KR101493615B1 - System for transmitting hybrid analog-digital beamformer - Google Patents

Abstract

The present invention relates to a hybrid analog-digital beamformer transmission system. According to an embodiment of the present invention, the hybrid analog-digital beamformer transmission system is used in a frequency selective channel in a multi-antenna array communications environment. The system includes: a TX digital baseband beamformer; a TX analog beamformer; an RX analog beamformer; and an RX digital baseband beamformer.

Description

[0001] The present invention relates to a hybrid analog-digital beamformer transmission system,

Field of the Invention [0002] The present invention relates to multi-antenna array communication, and more particularly, to effectively learning transmission beams and reception beams of an analog digital hybrid beam former in a channel having frequency-selective characteristics.

Beamforming technology has been used in mobile communication and wireless communication since the past. There is also a multiple-input multiple-output (MIMO) technique that has been studied and developed with great interest in recent mobile / wireless communications.

Both precoding and beamforming techniques of closed-loop MIMO have commonality in that they improve the performance by optimizing the shape of signals in the spatial domain using channel state information. However, a major difference between the two is that precoding of the closed loop MIMO is performed by digital signal processing in the baseband, and beamforming is performed by analog signal processing in the RF block. Thus, they are also referred to as digital beamforming and analog beamforming, respectively.

Therefore, a feature that shows a large difference between the two is that the closed root MIMO precoding can set different values for each subcarrier, that is, it can arbitrarily make beams of different shapes, Beamforming should be used to create a beam that applies equally to all subcarriers.

Closed-loop MIMO precoding, that is, digital beamforming, has better performance than analog beamforming, but has a disadvantage of high implementation complexity. Implementation of digital beamforming is constrained to achieve high capacity in a millimeter wave communication module that is expected to be implemented at a very small size. In recent years, it is difficult to implement a full beamforming function in a digital manner. Therefore, a hybrid analog / digital beamformer which implements a part in analog form and a part in digital form has been proposed .

Channels composed of multiple paths are often said to have frequency-selective properties. That is, there is a characteristic in which the signal gain value of the path from the transmitting antenna to the receiving antenna varies depending on the frequency. In such a channel, the optimum beamforming vector or matrix must be changed depending on the frequency. For reference, a beamforming vector is used for a single stream transmission, and a beamforming matrix is used for a multiple stream transmission.

However, if only analog beamforming is used, beamforming vectors or matrices can not be set to different values depending on the frequency. Thus, some of the digital beamforming techniques are included so that the beamforming vector or matrix values can be set differently depending on the frequency.

Beamforming In order to make the vector or matrix optimal at every frequency, the digital beamforming portion may become too large. Therefore, it is a major problem to be solved that a beamforming vector or a matrix can be optimally adapted to a frequency selective channel by making maximum use of a digital beamforming portion of a given size.

Although a solution for solving the above problem has been proposed, the conventional scheme has poor performance and has a limitation that only a single stream transmission is considered.

In a frequency selective channel environment, the optimal beamforming vector or matrix must be frequency dependent. However, an analog beamformer can not set different beamforming vectors or matrix values for different frequencies. Since the digital beamformer is processed in the baseband, different beamforming vectors or matrix values can be set for signals of different frequencies. However, if all of the beamforming processes are implemented in digital, the complexity of the implementation increases and the hardware becomes large.

Accordingly, a hybrid analog / digital beamformer that allows only a fraction of the digital beamformer is considered, such a hybrid analog / digital beamformer beamforming all frequency signals separately, You can not set a vector or matrix value. Therefore, there is a need to develop a learning algorithm that allows a hybrid analog / digital beamformer to optimally adapt to the frequency selectivity of a channel by taking full advantage of a given digital beamformer portion.

