KR100705444B1 - The method and apparatus of ici signals cancellation of hpi systems - Google Patents

Abstract

The present invention relates to a method and apparatus for removing an ICI signal in an HPI system. The method includes a) estimating a channel parameter for a data subcarrier using a preamble symbol and a pilot subcarrier included in the received OFDM signal; b) estimating reference data using channel parameters for the data subcarriers estimated in step a); c) multiplexing the reference data estimated in step b) using a specific weight; d) comparing the multiplexed data with data included in the received OFDM signal to calculate an estimated error signal; And e) changing the specific weight used in step c) with the calculated estimation error signal and repeating steps c) and d) until the estimation error signal is removed. According to the present invention, the performance of the HPI system is improved by eliminating ICI caused by phase noise.

ICI, Intercarrier Interference, OFDM, HPI, WiBro, LMS

Description

Method for removing IC signal in HPP system and apparatus therefor {THE METHOD AND APPARATUS OF ICI SIGNALS CANCELLATION OF HPI SYSTEMS}

1 illustrates an example of an OFDM frame having a pilot symbol used in an HPI system according to an embodiment of the present invention.

2 is a schematic functional block diagram of an OFDM transmitter in an HPI system according to an embodiment of the present invention.

3 is a schematic functional block diagram of an OFDM receiver according to an embodiment of the present invention.

4 is a detailed block diagram of an LMS channel equalizer according to an embodiment of the present invention.

FIG. 5 is a graph showing the relationship between the BER and the ratio between phase noise bandwidth and sub-spacing (16QAM) in a typical HPI system.

FIG. 6 is a graph showing the relationship between the BER and the ratio between phase noise bandwidth and subcarrier spacing (64QAM) in a typical HPI system.

7 is a graph showing the performance of a receiver according to an embodiment of the present invention.

The present invention relates to an inter-carrier-interference (hereinafter referred to as "ICI") for a high speed portable internet ("HPI") system based on an orthogonal frequency division multiplexed access (OFDMA) wireless communication system. The present invention relates to a signal removing device and a method thereof, and more particularly, to a method and an apparatus for removing an ICI signal using channel estimation and equalization using a Fourier transform technique in a receiver of an HPI system.

HPI systems are attracting attention due to the demand for various multimedia services such as speed, image and bit variable transmission in next generation wireless mobile communication systems. New services should be able to be used in different places regardless of location. This demand has led to the development of new radio access systems, in particular, where the cell radius is larger than the cell radius of the W-LAN system (e.g. up to 1 km) and can provide low to medium mobility at 2.3 GHz frequency. Development of the system is required.

The HPI system uses Orthogonal Frequency Division Multiplexing (OFDM) technology. This is why OFDM is simple to implement and has advantages for frequency selective fading by converting channels into flat fading subchannels. OFDM has already become a major component of the standard IEEE 802.11a LAN and IEEE 802.16a LAN / MAN standard, and is also considered as a standard for B3G / 4G.

Such OFDM systems are sensitive to time-varying distortion in OFDM such as oscillator phase noise, carrier and sampling frequency offsets, and Doppler spreading. Compared to the ICI generated by the carrier frequency offset, it can be seen that the ICI generated by the Doppler is easier. Also, phase noise, known as phase modulation, which is parasitic to the signal of an oscillator, is the difference between the phase of the carrier and that of the local oscillator. ICI caused by this phase noise degrades BER performance. Much research has been done on phase noise in OFDM communication systems. Phase analysis submitted by Armada is one of them. Here, a special phase noise model was analyzed by a spectrum analyzer. In 1995, C. Muschallik studied the effects of PLL's phase noise analysis. T. Pollet studied the BER performance when frequency offset and phase noise occurred.

It is an object of the present invention to provide a method and apparatus for removing an ICI signal in an HPI system for removing an ICI that degrades performance in an HPI system.

ICI signal removal method in a wireless communication system receiver according to an aspect of the present invention for achieving the above object,

a) estimating a channel parameter for a data subcarrier using a preamble symbol and a pilot subcarrier included in the received OFDM signal; b) estimating reference data using channel parameters for the data subcarriers estimated in step a); c) multiplexing the reference data estimated in step b) using a particular weight, wherein the particular weight is determined by a preamble of the received OFDM signal and a previous estimation error signal; d) comparing the multiplexed data with data included in the received OFDM signal to calculate an estimated error signal; And e) changing the specific weight used in step c) with the calculated estimation error signal and repeating steps c) and d) until the estimation error signal is removed.

