KR100860457B1 - Channel estimation apparatus and method for synchronous demodulation in wireless packet transmission system - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a channel estimation apparatus for synchronous demodulation in a wireless packet transmission system, a method thereof, and a recording medium thereof.

2. The technical problem to be solved by the invention

The present invention uses moving average filtering for each channel impulse response component of the guard interval, and performs the filtering repeatedly through the feedback of the obtained channel frequency response to the IFFT input to obtain an accurate channel estimate. A channel estimation apparatus for synchronous demodulation in a packet transmission system, a method thereof, and a computer-readable recording medium having recorded thereon a program for realizing the method.

3. Summary of Solution to Invention

A channel estimation apparatus for synchronous demodulation in a wireless packet transmission system, the apparatus comprising: instantaneous channel calculating means for calculating an instantaneous channel estimate from a fast fourier transform (FFT) output signal and a reference data symbol; Switching the fed back channel frequency response signal (filtered channel estimate) with respect to the instantaneous channel estimate calculated by the instantaneous channel calculating means, feedbacking the filtered channel estimate input from the channel frequency response signal converting means, and performing the channel frequency response signal. Switching means for outputting a channel estimate from which inter-carrier interference and noise input from the converting means are removed; Channel impulse response signal conversion means for converting the filtered channel estimate transmitted from the switching means into a channel impulse response signal (signal in time domain); Noise removal means for performing a filtering process by a moving average filter on the components within the guard interval of the channel impulse response signal, and removing the corresponding sample components on the components outside the guard interval to remove inter-carrier interference and noise; And the channel frequency response signal converting means for converting the channel impulse response signal from which the noise is removed through the noise removing means into a channel frequency response signal (filtered channel estimate).

4. Important uses of the invention

The present invention is used in a wireless packet transmission system.

Wireless packet transmission system, moving average filter, filtered channel estimate, instantaneous channel estimate, switch 1, switch 2

Description

Channel estimation apparatus and method and recording medium therefor for synchronous demodulation in wireless packet transmission system

1A and 1B are diagrams illustrating a configuration of a wireless packet OFDM system applying synchronous demodulation in a conventional wireless packet transmission system.

2 is a block diagram of a channel estimating apparatus in a conventional wireless packet OFDM system.

3 is a diagram illustrating an embodiment of a channel estimating apparatus for synchronous demodulation in a wireless packet transmission system according to the present invention.

4A and 4B are diagrams illustrating an embodiment of a switch in a channel estimating apparatus according to the present invention.

5 is a diagram illustrating a structure of a moving average filter in a channel estimating apparatus according to the present invention.

6A and 6B are a flowchart illustrating a signal processing procedure in a channel estimating apparatus according to the present invention.

* Explanation of symbols for the main parts of the drawings                 

31: Least Squares Channel Estimator 32: Switch 1 (SW1)

33: IFFT processor 34: moving average filter

35: FFT processor 36: switch 2 (SW2)

The present invention provides a channel estimation apparatus for synchronous demodulation in a wireless packet transmission system including an orthogonal frequency division multiplexing (OFDM) system, a method thereof, and a computer recording a program for realizing the method. The present invention relates to a readable recording medium, and provides accurate channel estimation for reception of multi-level modulation wireless OFDM packets such as 64-QAM (Quadrature Amplitute Modulation) in a wireless channel in a city environment with high inter-symbol / carrier interference and noise. In order to prevent interference and noise by using moving average filtering for the channel impulse response components of the guard period, and performing the filtering repeatedly through the feedback of the obtained channel frequency response to the Inverse Fast Fourier Transform (IFFT) input, Removable channel estimating apparatus and method thereof It relates to a computer-readable recording medium storing a program for groups.

In the mobile radio channel environment, multipath characteristics exist between the base station and the terminal due to radio interferences of various sizes and materials scattered throughout, and also show the time-varying characteristics of the received signal because the terminal or the radio interference moves. In addition, since the multipath between the base station and the terminal has a path having a different length, the received signal has a long delay spreading characteristic. Due to these characteristics, a wireless packet channel exhibits time-selective fading that varies with time and frequency-selective fading having frequency components of different magnitudes and phases due to delayed reception through multipaths having various lengths. That is, it causes distortion. Since the channel characteristics have different magnitudes and phases for each path according to time, in order to obtain the original transmission signal from the received signal, the synchronous demodulation receiver is a distortion source of the transmission signal, that is, channel state information which is a channel frequency response or channel impulse response. Use In other words, by dividing the received signal by the channel response, the original transmission signal can be obtained.

On the other hand, the delay spread characteristics of the channel cause inter-symbol interference where adjacent data symbols overlap each other and, in severe cases, reach the receiver as a signal having interference by overlapping even between symbols spaced apart. In an OFDM system, frequency selective fading by these delayed path components causes inter-arrival interference. In a channel environment having a large number of delay paths, inter-arrival interference becomes more severe due to more severe frequency selective fading. The increasing mobility of the wireless system causes frequency selective fading to have time-varying properties, resulting in instantaneous degradation of the transmission performance of the wireless packet system. Therefore, performance degradation becomes more severe due to time-varying fading, inter-symbol interference, and inter-barrier interference in urban environments rather than suburban or rural environments, and in mobile vehicle environments rather than indoor or pedestrian environments. Therefore, in a wireless packet system for broadband multimedia services supporting high-speed transmission, a countermeasure against time-varying fading and inter-symbol and inter-carrier interference is required to ensure reliable system performance.

A wireless packet OFDM system using OFDM packets for broadband multimedia services uses serial to parallel conversion to overcome such intersymbol interference. First, the wideband transmission band allocated for a system is divided into several narrowband channels. In the same concept, since the high speed serial data stream is converted into several low speed data streams, the symbol interval in the parallel stream is N times the serial stream in the case of N parallel streams. Each low-speed stream is assigned a bouquet carrier, which is the center frequency of the narrowband channel, for carrier modulation.

