KR101128287B1 - Ofdm receiver being capable of estimating timing error in multi-path fading channel, ofdm system having the same and timing error estimation method thereof - Google Patents

Abstract

The present invention has an effect of improving the performance of timing error estimation by eliminating timing errors that may occur in an OFDM system in a multipath fading channel. For this purpose, in particular, the timing error estimation is performed in the multipath fading channel, which uses the autocorrelation method of the received signal and the cross-correlation method between the preambles, and obtains the final timing error estimate by using the timing metric and the filter function. A possible OFDM receiver, an OFDM system including the same, and a timing error estimation method thereof are disclosed.

Description

OPDM receiver capable of estimating timing error in multipath fading channel, ODF system including the same and method for estimating the timing error thereof METHOD THEREOF}

The present invention relates to an OFDM system and a timing estimation method capable of timing estimation. More specifically, timing error in a multipath fading channel using autocorrelation of the received signal and cross-correlation between preambles and a final timing error estimate can be obtained by calculating the timing error estimates stepwise through timing metrics and filter functions. An OFDM receiver capable of estimating, an OFDM system including the same, and a timing error estimation method thereof.

Orthogonal Frequency Division Multiplexing (OFDM) systems are robust to impulse noise and multi-path fading channel environments, and can be used in wireless LANs such as IEEE 802.11a because of their efficient spectrum usage. Wireless standard modulation methods such as WLANs, Wireless Local Area Networks, Digital Audio Broadcasting (DAB), and Digital Video Broadcasting-Terrestrial (DVB-T) are used.

However, despite these advantages, the OFDM system has a problem in that it is very sensitive to carrier frequency errors and timing errors. In particular, the timing error affects the determination of the starting point at the time of the fast Fourier transform (FFT) input of the OFDM signal, and thus has a continuous influence on the processing after the FFT.

Schmidl (T. Schmidl and DC Cox, “Robust frequency and timing synchronization for OFDM systems,” IEEE Trans. Commun., Vol. 45, no. 12, pp. 1613-1621, Dec. 1997.) Proposed a timing estimation technique that uses a preamble consisting of two repetitive parts and autocorrelation between repetitive parts.

However, in this technique, the timing metric for timing estimation is difficult to find the correct timing point even though there is a flat area around the exact timing point without the influence of noise and channel.

To address this problem, Park (B. Park, H. Cheon, C. Kang, and D. Hong, “A novel timing estimation method for OFDM systems,” IEEE Commun. Lett., Vol. 7, no. 5 , pp. 239-241, May 2003.), Minn (H. Minn, VK Bhargava, and KB Letaief, “A robust timing and frequency synchronization for OFDM systems,” IEEE Trans.Wireless Commun., vol. 2, no. 4, pp. 822-839, July 2004.), shi (K. Shi, and E. Serpedin, “Coarse frame and carrier synchronization of OFDM systems: a new metric and comparison,” IEEE Trans.Wireless Commun., Vol. 3, no. 4, pp. 1271-1284, July 2004.) proposed a technique to remove the flat part of the existing timing metric and to make it appear sharp by using a new type of preamble.

However, since these techniques do not consider the multipath fading channel environment, there is a problem that the estimation performance is lowered when timing is estimated in the multipath fading channel environment. Therefore, there is a need for a receiver and a timing estimation method that can improve timing estimation even in a multipath fading channel environment.

SUMMARY OF THE INVENTION The present invention has been made in view of the above necessity, and an object of the present invention is to eliminate timing errors that may occur in an OFDM system in a multipath fading channel to improve timing error estimation performance in a multipath fading channel. An OFDM receiver capable of error estimation, an OFDM system including the same, and a timing error estimation method thereof are provided.

