KR100327373B1 - COFDM receiving system - Google Patents

Abstract

The present invention relates to a coded orthogonal frequency division multiplexing (COFDM) receiving system that automatically determines a transmission mode and a guard interval from a received signal. In particular, information about a transmission mode and a guard interval of a received signal may be obtained from a noisy received signal. By accurately and automatically acquiring errors, even if the channel environment becomes poor, the symbol start position of the FFT can be accurately found and the symbol timing performance of the receiver using the COFDM transmission method is significantly improved. In particular, since the guard interval discrimination unit discriminates the guard interval using the correlation between the four accumulator output values, the guard interval determination unit can accurately determine the guard interval mode regardless of the noise level or the signal size.

Description

Coding orthogonal frequency division multiplexing system {COFDM receiving system}

The present invention relates to a Coded Orthogonal Frequency Division (COFDM) transmission system using multiple carriers, and more particularly, to a COFDM reception system for automatically determining a transmission mode and a guard interval from a received signal.

Typically, the COFDM transmission system is a transmission method used in the terrestrial digital TV transmission system in Europe, and is currently being broadcast in the DVB-T (Digital Video Broadcasting Terrestrial) standard in some European countries. The DVB-T system uses COFDM to carry information on multiple carriers as a transmission method, and is divided into 2705 modes of 1705 and 8817 modes of 6817 according to the number of carriers.

In addition, such a DVB-T system transmits multiple carriers simultaneously at a low transmission rate, thereby lengthening the period of one Orthogonal Frequency Division Modulation (OFDM) symbol when viewed on the time axis. A guard interval is provided for each symbol, which has an advantage of improving system performance deterioration due to inter-symbol interference (ISI) and ghost.

Here, the 2K mode and 8K mode has four methods (depending on the length of the guard interval) Will be divided into That is, the length of the guard interval Means that the actual valid data ( ).

That is, in order to transmit desired data by the COFDM method, after passing through an Inverse Fast Fourier Transform (IFFT), a guard interval is inserted and transmitted over a frequency. Therefore, the DVB-T system enables demodulation in a general transmission scheme by FFTing the received signal.

In this case, in order to perform FFT in the DVB-T system, the FFT must be FFT from where the digital sample of the received signal (that is, the starting point of the data sample to be FFT) and how much (ie, the sample interval of the data to be FFT). It is important to know how to get accurate FFT results. As described above, each symbol is divided into a guard interval and a valid data interval. Since the data of the guard interval is a copy of the data of the last part of the valid data interval, the FFT should be performed only on the data of the valid interval. Because.

In addition, as mentioned above, in order to demodulate signals in 2K mode and 8K mode, respectively, a 2048-point FFT and an 8192-point FFT must be performed.

Therefore, the DVB-T system can FFT the received signal only if it knows whether the currently received signal is in 2K mode or 8K mode and the length of the guard interval in each mode. That is, the DVB-T receiver uses a 2048-point FFT when the received signal is in 2K mode and an 8192-point FFT when in the 8K mode.

1 is a simplified block diagram of a conventional DVB-T receiving system in which a signal received through an antenna is digitized via a tuner 101, an A / D converter 102, and an I / Q separator 103. The demodulated data is input to the FFT unit 104 after being demodulated into complex digital sample data (I, Q).

At this time, the receiver transmits the information of the transmission mode to the FFT unit 104 from the outside under the assumption that the transmission mode of the received signal is known, thereby enabling correct FFT. Therefore, if the receiver is not informed that the transmission mode has been changed, the receiver cannot correctly perform the FFT of the signal of the changed transmission mode.

Meanwhile, the DVB-T system transmits a Transmission Parameter Signaling (TPS) signal according to the standard, which transmits all information on transmission parameters such as the number of carriers of the currently transmitted COFDM signal and the length of the guard interval.

However, since the TPS information is information obtained after the received signal is FFTed, FFT should be possible before decoding of the TPS information in order to perform the FFT. Therefore, it is very important to be able to find out the transmission mode and the guard interval of the received signal before the FFT.

FIG. 2 is a simple block diagram showing another embodiment of a conventional DVB-T receiving system equipped with a transmission mode determining apparatus, in which an OFDM signal received through an antenna is tuner 201 and A / D converter 202. FIG. The signal is demodulated into complex digital sample data (I, Q) digitized via the I / Q separation unit 203, and is simultaneously input to the transmission mode determining device 204 and the FFT unit 205.

The transmission mode determination device 204 determines the transmission mode (ie, 2K mode or 8K mode) and the guard interval (1/32, 1/16, 1/8, 1/4) from the input signal. One method of determining is to use the cyclic extension shown in FIG. 3.

