KR101798341B1 - Method for Estimating Beam Pattern in Millimeter Wave Channel - Google Patents

Abstract

The present invention relates to a method for estimating a beam pattern in a millimeter wave channel. The method comprises: a step (a) of receiving omnidirectional signals from a terminal, applying N reception precoders, selecting a precoder having the greatest signal strength, and estimating a beam angle corresponding to the selected reception precoder as a transmission angle to the terminal; a step (b) of transmitting a first-1 beam which includes the transmission angle estimated in the step (a) and a first-2 beam adjacent to the first-1 beam and having the same beam width as that of the first-1 beam to the terminal, receiving feedback of reception power information for each of the first-1 beam and the first-2 beam from the terminal, and selecting one of the first-1 beam and the first-2 beam on the basis of the feedback information; and a step (c) of transmitting a second-1 beam and a second-2 beam being in the range of the beam selected in the step (b) and having a beam width narrower than that of the selected beam to the terminal, receiving feedback of reception power information for the second-1 beam and the second-2 beam from the terminal, selecting one of the second-1 beam and the second-b beam on the basis of the feedback information, and the selected beam as a final beam pattern. According to the method, it is possible to accurately estimate a beam pattern while requiring a relatively less number of time slots, and it is possible to estimate a beam pattern with low complexity.

Description

[0001] The present invention relates to a method for estimating a beam pattern in a millimeter wave channel,

Embodiments of the present invention relate to a beam pattern estimating apparatus and method, and more particularly, to an apparatus and method for beam pattern estimating in a millimeter wave channel.

As data traffic surges, research is being conducted on systems that can have high data rates to accommodate increased data traffic. Among them, millimeter wave communication is attracting attention as one of the technologies that can increase the transmission rate in addition to the Multi Input Multi Output (MIMO).

Since millimeter wave uses higher communication frequency band (30GHz) than existing MIMO system, attenuation due to path loss is very large. Therefore, accurate beamforming between the receiving terminal and the base station is required for smooth communication.

On the other hand, the demand for achieving both mobility and transmission rate simultaneously due to the appearance of Vehicle to everything (V2X) is increasing, and millimeter wave communication is expected to be used to solve such a demand.

In the millimeter wave environment, it is common that the beam estimation algorithm requires several time slots as the number of antennas increases. Therefore, it takes considerable time to estimate the beam and high complexity is required.

Therefore, a beam estimation algorithm with low complexity is required while reducing the time for beam estimation.

An aspect of the present invention is to propose a beam pattern estimation method and apparatus in a millimeter wave channel that can accurately estimate a beam pattern while requiring a relatively small number of time slots.

Another aspect of the present invention is to propose a beam pattern estimation method and apparatus in a millimeter wave channel capable of accurately estimating a beam pattern with low complexity.

According to an aspect of the present invention, there is provided an apparatus for receiving an omnidirectional signal from a terminal, selecting a precoder having the largest signal strength by applying N reception precoders, and outputting a beam angle corresponding to the selected reception precoder to the terminal (A) estimating at a transmission angle; A first beam having a width greater than the beam of step (a) and including a transmission angle estimated in step (a), and a second beam adjacent to the first beam and having the same beam width To the terminal, receiving power information for each of the first and second beams and the first and second beams from the terminal, and receiving, based on the feedback information, the first- And (b) selecting one of the first and second beams; And transmitting the second-1 beam and the second-2 beam, which are within the selected beam range in the step (b) and have a narrower beam width than the selected beam, to the terminal, (C) receiving received power information for the 2 < nd > -2 beam and selecting one of the 2-1 beam and the 2-2 beam as a final beam pattern based on the feedback information A method of beam pattern estimation in a millimeter wave channel is provided.

The beam width of each beam corresponding to the reception precoder of step (a) is equal to the beam width of the second-first beam and the second-second beam.

The step (a) sequentially applies a receiving precoder having a beam width divided by N by 360 degrees.

The 1-1 beam and the 1-2 beam have a beam width twice that of the 2-1 beam and the 2-2 beam.

