WO2017067591A1

WO2017067591A1 - A communication apparatus and a method of operating a communication apparatus

Info

Publication number: WO2017067591A1
Application number: PCT/EP2015/074384
Authority: WO
Inventors: Georgios ALEXANDROPOULOS
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2015-10-21
Filing date: 2015-10-21
Publication date: 2017-04-27
Anticipated expiration: 2018-04-21
Also published as: CN108141266A; CN108141266B

Abstract

The invention relates to a communication apparatus (100a) configured to communicate with another communication apparatus (100b), wherein the communication apparatus comprises an antenna array (101 a) configured to define a beam directivity pattern for communicating with an antenna array (101 b) of the other communication apparatus (100b), wherein the antenna array (101 a) is configured to adjust the beam directivity pattern on the basis of information about the position of the antenna array (101 a) of the communication apparatus (100a) and/or information about the position of the antenna array (101 b) of the other communication apparatus (100b).

Description

A COMMUNICATION APPARATUS AND A METHOD OF OPERATING A

COMMUNICATION APPARATUS

TECHNICAL FIELD

Generally, the present invention relates to a communication apparatus and a method of operating such a communication apparatus. More specifically, the present invention relates to a communication apparatus capable of beamforming and a method of operating such a communication apparatus.

BACKGROUND

Beamforming (BF) is a well-known and widely adopted signal processing technique for spatial filtering in multi-antenna communication systems (see, for instance, B. D. Van Veen and K. M. Buckley, "Beamforming: A versatile approach to spatial filtering," IEEE Acoustics, Speech and Signal Processing Magazine, vol. 5, no. 2, pp. 4-24, Apr. 1988). BF has been traditionally used for radiating/receiving energy to/from a specific location in space, or equivalently attenuating signal(s) to/from specific locations in space. BF is one of the most popular techniques for the physical layer of emerging wireless communication systems operating in high-frequency bands, as for example microwave and millimeter wave bands, and it has been considered both for access and backhaul communications. The popularity of BF in such systems is primarily due to the fact that it can be efficiently realized with large-sized phased antenna arrays that are able to offer a large BF gain, also known as large directional gain, with small and cheap individual antenna elements.

Especially in a high-frequency wireless communication link with a line-of-sight (LOS) component between two network nodes A and B that are both equipped with large-sized antenna arrays and are capable of realizing BF techniques, the following problem can arise. As already described above, a large BF gain can be achieved when node A radiates energy to the direction of node B and the latter receives energy from the direction that node A radiates to it, and vice versa, i.e. when the beams at both ends of the wireless communication link are geometrically aligned. When either network node A or B, or only their antenna arrays, move or change position/orientation, their beams obtained from BF may stop being geometrically aligned to an acceptable level, which usually degrades the performance of their communication link. The larger the misalignment is, the more severe the performance degradation. This problem, known as beam misalignment, becomes more frequent and its impact to the performance of the link more detrimental, when high- directive narrow beams are deployed at both nodes A and B. High-directive narrow beams are utilized in high-frequency wireless communication systems in order to confront the severe signal attenuation of communication signals with increasing distance between the communication ends. The higher the operating frequency, the more vulnerable to path loss communication systems become. Therefore, in such systems, robust beam alignment techniques need to be designed and adopted.

A beam alignment technique that samples the channel subspace adaptively using sub- codebook sets has been presented in S. Hur et al., "Millimeter wave beamforming for wireless backhaul and access in small cell networks," IEEE Transaction on

Communications, vol. 61 , no. 10, pp. 4391 -4403, Oct. 2013. This hard-alignment technique uses a set of candidate beam directivity patterns at any two communicating wireless network nodes and searches in a ping-pong fashion, i.e. in a multi-round fashion, between the nodes for the pair of beam directivity patterns maximizing the signal-to-noise ratio (SNR) performance of the communication link.

A three-stage BF protocol to set up communication between wireless network nodes in 60 GHz wireless personal area networks has been presented in J. Wang et al., "Beam codebook based beamforming protocol for multi-Gbps millimeter-wave WPAN systems," IEEE Journal on Selected Areas in Communication, vol. 27, no. 8, pp. 1390-1399, Oct. 2009. In this work, a beam-level search from predefined sets of beam directivity patterns, also known as BF codebooks, is included for beam alignment that replaces exhaustive beam search between any pair of two communicating network nodes.

A soft-decision beam alignment technique that exploits dual-polarized channels has been presented for millimeter wave wireless communications in J. Song et al., "Adaptive millimeter wave beam alignment for dual-polarized MIMO systems," arXiv preprint arXiv:1408.2098v2, Jan. 2015. This two-stage technique that is based on channel subspace estimation incorporates a subspace sampling using training beams, followed by a post-processing stage consisting of two rounds of beam alignment.

A BF technique that uses positioning data for receive network nodes to create transmit BF vectors, i.e. transmission beams, has been presented for LOS wireless communication systems in R. Maiberger et al., "Location base beamforming," in Proc. IEEE 26th

Convention of Electrical and Electronics Engineers in Israel, Eilat, Israel, 17-20 Nov. 2010, pp. 184-187. According to this technique, a multi-antenna transmit network node estimates the positions of intended single-antenna receiver nodes in order to construct transmit BF vectors. The position estimation of the receive nodes can be performed using either angle-of-arrival estimation techniques, global positioning systems (GPS) readings or location-based advertisement.

A one-sided beam search for wireless network nodes with large-sized antennas for wireless local area networks is described in IEEE, PHY/MAC complete proposal specification (TGad D0.1 ), IEEE 802.1 1-10/0433r2 Std., 2010. This method aims at establishing initial beam alignment between any two communicating network nodes.

A two-stage beam-search technique for wireless local area networks is included in IEEE 802.1 1 ad, Wireless LAN MAC and PHY specifications - amendment 3: Enhancements for very high throughput in the 60 GHz band, 2012. According to this technique, a coarse grained sector-level sweep is first performed, followed by a beam-level alignment phase. An exhaustive search over all possible transmission and reception directions is applied in each level.

An apparatus and method for correcting antenna beam misalignment between a transmit and a receive antenna on a mobile platform has been presented in US 6417803 B1. In this technique, sequential lobing at any two communicating network nodes is proposed in order to correct beam misalignment.

A beam alignment method that uses omnidirectional BF codebooks at any two

communicating wireless network nodes has been presented in US 2013/0229309.

According to this method, one network node utilizes a set of predefined BF patterns or beam directivity patterns and its intended for communication receive node indicates which beam needs to be used. The latter node informs the former one for which BF pattern to utilize by sending a feedback with the selected beam's entry in the codebook.

A steerable microwave backhaul multi-antenna transceiver architecture comprising of one or more sensors has been presented in US 2014/0347222. The sensor(s) may output readings/measurements that can be used to adjust the phase and/or amplitude coefficients of the transceiver. An apparatus and a method for maintaining beam alignment in a wireless communication system is provided in US 2014/0056256 A1. According to this method, the transmitting network node utilizes a set of predefined BF patterns or beam directivity patterns and when the quality of its communication link with a receiving network node falls below a certain threshold, the latter node feedbacks the preferred BF pattern that satisfies the quality requirement of their communication link.