An apparatus for removing an ICI signal in a wireless communication system receiver according to another aspect of the present invention,

A channel estimator estimating a channel parameter for a data subcarrier using a preamble symbol and a pilot subcarrier included in the received OFDM signal, and estimating reference data using the channel parameter for the estimated data subcarrier; And multiplexing and outputting the reference data estimated by the channel estimator using a specific weight, wherein the specific weight is determined by a preamble of a received OFDM signal and a previous estimation error signal. And a channel equalizer applying the generated estimated error signal to the specific weight until the estimated error signal generated by comparing the data included in the received OFDM signal is removed.

DETAILED DESCRIPTION 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. Like parts are designated by like reference numerals throughout the specification.

First, an ICI removal method in an HPI system according to an embodiment of the present invention will be described in detail.

는 N개의 부반송파를 사용하여 IFFT(Inverse Fast Fourier Transform)를 취함으로써 기저대역에서 생성된다. 시스템에서 직교성을 유지하고 채널 등화를 단순하게 하기 위해 OFDM 심볼을 전송하기 전에 주기적 전치부호(Cyclic Prefix, 이하 "CP"라고 함)가 삽입된다. IFFT의 출력은 다음의 [수학식 1]과 같다.Transmission signal

Is generated at baseband by taking an Inverse Fast Fourier Transform (IFFT) using N subcarriers. Cyclic Prefix (hereinafter referred to as "CP") is inserted before transmitting OFDM symbols to maintain orthogonality and simplify channel equalization in the system. The output of the IFFT is shown in Equation 1 below.

이고, N은 부반송파의 전체 개수이다. CP는 수신기에서 제거되기 때문에 설명의 편의를 위해서, 여기에서는 고려하지 않기로 한다. 그러나, 상이한 OFDM 심볼들이 서로 중첩되지 않는다는 것을 가정한다.here,

Where N is the total number of subcarriers. Since the CP is removed from the receiver, it is not considered here for convenience of description. However, assume that different OFDM symbols do not overlap each other.

In the HPI system, since the length of the CP is longer than the maximum delay of the multipath channel, the ICI due to the Doppler transition is omitted. The target ICI in this embodiment is due to phase noise.

에 의해서만 영향을 받으며, 다음의 [수학식 2]와 같이 나타낼 수 있다.The signal received at the receiver is phase noise

Affected only by and can be expressed as in Equation 2 below.

은 다중 경로의 채널 파라미터이고, L은 다중 경로 채널에 의해 지연된 샘플의 최대 개수이다. 주지하는 바와 같이, CP의 길이는 L보다 더 길고, 도플러 천이에 의한 ISI는 제거된 상태이다.here,

Is the channel parameter of the multipath, and L is the maximum number of samples delayed by the multipath channel. As noted, the length of the CP is longer than L, and the ISI due to the Doppler transition is removed.

After performing the Fast Fourier Transform (FFT) on the signal received by the receiver, it can be expressed as Equation 3 below.

이 작기 때문에

로 근사화될 수 있다.Here, to separate the signal and noise items, (compared to the initial generation of OFDM symbols)

Because it is small

Can be approximated by

In this case, Equation 3 may be expressed as Equation 4 below.

가 존재한다.Therefore, due to some combination of all carriers, an error item for each subcarrier inserted into the useful signal

Is present.

이면 오류 항목

는 다음의 [수학식 5]와 같이 나타낼 수 있다.if

Error item

Can be expressed as Equation 5 below.

This result is a complex number with white noise being inserted into the useful signal of each subcarrier. This is commonly known ICI or loss of orthogonality.

In an HPI system, each frame begins with a downlink, which is a transmission from a base station (BS) to a subscriber station (SS). This downlink transmission begins with two preambles. There are two types of subchannels, a diversity channel and an AMC channel in both downlink and uplink. For each data symbol a pilot subcarrier is inserted to track the phase. Pilot subcarriers in the preamble channel and data symbol may be used to estimate initial channel parameters.

