KR102025729B1 - Method and apparatus for estimating millimeter band channel - Google Patents

Abstract

Provided are a method and apparatus for channel estimation of a millimeter wave band channel. The terminal detects the first beam having the largest received signal based on the beam-specific received signals received from the base station, detects the second beam adjacent to the first beam, and receives the received signal and the second beam of the first beam. The position of the terminal is estimated based on the received signal. And estimating the channel gain of the first beam and the channel gain of the second beam based on the estimated terminal position, and when the estimated channel gain of the first beam and the channel gain of the second beam satisfy a setting condition, the position of the terminal Finally determine the angle and channel gain.

Description

Method and apparatus for channel estimation of millimeter band channel {Method and apparatus for estimating millimeter band channel}

The present invention relates to a method for estimating a channel between a terminal and a base station in a mobile communication system using beamforming in a millimeter band channel.

The fifth generation mobile communication system must support a data rate of up to 20Gbps for the terminal, as well as be able to maintain a data rate of 100Mbps ~ 1Gbps anywhere in the cell. In addition, it must support latency within 1ms, simultaneous connection of a large number of terminals, and the like. In order to achieve this technical goal, recently, the adoption of the millimeter wave band in the mobile communication system has been in the spotlight.

The millimeter wave band is easy to secure a wide bandwidth, which is very advantageous for high-speed data transmission, and has an advantage in lowering latency at the physical layer. However, the millimeter wave band channel has a very strong attenuation of radio waves with distance and blockage of radio waves due to buildings and terrain. Therefore, in the millimeter wave band mobile communication system, beamforming is necessary at the base station or / and the terminal to overcome the attenuation according to the distance of the radio wave. In addition, in order to completely cover the cell area serviced by the base station and to support multiple users, it is necessary to simultaneously use multiple beams at the base station. The simplest way to generate a directional beam is to use an antenna array. In particular, research using a uniform linear array (ULA) has been widely conducted.

Channels in the millimeter wave band corresponding to 30 GHz to 300 GHz have a strong straightness, so that the diffraction and reflection characteristics of objects on the path are not good, and the attenuation in the atmosphere is large. Therefore, there is usually only a very limited number of paths between the base station and the terminal. Especially, the channel corresponding to the line-of-ight (LoS) is very superior to the channel coming through other paths, so the channel is composed of LoS components only. Can be. The LoS channel consists of channel gain and phase information according to the position of the terminal. Therefore, the UE must estimate the values of these two parameters, respectively. However, since the terminal acquires only the information multiplied by these two parameters, it is difficult to estimate the values of the two parameters in a general manner.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a method and apparatus for accurately estimating channel information in a mobile communication system operating in a millimeter band.

A method according to an aspect of the present invention is a method for estimating a channel in a millimeter wave band mobile communication system, the method comprising: detecting a first beam having the largest received signal based on beam-specific received signals received from a base station; Detecting a second beam adjacent to one beam; Estimating the position of the terminal based on the received signal of the first beam and the received signal of the second beam; Estimating a channel gain of a first beam and a channel gain of a second beam based on the estimated terminal position; And when the estimated channel gain of the first beam and the channel gain of the second beam satisfy a setting condition, finally determining an angle and a channel gain according to the position of the terminal.

According to an embodiment of the present invention, in a mobile communication system operating in a millimeter band, channel gain and phase information, which are channel components of LoS, may be estimated in an iterative manner. Therefore, since two unknown variables multiplied by the terminal, the channel gain and the position of the terminal can be estimated simultaneously, more accurate channel estimation is achieved.

1 is an exemplary view showing a millimeter wave band channel according to an embodiment of the present invention.
2 is an exemplary view showing a beam generated based on a beam generation vector according to an embodiment of the present invention.
3 is an exemplary view showing the reception strength of a beam according to the position of the terminal according to an embodiment of the present invention.
4 is a diagram illustrating a reason why a channel gain estimate is different for each beam according to a position estimation value of a terminal.
5 is a flowchart of a channel estimation method according to an exemplary embodiment of the present invention.
6 is a structural diagram of a channel estimating apparatus of a terminal according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification and claims, when a portion is said to include a certain component, it means that it can further include other components, except to exclude other components unless specifically stated otherwise.

