KR20000002471A - Fft window position detecting device of dvb-t system - Google Patents

Abstract

The present invention relates to an apparatus for detecting a starting position of an FFT window in a digital TV terrestrial transmission system in Europe. In particular, an STS unit for outputting position data closest to a symbol start point within one OFDM symbol interval, and a position output from the STS unit STS analysis unit for analyzing the channel environment by analyzing the data, and FFT window position calculation unit for determining the start position of the FFT window using the position data output from the STS unit and the analysis information of the STS analysis unit, In a noisy channel environment, only a few OFDM symbols can be used to detect a more accurate position in a short time.In a noisy channel environment, a more accurate number can be detected using the most suitable number of OFDM symbols. I can do it. Therefore, the STS of the DVB-T system can be stabilized quickly, thereby reducing the initial stabilization time of the DVB-T system.

Description

FT window position detection device of DVB-T system

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital TV transmission, and more particularly to a DVB-T system for detecting the starting position of the FFT window of a signal received for a Fast Fourier Transform (FFT) in a Digital Video Broadcasting-Terrestrial (DVB-T) system. An FFT window position detection apparatus.

The DVB-T system is a European terrestrial digital TV transmission system that is currently being piloted in several European countries. The DVB-T system uses Coded Orthogonal Frequency Division Multiplexing (COFDM) modulation, which carries information on multiple carriers as a transmission method. It is divided into 2K mode and 8817 individual 8K mode.

The DVB-T system simultaneously transmits multiple carriers at a low transmission rate, thereby lengthening the period of one OFDM symbol when viewed on the time axis, and providing a guard interval for each symbol, thereby causing inter-symbol interference (Inter Symbol Interference; ISI) and ghosting have the advantage of improving system performance.

In this case, the 2K mode and the 8K mode are divided into four types (eg, 1/4, 1/8, 1/16, 1/32) according to the length of the guard interval.

In addition, since the DVB-T system transmits information to be transmitted by the inverse FFT on the frequency by the inverse FFT, demodulation in the general transmission scheme is possible by FFTing the signal received at the receiving side.

In this case, in order to perform a Fast Fourier Transform (FFT) at the receiver, from where (i.e., the starting point of the data sample to be FFT) and how much (i.e., the data to be FFT) from the digital sample of the received signal, Sample interval) You need to know if you need to do FFT, but you can get accurate FFT results. This is because 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, so the FFT should be performed only on the data of the valid interval. Coarse FFT window (CFW) is a signal that specifies the interval of the valid data, accurate CFW occurs and the FFT is made only when the start position of the CFW must be known correctly.

In this case, in order to demodulate signals in 2K mode and 8K mode, respectively, a 2048-point FFT and an 8192-point FFT should be used.

FIG. 1 is a block diagram of a conventional DVB-T system generating such a coarse FFT window (CFW), in which signals received through an antenna are tuner 11, A / D converter 12, and I / Q. After the demodulation unit 13 demodulates the complex digital sample data (I, Q) into the Coarse Symbol Timing Synchronization (STS) unit 14 and the FFT unit 16.

The coarse STS unit 14 detects the start position of the CFW by using the cyclic extension of the OFDM symbol. That is, the starting point of the symbol is found by using the fact that the data of the guard interval is a copy of the data at the end of the OFDM symbol as shown in FIG. In this manner, Equation 1 is used to find the starting point of the OFDM symbol, that is, the starting point of the FFT window.

fft_start_position = arg max {Z (d)}

d = [0, N + L-1]

In Equation 1, 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. That is, since the data in the guard interval is a copy of the data at the end of the OFDM symbol, the probability that the sum of the data in the guard interval becomes the maximum value is the greatest.

Figure 2 is designed as a system using the equation (1).

That is, the sample data to be input is input to the multiplier 23 through the conjugator 22 and to the delay 21 having N registers (for example, 2048 in the 2k mode). In 21, sample data delayed by N is input to the multiplier 23. Therefore, the multiplier 23 multiplies the sample data input after being conjugated with the sample data separated by N. The output of the multiplier 23 is input to the delay 24 with L registers and to the subtractor 25 at the same time. The subtractor 25 outputs the result obtained by subtracting the data delayed by L from the current input data to the accumulator 26 to accumulate the result. That is, the sum of L sample data spaced by N is accumulated.