Here, the cyclic extension is used to transmit an OFDM signal, and does not send any signal during the guard period of the OFDM signal, but the data located at the end of the OFDM symbol (that is, the data for the same time period as the guard period). ) Means copying and inserting it into the protective section.

Therefore, in the 2K mode, as shown in FIG. 3, if the received sample and the data 2048 samples away from the sample data are located in the portion where the data of the guard interval and the guard interval are copied, respectively, the two signals become the same signal sample. Otherwise it is different data.

4 is a detailed block diagram of the transmission mode determining unit 204. A correlation data generating unit 301 and the correlation data generating unit 301 which generate data used to determine a transmission mode and a protection interval are shown. The transmission mode and the guard interval determination unit 302 for determining the transmission mode and the guard interval using the data generated by the.

FIG. 5 is a detailed block diagram of the correlation data generating unit 301. The operation principle may determine whether data separated by 2048 samples are the same data or data separated by 8192 samples are the same data. To make it work.

That is, referring to FIG. 5, four 2048 word shift registers 401 to 404 that sequentially delay the received signal samples in a serial connection, and a conjugate that conjugates the received signal samples. A multiplier 406 multiplying the signal delayed for 2048 samples with the output signal of the conjugator 405 while passing through the 2048 word shift register 401 delays the output of the multiplier 406 by 64 samples. A subtractor 408 for obtaining a difference between a 64-word shift register 407, an output of the multiplier 406, and an output of the 64-word shift register 407, and a first accumulator for continuously accumulating the output of the subtractor 408. 409), a multiplier 410 multiplying the signal delayed for 8192 samples with the output signal of the conjugator 405 while sequentially passing through the four 2048 word shift registers 401 to 404, and outputs the output of the multiplier 410 to 256. Delay by sample A second word for continuously accumulating the output of the subtractor 412, a subtractor 412 for obtaining a difference between an output of the multiplier 410, and an output of the 256 word shift register 411 And an accumulator 413.

6 is a detailed block diagram of the transmission mode and the guard interval determination unit 302. The transmission mode determination unit 501 determines whether the transmission mode is 2K or 8K from the outputs of the first and second accumulators 409 and 413. And a guard interval discriminator 502 for outputting the output of the first or second accumulator 409 or 413 as guard interval information according to the output of the transmission mode discriminator 501.

That is, the received signal samples are sequentially input to the 2048 word shift register 401 and the conjugator 405, and the signal delayed by 2048 samples in the 2048 word shift register 401 is conjugated in the multiplier 406. It is multiplied by the output of the gator 405. That is, the output of the multiplier 406 is the result of conjugating one of two signals spaced 2048 samples from each other and then multiplying each other.

The output of the multiplier 406 is again input to the 64 word shift register 407 and the subtractor 408, which subtracts the signal delayed by 64 samples from the signal currently input from the multiplier 406. Is output to the first accumulator 409. That is, the signal input to the first accumulator 409 is a signal obtained by subtracting the sample output from the multiplier 406 before 64 samples from the sample currently output from the multiplier 406.

The first accumulator 409 continues to add the result obtained above. If this is expressed as an equation, Equation 1 below.

In Formula 1, 2048 is the number of useful data samples of the OFDM symbol in the 2K mode, and 64 is the length of the guard interval. The number of samples in the guard interval, s (k), is the k th sample data.

Accordingly, as shown in Equation 1, if d is located at the start of the guard interval, the first accumulator 409 is an absolute value of the sum of the product of 64 sample blocks and 64 sample blocks separated by 2048 samples. The output value will indicate the maximum value when the received signal is in 2K mode.

On the other hand, if the received signal is 8K mode, very little value is output. This result is shown in FIG.

This proves that the received signal is a 2K mode if a value exceeding a threshold A is output from the first accumulator 409 and a very small value is output from the second accumulator 413 as shown in FIG. 7.

In addition, a signal delayed by 8192 samples through four 2048 word shift registers 401-404 is multiplied by the output of the conjugator 405 in the multiplier 410. That is, the output of the multiplier 410 is a result of conjugating one of two signals separated by 8192 samples and multiplying each other.

The output of the multiplier 410 is again input to the 256 word shift register 411 and the subtractor 412, and the subtractor 412 is a difference between the signal delayed by 256 samples and the signal currently input from the multiplier 410. Is output to the second accumulator 413. That is, the signal input to the second accumulator 413 is a signal obtained by subtracting the sample output from the multiplier 406 before 256 samples from the sample currently output from the multiplier 406.

The second accumulator 413 continues to add the result obtained above. This expression is expressed by the following equation (2).

Similarly, in Equation 2, 8192 is the number of valid data samples of an OFDM symbol in 8K mode, and 256 is the length of the guard interval. The number of samples in the guard interval, s (k), is the k th sample data.

