KR100411893B1 - Apparatus for Symbol Synchronization in an Orthogonal Frequency Division Multiplexing Receiver System and Method Thereof - Google Patents

Abstract

The present invention relates to an apparatus and a method for symbol synchronization in an OFDM receiving system. An OFDM symbol synchronizing apparatus of the present invention comprises: input signal magnitude calculating means for calculating the magnitude of an applied input complex signal; First sample delay means for delaying a signal received from said input signal magnitude calculating means during a valid data interval; First adding means for obtaining a difference value between the signal delayed by the first sample delay means and the magnitude of the input complex signal; Absolute value calculating means for obtaining an absolute value of a signal received from said first adding means; Second sample delay means for delaying a signal received from the absolute value calculating means during a minimum guard period; Second adding means for obtaining a difference value between the signals received from the second sample delay means and the absolute value calculating means, respectively; Accumulating means for accumulating the signal received from the second adding means for a minimum guard period; Extraction means for comparing a value of the accumulation means during an effective data interval and a maximum guard interval to find a preset point; And guard interval removing means for removing the guard interval using the extracted position.

Description

Apparatus for Symbol Synchronization in an Orthogonal Frequency Division Multiplexing Receiver System and Method Thereof}

The present invention relates to a symbol synchronizer and a method of an orthogonal frequency division multiplexing (OFDM) receiving system, and more particularly, to high-speed demodulation in a receiver of an OFDM system having various types of guard intervals. The present invention relates to a symbol synchronizer of an OFDM receiving system and a method thereof for finding a starting point of valid data for Fourier transform.

OFDM is a multi-carrier modulation scheme in which a signal is divided into a plurality of carriers and transmitted in parallel. Therefore, the length of a symbol is relatively longer than that of a single carrier transmission method, which is effective in a multipath channel environment. In Europe, OFDM is adopted as a transmission method for digital audio broadcasting (DAB) and digital video broadcasting-terrestrial (DVB-T).

In an OFDM system, since the inverse fast Fourier transform (Invert Fast Fourier Transform (IFFT) / Fast Fourier Transform (FFT)) is performed by the symbol unit, the receiver performs the modulation / demodulation process Frequency synchronization, symbol synchronization (hereinafter referred to as 'OFDM symbol synchronization'), and frame synchronization (frame synchronization) are required for efficient and high performance.

At the transmitter, OFDM symbols of a total of (N + G) samples consisting of the N valid data intervals output from the IFFT and the guard intervals that are copied into the signal after copying the last G of them. Transmits sequentially. The receiver detects only the valid data section excluding the guard interval from the received signal using the FFT window and performs an FFT on the data to restore the original signal.

For OFDM symbol synchronization, the property that the data of the guard interval is equal to the value of a part of the valid data interval is used.

1 is a graph illustrating OFDM symbol characteristics in a time domain of an OFDM receiving system to which the present invention is applied.

As shown in the figure, it can be seen that the magnitude of the N sample delayed signal and the input signal in the time domain are the same when positioned at the beginning of the OFDM symbol.

The maximum likelihood (ML) algorithm using the correlation value between the guard interval and the original valid data as an OFDM symbol synchronization algorithm, and the minimum error using the difference between the guard interval and the original valid data value. An algorithm is referred to in Equations 1 and 2, respectively.

2A is a conceptual diagram of OFDM symbol synchronization using an ML algorithm in a typical OFDM system, and FIG. 2B is a conceptual diagram of OFDM symbol synchronization using an ME algorithm in a typical OFDM system.

The ML algorithm and the ME algorithm are derived from the concept that the signal of the guard interval and the latter part of the effective symbol interval coincide with each other. As shown in the drawing, the characteristics of the correlation between the input signal and the signal delayed by the effective data interval and It can be seen that the characteristic of the difference between the value of the input signal and the signal delayed by the effective data section is used.

However, since OFDM symbol synchronization is preceded by frequency synchronization, OFDM symbol synchronization must be possible in a state where a carrier frequency offset remains in an OFDM receiver. According to the above-described algorithm, an OFDM symbol when frequency offset such as a carrier frequency offset or a sampling frequency offset remains. Motivation is impossible

3 is a conceptual diagram illustrating OFDM symbol synchronization when there is no window offset and when there is a window offset in an OFDM receiving system to which the present invention is applied.

One OFDM symbol is N signals which are block data after IFFT modulation is performed using N parallel data. Copy as much as G at the end of the valid data interval as the guard interval. The copied signal is appended to the beginning of the OFDM symbol.

