KR20100095273A - A method for channel estimation in a wireless communication system and an apparatus thereof - Google Patents

Abstract

PURPOSE: A method for channel estimation in a wireless communication system and an apparatus thereof are provided to estimate a channel through a correlation matrix by estimating the correlation matrix through grouping. CONSTITUTION: A transmitter generates a pilot symbol modified according to BPSK(Binary Phase Shift Key)(S301). The pilot symbol corresponds to a pilot symbol which is identically known as to the transmitter and the receiver. The transmitter generates the data symbol by modifying the previous signal(S303). The data symbol is generated by using the 4QAM, and the modulation method like 8QAM and 16QAM.

Description

A method for channel estimation in a wireless communication system and an apparatus

The present invention relates to a method and apparatus for estimating a channel in a wireless communication system, and more particularly, to a method and apparatus for estimating a channel in a wireless communication system capable of stably estimating a channel even in the presence of interference from an adjacent base station.

Recently, orthogonal frequency division multiple access (hereinafter referred to as "OFDM") has been actively studied as a method useful for high-speed data transmission in a wireless channel. In order to restore the transmission signal in the wireless communication system as described above, the channel distortion technique must compensate for the distorted channel during transmission.

The minimum mean square error (MMSE) channel estimation method of the pilot-aided channel estimation method using a pilot signal in an OFDM-based system estimates a channel using statistical characteristics such as correlation of channels. Do this. However, since this is a channel estimation method in a conventional fading channel environment considering only additive white Gaussian noise (AWGN), performance degradation of channel estimation occurs at a cell edge that is strongly affected by co-channel interference (CCI). .

Assuming that the terminal is located at a cell edge of one base station, when the terminal receives pilot information of a desired signal from one base station, an interference signal from another base station adjacent to the one base station Pilot information is also received. In such a co-channel interference (CCI) environment, when an attempt is made to estimate a correlation matrix of a desired signal channel using pilot information, information of an interference channel may be included. The interference is greatly reduced the accuracy of the channel estimation (estimation).

One method used to prevent such degradation of channel estimation performance is to avoid interference through coordination between one base station and another base station. In an OFDM system, coordination may be performed to avoid interference in both time and frequency. In the time coordination scheme, one base station and another base station transmit pilot information by dividing the pilot information into the time 1 and the time 2 so that interference does not occur between each other. In the frequency coordination scheme, one base station and another base station locate pilot information at different subcarrier positions so that interference with each other does not occur. Therefore, this coordination method can perform correlation matrix estimation without interference by neighboring cells. However, the method of avoiding interference through the coordination described above requires coordination between adjacent cells and is inefficient in terms of time and frequency usage.

Therefore, there is a need for a method for estimating a channel by removing interference signals without coordination between adjacent cells in a CCI environment. There is also a need for a method for estimating a channel in an interference environment without estimating the correlation matrix of the desired signal and the interference signal in the CCI environment.

Accordingly, an object of the present invention is to provide a channel estimation method and apparatus for a wireless communication system capable of estimating a channel by effectively estimating a correlation matrix in a CCI environment and effectively removing interference signals from neighbor cells in a CCI environment. have.

Another object of the present invention is to provide a channel estimation method and apparatus for a wireless communication system capable of estimating a channel without estimating a correlation matrix in a CCI environment.

In accordance with another aspect of the present invention, there is provided a channel estimating method of a wireless communication system, including calculating a LS estimate using a pilot signal of a received signal and correlating the calculated LS estimate. Grouping the matrix by factors that may have the same value, subgrouping the grouped LS estimates into two subgroups according to the value of each factor, and taking a sample average for each subgroup to calculate a correlation matrix And adding a correlation matrix for each subgroup to calculate a correlation matrix from which an interference signal is removed, and estimating a channel using the correlation matrix from which the interference signal is removed.

The channel estimation method of the wireless communication system according to an embodiment of the present invention for achieving the above object, the process of calculating the LS estimate using the pilot signal of the received signal, and the PDP (Power Delay Profile) Assuming a uniform, the method includes deriving a correlation matrix from the assumed uniform PDP, and estimating a channel using the derived correlation matrix.