The accumulation result of the accumulator 26 is input to the Coarse FFT window position discriminator 27. The coarse FFT window position determining unit 27 determines the position at which the result of the accumulator 26 indicates the maximum value as a reference point for finding the starting point of the OFDM symbol and uses the result as the Coarse FFT window position data. Output to (15). The FFT window generator 15 generates an FFT window based on the Coarse FFT window position data of the position determiner 27, and the FFT unit 16 performs an FFT only on I, Q signals within a window range. .

If the transmission channel is poor and there is a lot of noise or ghost, the position value of the calculated Coarse FFT window may change every symbol. Therefore, a problem arises that it is difficult to determine which position value among the changing values is the correct value, and an error occurs when the position value is determined from a predetermined number of data.

However, the related art repeatedly calculates the Coarse FFT window difference value calculated in the above manner by a predetermined number of repetitions and determines the position of the Coarse FFT window based on the data. The problem that the probability of occurrence increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a FFT window position detection apparatus of a DVB-T system, which detects the required position of the FFT window accurately and quickly without error and FFT the received signal. In providing.

1 is a block diagram of a typical DVB-T system

FIG. 2 is a detailed block diagram of the Coarse STS unit of FIG. 1. FIG.

3 is a diagram illustrating a relationship between an OFDM symbol and a cyclic extension.

4 is a block diagram of a DVB-T system according to the present invention;

FIG. 5 is a detailed block diagram of the Coarse STS unit of FIG. 4. FIG.

FIG. 6 is a detailed block diagram of the Coarse STS analyzer of FIG. 4. FIG.

7 is a detailed block diagram of the CFW position calculation unit of FIG.

Explanation of symbols for main parts of the drawings

40: CFW position determination circuit 41: Coarse STS section

42: Coarse STS analysis unit 43: CFW position calculation unit

51: maximum position determination unit 61: position average calculation unit

62,73: memory 63: position distribution calculator

64: distributed comparison unit 71: CFW position calculation control unit

72: adder 74: CFW position determination unit

The FFT window position detection apparatus of the DVB-T system according to the present invention for achieving the above object, the STS unit for outputting the position data closest to the start point of the symbol in one OFDM symbol interval, and in the STS unit An STS analyzer for analyzing a channel environment by analyzing output position data, and an FFT window position calculator for determining a start position of an FFT window using position data output from the STS unit and analysis information of the STS analyzer. Characterized in that configured.

The symbol timing synchronization analyzer may include a position average calculator configured to calculate an average value of position data output from the symbol timing synchronizer, a memory configured to store position data output from the symbol timing synchronizer, and position data stored in the memory; The dispersion information is calculated by comparing the position dispersion calculator for calculating the variance of the position data from the position average value calculated by the position average calculator, the dispersion value calculated by the position dispersion calculator, and the reference dispersion value of the preset receiver. And a variance comparator for outputting to the FFT window position calculator.

The FFT window position calculator calculates the FFT window position data using more position data when the variance value calculated by the symbol timing synchronization analyzer is large, and uses a small number of position data when the variance value is small. Compute the FFT window position data.

The FFT window position calculator is configured to determine the position data having the largest sum result after adding current accumulated data to previous accumulated data having the same position data as FFT window position data.

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.

4 is an overall block diagram of a DVB-T system according to the present invention, in which the front end of the I / Q separation unit 13 and the rear end of the FFT unit 16 are the same as in FIG. Only circuit 40 is different.

The CFW position determination circuit 40 outputs the position data closest to the start point of the symbol and the accumulator data at that time within one OFDM symbol interval, and the position output from the coarse STS unit 41. STS analyzer 42 for analyzing the channel environment by analyzing the data, and CFW position calculator 43 for determining the position of the FFT window based on the position data and the accumulator data output from the Coarse STS unit 41. It is composed of

In the present invention configured as described above, the operation up to the front of the I / Q separation unit 13 and the operation after the FFT unit 16 are the same as in the prior art. That is, the tuner unit 11 selects a signal of a desired channel from the signal received through the antenna, and the A / D converter 12 converts the selected channel signal into digital sample data. The sample data thus converted is input to the I / Q separator 13 and demodulated into complex digital sample data I, Q having a real part and an imaginary part. The complex digital sample data I and Q are input to the CFW position discrimination circuit 40 and the FFT unit 16.

At this time, in order for the FFT unit 16 to operate correctly, the CFW position determination circuit 40 must be terminated. Therefore, the FFT unit 16 does not operate until the operation of the CFW position determination circuit 40 ends.