Throughout the specification, a terminal may be a user equipment (UE), a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS), a high reliability mobile station ( It may also refer to a high reliability mobile station (HR-MS), a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), and the like. It may also include all or part of the functions, such as AMS, HR-MS, SS, PSS, AT.

In addition, a base station (BS) may be an advanced base station (ABS), a high reliability base station (HR-BS), a node B (node B), an advanced node B (evolved node B, eNodeB or eNB), access point (access point (AP)), radio access station (radio access station (RAS)), base transceiver station (base transceiver station (BTS), mobile multihop relay (BSR) -BS, a relay that performs the role of a base station (relay station, RS), relay node (RN) serving as base station, advanced relay station (ARS) serving as base station, high reliability relay station serving as base station , HR-RS), small base station (femoto BS), home node B (HNB), home eNodeB (HeNB), pico base station (pico BS), metro base station (metro BS), micro base station ( micro BS), etc.), and may be referred to as eNode, ABS, Node B, eNodeB, eNB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station. It may also include all or part of the function.

Hereinafter, a method and apparatus for estimating a millimeter wave band channel according to an embodiment of the present invention will be described.

Channels in the millimeter wave band (eg, 30 GHz to 300 GHz) have strong straightness, resulting in poor diffraction and reflection characteristics caused by objects on the path, and high attenuation in the atmosphere. Therefore, there is usually only a very limited number of paths between the base station and the terminal. In particular, a channel corresponding to a line-of-ight (LoS) is superior to a channel coming through other paths, and thus, the channel is composed of only LoS components. can see.

1 is an exemplary view showing a millimeter wave band channel according to an embodiment of the present invention.

In FIG. 1, in a situation in which a one-dimensional uniform linear array (ULA) is installed in a base station, an arbitrary terminal (named user k here) is positioned at an angle θ _k with respect to a bore-sight of the base station ULA, and corresponding channel. This situation shows a gain of α _k .

As shown in FIG. 1, when a channel between a base station BS and a user k is represented by an equation, Equation 1 is expressed. In this case, it is assumed that there are M antenna elements in the ULA of the base station, and the spacing between the antenna elements is λ / 2.

Here, e ( θ _k ) represents an antenna array response according to a path difference between the user user k and the antenna element in the base station ULA, and may be referred to as a ULA response vector. h _k represents a channel generated by a phase difference according to a time delay occurring when a signal arrives at the antenna array ULA. α _k represents a complex channel gain, and specifically, α _k is a channel gain value determined according to the distance between the base station and the terminal. α _k can be assumed to have the same value for both the terminal and the base station antenna element. Therefore, the problem of estimating the channel between the terminal and the base station can be regarded as a problem of estimating the gain α _k and the angle θ _k of the channel between the terminal and the base station.

The attenuation is very large depending on the channel characteristics of the millimeter band. Therefore, the base station must generate a directional beam to overcome the channel attenuation. However, since the directional beams have a limited spatial area covered by one beam, the base station needs to generate and operate multiple beams to cover the entire area that the base station must service. If there are M antennas in the ULA of the base station, the base station may generate orthogonal M beams, and transmits data and pilot signals on the M beams. At this time, the most representative method of generating M beams is a Discrete Fourier Transfor (DFT) beam generation method. In order to generate the n- th beam ( n = 0, ..., M -1), the following beam generation vector is used for each antenna element of the ULA.

The DFT beam generation method has an advantage of generating a beam that is orthogonal in all directions. Therefore, it is advantageous to use when transmitting the reference signal to all the terminals in the coverage.

When M = 8, the beam generated using the beam generation vector according to Equation 2 above is shown in FIG.

2 is an exemplary view showing a beam generated based on a beam generation vector according to an embodiment of the present invention.