개의 OFDM 심볼로 구성되고 각 OFDM 심볼은 N개의 데이터 심볼로 구성된다. 그러므로, 패킷프레임은 2차원 구조를 가지며, 주파수-시간 그리드로 도시 가능하다. 즉, 주파수축 그리드는 데이터심볼에 의해 변조되는 각 부케리어의 순서번호에 의해, 그리고 시간축 그리드는 각 OFDM 심볼의 전송시점에 해당하는 전송순서에 의해 도시된다. 따라서, OFDM 패킷에서 각 데이터심볼은 다음과 같이 부케리어 번호 k와 OFDM 심볼의 순서번호 ℓ의 쌍으로 표현된다. The OFDM packet transmitted by the wireless packet OFDM system is

It consists of OFDM symbols and each OFDM symbol consists of N data symbols. Therefore, the packet frame has a two-dimensional structure and can be shown in a frequency-time grid. That is, the frequency axis grid is shown by the sequence number of each bouquetier modulated by the data symbol, and the time axis grid is shown by the transmission sequence corresponding to the transmission time of each OFDM symbol. Accordingly, each data symbol in the OFDM packet is represented by a pair of the bouquet number k and the sequence number l of the OFDM symbol as follows.

An OFDM packet consists of a preamble and a data field. The preamble is for facilitating packet detection at the receiver and is generally composed of a specific pattern of data sequences known to the receiver and is transmitted in the first OFDM symbol of the packet frame. In addition, it is very effective for symbol timing synchronization, frequency offset estimation, channel estimation, and so on. The data field includes pilot symbols in addition to data symbols. The pilot symbol is for tracking channel variation in the data field and is multiplexed with the data symbol at a constant rate. Since each pilot symbol is transmitted in place of the data symbol to effectively track channel variations, these pilot symbols have a certain shape when viewed in a packet frame. Therefore, various densities and various types of pilot patterns may be used according to channel characteristics in the transmission band.

1A and 1B are exemplary diagrams illustrating a configuration of a wireless packet OFDM system using synchronous demodulation in a conventional wireless packet transmission system.

As illustrated in FIGS. 1A and 1B, N in an arrow connecting blocks in a wireless packet OFDM system means that N signals are transmitted in parallel. An information bit is a binary bit sequence to be transmitted through a wireless mobile channel as multimedia data information such as a voice, a data file, and a video compressed by source data encoding. In the case of an OFDM transmitter, channel encoding outputs a parity bit and a current input bit generated through a predetermined correlation between a current input bit and a previously input bit. Usually, two or more bits are output for each input bit encoded by a convolutional code or a turbo code. The rate matching accompanying the channel encoding and interleaving unit outputs a constant bit rate by repeating or removing specific bits according to a predetermined rule for the input data block. As a result, the coded arbitrary bitrate is matched to the predetermined bitrate to be transmitted. The interleaver is intended to distribute the clustering errors occurring in the channel and creates a new output sequence that differs from the input sequence by writing and reading with certain rules.

비트 단위로 묶은 다음 복소수로 표현되는 데이터심볼로 변환한다. QAM의 경우 2비트가 하나의 데이터심볼을 구성하고 비트쌍 00, 01, 10, 11은 각각 1+j, 1-j, -1+j, -1-j으로 변환된다. 또한, M-QAM 심볼, 즉 16-QAM 심볼과 64-QAM심볼을 위해서는

비트에 각각 4비트와 6비트가 할당된다. 직병렬 변환은 입력되는 데이터심볼시퀀스를 저속의 병렬시퀀스로 변환한다. 따라서, N개의 부케리어를 사용하는 OFDM 시스템의 경우 N개의 병렬시퀀스가 만들어지고, N심볼 구간마다 한번씩 병렬 시퀀스를 출력한다. 이과정을 통해 출력심볼의 구간은 입력심볼 구간의 N배로 늘어난다. Data symbol mapping is based on the input bit sequence.

Bundled by bits and then converted to data symbols represented by complex numbers. In the case of QAM, two bits constitute one data symbol, and bit pairs 00, 01, 10, and 11 are converted into 1 + j, 1-j, -1 + j, and -1-j, respectively. Also, for M-QAM symbols, 16-QAM symbols and 64-QAM symbols,

4 bits and 6 bits are allocated to the bits, respectively. Serial-to-parallel conversion converts an input data symbol sequence into a low-speed parallel sequence. Therefore, in an OFDM system using N bouquetaries, N parallel sequences are generated, and a parallel sequence is output once every N symbol intervals. Through this process, the interval of the output symbol is increased by N times the interval of the input symbol.

이라면 IFFT의 출력신호인 OFDM 심볼은 하기의 [수학식 1]과 같은 연속신호로 얻어진다.
IFFT is an OFDM modulation process for modulating each parallel data symbol on a different bouquet area. In the following signal processing, when referring to the OFDM symbol, the sequence number l is not considered for convenience. The symbols entered in parallel

If the OFDM symbol is an output signal of the IFFT is obtained as a continuous signal as shown in Equation 1 below.

는 심볼구간 N을 가지며 k번째 부케리어를 변조할 k번째 데이터심볼이다. 또한,

은 k번째 부케리어이다. IFFT 과정은 기저대역에서 신호처리를 용이하게 하기 위해 1/N 간격으로 샘플링된 이산신호를 사용하고 따라서 IFFT는 OFDM심볼을 하기의 [수학식 2]와 같은 이산신호로 출력한다.
Where T is the indication that the rows and columns are swapped in the matrix,

Is a k-th data symbol having a symbol interval N and which is to modulate the k-th bouquetier. Also,

Is the kth bouquetier. The IFFT process uses discrete signals sampled at 1 / N intervals in order to facilitate signal processing at baseband. Therefore, the IFFT outputs OFDM symbols as discrete signals as shown in Equation 2 below.

Guard interval insertion is to remove the inter-symbol interference caused by delay spread, which is a characteristic of the radio packet channel, and adds the latter part of the OFDM symbol (that is, the L sample interval at the end of the OFDM symbol) before the OFDM symbol. Thus, an OFDM symbol composed of (L + N) sample components including a guard interval is generated. Digital / analog (D / A) converters convert baseband digital signals to analog signals. Thereafter, the converted signal is converted into an intermediate frequency and a carrier frequency after balanced modulation by an RF transmitter and radiated through a power amplifier and an antenna.

In the case of an OFDM receiver, the function of each block has the inverse function of that of the corresponding block of the OFDM transmitter. The received RF signal is converted to a low frequency by stepping down the frequency by carrier frequency synchronization in the RF receiver, and then converted into a discrete signal through A / D conversion.