Korean Patent Publication No. 10-2009-0113124

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hybrid analogue digital beamformer system that maximally utilizes a given digital beamformer portion to optimally apply the hybrid analogue digital beamformer to frequency selectivity of a channel in a hybrid analogue digital beamformer system. Learning algorithms.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, there is provided a hybrid analog-digital beamformer transmission system in a channel having frequency-selective characteristics in a multi-antenna array communication environment, A TX digital baseband beamformer for performing a digital baseband beamforming function by multiplying a TX digital baseband beamforming matrix by a TX digital baseband beamforming matrix, TX analog beamformer for performing an analog beamforming function by receiving a signal as a input and multiplying a TX analog beamforming matrix by a TX analog beamforming matrix and for transmitting the output signal through a multiplexing antenna, beamformer), and on the receiving side, An RX analog beamformer for performing an analog beamforming function by multiplying an RX analog beamforming matrix by a signal received from a reception antenna that receives the RX analog beamforming signal, And an RX digital baseband beamformer for performing a digital baseband beamforming function by multiplying an RX digital baseband beamforming matrix by a signal output from the RX digital baseband beamforming matrix generator do.

을 행렬 A 의 가장 도미넌트(dominant)한 N개의 라이트 싱귤러 벡터(right singular vector)들로 구성된 행렬이고,

을 행렬 A 의 가장 도미넌트(dominant)한 N개의 레프트 싱귤러 벡터(left singular vector)들로 구성된 행렬로 정의하고, s를 서브캐리어 인덱스(subcarrier index)라고 할 때, 모든 s에 대해

를 모아서,

(수학식1)로 정의하고, 이때 λ_k,s는 H[s]의 k번째로 도미넌트(dominant)한 싱귤러 밸류(singular value)로

을 구성하는 컬럼 벡터(column vector)의 영향력을 나타내는 가중치 값이며, 다음,

의 크기로 최소화하면서, 랭크(rank)가 N_TX인 최적화된 Q _TX를 찾는 수학식을,

(수학식2)로 나타낼 수 있고,

(수학식3)이고,

(수학식4)이고, 상기 TX 아날로그 빔포밍(analog beamforming) 행렬은,

(수학식5)의 수학식으로 결정될 수 있다.

Is the most dominant (dominant) matrix consisting of the N number of light Cingular vector (right singular vector) of the matrix A,

When said most dominant (dominant) of the matrix A is a vector of N Cingular left (left singular vector) to define a matrix, and, s the sub-carrier index (subcarrier index) consisting, for all s

Collect,

(1), where λ _{k, s} is a k-th dominant C singular value of H [s]

Is a weight value indicating the influence of a column vector constituting the matrix,

And finding an optimized Q _TX with a rank of N _TX ,

(2), < / RTI >

(3), < / RTI >

(Equation 4), and the TX analog beamforming matrix is:

(5). ≪ / RTI >

(수학식6)을 정의하고, 이때 λ_k,s는 H[s]의 k번째로 도미넌트(dominant)한 싱귤러 밸류(singular value)로

을 구성하는 컬럼 벡터(column vector)의 영향력을 나타내는 가중치 값이며, 다음

의 크기로 최소화하면서, 랭크(rank)가 N_RX인 최적의 Q _RX를 찾기 위하여,

(수학식7),

(수학식8)을 적용하고, 상기 RX 아날로그 빔포밍(analog beamforming) 행렬은,

(수학식9)의 수학식으로 결정될 수 있다.

(6), where lambda _{k, s} is the k-th dominant Cx value of H [s]

Is a weight value indicating the influence of a column vector constituting the column vector,

To find the optimal Q _RX with a rank of N _RX ,

(7),

(Equation 8), and the RX analog beamforming matrix may be expressed as:

(9). ≪ / RTI >

According to the present invention, the learning method in the transmission system of the hybrid analogue digital beamformer has an excellent performance in a frequency selective channel environment, that is, a larger channel capacity than the conventional method.

Also, the present invention can be applied to multiple stream transmission, and has an advantage that the performance is much better than the conventional method.

