KR101389891B1 - Data transmition method including impulse symbol of optimum magnitude for channel estimation, and channel estimation method by impulse symbol in ofdm system - Google Patents

Abstract

The present invention relates to a data transmission method including an impulse symbol of an optimal size for channel estimation in an orthogonal frequency division multiplexing (OFDM) communication system, and more particularly, in an OFDM system. For channel estimation, in applying the method of inserting an impulse symbol in the guard interval between data symbols on the time axis (Impulse Postfix, IP), an optimal channel estimation and bit The present invention relates to a method for transmitting data by determining an impulse symbol size maintaining bit error rate (BER) performance and inserting the data between data symbols.

According to the present invention, it is possible to maintain an improved bit error rate (BER) performance compared to existing channel estimation techniques while satisfying an appropriate level of Peak to Average Power Ratio (PAPR) in data transmission and reception of an OFDM system.

Impulse Postfix (IP), Impulse Size, OFDM

Description

DATA TRANSMITION METHOD INCLUDING IMPULSE SYMBOL OF OPTIMUM MAGNITUDE FOR CHANNEL ESTIMATION, AND CHANNEL ESTIMATION METHOD BY IMPULSE SYMBOL IN SYMBOL IN SYSTEM}

The present invention relates to a data transmission method including an impulse symbol of an optimal size for channel estimation in an orthogonal frequency division multiplexing (OFDM) communication system, and more particularly, in an OFDM system. For channel estimation, the optimal channel estimation and bit error rate are applied in applying the impulse symbol (IP) method to insert an impulse symbol into a guard interval between data symbols on a time axis. The present invention relates to a method for transmitting data by determining the size of an impulse symbol maintaining rate, BER) performance, and inserting the data into data symbols.

When transmitting a signal over a wireless channel, a multipath channel environment is formed between a transmitter and a receiver in which radio waves are reflected by various obstacles. In a wireless channel with multipath, there is a 'maximum delay spread', which is the time when the last reflected signal is received. In the case of a high-speed transmission using broadband, the transmission period of the signal is shorter than the maximum delay spread, so that the consecutive received signals Interference occurs and the received signal is subjected to Inter-Symbol Interference (ISI).

The OFDM scheme is proposed to solve this problem and is a kind of frequency division multiplexing (FDM) scheme in which data to be transmitted is divided into several small frequency bands (subchannels). In other words, by parallelizing a series of data sequences to be transmitted by the number of subchannels and modulating each parallel data into subcarriers corresponding to each subchannel, the total data transmission rate is maintained at the original transmission rate. The symbol period in the channel is lengthened by the number of subchannels, thereby obtaining the same effect as when the transmission period of the signal is longer than the maximum delay spread. In addition, the OFDM scheme arranges frequencies of subcarriers of each subchannel at positions where interference does not occur between the subchannels, while maintaining orthogonality, while allowing subcarriers to overlap each other so that a guard band is provided. It is a way to effectively use the entire band without having to have a guard band.

On the other hand, in such a wireless communication system, multipath attenuation causes symbol size and phase distortion, and a channel estimation technique is used to estimate and compensate for this. The conventional channel estimating technique is to use a pilot, and there are two methods of arranging pilots. One method is to periodically allocate pilots to all subcarriers of one OFDM symbol, and the other is to assign pilots to a specific subcarrier of every OFDM symbol. The former is vulnerable to time selectivity, and the latter has a problem of weakness in frequency selectivity.

In order to solve this problem, an impulse symbol for channel estimation may be used instead of a pilot. In this case, the channel estimation performance is improved as the size of the impulse symbol used increases, but there is a problem in that the Peak to Average Power Ratio (PAPR) of the OFDM symbol is increased.

The present invention was devised to solve such a problem, and an object of the present invention is to use an impulse postfix (IP) method having a strong advantage in both time selectivity and frequency selectivity as a channel estimation technique. In determining the size of the impulse symbol used for this, the probability of the OFDM signal so that the bit error rate (BER) can be improved while maintaining an appropriate peak to average power ratio (PAPR). This paper presents a method for determining the optimal size based on the distribution.