Timing / frequency synchronization obtains each sector frequency synchronization by finding the correct interval of the OFDM symbol and estimating and removing the offset frequency which is not synchronized even through the RF receiver. The guard interval removal is to remove the guard interval inserted in the OFDM symbol at the transmitting end. This guard interval is an interval containing adjacent symbol components that cause interference at the OFDM symbol boundary point by multipath delay spreading during the transmission of the radio packet channel.

Therefore, N samples per OFDM symbol are obtained and input to the FFT through serial-to-parallel conversion. In this case, the serial to parallel conversion is a process of outputting in parallel a single input sample into N samples, unlike the serial to parallel conversion of the transmitter. Therefore, a sample sequence constituting one OFDM symbol is made of N identical parallel sequences.

이 입력된다고 하자. 여기에서

이고

는 L샘플로 구성된 무선 패킷 채널의 채널임펄스응답이고, 샘플

은 상기 채널임펄스응답의 m번째 성분이다. Fast Fourier Transform (FFT) is a process of demodulating transmitted parallel data symbols from each bouquet. Any OFDM symbol, N samples

Let is input. From here

ego

Is the channel impulse response of the radio packet channel configured as L samples, and

Is the m th component of the channel impulse response.

The output of the FFT is each obtained by synchronizing these input sample sequences with the same coherent frequency used in the transmitter. In the case of the k-th data symbol, the received signal is the sum of the product of the input N sample and the N sample corresponding to the discrete signal of the k-th carrier, as shown in Equation 3 below. Since only k 'is the same, the result is that the transmitted data symbol is corrupted by channel response and noise.

Since only k and k 'are the same due to the orthogonality between the bouquets, the result is that the transmitted data symbols are corrupted by channel response and noise.

는 잡음성분이고,

는 주파수변환된 채널임펄스응답, 즉 채널주파수응답의 k번째 성분이다.here,

Is the noise component,

Is the k-th component of the frequency-converted channel impulse response, that is, the channel frequency response.

The received signal is synchronously demodulated in the channel equalization block by using a division operation and a channel response component accurately estimated through the channel estimation block.

Thereafter, signal processing processes such as parallel-to-serial conversion, data symbol history, deinterleaving, and channel decoding are inverse functions of the transmitter.

The conventional channel estimation method for synchronous demodulation in such a wireless packet OFDM system includes a process of generating an instantaneous channel estimate from a received signal and a low pass filtering process for removing noise components included in the instantaneous channel estimate. The instantaneous channel estimate is obtained directly from the received signal and the reference symbol. The low-pass filtering obtains the channel impulse response from the channel frequency response, which is an instantaneous channel estimate, using the IFFT, and then FFTs the channel impulse response in which the components of the remaining sections except for the guard interval corresponding to multipath delay spreading are replaced with zero. By frequency conversion, inter-carrier interference (ICI) and noise can be eliminated. Therefore, the least square channel estimator, the IFFT block, the FFT block, and the filtering for the instantaneous channel impulse response in the time domain are used to obtain an accurate estimate of the channel frequency response.

2 is a block diagram of a channel estimation apparatus in a conventional wireless packet OFDM system.

In the figure, "21" represents a least squares channel estimator, "22" represents an IFFT processor, and "23" represents an FFT processor, respectively.

와 그것의 전송심볼에 해당하는 참조데이터심볼

을 이용하여 채널주파수응답인 채널이득

을 각각 추정한다. Here, the least-squares channel estimator 21 inputs the received signal.

And reference data symbol corresponding to its transmission symbol

Channel gain with channel frequency response

Estimate respectively.

으로 얻어진다. 이 채널 추정치는 ICI 및 잡음성분을 포함하고 있어서 보다 정확한 채널추정치를 얻기 위해서는 ICI 및 잡음성분이 완전히 제거되어야 한다. Here, the reference data symbol is a pilot symbol known to the receiver or a transmission symbol reconstructed through a separate symbol detection process. As an example, the channel estimate corresponding to the kth component of the channel frequency response is

Obtained. This channel estimate includes ICI and noise components, so that the ICI and noise components must be completely removed to obtain more accurate channel estimates.

로 변환시키는 과정이다. 상기채널 추정치는 본래의 채널주파수응답에 ICI 및 잡음성분이 부가된 신호이기 때문에 IFFT에 의하면 채널주파수응답은 채널임펄스응답으로 변환되고 주파수영역의 ICI 및 잡음은 시간영역의 ICI 및 잡음으로 변환된다. 따라서, IFFT의 결과

는 이상적인 채널임펄스응답

에 시간영역의 ICI 및 잡음이 부가된 형태를 갖는다. ICI 및 잡음을 갖지 않는 이상적인 채널임펄스응답

은 그 길이가 상기 보호구간과 같기 때문에 보호구간을 벗어난 구간의 성분은 모두 ICI 및 잡음으로 간주될 수 있다. The IFFT processor 22 then estimates the channel estimate in the time domain as a channel impulse response.

Is the process of conversion. Since the channel estimate is a signal in which ICI and noise components are added to the original channel frequency response, the IFFT converts the channel frequency response into a channel impulse response and the ICI and noise in the frequency domain into the ICI and noise in the time domain. Therefore, the result of IFFT

Ideal channel impulse response

Has the form of adding time domain ICI and noise. Ideal Channel Impulse Response with No ICI and Noise

Since the length is equal to the guard interval, all components of the interval outside the guard interval can be regarded as ICI and noise.

와 같이 구성된다. Filtering the channel impulse response is a process of removing all channel impulse response components other than the guard interval. This process can be as simple as setting all of the components to be removed with zero energy or only ICI and noise to be considered as only effective components with energy above a certain value among delay signal components by multipath propagation. have. Therefore, the input to the FTT processing section 23 is a channel impulse response having only active ingredients.

It is composed as follows.

을 다시 채널주파수 영역으로 환원시키는 과정이다. 상기 시간영역에서의 ICI 및 잡음제거과정과 FFT 과정은 하나의 신호처리과정으로서 저역필터와 같은 기능을 수행한다. 따라서, FFT의 출력

은 상기 순시 채널 추정치, 즉 채널주파수응답

으로부터 간섭 및 잡음이 제거된 채널주파수응답으로 얻어진다. In addition, the FFT processor 23 responds to the channel impulse response.