Therefore, as shown in Equation 2, if d is located at the start of the guard interval, the second accumulator 413 is an absolute value of the sum of 256 sample blocks and 256 sample blocks separated by 8192 samples. The output value will show the maximum value when the received signal is in 8K mode. However, if the received signal is a 2K mode will output a very small value, these results are shown in FIG.

That is, if a value exceeding the threshold B is output from the second accumulator 413 and a very small value is output from the first accumulator 409, the received signal is proved to be in 8K mode.

The output values of the first accumulator 409 and the second accumulator 413 obtained by the calculation in this manner are input to the transmission mode determination unit 501 and used for transmission mode determination.

That is, according to the above-described method, if the received signal is the 2K mode, the output values of the first accumulator 409 and the second accumulator 413 will appear as shown in FIG. 7, and if the received signal is the 8K mode, the first accumulator ( 409 and the output value of the second accumulator 413 will appear as shown in FIG.

Therefore, the transmission mode determining unit 501 determines whether or not the output value of the first accumulator 409 exceeds the threshold value A when the 2K mode is exceeded. 2048 + 64) to (2048 + 512). If this condition is satisfied, it is determined that the currently received signal is a 2K mode OFDM signal and outputs transmission mode information in the 2K mode. Where 64 is the shortest guard interval in 2K mode, that is, Where 512 is the longest guard interval in 2K mode, When

Similarly, if the received signal is the 8K mode, the output values of the first accumulator 409 and the second accumulator 413 will appear as shown in FIG. 8. Therefore, the transmission mode determining unit 501 determines whether the output value of the second accumulator 413 exceeds the threshold B when the 8K mode is exceeded. Check if 2048 + 64) * 4 to (2048 + 512) * 4 is repeated. If this condition is satisfied, it is determined that the currently received signal is an 8K mode OFDM signal, and the transmission mode information is output in the 8K mode. Where 256 (= 64 * 4) is the shortest guard interval in 8K mode, i.e. 2048 (512 * 4) is the longest guard interval in 8K mode. When

The transmission mode information thus obtained is again input to the guard interval determination unit 502 and used to determine the code interval.

9 illustrates an accumulator output according to a guard interval of a received signal. That is, in the 2K mode, the output of the first accumulator 409 is input to the guard interval determination unit 502 in the 8K mode.

Therefore, the output value of the first accumulator 409 exceeding the threshold A when the received signal is in the 2K mode is one for the protection interval 1/32, 64 (= 128-64) for the 1/16, 1 If / 8, it is 192 (= 256-64), 1/4 is 448 (= 512-64). In addition, when the received signal is the 8K mode, the output value of the second accumulator 413 exceeding the threshold B is one when the guard interval is 1/32, 256 (= 512-256) when 1/16, 1 In the case of / 8, it is 768 (1024-256), in case of 1/4, it is 1792 (= 2048-256).

This result is obtained because the accumulation of as many as 64 sample data blocks in the 2K mode and the accumulation of 256 sample data blocks in the 8K mode is calculated by Equations 1 and 2 described above. For example, if the guard interval length is 1/16 (= 128) in 2K mode, up to 64 samples of the guard interval are sequentially increased to the maximum value at the 64th sample, but when the guard interval ends after 64 samples The maximum value is kept until.

Using this criterion, the guard interval determination unit 502 can determine the length of the guard interval of the signal currently being received.

The guard interval information thus obtained is input to the FFT unit 205 together with the transmission mode information and used to obtain a correct FFT output.

However, the prior art as described above determines the guard interval mode because the number of samples that exceed the threshold value is not accurate according to the guard interval mode when the channel environment in which the signal is transmitted is poor, that is, in a channel with a lot of noise. You can make a mistake in doing this.

The present invention is to achieve the above object, an object of the present invention to provide a COFDM receiving system that accurately detects the guard interval mode even in a bad channel environment.

Another object of the present invention is to provide a COFDM reception system that automatically and accurately determines the information of a transmission mode and a guard interval from a noisy received signal.

Another object of the present invention is to provide a COFDM receiving system that correctly receives a changed received signal even if the transmission mode and the guard interval of the received signal are changed.

1 is a block diagram of a prior art COFDM receiving system

2 is a block diagram of a COFDM receiving system having a transmission mode determining apparatus according to the related art.

3 shows a cyclic extension of a typical COFDM symbol.

4 is a detailed block diagram of the apparatus for determining a transmission mode of FIG. 2.

FIG. 5 is a detailed block diagram of the correlation data generator of FIG. 4. FIG.

6 is a detailed block diagram of a transmission mode and a guard interval determination unit of FIG. 4.

FIG. 7 is a signal waveform diagram illustrating outputs of the first and second accumulators when the transmission mode is 2K in FIG. 5. FIG.

