KR100921183B1 - Method and Apparatus for estimating channel based on pilot tones in wireless communication system - Google Patents

Abstract

Disclosed is a method and apparatus for pilot tone-based channel estimation that enables efficient channel estimation even when there is a symbol timing offset.

According to an embodiment of the present invention, an embodiment includes estimating a channel for a first subcarrier and a second subcarrier on which a pilot signal is located, and interpolating using magnitudes and phase components of channel estimation values of the first subcarrier and the second subcarrier. Obtaining a magnitude or phase component of a channel estimate value for a data subcarrier located between the first subcarrier and a second subcarrier by using an extrapolation using the magnitude and phase component of the channel estimate value of the first subcarrier and the second subcarrier The method provides a pilot tone-based channel estimation method comprising the step of obtaining a magnitude or phase component of a channel estimation value for a data subcarrier located outside the first subcarrier and the second subcarrier.

Pilot tones, interpolation, interpolation, extrapolation

Description

{Method and Apparatus for estimating channel based on pilot tones in wireless communication system}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to channel estimation in a wireless communication system, and more particularly, to a pilot tone-based channel estimation method and apparatus capable of efficient channel estimation even when there is a symbol timing offset.

The present invention is derived from research conducted as part of the IT growth engine technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. [Task Management Number: 2006-S-001-02, Title: Adaptive Wireless Access for 4th Generation Mobile Communications] And transmission technology development].

Since the transmission technology of the wireless communication system, for example, the OFDM transmission technology has a strong characteristic against multipath fading, it is mainly used in a wireless communication system requiring a high transmission speed.

In the OFMD system, channel estimation performs time synchronization before channel estimation using a preamble or a guard interval included in a received signal.

The channel estimation method may be classified into a pilot symbol based channel estimation method and a method using a pilot tone inserted at a predetermined interval of frequency and symbol period.

The pilot symbol based channel estimation method assumes slow fading with no channel change between repeated pilot symbols.

The pilot symbol-based channel estimation method includes a least square (Least Square) method and a minimum mean square error (MMSE) method. The MMSE channel estimation method is an LS channel estimation method. Although it shows better performance, it has a disadvantage of having a large amount of calculation.

The pilot tone-based channel estimation method is robust to fast fading in which channel changes can occur between pilot symbols, but requires channel estimation for subcarriers where pilot tones are located and interpolation for adjacent data subcarrier intervals.

Interpolation methods for channel estimation in adjacent data subcarrier intervals using channel values estimated from pilot tones include linear interpolation, quadratic interpolation, low-pass filter interpolation, and spline cubic interpolation. Quadratic interpolation shows better channel estimation performance than linear interpolation, and time-domain interpolation using low-pass filter generally shows better bit error rate (BER) than linear interpolation.

The pilot tone-based channel estimating technique removes the inserted guard interval to remove inter-symbol interference (ISI) and inter-carrier interference (ICI). The channel is estimated using the FFT output signal. At this time, if there is an FFT starting point in the protection interval due to incomplete time synchronization, phase rotation occurs in the frequency domain. This phase rotation in the frequency domain generates phase rotation at the channel value estimated at the pilot tone position, and phase and magnitude distortion occurs when channel interpolation is performed in the adjacent data subcarrier interval using the channel value estimated at the pilot tone position. do. In general, when a small symbol timing offset occurs within a guard interval, compensation is possible by using a conventional channel estimation method using a pilot tone and an interpolation method within a data subcarrier section.However, as the symbol timing offset increases, the channel estimation performance increases. The deterioration is greatly increased.

Accordingly, an aspect of the present invention is to provide a pilot tone-based channel estimation method and apparatus capable of estimating a channel of a data subcarrier interval without distortion regardless of a symbol timing offset.

In addition, the present invention eliminates the process for estimating the phase rotation and the process for compensating the estimated phase rotation by estimating the magnitude and phase of the channel estimate of the data subcarrier using the channel estimate of the subcarrier on which the pilot signal is transmitted. SUMMARY To provide a pilot tone based channel estimation method and apparatus.

In addition, the present invention provides a pilot tone-based channel estimation method and apparatus for estimating the magnitude and phase of the channel estimation value of the data subcarrier using the channel estimation value of the subcarrier on which the pilot signal is transmitted, To provide.