The 1-1 beam and the 1-2 beam are generated by applying a selected one of the transmission precoders corresponding to a beam width of 2W prepared in advance.

The 2-1 beam and the 2-2 beam are generated by applying a selected one of the transmission precoders corresponding to the beam width of W prepared in advance.

According to another aspect of the present invention, there is provided an apparatus for receiving an omnidirectional signal from a terminal, selecting a precoder having the largest signal strength by applying N reception precoders, and transmitting a beam angle corresponding to the selected reception precoder to the terminal (A) estimating at a transmission angle; (K-1) beams adjacent to a beam including the estimated transmission angle and a beam including the estimated transmission angle in the step (a) to the terminal, and outputs received power information for each beam to the terminal (B) receiving and selecting a specific beam from the beam; And transmits K beams having a beam width narrower than the beam selected in the step (b) to the terminal, receives the received power information from the terminal, selects a specific one of the K beams, A method for estimating a beam pattern in a millimeter wave channel comprising the step (c) of determining a beam pattern.

According to the present invention, a beam pattern can be accurately estimated while requiring a relatively small number of time slots, and a beam pattern can be estimated with low complexity.

1 is a diagram illustrating a structure of a mobile communication system to which a beam pattern estimation method according to an embodiment of the present invention is applied.
FIG. 2 shows a method for estimating a conventional beam pattern, and FIG. 3 shows a method for selecting a precoder for estimating a conventional beam pattern.
3 shows a method of selecting a precoder for estimating a conventional beam pattern.
FIG. 4 is a flowchart illustrating an overall flow of a beam pattern algorithm according to an embodiment of the present invention. FIG.
5 is a view for explaining a method of estimating a transmission angle in a first stage in a method of estimating a beam pattern according to an embodiment of the present invention.

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. Like reference numerals are used for like elements in describing each drawing.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a structure of a mobile communication system to which a beam pattern estimation method according to an embodiment of the present invention is applied.

Referring to FIG. 1, a mobile communication system to which a beam pattern estimation method according to an embodiment of the present invention is applied includes a base station 100 and a terminal 110.

For convenience of explanation, the present invention will be described by taking as an example a downlink in which a base station 100 transmits a signal and a terminal 110 receives a signal. However, even in the case of an uplink, It will be obvious to those skilled in the art that the present invention can be applied.

The base station 100 includes Nt antennas. For example, the base station may include an equally spaced linear array antenna. The terminal 110 includes Nr antennas, and the terminal may also include an equidistant linear array antenna.

Assuming that the channel between the terminal 110 and the base station 100 is H, the received signal y for the signal transmitted by the base station may be set as shown in Equation (1).

In Equation (1), W denotes a reception precoder of the UE, F denotes a transmission precoder of the base station, s denotes a transmission signal vector having a K dimension, and n denotes noise. For example, the noise may be an Nr-dimensional noise vector with an average of zero, a variance of 1, and a complex Gaussian distribution independent of each other.

Here, K means the number of beam patterns to be transmitted in one stage for beam pattern estimation, and K will be described as 2 in the present embodiment.

In such a system environment, the channel matrix H can be defined as: < EMI ID = 2.0 >

는 Rayleigh 분포를 갖는 채널의 복소 크기를 의미하고, a_t는 각도 송신 각도

에 대한 Nt 차원의 안테나 배열 응답 벡터이고, a_r은 수신 각도

에 대한 Nr 차원의 안테나 배열 응답 벡터를 의미한다. In the above equation (2)

Denotes a complex size of a channel having a Rayleigh distribution, and a _t denotes an angular transmission angle

Antenna array response vectors of dimension Nt for a, a _r is received angle

Dimensional antenna array response vector with respect to the Nr dimension.

에 대한 Nt 차원의 안테나 배열 응답 벡터는 다음의 수학식 3과 같이 표현될 수 있다. Assuming an isometric array antenna, the transmission angle

The antenna array response vector of the Nt-th antenna can be expressed by the following Equation (3).

는 신호의 파장을 의미하고, d는 안테나간 거리를 의미한다. In the above equation (3)

Denotes the wavelength of the signal, and d denotes the distance between the antennas.