FIG. 8 is a signal waveform diagram illustrating outputs of the first and second accumulators when the transmission mode is 8K in FIG. 5; FIG.

9 is a view illustrating a guard interval determination method of a guard interval determination unit of FIG. 6;

10 is a block diagram of a COFDM receiving system according to the present invention

FIG. 11 is a detailed block diagram of the Coarse STS unit of FIG. 10. FIG.

12 is a detailed block diagram of a guard section island of FIG. 11.

FIG. 13 is a detailed block diagram of a transmission mode and a guard interval determining unit of FIG. 11.

FIG. 14 is a signal waveform diagram showing outputs of the first to fourth accumulators of FIG. 12 when the guard interval is 1/32. FIG.

15 is a signal waveform diagram showing the output of the first to fourth accumulators of FIG. 12 when the guard interval is 1/16;

16 is a signal waveform diagram showing the output of the first to fourth accumulators of FIG. 12 when the guard interval is 1/8;

17 is a signal waveform diagram showing the output of the first to fourth accumulators of FIG. 12 when the guard interval is 1/4;

Explanation of symbols for main parts of drawings

601: tuner 602: A / D conversion unit

603: I / Q separation part 604: Coarse STS part

605: FFT window generating unit 606: FFT unit

701: delay 702: conjugate multiplier

703: guard section island 704: transmission mode and guard section determination unit

705: window position detection unit 801 to 804: FIFO

805 to 808: subtractor 809 to 812: accumulator

813: data selecting section 814 to 817: absolute value calculating section

The COFDM reception system according to the present invention for achieving the above object, the delay unit for delaying received sample data by N samples (N is the number of valid data samples of one symbol according to the mode), and the non-delayed received sample data And a conjugate multiplier for performing a conjugate product with data delayed by N samples in the delay unit, and an output of the conjugate multiplier by the length of each guard interval, and then sums the islands of the guard interval according to the guard interval data determined. And a transmission mode and a protection interval determination unit for determining a transmission mode and a protection interval from the output of the protection interval island and outputting the data back to the protection interval island.

The guard interval islander delays the input signal by a sample corresponding to the length of the first guard interval and a second delay delays the signal delayed by the first delay period by a sample corresponding to the length of the first guard interval. A delay delayer; a third delayer delaying the signal delayed by the second delayer by a sample corresponding to the second guard interval length; and a delay signal delayed by the third delayer by the sample corresponding to the third guard interval length. A fourth delayer for delaying, a first accumulator for accumulating the difference between the undelayed signal and the output signal of the first delayer, and outputting a result of summing the conjugate product for the first guard interval length, and the non-delayed signal A second accumulator for accumulating a difference between an output signal of the second delay unit and outputting a result of summing a conjugate product for a second guard interval length; A third accumulator for accumulating the difference between the non-delayed signal and the output signal of the third delayer and outputting the sum of the conjugate products for the third guard interval length; A fourth accumulator for accumulating a difference with an output signal and outputting a result of summing the conjugate products for a fourth guard interval length, and selecting one of the outputs of the first to fourth accumulators according to the determined guard interval data value It is characterized by comprising a data selector for outputting.

The transmission mode and the guard interval determination unit may determine a transmission mode of a received signal by comparing an output value of any one of the outputs of the first to fourth accumulators with a preset transmission mode threshold.

The transmission mode and the guard interval determination unit may determine the length of the guard interval from the mutual relationship between the first to fourth accumulators.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

10 is a block diagram of a DVB-T system according to the present invention, in which a signal received through an antenna is complex via a tuner unit 601, an A / D converter 602, and an I / Q separation unit 603. After demodulation into digital sample data (I, Q), it is input to the Coarse Symbol Timing Synchronization (STS) unit 604 and the FFT unit 606.

In the present invention, the Coarse STS unit 604 determines the transmission mode and the guard interval.

FIG. 11 is a detailed block diagram of the Coarse STS unit 604. The delay unit 701 delays received sample data by N samples, and performs a conjugate product of undelayed received sample data and data delayed by N samples. Guard interval summation unit 703 for adding the output of the conjugate multiplier 702, the conjugate multiplier 702 by the length of each guard interval, and outputs island data of the guard interval according to the guard interval data. ), A transmission mode and a guard interval determining unit 704 for determining a transmission mode and a guard interval from the output of the guard interval island 703 and outputting the guard mode to the guard interval island 703, and the guard interval island 703. The window position detection unit 705 detects a coarse window position from the guard interval island data output from the control unit.

Here, the delay unit 701 may be configured as a first input first output (FIFO) consisting of N memory cells, or may be configured as a shift register.

