WO2018190495A1

WO2018190495A1 - Weight determining method for antenna beamforming and weight determining device for beamforming

Info

Publication number: WO2018190495A1
Application number: PCT/KR2018/000381
Authority: WO
Inventors: 조동호; 성락주; 김윤식; 박대희; 노상미
Original assignee: 한국과학기술원
Priority date: 2017-04-14
Filing date: 2018-01-09
Publication date: 2018-10-18
Also published as: KR101894240B1

Abstract

A weight determining method for antenna beamforming comprises the steps in which: a computer device defines an initial beam for a specific antenna by applying a plurality of weights randomly selected from a set of previously configured weights, and determines a first difference of a side-lobe between the initial beam and a target beam that the specific antenna aims to generate; the computer device defines a new beam for the specific antenna by applying a plurality of new weights selected from among the previously unselected weights in the set of weights, if the first difference is equal to or greater than a threshold value, and determines a second difference of a side-lobe between the new beam and target beam; and the computer device determines the finally-selected plurality of weights as the final weight. If the second difference is equal to or greater than the threshold value, the computer device repeats the step of determining the second difference.

Description

Weight determination method for antenna beamforming and weight determination device for beamforming

The technique described below relates to a weight determination technique for beamforming.

Conventional mobile communication has performed communication using resources such as time, frequency, code, and space. Recently, a beam division multiple access technique has emerged. Beam splitting multiple access is basically a method of using each beam as a different resource by using a plurality of beams.

Interference between antennas may be a problem when performing beamforming using a plurality of antennas. The prior art corrects the radiation pattern for each antenna port to which the antenna interference is applied to an ideal radiation pattern when the interference is not applied.

The prior art has realized an ideal radiation pattern through a correction matrix. The correction matrix can be determined using the least-square method. However, when the radiation pattern is restored by using the least square method, it is difficult to restore the exact radiation pattern, which makes it difficult to reduce the influence of mutual interference between antennas. Furthermore, the prior art assumes a linearly arranged single polarized antenna structure, which is difficult to apply to a pattern / polarized antenna having a two-dimensional shape.

The technique described below is intended to provide a technique for determining weights for generating a desired beam shape.

In the weight determination method for antenna beamforming, a computer apparatus defines an initial beam for a specific antenna by applying a plurality of weights arbitrarily selected from a preset weight set, and between the target beam and the initial beam that the specific antenna intends to generate. Determining a first difference in a side-lobe of the specific antenna by applying a plurality of new weights selected from weights not selected in the weight set when the first difference is greater than or equal to a threshold Defining a new beam for, determining a second difference in side lobe between the target beam and the new beam, and determining, by the computer apparatus, a final weight of the plurality of finally selected weights. If the second difference is greater than or equal to the threshold, the computer device repeats the step of determining the second difference, and the initial beam and the new beam are defined using a radiation pattern that takes into account interference between a plurality of antennas.

The apparatus for determining weight for beamforming may include a storage device for storing a weight set including a plurality of weights for a specific antenna, a beam formed by the specific antenna by applying a plurality of weights selected from the weight sets, and the definition. And a computing device for determining a weight for the specific antenna based on a side-lobe difference between the beam and the target beam. If the difference is greater than or equal to the threshold, the operation unit repeats the step of determining the side lobe difference between the new beam and the target beam defined by applying a plurality of new weights selected from the weights not selected in the weight set, and finally The plurality of weights selected as are determined as final weights. The initial beam and the new beam are defined using a radiation pattern that takes into account interference between a plurality of antennas.

The technique described below determines the optimal weight for the antenna by repeatedly selecting suitable weights from the weight set. Furthermore, the technique described below is also applicable to an antenna having a two-dimensional shape.

1 shows an example of a BDMA system.

2 is an example illustrating the concept of a pattern / polarized BDMA system.

3 is an example of a weight determination apparatus for beamforming.

4 is an example of a flowchart for a weight determination method for beamforming.

5 is another example of a flowchart of a method for determining a weight for beamforming.

6 is a graph illustrating an effect of performing beamforming by applying weights.