FIG. 2 illustrates a method for estimating a conventional beam pattern, and FIG. 3 illustrates a conventional method for selecting a precoder for estimating a beam pattern.

The conventional beam pattern estimating method is performed over a plurality of stages. In the first stage, a beam having a relatively large beam width is transmitted to estimate a position of the terminal, and a beam having a narrow beam width is transmitted toward the next stage, .

The size of the beam width formed by the precoder may be inversely proportional to the number of precoders (the number of transmit antennas), and the number of beams is determined by the number of precoders Of the number of pixels). The number of precoders and the number of transmit antennas may not be equal to each other, but in this embodiment, the case where the number of transmit antennas is equal to the number of precoders will be described as an example.

On the other hand, the number of stages for beam pattern estimation may be proportional to the number of transmission (base station) antennas. The greater the number of transmit antennas, the more number of beam patterns can be formed, and the more the number of possible beam patterns, the more the final beam pattern is estimated.

로 정의될 수 있다. For example, when the number of beams transmitted in one stage is 2 (K = 2) and the number of transmitting antennas is Nt, the number of stages is

. ≪ / RTI >

FIGS. 2 and 3 show a conventional method of estimating a beam pattern by taking the case where the number Nt of transmission antennas is eight as an example. Since the number of transmission antennas is eight, the total number of stages is three.

When there are eight antennas, a total of eight beams can be transmitted, and the beam width of each beam can be 45 degrees divided by eight.

Referring to FIG. 2, in the first stage, a beam 201 having a beam width of 0 to 180 degrees and a beam 202 having a beam width of 180 to 360 degrees are respectively transmitted. In the first stage, the position of the UE 110 is primarily estimated through a beam having a beam width 2 ² times larger than a beam width that can be implemented.

For this beam transmission, a precoder codebook for forming a beam width of 0 to 180 degrees and a precoder codebook for forming a beam width of 180 to 360 degrees must be prepared in advance.

In FIG. 3, a precoder codebook for forming a beam width of 0 to 180 degrees is indicated as [F (1,1)] _{:, 1} in the first stage F1, and a beam width of 180 to 360 degrees is formed , The precoder codebook for this is indicated as [F (1,1)] _{: 2} .

In the first stage, the terminal 110 feeds back the received power information for the two beams to the base station 100, respectively. The UE 110 may feed back the received power values for the two beams and may feedback information about which of the two beams has a higher received power.

Referring to FIG. 2, the second stage transmits a beam having a narrower beam width than the first stage. For example, four beams 210, 211, 212, and 213 having a beam width of 90 degrees are prepared for the second stage. A beam having a beam width 2 ¹ times higher than the beam width that can be implemented with eight precoders is used.

At this time, the beam to be transmitted in the second stage is selected based on the received power information fed back by the receiving terminal in the first stage. For example, if higher received power is fed back in a beam having a beam width of 0 to 180 degrees, then in the second stage, a beam 210 having a beam width of 0 to 90 degrees and a beam having a beam width of 90 to 180 degrees 211 are selected. As a result, in the first stage only the beam corresponding to the higher received power is divided and transmitted in the second stage.

The codebook for each of the beam patterns having a beam width of 0 to 90 degrees, 90 to 180 degrees, 180 to 270 degrees, and 270 to 360 degrees is [F (2,1)] _: (2,1)] _{: 21} , [F (2,2)] _{:, 1} , and [F (2,2)] _{: 2} .

In the second stage, each terminal 110 feeds back the received power information of the two transmitted beams to the base station 100.

In the third stage, a beam having a beam width narrower than that of the second stage is transmitted, and only a beam obtained by dividing the beam corresponding to the largest received power in the second stage is transmitted. Referring to FIG. 3, a precoder codebook for eight beams 220, 221, 222, 223, 224, 225, 226, 227 at 45 degree intervals is prepared in advance. In the third stage, a beam having a beam width that can be implemented by eight antennas is used.