1 is a diagram illustrating a hybrid analogue digital beamformer transmission system structure according to an embodiment of the present invention.
FIG. 2 is a graph comparing performance of an ideal system, a conventional beamforming method, and a beamforming method proposed in the present invention, according to changes in SNR.
FIG. 3 is a diagram for comparing the performance of an ideal system, an existing beam forming system, and a beamforming system proposed in the present invention, according to the variation of the number of transmission and reception RF chains.
FIG. 4 is a diagram for comparing the performance of an ideal system, an existing beam forming system, and a beamforming system proposed in the present invention, according to changes in SNR.
FIG. 5 is a diagram for comparing the performance of the ideal system, the existing beamforming method, and the beamforming method proposed by the present invention, according to the variation of the number of transmitting and receiving RF chains.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted in an ideal or overly formal sense unless expressly defined in the present application Do not.

In the following description of the present invention with reference to the accompanying drawings, the same components are denoted by the same reference numerals regardless of the reference numerals, and redundant explanations thereof will be omitted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

The present invention is directed to a hybrid analog-digital beamformer transmission system in a channel with frequency-selective characteristics in a multi-antenna array communication environment.

1 is a diagram illustrating a hybrid analogue digital beamformer transmission system structure according to an embodiment of the present invention.

FIG. 1 shows a hybrid structure in which an analog beamformer and a digital baseband beamformer are combined.

1, the hybrid analogue digital beamformer transmission system of the present invention includes a TX digital baseband beamformer 110, a TX analog beamformer 120, a channel 130, An RX analog beamformer 140, and an RX digital baseband beamformer 150. The RX digital baseband beamformer 150 may be any of the following types.

A TX digital baseband beamformer 110 performs digital baseband beamforming on the transmit side by multiplying the input signal by a TX digital baseband beamforming matrix, Function.

 The TX analog beamformer 120 receives a signal output from the TX digital baseband beam former 110 and multiplies the TX analog beamforming matrix by an analog beamforming ) Function, and transmits the output signal through the multiple transmission antennas.

The RX analog beamformer 130 multiplies an RX analog beamforming matrix by a signal received from a reception antenna that receives signals transmitted from multiple transmission antennas at the reception side, and outputs the analog beamforming Function.

The RX digital baseband beamformer 140 receives a signal output from the RX analog beam former 130 as an input and multiplies the received RX digital baseband beamforming matrix by an RX digital baseband beamforming matrix, And serves to perform a band-beam forming function.

x [s] denotes a user information symbol vector. Suppose that a column vector has K rows. Here, s represents a subcarrier index.

A TX digital baseband beamformer 110 performs a digital baseband beamforming function at the transmitting end.

TX digital baseband beamformer 110 receives x [s] as input and performs x ₁ [s] = P _TX [s] x [s], and then sends x ₁ [s] to the next block. Here, the size of the matrix P _TX [s] is K, and the number of rows is N _TX . N _TX is the number of links from the baseband block to the analog block. Let N _{TX be} the number of RF chains on the transmitting side.

The TX digital baseband beamformer 110, which is performed in a digital baseband, is characterized in that it can be set to a different value according to the subcarrier s.

TX analog beam former (analog beamformer) (120) in the x ₁ [s] receive the input x ₂ After performing the _{[s] = W TX x 1} [s], x 2 [s] through the multiple transmit antennas send. Since analog beamforming can not be applied differently for each subcarrier in the analog processing, it is known that W _{TX, which} is an analog beamforming matrix, does not have a subcarrier index s. . Assume that the number of transmit antennas is M _TX . 1, an inverse fast fourier transform (IFFT) required for OFDM (Orthogonal Frequency Division Multiplexing) transmission is provided between a TX digital baseband beamformer 110 and a TX analog beamformer 120, ) Signal processing block.

The channel 130 is modeled as a frequency selective fading channel in which the channel gain between each transmit antenna and each receive antenna varies depending on the frequency because the reflected wave may be present. It can be seen that the channel matrix H (s) also includes a subcarrier index s.

의 기능을 수행한 후에 출력 y ₁[s] 를 다음 블록으로 보낸다.On the receiving side, if the symbol vector received from the receiving antenna is y ₂ [s], the RX analog beamformer 140 receives y ₂ [s] as an input

And sends the output y ₁ [s] to the next block.