FIG. 12 is a detailed block diagram of the GIS unit 703. The FIFO32 801 delays an input signal by 64 samples, the FIFO16 802 delays by 64 samples, and the FIFO8 803 delays by 128 samples. A FIFO4 804 is connected in serial that delays by a sample. The first subtractor 805 subtracting the output of the FIFO32 801 from the non-delayed signal, the first accumulator 809 and the first accumulator 809 accumulating the outputs of the first subtractor 805. A first absolute value calculator 814 taking an absolute value at the output, a second subtractor 806 that subtracts the output of the FIFO16 802 from a non-delayed signal, and a second accumulator that accumulates the output of the second subtractor 806 ( 810), a second absolute value calculator 815 taking an absolute value at the output of the second accumulator 810, a third subtractor 807, which subtracts the output of the FIFO8 803 from an undelayed signal, and the third subtractor ( A third accumulator 811 accumulating the output of 807, a third absolute value calculator 816 taking an absolute value at the output of the third accumulator 811, and subtracting the output of the FIFO4 804 from the undelayed signal. A fourth accumulator 808, a fourth accumulator 812 that accumulates the output of the fourth subtractor 808, and the fourth The fourth absolute value calculating unit 817 taking an absolute value at the output of the four accumulator 812, and the guard interval island data output from the first to fourth accumulators 809 to 812 according to the determined guard interval value. And a data selector 813 for selective output.

Here, the outputs of the first to fourth absolute value calculators 814 to 817 are inputted to the transmission mode & guard interval determination unit 704 and used to determine the transmission mode and the guard interval.

The FIFO32 801 and FIFO16 802 are each 64 memory cells, the FIFO8 804 is 128 memory cells, and the FIFO4 804 is 256 memory cells.

13 is a detailed block diagram of the transmission mode and the guard interval determination unit 704, and includes a guard interval determination unit 900 and a transmission mode determination unit 909. FIG.

In this case, the guard interval determination unit 900 finds and outputs the maximum value GISUM4max among the data values input by the fourth absolute value calculating unit 817 of the GIS unit 703 during one OFDM symbol. A second maximum value detector 902 which finds and outputs a maximum value GISUM8max among data values inputted by the third absolute value calculator 816 during one OFDM symbol, and inputs the second absolute value calculator 815 during one OFDM symbol. A third maximum value detector 903 that finds and outputs the maximum value GISUM16max among the data values, and a fourth maximum value GISUM32max that finds and outputs the maximum value GISUM32max among the data values inputted by the first absolute value calculator 814 during one OFDM symbol. First to obtain the difference Delta3 between the maximum value GISUM4max detected by the maximum value detector 904 and the first maximum value detector 901 and the maximum value GISUM8max detected by the second maximum value detector 902. The maximum value GISUM8max detected by the subtractor 905 and the second maximum value detector 902. And a second subtractor 906 for obtaining the difference Delta2 between the maximum value GISUM16max detected by the third maximum value detector 903 and the maximum value GISUM16max and the third value detected by the third maximum value detector 903. The third subtractor 907 for obtaining the difference Delta1 of the maximum value GISUM32max detected by the maximum value detector 904, and the outputs of the first to fourth maximum value detectors 901 to 904 and the first to fourth values. And a guard interval detector 908 for determining the length of the guard interval using the outputs of the third subtractors 905 to 907.

In the present invention configured as described above, the Coarse STS unit 604 determines the transmission mode and the guard interval value of the received signal from the input signal and finds the coarse window position that is most important for operating the FFT.

To this end, first, the received sample data is delayed by N samples, that is, 2048 samples, in the delay unit 701 and then output to the conjugate multiplier 702. In the conjugate multiplier 702, a conjugate product of data that is not delayed and data delayed by N samples in the delayer 701 is performed. That is, the relationship between two complex numbers that are symmetrical with respect to the real axis on the complex plane, that is, a + jb and a-jb, is called a conjugate to each other, and the result of the conjugate multiplier 702 becomes a real number.

In this case, if a maximum value is obtained by conjugating the result of conjugation of the data spaced by N samples with each other and then adding the guard intervals for one OFDM symbol, the current position becomes the start position of the FFT window. This is performed by the window position detection unit 705, which is expressed by Equation 3 below.

fft_start_position = arg max {Z (d)}

d = [0, N + L-1]

In Equation 3, N is the number of useful data samples of the OFDM symbol, L is the number of samples of the guard interval, x (k) is the k-th sample data. As described above, the position representing the maximum value of the absolute values of the conjugate product of the L sample data spaced by N from each other during the N + L period is a reference point for finding the starting point of the OFDM symbol. This is because the data in the guard interval is a copy of the data at the end in the OFDM symbol, and therefore the probability that the sum of the data in the guard interval becomes the maximum value is the greatest.

As shown in Equation 3, in order to find an accurate FFT starting position, N and L values must be known correctly. In order to detect this value, a transmission mode and a guard interval value are determined.