As described above, an object of the present invention is to estimate a timing error in a multipath fading channel by using a baseband OFDM sample signal having a cyclic prefix pre-inserted to remove interference between symbols and a preamble signal generated for timing error estimation of a receiver. In an OFDM receiver, a first timing for calculating a timing metric value based on an autocorrelation function of a received signal located at a receiving end and including a baseband OFDM sample signal and calculating a first timing error estimate based on the calculated timing metric value. An error estimator; Calculate a filtered timing metric value based on a cross-correlation function between the received signal and the preamble signal in a first timing error estimation range based on the first timing error estimate and based on the filtered timing metric value; A second timing error estimator for calculating an error estimate; And calculating a threshold value based on a variance operation and an average operation on a timing metric value filtered at a second timing error estimation range based on the second timing error estimate value, and determining a filter value by the calculated threshold value. It may be achieved by providing an OFDM receiver capable of timing error estimation in a multipath fading channel, including; a final timing error estimator for calculating a final timing error estimate based on a product operation of a filter function and a filtered timing metric value. .

The preamble signal is preferably a repetitive structure of a random sequence.

The baseband OFDM sample signal with the cyclic prefix inserted is expressed as

,

,

Where x (k) is the baseband OFDM sample signal, N is the total number of subcarriers, X (n) is the modulated symbol sample at the nth subcarrier, and N _G is the length of the cyclic prefix.

It is preferable to represent by.

The preamble signal is represented by the following equation

Where S is a preamble, A _{N / 2} is a random sequence of length N / 2, and N is the total number of subcarriers

It is preferable to represent by.

The autocorrelation function is

Where Ra (d) is the autocorrelation function, N is the total number of subcarriers, r (d + k) is the complex value of the received signal, and r (d + k + N / 2) is the N / 2 delay of the received signal. Complex, * is a conjugate complex operation)

It is preferable to represent by.

The timing metric value preferably applies a summing window to the autocorrelation function in order to remove the flat portion of the autocorrelation function due to the cyclic prefix.

The timing metric value is expressed as

(Where Ma (d) is the timing metric value, Ra (dk) is the autocorrelation function, and N _G is the length of the cyclic prefix)

It is preferable to represent by.

The first-order timing error estimate is

는 1차 타이밍 오차 추정치, Ma(d)는 타이밍 메트릭값임)(here,

Is the primary timing error estimate, and Ma (d) is the timing metric

It is preferable to represent by.

The cross-correlation function is

,

,

는 1차 타이밍 오차 추정치, N은 총 부반송파의 개수임)Where Rc (d) is a cross-correlation function, r (d + k) is a received signal, S (k) is a preamble, * is a complex conjugate operation, d is a first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)

It is preferable to represent by.

The filtered timing metric value is expressed as

,

,

는 1차 타이밍 오차 추정치, N은 총 부반송파의 개수임)Where Mc (d) is a filtered timing metric value, Rc (d) is a cross-correlation function, Ma (d) is a timing metric value, d is a first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)

It is preferable to represent by.

The second-order timing error estimate is

,

,

는 2차 타이밍 오차 추정치, Mc(d)는 필터링된 타이밍 메트릭값, d는 제 1타이밍 오차 추정범위,

는 1차 타이밍 오차 추정치, N은 총 부반송파의 개수임)(here,

Is the secondary timing error estimate, Mc (d) is the filtered timing metric value, d is the first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)

It is preferable to represent by.

The filter function is

Where F (d) is the filter function and T _th is the threshold

Represented by

C (d) is the following equation

,

,

는 2차 타이밍 오차 추정치, L은 채널의 탭 수, N_G는 순환 전치의 길이임)Where var {} is the variance operation, Mc (d) is the filtered timing metric value, d is the second timing error estimation range,

Is the second-order timing error estimate, L is the number of taps in the channel, N _G is the length of the cyclic prefix)

Saved by

The threshold is the following equation

는 2차 타이밍 오차 추정치임)Where T _th is the threshold, mean {} is the mean operation,

Is a second-order timing error estimate)

It is preferable to obtain | require by.

The final timing error estimate is

,

,

,

,

는 최종 타이밍 오차 추정치, Mc(d)는 필터링된 타이밍 메트릭값, F(d)는 필터함수, d는 제 2타이밍 오차 추정범위,

는 2차 타이밍 오차 추정치, L은 채널의 탭 수, N_G는 순환 전치의 길이임)(here,

Is the final timing error estimate, Mc (d) is the filtered timing metric value, F (d) is the filter function, d is the second timing error estimation range,

Is the second-order timing error estimate, L is the number of taps in the channel, N _G is the length of the cyclic prefix)

It is preferable to represent by.