OFDM symbol synchronization removes the guard interval and finds N samples of the original signal for accurate demodulation in the receiving system.

As shown in the figure, it can be seen that OFDM demodulation is impossible when there is a symbol synchronization error or an FFT window position recovery error, that is, when there is a window offset.

As a prior art for reducing the influence of such a frequency offset, an apparatus and method for restoring an FFT window position of an OFDM system receiver are disclosed in Korean Patent No. 1999-0234329.

FIG. 4 is a block diagram showing an FFT window position recovery apparatus of a conventional OFDM receiving system, which is disclosed in Korean Patent No. 1999-0234329.

As shown in the figure, the conventional FFT window position recovery apparatus converts the received OFDM signal into a digital complex sample and detects the position where the absolute value of the difference in power value between the samples is minimum as the beginning of the symbol. The FFT is activated by restoring the FFT window position with the detected symbol start information.

However, since the conventional FFT window position recovery apparatus needs to use a multiplier when calculating power in the power detector 120, there is a problem in that the complexity of the system increases and the computation speed also decreases.

In addition, the OFDM receiving system must know the exact length of the guard interval before applying the algorithm for OFDM symbol synchronization.

5 is a graph showing the types of various guard intervals of an OFDM system to which the present invention is applied, and shows the types of guard intervals of a system corresponding to the DVB-T standard.

Therefore, in a system such as DVB-T having various types of guard intervals used for transmission, there is a problem that a prior procedure of guard interval type search must exist before symbol synchronization.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and can be implemented as a simple system in an OFDM symbol synchronization method that operates stably even when a frequency offset exists, and is related to the type of guard interval. It is an object of the present invention to provide a symbol synchronization device of an OFDM receiving system to efficiently perform FFT window position recovery without using the above.

In addition, the present invention can be implemented as a simple system in the OFDM symbol synchronization scheme that operates stably even when there is a frequency offset, and the FFT window position recovery can be efficiently performed regardless of the type of guard interval. Another object is to provide a symbol synchronization method.

In addition, the present invention can be implemented in a simple system in the OFDM symbol synchronization method that operates stably even when there is a frequency offset, and to realize the function to efficiently restore the FFT window position regardless of the type of guard interval Another object is to provide a computer readable recording medium having recorded thereon a program.

1 is an OFDM symbol timing diagram of an OFDM receiving system to which the present invention is applied;

2A is a conceptual diagram of OFDM symbol synchronization using an ML algorithm in a general OFDM system;

2b is a conceptual diagram of OFDM symbol synchronization using a ME algorithm in a general OFDM system;

3 is a conceptual diagram illustrating OFDM symbol synchronization when there is no window offset and when there is a window offset in an OFDM receiving system to which the present invention is applied;

4 is a configuration diagram showing an FFT window position recovery apparatus of a conventional OFDM receiving system;

5 is a graph showing the types of various guard intervals in an OFDM system to which the present invention is applied;

6 is a block diagram of an embodiment of an OFDM symbol synchronization device of an OFDM receiving system according to the present invention;

7 is a configuration diagram of an input signal size calculator of a conventional OFDM receiving system;

8 is a block diagram of an embodiment of an input signal amplitude calculator of an OFDM symbol synchronization device according to the present invention;

9 is a configuration diagram of yet another embodiment of an input signal amplitude calculator of an OFDM symbol synchronization device according to the present invention;

FIG. 10 is an exemplary graph illustrating an output of each block of FIG. 6;

11 is a configuration diagram of still another embodiment of an OFDM symbol synchronization device in an OFDM receiving system according to the present invention;

12 is a graph illustrating an output of each block of FIG. 11;

FIG. 13 is a graph illustrating an embodiment of comparing an OFDM symbol synchronization method and a conventional OFDM symbol synchronization method in a situation in which a type of a protection interval is not known; FIG.

14 is a graph illustrating an embodiment of a comparison between an OFDM symbol synchronization method and an OFDM symbol synchronization method using an absolute value of a power difference according to the present invention;

FIG. 15 is a graph illustrating an embodiment of a comparison between an OFDM symbol synchronization method according to the present invention and an OFDM symbol synchronization method affected by a conventional frequency offset in a state where a relative frequency offset with respect to a subcarrier interval remains. FIG.