In accordance with another aspect of the present invention, a channel for a first subcarrier and a second subcarrier on which a pilot signal is located is estimated, and magnitudes and phases of channel estimation values of the first subcarrier and the second subcarrier are located. Obtaining a magnitude or phase component of a channel estimate value for a data subcarrier located between the first subcarrier and a second subcarrier by interpolation using a component, and a magnitude of a channel estimate value of the first subcarrier and the second subcarrier And obtaining a magnitude or phase component of a channel estimation value for data subcarriers located outside the first subcarrier and the second subcarrier by extrapolation using a phase component.

Another embodiment of the present invention provides a pilot tone channel estimator for estimating a channel for a first subcarrier and a second subcarrier in which a pilot signal is located in a received signal, and a phase of the first subcarrier estimated by the pilot tone channel estimator. An estimator for estimating a phase component of a data subcarrier by a component and a phase component of a second subcarrier, and a magnitude of a channel estimate value of a first subcarrier estimated by the pilot tone channel estimator and a channel estimate value of a second subcarrier Provided is a pilot tone-based channel estimating apparatus including a magnitude estimator for estimating a magnitude of a channel estimation value for a data subcarrier.

According to another embodiment of the present invention, the phase estimation of the data subcarrier is performed by using the phase component of the first subcarrier channel estimate value and the phase component of the second subcarrier channel estimate value to the center of the first subcarrier and the second subcarrier. Obtaining a phase component of a first data subcarrier located at the second data carrier, and using the phase component of the first subcarrier and a phase component of the first data subcarrier, the second data located at the center of the first subcarrier and the first data subcarrier The phase component of the subcarrier is estimated, and the phase component of the third data subcarrier located at the center of the second subcarrier and the first data subcarrier is calculated using the phase component of the second subcarrier and the phase component of the first data subcarrier. It includes estimating.

According to another embodiment of the present invention, the estimation of the magnitude of the channel estimate for the data subcarrier is performed by the interpolation using the magnitude of the channel estimate of the first subcarrier and the magnitude of the channel estimate of the second subcarrier. Estimating the magnitude of the channel estimate of the first data subcarrier positioned at the center of the two subcarriers, and interpolating the magnitude of the channel estimate of the first subcarrier and the magnitude of the channel estimate of the first data subcarrier with the first subcarrier. Estimating the magnitude of the channel estimate of the second data subcarrier located at the center of the first data subcarrier, and interpolating the magnitude of the channel estimate of the second subcarrier and the magnitude of the channel estimate of the first data subcarrier. A second data carrier positioned at the center of the second subcarrier and the first data subcarrier It involves estimating the size of the channel estimated value of the transmitting.

According to an embodiment of the present invention, the channel of the data subcarrier interval may be estimated without distortion regardless of the symbol timing offset.

Further, according to an embodiment of the present invention, by estimating the magnitude and phase of the channel estimate of the data subcarrier using the channel estimate of the subcarrier on which the pilot signal is transmitted, the process for estimating phase rotation and the estimated phase rotation are compensated for. The process for doing so can be eliminated.

In addition, according to an embodiment of the present invention, by reducing the amount of computation required for channel estimation, it is possible to estimate the channel for the data subcarriers without degrading hardware performance.

 Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In describing the present invention, when it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. Terminology used herein is a term used to properly express a preferred embodiment of the present invention, which may vary according to a user, an operator's intention, or a custom in the field to which the present invention belongs. Therefore, the definitions of the terms should be made based on the contents throughout the specification.

In the following description, definitions and concepts of terms are as follows.

Pilot subcarrier: a subcarrier on which a pilot signal is transmitted in an OFDM symbol

(Hereinafter, any two pilot subcarriers of the pilot subcarriers included in the OFDM symbol will be referred to as a first subcarrier and a second subcarrier.)

Data subcarriers: subcarriers through which data signals are transmitted in OFDM symbols

Channel Estimates for Pilot Subcarriers: Channel Values Estimated at Pilot Tone Locations

Channel Estimates for Data Subcarriers: Channel Values Estimated at Data Subcarrier Locations

1 is a block diagram showing the structure of a receiving end of an OFDM system according to an embodiment of the present invention.

Referring to FIG. 1, a receiving end of an OFDM system includes a serial / parallel converter 121 for converting a received signal into a parallel signal, a guard interval remover 222 for removing a guard interval of the parallelized signal, and the guard interval is removed. A fast Fourier transformer 223 for fast Fourier transforming the extracted signal, a channel estimator 224 for estimating and compensating for the channel of the Fourier transformed signal, a parallel / serial converter 225 for serializing the compensated signal, and And a signal detector 226 for detecting a binary signal from the serialized signal.