In addition, an object of the present invention includes an OFDM receiver capable of estimating a timing error in a multipath fading channel, comprising: a sample generator for generating a baseband OFDM sample signal located at a transmitting end and having a cyclic prefix inserted therein; And a preamble generator positioned at a transmitter and generating a preamble signal. The OFDM system may further include an OFDM system capable of timing error estimation in a multipath fading channel.

Meanwhile, an object of the present invention is another category, which is a timing of an OFDM receiver in a multipath fading channel using a baseband OFDM sample signal having a cyclic prefix pre-inserted for inter-symbol interference cancellation and a preamble signal generated for timing error estimation of a receiver. An error estimating method comprising: calculating a timing metric value based on an autocorrelation function of a received signal including a baseband OFDM sample signal by a first timing error estimator of a receiving end (S300); Calculating a first timing error estimate based on the timing metric value calculated by the first timing error estimator (S400); Calculating a filtered timing metric value based on a cross-correlation function between a received signal and a preamble signal in a first timing error estimation range based on a first timing error estimate by a second timing error estimator of the receiving end (S500); Calculating a second timing error estimate based on the filtered timing metric value (S600); Calculating a threshold value based on a variance operation and an average operation of the timing metric values filtered in the second timing error estimation range based on the second timing error estimation unit, at the reception timing final estimation unit (S700); And calculating a final timing error estimate based on a product of a filter function in which a filter value is determined based on a calculated threshold and a filtered timing metric value (S800). It can be achieved by providing a timing error estimation method of the OFDM receiver in.

The timing metric value calculating step (S300) of the first timing error estimator may be a step of applying a summing window to the autocorrelation function to remove a flat portion of the autocorrelation function due to the cyclic prefix.

Preferably, the first timing error estimation unit calculating step (S400) of the first timing error estimation unit is a step of estimating a timing error at which the timing metric value is maximized as the first timing error estimate.

In the filtered timing metric value calculation step S500 of the second timing error estimator, the preamble signal preferably has a repetitive structure of a random sequence.

Preferably, the second timing error estimate calculating step (S600) of the second timing error estimator is a step of estimating a timing error at which the filtered timing metric value is maximized as a second timing error estimate.

The final timing error estimate calculation step (S800) of the final timing error estimation unit is preferably a step of estimating the timing error at which the result value of the multiplication operation is maximized as the final timing error estimate.

It is also an object of the present invention to include a timing error estimation method of an OFDM receiver in a multipath fading channel,

Generating a baseband OFDM sample signal in which a cyclic prefix is inserted before the timing metric value calculating step S300 of the first timing error estimator; And a step (S200) of generating a preamble signal by the preamble generator of the transmitter. The timing error estimation method of the OFDM system in the multipath fading channel may be further included.

According to the embodiment of the present invention as described above, the timing error that may occur in the OFDM system in the multipath fading channel may be removed to improve the performance of the timing error estimation.

In addition, in an OFDM system in a multipath fading channel, in order to accurately demodulate a transmission signal, not only the frequency error but also the symbol synchronization should be taken into consideration. There is an effect that can restore the signal correctly.

In addition, there is an effect of improving timing error performance of various communication systems using an OFDM system such as WLAN, DVB, DAB, and the like.

1 is a block diagram showing a configuration according to an embodiment of an OFDM system capable of timing error estimation in a multipath fading channel of the present invention;
2A is a graph illustrating the absolute square of the cross-correlation function between a preamble and a received signal with respect to timing error, according to an embodiment of the present invention;
2B is a graph illustrating a timing metric value of a timing error obtained by applying a summation window to an autocorrelation function according to an embodiment of the present invention;
2C is a graph illustrating a filtered timing metric value for timing error represented by a product of an absolute square of a cross-correlation function and a timing metric value to which a summation window is applied, according to an embodiment of the present invention;
3A and 3B are graphs illustrating a timing error value when a filtered timing metric value in a multipath fading channel is largest and smallest in a first path according to an embodiment of the present invention, respectively;
4A is a graph illustrating an example of a filtered timing metric value with respect to timing error according to an embodiment of the present invention;
4b is a graph showing a filter function with respect to timing error according to an embodiment of the present invention;
FIG. 4C is a graph showing a cross product arithmetic value of the filtered timing metric value shown in FIG. 4A and the filter function shown in FIG. 4B with respect to timing error, according to an embodiment of the present invention; FIG.
5 is a flowchart sequentially illustrating an embodiment of a timing error estimation method of an OFDM system in a multipath fading channel according to the present invention.