As shown in FIG. 2, each beam will cover a specific space on the space. The location direction each beam is directed to isin ( 2n / M ) radians. The terminal may know which beam performs the best performance according to the angle θ located with respect to the direction angle of the base station. It is assumed that the terminal and the base station share information on a beam generation vector that can be used by the base station in advance.

Before all data and pilot signals transmitted at the base station are transmitted at the base station, a beam generation vector such as Equation 2 is multiplied by the data and the pilot signal, respectively. That is, if any scalar signal transmitted from the base station to the terminal k as s _k , the signal of length M transmitted from the base station toward the terminal k is expressed by Equation 3 below.

The terminal receives a signal having a scalar value as follows through a channel that can be represented by Equation 1.

In order for the base station to distinguish M beams, the base station may allocate a reference signal sequence having a length L (≥ M ) for each beam and transmit the same by using time or frequency resources. That is, a reference signal sequence s _n having a length L is assigned to the beam n , _{where the} reference signal sequence is < s _n , s _n > = M, and when n ≠ m , < s _n , s _m > = 0 Can have characteristics. Therefore, when transmitting the reference signal sequence using the same time and frequency resources in all beams of the base station, the terminal receives a signal as shown in Equation 5 below.

By correlating the received signal with the reference signal sequence corresponding to each beam, the terminal can separate a signal from each beam even if several beams are transmitted simultaneously using the same resource. For example, in order to extract signals from the beam n, by taking the received signal y and the reference signal sequence s _n of the correlation for the beam n, then it is possible to obtain the same value as the equation (6).

를 나타낸다. At this time, assuming that the effects of the noise can be ignored, the terminal obtains a value multiplied by the channel and the beam. That is, the channel gain α _k and the angle θ _k , which are values that the UE needs to find out, are not immediately known, and only the value obtained by multiplying α _k and g _n (θ _k ) . Therefore, a difficult problem occurs in channel estimation. Where g _n (θ _k ) is

Indicates.

If the terminal g _n (θ _k) to know, g _n (θ _k), the beam generation vector w _n and ULA response vector e (θ _k), so that the angle θ multiplied value _k Can be inferred. However, since the current terminal knows only the value of α _k and g _n (θ _k ) , the angle θ _k can not be determined and thus the channel gain α _k is not known.

An embodiment of the present invention provides a method for estimating a channel gain α _k and an angle θ _k by a terminal.

The M beams generated by the base station using the DFT beamforming scheme as shown in Equation 2 above all reflect the cover area of the base station, and the terminal is necessarily included in an area of any beam among the M beams. Therefore, the terminal receives the signal of the greatest intensity from the beam corresponding to the area to which it belongs, and receives the signal of the next intensity from the nearest neighboring beam.

3 is an exemplary view showing the reception strength of a beam according to the position of the terminal according to an embodiment of the present invention.

As illustrated in FIG. 3, when the terminal is located in an area of the beam n, the terminal receives a signal having the greatest intensity from a beam corresponding to the area to which it belongs (here, beam n), and the nearest nearest beam (( Here, the signal of the next intensity is received in beam n + 1)). The strength of the signal from the remaining beams is less than these two beams.

First, the terminal uses the pilot signal transmitted from the beam of the base station to estimate the terminal estimates in each beam { α _k g _n ( θ _k ), n = 0,. , M -1}. That is, the received signal y and the reference for the beam n signal by taking the correlation between a sequence s _n, obtaining a received value corresponding to the beam n, such as equation (6) above, and the terminal estimated value from the received value α _k g _n (θ _k ) is obtained. Through the above correlation process for all beams, { α _k g _n ( θ _k ), n = 0,... , M -1} can be obtained.

으로 한다. 즉,

는 다음과 같이 나타낼 수 있다. Then, the terminal takes the magnitude (absolute value) of the terminal estimate value {| α _k g _n ( θ _k ) | , n = 0,... Produces a set of estimated magnitudes such as M −1}. The terminal selects the largest one among the elements of the generated set of estimated magnitudes and selects the index of the corresponding beam.