In order to achieve the above object, in an orthogonal frequency division multiplexing (OFDM) communication system according to the present invention, an impulse symbol having an optimal size for channel estimation is used for each data. A method of transmitting data by inserting a data symbol after a symbol, comprising: (a) a complex random variable ( X ( k ) obtained by modulating an OFDM data bit stream, where k is a subcarrier number k = 0,1 Converting N −1) into an Inverse Discrete Fourier Transform (IDFT) to a signal in a time domain; (b) inserting a certain number of 'null symbols' and impulse symbols for channel estimation in a guard interval after each data symbol in the converted signal; (c) transmitting the OFDM data symbols in which an impulse symbol is inserted; wherein the size of the impulse symbol is a power boosting factor, which is a value indicating how many times the average power of the OFDM data symbol. power boosting factor).

The size of the impulse symbol may be determined as a square root of a value obtained by multiplying the power boosting factor by the variance of the complex random variable.

The method of obtaining the power boosting factor includes (a) a complex random variable X ( k ) having a variance of E _s obtained by modulating an OFDM data bit stream, where k is a subcarrier number k Obtaining, from 0 = 1, 2, ... N -1), the n th sample x ( n ) of the data symbols in the time domain by the following equation;

및 허수부의 PDF인

로부터 상기 x(n)의 PDF를 다음식에 의해 구하는 단계;(b) Probability Density Function (PDF) of the real part of x ( n )

And the imaginary part of the PDF

Obtaining a PDF of x ( n ) from the following equation;

(c) obtaining a Cumulative Distribution Function (CDF) from the PDF of x ( n ) by the following equation;

에 해당하는 CDF 값을 다음 식에 의해 구하는 단계;(d) when the power boosting factor is p , the size of an impulse sample

Obtaining a CDF value corresponding to the following equation;

일 경우의 파워 부스팅 팩터 p를 상기 CDF의 역함수인 다음 식에 의해 구하는 단계;(e) probability

Obtaining a power boosting factor p in one case by the following equation, which is an inverse function of the CDF;

. ≪ / RTI >

The modulation scheme of the OFDM data bit stream may be a quadrature phase shift keying scheme.

A modulation scheme for the OFDM data bit stream may be a quadrature amplitude modulation scheme.

According to another aspect of the present invention, in an orthogonal frequency division multiplexing (OFDM) communication system, an impulse symbol transmitted after being inserted after each data symbol for channel estimation A method for estimating a channel from an impulse response generated by a method comprising: (a) an impulse inserted in a channel estimation part after each of two adjacent data detection parts in a received signal; Constructing a channel matrix of the time domain by obtaining an approximation of the channel value of time between the responses (channel values); converting the channel matrix of the time domain into a Discrete Fourier Transform (DFT) to transform the channel matrix of the time domain into a channel matrix of the frequency domain; (c) detecting a signal transmitted from the channel matrix in the frequency domain; wherein the size of the transmitted impulse symbol is a numerical value representing how many times the average power of the OFDM data symbol. It may be determined by a power boosting factor.

In step (a), when there are two or more multipath delay components of the impulse response, step (a) is preferably performed for each.

Before the step (a), (a01) a value below a specific reference value in the impulse response is preferably set to zero;

In step (a), an approximation to the channel value may be applied to interpolation.

Prior to the step (a), (a02) applying the overlap-and-add method in the received signal to find the data; preferably further comprises a.

The size of the impulse symbol may be determined as a square root of a value obtained by multiplying the power boosting factor by the variance of the complex random variable.