For example, in the second stage, when the largest received power is fed back in the beam 211 having a beam width of 0 to 90 degrees, in the third stage, the beam 220 having a beam width of 0 to 45 degrees, A beam 221 having a beam width of 90 degrees is transmitted.

The terminal feeds back the received power information for the two beams to be transmitted, and the base station selects the beam pattern corresponding to the largest received power as the final beam pattern.

3, the codebook for the 8 beam pattern _{[F (3,1)]:,} 1, [F (3,1)]: 2, [F (3,2)]:, 1, [F (3 _{, 2)]: 2, [} F (3,3)]:, 1, [F (3,3)]: 2, [F (3,4)]:, 1, [F (3,4)] _{: 2} .

Meanwhile, the terminal 110 estimates the reception beam pattern in substantially the same manner as the method of estimating the transmission beam pattern. For example, when a beam having a beam width of 0 to 180 degrees is received in the first stage, a reception precoder for a beam width of 0 to 180 degrees and a reception precoder for a beam width of 180 to 360 degrees Respectively, to select a receiving precoder having a larger signal strength. This method is also applied to the second stage and the third stage.

Of course, in the case of the MISO system having one antenna of the terminal 110, only a process of estimating only the transmission beam pattern will be performed.

In such a conventional beam pattern estimation method, there is a problem that the number of stages increases as the number of antennas increases. In future 5G, it is expected to use a massive MIMO using a considerable number of antennas, and when a conventional beam pattern estimation method is applied to such a massive MIMO system, a considerable beam pattern estimation time is required due to a plurality of stages.

In addition, since a precoder codebook is prepared for each stage, the number of precode codebooks to be prepared increases as the number of antennas increases.

4 is a flowchart illustrating an overall flow of a beam pattern algorithm according to an embodiment of the present invention.

4, in the first stage, the terminal 110 transmits an omnidirectional signal and receives an omnidirectional signal from the terminal, and the base station 100 estimates a reception signal angle from the terminal 110 400).

Estimation of the angle of the received signal from the terminal 110 is performed by applying N prepared receive precoders to the received signal to estimate the beam angle realized by the precoder corresponding to the largest value as the received signal angle. In the first stage, a precoder having a beam width feasible with N receive pre-coder, i.e. a beam width corresponding to a value obtained by dividing 360 degrees by N, is used.

For example, when eight antennas are provided and eight reception precoders are prepared, eight reception precoders are applied to the omnidirectional signals from the terminal 110, and a precoder corresponding to the largest value is selected And estimates the beam angle information implemented by the selected precoder as the received signal angle.

)별로 프리코더를 적용하는데,

로 정의될 수 있다. 결국, u값을 변경해가면서 수신 각도를 추정하는 것이라 할 수 있다. More specifically, if there are N precoder codebooks, an even beam angle (

) Is applied to each precoder,

. ≪ / RTI > As a result, it can be said that the reception angle is estimated while changing the u value.

A method of finding the reception angle having the largest signal strength can be defined as Equation (4).

In Equation (4), a _r is an array response vector of an N-dimensional antenna with respect to a reception angle, H is a channel, and f _o is an omnidirectional signal from the UE.

If the reception angle with the largest signal strength is estimated, it is assumed that the reception angle is an appropriate transmission beam angle with the terminal 110. [

5 is a diagram for explaining a method of estimating a transmission angle in a first stage in a method of estimating a beam pattern according to an embodiment of the present invention.

In Fig. 5, it is assumed that the number of antennas of the base station is eight. As shown in Fig. 5, eight reception precoders are applied to the reception signals from the terminal, respectively. Estimates the beam angle of the precoder corresponding to the largest signal strength as a result of applying eight precoders.

When there are eight precoders, the range of 0 to 45 degrees, 45 to 90, 90 to 135, 135 to 180, 180 to 225, 225 to 270, 270 to 315, A precoder corresponding to an angle of 315 degrees to 360 degrees may be applied to the received signal from the terminal, respectively.

If the greatest signal strength is detected in a precoder of 0 to 45 degrees, an angle of 0 to 45 degrees is estimated as a transmission angle to the terminal.