< OFDM  System Configuration>

1 is a block diagram illustrating a configuration of an OFDM system capable of estimating timing error in a multipath fading channel according to the present invention. As shown in FIG. 1, one embodiment of an OFDM system includes an OFDM receiver 10 and an OFDM transmitter 20. In addition, the OFDM receiver 10 includes a first timing error estimator 110, a second timing error estimator 120, and a final timing error estimator 130, and also includes an RF receiver 140. And a fast fourier transform (FFT) unit 150. In addition, the OFDM transmitter 20 may include a sample generator 210 and a preamble generator 220, and may further include an RF transmitter 230.

Briefly describing the operation of the OFDM system of the present invention, when a baseband OFDM sample signal and a preamble signal in which a cyclic prefix (CP, Cyclic Prefix) is inserted in the transmitter 20 are transmitted and are transmitted by the RF transmitter 230, The receiver 10, which is a receiving end, calculates a first timing error estimate, a second timing error estimate, and a final timing error estimate based on a received signal including an OFDM sample signal and a preamble signal, and thus the timing error of the OFDM system in a multipath fading channel. The estimation performance is improved to obtain accurate symbol timing.

First, the configuration of the OFDM transmitter 20 will be described with reference to FIG.

The sample generator 210 generates a baseband OFDM sample signal in which a cyclic prefix is inserted in order to remove intersymbol interference (ISI). The sample generator 210 may include an encoding means (not shown), an encoding means (not shown), and a modulation means (not shown), etc. of the data source, but are outside the gist of the present invention or are known components. Detailed description will be omitted. Here, the OFDM sample signal is represented by Equation 1 below.

Where x (k) is the baseband OFDM sample signal, N is the total number of subcarriers, X (n) is the modulated symbol sample at the nth subcarrier, and N _G is the length of the cyclic prefix.

Can be represented by

The cyclic prefix acts as an inter-symbol interference protection section in the OFDM sample signal, and is inserted or copied in the last section or the first section of the effective symbol section in order to prevent the destruction of orthogonality between subcarriers. Signal.

The preamble generator 220 generates a preamble signal for timing error estimation, where the preamble signal is composed of a signal sequence having a repetitive structure of a random sequence. In particular, in the present embodiment, the following equation (2)

Where S is a preamble, A _{N / 2} is a random sequence of length N / 2, and N is the total number of subcarriers

Can be represented by

The RF transmitter 230 is a configuration for transmitting the baseband OFDM sample signal and the preamble signal in which the cyclic prefix is inserted.

In addition, the basic configuration of the OFDM transmitter may include Serial to Parallel (S / P), Inverse Fast Fourier Transform (IFFT), and Digital Analogue Converter (DAC). These configurations are the same as the known configurations. Detailed description will be omitted.

Hereinafter, the configuration of the OFDM receiver 10 will be described with reference to FIG. 1.

The first timing error estimator 110 calculates a timing metric value based on an autocorrelation function of a received signal including a baseband OFDM sample signal and calculates a first timing error estimate based on the calculated timing metric value. Do it.

The received signal may be represented as a complex value including Additive White Gaussian Noise (AWGN). The complex value of the received signal is expressed by the following equation (3).

Where r (k) is the complex value of the received signal, ε is the integer timing offset, w (k) is the complex additive white normal noise with an average of 0, h (m) is the impulse response of the frequency-selective channel, and L is the channel. Number of taps, N _G is the length of the cyclic prefix)

It is represented by

Therefore, the autocorrelation function is a complex sample and

Where Ra (d) is the autocorrelation function, N is the total number of subcarriers, r (d + k) is the complex value of the received signal, and r (d + k + N / 2) is the N / 2 delayed signal Sochi, * is a conjugate complex operation)

Can be represented by

The timing metric value is obtained by applying a summation window to the autocorrelation function to remove a flat portion of the autocorrelation function due to the cyclic transposition.