* Explanation of symbols for the main parts of the drawings

601: analog-to-digital converter 602: valid data interval sample delay

603, 606: adder 604: absolute value calculator

605: minimum guard interval sample delay 607: minimum guard interval accumulator

608: minimum or maximum point extractor

609: guard interval eliminator 610: fast Fourier transducer

620: input signal size calculator

According to an aspect of the present invention, there is provided an OFDM symbol synchronization apparatus for reconstructing an FFT window position of an OFDM system, comprising: input signal size calculating means for calculating a magnitude of an applied input complex signal; First sample delay means for delaying a signal received from said input signal magnitude calculating means during a valid data interval; First adding means for obtaining a difference value between the signal delayed by the first sample delay means and the magnitude of the input complex signal; Absolute value calculating means for obtaining an absolute value of a signal received from said first adding means; Second sample delay means for delaying a signal received from the absolute value calculating means during a minimum guard period; Second adding means for obtaining a difference value between the signals received from the second sample delay means and the absolute value calculating means, respectively; Accumulating means for accumulating the signal received from the second adding means for a minimum guard period; Extraction means for comparing a value of the accumulation means during an effective data interval and a maximum guard interval to find a preset point; And a guard section removing means for removing the guard section using the extracted position.

In addition, the present invention provides an OFDM symbol synchronization apparatus for reconstructing the FFT window position of an OFDM system, comprising: first sample delay means for delaying an applied input complex signal during a valid data period; Correlation value calculating means for obtaining a correlation value between the signal received from the first sample delay means and the input complex signal, respectively; Second sample delay means for delaying a signal received from said correlation value calculating means during a minimum guard period; Adding means for obtaining a difference value between the signals received from the second sample delay means and the correlation value calculating means, respectively; Accumulating means for accumulating the signal received from the adding means for a minimum guard period; Extraction means for comparing a value of the accumulation means during an effective data interval and a maximum guard interval to find a preset point; And guard interval removing means for removing the guard interval using the extracted position.

The present invention also provides an OFDM symbol synchronization method for restoring the FFT window position of an OFDM system, comprising: a first step of performing magnitude calculation of an applied input complex signal; A second step of delaying the signal calculated in the first step during a valid data period; A third step of obtaining a difference value between the signal delayed in the second step and the magnitude of the input signal and obtaining an absolute value thereof; Delaying the absolute value during the minimum guard period; A fifth step of obtaining a difference value between the signal delayed in the fourth step and the absolute value; Accumulating the difference value during a minimum guard period; A seventh step of finding a preset point by comparing the accumulated value during an effective data interval and a maximum guard interval; And an eighth step of removing the guard interval using the extracted position.

The present invention also provides an OFDM symbol synchronization method for restoring the FFT window position of an OFDM system, comprising: a first step of delaying an applied input complex signal during a valid data period; Obtaining a correlation value between the signal generated in the first and the input complex signal; Delaying the correlation value during a minimum guard period; A fourth step of obtaining a difference value between the signal delayed in the third step and the correlation value; Accumulating the difference value during a minimum guard period; A sixth step of finding a preset point by comparing the accumulated value during an effective data interval and a maximum guard interval; And a seventh step of removing the guard interval using the extracted position.

The present invention also provides an OFDM symbol synchronizer having a microprocessor for providing a function of restoring the FFT window position of an OFDM system, comprising: a first function of performing magnitude calculation of an applied input complex signal; A second function of delaying a signal calculated by the first function during a valid data period; A third function of obtaining a difference value between the magnitude of the signal delayed in the second function and the input signal and obtaining an absolute value thereof; A fourth function of delaying the absolute value for a minimum guard period; A fifth function of obtaining a difference value between the signal delayed in the fourth function and the absolute value; A sixth function of accumulating the difference value during a minimum guard period; A seventh function that compares the accumulated value during an effective data interval and a maximum guard interval to find a preset point; And a computer-readable recording medium having recorded thereon a program for realizing an eighth function of removing the guard interval by using the extracted position.

The present invention also provides an OFDM symbol synchronization apparatus having a microprocessor for providing a function of restoring the FFT window position of an OFDM system, comprising: a first function of delaying an applied input complex signal during a valid data period; A second function of obtaining a correlation value between the signal generated in the first and the input complex signal; A third function of delaying the correlation value during a minimum guard period; A fourth function of obtaining a difference value between the signal delayed in the third function and the correlation value; A fifth function of accumulating the difference value during a minimum guard period; A sixth function for finding a preset point by comparing the accumulated value during an effective data interval and a maximum guard interval; And a computer-readable recording medium having recorded thereon a program for realizing a seventh function of eliminating the guard interval using the extracted position.

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.

