KR20140098917A - Beam forming method and apparatus using hybrid multi antenna in mu-mimo communication system - Google Patents

Beam forming method and apparatus using hybrid multi antenna in mu-mimo communication system Download PDF

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KR20140098917A
KR20140098917A KR1020130010977A KR20130010977A KR20140098917A KR 20140098917 A KR20140098917 A KR 20140098917A KR 1020130010977 A KR1020130010977 A KR 1020130010977A KR 20130010977 A KR20130010977 A KR 20130010977A KR 20140098917 A KR20140098917 A KR 20140098917A
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South Korea
Prior art keywords
beamforming
analog
digital
user
vector
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KR1020130010977A
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Korean (ko)
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김광순
황해광
권중형
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연세대학교 산학협력단
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0417—Feedback systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/12—Wireless traffic scheduling
    • H04W72/121—Wireless traffic scheduling for groups of terminals or users

Abstract

When a base station in a multiple input / output communication system uses an analog beamforming group composed of multiple antennas and a digital beamforming group for analog beamformed signals, a hybrid beamforming antenna for performing beamforming in two stages A method and apparatus for determining an analog beamforming vector. By using analog beamforming and digital beamforming together, hybrid beamforming antennas can benefit from complexity over performance using only digital beamforming, rather than using only analog beamforming. The gain obtained from the digital beamforming stage is affected by the analog beamforming. In the present invention, when only the average beam direction and the statistical characteristic of each spread of the channel are used in the analog stage, To a method and apparatus for determining a multi-user analog beamforming vector.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a multi-user beamforming method and apparatus using a hybrid multi-antenna in a multi-user multiple input multiple output (MU-MIMO) communication system,

The present invention relates to a method and apparatus for determining an analog beamforming vector when a base station uses a hybrid antenna structure composed of analog beamforming and digital beamforming in a multiple input multiple output communication system, User analog beamforming from the viewpoint of the average capacity (ergodic capacity) obtained from the digital beamforming stage when only the statistical characteristics of the beam direction and each spread for each user can be known at the analog beamforming end of the base station Vector allocation method and apparatus thereof.

The beamforming technique using multiple antennas has a high data rate and a high transmission rate depending on the number of antennas of a transmitting end and a receiving end compared to a mobile communication system using a single antenna from an array gain, a diversity gain, a multiplexing gain, It is known to be able to obtain received signal quality and has been adopted in various standard specifications such as 3GPP long-term-evolution (LTE), IEEE 802.11n, and WiBro. The next-generation communication standard, which is currently being standardized, aims to increase the frequency efficiency by using more antennas to support higher data rates.

The beamforming technique using multiple antennas can be classified into an analog beamforming and a digital beamforming according to a position at which a beamforming weight vector is applied. In the analog beamforming, a beamforming weight vector is supplied to a signal received from each antenna through a phase shifter And then sends the signal to the baseband through the A / D converter. Analog beamforming has the advantage of low complexity because it uses a small number of A / D converters compared to the number of antennas. However, since the added signal from each antenna is visible in the baseband, it is difficult to find the optimal beam direction Performance degradation occurs. In the digital beamforming, one A / D converter is connected to each antenna, and the digital signal is transmitted to the baseband, thereby performing the digital signal processing. Therefore, the performance can be higher than that of the analog beamforming, but the complexity is increased. As the number of antennas increases, the advantages and disadvantages of both analog beamforming and digital beamforming become larger, resulting in a problem of selection between performance and complexity. Hybrid multi-antennas can improve performance rather than using only analog beamforming by performing analog beamforming and digital beamforming sequentially, and can lower complexity than using only digital beamforming. In addition, since the hybrid multi-antenna structure has a structure in which a plurality of antennas are connected to one antenna port (digital channel) in a commercialization system such as LTE, the conventional antenna structure and beam-forming technique can be utilized.

Because the hybrid multi-antenna architecture performs additional beamforming at the digital stage, the beamforming results at the analog stage affect the overall performance. In order to obtain higher beamforming performance, when the number of conventional antennas is small, the base station transmits a reference signal for channel measurement, and the user estimates the channel using the reference signal and transmits the result to the base station. As the number of the antennas increases, the transmission efficiency due to the channel feedback decreases, and the directivity of the beam formed in a fast fading environment in which the direction of the beam changes due to the mobility of the user increases the efficiency.

Therefore, in order to obtain beamforming gain as the number of antennas constituting each digital stage increases in a mobile communication environment using a hybrid multi-antenna, a multi-user beamforming method considering a change in beam direction between a base station and a user due to user mobility There is a need for a vector allocation device.

The present invention takes into account the statistical properties of the beam direction for each user of a base station and a scheduled user group when the base station has a hybrid antenna structure consisting of analog beamforming and digital beamforming stages in a multiple input / A method for allocating a multi-user beamforming vector to a case where an error exists in a beam directionality predicted by a base station and an actual beam directionality.