A method for radio-frequency transmit and receive BF using GPS guidance and preloaded locations of access points (APs) has been presented in US 2010/0124210A1. With this method, any wireless device wishing to connect to a network possesses the positions of the APs of a network and utilizes its GPS data to connect to one of them. The connection to the network is accomplished by the node wishing to connect to it by calculating the relative vector with one of the APs, and then sending a sounding packet to the chosen one. For this calculation, the wireless device obtains its position through GPS. Next, the chosen AP estimates the condition of its link with the wireless device, steers its beam towards to it and sends a packet to it to establish the desired connection.

A very similar method for radio-frequency transmit and receive BF has been presented in US 2010/0124212A1 . According to US 2010/0124212A1 , a wireless device wishing to connect to an AP of a network possesses a locating system that is comprised of a GPS and electronics compass. In addition, the AP broadcasts its position. Then, the device calculates the relative vector between its position and that of the AP, and then sends a sounding packet to it. Next, the AP estimates its channel condition with the wireless device, steers its beam towards it, and sends a packet to it to establish the desired connection.

Although the above beam alignment techniques can provide some improvements, still a couple of drawbacks exist. For instance, a one-sided codebook-based beam search technique is generally not adequate for high-frequency wireless communication systems, where narrow beams are utilized at both communicating ends and need to be aligned as precisely as possible. In two-sided codebook-based beam alignment techniques the beam pair selection generally requires multi-round ping-pong exchanges of information between any two communicating wireless network nodes. This mode of operation results in high computational load and large overhead for ping-pong signaling. In addition, it has been found to perform poorly at low SNR values, i.e. with high probability of beam

misalignment. Thus, current solutions for beam alignment are either inadequate for high-frequency wireless communication systems, falling short in providing acceptable levels of beam alignment between any two communicating nodes, and/or require high computational complexity as well as large overhead for ping-pong signaling between the communicating nodes. Consequently, there is a need for an improved beam alignment technique.

SUMMARY

It is an object of the invention to provide a communication apparatus and a method of operating a communication apparatus implementing an improved beam alignment technique.

The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, the invention relates to a communication apparatus configured to communicate with another communication apparatus, wherein the communication apparatus comprises: an antenna array configured to define a beam directivity pattern for communicating with an antenna array of the other communication apparatus, wherein the antenna array is configured to adjust the beam directivity pattern on the basis of information about the position of the antenna array of the communication apparatus and/or information about the position of the antenna array of the other communication apparatus.

In a first possible implementation form of the communication apparatus according to the first aspect, the information about the position of the antenna array of the other communication apparatus is based on an estimate of the position of the antenna array of the other communication apparatus computed by the communication apparatus or on data defining the position of the antenna array of the other communication apparatus provided by the other communication apparatus.

In a second possible implementation form of the communication apparatus according to the first aspect as such or the first implementation form thereof, the antenna array is configured to adjust the beam directivity pattern on the basis of information provided by a control entity in communication with the communication apparatus, wherein the control entity is configured to select a beam directivity pattern for the antenna array of the communication apparatus and a beam directivity pattern for the antenna array of the other communication apparatus on the basis of the information about the position of the antenna array of the communication apparatus and/or the information about the position of the antenna array of the other communication apparatus.

In a third possible implementation form of the communication apparatus according to the first aspect as such or the first or second implementation form thereof, the communication apparatus further comprises a position sensor configured to provide the information about the position of the antenna array of the communication apparatus.

In a fourth possible implementation form of the communication apparatus according to the first aspect as such or any one of the first to third implementation form thereof, the communication apparatus further comprises a communication interface configured to transmit the information about the position of the antenna array of the communication apparatus to the other communication apparatus and to receive from the other

communication apparatus the information about the position of the antenna array of the other communication apparatus. In an implementation form, the communication interface is configured to operate at frequencies, which are lower than the frequencies employed for the beam directivity pattern. This allows ensuring a more reliable communication link due to the fact that, at lower communication frequencies the probability of beam misalignment is reduced.

In a fifth possible implementation form of the communication apparatus according to the first aspect of the invention as such or any one of the first to fourth implementation form thereof, the communication apparatus further comprises an estimator configured to estimate a quality measure of the communication channel defined by the beam directivity pattern of the antenna array of the communication apparatus and the beam directivity pattern of the antenna array of the other communication apparatus, and wherein the antenna array is configured to adjust the beam directivity pattern of the antenna array of the communication apparatus in case the quality measure of the communication channel is smaller than a first quality measure threshold. In an implementation form, SNR is the preferred measure of quality of the communication channel between the communication apparatus and the other communication apparatus. Other quality measures of the communication channel are possible as well. In a sixth possible implementation form of the communication apparatus according to the first aspect as such or any one of the first to fifth implementation form thereof, the communication apparatus further comprises a selector configured to select the beam directivity pattern on the basis of the information about the position of the antenna array of the communication apparatus and/or the information about the position of the antenna array of the other communication apparatus.

In a seventh possible implementation form of the communication apparatus according to the sixth implementation form of the first aspect, the selector is configured to select the beam directivity pattern from a database, in particular a look-up table, wherein the database contains a quality measure of the communication channel defined by the beam directivity pattern of the antenna array of the communication apparatus and the beam directivity pattern of the antenna array of the other communication apparatus for a plurality of beam directivity patterns defined for a plurality of different positions of the antenna array of the communication apparatus and a plurality of different positions of the antenna array of the other communication apparatus.

In an eighth possible implementation form of the communication apparatus according to the seventh implementation form of the first aspect, the selector is configured to select the beam directivity pattern from the database by selecting the beam directivity pattern from those beam directivity patterns in the database, which are defined for a position of the antenna array of the communication apparatus being closest to a current position of the antenna array of the communication apparatus. In an implementation form, the distance between the current position of the antenna array of the communication apparatus and a position defined in the database can be estimated using an Euclidean distance measure. Other distance measures are possible as well.

In a ninth possible implementation form of the communication apparatus according to the seventh or eighth implementation form of the first aspect, the selector is configured to select the beam directivity pattern from those beam directivity patterns in the database, which are associated with a quality measure of the communication channel being larger than a second quality measure threshold.

In a tenth possible implementation form of the communication apparatus according to the ninth implementation form of the first aspect, the communication apparatus is configured to transmit the information about the position of the antenna array of the communication apparatus and information about the selected beam directivity pattern to the other communication apparatus, if the quality measure of the communication channel is lower than the second quality measure threshold, using the beam directivity pattern from the database, which provides the largest quality measure of the communication channel for a current position of the antenna array of the communication apparatus.

In an eleventh possible implementation form of the communication apparatus according to the seventh implementation form of the first aspect, the communication apparatus is configured to receive from the other communication apparatus the information about the position of the antenna array of the other communication apparatus and information about the beam directivity pattern selected by the other communication apparatus and wherein the selector is configured to select a beam directivity pattern from the database on the basis of the information about the position of the antenna array of the other

communication apparatus and the information about the beam directivity pattern selected by the other communication apparatus.

In a twelfth possible implementation form of the communication apparatus according to the eleventh implementation form of the first aspect, the selector is configured to select the beam directivity pattern by selecting the beam directivity pattern from those beam directivity patterns in the database, which are defined for a position of the antenna array of the communication apparatus being closest to the current position of the antenna array of the communication apparatus and which are associated with a quality measure of the communication channel being larger than a third quality measure threshold. In a thirteenth possible implementation form of the communication apparatus according to the twelfth implementation form of the first aspect, the communication apparatus is configured to compute an optimized beam directivity pattern on the basis of the information about the position of the antenna array of the communication apparatus, the information about the position of the antenna array of the other communication apparatus and the information about the beam directivity pattern selected by the other

communication apparatus.