The method of obtaining the power boosting factor includes (a) a complex random variable X ( k ) having a variance of E _s obtained by modulating an OFDM data bit stream, where k is a subcarrier number k Obtaining, from 0 = 1, 2, ... N -1), the n th sample x ( n ) of the data symbols in the time domain by the following equation;

및 허수부의 PDF인

로부터 상기 x(n)의 PDF를 다음식에 의해 구하는 단계;(b) Probability Density Function (PDF) of the real part of x ( n )

And the imaginary part of the PDF

Obtaining a PDF of x ( n ) from the following equation;

(c) obtaining a Cumulative Distribution Function (CDF) from the PDF of x ( n ) by the following equation;

에 해당하는 CDF 값을 다음 식에 의해 구하는 단계;(d) when the power boosting factor is p , the size of an impulse sample

Obtaining a CDF value corresponding to the following equation;

일 경우의 파워 부스팅 팩터 p를 상기 CDF의 역함수인 다음 식에 의해 구하는 단계;(e) probability

Obtaining a power boosting factor p in one case by the following equation, which is an inverse function of the CDF;

. ≪ / RTI >

According to the present invention, it is effective to maintain an improved bit error rate (BER) performance compared to existing channel estimation techniques while satisfying a proper level of Peak to Average Power Ratio (PAPR) in data transmission and reception of an OFDM system. have.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

1 is a diagram illustrating the configuration of a cyclic prefix (CP) -OFDM and zero-added postfix (ZP) -OFDM system.

The transmission of OFDM symbols is processed on a block-by-block basis, but is affected by previously transmitted symbols while OFDM symbols are transmitted over a multipath channel. In order to prevent such inter-symbol interference, guard intervals are inserted between consecutive OFDM blocks. At this time, the length of the guard interval should be longer than the maximum delay spread of the radio channel. The receiving end removes the guard interval and takes the remaining received signal to perform data demodulation. If all subcarriers of the received signal are received without delay after passing through the channel, orthogonality is maintained in the fast fourier transform (FFT) period. However, if a subcarrier of the N subcarriers is received with a time delay, the subcarrier does not become an integer multiple of the fundamental frequency within the FFT period, thereby destroying orthogonality. Therefore, interchannel interference that distorts other subcarriers occurs.

In order to solve this problem, the CP OFDM 100 inserts a Cyclic Prefix (CP) at the guard interval position on the time axis of the transmitter 110 (113). The last specific number of data of the OFDM symbol block is inserted into the guard interval before the OFDM symbol block. When the CP is inserted in this way, even if a delay occurs in an arbitrary subcarrier, the subcarrier maintains an integer multiple period within the FFT interval, thereby ensuring orthogonality. In the demodulated signal, only the rotation of the phase due to the delay occurs, so that no inter-channel interference occurs. The receiving end 120 removes the CP from the received signals in this way and then restores the signal. Description of blocks other than those shown on the drawing 100 is the same as in the case of IP (Impulse Postfix) -OFDM, which will be described later with reference to FIG. 3.

Meanwhile, the ZP (Zero-added Postfix) OFDM system 200 inserts a certain number of null data, that is, '0', into a guard interval after the OFDM symbol block without inserting a CP at the transmitting end 210 (Zero). Padding) 213, in this case, the guard interval is not removed at the receiving end 220, but performs an 'Overlap and Add' operation (222). 'Overlap and Add' operation is a method of performing fast block convolution. In other words, when an infinitely long signal enters the FIR (Finite Impulse Response) system, the signal is divided into blocks and convolution is applied.The original signal is divided into small units (usually the same length as the impulse response). It is a way to add all the responses for each part. Description of blocks other than those shown on the drawing 200 is the same as in the case of IP (Impulse Postfix) -OFDM, which will be described later with reference to FIG. 3.

2 is a diagram illustrating an embodiment of pilot arrangement for channel estimation in an OFDM system.

Each circle shown represents an OFDM symbol, and the horizontal axis represents the time axis and the vertical axis represents the frequency of the subcarrier according to the characteristics of the OFDM system. The diagram shown above is a method of periodically allocating pilots to all subcarriers of one OFDM symbol, and the diagram shown below shows a method of allocating pilots to a specific subcarrier of every OFDM symbol. In the figure, a portion indicated by a black circle indicates a portion to which a pilot is assigned. As mentioned above, the former is vulnerable to time selectivity, and the latter has a problem of weakness in frequency selectivity.

FIG. 3 is a diagram illustrating a configuration of an impulse postfix (IP) -OFDM system 300, and an impulse for channel estimation instead of 'Zero Padding' 213 as compared to the ZP-OFDM system 200 of FIG. 1. There is a difference that the impulse postfix 313 is inserted. Hereinafter, this will be described in detail with reference to the accompanying drawings.