Is a process of reducing back to the channel frequency domain. The ICI, noise reduction process and FFT process in the time domain perform a function as a low pass filter as one signal processing process. Thus, the output of the FFT

Is the instantaneous channel estimate, i.e., the channel frequency response.

It is obtained from the channel frequency response from which interference and noise are eliminated.

는 잡음성분을 가질 뿐만 아니라 도심지 채널환경에서는 다경로채널 특성때문에 더욱 증가된 채널추정 오차를 포함할 수 있고, 또한 M-QAM 방식의 데이터심볼전력에 대한 ICI 및 잡음전력의 비가 심한 편차를 갖기 때문에 M-QAM 방식의 수신 비트오류율이 증가되고 패킷수신 성능이 열화되는 문제점이 있다.
However, the method estimates channel estimates obtained due to ICI and noise on channel impulse response components on the non-removed guard intervals, since the method only filters on the energy-free channel impulse response components for time domain ICI and noise rejection.

Not only has a noise component, but can also include an increased channel estimation error due to multipath channel characteristics in urban channel environments, and also has a large variation in the ratio of ICI and noise power to the M-QAM data symbol power. There is a problem in that the reception bit error rate of the M-QAM scheme is increased and packet reception performance is degraded.

The present invention has been proposed to solve the above-mentioned problems. The present invention employs moving average filtering for each channel impulse response component of the protection section, and performs the filtering through feedback of the obtained channel frequency response to the IFFT input. By repeatedly performing, an object of the present invention is to provide a channel estimating apparatus for obtaining an accurate channel estimate, and a method and a computer readable recording medium having recorded thereon a program for realizing the method.

An apparatus of the present invention for achieving the above object, in the channel estimation apparatus for synchronous demodulation in a wireless packet transmission system, an instantaneous channel for calculating an instantaneous channel estimate from a fast fourier transform (FFT) output signal and a reference data symbol Calculating means; Switching the fed back channel frequency response signal (filtered channel estimate) with respect to the instantaneous channel estimate calculated by the instantaneous channel calculating means, feedbacking the filtered channel estimate input from the channel frequency response signal converting means, and performing the channel frequency response signal. Switching means for outputting a channel estimate from which inter-carrier interference and noise input from the converting means are removed; Channel impulse response signal conversion means for converting the filtered channel estimate transmitted from the switching means into a channel impulse response signal (signal in time domain); Noise removal means for performing a filtering process by a moving average filter on the components within the guard interval of the channel impulse response signal, and removing the corresponding sample components on the components outside the guard interval to remove inter-carrier interference and noise; And the channel frequency response signal converting means for converting the channel impulse response signal from which the noise is removed through the noise removing means into a channel frequency response signal (filtered channel estimate).

On the other hand, the method of the present invention, a channel estimation method for synchronous demodulation in a wireless packet transmission system, comprising: calculating an instantaneous channel estimate from a fast fourier transform (FFT) output signal and a reference data symbol; Converting the feedback channel frequency response signal (filtered channel estimate) with respect to the calculated instantaneous channel estimate to a channel impulse response signal (signal in time domain); Moving average filtering is performed on the components within the guard interval of the converted channel impulse response signal to perform the filtering process, and the sample components are removed from the components outside the guard interval of the converted channel impulse response signal to remove interference between carriers. Removing noise; Converting the noise-free channel impulse response signal into a channel frequency response signal (filtered channel estimate); And returning the transformed filtered channel estimate to the outside to remove the inter-carrier interference and noise.

On the other hand, the present invention provides a wireless packet transmission system having a processor, comprising: a function of calculating instantaneous channel estimates from a fast fourier transform (FFT) output signal and a reference data symbol; Converting the feedback channel frequency response signal (filtered channel estimate) with respect to the calculated instantaneous channel estimate to a channel impulse response signal (signal in time domain); Moving average filtering is performed on the components within the guard interval of the converted channel impulse response signal to perform the filtering process, and the sample components are removed from the components outside the guard interval of the converted channel impulse response signal to remove interference between carriers. The ability to remove noise; Converting the noise-free channel impulse response signal into a channel frequency response signal (filtered channel estimate); And a computer-readable recording medium having recorded thereon a program for realizing a function of outputting the channel estimated value from which the inter-carrier interference and noise have been removed by feeding back the converted filtered channel estimate.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a diagram illustrating an embodiment of a channel estimating apparatus for synchronous demodulation in a wireless packet transmission system according to the present invention.

As shown in FIG. 3, a channel estimation apparatus for synchronous demodulation in a wireless packet transmission system according to the present invention includes a least square channel estimator for calculating instantaneous channel estimates from an FFT output signal and a reference data symbol of FIG. 31), switch 1 (SW1) 32 for switching the feedback channel frequency response signal (filtered channel estimate) with respect to the instantaneous channel estimate passed through the least square channel estimator 31, and switch 1 ( IFFT processing unit 33 for converting the filtered channel estimate transmitted through 32 into a channel impulse response signal (signal in time domain), and filtering by a moving average filter for the components in the guard interval of the channel impulse response signal. And moving average filter 34 and moving average filter 34 to remove inter-carrier interference (ICI) and noise by removing the corresponding sample components for components outside the protection interval. The filtered channel estimate, which is transmitted through the output terminal of the FFT processor 35 and the FFT processor 35 for converting the noise-free channel impulse response signal back to the channel frequency response signal (filtered channel estimate), is converted into a switch 1 ( 32) and switches 2 (SW2) 36 for outputting channel estimates, which are fed back to remove inter-carrier interference and noise.

The operation of the channel estimation apparatus for synchronous demodulation according to the present invention having the structure as described above will be described in detail as follows.

First, an instantaneous channel estimate is obtained from the received signal, i.e., the FFT output and the reference data symbol in FIG. 1, through the least square channel estimator 31, and the value is transferred to the switch 1 (32).                     

The circuit configuration by switch 1 32 is optional and the channel frequency response, i.e., the filtered channel estimate, which is an instantaneous channel estimate or an FFT output, is transmitted to the IFFT processor 33 via the switch 1 32, respectively.