In a fourteenth possible implementation form of the communication apparatus according to the thirteenth implementation form of the first aspect, the communication apparatus is further configured to store the optimized beam directivity pattern in the database. According to a second aspect the invention relates to a method of operating a

communication apparatus configured to communicate with another communication apparatus using an antenna array configured to define a beam directivity pattern for communicating with an antenna array of the other communication apparatus, wherein the method comprises the step of: adjusting the beam directivity pattern on the basis of information about the position of the antenna array of the communication apparatus and/or information about the position of the antenna array of the other communication apparatus. The method according to the second aspect of the invention can be performed by the communication apparatus according to the first aspect of the invention. Further features of the method according to the second aspect of the invention result directly from the functionality of the communication apparatus according to the first aspect of the invention and its different implementation forms.

According to a third aspect the invention relates to a computer program comprising program code for performing the method according to the second aspect of the invention when executed on a computer. The invention can be implemented in hardware and/or software.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect to the following figures, in which:

Figure 1 shows a schematic diagram illustrating a communication apparatus according to an embodiment; Figure 2 shows a schematic diagram illustrating a method of operating a communication apparatus according to an embodiment;

Figure 3 shows a flow diagram illustrating the operation of a communication apparatus according to an embodiment; Figure 4 shows a schematic diagram illustrating an exemplary coordinate system to describe the spatial relation between a communication apparatus according to an embodiment and another communication apparatus at different instants of time; Figure 5 shows a table of quality measures in the form of a SNR of a communication channel between a communication apparatus according to an embodiment and another communication apparatus for a plurality of beam directivity patterns and a plurality of positions/displacements of both communication apparatuses; Figure 6 shows an exemplary diagram illustrating five exemplary beam directivity patterns for a communication apparatus according to an embodiment;

Figure 7 shows another exemplary diagram illustrating five exemplary beam directivity patterns for a communication apparatus according to an embodiment in communication with the communication apparatus of figure 6;

Figure 8 shows a flow diagram illustrating different steps of a first stage of operation taking place at a communication apparatus according to an embodiment; Figure 9 shows a flow diagram illustrating different steps of a second stage of operation taking place at a communication apparatus according to an embodiment;

Figure 10 shows a flow diagram illustrating different steps of a third stage of operation taking place at a communication apparatus according to an embodiment;

Figure 1 1 shows a flow diagram illustrating different steps of a fourth stage of operation taking place at a communication apparatus according to an embodiment;

Figure 12 shows a diagram illustrating the signaling between a communication apparatus according to an embodiment and another communication apparatus in a first scenario;

Figure 13 shows a diagram illustrating the signaling between a communication apparatus according to an embodiment and another communication apparatus in a second scenario; Figure 14 shows a diagram illustrating the signaling between a communication apparatus according to an embodiment and another communication apparatus in a third scenario; and Figure 15 shows a diagram illustrating the signaling between a communication apparatus according to an embodiment and another communication apparatus in a fourth scenario.

DETAILED DESCRIPTION OF EMBODIMENTS In the following detailed description, reference is made to the accompanying drawings, which form a part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the present invention may be practiced. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the present invention is defined by the appended claims.

For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure 1 shows a schematic diagram illustrating a communication apparatus 100a according to an embodiment. The communication apparatus 100a is configured to communicate with another communication apparatus 100b using BF. To this end, the communication apparatus 100a comprises an antenna array 101 a configured to define a beam directivity pattern for communicating with an antenna array 101 b of the other communication apparatus 100b. As will be explained in more detail further below, the antenna array 101 a is configured to adjust the beam directivity pattern on the basis of information about the position of the antenna array 101 a of the communication apparatus 100a and/or information about the position of the antenna array 101 b of the other communication apparatus 100b. In an embodiment, the other communication apparatus 100b can be essentially identical to the communication apparatus 100a, i.e. the communication apparatus 100b can have the same or similar components as the communication apparatus 100a, which will be described in more detail further below.

As schematically indicated in figure 1 , the communication apparatus 100a and the other communication apparatus 100b, which hereinafter will also be referred to as node 100a and node 100b, each can be mounted or supported in such a way that their respective position can be time dependent. In an embodiment, the antenna array 101 a of the communication apparatus 100 defines the shape and a central position of the beam directivity pattern for communicating with the other communication apparatus 100b. As will be explained in more detail further below, a change of position of the communication apparatus 100a leads to a change of position of the antenna array 101 a, which, in turn, can lead to a change of the central position of its beam directivity pattern.

In an embodiment, the information about the position of the antenna array 101 b of the other communication apparatus 100b is based on an estimate of the position of the antenna array 101 b of the other communication apparatus 100b computed by the communication apparatus 100a or on data defining the position of the antenna array 101 b of the other communication apparatus 100b provided by the other communication apparatus 100b.

In an embodiment, the antenna array 101 a is configured to adjust the beam directivity pattern on the basis of information provided by a control entity in communication with the communication apparatus 101 a, wherein the control entity is configured to select a beam directivity pattern for the antenna array 101 a of the communication apparatus 100a and a beam directivity pattern for the antenna array 101 b of the other communication apparatus 100b on the basis of the information about the position of the antenna array 101 a of the communication apparatus 100a and/or the information about the position of the antenna array 101 b of the other communication apparatus 100b. As can be taken from the embodiment shown in figure 1 , the communication apparatus 100a can further comprise a position sensor 102a configured to provide the information about the position of the antenna array 101 a of the communication apparatus 100a.

As can be taken from the embodiment shown in figure 1 , the communication apparatus 100a can further comprise a communication interface 103a configured to transmit the information about the position of the antenna array 101 a of the communication apparatus 100a to the other communication apparatus 100b and to receive from the other communication apparatus 100b the information about the position of the antenna array 101 b of the other communication apparatus 100b. In an embodiment, the communication interface 103a is configured to operate at lower frequencies. This allows ensuring a more reliable communication link due to the fact that, at lower communication frequencies the probability of beam misalignment is reduced.

As can be taken from the embodiment shown in figure 1 , the communication apparatus 100a can further comprise an estimator 105a configured to estimate a quality measure of the communication channel defined by the beam directivity pattern of the antenna array 101 a of the communication apparatus 100a and the beam directivity pattern of the antenna array 101 b of the other communication apparatus 100b and wherein the antenna array 101 a is configured to adjust the beam directivity pattern of the antenna array 101 a of the communication apparatus 100a in case the quality measure of the communication channel is smaller than a first quality measure threshold. In an embodiment, the measure of quality of the communication channel between the communication apparatus 100a and the other communication apparatus 100b is the signal to noise ratio.

As can be taken from the embodiment shown in figure 1 , the communication apparatus 100a can further comprise a selector 107a configured to select the beam directivity pattern on the basis of the information about the position of the antenna array 101 a of the communication apparatus 101 a and/or the information about the position of the antenna array 101 b of the other communication apparatus 100b.