Therefore, in order to determine the transmission mode and the guard interval length, the output of the conjugate multiplier 702 is input to the GIS unit 703. The GIS unit 703 outputs the outputs of the first to fourth absolute value calculators 814 to 817 to the transmission mode and the guard interval determination unit 704 to determine the transmission mode and the guard interval value. In order to find a value, one of the output values of the first to fourth accumulators 809 to 812 is selected according to the determined guard interval value and output to the window position detector 705.

In this case, since the GIS unit 703 does not know the current transmission mode and the guard interval value initially, it is assumed that the current transmission mode is the 2K mode (in the case of DVB-T), that is, the value of N is 2048. In addition, it is assumed that the value of the guard interval is 1/32.

If the transmitted signal is assumed to be in the 2K mode, the output value of the first accumulator 809 at this time has a certain size, but if the transmitted signal is the 8K mode, the output value of the first accumulator 809 is Will print a very small value. This result can be used to determine the transmission mode.

Therefore, according to Equation 4 below, the transmission mode determination unit 909 of the transmission mode and the guard interval determination unit 704 determines the transmission mode.

That is, if the condition of Equation 4 is satisfied, the currently transmitted signal may be determined to be a 2K mode, otherwise it is determined to be an 8K mode.

Meanwhile, the received sample data is sequentially delayed by 64 samples in the FIFO32 801, 64 samples in the FIFO16 802, 128 samples in the FIFO8 803, and 256 samples in the FIFO4 804. For example, if the received sample data sequentially passes through FIFO32, FIFO16, FIFO8, and FIFO4 (801 to 804), a signal delayed by 512 samples is output.

After dividing the FIFO in this manner, the first subtractor 805 subtracts the output of the FIFO32 801 from the non-delayed signal and accumulates in the first accumulator 809, and the second subtractor 806 from the non-delayed signal. The output of the FIFO16 802 is subtracted and accumulated in the second accumulator 810. The third subtractor 807 subtracts the output of the FIFO8 803 from the non-delayed signal and accumulates in the third accumulator 811, and the fourth subtractor 808 stores the FIFO4 804 from the non-delayed signal. The output of is subtracted and accumulated in the fourth accumulator 812.

That is, in the case of the FIFO32 801, a result of continuously accumulating the difference between the sample value inputted using the first subtractor 805 and the first accumulator 809 and the output value of the FIFO32 is eventually generated during the 1/32 guard period. The result of the sum of the conjugate products is expressed as an equation. The output value of the first accumulator 809 may be expressed as in Equation 5 below.

Similarly, output values of the second to fourth accumulators 810 to 812 may be represented by Equations 6 to 8, respectively.

The outputs of the first to fourth accumulators 809 to 812 calculated as described above are output to the data selector 813 and output to the first to fourth absolute value calculators 814 to 817, respectively, to take an absolute value. The output values GISUM32, GISUM16, GISUM8, and GISUM4 of the first to fourth absolute value calculating units 814 to 817 are input to the transmission mode & guard interval discriminating unit 704.

The transmission mode determination unit 909 of the transmission mode and the protection interval determination unit 704 determines the transmission mode as shown in Equation 4 above, and the protection interval determination unit 900 uses all four input GISUM data. To determine the length of the guard interval.

That is, the first to fourth maximum value detectors 901 to 904 of the guard interval determination unit 900 find the maximum value among the data values input during the symbol period of one OFDM.

At this time, the guard interval value is calculated by assuming 1/4, so that the entire OFDM symbol interval Becomes

The maximum values obtained by the first to fourth maximum value detectors 901 to 904 are referred to as GISUM4max, GISUM8max, GISUM16max, and GISUM32max, respectively, and the outputs of the first to third subtractors 905 to 907, that is, adjacent guard intervals. The difference between the maximum values is called Delta3, Delta2, and Delta1. When this is expressed by an equation, it is expressed as in Equation 9 below.

At this time, the guard interval detecting unit 908 determines the guard interval using seven values of the values GISUM4max, GISUM8max, GISUM16max, GISUM32max, Delta1, Delta2, and Delta3 calculated in the same manner as described above.

Here, the sign parameter is used for further calculation. The sign parameter is represented by Equation 10 below.

First, the largest value among the three delta values Delta1, Delta2, and Delta3 obtained from Equation 9 is found.

This is shown for each case as follows.

Case 1) Delta3 is the largest

1-a) If Sign1> 0, Sign2> 0, and Sign3> 0, the length of the guard interval is determined to be 1/4.

1-b) If Delta1> Delta2 and Delta3> Low_limit, the length of the guard interval is determined to be 1/16.

In cases other than 1-c), the length of the guard interval is determined to be 1/32.