In accordance with an aspect of the present invention, there is provided an apparatus for channel estimation in a wireless communication system, including: a pilot extractor for extracting a pilot symbol from a received signal; An LS estimator for calculating an LS estimate from the pilot symbols; A grouping group for grouping by a factor that the correlation matrix may have the same value in the calculated LS estimate, and forming a subgroup according to the values of the grouped LS estimates (1, -1); And a correlation matrix calculator for taking a sample average into the LS estimates for each subgroup, calculating a correlation matrix for each subgroup, and adding a correlation matrix for each subgroup to calculate a correlation matrix from which interference is eliminated. An MMSE channel estimator for estimating a channel according to an MMSE scheme by using the correlation matrix from which the interference is removed; And an equalizer for compensating for the distorted channel based on the estimated channel.

According to an aspect of the present invention, there is provided a channel estimation apparatus for a wireless communication system, including: a pilot extractor extracting a pilot symbol from a received signal; An LS estimator for calculating an LS estimate from the pilot symbols; A correlation matrix calculator that assumes a power delay profile (PDP) as a uniform and derives a correlation matrix from the assumed uniform PDP; An MMSE channel estimator for estimating a channel according to an MMSE scheme by using the correlation matrix from which the interference is removed; And an equalizer for compensating for the distorted channel based on the estimated channel.

According to the embodiment of the present invention as described above, in the CCI environment, the correlation matrix is estimated through grouping so that the correlation matrix of the interference signal can be cancelled, and through this, the interference signal of the adjacent cell is effectively removed by estimating the channel. A method and apparatus for estimating a channel may be provided.

In addition, by obtaining a correlation matrix from the uniform PDP and estimating the channel through it, even if the correlation matrix of the desired signal and the interference signal is not known in the interference environment, the channel in the interference environment is estimated without any additional work or device for estimating the correlation matrix. can do.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, only parts necessary for understanding the operation according to the embodiment of the present invention will be described, and the description of other parts will be omitted so as not to disturb the gist of the present invention.

The terms or words used in the specification and claims described below should not be construed as being limited to the ordinary or dictionary meanings, and the inventors are appropriate to the concept of terms in order to explain their invention in the best way. It should be interpreted as meanings and concepts in accordance with the technical spirit of the present invention based on the principle that it can be defined. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only one of the most preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

First, a configuration of a wireless communication network according to an embodiment of the present invention will be described. 1 is a view for explaining the configuration of a wireless communication network according to an embodiment of the present invention.

Referring to FIG. 1, a wireless communication network according to an embodiment of the present invention uses an OFDM system, and the configuration of the wireless communication network includes a terminal 101, a serving base station 103 of the terminal, and a serving base station ( Adjacent base station 105 adjacent to 103. Here, it is assumed that the terminal is located at the cell edge of the serving base station 103.

According to an embodiment of the present invention, it is assumed that the serving base station 103 and the neighbor base station 105 transmit pilot symbols at the same position in the downlink frame. In addition, the terminal 101 has such pilot information.

Then, the frame structure of the OFDM communication system according to an embodiment of the present invention will be described in detail. 2 is a diagram illustrating a frame structure of an OFDM communication system according to an exemplary embodiment of the present invention.

개의 부반송파를 갖는다. 주파수 동기 및 타이밍 동기 그리고 채널 추정을 위해 이용되는 파일럿 심벌(210)은 기지국(또는 송신기) 및 단말기(또는 수신기)가 미리 알고 있는 신호를 할당한다. 도면부호 230을 참조하면, 먼저 파일럿 심벌(210)을 동일 간격

의 파일럿 용 부반송파(240)에 할당한다. 그런 다음, 데이터 전송을 위한 데이터 심벌(220)을 나머지 모든 가용 부반송파들에 할당하여 데이터 용 부반송파(250)로 이용한다. 도면부호 260을 참조하면, 데이터 심벌(220)에 할당되는 파일럿 심벌은 분산 파일럿(Scattered pilot subcarrier)이 적용된다. 2, the OFDM frame structure is composed of a pilot symbol 210 and a data symbol 220, each OFDM symbol

Subcarriers The pilot symbol 210 used for frequency synchronization and timing synchronization and channel estimation allocates a signal known to the base station (or transmitter) and the terminal (or receiver) in advance. Referring to 230, first, pilot symbols 210 are equally spaced.