In the transmitting end 310, the signal X (k) of the frequency band is divided into parallel data (311), and is changed into a signal x on the time axis through an Inverse Discrete Fourier Transform (IDFT) (312). An impulse signal is inserted (guard pulse) between (impulse postfix) (313). Thereafter, the signal x ' into which the IP is inserted is converted back to serial, and the converted signal x (n) is transmitted from the antenna. h (n, l) is a channel value representing the characteristics of the channel through which this signal is transmitted, and implies an impulse response. n is the sampling index of the data on the time axis, and l is the index of the multipath delay component. After the transmitted signal x (n) is converted by h (n, l) , Z (n) , which is additive white gaussian noise (AWGN), and the added signal y (n) are inputted to the receiver 320 and parallelized ( In operation 321, the receiver 320 performs an overlap and add operation as in the case of the ZP-OFDM system 200 (322). Thereafter, the frequency band signal is converted into a serial signal through a discrete fourier transform (DFT) (323), and then the original transmission signal X is restored.

This process is described using a formula as follows.

The OFDM signal after the IDFT (Inverse Discrete Fourier Transform) operation in the transmitter 310 is represented by Equation 1.

수식 1

Equation 1

In the above formula, ( · ) ^T operation means transpose matrix operation. When the guard interval length is L , if the impulse postfix is added to Equation 1, the result is the same as Equation 2.

수식 2

Equation 2

In the above equation, O _L is a 1 × L null vector and c is an impulse sample for channel estimation.

After passing through the time-frequency-selective channel, the signal received at the receiver 320 is expressed as Equation 3.

수식 3

Equation 3

Where h ( n, l ) denotes a channel value with a sampling index of n and a multipath delay index of l , and z ( n ) is AWGN (Additive White Gaussian Noise).

4 is a diagram illustrating a transmission signal and a reception signal of an IP-OFDM system.

The signal 420 received at the receiver 320 is also shown in Equation 4 in the form of a vector.

수식 4

Equation 4

A portion 411 enclosed by a dashed line in the transmission signal 410 and a portion 421 enclosed by a dashed line in the received signal 420 are data detection parts used to estimate data. A portion 412 enclosed by a dotted line at 410 and a portion 422 enclosed by a dotted line at the back of the received signal 420 are channel estimation parts used to estimate a channel. The impulse symbol 412.1 transmitted by the transmitting end 310 and thus the multipath delay component 422.1 received by the receiving end 320 is shown. The method of finding data in the IP-OFDM system 300 uses an overlap-and-add operation as described above in the ZP-OFDM system 200 with reference to FIG. 1. The signal after the overlap-and-add operation is shown in Equation 5.

수식 5

Equation 5

이고

이다.In the above equation

ego

to be.

The channel matrix of the time domain is given by Equation 6. Where h _{n , l} is the same as h ( n, l ).

수식 6

Equation 6

In order to equalize the received signal in the frequency domain, Equation 6 is converted into the channel matrix of the frequency domain. In this case, an N- point Discrete Fourier Transform (DFT) matrix is required, and the components of p rows q columns are shown in Equation 7.

수식 7

Equation 7

The received signal in the frequency domain is obtained as shown in Equation 8.

수식 8

Equation 8

In the above equation, (·) ^H means Hermitian transpose, and G is the channel matrix in the frequency domain. The transmitted signal is detected by multiplying the received signal by the inverse of G to the left.

수식 9

Equation 9

5 is a diagram illustrating a process of estimating a channel.

Upon receipt of the received signal 500 on the time base, the impulse response of the channel is directly obtained as shown in FIG. The signal graph 510 of the channel estimation signal part added to the m th OFDM symbol in the received signal 500 on the time axis and the signal graph 540 of the channel estimation signal part added to the m + 1 th OFDM symbol. ) Is shown. Among them, signals 503 and 505 below a certain threshold are set to 0 (504,506), and the remainder (501.1, 501.2, 502.1, 502.2) is used as a multipath delay component, and a graph is shown (520, 550). ).