5 is a detailed block diagram of the Coarse STS unit 41 of the CFW position determining circuit 40, in which the transmission mode of the DVB-T system is the 2K mode.

Referring to FIG. 5, the delay register 21 of N registers, the conjugator 22, the multiplier 23, the delay 24 of the L registers, the subtractor 25, and the accumulator 26 are described. Since the same operation as in FIG. 2 is used, the same code is used, and the maximum of outputting the position data and the accumulator data at that time are the maximum values of the accumulator 26 data values calculated during one OFDM symbol period. Only the value position discriminating unit 51 is different. In this case, the obtained position data is merely data and does not mean a position value of the FFT window. Therefore, this operation is repeated until the end of the Coarse STS and outputted to the Coarse STS analyzer 42 and the CFW position calculator 43.

That is, the position data and the accumulator data output from the coarse STS unit 41 are input to the CFW position determiner 43, and the position data is also input to the coarse STS analyzer 42.

FIG. 6 is a detailed block diagram of the Coarse STS analyzer 42. The position average calculator 61 calculates an average value of the input position data, the memory 62 storing the input position data, and the memory 62. A position variance calculator 63 for calculating variance from the position data stored in the position average value calculated by the position average calculator 61, and a variance value σ calculated by the position variance calculator 63 and the receiver It consists of a variance comparator 64 for comparing the reference values of.

In the Coarse STS analysis unit 42 of FIG. 6 configured as described above, the number of position data for obtaining the average and the variance is divided into several steps, such as 5, 10, 15, 20,... That is, the position average calculation unit 61 first receives the smallest number of position data from the Coarse STS unit 41 to calculate the average value m, and the memory 62 stores the position data at that time. The position variance calculator 63 calculates the variance of the position data σ from the position average value m of the position average calculator 61 and the position data stored in the memory 62. The variance value thus calculated is input to the variance comparator 64 and compared with the reference variance set by the receiver, and as a result, the variance information N _σ is output to the CFW position calculator 43.

If the calculated variance value σ is smaller than the reference variance value, since the current channel environment is in a very good state, it can be seen that almost constant position data is output from the coarse STS unit 41. Accordingly, the CFW position calculation unit 43 can obtain reliable CFW position data using only the position data and accumulator data obtained to date without any further calculation of the Coarse STS unit 41.

However, if the calculated variance value σ is larger than the reference variance value, it means that the channel environment is not good. That is, the position data value is not constant and changes rapidly. In this case, for example, as much data as 10 data is calculated and input from the Coarse STS unit 41, the average and the variance are calculated again. The recalculated variance is again subjected to the same process as above, and is repeated until the calculated variance becomes less than the reference variance.

At this time, since more position data is calculated and stored in the CFW position calculator 43, the CFW position data obtained from these data will be a more accurate position value. This makes it possible to calculate fast and accurate CFW position with less position data for a good channel with little noise, and calculates more position data if the channel environment is bad, but it is not fast but can detect the exact position. Will be.

That is, the CFW position calculator 43 determines how many position data should be calculated based on the dispersion information N _σ of the position data analyzed by the Coarse STS analyzer 42 and calculates the position of the CFW. do.

FIG. 7 is a detailed block diagram of the CFW position calculation unit 43. The FFT window position data calculation is performed using the position data of the Coarse STS unit 41 and the variance information Nσ of the Coarse STS analyzer 42. FIG. The accumulated data continuously output from the Coarse STS unit 41 under the control of the CFW position calculation control unit 71 and the CFW position calculation control unit 71; The addition result of the adder 72 outputted to the CFW position calculation control unit 71 and the CFW position calculation control unit 71 and the accumulated result corresponding to the position data are included in the place where the accumulated data corresponding to the position data existed. The memory 73 to store and the CFW position determination unit 74 which reads position data and accumulated data from the memory 73 under the control of the CFW position calculation control unit 71 and determines final position data of the FFT window. It is configured.

In FIG. 7 configured as described above, the CFW position calculation control unit 71 analyzes the input position data value when the position data is input from the coarse STS unit 41. Is checked from the memory 73. If the position data has been input previously, the accumulator data of the position data stored previously is read from the memory 73, the accumulator data that is currently input and the adder 72 are summed, and the sum result is stored in the memory 73 ) And store it in the place where accumulator data corresponding to the position data existed.