It is done. In other words,

Can be expressed as:

에 속해 있다고 볼 수 있다. 단말이 속한 빔이 검출되면, 추정값 크기 집합으로부터 검출된 빔의 인덱스(제1 빔 인덱스라고도 명명할 수 있음)

의 좌우에 있는 빔 인덱스들의 추정값들

중에서, 큰 값에 해당하는 빔 인덱스를 골라

(제2 빔 인덱스라고도 명명할 수 있음)이라고 한다. 이와 같은 과정을 통해 단말은 자신의 위치가 빔

이 가리키는 곳과 빔

이 가리키는 곳 사이에 있다고 유추할 수 있다.

빔과

이 결정되면, 단말은 다음 수학식 8을 토대로 γ값을 계산한다. Terminal beam

It can be said to belong to. When the beam to which the terminal belongs is detected, the index of the beam detected from the estimated magnitude set (also called the first beam index)

Estimates of beam indices to the left and right of

Choose the beam index that corresponds to the larger value

(Also called a second beam index). Through this process, the terminal beams its own location.

Where it points and beam

It can be inferred that it is between these points.

Beam and

If this is determined, the terminal calculates a value of γ based on Equation 8 below.

의 중심 각도에서 얼마나 가까이 있는지 나타내는 값이다. 만약, 단말이 빔

과 빔

의 사이에 정확하게 있다면,

으로, 이는 γ=0을 나타낸다. 단말이 빔

의 중심에 정확하게 있다면,

으로 이는 γ=1을 나타낸다. Here, γ is the terminal beam

This is how close to the center angle of the. If, the terminal beam

And beam

If you are exactly in between

, Which represents γ = 0. Terminal beam

If you are exactly at the center of

This indicates γ = 1.

Therefore, the initial position is estimated using γ. That is, the initial angle estimation value θ _k, θ _{k 0} of the angle is set as follows.

에 해당하는 g _n ( θ _k ) 인

와, 빔

에 해당하는 g _n ( θ _k ) 인

를 구할 수 있다.

및

을 구하면, 이를 토대로 각각 채널 이득 α _k 를 다음과 같이 구할 수 있다. 즉, 빔

에 해당하는 채널 이득

과 빔

에 해당하는 채널 이득

을 각각 구할 수 있다. When the initial angle estimate θ _{k, 0} is obtained as described above _, the beam is obtained by using the initial angle estimate θ _{k, 0} according to the definition of Equation 6 above.

Is equivalent to g _n ( θ _k )

With, beam

Is equivalent to g _n ( θ _k )

Can be obtained.

And

Based on this, the channel gain α _k can be obtained as follows. Ie beam

Corresponding channel gain

And beam

Corresponding channel gain

Can be obtained respectively.

과

의 값은 일치할 것이다. 하지만, 초기 각도 추정값 θ _k,0 와 단말의 위치에 따른 각도 θ _k 가 다르면

과

의 값이 다르다. Where initial angle estimate θ _{k, 0} If and the angle θ _k according to the position of the actual terminal exactly match,

and

The value of will match. However, if the initial angle estimate θ _{k, 0} and the angle θ _k according to the position of the terminal are different

and

Is different.

4 is a diagram illustrating a reason why a channel gain estimate is different for each beam according to a position estimation value of a terminal.

Initial angle estimate θ _{k, 0} Repeatedly update in the following way.

Where θ _{k, i} Denotes the position of the terminal estimated at the i th iteration. λ _i is a positive number and corresponds to the step size in the i th iteration. The step size may be determined according to Armijo's rule.

에 해당하는 g _n ( θ _k ) 인

와, 빔

에 해당하는 g _n ( θ _k ) 인

을 구하고, 이를 토대로 위의 수학식 10과 수학식 11을 이용하여 각각 채널 이득

와

을 획득한다. Using the estimated terminal position θ _{k, i} obtained according to Equation 12 above, the beam is defined according to Equation 6 above.

Is equivalent to g _n ( θ _k )

With, beam

Is equivalent to g _n ( θ _k )

, And channel gains using the above Equations 10 and 11, respectively.

Wow

Acquire.

As described above, the process of obtaining the estimated terminal position θ _{k, i} and obtaining the channel gain using the same is continued until the setting condition is satisfied.

