according to any of the embodiments described herein. According to some embodiments, a computer program product comprises a computer readable medium such as, for example a universal serial bus (USB) memory, a plug-in card, an embedded drive or a read only memory (ROM). Figure 9 illustrates an example computer readable medium in the form of a compact disc (CD) ROM 900. The computer readable medium has stored thereon a computer program comprising program instructions. The computer program is loadable into a data processor (PROC) 920, which may, for example, be comprised in a wireless communication device or a network node 910. When loaded into the data processing unit, the computer program may be stored in a memory (MEM) 930 associated with or comprised in the data-processing unit. According to some embodiments, the computer program may, when loaded into and run by the data processing unit, cause execution of method steps according to, for example, any of the methods illustrated in Figures 1-3.

Reference has been made herein to various embodiments. However, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the claims. For example, the method embodiments described herein discloses example methods through steps being performed in a certain order. However, it is recognized that these sequences of events may take place in another order without departing from the scope of the claims. Furthermore, some method steps may be performed in parallel even though they have been described as being performed in sequence.

In the same manner, it should be noted that in the description of embodiments, the partition of functional blocks into particular units is by no means intended as limiting. Contrarily, these partitions are merely examples. Functional blocks described herein as one unit may be split into two or more units. Furthermore, functional blocks described herein as being implemented as two or more units may be merged into fewer (e.g. a single) unit.

Hence, it should be understood that the details of the described embodiments are merely examples brought forward for illustrative purposes, and that all variations that fall within the scope of the claims are intended to be embraced therein.

Claims

1. A beam selection method of a network node adapted to use one or more of a plurality of transmission beams to accommodate communication with a plurality of wireless communication devices, wherein each transmission beam comprises a main lobe and one or more of the transmission beams further comprises one or more auxiliary lobes, and wherein the plurality of wireless communication devices comprises a first wireless communication device and one or more second wireless communication devices, the method comprising: determining (110) an indication of a position of the first wireless communication device; selecting (131), from the plurality of transmission beams, one or more candidate beams for use in communication with the first wireless communication device based on the determined indication; for beams used to communicate with the one or more second wireless communication devices, identifying (132) auxiliary lobes causing interference to the main lobe of any of the one or more candidate beams; and selecting (130, 137) a beam to be used in communication with the first wireless communication device based on the one or more candidate beams and the identified auxiliary lobes.

2. The method of claim 1 wherein selecting the one or more candidate beams comprises: acquiring (120) beam coverage statistics in relation to the position of the first wireless communication device based on the indication; and selecting (131a) the one or more candidate beams based on the acquired beam coverage statistics.

3. The method of claim 2 wherein the candidate beams are selected as beams for which the acquired beam coverage statistics indicate a coverage value above a coverage threshold.

4. The method of any of claims 2 through 3 wherein the acquired beam coverage statistics is based on previously performed coverage statistics measurements in relation to the plurality of transmission beams.

5. The method of claim 4 further comprising: causing (140) the first wireless communication device to perform coverage statistics measurements in relation to one or more of the plurality of transmission beams; receiving (150) a coverage statistics measurement report from the first wireless communication device, wherein the coverage statistics measurement report is indicative of a result of the performed coverage statistics measurements; and updating (160) the beam coverage statistics in relation to the position of the first wireless communication device based on the result of the performed coverage statistics measurements.

6. The method of any of claims 1 through 5 wherein selecting the beam to be used in communication with the first wireless communication device comprises: causing (134) the first wireless communication device to perform candidate coverage measurements in relation to the one or more candidate beams; receiving (135) a candidate measurement report from the first wireless communication device, wherein the candidate measurement report is indicative of a result of the performed candidate coverage measurements; and selecting (137) the beam to be used in communication with the first wireless communication device based on the result of the performed candidate coverage measurements and the identified auxiliary lobes.

7. The method of any of claims 1 through 6 wherein selecting the beam to be used in communication with the first wireless communication device comprises: determining, for a prospect beam of the one or more candidate beams, whether the interference of the identified auxiliary lobes exceeds an interference threshold; and when the interference of the identified auxiliary lobes does not exceed the interference threshold, selecting the prospect beam as the beam to be used in communication with the first wireless communication device.