For each of the selected multipath delay components, graphs for applying interpolation to the channel value obtained from two adjacent OFDM symbols 501.1 and 501.2, 502.1 and 502.2 are shown (530 and 560). . That is, the first multipath delay component 501.1 of the channel estimation signal portion 501.1 of the channel estimation signal portion of the m th OFDM symbol and the first multipath delay component 501.2 of the channel estimation signal portion of the m + 1th OFDM symbol are shifted into one graph (530). It estimates the channel value by applying the second multipath delay components (502.1, 502.2) to a single graph (560) and estimates the channel value by applying interpolation.

As a result, sample values are obtained at a sampling frequency of F _s , and a diagram 570 is shown, in which (531, 561) the respective values are cut out (531, 561) and the respective values are displayed (532, 562) in space (time-delay). From this, the channel matrix of the time domain (Equation 6) can be constructed.

Hereinafter, a method of optimally determining the size of an impulse symbol used in the aforementioned IP-OFDM system will be described with reference to FIGS. 3 to 5.

After the IDFT operation, the n th sample in one OFDM symbol is given by Equation 10.

수식 10

Equation 10

X ( k ) is a signal in the frequency domain, iid (independent and identically distributed) complex random variable with an average of 0 and a variance of E _s . The mean and variance of x _R ( n ) and x _l ( n ) are the same as Equations 11 and 12, respectively.

수식 11

Equation 11

수식 12

Equation 12

Covariance is also shown in Equation 13.

수식 13

Equation 13

As N , the length of the FFT increases, x _R ( n ) and x _l ( n ) become Gaussian random variables due to the central limit theorem. In addition, x _R ( n ) and x _l ( n ) are independent of each other since they are unrelated. Therefore, two components of the Probability Density Function (PDF) are given by Equations 14 and 15.

수식 14

Equation 14

수식 15

Equation 15

Thus x ( n ) has a Rayleigh distribution and PDF is equal to Eq.

수식 16

Equation 16

In addition, a Cumulative Distribution Function (CDF) is given by Equation 17.

수식 17

Equation 17

일 때, 수식 17에 의해서 이에 해당되는 CDF 값은 수식 18과 같다.The size of the impulse sample

In Equation 17, the corresponding CDF value is equal to Equation 18.

수식 18

Equation 18

으로 평균이 1인 지수 확률 변수(exponential random variable)이다. 따라서 주어진 확률이

일 경우 임펄스 샘플의 크기를 결정하는 파워 부스팅 계수(power boosting factor)인 p는 수식 19와 같이 얻어진다.In the above equation

This is an exponential random variable with an average of 1. So given the probability

In this case, p , a power boosting factor for determining the size of an impulse sample, is obtained as shown in Equation 19.

수식 19

Equation 19

은 평균이 1인 지수 확률 변수의 역(inverse) CDF이다. OFDM 샘플의 개수가

이면 확률적 특성에 의해

개의 샘플은 채널 추정에 이용되는 임펄스 샘플보다 낮은 크기를 갖는다.At this time

Is the inverse CDF of the exponential random variable with mean 1. The number of OFDM samples

By stochastic properties

Samples have a lower magnitude than the impulse samples used for channel estimation.

FIG. 6 is a diagram illustrating a channel estimation mean square error (MSE) of an IP OFDM system. It can be seen that as the size of the impulse sample increases, the MSE of channel estimation decreases.

FIG. 7 is a diagram illustrating a bit error rate (BER) of an impulse postfix (IP) OFDM system. As described above with reference to FIG. 6, as the size of the impulse sample is increased, the MSE of channel estimation decreases, thereby increasing bit error rate performance. In addition, it can be seen that the channel estimation method using the impulse postfix method shows an excellent performance compared to the channel estimation through pilot-based channel estimation or training symbol. Therefore, it is very important to determine the size of the appropriate impulse sample that satisfies the appropriate peak to average power ratio (PAPR) to maintain channel estimation and bit error rate performance.