In an embodiment, the selector 107a is configured to select the beam directivity pattern from a database 109a, wherein the database 109a contains a quality measure of the communication channel defined by the beam directivity pattern of the antenna array 101 a of the communication apparatus 100a and the beam directivity pattern of the antenna array 101 b of the other communication apparatus 100b for a plurality of beam directivity patterns defined for a plurality of different positions of the antenna array 101 a of the communication apparatus 100a and a plurality of different positions of the antenna array 101 b of the other communication apparatus 100b. In an embodiment, the database 109a can contain a look-up table. In an embodiment, the database 109a can be part of the communication apparatus 100a, as shown in the embodiment of figure 1. In another embodiment, the database 109a can be an entity separate from the communication apparatus 100a, which can be accessed by both the communication apparatus 100a and the other communication apparatus 100b. In an embodiment, the selector 107a is configured to select the beam directivity pattern from the database 109a by selecting the beam directivity pattern from those beam directivity patterns in the database 109a, which are defined for a position of the antenna array 101 a of the communication apparatus 100a being closest to a current position of the antenna array 101 a of the communication apparatus 100a. In an embodiment, the selector 107a can be configured to determine a measure of closeness or distance using an Euclidean distance measure.

In an embodiment, the selector 107a is configured to select the beam directivity pattern from those beam directivity patterns in the database 109a, which are associated with a quality measure of the communication channel being larger than a second quality measure threshold. In an embodiment, the second quality measure threshold can be equal to the first quality measure threshold. In an embodiment, the communication apparatus 100a is configured to transmit the information about the position of the antenna array 101 a of the communication apparatus 100a and information about the selected beam directivity pattern to the other

communication apparatus 100b, using for instance the communication interface 103a, if the quality measure of the communication channel is lower than the second quality measure threshold, using the beam directivity pattern from the database 109a, which provides the largest quality measure of the communication channel for a current position of the antenna array 101 a of the communication apparatus 100a.

In an embodiment, the communication apparatus 100a is configured to receive from the other communication apparatus 100b the information about the position of the antenna array 101 b of the other communication apparatus 100b and information about the beam directivity pattern selected by the other communication apparatus 100b and wherein the selector 107a is configured to select a beam directivity pattern from the database 109a on the basis of the information about the position of the antenna array 101 b of the other communication apparatus 100b and the information about the beam directivity pattern selected by the other communication apparatus 100b.

In an embodiment, the selector 107a is configured to select the beam directivity pattern by selecting the beam directivity pattern from those beam directivity patterns in the database 109a, which are defined for a position of the antenna array 101 a of the communication apparatus 100a being closest to the current position of the antenna array 101 a of the communication apparatus 100a and which are associated with a quality measure of the communication channel being larger than a third quality measure threshold. In an embodiment, the third quality measure threshold can be equal to the first quality measure threshold and/or the second quality measure threshold.

In an embodiment, the communication apparatus 100a is further configured to compute an optimized beam directivity pattern on the basis of the information about the position of the antenna array 101 a of the communication apparatus 100a, the information about the position of the antenna array 101 b of the other communication apparatus 100b and the information about the beam directivity pattern selected by the other communication apparatus 100b.

In an embodiment, the communication apparatus 100a is further configured to store the optimized beam directivity pattern in the database 109a.

Figure 2 shows a schematic diagram illustrating steps of a method 200 of operating a communication apparatus 100a. The method 200 comprises a step 201 of using an antenna array 101 a of the communication apparatus or node 100a configured to define a beam directivity pattern for communicating with an antenna array 101 b of another communication apparatus or node 100b. The method 200 further comprises a step 203 of adjusting the beam directivity pattern on the basis of information about the position of the antenna array 101 a of the communication node 100a and/or information about the position of the antenna array 101 b of the other communication node 100b. In the following, further implementation forms, embodiments and aspects of the communication apparatus 100a and the method 200 will be described.

As can be taken from the embodiment shown in figure 3, when the performance of the communication link between the nodes 100a, 100b becomes unacceptable, i.e. lower than a desired performance level (reference sign 301 of figure 3), each node 100a, 100b can obtain its position information or the position information of its antenna array 101 a, 101 b (reference sign 303 of figure 3). Then, based on a master-slave fashion, the nodes 100a, 100b can exchange their position information or the position information of their antenna array 101 a, 101 b together with their utilized beam directivity pattern (predefined or computed; reference sign 305 of figure 3). Under the aforementioned fashion, each node 100a, 100b can search in the commonly available database (e.g. look-up table) for the predefined beam directivity pattern yielding acceptable level of beam alignment, i.e.

desired performance level (reference sign 307 of figure 3). For cases where there is no pair of predefined beam directivity patterns in the commonly available database yielding acceptable level of beam alignment, each node 100a, 100b makes use of the information available to it, namely from the phase of BF information exchange, position of the other node or this node's antenna array, to design the optimum beam directivity pattern steering to it. This position information is utilized together with the latter optimum beam directivity pattern as well as the resulting performance indicator to enrich/update the commonly available database 109a with the precomputed performance indicators (reference sign 309 of figure 3).

The present invention can be implemented using hardware and software modules for: i) measuring the position/displacement of the communicating network nodes 100a, 100b and/or their antenna arrays 101 a, 101 b; ii) reliably exchanging control communication signals including BF information, comprising of the latter position information together with the utilized beam directivity patterns (predefined or computed) from the nodes 100a, 100b; and iii) for providing the database 109a, in particular look-up table, with the performance indicators for the link between them for different combinations of predefined beam directivity patterns for both nodes 100a, 100b and preplaced positions/displacements of the nodes 100a, 100b and/or their antenna arrays 101 a, 101 b.

As already mentioned above, the estimation of the position/displacement of each node 100a, 100b and/or its antenna array 101 a, 101 b can be accomplished with one or more instruments/sensors, such as the position sensor 102a, which can comprise highly accurate special purpose devices, GPS devices, displacement sensor(s) and/or electronical compasses, attached to each node 100a, 100b and/or their antenna array 101 a, 101 b. The exchange of BF information, including, e.g. the utilized beam directivity pattern and position/displacement of the node 100a, 100b and/or its antenna array 101 a, 101 b, between the network nodes 100a, 100b wishing to communicate can be

accomplished by one or more hardware and software modules that minimize the probability of erroneous reception of this information. To achieve this goal in high- frequency wireless communication networks comprising network nodes, such as nodes 100a, 100b, deploying large-sized antenna arrays and realizing high-directive BF techniques, a dedicated low-frequency conventional transceiver system, such as the communication interface 103a described above, can be used. In an embodiment, this transceiver system consists of one antenna or antenna array with a wider beam width than that of the highly directive antenna array 101 a, 101 b in order to ensure a reliable exchange of control communication signals carrying the aforementioned BF information. As already mentioned above, in an embodiment, both communicating network nodes 100a, 100b hold a common database 109a, in particular look-up table, containing the performance indicators described before. In an embodiment, this common database 109a can be constructed during an initial calibration phase or enriched/updated over certain periods of time. For the latter purpose, dedicated software can be deployed in order to enrich/update the database, in particular look-up table, 109a according to certain objectives (e.g. increased resolution of the look-up table aiming at adapting to changing environmental conditions).