According to an aspect of the present invention, there is provided an apparatus for estimating a beam direction and a spread for each user in a base station having hybrid multiple antennas, an estimated beam direction and a spatial correlation A beam vector determiner for determining an analog beam beamforming vector for each digital channel for maximizing an average transmission capacity using a spatial correlation for a part for calculating a relation and a scheduled user group, And a beamformer for applying a beamforming signal to a signal received from the RF unit.

Hybrid multi-antennas connect multiple antennas that can give different amplitude gain and phase gain to one digital channel when there are more antennas than the maximum number of digital streams. And transmits signals received through a plurality of antennas to different amplitudes and phase gains to be connected to one digital stream.

The beamformer applies a signal received from users to each digital channel to form a beam and transmits the beam to a baseband digital channel.

The beam vector determiner uses an average transmission capacity for a scheduled user group as a beamforming vector decision matrix for each user.

The beam vector determiner periodically updates an uplink analog weight to be used for a scheduled user group through a received signal from the UEs. Upon downlink, the beam vector determiner reflects a calibration signal based on the analog weight of the uplink, hardware error, To update the analog weights to use.

In order to maximize the lower bound of the average transmission capacity of the scheduled user group, the beam vector determiner determines an analog beamforming vector corresponding to the first digital channel as an average beam direction and an analog beamforming vector corresponding to the remaining digital channels And sequentially predicts the lower bound of the average transmission capacity from this.

The beam vector determiner determines that the lower bound of the average transmission capacity predicted for the scheduled user group is equal to or greater than the reference transmission power of each digital channel The analog beamforming vector values are repeatedly determined using the analog beamforming vector values of the analog beamforming vector values.

As described above, according to the present invention, although the accurate beam directionality between the base station and each user can not be known at every moment, the longer the time of maintaining the statistical characteristics of the channel between the base station and the user, Lt; RTI ID = 0.0 > a < / RTI >

FIG. 1 illustrates an example of a multi-antenna beamforming apparatus using a hybrid multiple antenna according to an embodiment of the present invention.
Figure 2 illustrates operation within an analog beamformer according to an example of the present invention.
FIG. 3 illustrates an operation flow in the hybrid beamforming controller according to an exemplary embodiment of the present invention.

FIG. 1 illustrates an example of a multi-antenna beamforming apparatus using a hybrid multiple antenna according to an embodiment of the present invention. The hybrid multiple antennas include an analog beamformer capable of adjusting amplitude and phase with respect to an antenna group composed of a plurality of antennas independently performing analog beamforming with respect to an antenna port and a digital beamformer performing digital beamforming with respect to each antenna port, And a forming unit.

In one embodiment of the present invention, a received signal that passes through an analog beamformer in an uplink transmission environment and is visible at each antenna port can be expressed by Equation (1).

Figure pat00001

In Equation (1)

Figure pat00002
Is a signal component that reflects the analog beamforming seen at the mth antenna port
Figure pat00003
Is a channel value as seen from the antennas corresponding to the m < th > antenna port of the channel between the k < th > user and the base station
Figure pat00004
Is an analog beamforming vector value reflected to the antennas corresponding to the m-th antenna port.
Figure pat00005
Is the signal transmitted by the k-th user to the base station
Figure pat00006
Is the noise seen at the mth antenna port. The signals received at an arbitrary mth antenna port are respectively regarded as the sum of the signals reflected from the user and the channel values reflected from the antenna connected to the mth antenna port. The signals received at the respective antenna ports pass through the digital beamformer and are separated into respective user signals.

The beam searcher is a device for searching the beam direction between the user and the base station. The result of the beam searcher is transmitted to the hybrid beamforming controller and is reflected when the analog beamforming vector corresponding to each antenna port is determined in the analog beamformer.

The hybrid beamforming controller finds spatial correlation characteristics between the user and the base station from the results of the beam searcher and determines an analog beamforming vector to be used in each antenna port from a given performance prediction metric.

Figure 2 illustrates operation within an analog beamformer according to an example of the present invention. The analog beamforming vector value determined by the analog beamforming vector determination unit of the hybrid beamforming controller is transmitted to the analog beamforming vector control unit for each port in the analog beamformer, and the port-based analog beamforming vector control unit After adjusting the gain and phase of the received signal, the signal is converted into a digital signal through an A / D converter and transmitted to the corresponding antenna port.

FIG. 3 illustrates an operation flow in the hybrid beamforming controller according to an exemplary embodiment of the present invention. The beam searcher connected to the antennas transmits the beam search information to the user channel characteristic estimator. The user channel characteristic estimator estimates channel characteristics such as spatial channel correlation between the base station and the user and stores the channel characteristics in the user channel specific storage unit for each user. The estimated user channel characteristics are updated within the channel correlation time (Coherence time) between the base station and the user to reflect recent channel conditions.