2 is a block diagram illustrating a configuration of an apparatus for estimating a pilot tone based channel according to an embodiment of the present invention.

Referring to FIG. 2, the channel estimating apparatus includes a pilot tone channel estimator 210 estimating a channel for a first subcarrier and a second subcarrier on which a pilot signal is located in a received signal, and a pilot tone channel estimator 210. Phase estimators 221 and 231 for estimating the phase of the data subcarriers based on the estimated phase components of the first subcarrier and the phase components of the second subcarrier, and magnitudes of the channel estimates of the first subcarrier estimated by the pilot tone channel estimator 210. And magnitude estimators 222 and 232 of the channel estimates for estimating the magnitude of the channel estimates of the data subcarriers based on the magnitudes of the channel estimates of the second subcarriers.

The phase estimators 221 and 231 may include an interpolation phase estimator 221 for estimating a phase of a data subcarrier positioned between the first subcarrier and a second subcarrier, and a data subcarrier located outside the first subcarrier and the second subcarrier. An extrapolation phase estimator 231 estimating a phase and a code estimator 223 estimating a sign of a phase estimated by the interpolation phase estimator and the extrapolation phase estimator may be included.

According to another embodiment of the present invention, the channel estimating apparatus includes a pilot tone channel estimator 210 for estimating a channel of a pilot tone input from a receiver, and an interpolation for estimating a channel of a data subcarrier according to the channel estimate value of the pilot tone. An estimator 220 and an extrapolator estimator 230, and a channel compensator 240 for compensating for channels according to the values estimated by the estimators 220 and 230 may be included.

In this case, the interpolation estimator 220 includes an interpolation phase estimator 221 for estimating the phase of the data subcarrier by interpolation, and an interpolation channel size estimator 222 for estimating the magnitude of the channel estimate value of the data subcarrier by interpolation, and the estimated interpolation channel size estimator 222. And a sign estimator 233 for estimating the sign of the channel.

The extrapolation estimator 230 may include an extrapolation phase estimator 231 estimating the phase of the data subcarrier by extrapolation and an extrapolation channel size estimator 232 estimating the magnitude of the channel estimate value of the data subcarrier by extrapolation. have.

The pilot tone channel estimator 210 estimates a channel for two subcarriers (pilot subcarriers) in which a pilot signal is located in an OFDM symbol including the received pilot signal.

In this case, it is assumed that the start position of the received OFDM symbol is frame synchronization performed between b and c sections of FIG. 3 using a pilot symbol. In addition, channel estimation of a pilot subcarrier on which a pilot signal is located may be estimated by a Least Square (LS) technique.

The interpolation phase estimator 221 uses a phase component of the first subcarrier channel estimate value and a phase component of the second subcarrier channel estimate value to determine the first data subcarrier located at the center of the first subcarrier and the second subcarrier. Find the phase component.

The interpolation phase estimator 221 uses a phase component of the first subcarrier and a phase component of the first data subcarrier to select a phase component of a second data subcarrier positioned at the center of the first subcarrier and the first data subcarrier. Estimate.

The interpolation phase estimator 221 uses a phase component of the second subcarrier and a phase component of the first data subcarrier to select a phase component of a third data subcarrier positioned at the center of the second subcarrier and the first data subcarrier. Estimate.

The extrapolation phase estimator 231 is disposed between the first subcarrier and the second subcarrier and is disposed by the phase of the fourth data subcarrier adjacent to the first subcarrier and the phase of the first subcarrier. A phase of a fifth data subcarrier located outside and adjacent to the first subcarrier is estimated.

The interpolation channel size estimator 222 is located at the center of the first subcarrier and the second subcarrier by interpolation using the magnitude of the estimated channel estimate of the first subcarrier and the estimated channel estimate of the second subcarrier. The magnitude of the channel estimate of the first data subcarrier is estimated.

The interpolation channel size estimator 222 is located at the center of the first subcarrier and the first data subcarrier by interpolation using the magnitude of the channel estimate of the first subcarrier and the magnitude of the channel estimate of the first data subcarrier. Estimate the magnitude of the channel estimate of the second data subcarrier,

The interpolation channel size estimator 222 is positioned at the center of the second subcarrier and the first data subcarrier by interpolation using the magnitude of the channel estimate of the second subcarrier and the magnitude of the channel estimate of the first data subcarrier. 3 Estimate the magnitude of the channel estimate of the data subcarrier.