The following description may be made in various ways and have a variety of embodiments, specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the technology described below to specific embodiments, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the technology described below.

The terms first, second, A, B, etc. may be used to describe various components, but the components are not limited by the terms, but merely for distinguishing one component from other components. Only used as For example, the first component may be referred to as the second component, and similarly, the second component may be referred to as the first component without departing from the scope of the technology described below. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

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 to be understood that the present invention means that there is a part or a combination thereof, and does not exclude the presence or addition possibility of one or more other features or numbers, step operation components, parts or combinations thereof.

Prior to the detailed description of the drawings, it is to be clear that the division of the components in the present specification is only divided by the main function of each component. That is, two or more components to be described below may be combined into one component, or one component may be provided divided into two or more for each function. Each of the components to be described below may additionally perform some or all of the functions of other components in addition to the main functions of the components, and some of the main functions of each of the components are different. Of course, it may be carried out exclusively by.

In addition, in carrying out the method or operation method, each process constituting the method may occur differently from the stated order unless the context clearly indicates a specific order. That is, each process may occur in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

The technique described below is a technique for removing interference between antennas in a communication system that performs communication using a plurality of beams. The technique described below is a technique for reducing the interference between adjacent beams by constantly adjusting the beam pattern. The technique described below can be applied to a system using a plurality of antennas. The technique described below may be applied to a beam division multiple access (BDMA) system. Furthermore, the technique described below can be applied to a BDMA system (hereinafter referred to as a pattern / polarized BDMA system) using a pattern / polarized antenna.

First, the BDMA system will be described. 1 shows an example of a BDMA system. BDMA system means a wireless communication system based on BDMA technology. In the BDMA system, the AP device 10 transmits beams to the terminals 5 at different angles (directions), respectively, and simultaneously transmits data to several terminals 5 (downlink). It is assumed that the AP device 10 knows the position of the terminal 5 in advance. The AP device 10 may use an antenna capable of changing the direction of the beam or beamforming a predetermined area.

Similarly, when the terminal 5 sends data to the base station, the terminal 5 transmits a beam directed to the AP device 10. One terminal does not dedicate one beam, and terminals at similar angles may communicate with the base station by sharing one beam. For example, in FIG. 1, Beam 2 becomes a channel through which three terminals and the AP device 10 communicate. In this case, it is preferable that terminals sharing one beam share frequency / time resources.

The AP device 10 includes a device such as a base station of mobile communication. For example, the AP device 10 includes a base station constituting a macro cell of mobile communication, an AP device constituting a small cell of mobile communication, an AP device of WiFi, and an AP device for short range communication such as ZigBee. It is a concept. In the following description, the AP device 10 refers to a device that communicates with the terminal 5 using a specific communication scheme. The AP device 10 may perform a function of connecting the core network and the terminal 5. For convenience of explanation, it is assumed that the AP device 10 is a base station (nodeB, eNodeB, etc.) of a mobile communication network.

The terminal 5 includes various devices that perform wireless communication through the AP device 10. For example, the terminal 5 includes a smartphone, a tablet PC, a notebook computer, a wearable device, and the like. The terminal 5 is basically carried by the user and has mobility. Alternatively, the terminal 5 may be attached to a moving device (vehicle, etc.) to have mobility. For convenience of explanation, it is assumed that the terminal 5 is a portable device such as a smart phone possessed by a user.

2 is an example illustrating the concept of a pattern / polarized BDMA system. Pattern / polarized BDMA system means a wireless communication system based on pattern / polarized BDMA technology. Pattern / polarization BDMA uses different beams for at least one of a pattern and polarization. In this way, pattern / polarized BDMA additionally imparts pattern and / or polarization diversity.