The transmission angle to the terminal estimated through the above process may be inaccurate. In the second stage, two beams using a precoder having a beam width wider than the beam width of the precoder used in the first stage are transmitted to the terminal (step 402). Wherein the first one of the two beams is a beam comprising a transmission angle estimated at the first stage and the other beam is a beam adjacent to the first beam.

Preferably, the beam width of the beam transmitted in the second stage may be twice as wide as the beam width of the precoder used in the first stage. As a result, in the second stage, a beam having a beam width twice as wide as the beam width that can be implemented with N precoders is transmitted, and the received power information on the beam is fed back from the terminal.

For example, if the angle to the terminal in the first stage is estimated to be 0 to 45 degrees, the first beam of 0 to 90 degrees and the second beam of 90 to 180 degrees adjacent to the first beam are transmitted.

Receives the received power information of the terminal with respect to the two beams, and estimates whether the terminal is located in which beam direction of the two beams.

In the third stage, two beams having a beam width narrower than the beam of the selected precoder within the beam range of the selected precoder in the second stage are transmitted, and the received power information about the two beams is fed back from the terminal ). In the third stage, a beam having a beam width corresponding to a value obtained by dividing 360 degrees by the number of precoders (number of antennas of the base station) (beam width capable of being implemented with N precocoders) can be transmitted, May have a beam width that is 1/2 of the beam width of the beam transmitted in the second stage.

For example, in a second stage, when a beam having a beam width of 0 to 90 degrees is received at a higher power, a beam having a beam width of 0 to 45 degrees and a beam having a beam width of 45 to 90 degrees are transmitted do.

The final beam pattern is selected by receiving information on the received power of the two beams from the terminal. When the beam pattern selection is completed, communication with the terminal is performed by applying a precoder corresponding to the beam pattern selected in the future.

Meanwhile, a process of selecting a transmission precoder and a process of selecting a reception precoder when the terminal has a plurality of antennas can be performed. The selection of the receive precoder may also be made in the same process.

In the first stage, omnidirectional signals transmitted by the base station are applied to a plurality of reception precoders to primarily estimate reception angles. In the second stage and the third stage, the final receiving precoder may be selected while applying the receiving precoder to the two beams transmitted by the base station.

Since the beam pattern estimation method of the present invention as described above proceeds with three stages regardless of the number of antennas, it is possible to estimate the beam pattern in a short time even if the number of antennas increases, There are advantages.

In the above embodiment, two beams are transmitted at each stage. However, it is easily understood by those skilled in the art that a beam pattern can be estimated while transmitting arbitrary K beams.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (10)

Selecting a precoder having the largest signal strength by applying an N omnidirectional precoder to the omnidirectional signal from the terminal and estimating a beam angle corresponding to the selected receiving precoder as a transmission angle to the terminal );
A first beam having a width greater than the beam of step (a) and including a transmission angle estimated in step (a), and a second beam adjacent to the first beam and having the same beam width To the terminal, receiving power information for each of the first and second beams and the first and second beams from the terminal, and receiving, based on the feedback information, the first- And (b) selecting one of the first and second beams;
To the terminal, a second-1 beam and a second-2 beam having a narrower beam width in the selected beam range than the selected beam in the step (b), and transmit the second- (C) receiving feedback information on the received power information for the 2-2 beam, and selecting one of the 2-1 beam and the 2-2 beam as the final beam pattern based on the feedback information,
The beam width of each beam corresponding to the reception precoder of step (a) is equal to the beam width of the second-first beam and the second-second beam,
Wherein the step (a) sequentially applies a receiving precoder having a beam width divided by N by 360 degrees.
delete delete The method according to claim 1,
Wherein the 1-1 beam and the 1-2 beam have a beamwidth twice that of the 2-1 beam and the 2-2 beam.
The method according to claim 1,
Wherein the 1-1 beam and the 1-2 beam are generated by applying a selected one of the transmission precoders corresponding to a beam width of 2W prepared in advance.
6. The method of claim 5,
Wherein the second-1 beam and the second-2 beam are generated by applying a selected one of the transmission precoders corresponding to a beam width of W prepared in advance.




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