Is assigned to the pilot subcarrier 240. Then, the data symbol 220 for data transmission is allocated to all remaining available subcarriers and used as the data subcarrier 250. Referring to 260, a scattered pilot subcarrier is applied to a pilot symbol allocated to the data symbol 220.

As described above, the positions of the pilot symbols 210 allocated to the pilot subcarriers 240 of the serving base station 103 and the neighboring base station 105 are the same.

According to an embodiment of the present invention, as described above, the pilot signal received at the same position interferes with the terminal 101 at the cell edge. In this case, the present invention provides a method for improving the accuracy of channel estimation by eliminating interference.

First, a data transmission method of a transmitter according to an embodiment of the present invention will be described. The transmitter according to the embodiment of the present invention may be the serving base station 103 and the neighbor base station 105. In addition, the receiver may be the terminal 101.

3 is a diagram illustrating a data transmission method of a transmitter according to an embodiment of the present invention.

Referring to FIG. 3, the transmitter generates a pilot symbol modulated according to a binary phase shift key (BPSK) at step S301. In this case, the pilot symbol is generated a pilot symbol that the transmitter and the receiver know the same.

Then, the transmitter modulates the binary data to be transmitted in step S303 to generate data symbols. The data symbols may use various modulation methods. That is, modulation methods such as 4QAM, 8QAM, and 16QAM can be used.

The transmitter allocates the data symbols and pilot symbols generated in step S305 to the subcarriers. Then, the transmitter converts these symbols into a time domain signal through the IFFT in step S307, and generates and transmits a baseband signal that is finally transmitted by inserting a guard interval (GI) in step S309.

First embodiment

First, according to an embodiment of the present invention, as described above, the serving base station and the neighboring base station transmit pilot symbols at the same location, and the terminal 101 is located at the cell edge of the serving base station and is sufficient for channel estimation. Assume a situation in which a number of pilot symbols can be received.

Next, the operation of the receiver for receiving the transmitted signal will be described as described with reference to FIG. 3. That is, a method of estimating a channel by extracting a pilot symbol from the signal as described above and receiving a data symbol using the estimated channel will be described.

4 is a flowchart illustrating a channel estimation method according to an embodiment of the present invention.

Referring to FIG. 4, the receiver receives a signal in step S401. The received signal can be expressed as Equation 1 below.

)는 서빙 기지국으로부터 수신된 신호(

), 인접 기지국으로부터 수신되는 간섭 신호(

) 및 잡음(

)으로 이루어진다. Receive signal (

) Is the signal received from the serving base station (

), The interference signal received from the adjacent base station (

) And noise (

)

는 채널을 의미하며,

는 송신 심볼을 의미한다. 또한, i는 OFDM 심볼 인덱스(OFDM symbol index), k는 부반송파 인덱스(subcarrier index)이다. 어깨글자(Superscript)인 "(0)"과 "(1)"은 각각 서빙 기지국으로부터 수신한 원하는 신호(desired signal)와 인접 기지국으로부터 수신한 간섭 신호(interferer)를 의미한다. here,

Means channel,

Denotes a transmission symbol. In addition, i is an OFDM symbol index and k is a subcarrier index. Superscripts " (0) " and " (1) " refer to a desired signal received from a serving base station and an interference signal received from a neighboring base station, respectively.

)를 구한다. 구해진 LS 추정치는 다음의 <수학식 2>와 같이 표현할 수 있다. Then, the receiver according to the LS (Least square) estimation technique in step S403, LS estimator,

) The obtained LS estimate can be expressed as Equation 2 below.

As shown in Equation 2, the LS estimation technique estimates the received symbol by dividing the received symbol into one-to-one pilot symbols known to the transmitter and the receiver without considering the statistical characteristics of noise.

)는 <수학식 1>에서 보인 수신 신호를 수신기 및 수신기의 서빙 기지국의 송신기가 동일하게 알고 있는 파일럿 심벌(

)로 나눈 값이다. 잡음을 논외로 하면, 이러한 LS 추정치는 간섭 신호(

)의 영향으로 그 성능이 열화된다. 또한, 이러한 LS 추정치에서 샘플 평균(sample mean)을 취해 구해진 상관 행렬(correlation matrix)은 매우 부정확하다. That is, LS estimator shown in Equation 2

) Denotes a pilot symbol (I) that the receiver and the transmitter of the serving base station of the receiver know the received signal shown in Equation (1).