Hereinafter, the pattern antenna refers to an antenna device in which a plurality of antenna elements having a predetermined pattern are constantly arranged. Here, the pattern means a radiation pattern. The plurality of antenna apparatuses may generate different radiation patterns using differences in the types and / or arrangement of antenna elements. The polarized antenna means an antenna device in which antenna elements having a constant polarization pattern are constantly arranged. As described above, the polarized antenna refers to an antenna that transmits signals that are distinguished from each other in an electric field and a magnetic field area by simultaneously using an electric field antenna and a magnetic field antenna. The pattern / polarized antenna means an antenna device using both a plurality of antenna elements having a constant pattern and an antenna element having a constant polarization pattern.

2 shows an example of a pattern / polarization antenna on top. As shown in FIG. 2, the pattern / polarization antenna 100 may be an antenna array. That is, the pattern / polarization antenna may include a plurality of unit patterns / polarization antennas. An antenna array composed of a plurality of unit pattern / polarization antennas is referred to as pattern / polarization antenna array 100 hereinafter. In FIG. 3, one unit pattern / polarization antenna 50 is represented by a dotted dotted line. One unit pattern / polarization antenna 50 includes a plurality of

antenna elements

51, 52, 53. 54. The plurality of

antenna elements

51, 52, 53. 54 may each have a different radiation pattern.

The pattern / polarization antenna array 100 may configure B beam sectors through beamforming. The pattern / polarization antenna array 100 spatially separates the beams into beamsectors using beamformers having unique weights for each sector, and uses the same pattern of polarization antennas for different AoDs. Can transmit beams. Through this, the pattern polarization antenna array may transmit a signal having a plurality of pattern / polarization characteristics simultaneously in each beam sector. Referring to FIG. 3, K different radiation patterns are simultaneously transmitted using K patterns / polarized antennas. That is, multiple-input multiple-output (MIMO) transmission is possible using a patterned polarization antenna array. If the terminal 5 uses one antenna, multiple-input single-output (MISO) transmission is possible.

A BDMA system using a pattern / polarized antenna is called a pattern / polarized BDMA system. In a pattern / polarized BDMA system, interference between multiple pattern / polarized signals constituting the same beam sector is previously removed by a precoder and then transmitted. The pattern / polarization BDMA system can simultaneously obtain the beamforming gain of the conventional BDMA system and the pattern polarization gain using the pattern / polarization antenna.

The antenna array shown in FIG. 2 includes a plurality of unit antennas. As mentioned above, each unit antenna includes a plurality of antenna elements. One unit antenna may form one beam. Furthermore, a plurality of unit antennas may cooperate to form one beam. The technique described below is to uniformly adjust the beams formed by the entire antenna device to exclude interference with each other.

The analog beamforming system includes a phase shifter, an attenuator and a power amplifier. Analog beamforming systems adjust phase and power values to form specific beams. A specific phase is generated by applying weights to the phase converter and the like. In a digital beamforming system, a controller for forming a beam constantly controls a digital beamformer to form a beam. This process also uses weights to determine the beam pattern. Eventually it may vary depending on the type of antenna, but certain weights are involved in the formation of the beam.

The technique described below determines weights required for each unit antenna to form a beam pattern. The technique described below may determine weights in which adjacent beams do not interfere with each other as much as possible. The technique described below determines weights that can form a beam pattern that is the same as or similar to the target beam pattern for a specific region.

3 is an example of a weight determination apparatus for beamforming. Weight determination apparatus for beamforming may be implemented in a variety of physical devices. The weight determination apparatus may vary from a computer apparatus 310, an AP apparatus 320, a separate apparatus 330 connected to a network, and the like. The process of determining the weight by each device will be described later.

3A shows an example in which the computer device 310 determines a weight. Computer device 310 may use a program that can simulate beamforming for a particular antenna. That is, the computer device 310 may receive a data and weight set for forming a beam in a specific antenna in advance, and determine a specific weight from the weight set. The finally determined weight may be delivered to the antenna device for actual beamforming.

3B illustrates an example in which the AP device 320 determines a weight. The AP device 320 may finally select a specific weight from the weight set. The AP device 320 applies the selected weight to the antenna to form a specific beam.

3C illustrates an example in which a device 330 connected to a network determines a weight. The device 330 connected to the network may be a control device or a gateway located in a mobile communication core network. The device 330 connected to the network may be a separate device that is wired or wirelessly connected to the AP device.