는 W _RX 의 에르미트 트랜스포즈(Hermitian transpose) 즉, 공액 복소수(complex conjugate)를 적용한 후에 트랜스포즈(transpose)를 적용하는 것을 나타낸다. 이 역시 아날로그 프로세싱(analog processing)이기 때문에 서브캐리어(subcarrier) 별로 RX 아날로그 빔포밍(analog beamforming) 행렬이 동일하다.

Indicates that a transpose is applied after applying Hermitian transpose of W _RX , that is, a complex conjugate. Since this is also analog processing, the RX analog beamforming matrix is the same for each subcarrier.

를 수행하게 된다.Finally, the RX digital baseband beamformer 150 receives y ₁ [s] as an input

.

The digital baseband beamforming matrix P _{R X} [s] may be set to a different value for each subcarrier s. The number of receiving antennas is assumed to be M _RX , and the number of receiving RF chains is denoted by N _RX .

을 행렬 A 의 가장 도미넌트(dominant)한 N개의 라이트 싱귤러 벡터(right singular vector)들로 구성된 행렬로 정의한다.First, for the matrix A

Is defined as a matrix composed of N most dominant right singular vectors of matrix A. [

을 행렬 A 의 가장 도미넌트(dominant)한 N개의 레프트 싱귤러 벡터(left singular vector)들로 구성된 행렬로 정의한다.Also,

This is defined as the most dominant (dominant) matrix consisting of the N number of left Cingular vector (left singular vector) of the matrix A.

를 모아서 다음과 같은 행렬을 정의한다.For all s

The following matrix is defined.

을 구성하는 컬럼 벡터(column vector)의 영향력을 나타내는 가중치 값이다.In this case, λ _{k, s} is a k-th dominant C singular value of H [s]

Is a weight value indicating the influence of a column vector constituting the column vector.

의 크기로 최소화하면서, 랭크(rank)가 N_TX인 Q _TX를 찾는다.next,

And finds Q _TX whose rank is N _TX .

The solution to this optimization problem is known as the Eckart-Young-Mirsky matrix approximation theorem:

Then, a TX analog beamforming matrix is determined according to the following equation.

은 다음과 같은 방식으로 결정된다.In a similar manner, the RX analog beamforming matrix

Is determined in the following manner.

을 구성하는 컬럼 벡터(column vector)의 영향력을 나타내는 가중치 값이다.In this case, λ _{k, s} is a k-th dominant C singular value of H [s]

Is a weight value indicating the influence of a column vector constituting the column vector.

의 크기로 최소화하면서, 랭크(rank)가 N_RX인 Q _RX를 찾는다.next,

And finds Q _RX whose rank is N _RX .

Then, we solve the optimization problem using the Eckart-Young-Mirsky matrix approximation theorem.

Then, the RX analog beamforming matrix is determined according to the following equation.

과 아날로그 수신 빔포밍(beamforming) 행렬

의 설계를 제안하였다. In the above, the analog transmission beamforming matrix

And an analog receive beamforming matrix

The design of

에 대해 폐루프 MIMO의 이론을 이용하여 구할 수 있으므로 자세한 유도방법의 기술은 생략하기로 한다.
The optimal value of the digital transmit beamforming matrix P _TX (s) or the optimal value of the digital receive beamforming matrix P _RX (s)

The description of the detailed derivation method will be omitted since it can be obtained by using the theory of closed loop MIMO.

2 to 5 are graphs showing the performance of the method proposed in the present invention.

FIG. 2 is a graph comparing performance of an ideal system, a conventional beamforming method, and a beamforming method proposed in the present invention, according to changes in SNR. 2, the number of transmission streams is 1, the number of transmission RF chains is 2, and the number of reception RF chains is 2.

FIG. 3 is a diagram for comparing the performance of an ideal system, an existing beam forming system, and a beamforming system proposed in the present invention, according to the variation of the number of transmission and reception RF chains. In FIG. 3, the number of transport streams is 1 and the SNR is 0 dB.