Divided by). Apart from noise, these LS estimates are interfering signals (

), The performance deteriorates. In addition, the correlation matrix obtained by taking the sample mean from these LS estimates is very inaccurate.

Therefore, in an embodiment of the present invention, the receiver that has obtained the LS estimate is grouped by the factors in which the correlation matrix may have the same value in step S405.

)의

행

열의 인자는

번째 부반송파 위치에서의 LS 추정치와,

번째 부반송파 위치에서의 LS 추정치의 허미션을 곱한 값에 샘플 평균을 취해 얻을 수 있다. 본 발명의 실시 예에서 그룹화는 상관 행렬(Correlation matrix,

)이

에서 종속(dependent)되는 특성을 이용한다. 상관 행렬은 그 행렬의 각 인자가 대각선에서 동일한 값을 갖는다. Correlation matrix,

)of

line

The argument of the column is

LS estimate at the first subcarrier position,

A sample average may be obtained by multiplying the hermit of the LS estimate at the second subcarrier position. In an embodiment of the present invention, the grouping is performed by a correlation matrix,

)this

Use properties that are dependent on Correlation matrices have the same value on the diagonal of each factor of the matrix.

n). 또한, 상관 행렬의 행의 인덱스를

, 열의 인덱스를

라 한 경우,

는 수신 신호의 부반송파 인덱스

에서의 LS 추정치이며,

은 수신 신호의 부반송파 인덱스

에서의 LS 추정치의 허미션이다. 여기서, 상관 행렬(Correlation matrix,

)이

에서 종속(dependent)되는 특성이라 함은, (

-

) 값이 동일한 인자는 그 상관 행렬의 값이 동일한 값을 가진다. 부반송파 인덱스

,

에 의거하여, (

-

) 값이 동일한 인자별로 그룹화한다. In detail, the correlation matrix may be obtained by taking a sample average from a product of the LS estimate and the hermition of the LS estimate. In this case, since the rows and columns of the correlation matrix correspond to the LS estimate and the hermition of the LS estimate, the correlation matrix has the same number of rows and columns (n

n). In addition, the index of the row of the correlation matrix

, Index the column

If one

Is the subcarrier index of the received signal.

LS estimate at

Is the subcarrier index of the received signal.

The hermit of the LS estimate at. Here, the correlation matrix (Correlation matrix,

)this

Dependent characteristics in (

-

) The same arguments have the same values in the correlation matrix. Subcarrier index

,

In accordance with, (

-

) Group by the same factor.

3 크기를 가지는 상관 행렬인 경우, "1행 1열, 2행 2열, 3행 3열", "1행 2열, 2행 3열", 및 "2행 1열, 3행 2열"이 동일한 값을 가진다. 이에 따라 수신기는 상관 행렬이 동일한 값을 가질 수 있는 파일럿 심벌별로 다음의 <수학식 3>과 같이 그룹화를 수행한다. For example, 3

For a correlation matrix with 3 sizes, "1 row 1 column, 2 rows 2 columns, 3 rows 3 columns", "1 row 2 columns, 2 rows 3 columns", and "2 rows 1 column, 3 rows 2 columns" Has the same value. Accordingly, the receiver performs grouping as shown in Equation 3 below for each pilot symbol whose correlation matrix may have the same value.

일 때,

when,

이라고 정의하고, 이러한 정의에 따라, 전체 파일럿 심벌을 다수개의 파일럿 심벌 그룹으로 그룹화한다. That is, according to <Equation 3>

According to this definition, the entire pilot symbol is grouped into a plurality of pilot symbol groups.

Then, in step S407, the receiver divides each pilot group into two subgroups. The two subgroups can be classified according to Equation 4 below of the transmitter.

"는 1 또는 -1의 값을 가진다. 또한, LS 추정치의 허미션 값의 "

"도 1 또는 -1의 값을 가진다. Referring to <Equation 2> and <Equation 4>, since the transmitter modulated and transmitted in the BPSK method, the LS estimate of <Equation 2> is "

"Has a value of 1 or -1. Also, the"

"Has a value of 1 or -1.

Accordingly, the receiver forms a subgroup for each factor having such a value of 1 or -1. In Equation 4, the first equation is a subgroup having a value of 1, and the second equation is a subgroup having a value of -1.