The extrapolation channel size estimator 232 estimates the magnitudes of the channel estimation values of the data subcarriers located outside the first subcarrier and the second subcarrier by extrapolation in the same manner as the size estimation of the channel estimation values by interpolation.

Hereinafter, a phase estimation and magnitude estimation method for a data subcarrier will be described in detail with reference to the accompanying drawings.

First, it is assumed that one received OFDM symbol consists of N subcarriers. In addition, it is assumed that the N subcarriers multiplex the data and the pilot signal in a symbol period S _t at intervals S _f .

At this time, the minimum pilot interval that satisfies the Nyquist sampling theory is determined by the bandwidth of the channel change and the maximum propagation delay value on the time axis and the frequency axis, and can be expressed by Equation 1 below.

[Equation 1]

는 각각 주파수 축에서의 도플러 확산과 시간 축에서의 최대 지연 확산을 나타낸다.B _d in Equation 1 and

Denotes Doppler spread on the frequency axis and maximum delay spread on the time axis, respectively.

(

)이 일정한 간격으로 존재하면, 각 부반송파 채널은 L_g=N/N_p개의 그룹으로 나눠지고, k번째 부반송파는 다음의 수학식 2와 같이 나타낼 수 있다.N _p pilot tones in one OFDM symbol

(

) At regular intervals, each subcarrier channel is divided into L _g = N / N _p groups, k-th subcarrier can be represented by the following equation (2).

[Equation 2]

Referring to Equation 2, the inverse fast Fourier transformed received signal is an impulse response length is larger N _g of the guard interval than the L channel is inserted in order to maintain the orthogonality between removing ISI caused by multipath fading and subcarriers N _s = N + N _g samples are OFDM symbols.

Here, the n th sample in the received i th OFDM symbol time domain may be represented by Equation 3 below.

[Equation 3]

은 각각 i 번째 OFDM 심벌의 n 번째 샘플, 채널의 임펄스 응답, 위상 잡음, 컨볼루션(convolution)을 나타낸다. Referring to Equation 3,

Are the n th sample of the i th OFDM symbol, the impulse response of the channel, phase noise, and convolution, respectively.

In addition, z _i (n) and ε (epsilon) represent Additive White Gaussian Noise (AWGN) and normalized frequency offset, respectively.

Here, assuming that the symbol timing offset is the same between every symbol and that the frequency of the transceiver is precisely synchronized so that there is no phase noise, the fast Fourier transform output of the received signal may be expressed by Equation 4 below.

[Equation 4]

는 수신 OFDM 심벌의 심벌 타이밍 오프셋

에 의해 발생하는 ISI와 ICI를 나타낸다. 한편, 수학식 3을 참조하면, 수학식 4에서

는 고속 푸리에변환 출력에 포함되어 있는 가산 백색 가우시안 잡음임을 알 수 있다.In Equation 4,

Is the symbol timing offset of the received OFDM symbol

Indicates ISI and ICI generated by. Meanwhile, referring to Equation 3, Equation 4

It can be seen that is the added white Gaussian noise included in the fast Fourier transform output.

As described above, the time synchronization error generated in the time domain generates linear phase rotation, ISI, and ICI in the frequency domain output signal after the FFT.

에 대해, 다음의 도 3을 참조하여 설명한다.remind

This will be described with reference to the following FIG. 3.

3 is a diagram illustrating a time synchronization range of an OFDM symbol.

와

는 제거된다. Referring to FIG. 3, if the start position of the FFT window for the time-domain received signal of Equation 4 is exactly located at c,

Wow

Is removed.

로 인한 주파수영역에서 선형 위상회전은 발생하지만

는 제거된다. However, if it is located between the a and b intervals or between the c and d intervals, ISI and ICI occur and the orthogonality between subcarrier channels is destroyed.

Linear phase rotation occurs in the frequency domain due to

Is removed.

Therefore, in the present invention, it can be assumed that frame detection and approximate symbol timing offset estimation are performed to determine an OFDM symbol start position between b and c intervals.

An OFDM signal considering only phase rotation in a frequency domain due to time synchronization error while maintaining orthogonality between subcarriers may be represented by Equation 5 below.

[Equation 5]

Hereinafter, in the following description, it is assumed that the OFDM signal is a signal of the above expression (5).

4 is a view for explaining a pilot tone-based channel estimation method according to an embodiment of the present invention.