6 is a diagram illustrating an embodiment of an OFDM symbol synchronization device of an OFDM receiving system according to the present invention.

As shown in the figure, the OFDM symbol synchronization device of the present invention includes an analog-to-digital converter 601, an input signal magnitude calculator 620, an effective data interval sample delayer 602, an adder 603, an absolute value calculator ( 604, minimum guard interval sample delayer 605, adder 606, minimum guard interval accumulator 607, minimum or maximum point extractor 608, guard interval remover 609, and fast Fourier transformer 610. ) Is included.

The analog-to-digital converter 601 is responsible for converting an analog signal received as an input signal into a digital complex signal, and the input signal magnitude calculator 620 is responsible for calculating the magnitude of the converted digital signal.

The input signal magnitude calculator 620 may be applied to any algorithm using the magnitude of the signal in order to use the concept of FIG. 2B.

Hereinafter, referring to FIG. 7, a prior art of the input signal magnitude calculator 620 is described, and one embodiment according to the present invention is presented.

7 is a configuration diagram of an input signal magnitude calculator of a conventional OFDM receiving system.

As shown in the figure, the conventional input signal magnitude calculator is composed of a squarer and a square root calculator, and calculates squared values of the real part and the imaginary part of the input signal, respectively, and adds the values to obtain the square root of the signal. Find the correct size.

However, in the hardware implementation of the conventional input signal magnitude calculator, there is a problem in that the complexity of the system increases and the computation speed decreases due to the use of a squarer and a square root calculator.

In addition, since the information of a signal necessary for OFDM symbol synchronization is not an exact input signal size, the G samples of the last part of the valid data and the G samples of the guard interval are the same signals. The way would be possible.

8 is a configuration diagram of an input signal size calculator of an OFDM symbol synchronization device according to the present invention.

The LS algorithm generates a larger signal among the absolute values of the real part and the imaginary part of the input complex signal. Called the signal When used, it is used that the magnitude of the input signal is substantially equal to Equation (3).

here Is the size of the signal, Denotes a digitally converted complex signal.

In hardware implementation of the above algorithm, three 1-bit transitions may be used.

As shown in the figure, the input signal magnitude calculator 620 of the OFDM symbol synchronizer of the present invention includes an absolute value calculator 621, 622, a comparator 623, a one-bit shifter 624, 625, 626, and an adder. (627).

The absolute value calculators 621 and 622 are responsible for calculating the absolute values of the real and imaginary parts of the applied complex signal, and the comparator 623 passes through the absolute value calculators 621 and 622. By comparing the magnitude of the signal And It is in charge of distinguishing by signal.

Three one-bit shifters (624, 625, 626) Signals each , , The function of reducing by as much as the adder 627 is A signal and a signal passing through the one-bit shifters 624 and 626 are added to each other, and a signal passing through the one-bit shifter 625 is subtracted.

The algorithm as described above is represented by Equation 4.

9 is a configuration diagram of yet another embodiment of an input signal size calculator of an OFDM symbol synchronization device according to the present invention.

As shown in the figure, the input signal magnitude calculator 620 of the OFDM symbol synchronization apparatus of the present invention includes the absolute value calculators 628 and 629 and the adder 630.

The absolute value calculators 621 and 622 are responsible for calculating the absolute values of the real and imaginary parts of the applied complex signal, and the adder 630 is detected by the absolute value calculators 628 and 629. It is responsible for summing the magnitudes of the absolute values of the real part and the imaginary part of the complex signal.

This is represented by the equation (5).

here Represents the real part of the complex signal, Denotes the imaginary part of the complex signal.

The valid data interval sample delay unit 602 is the magnitude of the input signal calculated by the input signal magnitude calculator 620. It is responsible for delaying the during the valid data interval, the adder 1 (603) is a signal delayed by the valid data interval sample delayer 602 and the In charge of finding the difference between.

The absolute value calculator 604 is also responsible for obtaining the absolute value d (n) of this value with respect to the signal received from the adder 1 (603).

This is represented by Equation 6 below.

The minimum guard interval sample delayer 605 is responsible for delaying d (n) received from the absolute value calculator 604 during the minimum guard interval, and the adder 2 606 is the minimum guard interval sample delay. It is responsible for calculating the difference between the signal d (n + N) received from the device 605 and the d (n) .

The minimum guard period accumulator 607 is responsible for accumulating the signals received from the adder 2 606 during the minimum guard period.