Table 1 is a table showing an embodiment of the main variable used in the experiment for determining the size of the impulse sample in the channel estimation, Table 2 is a key variable of the channel used in the experiment for determining the size of the impulse sample in the channel estimation A table showing examples of values. The channel is a 2-ray Rayleigh fading model and each multipath delay component has the same power on average.

Modulation method 변조 ) QPSK FFT / IFFT size 64 Guard interval length 16 System frequency bandwidth 500kHz

channel number One 2 3 nrmalized Doppler frequency 0.05 0.1 0.05 RMS delay spread [μs] 2 2 10

FIG. 8 is a diagram illustrating bit error rate in an IP-OFDM system and another system using an impulse symbol sized according to the method presented in the present invention in channel 1. FIG. It can be seen that the IP-OFDM system using the proposed scheme shows the best bit error rate performance at SNR (E _b / N ₀ ) over 10-12dB than the conventional system.

FIG. 9 is a diagram illustrating bit error rates in an IP OFDM system and another system using an impulse symbol sized according to the method of the present invention in channel 2 in which the Doppler spread is twice as large as that of channel 1. FIG. In contrast to the ZP-OFDM training symbol scheme, the IP-OFDM scheme according to the present invention shows not only deterioration but also the best bit error rate performance.

FIG. 10 is a diagram illustrating bit error rates in an IP OFDM system and another system using an impulse symbol sized according to the method of the present invention in channel 3 in which a delay spread is increased five times than that of channel 1. FIG. While ZP-OFDM pilots show performance degradation, IP-OFDM shows the best performance. Therefore, it can be seen that the advantages of IP-OFDM are maintained even if the size of the impulse sample is designed by the proposed technique.

11 is a diagram illustrating a complementary cumulative distribution function (CCDF) curve. PAPR was calculated for every OFDM symbol and CCDF was obtained from 10 ⁶ OFDM symbols. 'IP-OFDM ( p = 1)' is a case where the size of the impulse sample is the same as the average size of the OFDM sample and the power boosting is not used. The initial IP-OFDM was p = 17, but it can be seen that the PAPR was significantly reduced by applying the existing technique.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the configuration of a Cyclic Prefix (CP) OFDM and Zero Padded (ZP) OFDM system.

2 illustrates an embodiment of a pilot arrangement for channel estimation in an OFDM system.

3 is a diagram illustrating a configuration of an impulse postfix (IP) OFDM system.

4 is a diagram illustrating a transmission signal and a reception signal of an IP (Impulse Postfix) OFDM system.

5 is a diagram illustrating a process of estimating a channel.

FIG. 6 illustrates channel estimation Mean Square Error (MSE) of an Impulse Postfix (IP) OFDM system. FIG.

FIG. 7 illustrates a Bit Error Rate (BER) of an Impulse Postfix (IP) OFDM system. FIG.

8 shows bit error rate in channel 1 (see Table 2) in an IP OFDM system and other systems using impulse symbols sized according to the method presented in the present invention.

9 shows bit error rate in an IP OFDM system and another system using an impulse symbol sized according to the method of the present invention in channel 2 (see Table 2) in which the Doppler spread is twice as large as that of channel 1. A diagram showing.

FIG. 10 shows bit error rate in an IP OFDM system and another system using an impulse symbol sized according to the method of the present invention in channel 3 (see Table 2) in which the delay spread is five times higher than that of channel 1. A diagram showing.

11 shows a Complementary Cumulative Distribution Function (CCDF) curve.

Claims (12)

In an orthogonal frequency division multiplexing (OFDM) communication system, a method of transmitting data by inserting an impulse symbol after each data symbol for channel estimation, (a) a complex random variable ( X ( k ) obtained by modulating an OFDM data bit stream, where k is a subcarrier number and k = 0,1,2, ... N -1) is an inverse discrete Fourier transform ( Inverse Discrete Fourier Transform (IDFT) to transform the signal into a time domain signal; (b) inserting a certain number of 'null symbols' and impulse symbols for channel estimation in a guard interval after each data symbol in the converted signal; (c) transmitting the OFDM data symbols with an impulse symbol inserted therein, The size of the impulse symbol is determined by a square root of a value obtained by multiplying a power boosting factor, which is a number indicating an average power of an OFDM data symbol, and a variance of the complex random variable. A data transmission method comprising an impulse symbol for channel estimation in an OFDM system. delete The method according to claim 1, The method of obtaining the power boosting factor, (a) A complex random variable ( X ( k ) with variance of E _s , obtained by modulating the OFDM data bit stream, where k is the subcarrier number k = 0,1,2, ... N -1) From n , obtain the n th sample x ( n ) of the data symbols in the time domain by the following equation ;