Referring to Equation 4, since the preamble symbol is 1 or -1, initial channel estimation may be performed based on a Least Square (LS) rule. Here, the initial channel parameter may be estimated by a multiplication operation instead of a division operation, that is, it may be expressed as Equation 6 below.

In addition, the pilot pattern is included in the data symbols to accurately estimate the initial channel parameters. In the data symbol, the initial channel parameters based on the pilot subcarrier can be obtained by the following equation (7).

로써 추정될 수 있다. 여기서 L은 파일롯 부반송파들 사이의 간격이고, M은 하나의 데이터 심볼에 있는 파일롯 부반송파의 개수이다. 데이터 부반송파의 채널 파라미터들은 다음의 [수학식 7]과 같이 표현된 Lagrange 보간법에 따른 다항식을 품으로써 다항식 보간으로부터 추정될 수 있다.The same processing is performed for Equation 6, and channel parameters are located at the position of the pilot subcarrier.

Can be estimated as Where L is an interval between pilot subcarriers and M is the number of pilot subcarriers in one data symbol. The channel parameters of the data subcarrier can be estimated from the polynomial interpolation by having a polynomial according to the Lagrange interpolation method expressed by Equation 7 below.

Accordingly, the channel parameters at the data position may be estimated from corresponding preamble data and pilot subcarriers by applying a weight method. The k-th data subcarrier channel parameter for the n-th data symbol may be expressed by Equation 8 below.

은 데이터 심볼과 프리앰블 심볼 사이의 거리이고,

는 프레임 내에 있는 데이터 심볼의 개수이다. 따라서, SNR이 높을 때 초기 데이터는 다음의 [수학식 9]와 같이 추정될 수 있다.here,

Is the distance between the data symbol and the preamble symbol,

Is the number of data symbols in the frame. Therefore, when the SNR is high, the initial data may be estimated as in Equation 9 below.

은 하드 판정(Hard Decision)을 적용함으로써 추정될 수 있다. 데이터 부반송파는 OFDM 심볼에서 위상 잡음에 의해 다른 데이터 부반송파로부터 간섭을 받기 때문에 이러한 ICI를 해결하기 위해 등화기가 사용되어야 한다. 실제 구현에 있어서 등화기의 탭(tap) 수는 충분히 작아야 그 알고리즘이 구현될 수 있다. 여기에서는 구현을 위해 LMS(Least-Mean-Square) 알고리즘이 선택된 것으로 한다.On the other hand, data symbols based on modulation modes (QPSK, 16QAM, 64QAM)

Can be estimated by applying a hard decision. Since data subcarriers are interfered with by other data subcarriers by phase noise in OFDM symbols, an equalizer must be used to solve this ICI. In practical implementations, the number of taps in the equalizer must be small enough so that the algorithm can be implemented. The Least-Mean-Square (LMS) algorithm is chosen here for implementation.

를 처리하기 위해 요구 응답

이 제공된다. 입력이 발생되면 필터는 요구 응답

을 추정하기 위해 사용되는 출력

를 생성한다. 한편,

는 요구 응답과 실제 필터 출력 사이의 차이이다.

와

에 대해 제어 메커니즘이 적용된 후, 피드백 루프가 사용된다. In the filtering process on the equalizer, the tap input vector

Request response to handle

This is provided. When an input occurs, the filter responds to the request

Output used to estimate

Create Meanwhile,

Is the difference between the request response and the actual filter output.

Wow

After the control mechanism is applied to, the feedback loop is used.

The filter output is shown in Equation 10 below.

이고,here,

ego,

이다.

to be.

In addition, the estimation error signal is expressed by Equation 11 below.

In addition, the tap-weight should be adopted as shown in Equation 12 below.

는 스텝-사이즈(step-size) 파라미터이고, 웨이트

의 초기값은 프리앰블 심볼로부터 얻어진다.here,

Is a step-size parameter, and the weight

The initial value of is obtained from the preamble symbol.

Hereinafter, an apparatus for removing ICI in an HPI system according to an embodiment of the present invention will be described in detail.

1 illustrates an example of an OFDM frame having a pilot symbol used in an HPI system according to an embodiment of the present invention.