Subsequently, the receiver calculates a correlation matrix for each subgroup by taking a sample mean for each subgroup in step S409. In this way, the correlation matrix for each subgroup obtained by taking the sample average in each subgroup is shown in Equation 5 below.

는 OFDM 심볼 수를 의미하고

와

는 각 서브 그룹의 인자 수를 의미한다. From here

Is the number of OFDM symbols

Wow

Denotes the number of arguments in each subgroup.

Equation 5 may be expressed as Equation 6 below.

(1)

(One)

(2)

(2)

Then, in step S411, the receiver adds the correlation matrix for each subgroup to remove interference and calculates a correlation matrix of a desired signal.

As shown in Equation 7, the interference matrix is removed to calculate a correlation matrix of the desired signal or the interference signal.

"만 남게 되며, 간섭 신호의 상관 행렬인 "

"는 제거된다. Referring to <Equation 6> and <Equation 7>, when the correlation matrix calculated for each subgroup is added as in the first equation of <Equation 7>, the correlation matrix of the desired signal is "2".

"Only remains, which is the correlation matrix of the interfering signal"

"Is removed.

"는 제거되며, 간섭 신호의 상관 행렬인 "

"만 남게 된다. On the other hand, if the correlation matrix calculated for each subgroup is subtracted as in the second equation of Equation 7, the correlation matrix of the desired signal is &quot;

"Is removed, and the correlation matrix of the interfering signal"

"Only left.

Therefore, when the correlation matrix calculated for each subgroup is added, a correlation matrix of a desired signal can be obtained. When the correlation matrix calculated for each subgroup is subtracted, a correlation matrix of the interference signal can be obtained.

Accordingly, a correlation matrix for each of the serving base station 103 and the neighbor base station 105 may be separately obtained. In particular, when the correlation matrix calculated for each subgroup is added, the correlation matrix of the signal received from the serving base station 103 of the terminal can be obtained.

Subsequently, the receiver estimates a channel using the correlation matrix obtained in operation S413. In this case, the channel estimation method is preferably estimated according to the minimum mean square error (MMSE) method. Then, the receiver compensates for the channel of the desired signal using the channel estimated in step S415. In this way, the receiver demodulates data symbols in which the channel is compensated by the estimated channel to receive the data.

Second embodiment

Next, a channel estimation method according to another embodiment of the present invention will be described.

According to another embodiment of the present invention, as described above, although the serving base station and the neighboring base station transmit the pilot symbols at the same location, the terminal 101 may receive a sufficient number of pilot symbols for channel estimation. Assume no situation. If the terminal has a very fast moving speed, the terminal cannot receive the required number of pilot symbols for channel estimation.

Next, the operation of the receiver for receiving the transmitted signal will be described as described with reference to FIG. 3. That is, a method of estimating a channel by extracting a pilot symbol from the signal as described above and receiving a data symbol using the estimated channel will be described.

5 is a flowchart illustrating a channel estimation method according to another embodiment of the present invention.

Referring to FIG. 5, the receiver receives a signal in step S501. The received signal may be expressed as Equation 1 above.

)를 구한다. LS 추정치는 상기 <수학식 2>에 따라 구해진다. Then, the receiver according to the LS (Least square) estimation technique in step S503, LS estimator,

) The LS estimate is obtained according to Equation 2 above.

Then, the receiver obtains a correlation matrix from a power delay profile (PDP) in step S505. The PDP has characteristic values such as time delay and average power of the channel. Therefore, the receiver assumes that the PDP is uniform and derives a correlation matrix from this uniform PDP. This correlation matrix includes an auto-correlation matrix and a cross-correlation matrix, and is shown in Equation 8 below.

: Auto-correlation matrix

: Auto-correlation matrix

: Cross-correlation matrix:

Cross-correlation matrix:

과

은 원하는 신호(desired signal)와 간섭 신호(interferer) 상관 행렬이며, PDP로부터 도출할 수 있다. 이때, 아래글자(subscript) p는 파일럿 심벌의 위치를 의미하고, 원하는 신호와 간섭 신호의 파일럿 시퀀스는 수신기에 제공되는 것으로 가정한다. In Equation 8

and

Is a desired signal and interferer correlation matrix and can be derived from the PDP. In this case, it is assumed that the subscript p means the position of the pilot symbol, and the pilot sequence of the desired signal and the interference signal is provided to the receiver.