,

)을 이용한 내삽에 의하여 상기 제1 부반송 파 및 제2 부반송파 사이에 위치하는 데이터 부반송파에 대한 채널을 추정하는 단계(1단계~3단계) 및 상기 제1 부반송파 및 제2 부반송파의 채널 추정 값을 이용한 외삽에 의하여 상기 제1 부반송파 및 제2 부반송파 외부에 위치하는 데이터 부반송파에 대한 채널을 추정하는 단계(4단계~5단계)를 포함한다. Referring to FIG. 4, the channel estimation method estimates a channel for a first subcarrier and a second subcarrier on which a pilot signal is located, and estimates channel values of the first subcarrier and the second subcarrier (

,

Estimating a channel for the data subcarriers located between the first subcarrier and the second subcarrier (steps 1 to 3) and interpolating channel estimation values of the first subcarrier and the second subcarrier by interpolation. Estimating a channel for data subcarriers located outside the first subcarrier and the second subcarrier by using extrapolation (steps 4 to 5).

Therefore, according to an embodiment of the present invention, in obtaining a channel estimation value of a data subcarrier, phase and magnitude may be separately estimated.

In FIG. 4, channel estimation values of the first subcarrier and the second subcarrier can be expressed by Equations 6 and 7 below.

[Equation 6]

[Equation 7]

)를 추정할 수 있다(1단계). The interpolation size estimator 222 is positioned at the center of the first subcarrier and the second subcarrier by interpolation using the magnitude of the estimated channel estimate of the first subcarrier and the estimated channel estimate of the second subcarrier. The magnitude of the channel estimate of the 1 data subcarrier (

) Can be estimated (step 1).

,

및

을 이용한 내삽에 의하여 상기 제1 부반송파와 상기 제1 데이터 부반송파의 중심에 위치하는 제2 데이터 부반송파의 채널 추정값의 크기(

) 및 상기 제2 부반송파와 상기 제1 데이터 부반송파의 중심에 위치하는 제3 데이터 부반송파의 채널 추정값의 크기(

)를 추정할 수 있다(2단계). The interpolation size estimator 222

,

And

The magnitude of the channel estimate of the second data subcarrier located at the center of the first subcarrier and the first data subcarrier by interpolation using

And the magnitude of the channel estimate of the third data subcarrier located at the center of the second subcarrier and the first data subcarrier

) Can be estimated (step 2).

,

및

를 이용한 내삽에 의하여

,

,

및

을 추정할 수 있다. In the same way, above

,

And

By interpolation

,

,

And

Can be estimated.

= (

+

)/2와 같이 정의 할 수 있다. At this time, the magnitude of the estimated channel estimate is

= (

+

Can be defined as

, )는

,

,

및

을 이용한 외삽에 의하여 구할 수 있다. Referring to FIG. 4, the magnitudes of channel estimates of data subcarriers located outside the first subcarrier and the second subcarrier (

,)

,

,

And

It can be obtained by extrapolation using.

Here, FIG. 4 assumes an odd number of data subcarriers located between the first subcarrier and the second subcarrier.

If the number of data subcarriers located between the first subcarrier and the second subcarrier is an even number, the magnitude of the channel estimate value can be estimated in the same manner as the odd case, and the estimated value can be used as an approximation value.

,

,

,

를 추정하는 경우에,

및

는 상기 제1 부반송파와 제2 부반송파의 중심에 위치하는 가상의 데이터 부반송파의 채널 추정값의 크기를 이용하여 추정할 수 있다.That is, the channel size of the data subcarrier located between the first subcarrier and the second subcarrier

,

,

,

If we estimate

And

May be estimated using the magnitudes of channel estimates of the virtual data subcarriers located at the centers of the first subcarrier and the second subcarrier.

5 is a diagram for describing a concept of estimating the magnitude of a channel estimate of a data subcarrier according to an embodiment of the present invention.

과

는 서로 크기가 같으므로,

,

, 및

도 모두 동일한 크기로 보간할 수 있다.5, the estimated channel for the pilot subcarrier

and

Are the same size as each other,

,

, And

All can be interpolated to the same size.

That is, by using a virtual line that virtually connects the estimated channel sizes of the pilot subcarriers having different phases, the size of the channel estimates of the data subcarriers is compensated to the size of the virtual connection.

On the other hand, the interpolation size estimator 222 may estimate the size of the subcarrier channel, as shown in Figure 6 when the estimated channel size of the pilot subcarrier is different.

6 is a diagram for describing a concept of estimating the magnitude of a channel estimate of a data subcarrier according to another embodiment of the present invention.