(Where Ma (d) is the timing metric value, Ra (dk) is the autocorrelation function, and N _G is the length of the cyclic prefix)

Can be represented by

The first timing error estimate is obtained by calculating a timing error at which the timing metric value Ma (d) is maximum.

는 1차 타이밍 오차 추정치, Ma(d)는 타이밍 메트릭값임)(here,

Is the primary timing error estimate, and Ma (d) is the timing metric

Can be represented by

)에 기초한 제 1타이밍 오차 추정범위에서 수신 신호와 프리앰블 신호 사이의 상호상관(cross-correlation) 함수에 기반한 필터링된 타이밍 메트릭값을 연산하고, 필터링된 타이밍 메트릭값을 기초로 2차 타이밍 오차 추정치를 연산하는 역할을 한다.Meanwhile, the second timing error estimator 120 estimates the first timing error (

Calculates a filtered timing metric value based on a cross-correlation function between the received signal and the preamble signal in the first timing error estimation range based on C), and estimates the second timing error estimate based on the filtered timing metric value. It is responsible for calculating.

Here, the cross-correlation function is

는 1차 타이밍 오차 추정치, N은 총 부반송파의 개수임)Where Rc (d) is a cross-correlation function, r (d + k) is a received signal, S (k) is a preamble, * is a conjugate complex operation, d is a first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)

Can be represented by

The filtered timing metric value is represented by Equation 8 below.

는 1차 타이밍 오차 추정치, N은 총 부반송파의 개수임)Where Mc (d) is a filtered timing metric value, Rc (d) is a cross-correlation function, Ma (d) is a timing metric value, d is a first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)

Can be represented by

The second timing error estimate calculated based on the filtered timing metric value Mc (d) is expressed by Equation 9 below.

는 2차 타이밍 오차 추정치, Mc(d)는 필터링된 타이밍 메트릭값, d는 제 1타이밍 오차 추정범위,

는 1차 타이밍 오차 추정치, N은 총 부반송파의 개수임)(here,

Is the secondary timing error estimate, Mc (d) is the filtered timing metric value, d is the first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)

Can be obtained.

Meanwhile, the final timing error estimator 130 calculates a threshold value based on a variance operation and an average operation on the timing metric value filtered in the second timing error estimation range based on the second timing error estimate value, and calculates the calculated threshold value. It calculates the final timing error estimate based on the product operation of the filter function is determined by the filter function and the filtered timing metric value.

The final timing error estimate is obtained from Equations 10 to 13 below based on the fact that the above-mentioned Mc (d) values before timing point 0 are very small values from 0 to L-1 even though they pass through the multipath. Therefore, the final timing error estimate is

는 최종 타이밍 오차 추정치, Mc(d)는 필터링된 타이밍 메트릭값, F(d)는 필터함수, d는 제 2타이밍 오차 추정범위,

는 2차 타이밍 오차 추정치, L은 채널의 탭 수, N_G는 순환 전치의 길이임)(here,

Is the final timing error estimate, Mc (d) is the filtered timing metric value, F (d) is the filter function, d is the second timing error estimation range,

Is the second-order timing error estimate, L is the number of taps in the channel, N _G is the length of the cyclic prefix)

Can be represented by

Here, the filter function is represented by Equation 11 below.

Where F (d) is the filter function and T _th is the threshold

Represented by

C (d) is represented by Equation 12

는 2차 타이밍 오차 추정치, L은 채널의 탭 수, N_G는 순환 전치의 길이임)Where var {} is the variance operation, Mc (d) is the filtered timing metric value, d is the second timing error estimation range,

Is the second-order timing error estimate, L is the number of taps in the channel, N _G is the length of the cyclic prefix)

Saved by

The threshold is expressed by the following equation (13).

는 2차 타이밍 오차 추정치임)Where T _th is the threshold, mean {} is the mean operation,

Is a second-order timing error estimate)

Can be obtained by

RF receiver 140 serves to receive the received signal including the baseband OFDM sample signal and the preamble signal described above, and the FFT (Fast Fourier Transform) unit 150 inputs based on the final timing error estimate. The fast Fourier transform of the received signal is performed based on the starting point information.