The device 330 connected to the network includes a storage device 331, a computing device 332, and a communication module 333. The storage device 331 stores a weight set, data and a program necessary for weight determination. The computing device 332 performs a weight determination process to be described later, and finally determines a specific weight. The communication module 333 may externally receive data necessary for the weight determination process. The communication module 333 may deliver the finally determined weight to the antenna device side.

The AP device 320 includes a storage device 321, a computing device 322, a beamforming circuit 323, and an antenna 324. The storage device 321 stores a weight set, data and a program necessary for weight determination. The computing device 322 performs a weight determination process to be described later, and finally determines a specific weight. The beamforming circuit 323 determines the finally determined weight and performs control on beamforming. The antenna 324 generates a beam according to control commands or data transmitted by the beamforming circuit 323.

Although not shown, the computer device 310 basically includes a storage device and a computing device. The storage device and the computing device perform the same operations as the same device described above.

Hereinafter, a process of determining the weight by the weight determination device will be described. A plurality of antennas form one beam. Assume that the entire antenna forms N beams. The total number of antennas is defined as N _t . The number of antennas forming one beam (i-th) is defined as N _i . In this case, N _t may be expressed as Equation 1 below.

The weight determination apparatus determines weights for at least one antenna forming one beam. The weight determining apparatus repeats a process of determining weights for one beam to determine weights for all N beams. For convenience of explanation, a description will be given based on a process of determining a weight of one beam.

4 is an example of a flowchart for a weight determination method 400 for beamforming. The weight determination apparatus first receives a beam pattern for antennas forming an i th beam (410). At this time, the input value is a beam pattern to be formed using specific antennas. This is called the target beam. The target beam may be called an optimal beam. The beam pattern may be defined as an elevation and azimuth with respect to a specific one side. The input value representing the beam pattern may be represented by a matrix having elements of (θ, Φ). The input values are represented by a matrix, and the elements of the matrix may be represented by E-field values of the beam corresponding to a specific high angle θ and azimuth angle Φ. Of course, the beam pattern may be defined as another value.

If the matrix is formed by the number of samples of s _ele and s _{azi in} the elevation (θ) and azimuth (Φ) directions, the input value B _des is

It is represented by the matrix of.

The weight determination apparatus prepares a weight set including a plurality of weights applicable to the antenna in advance. The weight set may include quantized weights. The weight set includes the values that each element can obtain in the case of an analog beamforming system. The weight set includes quantized values for the desired resolution in the case of a digital beamforming system. The weight controls beamforming for the beam. The weight may determine the position and shape of the beam.

The weight determination apparatus selects a weight that has not been selected yet from the weight set (420). If the weight determination apparatus selects a weight, the weight determination apparatus may define a beam pattern that can be formed by a specific antenna (420). The weight determination apparatus may simulate the beam pattern to which the selected weight is applied using a specific program. Alternatively, in some cases, the weight determination device may actually form a beam using a weight selected using the antenna device.

The weight determining apparatus may arbitrarily select the N _i weights w in the weight set in a redundant manner. The weight you choose

Forms the vector of.

The radiation pattern of the kth (k = 1, 2, ..., N _i ) antenna element reflecting the mutual interference between antennas obtained through measurement or simulation

Assume In a specific antenna device including a plurality of antennas, interference between antennas may occur. If interference occurs, the radiation pattern of the antenna element has a different pattern from that without interference. After all, Ek means a radiation pattern emitted by the k-th antenna element when interference between antennas occurs. In an interference situation, the radiation pattern of the antenna element can be identified through actual measurements or by simulation.

In this case, B generated using w may be defined as in Equation 2 below. B below means the beam in consideration of the interference between the antennas after all.

There is a specific area where a particular antenna forms a beam and is serviceable. The service area A _s that a specific antenna serves

Assume that At this time, the beam width A _BW of the desired beam pattern is

In this case, the area A _side corresponding to the side-lobe of the beam may be expressed as A _side = S-BW.