In an embodiment, the communication apparatus 100a and the other communication apparatus can be, for instance, two fixed-position multi-antenna network nodes operating in a wireless environment including a LOS component providing a high-frequency communication link, for example in a microwave or millimeter wave frequency band. When the performance of this communication link becomes unacceptable, i.e. lower than a desired performance level, due to small movement/displacement of one or both network nodes 100a, 100b (e.g. sway of the support structures of the nodes 100a, 100b due to wind or ground vibration), both nodes 100a, 100b first monitor their position information. Then, using both a low-frequency transceiver system with an omnidirectional antenna, such as the communication interface 103a, the nodes 100a, 100b can exchange in a master-slave fashion their position information together with their utilized beam directivity pattern. Finally, the latter BF information, such as utilized beam directivity pattern and coordinates, or relative coordinates, of the node 100a, 100b to communicate and/or its antenna array 101 a, 101 b, is used by each node 100a, 100b in order to search in the commonly available look-up table 109a for the beam directivity pattern yielding acceptable level of beam alignment, i.e. desired performance level. In an embodiment, the commonly available look-up table 109a includes the performance indicators for the link between the communicating network nodes 100a, 100b for different combinations of predefined beam directivity patterns for both nodes 100a, 100b and preplaced positions/displacements of the nodes 100a, 100b and/or their antenna arrays 101 a, 101 b.

In another embodiment, where the communication apparatus 100a and the other communication apparatus can be, for instance, two fixed-position multi-antenna network nodes operating in a wireless environment including a LOS component providing a high- frequency communication link, for example in a microwave or millimeter wave frequency band, in case the performance of the communication link between the two nodes 100a, 100b becomes unacceptable, i.e. lower than a desired performance level, both nodes 100a, 100b first monitor their position/displacement information but do not exchange it with each other. Instead, in this embodiment, each network node 100a, 100b can utilize its own measured position/displacement information together with an estimate or prediction of the position/displacement of the other node 100a, 100b (e.g. node movement prediction using wind information available from weather forecast) in order to find in the common available look-up table 109a, which includes the performance indicators for the link between the nodes 100a, 100b for different combinations of predefined beam directivity patterns for both nodes 100a, 100b and preplaced positions/displacements of the nodes 100a, 100b and/or their antenna arrays 101 a, 101 b, an adequate beam directivity pattern yielding an acceptable level of beam alignment, i.e. a desired performance level.

In an embodiment, the communication apparatus 100a and the other communication apparatus 100b can be implemented in form of multi-antenna network nodes 100a, 100b wishing to communicate through a high-frequency wireless link with a LOS component and can be configured to periodically monitor the performance of their communication link (e.g. the SNR value). When the performance of the communication link becomes unacceptable, i.e. lower than a desired performance level, both nodes 100a, 100b measure their position/displacement or the position/displacement of their antenna arrays 101 a, 101 b and exchange this information. Each network node 100a, 100b utilizes the position/displacement information of the node wishing to communicate with in order to design the optimum beam directivity pattern steering to it. In an embodiment, the communication apparatus 100a and the other communication apparatus 100b can be implemented in form of two multi-antenna network nodes 100a, 100b communicating through a high-frequency wireless communication link, for example a microwave or millimeter wave link, with a LOS component. The nodes 100a, 100b can move on fixed route trajectories and each node 100a, 100b can possess a certain number of predefined beam directivity patterns. When the quality of their communication link falls below a minimum required level, each node 100a, 100b measures its position or the position of its antenna array 101 a, 101 b and forwards it, in particular using a dedicated low-frequency transceiver system, such as the communication interface 103a, to a network control entity maintaining the look-up table 109a with the performance indicators for the link between the communicating nodes 100a, 100b for different combinations of predefined beam directivity patterns for both nodes 100a, 100b and preplaced positions of the nodes 100a, 100b or their antenna arrays 101 a, 101 b on the fixed route trajectories. Next, the network control entity searches in the look-up table 109a for a pair of beam directivity patterns yielding an acceptable performance, and then forwards the identifier of the respective beam directivity pattern to each of the nodes 100a, 100b allowing each node 100a, 100b to adopt the corresponding beam directivity pattern.

In an embodiment, the communication apparatus 100a is implemented in the form of a node A and the other communication apparatus 100b is implemented in the form of a node B, wherein node A is considered as the master node and node B as the slave node and both nodes lie in the two-dimensional space as illustrated in figure 4. An extension of this implementation example to three-dimensional space is straightforward. Each node 100a, 100b is considered to be mounted on a pole and both poles are assumed to sway due to wind or ground vibration. As a result of pole sway, both network nodes 100a and 100b move in arbitrary directions, but within specific displacement limits that depend on the material and structure of the poles. In this example, pole sway in excess of these specific displacement limits can result in pole break, which is considered as an extreme case. Both network nodes 100a and 100b deploy one or more instruments/sensors for position/displacement monitoring, such as the position sensor 102a, as well as an extra low-frequency conventional transceiver system, such as the communication interface 103a, for exchanging BF information, e.g. utilized beam directivity patterns and position/displacement of the nodes 100a, 100b. Upon installation of the communication link between the nodes 100a, 100b, their initial distance d₀, i.e. at the time instant t=1 , is assumed to be accurately measured, using for example one or more highly accurate instruments for this purpose. After obtaining the distance d₀, the exemplary coordinate system shown in figure 4 with the origin defined by the position of the master node 100a is adopted. In particular, the (0,0) point of the two-dimensional coordinate system in figure 4 is the position point M₀ ^(A) of master node 100a, and the position of slave node 100b is defined by point M₀ ^(B) with coordinates (0,c/₀)- At any time instant t>1 , the position of node 100a in the two-dimensional coordinate system of figure 4 is given by the coordinates of point M_t ^(A), the position of node 100b is given by the coordinates of point M_t ^(B), and d_t represents the distance of the nodes at this time instant t. For example, as shown in figure 4, prior to time instant t=1 master node 100a moves from the position M₀ ^(A) to the new position Mi^(A) having coordinates (-Xi^(A), yi^<A)), whereas slave node 100b moves from the position M₀ ^(B) to the new position M- ⁶' with coordinates (xi^(B), do- yi^<B))- Consequently, in an exemplary embodiment the angle ζΊ of the line segment joining the points Mi^(A) and M-i^(B) can be computed as follows:

Therefore, in order for each node 100a, 100b to calculate the direction to the other node, i.e. the direction to steer a beam, the coordinates of the position of both nodes 100a, 100b are needed at each node as well as the original distance of the nodes 100a, 100b, i.e. d₀.

In an embodiment, the position of a network node 100a, 100b can be defined as the position of the center of its antenna array 101 a, 101 b and distances refer to the distances between the centers of the antennas arrays 101 a, 101 b of the nodes 100a, 100b. Even if one or more instruments/sensors monitoring position/displacement and/or one or more instruments measuring the distance between the nodes 100a, 100b are not attached to the centers of the antenna arrays 101 a, 101 b of the nodes 100a, 100b, but to other portions of the nodes 100a, 100b or the poles supporting the nodes 100a, 100b, the positions of the centers of the antenna arrays 101 a, 101 b can be still calculated, as can be appreciated from the following example. Suppose that, in the two-dimensional coordinate system of figure 4 at time instant t, the position of the center of the antenna array 101 a of the master network node 100a is given by the coordinates (a,b). Since the shape of the structure of the node 100a is known, i.e. the geometry of the node 100a as a whole, any movement/displacement of node 100a from the initial point (0,0) can be translated to a movement/displacement of the center of its antenna array 101 a. Thus, there exists a definite relationship between the position/displacement of a node 100a, 100b and the position/displacement of the center of a node's antenna array 101 a, 101 b so that the terms position/displacement of a node 100a, 100b position/displacement of the center of a node's antenna array 101 a, 101 b are herein used interchangeably.