Of course, the fast Fourier transformed input signal symbol is restored to a data symbol which is a signal transmitted through the data symbol recovery unit 160. For this purpose, the data symbol recovery unit 160 of the OFDM receiver 10 may include decoding means of a data source ( Not shown), decoding means (not shown), P / S (Parallel to Serial, not shown) and ADC (Analogue Digital Converter, not shown), etc. may be further included, these configurations are beyond the gist of the present invention Or it is the same as the known configuration so detailed description thereof will be omitted.

<Experiment graph>

Figure 2a is a graph showing the absolute square of the cross-correlation function between the preamble and the received signal as the vertical axis and the timing error in the horizontal axis according to an embodiment of the present invention, Figure 2b is autocorrelation according to an embodiment of the present invention Fig. 2C is a graph showing a timing metric value in which a summation window is applied to a function as a vertical axis and a timing error as a horizontal axis. This is a graph showing the filtered timing metric value expressed as the product of the values on the vertical axis and the timing error on the horizontal axis.

를 구할 수 있는 것이다.In the graphs of FIGS. 2A to 2C, N = 256, N _G = 16 and no noise were used as experimental conditions. 2A to 2C, it can be seen that the peripheral peaks of Rc (d) are multiplied by (± N / 2) Ma (d) and are removed. Second-order timing error estimate

Can be obtained.

Also, as shown in FIGS. 2A-2C, Mc (d) has a metric that is nearly impulse, and using it, the effects of noise can be almost completely overcome.

However, in the multipath channel, since the transmission signals overlap through various paths, as shown in FIGS. 3A and 3B, the metric of Mc (d) is also a form in which several impulses overlap. Therefore, in this case, as shown in FIG. 3B, if the gain of the first multipath is not the greatest, an accurate timing error point cannot be found. Accordingly, the calculation of the final timing error estimate of the final timing error estimation unit 130 is necessary to provide accurate timing error points even under the influence of multipath.

4A is a graph illustrating a filtered timing metric value as a vertical axis and a timing error as a horizontal axis according to an embodiment of the present invention. FIG. 4B illustrates a filter function value as a vertical axis and a timing error according to an embodiment of the present invention. 4C is a graph showing the horizontal axis, and FIG. 4C is a vertical axis with a cross product calculation value of the filtered timing metric value shown in FIG. 4A and the filter function shown in FIG. 4B according to an embodiment of the present invention, and the timing error is represented as the horizontal axis. It is a graph shown.

As shown in Figs. 4A to 4C, it is shown that Mc (d)? F (d) has the largest value at the timing error point 0 even when the gain of the first multipath is not the greatest.

Timing Error Estimation Method

5 is a flowchart sequentially illustrating an embodiment of a timing error estimation method of an OFDM system in a multipath fading channel according to the present invention. As described above, since the OFDM system includes the OFDM receiver 10 and the OFDM transmitter 20, the following description includes all of the steps performed in each configuration.

An embodiment of the timing error estimation method will be described with reference to FIG. 5. First, a sample generator of a transmitter generates a baseband OFDM sample signal in which a cyclic prefix is inserted (S100).

Next, the preamble generator of the transmitter generates a preamble signal (S200).

Next, the first timing error estimation unit of the receiver calculates a timing metric value based on an autocorrelation function of the received signal including the baseband OFDM sample signal (S300). In particular, the timing metric value calculating step S300 is performed by applying the summation window to remove the flat portion of the autocorrelation function due to the cyclic prefix to the autocorrelation function.

Next, the first timing error estimator calculates a first timing error estimate based on the calculated timing metric value (S400). Here, the timing error at which the timing metric value is maximized is calculated as the primary timing error estimate.

Next, the second timing error estimation unit of the receiver calculates the filtered timing metric value based on the cross-correlation function between the received signal and the preamble signal in the first timing error estimation range based on the first timing error estimate (S500). Here, the preamble signal preferably has a repetitive structure of a random sequence.

Next, the second timing error estimator calculates a second timing error estimate based on the filtered timing metric value (S600). Here, the timing error at which the filtered timing metric value is maximized is calculated as the secondary timing error estimate.