및

는 서로 크기가 다르기 때문에, 상기

및

의 크기를 연결하여 생성되는 가상선(610)을 기준으로

,

및

의 채널 추정값의 크기를 보간할 수 있다. 6, the magnitude of the estimated channel estimate of the pilot subcarrier

And

Since the sizes are different from each other,

And

Based on the virtual line 610 generated by connecting the sizes of

,

And

The magnitude of the channel estimate of may be interpolated.

The phase estimators 221 and 231 may estimate phases of the first data subcarriers positioned at the centers of the first and second subcarriers using Equations 6 and 7.

According to an exemplary embodiment of the present invention, the interpolation phase estimator 221 is configured to reduce the amount of calculation from the phase component (cosine value and sin value) of the first subcarrier and the phase component of the first data subcarrier from the phase component of the first data subcarrier. Estimate the phase component.

More specifically, first, it is assumed that the estimated channel value of the first data subcarrier is expressed by Equation 8 below.

[Equation 8]

가 아닌,

및

임을 알 수 있다. Referring to Equation (8), what one wants to know from the channel estimation of the first data subcarrier is phase

Not

And

It can be seen that.

이기 때문에,

는 하기 표 1에 나타낸 유도식에 의하여 구할 수 있고, 유사한 방법으로

를 구할 수 있다. And,

Because

Can be obtained by the induction formula shown in Table 1 below,

Can be obtained.

TABLE 1

을 통하여

를 구하고, 유사한 방법으로

를 구한 후에

를 구하는 방법에 비하여 계산량을 크게 줄일 수 있다. According to the above method,

Through

To obtain and in a similar way

After getting

Computation can be greatly reduced compared to the method of obtaining.

에 대한 룩-업 테이블에 값을 저장하여 이용하는 방법은 메모리가 많이 소모되는 단점이 있다.Also, separate

The method of storing and using a value in a look-up table for VW uses a lot of memory.

Using a similar method, the interpolation phase estimator 221 is positioned at the center of the first subcarrier and the first data subcarrier using the phase component of the first subcarrier and the phase component of the first data subcarrier. Estimating a phase component of a data subcarrier, and using the phase component of the second subcarrier and the phase component of the first data subcarrier, a phase component of a third data subcarrier positioned at the center of the second subcarrier and the first data subcarrier Can be estimated.

7 illustrates an interpolation code determination method according to an embodiment of the present invention.

과

로 정규화된 크기를 가지는 채널의 중심 값 위상은 inphase와 quadrature를 각각 선형 보간한 위상과 일치하기 때문에 용이하게

삼각함수 부호를 결정할 수 있게 되어

범위의 위상을 추정할 수 있다. 수학식 1에서 설명된 바와 같이, m은 파일럿 톤의 개수이고, k는 부반송파의 인덱스를 나타낸다. Referring to Figure 7,

and

The center value phase of a channel with a magnitude normalized to is easily matched with the linear interpolated phase of inphase and quadrature, respectively.

To determine the trigonometric sign

The phase of the range can be estimated. As described in Equation 1, m is the number of pilot tones, k represents the index of the subcarrier.

8 is a view for explaining a phase estimation method according to another embodiment of the present invention.

(k)는 제1 부반송파의 채널 추정값이고,

(k+N_p)는 제2 부반송파의 채널 추정 값이다.Referring to FIG. 8,

(k) is the channel estimate of the first subcarrier,

(k + N _p ) is a channel estimate value of the second subcarrier.

(k+N_p +m)는 제1 부반송파 및 제2 부반송파의 외부에 존재하는 부반송파의 채널 값이며,

(k+N_p-1)은 제2 부반송파에 가장 근접하며 제1 부반송파 및 제2 부반송파의 내부에 존재하는 부반송파의 채널 값이다. 이때, m=1이라 가정하면,

(k+N_p +1)는 제1 부반송파 및 제2 부반송파의 외부에 존재하며, 제2 부반송파에 가장 근접하는 부반송파의 채널 값이라 할 수 있다. Also,

(k + N _p + m) is a channel value of subcarriers outside of the first subcarrier and the second subcarrier,

(k + N _p -1) is a channel value of a subcarrier that is closest to the second subcarrier and exists inside the first subcarrier and the second subcarrier. If m = 1,

(k + N _p +1) exists outside the first subcarrier and the second subcarrier, and may be referred to as a channel value of a subcarrier closest to the second subcarrier.