Referring back to the embodiment described in the context of figure 4, both the master node 100a and the slave node 100b can maintain in their memory a look-up table, such as the look-up table 109a described above, with the SNR performance indicators for the link between the nodes 100a, 100b for all combinations of predefined beam directivity patterns for both nodes 100a, 100b and preplaced positions/displacements of them and/or their antenna arrays 101 a, 101 b. For the two-dimensional example shown in figure 4 an exemplary look-up table Γ for K predefined beam directivity patterns for both nodes 100a, 100b as well as M preplaced positions/displacements in the x-axis and N preplaced positions in the y-axis of both nodes 100a and 100b is given in the table shown in figure 5. In general, the number of predefined beam directivity patterns and/or the number of preplaced positions/displacements can be different between the nodes 100a, 100b. The exemplary look-up table Γ shown in figure 5 is a m x n matrix with m=n=KMN and notation r,_j denotes the (/,y^')-th element of Γ, where /^'=1 ,2, ...,m and y^'=1 ,2, ...,n. In the table shown in figure 5, notations X_e ^(A) and X_e ^(B) represent the e-th preplaced position/displacement in the x-axis for node 100a and 100b, respectively, and Y_C ^(A) and Y_C ^(B) denote the c-th preplaced position/displacement in the y-axis for node 100a and 100b, respectively, with e e{1 ,2,...,M} and c e{1 ,2, ...,N}. In addition, notations b„^(A) and b„^(B) represent the n-th predefined beam directivity pattern of the antenna array 101 a, 101 b of node 100a and 100b, respectively, with n e{1 ,2, ...,K}.

An example of K=5 predefined beam directivity patterns for the master node 100a and the slave node 100b shown in figure 4 is provided in figures 6 and 7. These beam directivity patterns have been obtained from uniform sampling within the angles 60 and 120 degrees for node 100a and within the angles 240 and 300 degrees for node 100b.

In an embodiment, the look-up table Γ 109a commonly available to both nodes 100a and 100b is constructed in an initial calibration phase, where both nodes 100a, 100b are placed at M different positions/displacements along the x-axis and N different

positions/displacements along the y-axis of the coordinate system shown in figure 4. The SNR performance of the wireless communication link between the nodes 100a, 100b is measured for different combinations of positions/displacements and predefined beam directivity patterns of the nodes 100a, 100b. In principle, the number of entries in the lookup table 109a will increase with the number of the aforementioned combinations. A look- up table 109a with an increased size translates consequently to an increased resolution in terms of SNR performance indicators for different positions/displacements and predefined beam directivity patterns. Generally, the size of the commonly available look-up table 109a can depend on the application and more specifically: /^') an increased resolution in specific angular sectors can be required in some applications (see e.g. figures 4, 6 and 7 where nodes 100a and 100b are placed so as to steer one another and beam alignment needs to be guaranteed even when the nodes 100a, 100b slightly move e.g. due to wind or ground vibration), which reduces the available space to sample, and hence renders the size of the look-up table 109a reasonable (as already mentioned above, in an

embodiment, the look-up table 109a, instead of being hosted in the nodes 100a, 100b can be hosted on a network control entity with increased storage and big data recovery capabilities); /^'/^') the size of the look-up table 109a can be kept reasonable for extreme positions/displacements and whenever a position/displacement not included in the look-up table 109a occurs (in this case one or more threshold values on how close the measured positions/displacements are to the available preplaced positions/displacements can be used), beam alignment can be accomplished by exchanging the actual measured positions/displacements of the nodes 100a, 100b between the nodes 100a, 100b; and /^'/ ) the content of a fixed-size look-up table 109a is periodically updated in order to dynamically capture the environment where the two network nodes 100a, 100b are operating. In an embodiment, beam misalignment is considered to occur when the instantaneous SNR value of the wireless communication link between the master node 100a and the slave node 100b falls below a minimum SNR threshold _h, i.e. a first quality measure threshold. This threshold can depend on the particular application and reveals the required level of quality of service of the communication link. To monitor the instantaneous SNR performance of the link between the nodes 100a, 100b, one or both of the nodes 100a, 100b can measure the SNR performance at each time instant t, and obtain an estimate g_t for the instantaneous SNR performance. In order for the transmitting node to know the SNR of its communication link with an intended receiving node at time instant t, a feedback from the latter node to the former with the estimated SNR value g_t is provided in an embodiment. This feedback operation can take place either with: /^') conventional feedback of the g_t value, possibly a quantized version of it; or with /^'/^') dedicated signals in a time-division-duplexing system from the receiving node to the transmitting one in order for the latter to estimate the SNR value of their communication link. In an embodiment, the g_t value can be exchanged using the communication interface 103a to ensure a reliable exchange.

In an embodiment, first the master node 100a initiates a set of actions when g_t<y_t and then, if needed, a set of actions from the slave node 100b follows. If still g_t<y_t , a final set of actions from master node 100a can be used. In an embodiment, the following three stages for achieving an acceptable level of beam alignment between the communicating network nodes 100a and 100b can be used: i) Master Recovery 1 (MR1 ) Stage; ii) Slave Recovery (SR) Stage; and iii) Master Recovery 2 (MR2) Stage. Hereinafter for the sake of clarity indices are used in the exchanged signals between nodes 100a and 100b in order to indicate either pure control communication signals including BF information (utilized beam directivity pattern and coordinates, or relative coordinates, of the node 100a, 100b or its antenna array 101 a, 101 b) or data signals including data and/or the aforementioned BF information.

The steps of an embodiment of a MR1 stage taking place at master node 100a are summarized in the flowchart of figure 8. In this figure and the following ones, b_s ^(A) and b_s ^(B) with s e{1 ,2, ...,K}, denote the selected predefined beam directivity pattern of the antenna array 101 a, 101 b of node A and B, respectively, yielding an acceptable SNR performance level (with, as already mentioned above, K denoting the number of elements of the set of available BF patterns). The beam directivity pattern of the antenna array 101 a, 101 b of node 100a and 100b designed so as to steer towards the respective other node is denoted by b_opt^(A) and b_opt^(B), respectively. g_max denotes the maximum SNR performance that is measured at one of the nodes 100a, 100b at a particular time instant using all available predefined beam directivity patterns. As can be taken from the embodiment shown in figure 8, master node 100a estimates the instantaneous SNR value g_t, and only when g_t< _h the following actions follow (reference sign 801 of figure 8). Whenever g_t< _h, master node 100a obtains its current

position/displacement information (reference sign 803 of figure 8) from its one or more instruments/sensors, such as the position sensor 102a, and finds the preplaced position/displacement in its look-up table 109a that is closest to its current

position/displacement (reference sign 805 of figure 8). One way to compute the closest preplaced position/displacement is to make use of a Euclidean distance measure. The latter preplaced position/displacement is used together with the BF information (utilized beam directivity pattern and position/displacement) for the slave node 100b from the previous time slot in order for master node 100a to search in the look-up table 109a for a predefined beam directivity pattern yielding g_t≥y_t (reference sign 807 of figure 8). Initially, master node 100a can perform a sequential scanning with all available beam directivity patterns and use the first one meeting the SNR requirement or the one yielding the maximum SNR performance. If such a predefined beam directivity pattern exists, i.e. if an acceptable level of beam alignment has been achieved, master node 100a can utilize it to send data to the slave node 100b (reference signs 809 and 81 1 of figure 8). Otherwise, master node 100a can utilize its predefined beam directivity pattern yielding maximum SNR performance for the intended communicating link to send data to slave node 100b together with its BF information (reference signs 809 and 813 of figure 8), such as utilized beam directivity pattern for node 100a and its position/displacement information obtained from its one or more instruments/sensors. In an embodiment, the BF information mentioned in the context of reference sign 813 can be sent by means of the

communication interface 103a, preferably operating at low frequencies. The data mentioned in the context of reference sign 813 can be send using the antenna array 101 a at high frequencies.