Next, the final timing error estimator of the receiver calculates a threshold value based on a variance operation and an average operation on the timing metric values filtered in the second timing error estimation range based on the second timing error estimate (S700).

Finally, the final timing error estimator calculates the final timing error estimate based on the product of the filter function in which the filter value is determined by the calculated threshold value and the filtered timing metric value (S800). An embodiment of a method for estimating timing error is performed.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be practiced. Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all aspects. In addition, the scope of the present invention is indicated by the appended claims rather than the detailed description above. Also, it is to be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention.

10: OFDM receiver
20: OFDM transmitter
110: first timing error estimation unit
120: second timing error estimation unit
130: final timing error estimation unit
140: RF receiver
150: FFT part
160: data symbol recovery unit
210: sample generator
220: preamble generation unit
230: RF transmitter

Claims (21)

An OFDM receiver capable of estimating timing error in a multipath fading channel using a baseband OFDM sample signal having a cyclic prefix pre-inserted for inter-symbol interference cancellation and a preamble signal generated for estimating timing error of a receiver,
A first timing error estimate that calculates a timing metric value based on an autocorrelation function of the received signal located at the receiving end and includes the baseband OFDM sample signal and calculates a first timing error estimate based on the calculated timing metric value government;
Calculate a filtered timing metric value based on a cross-correlation function between the received signal and the preamble signal in a first timing error estimation range based on the first timing error estimate value, and calculating the filtered timing metric value A second timing error estimator calculating a second timing error estimate based on the second timing error estimate; And
A threshold value located at the receiving end, and calculating a threshold value based on a variance operation and an average operation on the filtered timing metric value in a second timing error estimation range based on the second timing error estimate value, and filtering by the calculated threshold value A final timing error estimator for estimating a timing error at which the result of the multiplication of the filter function and the filtered timing metric value determined as a final timing error estimate is a final timing error estimate; 2 OFDM receiver available.
The method of claim 1,
The preamble signal is an OFDM receiver capable of timing error estimation in a multipath fading channel, characterized in that the repetitive structure of a random sequence.
The method of claim 1,
The baseband OFDM sample signal with the cyclic prefix inserted is represented by the following equation

,

Where x (k) is the baseband OFDM sample signal, N is the total number of subcarriers, X (n) is the modulated symbol sample at the nth subcarrier, and N _G is the length of the cyclic prefix.
An OFDM receiver capable of timing error estimation in a multipath fading channel, characterized in that represented by.
The method of claim 1,
The preamble signal is represented by the following equation

Where S is a preamble, A _{N / 2} is a random sequence of length N / 2, and N is the total number of subcarriers
An OFDM receiver capable of timing error estimation in a multipath fading channel, characterized in that represented by.
The method of claim 1,
The autocorrelation function is

Where Ra (d) is the autocorrelation function, N is the total number of subcarriers, r (d + k) is the complex value of the received signal, and r (d + k + N / 2) is the N / 2 delay of the received signal. Complex, * is a conjugate complex operation)
An OFDM receiver capable of timing error estimation in a multipath fading channel, characterized in that represented by.
6. The method of claim 5,
And a timing window is applied to the autocorrelation function to remove a flat portion of the autocorrelation function due to the cyclic prefix.
The method of claim 6,
The timing metric value is represented by the following equation

(Where Ma (d) is the timing metric value, Ra (dk) is the autocorrelation function, and N _G is the length of the cyclic prefix)
OFDM receiver capable of estimating timing error in a multipath fading channel, characterized in that:
The method of claim 7, wherein
The first timing error estimate is expressed by the following equation

(here,

Is the primary timing error estimate, and Ma (d) is the timing metric
OFDM receiver capable of estimating timing error in a multipath fading channel, characterized in that:
The method of claim 8,
The cross-correlation function is

,

Where Rc (d) is a cross-correlation function, r (d + k) is a received signal, S (k) is a preamble, * is a complex conjugate operation, d is a first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)
OFDM receiver capable of estimating timing error in a multipath fading channel, characterized in that:
The method of claim 9,
The filtered timing metric value is represented by the following equation