은 다음의 [수학식 1]에 의해 구할 수 있다.Referring to FIG. 1, the first two symbols in the OFDM frame used in the HPI system are preamble symbols. The symbols that follow are the data symbols that carry user information. Meanwhile, pilot subcarriers are inserted in the data symbol to track the phase change. The number of pilots to space the pilots in the time domain, according to the sampling principle

Can be obtained by the following Equation 1.

[Equation 1]

는 최대 도플러 주파수이고,

는 CP를 포함하는 전송된 심볼의 지속시간이다.here,

Is the maximum Doppler frequency,

Is the duration of the transmitted symbol containing the CP.

2 is a schematic functional block diagram of an OFDM transmitter in an HPI system according to an embodiment of the present invention.

Referring to FIG. 2, the OFDM transmitter 200 includes an encoder 201, a preamble and pilot insertion 202, a modulator 203, and a serial / parallel converter (S / P) 204. ), IFFT unit 205, CP inserter (CP add, 206), parallel / serial converter (P / S, 207) and D / A converter 208.

The transmission bits are encoded by an encoder 201 including a convolutional coder, a turbo coder, a low density parity coder (LDPC), and the like. For each frame, the first symbol is a preamble known to the receiver.

Pilot bits known to the receiver 300 are inserted according to certain principles by the preamble and pilot inserter 202 for the following symbols.

The transmit bits are then modulated into symbols by modulator 203, which includes 64QAM, 16QAM, and QPSK.

The modulated data is converted into parallel data by the serial / parallel converter 204 for an Inverse Fast Fourier Transform (IFFT) operation.

After the IFFT by the IFFT unit 205, a CP is inserted into the OFDM symbol by the CP inserter 206 to remove the ISI.

The parallel / serial converter 207 then converts the parallel symbols into serial symbols.

The transmitted signal is converted into an analog signal by the D / A converter 208 before being transmitted to the wireless channel through the transmitting antenna.

3 is a schematic functional block diagram of an OFDM receiver according to an embodiment of the present invention.

Referring to FIG. 3, the OFDM receiver 300 includes an A / D converter 301, a CP remover 302, an FFT 303, a channel estimator 304, and a channel equalizer. , 305), demodulator 306, and decoder 307.

The received signal is sampled in the A / D converter 301 and then converted into a digital bit stream.

Prior to the FFT by the FFT 303, the CP canceller 302 removes the CPs in the OFDM symbol. The received signal is converted into a signal in the frequency domain by the FFT 303.

With a multipath channel, channel estimator 304 can be represented as a transfer function of the channel in the frequency domain. Channel estimator 304 may implement an algorithm for channel estimation, including, for example, an averaging / or smoothing algorithm, maximum likelihood estimation in the frequency domain, and the like.

A channel estimation algorithm according to an embodiment of the present invention is as follows.

The preamble symbol may be used to estimate an initial channel parameter as shown in Equation 6. The same processing is performed for Equation 6, and channel parameters can be estimated at the position of the pilot subcarrier.

The channel parameters of the data subcarrier can be estimated from the polynomial interpolation by having a polynomial according to the Lagrange interpolation method expressed by Equation 7 below. Accordingly, the channel parameters at the data position may be estimated from corresponding preamble data and pilot subcarriers by applying a weight method such as Equation (8). Therefore, initial data determination is performed as shown in [Equation 9].

Channel equalizer 305 generates channel equalized frequency domain symbols using the channel parameters provided by channel estimator 305, which will be described in detail later.

The equalized frequency domain symbol is demodulated by demodulator 306. The demodulator 306 demodulates the subcarriers in a manner in which the subcarriers are modulated by the transmitter 200, for example, 64QAM, 16QAM, and QPSK. Parallel symbols output from the demodulator 306 are converted into a serial stream.

Decoder 308 decodes the serial stream to produce a decoded serial stream.

4 is a detailed block diagram of an LMS channel equalizer 305 in accordance with an embodiment of the present invention.

Referring to FIG. 4, the channel equalizer 305 includes delay units 401, 402, and 403, weight change units 404, 405, 406, 407, 408, and adders 409, 410, 411, and 412. Include.

As shown in Equation 10, the received data signals are sequentially input to the delay units 401, 402, and 403, and the delayed data signals are corresponding weight change units 404, 405, 406, 407, and 408. Are multiplexed at, and added at adders 409, 410, 411, 412.