The minimum or maximum point extractor 608 may use a comparator to find a minimum or maximum value among the values accumulated in the minimum guard interval accumulator 607, and the minimum during the valid data interval and the maximum guard interval. The guard interval accumulator 607 compares the values and finds a point representing the minimum or maximum value. When this is expressed as an equation, the minimum value may be represented by Equation 7 and the maximum value may be represented by Equation 8.

The method is repeated two or more times, and the position is estimated by calculating an average of the obtained OFDM symbol synchronization values.

The guard interval remover 609 may convert the signal corresponding to the effective symbol interval from the signal preceding the minimum guard interval at the minimum or maximum value point found by the minimum or maximum value point extractor 608 to the fast Fourier transformer 610. It is in charge of inputting to).

FIG. 10 is an exemplary graph illustrating an output of each block of FIG. 6.

All methods for symbol synchronization in the conventional OFDM system must know the length of the guard interval in advance. If the size of the guard interval transmitted from the receiving system is not known in advance, the signal usage characteristics of the algorithm using the signal difference among the symbol synchronization algorithms using the matching of the signal of the valid data interval and the guard interval are the same as D in FIG. There is a problem that the accuracy is significantly reduced. In addition, even if the start point is found, there is a problem in that the guard interval cannot be removed without knowing the type of the guard interval.

Therefore, in the system having several kinds of guard intervals, the symbol synchronization methods up to now cannot be used. However, using G of FIG. 10, symbol synchronization may be possible even by knowing the length of the minimum guard interval of the system.

As shown in the figure, A represents the output of the input signal magnitude calculator 620 of FIG. 6, and B represents the output of the valid data interval sample delay 602.

C denotes the output of the absolute value calculator 604, and D denotes the output of the absolute value calculator 604 when D does not know the type of the guard interval and has information of the minimum guard interval length at the beginning of the system. The output of the conventional guard interval accumulator used is shown. As shown in the figure, it can be seen that accurate symbol synchronization is not possible.

E denotes the output of the minimum guard interval sample delay 605 and F denotes the output of the adder 606.

G represents the output of the minimum guard interval accumulator 607. It can be seen that the maximum value detector is used in the minimum or maximum value point extractor 608 when using d '(n), and the minimum value detector is used when using d''(n) .

11 is a configuration diagram of another embodiment of an OFDM symbol synchronization device of an OFDM receiving system according to the present invention.

As shown in the figure, the OFDM symbol synchronization device of the present invention includes an analog-to-digital converter 1101, a valid data interval sample delayer 1102, a correlation value calculator 1103, a minimum guard interval sample delayer 1104, An adder 1105, a minimum guard interval accumulator 1106, a minimum or maximum point extractor 1107, a guard interval remover 1108 and a fast Fourier transformer 1109 are included.

The analog-to-digital converter 1101 is responsible for converting an analog signal received as an input signal into a digital complex signal, and the valid data interval sample delayer 1102 is configured to convert the signal received from the analog-to-digital converter 1101. It is responsible for delaying the effective data section.

The correlation calculator 1103 is responsible for obtaining a correlation value c (n ) of signals received from the analog-to-digital converter 1101 and the valid data interval sample delayer 1102, respectively. It can be applied to any algorithm that uses the magnitude of the correlation value of the signal in order to use.

The minimum guard interval sample delayer 1104 is responsible for delaying the signal c (n ) received from the correlation calculator 1103 during the minimum guard interval, and the adder 1105 is the minimum guard interval sample delay. It is responsible for calculating the difference between the signal c (n + N) received from the device 1104 and the c (n) .

The minimum guard period accumulator 1106 is responsible for accumulating the output signal of the adder 1105 during the minimum guard period.

The minimum or maximum value point extractor 1107 may use a comparator to find a minimum or maximum value among the values accumulated in the minimum guard interval accumulator 1106, and the minimum during the valid data interval and the maximum guard interval. The guard interval accumulator 1106 is responsible for comparing the values to find a point representing the minimum or maximum value. If this is expressed as an equation, the minimum value may be represented by Equation 9, and the maximum value may be represented by Equation 10.

The method is repeated two or more times, and the position is estimated by calculating an average of the obtained OFDM symbol synchronization values.

The guard interval remover 1108 converts a signal corresponding to a valid symbol interval from a signal preceding the minimum guard interval at the minimum or maximum value point found by the minimum or maximum value point extractor 1107 to the fast Fourier transformer 1109. It is in charge of inputting to).

FIG. 12 is an exemplary graph illustrating an output of each block of FIG. 11.