및

)를 얻기 위해서는 원하는 신호(desired signal)의 채널에 대한 상관 행렬(correlation matrix,

) 및 간섭 신호(interferer)의 채널에 대한 상관 행렬(

)이 필요하다. MMSE channel estimator (

And

To obtain the correlation matrix for the channel of the desired signal.

) And the correlation matrix for the channel of the interferer (

) Is required.

According to the second embodiment, if the correlation matrix of the desired signal and the interference signal cannot be obtained or is not given, the correlation matrix is derived from the PDP.

According to the assumption in the second embodiment, there is a situation where a sufficient number of pilot symbols for obtaining a correlation matrix cannot be obtained. For this reason, in the second embodiment, a channel impulse response is assumed as in Equation 9 below.

According to Equation 9, the coefficient of the correlation matrix may be calculated as in Equation 10 below.

)의 값이 필요하다. Therefore, in order to obtain a channel correlation matrix, an average power and time delay determined by a power delay profile (PDP)

Is required.

For this reason, according to the second embodiment of the present invention, in order to obtain a correlation matrix required for MMSE channel estimation, it is assumed that the desired signal and the PDP of the interference signal are uniform. Assuming a uniform PDP, the channel impulse response is expressed by Equation 11 below.

The channel correlation matrix coefficient obtained from Equation 11 may be expressed as Equation 12 below.

As such, if a correlation matrix between a desired signal and an interference signal cannot be obtained or is not given, as described above, a uniform PDP is assumed and a correlation matrix is assumed from the assumed uniform PDP. To derive The derived correlation matrix is shown in Equation 7.

On the other hand, if a PDP is given, the channel response and correlation matrix coefficients can be obtained using the given PDP, and a correlation matrix can be derived.

Subsequently, the receiver estimates a channel using the correlation matrix obtained through the uniform PDP in step S507. In this case, the channel estimation method is preferably estimated according to the minimum mean square error (MMSE) method. Then, the receiver compensates for the channel of the desired signal using the channel estimated in step S509. In this way, the receiver demodulates the data symbols in which the channel is compensated by the estimated channel and receives the data.

Next, the configuration of a transmitter and a receiver according to an embodiment of the present invention will be described.

First, the structure of a transmitter according to an embodiment of the present invention will be described. 6 is a diagram illustrating a transmitter structure according to an embodiment of the present invention.

Referring to FIG. 6, the transmitter includes a binary data generator 610, a data symbol mapper 620, a pilot symbol generator 630, and a symbol inserter 620. 640, an Inverse Fast Fourier Transform (IFFT) 650, and a Guard Interval (GI) Inserter 660.

The binary data to be transmitted is generated from the binary data generator 610, and is modulated (mapping / modulated) by the data symbol mapper 620, and the pilot symbol generator 630 generates pilot symbols that are identically known between the transmitter and the receiver. do. The mapped data symbols and pilot symbols are assigned to the subcarriers in the symbol inserter 130. At this time, both the serving base station 103 and the neighboring base station 105 are inserted in the same position pilot symbols. This signal is converted into a signal in the time domain via IFFT 150, which produces a baseband signal that is finally transmitted via GI inserter 160.

In particular, according to the first embodiment of the present invention, the pilot symbol generator generates a modulated pilot symbol according to the BPSK. A pilot symbol modulated according to BPSK has a value of 1 or -1. Therefore, in the first embodiment of the present invention, two subgroups of groups in which the correlation matrix must have the same value may be formed according to the pilot symbol value.

Next, a structure of a receiver according to an embodiment of the present invention will be described.

7A to 7C are diagrams for describing a structure of a receiver for channel estimation according to an embodiment of the present invention. In particular, Figure 7b is a configuration according to a first embodiment of the present invention, Figure 7c is a configuration according to a second embodiment of the present invention.

7A to 7C, a receiver according to an embodiment of the present invention includes a guard interval removal (GI) device 710, a fast fourier transform (FFT) device 720, and a pilot symbol extraction device (FFT). 730, a data extractor 740, an equalizer 750, a data symbol demapper 760, and a channel estimator 770.

The GI remover 710 removes and outputs a guard interval of the received OFDM symbol. The fast fourier transform unit 720 performs a fast Fourier transform on the input time domain signal and outputs the signal in the frequency domain.