,

Where Mc (d) is a filtered timing metric value, Rc (d) is a cross-correlation function, Ma (d) is a timing metric value, d is a first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)
OFDM receiver capable of estimating timing error in a multipath fading channel, characterized in that:
The method of claim 10,
The second timing error estimate is expressed by the following equation

,

(here,

Is the secondary timing error estimate, Mc (d) is the filtered timing metric value, d is the first timing error estimation range,

Is the primary timing error estimate, N is the total number of subcarriers)
OFDM receiver capable of estimating timing error in a multipath fading channel, characterized in that:
12. The method of claim 11,
The filter function is

Where F (d) is the filter function and T _th is the threshold
Represented by
C (d) is the following equation

,

Where var {} is the variance operation, Mc (d) is the filtered timing metric value, d is the second timing error estimation range,

Is the second-order timing error estimate, L is the number of taps in the channel, N _G is the length of the cyclic prefix)
Saved by
The threshold is the following equation

Where T _th is the threshold, mean {} is the mean operation,

Is a second-order timing error estimate)
OFDM receiver capable of timing error estimation in a multipath fading channel, characterized in that
The method of claim 12,
The final timing error estimate is

,

,

(here,

Is the final timing error estimate, Mc (d) is the filtered timing metric value, F (d) is the filter function, d is the second timing error estimation range,

Is the second-order timing error estimate, L is the number of taps in the channel, N _G is the length of the cyclic prefix)
An OFDM receiver capable of timing error estimation in a multipath fading channel, characterized in that represented by.
14. An OFDM receiver according to any one of the preceding claims,
A sample generation unit positioned at a transmitter and generating a baseband OFDM sample signal having the cyclic prefix inserted therein; And
And a preamble generator positioned at the transmitter and generating the preamble signal. The OFDM system capable of timing error estimation in a multipath fading channel.
A method of estimating timing error of an OFDM receiver in a multipath fading channel using a baseband OFDM sample signal having a cyclic prefix added for intersymbol interference and a preamble signal generated for estimating a timing error of a receiver,
Calculating a timing metric value based on an autocorrelation function of a received signal including the baseband OFDM sample signal by a first timing error estimator of the receiving end (S300);
The first timing error estimator calculating a first timing error estimate based on the calculated timing metric value (S400);
Calculating a filtered timing metric value based on a cross-correlation function between the received signal and the preamble signal in a first timing error estimation range based on the first timing error estimate by the second timing error estimator of the receiver (S500) ;
Calculating, by the second timing error estimator, a second timing error estimate based on the filtered timing metric value (S600);
Calculating a threshold value based on a variance operation and an average operation on the filtered timing metric values in a second timing error estimation range based on the second timing error estimate by the final timing error estimator of the receiver (S700); And
Estimating, by the final timing error estimator, a timing error at which a result of a multiplication of the filter function in which a filter value is determined by the calculated threshold value and the filtered timing metric value is a maximum (S800). Timing error estimation method of an OFDM receiver in a multipath fading channel comprising a.
16. The method of claim 15,
The timing metric value calculating step (S300) of the first timing error estimator,
And applying a summing window to the autocorrelation function to remove the flat portion of the autocorrelation function due to the cyclic prefix.
16. The method of claim 15,
The first timing error estimate calculation step (S400) of the first timing error estimator,
Estimating a timing error at which the timing metric is maximized as a primary timing error estimate.
16. The method of claim 15,
In operation S500 of filtering timing metric values of the second timing error estimator,
The preamble signal has a repeating structure of a random sequence, the timing error estimation method of the OFDM receiver in a multipath fading channel.
16. The method of claim 15,
In operation S600, the second timing error estimate calculation unit of the second timing error estimator includes:
Estimating a timing error at which the filtered timing metric is maximized as a second timing error estimate.
delete 20. A method for estimating timing error of an OFDM receiver according to any one of claims 15 to 19,
Before the timing metric value calculation step (S300) of the first timing error estimation unit,
Generating a baseband OFDM sample signal to which the cyclic prefix is inserted (S100); And
And a step (S200) of generating a preamble signal by the preamble generator of the transmitter. The timing error estimation method of an OFDM system in a multipath fading channel, further comprising:

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