Among the symbol synchronization algorithms using the signal matching between the valid data interval and the guard interval, the signal usage characteristics of the algorithm using the correlation of the signal become as shown in FIG. In addition, even if the start point is found, there is a problem in that the guard interval cannot be removed without knowing the type of the guard interval.

Therefore, in the system having several kinds of guard intervals, the symbol synchronization methods up to now cannot be used. However, using G of FIG. 12, symbol synchronization may be possible even by knowing the length of the minimum guard interval of the system.

As shown in the figure, A represents the output of the analog-to-digital converter 1101, and B represents the output of the valid data interval sample delayer 1102. As shown in FIG.

C denotes the output of the correlation calculator 1103, and D denotes the minimum guard interval in the initial stage of the system without knowing the type of the guard interval, that is, the conventional minimum guard interval using the output of the correlation calculator. Indicates the output of the accumulator. As shown in the figure, it can be seen that accurate symbol synchronization is not possible.

E denotes the output of the minimum guard interval sample delayer 1104 and F denotes the output of the adder 1105.

G represents the output of the minimum guard interval accumulator 1106. In the case of using c '(n) , the minimum value detector is used in the symbol synchronization position detector, and in the case of using c ''(n) , the maximum value detector is used.

FIG. 13 is a graph illustrating an embodiment of comparing an OFDM symbol synchronization method according to the present invention with a conventional OFDM symbol synchronization method without knowing the type of a protection period.

In the performance evaluation, a transmission standard with a guard interval of 1 / 16th of an effective data interval was used in a DVB-T system, and 15 dB of AWGN (Added White Gaussian Noise) was used.

In the above environment, when the symbol synchronization is performed without the information on the protection interval of the transmission standard in the receiving system, the performance of the conventional methods and the method of the present invention are compared.

The horizontal axis represents the absolute value of the estimation error, and the vertical axis represents the cumulative probability of estimating symbol synchronization within the absolute value of the estimated error. The better the estimation probability approaches 1 with less estimation error, such as ideal performance, the better.

As shown in the figure, it can be seen that the OFDM symbol synchronization method of the present invention has much better performance than the conventional symbol synchronization method.

14 is a graph illustrating an embodiment of a comparison between an OFDM symbol synchronization method and an OFDM symbol synchronization method using an absolute value of a power difference according to the present invention.

For performance evaluation, transmission standard III of EUREKA147 was used, and AWGN of 15 dB was used for the channel.

In the above environment, the conventional method of using Equation 4 and Equation 5 proposed in the present invention is compared with the performance of symbol synchronization using the absolute value of the conventional power difference.

The horizontal axis represents the absolute value of the estimation error, and the vertical axis represents the cumulative probability of estimating symbol synchronization within the absolute value of the estimated error.

As shown in the figure, the OFDM symbol synchronization method of the present invention can be seen that the performance is not degraded even if the implementation is simple compared to the symbol synchronization method using the absolute value of the power difference.

FIG. 15 is a graph illustrating an embodiment of a comparison between an OFDM symbol synchronization method according to the present invention and a conventional OFDM symbol synchronization method affected by a frequency offset in a state where a relative frequency offset with respect to a subcarrier interval remains.

In the performance evaluation, a transmission standard having a guard interval length of 1/32 of an effective data interval in a DVB-T system was used, an AWGN of 15 dB was used as a channel, and a reception frequency offset of 0.25 in a reception system. The frequency offset is relative to the carrier spacing.

The horizontal axis represents the absolute value of the estimation error, and the vertical axis represents the cumulative probability of estimating symbol synchronization within the absolute value of the estimated error.

As shown in the figure, OFDM symbol synchronization methods that do not take into account the existing frequency offset are impossible symbol synchronization when the frequency offset remains, while the OFDM symbol synchronization method proposed in the present invention is reliable even when the frequency offset remains. It can be seen that the present operation is possible.

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

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.

As described above, the present invention finds a starting point of valid data for an FFT used for demodulation in an OFDM receiving system using a magnitude and a correlation value of an input signal, thereby causing synchronization errors such as carrier frequency offset and sampling frequency offset. Even in this case, it is possible to obtain reliable OFDM symbol synchronization results.

In addition, the present invention has an effect of reducing the hardware complexity and the computation time by using a simplified method such as an absolute value calculator, a 1-bit shifter, and an adder in the method of obtaining the signal size.

In addition, the present invention finds the starting point of the valid data for the FFT used for demodulation in the OFDM receiving system irrespective of the type of the guard interval. This has the effect of enabling symbol synchronization without the need.