The pilot extractor 730 extracts a pilot symbol from the signal converted into the frequency domain and inputs it to the channel estimator 780.

The data extractor 740 extracts the data symbols from the signal converted into the frequency domain and inputs them to the equalizer 750.

The equalizer 750 equalizes input data symbols according to channel estimation of the channel estimator 770 to compensate for the influence of the channel.

The demodulator 760 outputs binary data by demodulating and demodulating the input data symbols according to a modulation scheme.

The channel estimator 770 estimates a channel according to an embodiment of the present invention, but the channel estimating method of the channel estimator varies according to the first and second embodiments.

Referring to FIG. 7B, the channel estimator 770 according to the first embodiment of the present invention may include an LS estimator 801, a grouping unit 803, a correlation matrix calculator 805, An interpolator 807 and an MMSE channel estimator 809.

LS estimation is calculated according to a LS estimation (LS) estimator (801) and an LS estimation method. The LS estimate is calculated by dividing the received symbol into one-to-one at a pilot symbol position by a pilot symbol known to the transmitter and the receiver. This is shown in (Equation 2).

As described above, the grouper 803 groups the correlation matrices by the factors in which the correlation matrix may have the same value in the LS estimate, and forms subgroups according to the values (1, -1) of the grouped LS estimate.

The correlation matrix calculator 805 calculates a correlation matrix for each subgroup by taking a sample average of LS estimates for each subgroup. This is shown in Equation 6. In addition, the correlation matrix calculator 805 may remove interference and calculate a correlation matrix of a desired signal by adding or subtracting a correlation matrix for each subgroup obtained as shown in Equation (6).

The interpolator 807 interpolates the values at the data symbol positions of the correlation matrix described above. Such interpolation can optionally be performed.

The MMSE channel estimator 809 receives a correlation matrix and estimates a channel according to the MMSE method through the received correlation matrix. MMSE channel estimator 809 then provides the estimated channel value to equalizer 750.

Referring to FIG. 7C, the channel estimator 770 according to the second embodiment of the present invention may include an LS channel estimator 901, a correlation matrix calculator 903, and an MMSE channel estimator 770. 809).

An LS estimate is calculated according to an LS channel estimator 901 and an LS estimation method. The LS estimate is a pilot symbol that is known to both the transmitter and the receiver and is calculated by dividing the received symbol one-to-one at the pilot symbol position. This is shown in (Equation 2).

The correlation matrix calculator 903 derives a correlation matrix based on the PDP. That is, the correlation matrix calculator 903 assumes a specific channel response and derives a correlation matrix using a power delay profile (PDP) from the assumed channel response.

The MMSE channel estimator 905 receives a correlation matrix and estimates a channel through the received correlation matrix. MMSE channel estimator 809 then provides the estimated channel value to equalizer 750.

Next, effects of the channel estimation method according to the second embodiment of the present invention will be described. 8A and 8B are diagrams for describing an effect of a channel estimation method according to a second embodiment of the present invention.

According to the second embodiment of the present invention, the channel estimation method in the interference environment using the uniform PDP improves the channel estimation performance in the interference environment compared to the conventional channel estimation method in which the interference is not considered. It became.

In addition, as the estimated channel of the desired signal and the interference signal can be obtained, " CCI suppression " using two receive antennas is possible. Accordingly, it is possible to obtain BER performance improvement of the desired signal. Since this method does not need to directly estimate a correlation matrix between a desired signal and an interference signal, a gain in complexity can be obtained in comparison with the same method as the first embodiment in which the correlation matrix is directly estimated.

8A and 8B, the channel estimation method (Uniform PDP) in the interference environment using the uniform PDP has a performance degradation compared to the case where a correlation matrix is given (Known PDP), but does not consider interference. It can be seen that the MSE and BER performances are better than those of the MMSE channel estimation method (No CCI consideration).

Next, effects of the channel estimation method according to the first embodiment of the present invention will be described. 9A and 9B are diagrams for describing an effect of a channel estimation method according to the first embodiment of the present invention.