Setting conditions are as follows.

Where ε is any small number greater than zero.

과 채널 이득

의 차이의 절대값이 설정값 ε를 만족하면, 위의 채널 이득을 획득하는 과정을 종료하고, 수학식 13에 따른 설정 조건을 만족할 때의 추정 단말 위치 θ _k,i 를 최종적인 단말 위치에 따른 각도 θ _k 로 하고, 채널 이득

이 최종적인 채널 이득(α _k )으로 사용된다. Channel gain

And channel gain

If the absolute value of the difference satisfies the set value ε, the process of acquiring the channel gain is terminated, and the estimated terminal position θ _{k, i} when satisfying the setting condition according to Equation 13 is determined according to the final terminal position. Channel gain with angle θ _k

This final channel gain α _k is used.

Through the processes as described above, the UE can estimate the channel gain α _k and the angle θ _k .

5 is a flowchart of a channel estimation method according to an exemplary embodiment of the present invention.

As shown in FIG. 5, the terminal receives the reference signal sequence of all beams transmitted from the base station and detects the received signal for each beam by using the reference signal sequence for each beam (S100 and S110).

A second beam corresponding to the received signal having a size smaller than the first beam (the beam to which the terminal belongs) and having a size larger than the remaining beams, based on the detected beam-specific received signals; The beam (adjacent beam of the terminal) is detected (S120).

Based on the terminal estimate obtained from the received signal of the first beam and the terminal estimate obtained from the received signal of the second beam, γ according to Equation 8 above, that is, a value indicating how close the terminal is to the center angle of the first beam Obtain (S130).

Thereafter, the terminal estimates the initial position of the terminal using γ (see Equation 9 above) (S140), and estimates the channel gain of the first beam and the channel gain of the second beam based on the estimated initial position ( (10) (S150).

The initial position of the terminal is updated based on the estimated channel gain of the first beam and the channel gain of the second beam (see Equation 12) (S160), and the channel gain of the estimated first beam and the channel gain of the second beam are updated. It is determined whether the difference satisfies the set value (S170, S180).

If the difference between the estimated channel gain of the first beam and the channel gain of the second beam does not satisfy the setting value, the channel gain of the first beam and the estimated terminal position are again used using the initial position of the updated terminal, that is, the estimated terminal position. Estimate the channel gain of the two beams.

As such, the channel gain of the estimated first beam is continuously updated while the estimated terminal position is continuously updated until the difference between the channel gain of the first beam and the channel gain of the second beam estimated based on the estimated terminal position satisfies a setting value. The process of estimating the channel gain of the second beam is repeated.

On the other hand, when the difference between the estimated channel gain of the first beam and the channel gain of the second beam satisfies the set value, the current estimated terminal position is determined as the final terminal position θ _k , and the current The channel gain of one beam is determined as the final channel gain α _k , thereby completing channel estimation (S190).

6 is a structural diagram of a channel estimating apparatus of a terminal according to an embodiment of the present invention.

As shown in FIG. 6, the channel estimating apparatus 1 according to an exemplary embodiment of the present invention includes a processor 10, a memory 20, and a transceiver 30.

The processor 10 may be configured to implement the method described based on FIGS. 1 to 5 above.

The memory 20 is connected to the processor 10 and stores various information related to the operation of the processor 10. The memory 20 may store instructions for execution in the processor 10 or temporarily load the instructions from a storage device (not shown).

The processor 10 may execute instructions stored or loaded in the memory 20. The processor 10 and the memory 20 may be connected to each other through a bus (not shown), and an input / output interface (not shown) may also be connected to the bus.

An embodiment of the present invention is not implemented only through the above-described apparatus and / or method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention, a recording medium on which the program is recorded, and the like. Such implementations may be readily implemented by those skilled in the art from the description of the above-described embodiments.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of the operator using the basic concepts of the present invention as defined in the following claims are also provided. It belongs to the scope of rights.