In addition, the present invention has an effect of reducing the memory allocation and the amount of calculation by applying the accumulation during the minimum guard interval.

In addition, the present invention has the effect that it can be efficiently utilized in the high-speed data transmission that is inevitably required for the next generation mobile communication service by reducing the calculation time and the amount of calculation.

Claims (21)

An OFDM symbol synchronizer for restoring the FFT window position of an OFDM system, Input signal magnitude calculating means for calculating a magnitude of an applied input complex signal; First sample delay means for delaying a signal received from said input signal magnitude calculating means during a valid data interval; First adding means for obtaining a difference value between the signal delayed by the first sample delay means and the magnitude of the input complex signal; Absolute value calculating means for obtaining an absolute value of a signal received from said first adding means; Second sample delay means for delaying a signal received from the absolute value calculating means during a minimum guard period; Second adding means for obtaining a difference value between the signals received from the second sample delay means and the absolute value calculating means, respectively; Accumulating means for accumulating the signal received from the second adding means for a minimum guard period; Extraction means for comparing a value of the accumulation means during an effective data interval and a maximum guard interval to find a preset point; And Guard interval removal means for removing the guard interval using the extracted position Symbol synchronization apparatus of the OFDM receiving system comprising a. The method of claim 1, The input signal magnitude calculating means, First absolute value calculating means for obtaining an absolute value of a real part of the input complex signal; Second absolute value calculating means for obtaining an absolute value of the imaginary part of the input complex signal; Comparison means for comparing magnitudes of signals respectively received from the first absolute value calculating means and the second absolute value calculating means; The value of the smaller signals among the signals compared by the comparison means First transition means for converting to; The value of the signal received from the first bit transition means is Second transition means for converting to; The value of the signal received from the second bit transition means is Third transition means for converting to; And A third that sums up a larger signal among the signals compared by said comparing means, a signal received from said first transition means, and a signal received from said third transition means, respectively, and subtracts the signal received from said second transition means; Addition means Symbol synchronization apparatus of the OFDM receiving system comprising a. The method of claim 2, The input signal magnitude calculation, Symbol synchronization apparatus of the OFDM receiving system, characterized in that for calculating the magnitude of the input complex signal according to the following equation. (only, Is the size of the signal, Indicates an applied complex signal. Also, Represents the larger of the signals compared by the comparison means, Represents the lesser of the signals compared by the comparison means) The method of claim 1, The input signal magnitude calculating means, First absolute value calculating means for obtaining an absolute value of a real part of the input complex signal; Second absolute value calculating means for obtaining an absolute value of the imaginary part of the input complex signal; And Fourth adding means for summing signals received from the first absolute value calculating means and the second absolute value calculating means, respectively; Symbol synchronization apparatus of the OFDM receiving system comprising a. The method of claim 4, wherein The input signal magnitude calculation, Symbol synchronization apparatus of the OFDM receiving system, characterized in that for calculating the magnitude of the input complex signal according to the following equation. (only, Represents the real part of the complex signal, Represents the imaginary part of the complex signal) An OFDM symbol synchronizer for restoring the FFT window position of an OFDM system, First sample delay means for delaying the applied input complex signal during a valid data interval; Correlation value calculating means for obtaining a correlation value between the signal received from the first sample delay means and the input complex signal, respectively; Second sample delay means for delaying a signal received from said correlation value calculating means during a minimum guard period; Adding means for obtaining a difference value between the signals received from the second sample delay means and the correlation value calculating means, respectively; Accumulating means for accumulating the signal received from the adding means for a minimum guard period; Extraction means for comparing a value of the accumulation means during an effective data interval and a maximum guard interval to find a preset point; And Guard interval removal means for removing the guard interval using the extracted position Symbol synchronization apparatus of the OFDM receiving system comprising a. The method according to claim 1 or 6, The extraction means, And a point indicating a minimum value by comparing the values of the accumulation means during an effective data interval and a maximum guard interval. The method of claim 7, wherein The extraction means, And extracting the position having the minimum value during the valid data interval and the guard interval by a preset number to estimate the position of the correct minimum value point. The method of claim 7, wherein The minimum value point extraction, Symbol synchronization apparatus of the OFDM receiving system, characterized in that for extracting the minimum value point according to the following equation. ( N is a valid data interval, G is the maximum guard interval. D (n) represents the output of the absolute value calculation means) The method of claim 7, wherein The minimum value point extraction, Symbol synchronization apparatus of the OFDM