The error signal is obtained by the adder 413 as shown in [Equation 11] by the initial determination data signal and the output in Equation (10). The initial weight is selected according to the preamble symbol.

FIG. 6 is a graph showing the relationship between the BER and the ratio between phase noise bandwidth and sub-spacing (64QAM) in a typical HPI system.

The downlink is formed according to the physical layer of the HPI system. Basic parameters are shown in Table 1 below. The simulation channel includes AWGN, three kinds of radio channels.

가 위상 잡음의 대역폭이고,

가 부반송파 간격이라고 가정한다.

라고 정의한다. 위상 잡음(PN)의 대역폭과 부반송파의 간격 사이의 비율(

)대 BER 성능에 대해서는 AWGN과 다중 경로 채널에 대해 각각 알려져 있다. 두 경우를 참조하면,

일 때,

이고 OFDM 심볼의 지속시간이

이므로,

은 상수이거나 또는 OFDM 심볼 동안 매우 느리게 변한다. 이와 반대로,

이면,

은 OFDM 심볼동안에 매우 빠르게 변한다.

Is the bandwidth of phase noise,

Assume that is the subcarrier spacing.

It is defined as. The ratio between the bandwidth of phase noise (PN) and the spacing of subcarriers (

Large BER performance is known for AWGN and multipath channels, respectively. In both cases,

when,

And the duration of the OFDM symbol

Because of,

Is constant or varies very slowly during an OFDM symbol. On the contrary,

If,

Changes very quickly during an OFDM symbol.

일 때, BER 성능이 매우 심하게 영향을 받는 것을 알 수 있다. 따라서 수신기가 정상적으로 동작할 수가 없다. 두 가지 방식이 이러한 문제를 해결하는데 사용될 수 있다. 하나는 수신기에서 보다 정확한 발진기를 사용하는 것이다. 보다 나은 발진기가 기지국에서 사용되는 것이 바람직하다. 그러나, 보나 나은 발진기는 단말기에서 사용되면 대량 생산시에 비용이 상승한다. 나머지 한 가지 방식은 ICI를 완전하게 또는 부분적으로 제거하기 위해 등화기를 사용한 채널 추정을 적용하는 것이다.For this HPI system, from FIGS. 5 and 6

It can be seen that when BER performance is severely affected. Therefore, the receiver cannot operate normally. Two approaches can be used to solve this problem. One is to use a more accurate oscillator at the receiver. It is desirable that a better oscillator be used at the base station. However, better oscillators, when used in handsets, increase costs in mass production. The other approach is to apply channel estimation using the equalizer to completely or partially remove the ICI.

7 is a graph showing the performance of the receiver 300 according to an embodiment of the present invention.

In FIG. 7, the above algorithm is used in the receiver 300 of the HPI system. In a multipath channel, channel estimation is needed to estimate channel parameters.

의 초기값은 0.001로 한다. 도 7에 도시된 바와 같이, SNR이 26dB일 때, 채널 등화기(305)가 채널 추정기(304)와 함께 사용되는 경우 성능이 개선된다.In an embodiment of the invention a channel equalizer 305 is used in the receiver 300. Considering the complexity of the actual use, the number of taps of the channel equalizer is 4, and the step size

The initial value of is set to 0.001. As shown in FIG. 7, when the SNR is 26 dB, the performance is improved when the channel equalizer 305 is used with the channel estimator 304.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto, and various other changes and modifications are possible.

According to the present invention, the performance of the HPI system is improved by eliminating ICI caused by phase noise.

Claims (13)