Claims (10)

A method of estimating a channel by a terminal in a millimeter wave band mobile communication system,
Detecting the first beam and the second beam based on beam-specific received signals received from the base station;
Estimating an initial position of the terminal based on the received signal of the first beam and the received signal of the second beam;
Estimating a channel gain of the first beam and a channel gain of the second beam based on the estimated initial position of the terminal;
Updating the initial position of the terminal based on the channel gain of the first beam and the channel gain of the second beam;
Determining whether the estimated channel gain of the first beam and the channel gain of the second beam satisfy a set condition; And
Determining an initial position of the terminal as a final terminal position and determining a channel gain of the first beam as a final channel gain when the setting condition is satisfied.
Including,
Estimating, updating, and determining the channel gain are repeatedly performed until the set condition is satisfied, and
In the performing of repetition, estimating the channel gain estimates the channel gain of the first beam and the channel gain of the second beam based on the initial position of the updated terminal. The method of claim 1,
The detecting step,
And detecting a beam corresponding to the received signal having the largest size as the first beam, and detecting a beam adjacent to the first beam as the second beam based on the beam-specific received signals received from the base station. The method of claim 1,
The determining may include determining whether a set condition is satisfied by using a difference between a channel gain of the first beam and a channel gain of the second beam. The method of claim 1,
Wherein the last terminal position indicates an angle at which the terminal is located relative to the orientation angle of the base station. The method of claim 1,
The estimating of the initial position of the terminal may include estimating the position of the terminal based on a value indicating how close the terminal is to the central angle of the first beam, and wherein the terminal is configured to estimate the first beam and the second beam. When the value is 0, the value is 1 when the terminal is in the center of the first beam,
The setting condition is that the absolute value of the difference between the channel gain of the first beam and the channel gain of the second beam satisfies the setting value. A method of estimating a channel by a terminal in a millimeter wave band mobile communication system,
Detecting the first beam and the second beam based on beam-specific received signals received from the base station;
Estimating the position of the terminal based on the received signal of the first beam and the received signal of the second beam;
Estimating a channel gain of the first beam and a channel gain of the second beam based on the estimated terminal position; And
If the estimated channel gain of the first beam and the channel gain of the second beam satisfy a setting condition, the position of the estimated horse is determined as the final terminal position, and the channel gain of the first beam is the final channel gain. Step to decide
Including,
The estimating of the position of the terminal may include estimating the position of the terminal based on a value indicating how close the terminal is to the central angle of the first beam, wherein the terminal is located between the first beam and the second beam. The value is 0 when in the value, and the value is 1 when the terminal is in the center of the first beam. The method of claim 6,
After estimating the channel gain
Updating the estimated position of the terminal based on the estimated channel gain of the first beam and the channel gain of the second beam.
More,
Estimating and updating the channel gain repeatedly until the estimated channel gain of the first beam and the channel gain of the second beam satisfy a set condition;
In the repetition, estimating the channel gain may estimate the channel gain of the first beam and the channel gain of the second beam based on the initial position of the updated terminal. A method of estimating a channel by a terminal in a millimeter wave band mobile communication system,
Detecting the first beam and the second beam based on beam-specific received signals received from the base station;
Estimating the position of the terminal based on the received signal of the first beam and the received signal of the second beam;
Estimating a channel gain of the first beam and a channel gain of the second beam based on the estimated terminal position; And
If the estimated channel gain of the first beam and the channel gain of the second beam satisfy setting conditions, the position of the estimated terminal is determined as the final terminal position, and the channel gain of the first beam is final channel gain. Step to decide
Including;
The setting condition is that the absolute value of the difference between the channel gain of the first beam and the channel gain of the second beam satisfies the setting value. The method of claim 8,
After estimating the channel gain
Updating the estimated position of the terminal based on the estimated channel gain of the first beam and the channel gain of the second beam.
The channel estimation method further comprises. The method of claim 9,
Estimating and updating the channel gain repeatedly until the estimated channel gain of the first beam and the channel gain of the second beam satisfy a set condition;
In the repetition, estimating the channel gain may estimate the channel gain of the first beam and the channel gain of the second beam based on the initial position of the updated terminal.

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