At this time, the portion of the side lobe of B smaller than B _des in the specific θ, Φ should not be considered. The side lobe of B is smaller than B _des

Assume that In this case, the difference e in the side lobe between the beam B generated by the weight w for the beam and the target beam may be expressed by Equation 3 below. The weight determination apparatus determines a difference e between the specific beam to which the selected weight is applied and the target beam using Equation 3 below (430).

The weight determination apparatus compares the difference e with a specific threshold ε 440. If the difference e is greater than the threshold ε, the currently selected weight may not be the optimal weight. The weight determination apparatus tries to determine a plurality of weights having a difference smaller than the threshold value ε. To this end, the weight determination apparatus selects another weight again from the weight set and repeatedly performs the process of comparing the difference e with the threshold value ε.

The weight determination apparatus selects a new weight that replaces the currently selected weight in the weighted set. The weight determination apparatus selects a new weight from among the weights not yet selected. A new weight is selected for each of the weights for each of the plurality of antennas. This process may be referred to as weight update.

The criteria for selecting a new weight may vary. (i) The weight determination apparatus may arbitrarily select a new weight. (ii) Alternatively, the weight determining apparatus may select any one of the weights having a specific relationship with the currently selected weight as the new weight. For example, the weight determining apparatus may select a specific weight nearest to the currently selected weight as a new weight. Each weight in the weight set may be identified by a specific location. If the weight set is represented by a constant matrix, the weight determination apparatus may determine a new weight based on the position in the matrix. The weight determination apparatus may select the nearest value in the horizontal direction, the vertical direction, or all directions as the new value in the weight set. In this case, when there are several nearest values, the weight determination device may select an arbitrary value.

The weight determination device determines the newly selected weight

Create Calculate the difference e 'in the side load portion between B' and B _des generated using w '. If e? E ', update to w = w', e = e ', B = B'. If not, the values of w, e and B do not change. This performance is repeated until e <ε. e <ε ends this execution at the moment and calculates w as the output value. The weight determination apparatus determines the finally selected beam as the final weight (450).

In addition, when the number of times of repeating the process of selecting the weight and comparing the difference between the side lobe and the threshold exceeds iter _max , the weight determination process may be terminated. In this case, the weight determination apparatus determines the finally selected beam as the final weight. 5 is an example in which the number of times of repeating the process of comparing the difference between the side lobes and the threshold is constantly limited.

5 is another example of a flowchart of a method 500 for determining a weight for beamforming. The weight determination apparatus first receives a beam pattern for antennas forming an i th beam (510). A variable is used to identify the number of repetitions in the process of comparing the side lobe difference and the threshold. "iter" represents the number of repetitions. For example, initial iter = 0. The weight determination apparatus selects a weight that has not yet been selected from the weight set, and defines a beam pattern that can be formed by applying the selected weight to a specific antenna (520). The weight determination apparatus determines a difference e between the specific beam to which the selected weight is applied and the target beam by using Equation 3 described above (530).

The weight determination apparatus checks whether the number of times iter comparing the difference between the current specific beam and the target beam is less than or equal to a preset threshold iter _max (540). iter _max If ≥ iter, the weight determination apparatus compares the difference e with a specific threshold ε (550). iter _max If it is <iter and e <ε, the weight determining apparatus determines the current finally selected beam as the final weight (560). iter _max When ≥ iter and e ≥ ε, the weight determination apparatus selects a new plurality of weights again, and repeats the process of comparing the difference between the beam defined by the selected weight and the target beam luxury.

Iter _{max on the} other If> iter the weight determination apparatus determines the current finally selected beam as the final weight (560).

The weight determination apparatus repeats a process of determining weights for all N beams. When the whole process is completed, the weight determination apparatus determines the weights for the N antennas. Assuming that the weight t for generating the i-th beam is w ⁱ , the weight w _final finally applied to the entire system may be expressed in the form of a block diagonal matrix as shown in Equation 4 below.

The weight determination apparatus delivers the finally determined weight w _final to the antenna apparatus. The antenna device performs beamforming by using w _final .