8. The method of claim 7 further comprising, when the interference of the identified auxiliary lobes exceeds the interference threshold, performing one or more of: selecting the prospect beam and reducing the interference caused by the identified auxiliary lobes by adjusting beam-forming weights of one or more of the beams used to communicate with the one or more second wireless communication devices; selecting the prospect beam and reducing the interference caused by the identified auxiliary lobes by reducing a transmission power of one or more of the beams used to communicate with the one or more second wireless communication devices; selecting the prospect beam and adjusting its beam-forming weights; and selecting a beam of the one or more candidate beams other than the prospect beam.

9. A computer program product comprising a computer readable medium, having thereon a computer program comprising program instructions, the computer program being loadable into a data processing unit and configured to cause execution of the method according to any of claims 1 through 8 when the computer program is run by the data processing unit.

10. A beam selection arrangement for a network node adapted to use one or more of a plurality of transmission beams to accommodate communication with a plurality of wireless communication devices, wherein each transmission beam comprises a main lobe and one or more of the transmission beams further comprises one or more auxiliary lobes, and wherein the plurality of wireless communication devices comprises a first wireless communication device and one or more second wireless communication devices, the arrangement comprising a controller (710) configured to cause: determination of an indication of a position of the first wireless communication device; selection, from the plurality of transmission beams, of one or more candidate beams for use in communication with the first wireless communication device based on the determined indication; for beams used to communicate with the one or more second wireless communication devices, identification of auxiliary lobes causing interference to the main lobe of any of the one or more candidate beams; and selection of a beam to be used in communication with the first wireless communication device based on the one or more candidate beams and the identified auxiliary lobes.

11. The arrangement of claim 10 wherein the controller is configured to cause selection of the one or more candidate beams by causing: acquirement of beam coverage statistics in relation to the position of the first wireless communication device based on the indication; and selection of the one or more candidate beams based on the acquired beam coverage statistics.

12. The arrangement of claim 11 wherein the controller is configured to cause selection of the candidate beams as beams for which the acquired beam coverage statistics indicate a coverage value above a coverage threshold.

13. The arrangement of any of claims 11 through 12 wherein the acquired beam coverage statistics is based on previously performed coverage statistics measurements in relation to the plurality of transmission beams.

14. The arrangement of claim 13 wherein the controller is further configured to cause: the first wireless communication device to perform coverage statistics measurements in relation to one or more of the plurality of transmission beams; reception of a coverage statistics measurement report from the first wireless communication device, wherein the coverage statistics measurement report is indicative of a result of the performed coverage statistics measurements; and updating of the beam coverage statistics in relation to the position of the first wireless communication device based on the result of the performed coverage statistics measurements.

15. The arrangement of any of claims 10 through 14 wherein the controller is configured to cause selection of the beam to be used in communication with the first wireless communication device by causing: the first wireless communication device to perform candidate coverage measurements in relation to the one or more candidate beams; reception of a candidate measurement report from the first wireless communication device, wherein the candidate measurement report is indicative of a result of the performed candidate coverage measurements; and selection of the beam to be used in communication with the first wireless communication device based on the result of the performed candidate coverage measurements and the identified auxiliary lobes.

16. The arrangement of any of claims 10 through 15 wherein the controller is configured to cause selection of the beam to be used in communication with the first wireless communication device by causing: determination, for a prospect beam of the one or more candidate beams, of whether the interference of the identified auxiliary lobes exceeds an interference threshold; and when the interference of the identified auxiliary lobes does not exceed the interference threshold, selection of the prospect beam as the beam to be used in communication with the first wireless communication device.

17. The arrangement of claim 16 wherein the controller is further configured to cause, when the interference of the identified auxiliary lobes exceeds the interference threshold, one or more of: selection of the prospect beam and reduction of the interference caused by the identified auxiliary lobes by adjustment of beam-forming weights of one or more of the beams used to communicate with the one or more second wireless communication devices; selection of the prospect beam and reduction of the interference caused by the identified auxiliary lobes by reduction of a transmission power of one or more of the beams used to communicate with the one or more second wireless communication devices; selection of the prospect beam and adjustment of its beam-forming weights; and selection of a beam of the one or more candidate beams other than the prospect beam.

18. A network node comprising the arrangement of any of claims 10 through 17.