A method of removing an intercarrier interference (ICI) signal from an orthogonal frequency division multiplexing (OFDM) signal received at a receiver of a wireless communication system, a) estimating a channel parameter for a data subcarrier using a preamble symbol and a pilot subcarrier included in the received OFDM signal; b) estimating reference data using channel parameters for the data subcarriers estimated in step a); c) multiplexing the reference data estimated in step b) using a particular weight, wherein the particular weight is determined by a preamble of the received OFDM signal and a previous estimation error signal; d) comparing the multiplexed data with data included in the received OFDM signal to calculate an estimated error signal; And e) changing the specific weight used in step c) with the calculated estimation error signal and repeating steps c) and d) until the estimation error signal is removed; Method for removing inter-carrier interference signal in a radio frequency system receiver comprising a. The method of claim 1, Step a) is i) estimating a channel parameter using a preamble symbol included in the OFDM signal; ii) estimating a channel parameter using a pilot subcarrier included in the OFDM signal; And iii) estimating a channel parameter for a data subcarrier included in the OFDM signal using the channel parameter estimated in step i) and the channel parameter estimated in step ii). Subcarrier interference signal cancellation method in a wireless communication system receiver comprising a. The method of claim 1, C), i) delaying the received OFDM signal by a specific time; ii) providing the specific weight for each of the received OFDM signal and the delayed signal, and applying and multiplexing the received OFDM signal and the delayed signal, respectively; And iii) adding each multiplexed signal; Subcarrier interference signal cancellation method in a wireless communication system receiver comprising a. The method of claim 2, The channel parameter estimated in step i)

) Is the relation

here,

Is the received OFDM signal,

Is a signal transmitted from a transmitter of a wireless communication system, and is 1 or -1 in the case of the preamble,

Is an inter-carrier interference signal. Method for removing the inter-carrier interference signal in a wireless communication system receiver, characterized in that the following. The method of claim 4, wherein The channel parameter estimated in step ii)

) Is the relation

here,

,

And

Is a channel parameter according to the position of the pilot subcarriers, and L is an interval between the pilot subcarriers. Subcarrier interference signal cancellation method in a wireless communication system receiver according to the following. The method of claim 5, The channel parameter for the k th data subcarrier for the n th data symbol estimated in step iii)

) Is the relation

here,

Is a distance between a symbol to which the data subcarrier belongs and the preamble symbol,

Is the number of data symbols in the OFDM frame. Subcarrier interference signal cancellation method in a wireless communication system receiver according to the following. The method of claim 6, The reference data estimated in step b)

) Is the relation

Subcarrier interference signal cancellation method in a wireless communication system receiver according to the following. The method of claim 7, wherein A signal multiplexed and output in step c)

)

Where the weight

ego, The reference data

being. Subcarrier interference signal cancellation method in a wireless communication system receiver according to the following. The method of claim 8, The weight (

) Is the relation

here,

Is a step-size parameter,

Is the estimated error signal, The weight (

Is obtained from the preamble symbol. Subcarrier interference signal cancellation method in a wireless communication system receiver according to the following. The method of claim 9, The estimation error signal (

) Is the relation

here,

Is data estimated by hard determining data included in the received OFDM signal. Subcarrier interference signal cancellation method in a wireless communication system receiver according to the following. An apparatus for removing an inter-carrier interference (ICI) signal from an orthogonal frequency division multiplexing (OFDM) signal received at a receiver of a wireless communication system, A channel estimator estimating a channel parameter for a data subcarrier using a preamble symbol and a pilot subcarrier included in the received OFDM signal, and estimating reference data using the channel parameter for the estimated data subcarrier; And Multiplexes and outputs the reference data estimated by the channel estimator using a particular weight, where the particular weight is determined by a preamble of a received OFDM signal and a previous estimation error signal, wherein the multiplexed data and the received A channel equalizer for applying the generated estimation error signal to the specific weight until the estimation error signal generated by comparing the data included in the OFDM signal is removed Apparatus for removing inter-carrier interference signals in a wireless communication system receiver comprising a. The method of claim 11, The channel equalizer, A plurality of delay units for delaying reference data output from the channel estimator; A plurality of weight changing units configured to multiplex by applying the specific weight corresponding to the reference data and data output from each of the plurality of delay units; A plurality of adders each adding data multiplexed by the plurality of weight changers to generate the output of the channel equalizer; And Outputting the estimated error signal by subtracting the data finally outputted by the plurality of adders from the data included in the received OFDM signal and outputting the estimated error signal to the plurality of weight changing units to change the respective weights. 2 Addition Apparatus for removing inter-carrier interference signals in a wireless communication system receiver comprising a. The method according to claim 11 or 12, wherein An FFT unit performing a fast fourier transform (FFT) on the received OFDM signal, converting the signal into a frequency domain signal and outputting the converted signal to the channel estimator and the channel equalizer; A demodulator for demodulating data output from the channel equalizer; And And a decoder for decoding the data demodulated by the demodulator to generate an original signal transmitted from a transmitter of the wireless communication system.

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