For the exemplary look-up table 109a shown in figure 5, B bits are needed for the exchange of BF information between the communicating nodes 100a, 100b, wherein

B = |^~log₂ (£ N)]

In response to the reception of a control signal with the BF information of master node 100a at slave node 100b (reference sign 901 of figure 9), the slave node 100b can enter the SR stage and follow the set of actions shown in figure 9. Initially, the slave node 100b obtains its current position/displacement information from its one or more

instruments/sensors (reference sign 903 of figure 9) and finds the preplaced

position/displacement available in its look-up table, which is closest to its current position/displacement (e.g. using the Euclidean distance measure). In addition, node 100b can utilize the position/displacement information received from master node 100a to find the preplaced position/displacement available in its look-up table that is closest to the current position of node 100a. These preplaced positions/displacements for both nodes 100a, 100b are used together with the information for the predefined beam directivity pattern selected by master node 100a in order for slave node 100b to search in the lookup table for a predefined beam directivity pattern yielding g_t≥y_t (reference sign 905 of figure 9). If such a predefined beam directivity pattern exists, i.e. if acceptable level of beam alignment has been achieved, the slave node 100b utilizes it to send data to the master node 100a (reference signs 909 and 91 1 of figure 9). Otherwise, the slave node 101 b makes use of the position/displacement information received from the master node 100a to design the optimum beam directivity pattern steering to it (reference sign 913 of figure 9). If the utilization of this optimized beam directivity pattern by the slave node 100b results in g_t≥ _h, this beam directivity pattern is used to send data to the master node 100a (reference signs 915 and 919 of figure 9). In addition, this optimized beam directivity pattern together with the position/displacement information of the slave node 100b and the value g_t is stored in the look-up table in order to enrich/update the look-up table of node 100b and is also sent to the master node 100a for the same purpose (reference sign 917 of figure 9). In an embodiment, this information can be send using the communication interface 103a operating at lower frequencies to ensure a reliable exchange. In an alternative embodiment, however, this information can be send using the antenna array 101 a operating at higher frequencies, because g_t≥¼_h- If the utilization of the optimized beam directivity pattern by the slave node 100b still yields g_t< _h, the slave node 100b can still utilize this beam directivity pattern to send data to the master node 100a as well as the optimum beam directivity pattern information together the position/displacement information of slave node 100b (reference signs 915 and 919 of figure 9). In this case, since g_t<y_t , the BF information is preferably send using the communication interface 103a operating at lower frequencies. In an embodiment, the BF information can be sent without the value g_t or can include a predefined value, e.g. "0", used for this case.

In an embodiment, at the beginning of the MR2 stage the master node 100a receives data and BF information from the slave node 100b, such as the optimal beam directivity pattern as well as position/displacement information of node 100b. This BF information can include the g_t value measured from node 100b. In the case that this value is included, this means that an acceptable level of beam alignment has been achieved in the SR stage. The action followed by master node 100a within the MR2 stage, when an acceptable level of beam alignment has been achieved in the SR stage, is shown in figure 10. In this embodiment, master node 100a proceeds with decoding the data received from the slave node 100b (reference sign 1001 of figure 10) and keeps the BF information received from slave node 100b together with its BF information from the MR1 stage shown in figure 8, such as the selected predefined beam directivity pattern, the value g_t and position/displacement information of the node 100a, to enrich/update its lookup table 109a.

Figure 1 1 shows the steps followed by the master node 100a within the MR2 stage according to an embodiment, when the g_t value measured from node 100b is not received (or the value for this is a predefined one, e.g. 0). First, the master node 100a utilizes the position/displacement information received from slave node 100b to design the optimum beam directivity pattern steering to it (reference signs 1 101 and 1 103 of figure 1 1 ). Then, node 100a measures g_t for this beam (reference sign 1 105 of figure 1 1 ). Then, the master node 100a makes use of this optimum BF pattern together with its position/displacement information and the previously measured g_t as well as the received BF information for slave node 100b in order to enrich/update its look-up table 109a (reference sign 1 107 of figure 1 1 ). Then, the master node 100a uses the optimum beam directivity pattern steering to slave node 100b to send data to the slave node 100b (reference sign 1 109 of figure 1 1 ), including information about the optimum beam directivity pattern determined by the master node 100a., the value g_t and position/displacement information of master node 100a, in order for slave node 100b to enrich/update its look-up table. In case node 100a has not moved from its previous position, i.e. its position in the MR1 stage, information about its unchanged position does not have to be sent in step 1 109 of figure 1 1 once more to node 100b.

The signaling that takes place within the aforementioned stages implemented in a communication apparatus and/or a method for beam alignment according to an embodiment is shown in figures 12 to 15. Figure 12 illustrates the signaling between master node 100a and slave node 100b according to an embodiment when an acceptable level of beam alignment is achieved requiring only the actions within the MR1 stage 1201 at master node 100a. Figure 13 illustrates the signaling when an acceptable level of beam alignment is achieved with the actions within the MR1 stage 1301 at the master node 100a and the SR stage 1303 at the slave node 100b. Figure 13 refers to the case where after the MR1 stage 1301 the available information in the look-up table of slave node 100b is used in the SR stage 1303 and results in an acceptable level of beam alignment. For the cases where slave node 100b utilizes the position/displacement of master node 100a to design the optimum beam directivity pattern steering to it, the signaling that takes place within the MR1 stage 1401 and the SR stage 1403 is shown in figure 14. Finally, figure 15 depicts the signaling when an acceptable level of beam alignment is achieved with the actions of all three stages, namely the MR1 stage 1501 , the SR stage 1503 and the MR2 stage 1505. Contrary to the SR stage 1403 in figure 14, in the SR stage 1503 of figure 15 the g_t value is not sent. Rather in the MR2 stage 1505 of figure 15 the g_t value and the optimal beam directivity pattern for the master node 100a are sent to the slave node 100b.

Embodiments of the invention provide amongst others the following advantages in dealing with beam misalignment in high-frequency wireless communication networks operating in a wireless environment with a LOS component.