(k+N_p +1)의 위상은

(k+N_p-1) 및

(k+N_p)을 이용하여 추정할 수 있다. 즉,

(k+N_p-1) 의 위상을 a,

(k+N_p)의 위상을 b,

(k+N_p +1)의 위상을 c라고 하면, 2b -a = c의 관계가 성립한다. remind

The phase of (k + N _p +1) is

(k + N _p −1) and

It can be estimated using (k + N _p ). In other words,

The phase of (k + N _p -1) is a,

The phase of (k + N _p ) is b,

If the phase of (k + N _p +1) is c, the relationship of 2b -a = c is established.

Hereinafter, the results of the performance experiment on the channel estimation apparatus according to the embodiment of the present invention will be described.

Table 2 below shows the parameters used to confirm the performance of the pilot tone-based channel estimation scheme through simulation, and FIG. 9 shows the arrangement of pilot subcarriers used in the simulation.

TABLE 2

The simulation results below consider the moving speed of 3km / h assuming nomadic environment without considering the carrier frequency offset.

10 to 13 illustrate the performance of channel estimation techniques in the case of 16QAM in terms of MSE and BER.

It can be seen from FIG. 10 to FIG. 13 that there is an error floor in the existing linear interpolation channel estimation technique when there is a symbol timing offset, but the method according to the embodiment of the present invention shows a performance close to an ideal case.

The Meng-Han Hsieh's MMSE technique also exhibits near-ideal performance, but preliminary estimation of symbol timing offsets, etc., must be made to achieve this approach.

14 to 17 show the estimated channel values for the data subcarriers between pilot subcarriers in a complex plane.

14 shows an ideal channel (Ideal Ch), FIG. 15 is a real channel (Conventional CH), FIG. 16 is an MMSE channel, and FIG. 17 is a real measurement of the proposed channel (Proposed).

Referring to FIG. 15, the channel is distorted and estimated in the case of using the conventional linear interpolation method. Referring to FIG. 17, Meng-Han Hsieh's is ideal in the embodiment of the present invention without estimating symbol timing offset. Results similar to MMSE.

The pilot tone-based channel estimation method according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer-readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. The medium may be a transmission medium such as an optical or metal wire, a waveguide, or the like including a carrier wave for transmitting a signal specifying a program command, a data structure, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

1 is a block diagram showing the structure of a receiving end of an OFDM system according to an embodiment of the present invention.

2 is a block diagram illustrating a configuration of an apparatus for estimating a pilot tone based channel according to an embodiment of the present invention.

3 is a diagram illustrating a time synchronization range of an OFDM symbol.

4 is a view for explaining a pilot tone-based channel estimation method according to an embodiment of the present invention.

5 is a diagram for describing a concept of estimating the magnitude of a channel estimate of a data subcarrier according to an embodiment of the present invention.

6 is a diagram for describing a concept of estimating the magnitude of a channel estimate of a data subcarrier according to another embodiment of the present invention.

7 illustrates an interpolation code determination method according to an embodiment of the present invention.

8 is a view for explaining a phase estimation method according to another embodiment of the present invention.

9 shows an arrangement structure of pilot subcarriers used in the simulation.

10 to 13 are diagrams illustrating performance of channel estimation techniques in terms of MSE and BER in case of 16QAM.

14 to 17 are diagrams comparing channel values estimated for data subcarriers between pilot subcarriers in a complex plane.

Claims (14)

Estimating a channel for a first subcarrier and a second subcarrier in which a pilot signal is located in the received signal; Obtaining a magnitude of a channel estimate value for a data subcarrier located between the first subcarrier and the second subcarrier by interpolation using an imaginary line virtually connecting the magnitudes of the channel estimate values of the first subcarrier and the second subcarrier, Obtaining a phase component for a data subcarrier located between the first subcarrier and the second subcarrier by interpolation using phase components of the first subcarrier and the second subcarrier. At least one of a cosine value or a sine value; And Obtaining a magnitude of a channel estimate value for a data subcarrier located outside the first subcarrier and the second subcarrier by extrapolation using an imaginary line virtually connecting the magnitudes of the channel estimate values of the first subcarrier and the second subcarrier, And obtaining a phase of a data subcarrier located outside the first subcarrier and the second subcarrier by extrapolation using the phases of the first subcarrier and the second subcarrier. The method of claim 1, The magnitude of the channel estimate value for the data subcarrier located between the first subcarrier and the second subcarrier is: Channel estimation for the first data subcarrier located at the center of the first subcarrier and the second subcarrier up to an imaginary line virtually connecting the magnitude of the channel estimate value of the first subcarrier and the channel estimate value of the second subcarrier Compensate for the magnitude of the value, A third data subcarrier positioned at the center of the second subcarrier and the first data subcarrier up to an imaginary line virtually connecting the magnitude of the channel estimate value of the second subcarrier and the channel estimate value of the first data subcarrier. And determining by compensating the magnitude of the channel estimation value. The method of claim 1, The phase component for the data subcarrier located between the first subcarrier and the second subcarrier is: Estimating a phase component of a first data subcarrier positioned at the center of the first subcarrier and the second subcarrier using the phase component of the first subcarrier and the phase component of the second subcarrier, And determining a phase component of a third data subcarrier positioned at the center of the second subcarrier and the first data subcarrier using the phase component of the second subcarrier and the phase component of the first data subcarrier. Pilot tone based channel estimation method. delete delete delete  The method of claim 1, The phase component for the data subcarrier located between the first subcarrier and the second subcarrier is: Inferred using the following half angle formula,