The input channel estimates are converted into channel impulse response sample components, which are signals in the time domain, by the IFFT processor 33, respectively. Then, to remove the ICI and noise for the channel impulse response, the sample components having the energy of the guard period among each component are averaged by a moving average filter having a finite tap, and the sample components having no energy other than the guard period are removed. Is set to the value "0". The channel impulse response obtained by this filtering is converted into a channel frequency response by the FFT processor 35 and obtained as a channel estimate with reduced ICI and noise.

As described above, since the signal processing processes leading to the IFFT processor 33, the moving average filter 34, and the FFT processor 35 include both the filtering in the time domain and the filtering in the frequency domain, the FFT processor 35 The output from is obtained as a filtered channel estimate that reduces the ICI and noise of the instantaneous channel estimate through a low-pass filter in the time and frequency domains.

The output signal of the FFT processing unit 35 is transmitted to the channel equalization stage of FIG. 1 as the output of the channel estimating apparatus through the switch 2 36, or via the feedback circuit composed of the feedback loop and the switch 1 32. Forwarded to (33). The FFT output via the feedback circuit becomes a new input of the IFFT and is obtained with more refined channel estimates through the signal processing of the IFFT-moving average filter-FFT. Since the signal processing procedure made by the feedback circuit as one closed circuit is one time-frequency filter function, the instantaneous channel estimate is repeatedly filtered a predetermined number of times, so that a complete channel estimate can be obtained.

Details about each block are as follows. Among the channel estimation apparatus components of the present invention, the least square channel estimator 31, the IFFT processor 33, and the FFT processor 35 are the same as those in the related art. Therefore, detailed description thereof will be omitted here.

4A and 4B are exemplary diagrams illustrating the structure of a switch in the channel estimating apparatus according to the present invention, and show the switch 1 32 and the switch 2 36 in detail.

As shown in Figures 4A and 4B, the circuitry required to provide appropriate input to the signal processing stage is constituted by them. Prior to explaining their operation, the symbols of the relevant signals are defined.

는 채널 추정치 벡터이고, 위첨자 괄호내 m값은 상기 시간주파수필터링과정을 경유한 횟수, 즉 필터링 횟수를 나타낸다. 그러므로,

는 상기 시간주파수 필터링 과정을 경유하지 않은 것으로서 상기 최소 자승 채널 추정기의 출력인 순시 채널 추정치 벡터이고,

은 m-1회 반복 여파되었고 m회째 반복 여파되어야 할 채널추정치 벡터로서 IFFT의 입력이고,

은 FFT의 출력으로서 m회 반복 여파된 채널추정치 벡터를 나타낸다. m은 1부터 1씩 증가하여 최대값

까지 증가하며, 그때의 값은 하나의 OFDM 심볼 을 위한 무잡음의 채널 추정치를 얻기 위해 반복 여파 처리되는 최대 횟수이다.

Is a channel estimate vector, and the m value in the superscript parenthesis represents the number of times through the time frequency filtering process, that is, the number of times of filtering. therefore,

Is an instantaneous channel estimate vector that is the output of the least squares channel estimator without passing through the time frequency filtering process,

Is the input of the IFFT as the channel estimate vector to be filtered repeatedly m-1 times and to be filtered repeatedly m times,

Denotes a channel estimate vector that has been filtered repeatedly m times as the output of the FFT. m increases from 1 to 1 in maximum

And then the value is the maximum number of times iteratively filtered to obtain a noise-free channel estimate for one OFDM symbol.

회 반복 여파된다. 그리고 구성성분

는 n번째 부케리어에 대한 m회째 반복 여파될 채널추정치이다.That is, the channel estimate is for one OFDM symbol period

Aftermath repeats. And components

Is the channel estimate to be repeated m times for the nth bouquetier.

로 전환되고 순시 채널 추정치가 IFFT로 전달된다. 즉, IFFT 입력

은

으로 제공된다. 다음 시점(m≥2)에 스위치1(32)은 접점

로 전환되고 궤환회로를 통해 전달된 FFT 처리부(35)의 출력 신호가 IFFT 처리부(33)로 전달된다. 이 경우에 IFFT 입력

은 m회 여파된 채널추정치로서

으로 제공된다. 여기에서

에서 첨자 m의 시점은

에서 첨자 m의 시점보다 한 시점이 늦은 시점이다. 이러한 사실은 예를 통해서 확인될 수 있다. 예를 들어, m=1일 때 상기 시간주파수필터의 입력은

이고 그 출력이

인데 반해, m=2일 때 상기 시간주파수필터의 입력은

이지만 상기 m=1일 때의 출력

을 대체 사용하고 있으므로 서로 다른 시점임이 명확해진다. 스위치1(32)은 모두 N개이고 각각이 해당 부케리어의 채널 추정치를 스위칭하며 상기 동작이 N개 모두 동시에 이루어진다. Thus, switch 1 32 is the first (m = 1) contact for any OFDM symbol.

And instantaneous channel estimates are passed to the IFFT. Ie IFFT input

silver

Is provided. At the next time point (m≥2), switch 1 (32)

The output signal of the FFT processor 35 transferred to the feedback circuit through the feedback circuit is transferred to the IFFT processor 33. IFFT input in this case

Is the m estimated channel estimate

Is provided. From here

At the point of subscript m

Is a point in time that is later than the point in subscript m. This can be confirmed by example. For example, when m = 1, the input of the time frequency filter is

And the output is

In contrast, when m = 2, the input of the time frequency filter is

But output when m = 1 above

It is clear that this is a different time since we are using. Switch 1 32 is N in number, each of which switches the channel estimate of the corresponding bouquet area, and all of the N operations are performed simultaneously.

일 때 접점

로 전환되고 FFT의 출력

이 반복 여파를 위해 IFFT로 전달된다.

일 때는 접점

로 전환되고 FFT의 출력

이 스위치 SW2를 통해 본 채널 추정 장치의 출력

으로 제공된다. 스위치2(36) 역시 모두 N개이고 각각 해당 부케리어의 채널추정치를 스위칭하며 상기 동작이 N개 모두 동시에 이루어진다. Switch 2 36 operates differently from switch 1 32. For any OFDM symbol, switch 2 36

Contact

To the output of the FFT

This is passed to the IFFT for the aftermath.