According to embodiments of the invention beam alignment between communicating multi-antenna network nodes 100a, 100b can be achieved in at most three control communication stages. The performance level of beam alignment will depend on the LOS conditions of the wireless communication channel between any two communicating network nodes 100a, 100b. According to the embodiments of the invention, the more dominant the LOS component is, the closer the performance of the invention can be to the optimum BF. In this context, it should be mentioned that an optimum BF requires perfect channel state information at both communicating nodes 100a, 100b and according to this the nodes utilize the dominant left and right singular vectors of the channel matrix.

According to embodiments of the invention, each control communication signal exchanged by the communicating nodes 100a, 100b includes BF information, such as information about the utilized beam directivity pattern and coordinates of the node 100a, 100b and/or its antenna array 101 a, 101 b of one of the communicating nodes 100a, 100b.

Embodiments of the invention do not require channel estimation by any of the

communicating multi-antenna network nodes 100a, 100b. Thus, according to

embodiments of the invention channel estimation techniques for high-frequency wireless communication systems employing antenna arrays with much less radio-frequency chains than antenna elements, e.g. large-sized phased-arrays with few or even one radio- frequency chains, and requiring a large number of training symbols are avoided.

The complexity of the mode of operation for beam alignment according to embodiments of the invention deriving from the exchange of BF information, such as utilized beam directivity pattern and position/displacement of the node 100a, 100b and/or its antenna array 101 a, 101 b, between the network nodes 100a, 100b is low, since at most three control communication stages are utilized.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms "coupled" and "connected", along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other. Although specific aspects have been illustrated and described herein, it will be

appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein. Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence. Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A communication apparatus (100a) configured to communicate with another communication apparatus (100b), wherein the communication apparatus comprises: an antenna array (101 a) configured to define a beam directivity pattern for communicating with an antenna array (101 b) of the other communication apparatus (100b), wherein the antenna array (101 a) is configured to adjust the beam directivity pattern on the basis of information about the position of the antenna array (101 a) of the communication apparatus (100a) and/or information about the position of the antenna array (101 b) of the other communication apparatus (100b).

2. The communication apparatus (100a) of claim 1 , wherein the information about the position of the antenna array (101 b) of the other communication apparatus (100b) is based on an estimate of the position of the antenna array (101 b) of the other

communication apparatus (100b) computed by the communication apparatus (100a) or on data defining the position of the antenna array (101 b) of the other communication apparatus (101 b) provided by the other communication apparatus (101 b).

3. The communication apparatus (100a) of claims 1 or 2, wherein the antenna array (101 a) is configured to adjust the beam directivity pattern on the basis of information provided by a control entity in communication with the communication apparatus (101 a), wherein the control entity is configured to select a beam directivity pattern for the antenna array (101 a) of the communication apparatus (100a) and a beam directivity pattern for the antenna array (101 b) of the other communication apparatus (100b) on the basis of the information about the position of the antenna array (101 a) of the communication apparatus (100a) and/or the information about the position of the antenna array (101 b) of the other communication apparatus (100b).

4. The communication apparatus of any one of the preceding claims, wherein the communication apparatus (100a) further comprises a position sensor (102a) configured to provide the information about the position of the antenna array (101 a) of the

communication apparatus (100a).

5. The communication apparatus (100a) of any one of the preceding claims, wherein the communication apparatus (100a) further comprises a communication interface (103a) configured to transmit the information about the position of the antenna array (101 a) of the communication apparatus (100a) to the other communication apparatus (100b) and to receive from the other communication apparatus (100b) the information about the position of the antenna array (101 b) of the other communication apparatus (100b).

6. The communication apparatus (100a) of any one of the preceding claims, wherein the communication apparatus (100a) further comprises an estimator (105a) configured to estimate a quality measure of the communication channel defined by the beam directivity pattern of the antenna array (101 a) of the communication apparatus (100a) and the beam directivity pattern of the antenna array (101 b) of the other communication apparatus

(100b) and wherein the antenna array (101 a) is configured to adjust the beam directivity pattern of the antenna array (101 a) of the communication apparatus (100a) in case the quality measure of the communication channel is smaller than a first quality measure threshold.

7. The communication apparatus (100a) of any one of the preceding claims, wherein the communication apparatus (100a) further comprises a selector (107a) configured to select the beam directivity pattern on the basis of the information about the position of the antenna array (101 a) of the communication apparatus (101 a) and/or the information about the position of the antenna array (101 b) of the other communication apparatus (100b).

8. The communication apparatus (100a) of claim 7, wherein the selector (107a) is configured to select the beam directivity pattern from a database (109a), wherein the database (109a) contains a quality measure of the communication channel defined by the beam directivity pattern of the antenna array (101 a) of the communication apparatus (100a) and the beam directivity pattern of the antenna array (101 b) of the other communication apparatus (100b) for a plurality of beam directivity patterns defined for a plurality of different positions of the antenna array (101 a) of the communication apparatus (100a) and a plurality of different positions of the antenna array (101 b) of the other communication apparatus (100b).

9. The communication apparatus (100a) of claim 8, wherein the selector (107a) is configured to select the beam directivity pattern from the database (109a) by selecting the beam directivity pattern from those beam directivity patterns in the database (109a), which are defined for a position of the antenna array (101 a) of the communication apparatus (100a) being closest to a current position of the antenna array (101 a) of the communication apparatus (100a).

10. The communication apparatus (100a) of claims 8 or 9, wherein the selector (107a) is configured to select the beam directivity pattern from those beam directivity patterns in the database (109a), which are associated with a quality measure of the communication channel being larger than a second quality measure threshold.

1 1. The communication apparatus (100a) of claim 10, wherein the communication apparatus (100a) is configured to transmit the information about the position of the antenna array (101 a) of the communication apparatus (100a) and information about the selected beam directivity pattern to the other communication apparatus (100b), if the quality measure of the communication channel is lower than the second quality measure threshold, using the beam directivity pattern from the database (109a), which provides the largest quality measure of the communication channel for a current position of the antenna array (101 a) of the communication apparatus (100a).

12. The communication apparatus (100a) of claim 8, wherein the communication apparatus (100a) is configured to receive from the other communication apparatus (100b) the information about the position of the antenna array (101 b) of the other communication apparatus (100b) and information about the beam directivity pattern selected by the other communication apparatus (100b) and wherein the selector (107a) is configured to select a beam directivity pattern from the database (109a) on the basis of the information about the position of the antenna array (101 b) of the other communication apparatus (100b) and the information about the beam directivity pattern selected by the other communication apparatus (100b).

13. The communication apparatus (100a) of claim 12, wherein the selector (107a) is configured to select the beam directivity pattern by selecting the beam directivity pattern from those beam directivity patterns in the database (109a), which are defined for a position of the antenna array (101 a) of the communication apparatus (100a) being closest to the current position of the antenna array (101 a) of the communication apparatus (100a) and which are associated with a quality measure of the communication channel being larger than a third quality measure threshold.

14. A method (200) of operating a communication apparatus (100a) configured to communicate with another communication apparatus (100b) using an antenna array (101 a) configured to define a beam directivity pattern for communicating with the antenna array (101 b) of the other communication apparatus (100b), wherein the method (200) comprises the step of: adjusting (203) the beam directivity pattern on the basis of information about the position of the antenna array (101 a) of the communication apparatus (100a) and/or information about the position of the antenna array (101 b) of the other communication apparatus (100b).

15. A computer program comprising program code for performing the method (200) of claim 14 when executed on a computer.