If the new position data has not been previously input, the CFW position calculation control unit 71 stores the position data and the accumulator data in the memory 73. That is, since there is no previous data to be added in the adder 72, the accumulator data currently input is input to the CFW position calculation control unit 71 as it is through the adder 72.

This operation is repeated each time while data is inputted and stored together with the previous value in the memory 73.

At this time, the number of position data to be repeated for a while is determined by the dispersion information (N _σ ) obtained from the Coarse STS analysis section 42. As described above, when the channel environment is good, only a small number of position data and accumulator data are added and stored by variance information N _σ of the Coarse STS analysis unit 42. Otherwise, more data is repeatedly stored. do. When the variance value σ of the position data becomes smaller than the reference variance value after calculating the data variably as described above, the CFW position determination unit 74 reads the data calculated so far from the memory 73 to determine the position of the CFW. You will be judged.

That is, the CFW position determiner 74 reads the position data and accumulator data calculated so far from the memory 73 and finds the position data having the largest accumulator value. The position data thus found is determined to be position data of the CFW, and is output to the FFT window generator 15.

The FFT window generating unit 15 generates an FFT window by finding the starting position of the CFW based on the CFW position data of the CFW position determining unit 74, and the FFT unit 16 generates an FFT window within the window range. Only perform FFT. That is, the CFW position data is a reference point for finding the window starting point of the OFDM symbol.

By detecting the starting position of CFW by the method described so far, in case of noiseless channel environment according to channel environment, it is possible to detect more accurate position in a short time by using only a few OFDM symbols. In this case, the correct position can be detected using the most suitable number of OFDM symbols. In other words, the most accurate position can be detected within the least time.

As described above, according to the CFW position detection apparatus of the DVB-T system according to the present invention, the least number of OFDMs capable of detecting the position of the CFW without error according to the channel environment without using a constant number of OFDM symbols. By using the symbol to detect the start position of the FFT window required for FFT of the received signal, the start position of the FFT window can be detected quickly and without error, and the symbol timing synchronization (STS) of the DVB-T system can be stabilized quickly. . Therefore, there is an effect of reducing the initial stabilization time of the DVB-T system.

Claims (4)

In the FFT window position detection apparatus of the DVB-T system for detecting the FFT window start position in order to fast Fourier transform (FFT) the data transmitted and received in the coded orthogonal frequency division multiplexing (COFDM) method only within the FFT window, A symbol timing synchronization (STS) unit for outputting position data closest to a start point of a symbol in one OFDM symbol period; A symbol timing synchronization analyzer for analyzing a channel environment by analyzing position data output from the symbol synchronization timing unit; FFT window of the DVB-T system, characterized in that it comprises a FFT window position calculation unit for determining the start position of the FFT window by using the position data output from the symbol timing synchronization unit and the analysis information of the symbol timing synchronization analyzer. Position detection device. The method of claim 1, wherein the symbol timing synchronization unit A sample operation unit configured to accumulate the input complex sample data by data conjugated with data delayed by the number of effective data samples (N) of the OFDM symbol, and then add and accumulate the samples corresponding to the guard interval of the OFDM symbol, and And a maximum position determination unit for outputting position data such that the maximum value is the maximum value among the data values of the sample calculating unit and accumulated data at that time. The method of claim 1, wherein the symbol timing synchronization analyzer A position average calculation unit calculating an average value of the position data output from the symbol timing synchronization unit; A memory for storing position data output from the symbol timing synchronizer; A position variance calculator for calculating a variance of the position data from the position data stored in the memory and the position average value calculated by the position average calculator; The FFT window position detection of the DVB-T system, comprising: a variance comparator for comparing the variance value calculated by the position variance calculator with a reference variance value of a preset receiver and outputting variance information to the FFT window position calculator Device. The method of claim 1, wherein the FFT window position calculation unit An FFT window position calculation control unit for controlling FFT window position data calculation by using position data of the symbol timing synchronization unit and distribution information of the symbol timing synchronization analyzer; An adder which adds accumulated data output from the symbol timing synchronizer under control of the FFT window position calculation control unit with accumulated data of the same position data previously stored and outputs the accumulated data to the FFT window position calculation control unit; A memory for storing the addition result of the adder where the accumulated data corresponding to the position data existed under the control of the FFT window position calculation control unit; FFT window position detection device, characterized in that the FFT window position determination unit for reading the position data and accumulated data from the memory under the control of the FFT window position calculation control unit to determine the final position data of the FFT window .