Contact

To the output of the FFT

Output of the channel estimation device seen through this switch SW2

Is provided. Switch 2 36 is also N in number and each switches channel estimates of the corresponding bouquet area, and all of the above N operations are performed simultaneously.

개의 지연탭으로 구성되기 때문에 유한 임펄스 응답(FIR) 필터와 같은 구조이다. 각 지연탭의 내용은 해당 가중치와 곱해지고 가산부(∑)를 통해 하나의 값으로 출력된다. 모든 가중치가

로 각각 설정된다면 평균화 효과에 의해 ICI 및 잡음성분이 감소하게 되고 상기 필터의 출력에서는 신호대 잡음비가 개선된 샘플 성분이 나타난다. 지연탭의 갯수

는 필터의 복잡도와 성능에 높은 상관성을 가지고 있다.

가 클수록 복잡도는 증가하고 평균화에 따른 ICI 및 잡음성분의 감소폭이 커지는 반면,

가 작으면 복잡도는 작아지고 그에 비례하여 잡음감소폭도 작아진다. 따라서, 복잡도와 성능을 고려하여 적절한

값을 선택할 필요가 있다. The moving average filter 34 is a process of taking an average for a predetermined sample interval for all the samples in the guard period among the channel impulse response samples converted by the IFFT processor 33. Moving average filter 34

Because it consists of two delay taps, it has the same structure as a finite impulse response (FIR) filter. The content of each delay tap is multiplied by the corresponding weight and output as one value through the adder. All weights

If set to, respectively, the ICI and noise component are reduced by the averaging effect, and the sample component with improved signal-to-noise ratio appears at the output of the filter. Number of delayed tabs

Has a high correlation with filter complexity and performance.

The larger value increases the complexity and decreases the ICI and noise components due to the averaging.

The smaller is, the smaller the complexity is, and the proportion of the noise reduction is proportionately smaller. Therefore, considering the complexity and performance,

You need to choose a value.

FIG. 5 is a diagram illustrating the structure of a moving average filter 34 in the channel estimation apparatus according to the present invention.

은 가중치인 필 터 계수이다.

는 (m-1)회째 여파되는 n번째 채널임펄스응답 샘플 성분으로서 이동평균필터(34)의 입력이고,

는 (m-1)회째 여파된 이동평균필터(34)의 출력이다. As shown in Fig. 5, D is a delay tap,

Is the filter coefficient which is the weight.

Is the input of the moving average filter 34 as the n-th channel impulse response sample component (m-1) times filtered,

Is the output of the moving average filter 34 filtered after the (m-1) th time.

이 입력되면 이 샘플성분은 첫 번째 지연탭에 저장되고 동시에 필터의 출력을 위해 전달된다. 첫 번째 지연탭의 내용은 다시 두 번째 지연탭으로 전달되면서 이러한 전달과정이 연쇄적으로 이루어고 마지막

번째 지연탭의 내용은 상기 필터의 출력을 위해 전달된다.

과

이 서로 다른 값이라면 이전 OFDM 심볼에 대한 채널임펄스응답 샘플성분이 필터의 일부 지연탭에 저장되고 필터의 출력에 나타날 수 있다. 따라서,

번째 OFDM 심볼에 대한 n번째 채널임펄스응답 샘플성분

이 입력될 때 필터의 출력은 하기의 [수학식 4]와 같이 얻어진다.
Initially all delay taps are set to zero, and at any point

When this is entered, this sample component is stored in the first delay tap and delivered at the same time for the output of the filter. The contents of the first delayed tab are passed back to the second delayed tab, so this delivery process is chained.

The contents of the first delay tap are passed for the output of the filter.

and

If these values are different, the channel impulse response sample components for the previous OFDM symbol may be stored in some delay taps of the filter and appear in the output of the filter. therefore,

Nth channel impulse response sample component for the 1st OFDM symbol

When this is input, the output of the filter is obtained as shown in [Equation 4] below.

이고

는 양의 무한대쪽으로 가장 가까운 정수 를 나타낸다. 예를들면,

,

으로 설정된 경우에 입력

에 대한 이동평균필터(34)의 출력은 이전 OFDM 심볼에 대한 채널임펄스응답 샘플성분

과

이 3개의 지연탭 중에서 두 번째 지연탭과 세 번째 지연탭에 저장되어 있기 때문에 하기의 [수학식 5]와 같이 얻어진다.
here,

ego

Denotes the nearest integer toward positive infinity. For example,

,

Enter when set to

The output of the moving average filter 34 for is the channel impulse response sample component for the previous OFDM symbol.

and

Since these are stored in the second delay tab and the third delay tap among the three delay taps, Equation 5 is obtained.

값의 선택으로 결정되지만 본 발명의 채널추정기의 성능은

값 뿐만 아니라

값에 의해서도 결정되기 때문에

값의 선택은 이동평균필터(34)의 복잡도와 채널 추정 장치의 전체 성능 측면에서 고려되어야 한다. 적절한 기준은 이동평균필터(34)의 복잡도를 낮추면서 만족할 만한 성능을 얻을 수 있는 값으로서

값이

값의 2배이상 되도록 정하는 것이다. The performance of the moving average filter 34 is combined with its complexity as described above.

Although determined by the choice of values, the performance of the channel estimator of the present invention

As well as value

Because it is also determined by the value

The choice of values should be considered in terms of the complexity of the moving average filter 34 and the overall performance of the channel estimation apparatus. An appropriate criterion is a value that can achieve satisfactory performance while reducing the complexity of the moving average filter 34.

Value is

The value is set to be more than twice the value.

The moving average filter 34 of FIG. 5 is used as the number L of channel impulse response samples of a guard interval, and all of them are the same. The moving average filter 34 is applied to the channel estimation apparatus of the present invention in parallel, and processes only corresponding sample components. The channel impulse response, which is the output of the IFFT filtered by the moving average filter 34 for an arbitrary OFDM symbol interval, is obtained as shown in Equation 6 below.