Case 2) Delta2 is the largest

2-a) If Sign1> 0 and Sign2> 0, the length of the guard interval is determined to be 1/8.

In other cases, the length of the guard interval is determined to be 1/32.

Case 3) Largest Delta1

3-a) If Sign1> 0, the length of the guard interval is determined to be 1/16.

In other cases, the length of the guard interval is 1/32.

Case 4) When Delta1 <Low_limit, Delta2 <Low_limit, and Delta3 <Low_limit, the length of the guard interval is determined to be 1/32.

When the guard interval is determined in this manner, the guard interval is not sensitive to the change of the channel, so that the guard interval can be accurately determined even in a poor channel environment.

Therefore, the data selector 813 of the GIS unit 703 uses the detection result of the guard interval detector 908 as a selection signal to output any one of the outputs of the first to fourth accumulators 809 to 812. The guard interval island data is selected and output to the window position detector 705. The window position detector 705 detects the FFT coarse window position by applying Equation 3 and outputs the FFT window generator 605 to the FFT window generator 605.

Here, each symbol is divided into a guard interval and a valid data interval. Since the data of the guard interval is a copy of the data of the last part of the valid data interval as it is, the FFT should be performed only on the data of the valid interval. Therefore, the Coarse FFT window is a signal specifying a section of valid data. The FFT window generator 605 generates an FFT window based on the FFT coarse position data of the window position detector 705, and the FFT unit 606 performs FFT only on I, Q signals within a window range.

14 to 17 show the relationship between the difference between the output value of the first to fourth accumulators and the maximum value between adjacent guard intervals when the guard interval length is 1/32, 1/16, 1/8, and 1/4, respectively. Signal waveform diagram.

For example, referring to FIG. 14, the output values of the first to fourth accumulators when the guard interval is 1/32 is shown, and it can be seen that there is almost no difference between the output values. However, in FIG. 15 where the guard interval is 1/16, the difference between the output values of the first and second accumulators is clearly shown, but the difference between the output values of the second and fourth accumulators is almost insignificant.

Using this property, the guard interval of the received signal can be accurately determined, and the guard interval can be accurately determined even if the transmission mode and the guard interval of the received signal are changed.

As described above, according to the COFDM reception system according to the present invention, the information on the transmission mode and the guard interval of the received signal can be automatically and accurately obtained without error even from a noise-rich reception signal, even if the channel environment becomes poor. By accurately finding the symbol start position, the symbol timing performance of the receiver using the COFDM transmission method is significantly improved. In particular, since the guard interval discrimination unit discriminates the guard interval using the correlation between the four accumulator output values, the guard interval determination unit can accurately determine the guard interval mode regardless of the noise level or the signal size.

Claims (19)