The performance metric prediction unit is an apparatus that determines an analog beamforming vector value for each antenna port according to a predetermined criterion. In an exemplary embodiment of the present invention, the average capacity may be used as a performance prediction metric. When the average capacity is used as a performance prediction metric, an analog beamforming vector value for each antenna port can be obtained from Equation (2).

Figure pat00007

In Equation 2,

Figure pat00008
Is the sum of the power values used by each user
Figure pat00009
Is the number of antenna ports
Figure pat00010
Is the dispersion of the complex white Gaussian noise seen at each antenna port. Equation 2 is to determine each analog beamforming vector in a direction that maximizes the average capacity (Ergodic capacity) that can be obtained at the digital stage when the analog beamforming vector corresponding to each antenna port is reflected in the received signal. In order to determine an analog beamforming vector satisfying Equation (2), an analog beamforming vector corresponding to each antenna port changes according to a channel value at every moment. Therefore, Jensen's inequality is used to calculate a lower bound of Equation 3 as a performance metric.

Figure pat00011

In the performance metric of Equation (3)

Figure pat00012
Is defined as the spatial correlation matrix of the channel seen in the digital beamformer through the analog beamformer.

Figure pat00013

In Equation 4,

Figure pat00014
Is a correlation matrix between the channel seen from the antennas connected to the a < th > antenna port and the channel seen from the antennas connected to the b < th > As an example of the present invention, finding an analog beamforming vector per antenna port satisfying Equation (2) from equations (3) and (4) which are lower boundaries can be found by a Nash equilibrium method. Assuming a high signal-to-noise ratio, the equation for the analog beamforming vector corresponding to the m-th antenna port in the determinant of Equation (3) can be summarized as Equation (5).

Figure pat00015

The analog beamforming vector determined by repeating the process of finding the analog beamforming vector corresponding to each antenna port using Equation (5) is stored in the analog beamforming vector storage unit.

The analog beamforming vector determination unit finds an analog beamforming vector for each antenna port stored in the analog beamforming vector storage unit according to the user group determined by the multiuser scheduler and transmits the analog beamforming vector to the analog beamforming vector control unit for each port of the analog beamformer. According to an exemplary embodiment of the present invention, a user group may include both a group of users operating according to a predetermined user group by the scheduler or a group of users according to another exemplary embodiment of the present invention. According to embodiments of the present invention, if an analog beamforming vector is determined according to a user group, the result can be stored in an analog beamforming vector storage unit.

According to an embodiment of the present invention, the determined analog beamforming vector continuously updates the correlation matrix of the channel based on the signal received in the uplink in the case of the uplink state, and uses the correlation matrix of the updated channel to calculate the analog beamforming weight It can be continuously updated. In the downlink situation, the analog beamforming vector determined in the uplink can be used according to the user group. According to another example of the present invention, the calibration signal by the analog beamforming vector used in the uplink, hardware error, Feedback can be used to determine the analog beamforming vector to use for the downlink.

Claims (4)

CLAIMS What is claimed is: 1. A method for determining a beamforming vector for a base station using a hybrid multiple antenna configured with an analog beamforming stage and a digital beamforming stage and a plurality of users using at least one antenna,
Obtaining statistical information on the beam direction for the base station and each of the plurality of users;
Generating a correlation matrix of channels for each user;
Determining a beamforming vector of antennas connected to each digital channel of a hybrid multiple antenna that satisfies a performance prediction metric for a plurality of scheduled users;
User beamforming method. The method according to claim 1,
Wherein a beamforming vector of an antenna coupled to each digital channel of the hybrid multiple antenna is determined from channel correlation matrices between each user and a base station of a plurality of scheduled users. The method according to claim 1,
Wherein the performance is a metric of the performance at a digital stage in which a beamforming vector of an analog end of a hybrid multiple antenna is reflected as a performance prediction metric. The method according to claim 1,
Wherein the beamforming vector is determined by reflecting the characteristics of the beamforming vectors at the digital stage in determining the beamforming vector at the analog stage.
KR1020130010977A 2013-01-31 2013-01-31 Beam forming method and apparatus using hybrid multi antenna in mu-mimo communication system KR20140098917A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114039636A (en) * 2021-09-30 2022-02-11 华为技术有限公司 Network device, beam forming method and wireless communication system
CN114039636B (en) * 2021-09-30 2024-05-17 华为技术有限公司 Network device, beam forming method and wireless communication system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114039636A (en) * 2021-09-30 2022-02-11 华为技术有限公司 Network device, beam forming method and wireless communication system
CN114039636B (en) * 2021-09-30 2024-05-17 华为技术有限公司 Network device, beam forming method and wireless communication system

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