FIG. 4 is a diagram for comparing the performance of an ideal system, an existing beam forming system, and a beamforming system proposed in the present invention, according to changes in SNR. In FIG. 4, the number of transport streams is 2, the number of transmitted RF chains is 2, and the number of received RF chains is 4.

FIG. 5 is a diagram for comparing the performance of the ideal system, the existing beamforming method, and the beamforming method proposed by the present invention, according to the variation of the number of transmitting and receiving RF chains. In FIG. 5, the number of transport streams is 2 and SNR = 0 dB.

In FIG. 2 to FIG. 5, 'Ideal' denotes performance in an ideal case where the number of chains of RF is sufficiently large. The graph labeled 'Conventional' or 'Proposed' shows performance when the number of RF chains is limited.

FIG. 2 and FIG. 3 show performance when the number of streams transmitted at the same time is K = 1.

4 and 5 show performance when the number of streams transmitted at the same time is K = 2.

The graph labeled 'Conventional' indicates the performance when an analog beamforming matrix is designed according to the conventional method, and the graph labeled 'Proposed' indicates an analog beamforming matrix by the method proposed in the present invention. It shows the performance when designing.

In FIGS. 2 and 4, the number of limited RF chains is assumed to be two and four, respectively, and a performance comparison according to the variation of the SNR is shown.

On the other hand, FIG. 3 and FIG. 5 show performance comparisons according to the variation of the limited number of RF chains assuming SNR = 0 dB.

2 to 5, it can be seen that the method proposed by the present invention has a much larger capacity than the conventional method.

While the present invention has been described with reference to several preferred embodiments, these embodiments are illustrative and not restrictive. It will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

110 TX Digital Baseband Beamformer
120 TX Analog Beam Shaper
130 channels
140 RX analog beam former
150 RX digital baseband beamformer

Claims (3)

1. A hybrid analog-digital beamformer transmission system in a channel having frequency-selective characteristics in a multi-antenna array communication environment,
A TX digital baseband beamformer for performing a digital baseband beamforming function by multiplying an input signal by a TX digital baseband beamforming matrix at a transmitting side, );
An analog beamforming function is performed by receiving a signal output from the TX digital baseband beam former and a TX analog beamforming matrix, and the output signal is transmitted through a multiplex transmission antenna A TX analog beamformer for transmission;
An RX analog beamformer for performing an analog beamforming function by multiplying an RX analog beamforming matrix by a signal received from a reception antenna that receives a signal transmitted from the multiple transmission antennas at a reception side, beamformer); And
An RX digital baseband beamformer for performing a digital baseband beamforming function by receiving a signal output from the RX analog beamformer as an input and multiplying the received RX digital baseband beamforming matrix by an RX digital baseband beamforming matrix; beamformer,

Is the most dominant (dominant) matrix consisting of the N number of light Cingular vector (right singular vector) of the matrix A,

When called the most dominant of the matrix A (dominant) by the N left Cingular vector (left singular vector) to define a matrix, and, s the sub-carrier index (subcarrier index) consisting of,
For all s

Collect,

(1), where λ _{k, s} is a k-th dominant C singular value of H [s]

Is a weight value indicating the influence of a column vector constituting the column vector,
next,

And finding an optimized Q _TX with a rank of N _TX ,

(2), < / RTI >

(3), < / RTI >

(4), < / RTI >
Wherein the TX analog beamforming matrix comprises:

Is determined by the following equation (5). ≪ EMI ID = 6.0 >
delete The method according to claim 1,

(6), where lambda _{k, s} is the k-th dominant Cx value of H [s]

Is a weight value indicating the influence of a column vector constituting the column vector,
next,

To find the optimal Q _RX with a rank of N _RX ,

(7),

(Equation 8) is applied,
Wherein the RX analog beamforming matrix comprises:

Is determined by the following equation (9). ≪ EMI ID = 7.0 >

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