In a coded orthogonal frequency division multiplexing (COFDM) receiving system for demodulating complex digital sample data (I, Q) on a signal received through an antenna and performing fast Fourier transform (FFT), A delay unit for delaying the received sample data by N samples (N is the number of valid data samples of one OFDM symbol according to the mode); A conjugate multiplier for performing a conjugate product of undelayed received sample data with data delayed by N samples in the delay unit; The output of the conjugate multiplier is sequentially delayed by a predetermined length of a plurality of guard intervals, and the difference between the delayed data and the non-delayed original data for each guard interval length is accumulated and output, respectively, to the determined guard interval length data. A guard interval island part that selects one accumulation result from the accumulation results for each guard period and outputs the island data of the corresponding guard period; The guard interval length data is discriminated from the correlation of each accumulation result output from the guard interval island part, and the transmission mode is determined by comparing the accumulation result for each guard interval with a preset threshold value. Coded orthogonal frequency division multiplexing system characterized in that it comprises a transmission mode and a guard interval discrimination unit for outputting to the island. The method of claim 1, And a window position detector for detecting a window position for the FFT from the guard interval island data selectively output from the guard interval island. The method of claim 1, wherein the delay unit A coded orthogonal frequency division multiplexing system comprising a first-in first-out memory consisting of N memory cells. The method of claim 1, wherein the guard interval islands A first delayer configured to delay the input signal by a sample corresponding to the first guard interval length; A second delayer delaying the signal delayed by the first delayer by a sample corresponding to the second guard interval length; A third delayer delaying the signal delayed by the second delayer by a sample corresponding to the third guard interval length; A fourth delayer delaying the signal delayed by the third delayer by a sample corresponding to a fourth guard interval length; A first accumulator for accumulating a difference between an undelayed signal and an output signal of the first delayer and outputting a result of summing a conjugate product for a first guard interval length; A second accumulator for accumulating the difference between the undelayed signal and the output signal of the second delayer and outputting a result of summing the conjugate product for the second guard interval length; A third accumulator for accumulating the difference between the non-delayed signal and the output signal of the third delayer and outputting the sum of the conjugate products for the third guard interval length; A fourth accumulator for accumulating the difference between the undelayed signal and the output signal of the fourth delayer and outputting the sum of the conjugate products for the fourth guard interval length; And a data selector configured to select any one of the outputs of the first to fourth accumulators according to the guard interval length data value output from the transmission mode and the guard interval determination unit and output the sum data as island data of the guard interval. Coded Orthogonal Frequency Division Multiplexing System. The method of claim 4, wherein The coded orthogonal frequency division multiplexing system, characterized in that the number of samples corresponding to the first guard interval length is 64 in 2K mode and 256 in 8K mode. The method of claim 4, wherein The coded orthogonal frequency division multiplexing system, characterized in that the number of samples corresponding to the second guard interval length is 128 in the 2K mode and 512 in the 8K mode. The method of claim 4, wherein The coded orthogonal frequency division multiplexing system, characterized in that the number of samples corresponding to the third guard interval length is 256 in 2K mode and 1024 in 8K mode. The method of claim 4, wherein The coded orthogonal frequency division multiplexing system, characterized in that the number of samples corresponding to the fourth guard interval length is 512 in 2K mode and 2048 in 8K mode. The method of claim 4, wherein And the first to fourth delay units are configured as a first-in, first-out memory. The method of claim 1 or 4, wherein the transmission mode and the guard interval determination unit The encoding orthogonal frequency division multiplexing system of claim 1, wherein the transmission mode of the received signal is determined by comparing an output value of any one of the outputs of the first to fourth accumulators with a preset transmission mode threshold. The method of claim 10, wherein the transmission mode and the guard interval determination unit The coded orthogonal frequency division multiplexing system, characterized in that the following conditions are satisfied, 2K mode, if not satisfied 8K mode. (Where d = [0,2048 + 64-1], 2048 is the number of valid data samples of the OFDM symbol in 2K mode, 64 is the number of samples in the guard interval when the length of the guard interval is 1/32 in 2K mode, x (k) is the kth sample data.) The method of claim 1 or 4, wherein the transmission mode and the guard interval determination unit The coded orthogonal frequency division multiplexing system, characterized in that the length of the guard interval is determined from the mutual relationship between the first to fourth accumulators. The method of claim 1 or 4, wherein the transmission mode and the guard interval determination unit A first maximum value detector for finding and outputting a maximum value among data values input by the fourth accumulator during one OFDM symbol; A second maximum value detector for finding and outputting a maximum value among data values input from the third accumulator during one OFDM symbol; A third maximum value detector for finding and outputting a maximum value among data values input by the second accumulator during one OFDM symbol; A fourth maximum value detector for finding and outputting a maximum value among data values input by the first accumulator during one OFDM symbol; A first subtractor for outputting a difference between the maximum value detected by the first maximum value detector and the maximum value detected by the second maximum value detector; A second subtractor for outputting a difference between the maximum value detected by the second maximum value detector and the maximum value detected by the third maximum value detector; A third subtractor for outputting a difference between the maximum value detected by the third maximum value detector and the maximum value detected by the fourth maximum value detector; A coded quadrature frequency detector configured to determine a length of a guard interval of a received signal by using a correlation between the outputs of the first to fourth maximum value detectors and the outputs of the first to third subtractors. Split Multiple Receive System. The method of claim 13, wherein the guard interval detection unit An encoding orthogonal frequency division multiplexing system characterized by obtaining a sign parameter and using the same to determine a guard interval length. The method of claim 14, wherein the guard interval detection unit And multiplying the output of each maximum value detector by a weight less than one and obtaining the first to third code parameters by 뺌 from the output of the subtractor. The method of claim 13, wherein the transmission mode and the guard interval determination unit The coded orthogonal frequency division multiplexing system, characterized in that the length of the guard interval is determined to be 1/4 if the output value of the third subtractor is the largest and all the sign parameters are greater than zero. The method of claim 13, wherein the transmission mode and the guard interval determination unit The coded orthogonal frequency division multiplexing system, characterized in that the length of the guard interval is determined to be 1/8 when the output value of the second subtractor is largest and the first and second code parameters are larger than zero. 15. The apparatus of claim 13, wherein the transmission mode and the code interval determination unit At least one of when the output of the third subtractor is greater than the output of the second subtractor and at the same time the output of the third subtractor is greater than the threshold value, or when the output of the third subtractor is the largest and the first sign parameter is greater than zero. If it satisfies the encoding orthogonal frequency division multiplexing system characterized in that the length of the guard interval is determined to be 1/16. 19. The apparatus of claim 16, wherein the transmission mode and the code interval determination unit If the conditions are not satisfied, the coded orthogonal frequency division multiplexing system characterized in that the length of the guard interval is determined to be 1/32.