(Where N is a natural number) (b) Probability Density Function (PDF) of the real part of x ( n )

And the imaginary part of the PDF

Obtaining a PDF of x ( n ) from the following equation;

(c) obtaining a Cumulative Distribution Function (CDF) from the PDF of x ( n ) by the following equation;

(d) when the power boosting factor is p , the size of an impulse sample

Obtaining a CDF value corresponding to the following equation;

(e) probability

Obtaining a power boosting factor p in one case by the following equation, which is an inverse function of the CDF;

A data transmission method comprising an impulse symbol for channel estimation in an OFDM system comprising a. The method according to claim 1, The modulation method of the OFDM data bit stream is a data transmission method comprising an impulse symbol for channel estimation in an OFDM system, characterized in that for applying a quadrature phase shift keying (quadrature phase shift keying) method. The method according to claim 1, The modulation method of the OFDM data bit stream includes an impulse symbol for channel estimation in an OFDM system, characterized in that for applying a quadrature amplitude modulation (quadrature amplitude modulation) method. In an orthogonal frequency division multiplexing (OFDM) communication system, a channel from an impulse response generated by an impulse symbol inserted after a data symbol and transmitted after each data symbol for channel estimation As a method of estimating (a) In the received signal, from the impulse response (channel value) inserted into the channel estimation part at the rear of each of two adjacent data detection parts, for the channel value of time therebetween. Obtaining an approximation value to construct a channel matrix of the time domain; converting the channel matrix of the time domain into a Discrete Fourier Transform (DFT) to transform the channel matrix of the time domain into a channel matrix of the frequency domain; (c) detecting a signal transmitted from the channel matrix in the frequency domain, The transmitted impulse symbol has a size of a complex random variable obtained by modulating a power boosting factor and an OFDM data bit stream, which are values indicating how many times the average power of an OFDM data symbol. A channel estimation method using impulse symbols in an OFDM system, characterized in that determined by the square root of the value multiplied by the variance. The method of claim 6, In the step (a) If the multipath delay component of the impulse response is more than one, performing step (a) for each of the channel estimation method using an impulse symbol in the OFDM system. The method of claim 6, Before step (a), (a01) setting a value below a specific reference value in the impulse response to 0; Containing more Channel estimation method using an impulse symbol in an OFDM system characterized in that. The method of claim 6, In the step (a) Approximate value for the channel value, Applying interpolation Channel estimation method using an impulse symbol in an OFDM system characterized in that. The method of claim 6, Before step (a), (a02) finding data by applying an overlap-and-add method to the received signal; Channel estimation method using an impulse symbol in the OFDM system, characterized in that further comprising. delete 11. The method according to any one of claims 6 to 10, The method of obtaining the power boosting factor, (a) A complex random variable ( X ( k ) with variance of E _s , obtained by modulating the OFDM data bit stream, where k is the subcarrier number k = 0,1,2, ... N -1) From n , obtain the n th sample x ( n ) of the data symbols in the time domain by the following equation ;

(Where N is a natural number) (b) Probability Density Function (PDF) of the real part of x ( n )

And the imaginary part of the PDF

Obtaining a PDF of x ( n ) from the following equation;

(c) obtaining a Cumulative Distribution Function (CDF) from the PDF of x ( n ) by the following equation;

(d) when the power boosting factor is p , the size of an impulse sample

Obtaining a CDF value corresponding to the following equation;

(e) probability

Obtaining a power boosting factor p in one case by the following equation, which is an inverse function of the CDF;

Including Channel estimation method using an impulse symbol in an OFDM system characterized in that.

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