Here, the channel impulse response is set to a value of " 0 " for a sample component having no energy outside the guard interval as in the corresponding part of the prior art. The remaining channel impulse response samples are filtered through the moving average filter 34 and output as ICI and noise reduced samples. Therefore, the channel impulse response which is the output of the moving average filter 34 and is the input of the FFT is obtained as shown in Equation 7 below.

Here, L corresponds to the number of components delayed by the multipath propagation as a protection interval.

을 채널주파수응답으로 변환시킴으로써, 새로운 채널추정치

를 제공한다. As a next process, the FFT processor 35 responds to the channel impulse response.

New channel estimate by converting

To provide.

는 m회째 FFT 출력이고 m-1회째 여파처리된 채널추정치

에 비해 잡음이 감소된 것이다. 상기 FFT 과정은 보호구간의 채널임펄스응답 성분에 대해서만 주파수변환하는 것이기 때문에 주어진 채널대역폭 전체중 일부대역의 성분, 즉 낮은 대역의 성분만을 고려하는 효과를 나타낸다. Where channel estimates

Is the mth FFT output and the m-1th filtered channel estimate

Compared to the noise reduction. Since the FFT process performs frequency conversion only on the channel impulse response component of the guard period, it has an effect of considering only a part of a band, that is, a low band component of the entire channel bandwidth.

Therefore, this gives the same result as the low pass filter. Nevertheless, the noise included in the channel impulse response component of the guard period is distributed throughout the channel bandwidth according to its frequency component during frequency conversion.

에 대한 상기 IFFT - 평균이동필터 - FFT의 신호처리과정을 반복적으로 수행한다. The channel estimating apparatus according to the present invention provides an instantaneous channel estimation value through a feedback circuit composed of two switches and a feedback loop.

The signal processing of the IFFT-average shift filter-FFT is repeatedly performed.

가 얻어진다. Since the signal processing is an equivalent filter including a filter in the time domain and a filter in the frequency domain, as mentioned above, the ICI and noise components included in the instantaneous channel estimate are gradually decreased as the signal processing process is repeated, and the constant number of times is repeated. Flawless channel estimate with noise completely removed when

Is obtained.

값과 반복횟수

값이 각각 설정되어야 한다. In this process, since the noise cancellation is performed in the average shift filtering process for the channel impulse response component and the step of setting the "0" value for the channel response component other than the guard interval, the operation of the channel estimator is preferred.

Value and repeat count

Each value must be set.

6A and 6B are flowcharts illustrating an example of a signal processing procedure in a channel estimating apparatus according to the present invention.

개의 OFDM 심볼을 갖는 하나의 패킷 프레임에 대한 것이며 패킷 프레임 단위로 반복적으로 이루어진다. As shown in Figure 6a and 6b, the signal processing in the channel estimation apparatus according to the present invention,

It is for one packet frame having OFDM symbols and is repeated repeatedly in packet frame units.

를 "0"으로 재설정하고(601), 현 시점에서 채널 추정될 OFDM 심볼을 지정하기 위해 "1"을 가산한다(602). When the receiver starts receiving any OFDM packet, the channel estimation apparatus according to the present invention orders the OFDM symbols to be channel estimated.

Resets to " 0 " (601) and adds " 1 " to specify an OFDM symbol to be channel estimated at this point (602).

와

와의 비교를 통해 판단한다(603).Then, whether channel estimation has been completed for all OFDM symbols in the packet.

Wow

Determination is made by comparison with (603).

개의 OFDM 심볼에 대해 채널추정이 완료되었다면 본 발명에 따른 채널 추정 장치의 동작을 종료하고, 그렇지 않다면 수신된 OFDM 심볼을 도 1b의 FFT로부터 입력한다(604). Judgment Results,

If channel estimation is completed for the OFDM symbols, the operation of the channel estimation apparatus according to the present invention is terminated. Otherwise, the received OFDM symbol is input from the FFT of FIG. 1B (604).

를 출력한다(605). Subsequently, a channel estimation is performed on the received OFDM symbol using the reference data symbol and as a result, an instantaneous channel estimate

It outputs (605).

Thereafter, m = 1 is set as the number of times iteratively filtered for the instantaneous channel estimate (606). This means that the signal processing of IFFT-Moving Average Filter-FFT is the first for the instantaneous channel estimate.                     

로 전환하여 IFFT에 이르는 전달경로를 만들고 또한 FFT의 출력을 IFFT단으로 궤환시킬 수 있는 전달경로를 만든다(607). Then, switch 1 and switch 2 are respectively contacted.

In this case, the transfer path to the IFFT is converted to the IFFT stage (607).

로 전환하고(609), m이 2가 아니면 순시 채널 추정치가 IFFT 처리부로 전달될 수 있도록 스위치1이 접점

로 전환되어 있는 상태이거나 또는 FFT 출력인 여파된 채널 추정치가 IFFT 처리부로 전달될 수 있도록 스위치1이 접점

로 전환되어 있는 상태이다. Then, it is compared and judged whether the number of repetition filters m is 2 (608), and if m is 2, the switch SW1 is contacted.

Switch 609, and if m is not 2, switch 1 is contacted so that the instantaneous channel estimate can be passed to the IFFT processor.

Switch1 is contacted so that the filtered channel estimate, either switched to or the FFT output, can be passed to the IFFT processor.

Has been switched to.

에 이르렀는지를 비교 판단하여(610), m이

보다 크다면 순시 채널 추정치가 정해진

회 반복 여파를 완료한 상태이므로 스위치2를 접점

로 전환하고(612), 얻어진 채널추정치

를 본 채널 추정기의 출력으로서 상기 도 1의 채널등화단으로 전달하고 새로운 OFDM 심볼에 대한 채널추정을 위해, 신호처리 흐름도의 시작부분으로 이동한다. 이후, 현 시점에서 채널 추정될 OFDM 심볼을 지정하기 위해 "1"을 가산하는 과정(602)으로 진행한다(613). 만약, 반복횟수 m이

와 같거나 작다면, m번째 여파처리를 위해 FFT의 출력

을 IFFT의 새로운 입력

으로서 전달받는다(614). After this, the repetition number m is set to the maximum value

To determine whether or not to reach (610), m is

If greater than instantaneous channel estimate

Switch 2 is contacted because the filter has been completed

Switch to 612, the obtained channel estimate

Is sent to the channel equalizer of FIG. 1 as the output of the present channel estimator and moves to the beginning of the signal processing flow diagram for channel estimation for the new OFDM symbol. Subsequently, the process proceeds to step 602 of adding "1" to designate an OFDM symbol to be channel estimated at this time (613). If m is repeated

Is less than or equal to, the output of the FFT for the mth filter

New input of IFFT

Received as (614).