(here,

Is a phase component for the data subcarrier located between the first subcarrier and the second subcarrier, α is the phase of the first subcarrier, and β is the phase of the second subcarrier) Pilot tone based channel estimation method. The method of claim 1, A phase with respect to the data subcarriers located outside the first subcarrier and the second subcarrier, And a phase of the data subcarrier positioned between the first subcarrier and the second subcarrier as a and a phase of the second subcarrier as b are determined as 2b-a. The method of claim 1, And the number of data subcarriers located inside the first subcarrier and the second subcarrier is an odd number. A pilot tone channel estimator estimating a channel for a first subcarrier and a second subcarrier on which a pilot signal is located in a received signal; Obtain a phase component of a data subcarrier located between the first subcarrier and the second subcarrier by interpolation using the phase components of the first subcarrier and the second subcarrier, and extrapolate using the phases of the first subcarrier and the second subcarrier. A phase estimator for obtaining phases of data subcarriers located outside the first subcarrier and the second subcarrier; Obtaining a magnitude of a channel estimate value for a data subcarrier located between the first subcarrier and the second subcarrier by interpolation using an imaginary line virtually connecting the magnitudes of the channel estimate values of the first subcarrier and the second subcarrier, The magnitude of the channel estimate value for the data subcarrier located outside the first subcarrier and the second subcarrier by extrapolation using an imaginary line that virtually connects the channel estimate values of the first subcarrier and the second subcarrier. Estimator; And And a channel compensator for compensating for the channel according to the value estimated by the phase estimator and the magnitude estimator. The method of claim 10, wherein the phase estimator, An interpolation phase estimator estimating a phase of a data subcarrier located between the first subcarrier and a second subcarrier; An extrapolation phase estimator estimating phases of data subcarriers located outside the first subcarrier and the second subcarrier; And And a code estimator for estimating a sign of a phase estimated by the interpolated phase estimator and the extrapolated phase estimator. The method of claim 11, wherein the interpolation phase estimator, Obtaining a phase component of a first data subcarrier positioned at the center of the first subcarrier and the second subcarrier by using a phase component of the first subcarrier channel estimate and a phase component of the second subcarrier channel estimate; Estimating a phase component of a second data subcarrier positioned at the center of the first subcarrier and the first data subcarrier using the phase component of the first subcarrier and the phase component of the first data subcarrier, And estimating a phase component of a third data subcarrier located at the center of the second subcarrier and the first data subcarrier using the phase component of the second subcarrier and the phase component of the first data subcarrier. Channel estimation device based. The method of claim 10, wherein the size estimator, An interpolation size estimator estimating a magnitude of a channel estimate value for a data subcarrier located between the first subcarrier and a second subcarrier; And And an extrapolation size estimator estimating a magnitude of a channel estimate value for the data subcarriers located outside the first subcarrier and the second subcarrier. The method of claim 13, wherein the interpolation size estimator, The magnitude of the channel estimate value for the first data subcarrier located at the center of the first subcarrier and the second subcarrier by interpolation using the magnitude of the channel estimate value of the first subcarrier and the channel estimate value of the second subcarrier. To estimate, A channel estimate value for the second data subcarrier positioned at the center of the first subcarrier and the first data subcarrier by interpolation using the magnitude of the channel estimate value of the first subcarrier and the magnitude of the first data subcarrier channel estimate. Estimate the size of, Channel estimation for the third data subcarrier located at the center of the second subcarrier and the first data subcarrier by interpolation using the magnitude of the channel estimate value of the second subcarrier and the channel estimate value of the first data subcarrier Pilot tone-based channel estimation device, characterized in that for estimating the magnitude of the value.

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