The method according to the first embodiment improves channel estimation performance in an interference environment as compared to the method according to the second embodiment. In addition, as the channel estimation performance is improved, the accuracy of "CCI suppression" is also increased, and thus the BER performance of the desired signal can be improved as compared with the uniform PDP. Although there is an increase in complexity due to correlation matrix estimation, a corresponding performance improvement can be obtained. In order to secure enough pilot information, the pilot information for several frames should be used, but the channel correlation matrix, which is a statistical characteristic of the channel, will not change significantly for several frames. However, the error due to the change in the channel correlation value will not be large while using the pilot information of several frames.

Referring to FIG. 9A, when the correlation matrix estimated when the MMSE channel is estimated according to the first embodiment is used, a correlation matrix from a uniform PDP is obtained (Uniform PDP). It can be seen that the estimation performance is excellent, and that the estimation performance is close to the channel estimation performance given a correlation matrix ('Known PDP').

Referring to FIG. 9B, when the correlation matrix is estimated by using the correlation matrix of the desired signal and the interference signal (Uniform PDP), and the MMSE channel is estimated, the BER performance of the desired signal may be better. It also shows close performance even assuming a correlation matrix (Known PDP).

Here, "Known channel" is a case where the channel is assumed to be perfectly estimated, "Proposed 1FRM" uses a pilot for 1 frame based on LTE, and "Proposed 10FRM" uses a pilot for 10 frames. will be.

While the present invention has been described with reference to several preferred embodiments, these embodiments are illustrative and not restrictive. As such, those of ordinary skill in the art will appreciate that various changes and modifications can be made according to equivalents without departing from the spirit of the present invention and the scope of rights set forth in the appended claims.

1 is a view for explaining the configuration of a wireless communication network according to an embodiment of the present invention.

2 is a diagram illustrating a frame structure of an OFDM communication system according to an exemplary embodiment of the present invention.

3 is a diagram illustrating a data transmission method of a transmitter according to an embodiment of the present invention.

4 is a flowchart illustrating a channel estimation method according to an embodiment of the present invention.

5 is a flowchart illustrating a channel estimation method according to another embodiment of the present invention.

6 is a diagram illustrating a transmitter structure according to an embodiment of the present invention.

7A to 7C are diagrams for describing a structure of a receiver for channel estimation according to an embodiment of the present invention.

8A and 8B illustrate the effects of a channel estimation method according to a second embodiment of the present invention.

9A and 9B are diagrams for explaining the effect of a channel estimation method according to the first embodiment of the present invention.

Claims (4)

In the channel estimation method of a wireless communication system, Calculating an LS estimate using a pilot signal of the received signal; Grouping the calculated LS estimates into factors in which a correlation matrix may have the same value, and subgrouping the grouped LS estimates into two subgroups according to values of each factor; Calculating a correlation matrix by taking a sample average for each subgroup; Calculating a correlation matrix from which interference signals are eliminated by adding a correlation matrix for each subgroup, And estimating a channel using the correlation matrix from which the interference signal has been removed. In the channel estimation method of a wireless communication system, Calculating an LS estimate using a pilot signal of the received signal; A process of deriving a correlation matrix from the assumed uniform PDP, assuming a PDP (Power Delay Profile) as a uniform; And estimating a channel by using the derived correlation matrix. An apparatus for channel estimation of a wireless communication system, A pilot extractor for extracting pilot symbols from the received signal; An LS estimator for calculating an LS estimate from the pilot symbols; A grouping group for grouping by a factor that the correlation matrix may have the same value in the calculated LS estimate, and forming a subgroup according to the values of the grouped LS estimates (1, -1); And A correlation matrix calculator for taking a sample average of the LS estimates for each subgroup, calculating a correlation matrix for each subgroup, and adding a correlation matrix for each subgroup to calculate a correlation matrix from which interference is eliminated; An MMSE channel estimator for estimating a channel according to an MMSE scheme by using the correlation matrix from which the interference is removed; And And an equalizer for compensating for the distorted channel based on the estimated channel. In the channel estimation apparatus of a wireless communication system, A pilot extractor for extracting pilot symbols from the received signal; An LS estimator for calculating an LS estimate from the pilot symbols; A correlation matrix calculator that assumes a power delay profile (PDP) as a uniform and derives a correlation matrix from the assumed uniform PDP; An MMSE channel estimator for estimating a channel according to an MMSE scheme using the correlation matrix from which the interference is removed; And And an equalizer for compensating for the distorted channel based on the estimated channel.

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