를

로 변환시킨다(615). 다음 단계에서는 보호구간내에 있는 채널임펄스응답 성분

에 대해 상기 이동평균필터(34)에 의한 여파를 수행하고 보호구간 밖에 있는 채널임펄스응답 성분에 대해서는 "0"값으로 설정한다(616). 본 단계에서는

이 결과로서 얻어진다. Next, perform an IFFT

To

(615). The next step is the channel impulse response component within the protection interval

Filter is performed by the moving average filter 34, and the channel impulse response component outside the guard interval is set to a value of " 0 " (616). In this step

This is obtained as a result.

가 채널주파수응답

으로 변환된다(617). 이것은

을 대체하는 새로운 채널추정치다.After that, the FFT is performed and through this process the channel impulse response

Channel frequency response

Is converted to 617. this is

It is a new channel estimate that replaces.

Subsequently, m is increased by 1 to perform the process of the IFFT-Moving Average Filter-FFT on the new channel estimate again.

회 반복되며, 패킷 프레임에 속하는 모든 OFDM 심볼에 대해 수행된다.This process is performed for every OFDM symbol.

Repeated once, it is performed for all OFDM symbols belonging to the packet frame.

The method of the present invention as described above may be implemented as a program and stored in a computer-readable recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.).

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

In the present invention as described above, in channel estimation for synchronous demodulation in a wireless packet OFDM system, moving average filtering is applied to a sample component in a guard period among channel impulse response components obtained through IFFT, and is applied to a sample component outside the guard interval. In this case, filtering is performed in the time domain, which is a process of setting a value of "0", and the filtering process is repeatedly performed through a feedback circuit composed of two switches and a feedback loop for the obtained channel estimate. Since it can be eliminated, accurate channel estimates can be obtained not only for various operating environments but also for OFDM packet schemes of multi-level modulation symbols.

Claims (7)

A channel estimating apparatus for synchronous demodulation in a wireless packet transmission system, Instantaneous channel calculation means for calculating an instantaneous channel estimate from an FFT (Fast Fourier Transform) output signal and a reference data symbol; Switching the fed back channel frequency response signal (filtered channel estimate) with respect to the instantaneous channel estimate calculated by the instantaneous channel calculating means, feedbacking the filtered channel estimate input from the channel frequency response signal converting means, and performing the channel frequency response signal. Switching means for outputting a channel estimate from which inter-carrier interference and noise input from the converting means are removed; Channel impulse response signal conversion means for converting the filtered channel estimate transmitted from the switching means into a channel impulse response signal (signal in time domain); Noise removal means for performing a filtering process by a moving average filter on the components within the guard interval of the channel impulse response signal, and removing the corresponding sample components on the components outside the guard interval to remove inter-carrier interference and noise; And The channel frequency response signal converting means for converting the channel impulse response signal from which the noise is removed through the noise removing means into a channel frequency response signal (filtered channel estimate) Channel estimation apparatus for synchronous demodulation in a wireless packet transmission system comprising a. The method of claim 1, The noise removing means, selected

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According to the following equation, each channel impulse response signal of the guard interval is processed according to the following equation to remove the intercarrier interference (ICI) and noise while preserving the energy of the channel impulse response sample signal. Channel estimation apparatus for demodulation.

(here,

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Represents the nearest integer toward positive infinity) The method of claim 1, The switching means, First switching means for outputting a channel frequency response signal (filtered channel estimate) fed back from a second switching means to the channel impulse response signal conversion means with respect to the instantaneous channel estimate calculated by the instantaneous channel calculating means; And A channel estimate value from which the filtered channel estimate input from the channel frequency response signal converting means is returned to the first switching means, and the interference and noise between the carriers are removed by the noise removing means input from the channel frequency response signal converting means; The second switching means for outputting the outside Channel estimation apparatus for synchronous demodulation in a wireless packet transmission system comprising a. A channel estimation method for synchronous demodulation in a wireless packet transmission system, Calculating an instantaneous channel estimate from a fast fourier transform (FFT) output signal and a reference data symbol; Converting the feedback channel frequency response signal (filtered channel estimate) with respect to the calculated instantaneous channel estimate to a channel impulse response signal (signal in time domain); Moving average filtering is performed on the components within the guard interval of the converted channel impulse response signal to perform the filtering process, and the sample components are removed from the components outside the guard interval of the converted channel impulse response signal to remove interference between carriers. Removing noise; Converting the noise-free channel impulse response signal into a channel frequency response signal (filtered channel estimate); And Feedbacking the transformed filtered channel estimate to output the channel estimate from which inter-carrier interference and noise have been removed. Channel estimation method for synchronous demodulation in a wireless packet transmission system comprising a. The method of claim 4, wherein The step of removing the inter-carrier interference and noise, selected

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According to the following equation, each channel impulse response signal of the guard interval is processed according to the following equation to remove the intercarrier interference (ICI) and noise while preserving the energy of the channel impulse response sample signal. Channel Estimation Method for Demodulation.

(here,

ego

Represents the nearest integer toward positive infinity) delete In a wireless packet transmission system having a processor, Calculating instantaneous channel estimates from an FFT (Fast Fourier Transform) output signal and a reference data symbol; Converting the feedback channel frequency response signal (filtered channel estimate) with respect to the calculated instantaneous channel estimate to a channel impulse response signal (signal in time domain); Moving average filtering is performed on the components within the guard interval of the converted channel impulse response signal to perform the filtering process, and the sample components are removed from the components outside the guard interval of the converted channel impulse response signal to remove interference between carriers. The ability to remove noise; Converting the noise-free channel impulse response signal into a channel frequency response signal (filtered channel estimate); And A function of outputting the channel estimate value from which the interference and noise between carriers is removed by feedbacking the transformed filtered channel estimate value A computer-readable recording medium having recorded thereon a program for realizing this.

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