6 is a graph illustrating an effect of performing beamforming by applying weights. The simulation environment assumes a two-port integrated antenna array structure. In addition, it is assumed that the service providing area is -60 to 60 °, which is generally used in the 3-sector environment, and the beam direction is 40 ° in the azimuth direction. In FIG. 6, the target value represents the most ideal beam pattern when there is no interference between antennas as a desired beam pattern. The contrast scheme represents a beam pattern in the presence of interference between antennas. The proposed technique represents a beam pattern generated through the above-described weight determination process. As shown in FIG. 6, the proposed technique can be seen that the beam pattern is close to the desired target beam. The proposed scheme can reduce side lobes by up to 10 dB compared to the control scheme.

The embodiments and the drawings attached to this specification are merely to clearly show a part of the technical idea included in the above-described technology, and those skilled in the art can easily make it within the scope of the technical idea included in the description and the drawings of the above-described technology. It will be apparent that both the inferred modifications and the specific embodiments are included in the scope of the above-described technology.

Claims

The computer apparatus defines an initial beam for a specific antenna by applying a plurality of weights arbitrarily selected from a preset weight set, and determines a side-lobe between the target beam and the initial beam to be generated by the specific antenna. Determining a first difference;

If the first difference is greater than or equal to a threshold, the computer device defines a new beam for the particular antenna by applying a plurality of new weights selected from among the weights not selected in the weight set, and between the target beam and the new beam. Determining a second difference in the side lobes; And

Determining, by the computer device, a final weight of the finally selected plurality of weights,

Repeating the computer device determining the second difference when the second difference is greater than or equal to the threshold value, wherein the initial beam and the new beam are defined using a radiation pattern considering interference between a plurality of antennas Weight determination method for beamforming.
The method of claim 1,

And the weight set stores a plurality of weights according to a preset order, and the plurality of weights are identified at a predetermined position.
The method of claim 2,

In defining the new beam

And the computer apparatus determines the plurality of new weights by determining one of adjacent weights based on the position for each of the plurality of currently selected weights.
The method of claim 3,

And the computer apparatus determines a plurality of currently selected weights as the final weight when the second difference is greater than or equal to the threshold but the number of repetitions is greater than or equal to a reference value.
The method of claim 1,

The computer device is at least one of a device for performing beamforming, an antenna device for beamforming, a base station including an antenna device and a network device for transmitting information to the base station.
The method of claim 1,

And the computer device determines a difference between the side lobes based on a pattern of beams defined by elevation and azimuth.
The method of claim 1,

And the computer apparatus determines a difference from the target beam except for a portion smaller than the side lobe of the target beam in a side lobe region of the beam defined by applying a plurality of selected weights.
The method of claim 1,

And the weights determine the position and shape of the beams.
A storage device for storing a weight set including a plurality of weights for a specific antenna;

Define a beam formed by the specific antenna by applying a plurality of weights selected from the weight sets, and determine a weight for the specific antenna based on a side-lobe difference between the defined beam and the target beam. Including computing devices,

If the difference is greater than or equal to the threshold, the operation unit repeats the step of determining the side lobe difference between the new beam and the target beam defined by applying a plurality of new weights selected from the weights not selected in the weight set, and finally Determine a plurality of weights selected as final weights,

And the initial beam and the new beam are defined using a radiation pattern in consideration of interference between a plurality of antennas.
The method of claim 9,

And the weight set stores a plurality of weights according to a preset order, and the plurality of weights are identified at a predetermined position.
The method of claim 10,

And the computing device determines the plurality of new weights by determining one of adjacent weights based on the position for each of the plurality of currently selected weights.
The method of claim 9,

And the computing device determines a plurality of weights currently selected as the final weight when the difference is greater than or equal to the threshold but the number of repetitions is greater than or equal to a reference value.
The method of claim 9,

And the computing device determines a difference from the target beam except for a portion smaller than the side lobe of the target beam in the side lobe region of the beam defined by applying a plurality of selected weights.
The method of claim 9,

And a beamforming circuit for beamforming by applying the final weight.