receiving system, characterized in that for extracting the minimum value point according to the following equation. ( c (n) represents the output of the correlation value calculating means) The method according to claim 1 or 6, The extraction means, And a point indicating a maximum value by comparing the values of the accumulation means during an effective data interval and a maximum guard interval. The method of claim 11, The extraction means, And extracting the position having the maximum value during the valid data interval and the guard interval by a preset number to estimate the position of the maximum value point. The method of claim 11, The maximum value point extraction, Symbol synchronization apparatus of the OFDM receiving system, characterized in that for extracting the minimum value point according to the following equation. The method of claim 11, The maximum value point extraction, Symbol synchronization apparatus of the OFDM receiving system, characterized in that for extracting the minimum value point according to the following equation. The method according to claim 1 or 6, The guard section removing means, And a signal corresponding to a valid data interval from the signal preceding the minimum guard interval at the point where the extraction means is extracted. In the OFDM symbol synchronization method for recovering the FFT window position of an OFDM system, A first step of performing magnitude calculation of an applied input complex signal; A second step of delaying the signal calculated in the first step during a valid data period; A third step of obtaining a difference value between the signal delayed in the second step and the magnitude of the input signal and obtaining an absolute value thereof; Delaying the absolute value during the minimum guard period; A fifth step of obtaining a difference value between the signal delayed in the fourth step and the absolute value; Accumulating the difference value during a minimum guard period; A seventh step of finding a preset point by comparing the accumulated value during an effective data interval and a maximum guard interval; And Eighth step of removing the guard interval using the extracted position Symbol synchronization method of the OFDM receiving system comprising a. The method of claim 16, The first step, A ninth step of obtaining an absolute value of a real part of the input complex signal; A tenth step of obtaining an absolute value of an imaginary part of the input complex signal; An eleventh step of comparing magnitudes of the absolute values obtained in the ninth step and the tenth step; For the smaller of the compared signals, Converting to a twelfth step; The value of the signal converted in the twelfth step is Converting to a thirteenth step; The value of the signal converted in the thirteenth step is Converting to a fourteenth step; And A fifteenth step of adding the larger signal among the compared signals and the signals generated in the twelfth and fourteenth steps, respectively, and subtracting the signal generated in the thirteenth step; Symbol synchronization method of the OFDM receiving system comprising a. The method of claim 16, The first step, A ninth step of obtaining an absolute value of a real part of the input complex signal; A tenth step of obtaining an absolute value of an imaginary part of the input complex signal; And An eleventh step of adding up the signals generated in the ninth and tenth steps Symbol synchronization method of the OFDM receiving system comprising a. In the OFDM symbol synchronization method for recovering the FFT window position of an OFDM system, Delaying an applied input complex signal during a valid data interval; Obtaining a correlation value between the signal generated in the first and the input complex signal; Delaying the correlation value during a minimum guard period; A fourth step of obtaining a difference value between the signal delayed in the third step and the correlation value; Accumulating the difference value during a minimum guard period; A sixth step of finding a preset point by comparing the accumulated value during an effective data interval and a maximum guard interval; And A seventh step of removing the guard interval using the extracted position; Symbol synchronization method of the OFDM receiving system comprising a. In an OFDM symbol synchronizer with a microprocessor to provide a function to recover the FFT window position of an OFDM system, A first function of performing magnitude calculation of an applied input complex signal; A second function of delaying a signal calculated by the first function during a valid data period; A third function of obtaining a difference value between the magnitude of the signal delayed in the second function and the input signal and obtaining an absolute value thereof; A fourth function of delaying the absolute value for a minimum guard period; A fifth function of obtaining a difference value between the signal delayed in the fourth function and the absolute value; A sixth function of accumulating the difference value during a minimum guard period; A seventh function that compares the accumulated value during an effective data interval and a maximum guard interval to find a preset point; And An eighth function of removing the guard section using the extracted position A computer-readable recording medium having recorded thereon a program for realizing this. In an OFDM symbol synchronizer with a microprocessor to provide a function to recover the FFT window position of an OFDM system, A first function of delaying an applied input complex signal during a valid data interval; A second function of obtaining a correlation value between the signal generated in the first and the input complex signal; A third function of delaying the correlation value during a minimum guard period; A fourth function of obtaining a difference value between the signal delayed in the third function and the correlation value; A fifth function of accumulating the difference value during a minimum guard period; A sixth function for finding a preset point by comparing the accumulated value during an effective data interval and a maximum guard interval; And A seventh function of removing the guard section using the extracted position; A computer-readable recording medium having recorded thereon a program for realizing this.