KR20100059569A - Apparatus and method for detecting time synchronization of ofdm system - Google Patents

Abstract

PURPOSE: A time synchronization detecting device and method of an OFDM system is provided to perform initial alignment and symbol synchronization by using cross correlation that is superior to the autocorrelation mode. CONSTITUTION: A correlator(10) obtains a correlation value through the cross correlation of a preamble signal which has been saved in advance with a received signal. A comparator(20) compares the correlation value with a predetermined critical value. A maximum value detector(30) detects the maximum value of the correlation value. A synchronous detector(40) detects the starting point of a frame from the point when the critical value of the correlation value is exceeded. The synchronous detector detects the location of a symbol in the frame from the location of the detected maximum value. The preamble symbol comprises a training symbol. The correlator comprises a plurality of delaying units, a plurality of multipliers, and a summing unit.

Description

Apparatus and Method for Detecting Time Synchronization of OPDM System {APPARATUS AND METHOD FOR DETECTING TIME SYNCHRONIZATION OF OFDM SYSTEM}

The present invention relates to an apparatus and method for detecting time synchronization in an OFDM system.

The present invention is derived from a study conducted as part of the IT source technology development of the Ministry of Knowledge Economy and the Ministry of Information and Communication Research and Promotion. [Task management number: 2007-F-039-02, Task name: VMC technology development].

Orthogonal Frequency Division Multiplexing (hereinafter referred to as “OFDM”) in a vehicle system that provides vehicle to vehicle and vehicle to infrastructure around a fast moving vehicle. I'm using the method.

In general, an OFDM-based transmitting apparatus converts a serially input data string into a plurality of parallel data strings and transmits the same on a plurality of subcarriers having mutual orthogonality. By doing so, the data rate can be increased, and since the symbol interval is wider than that of a single carrier signal, interference effects between adjacent symbols are reduced, so that reliable demodulation can be performed even in a multipath channel. In this case, time and frequency synchronization are required to accurately demodulate a signal transmitted from an OFDM-based transmission apparatus.

In general, in order to detect time synchronization, an OFDM-based receiving device detects an initial point of time at which a frame starts using a correlation between a received signal and a signal (eg, a phase reference symbol) previously known to the receiving device. A symbol synchronization for detecting synchronization and a start position of a symbol is performed respectively. However, the correlation method requires multiple multiplications and additions, which increases hardware complexity and decreases data processing speed.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide an apparatus and method for detecting time synchronization of an OFDM system capable of reducing hardware complexity.

According to an embodiment of the present invention, a method for detecting time synchronization of a received signal in an orthogonal frequency division multiplexing (OFDM) system is provided. According to a time synchronization detection method, obtaining a correlation value through cross correlation of the received signal and a preamble signal stored in advance, comparing the correlation value with a preset threshold value, and comparing the correlation value with the threshold value. Detecting a starting point of a frame in the received signal, detecting a maximum value of the correlation value, and detecting a position of a symbol in the frame from the detected position of the maximum value.

According to another embodiment of the present invention, an apparatus for detecting time synchronization of a received signal in an orthogonal frequency division multiplexing (OFDM) system is provided. The time synchronization detecting device includes one correlator, a comparator, a maximum value detector, and a synchronization detector. One correlator obtains a correlation value through cross correlation of the received signal and a pre-stored preamble signal, a comparator compares the correlation value with a preset threshold value, and a maximum detector detects the maximum value of the correlation value. do. The sync detector detects the starting point of the frame from the time when the correlation value exceeds the threshold, and detects the position of the symbol in the frame from the position of the detected maximum value.

According to an embodiment of the present invention, the hardware configuration of time synchronization of an OFDM system can be simplified by performing initial synchronization and symbol synchronization using cross correlation which is superior to autocorrelation.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification and claims, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise. In addition, the terms “… unit”, “… unit”, “module”, “block”, etc. described in the specification mean a unit that processes at least one function or operation, which is hardware or software or a combination of hardware and software. It can be implemented as.

An apparatus and method for detecting time synchronization of an OFDM system according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

1 is a block diagram schematically illustrating an OFDM system according to an exemplary embodiment of the present invention, and FIG. 2 is a diagram illustrating a frame structure of an OFDM system.

Referring to FIG. 1, an OFDM system includes a transmitter 100 and a receiver 200.

The transmitter 100 includes a channel encoder 102, a modulator 104, a multiplexer 106 and 108, a serial / parallel converter 110, an inverse fast Fourier transform 112, and a parallel / serial converter. 114, a guard interval inserting portion 116, and a digital-to-analog converter 118.

The channel encoder 102 encodes data to be transmitted by using a predetermined encoding method to generate predetermined bit signals, and outputs the predetermined bit signals to the modulator 104. As a coding scheme, a turbo coding scheme, a convolutional coding scheme, or the like having a predetermined coding rate may be used.

The modulator 104 modulates the bit signals output from the channel encoder 102 in a predetermined manner and outputs them to the multiplexer 106. As a modulation method, the amount of data that can be transmitted in one subcarrier may include one bit BPSK, two bits QPSK, four bits 16-QAM, six bits 64-QAM, and eight bits 256-QAM.

The multiplexer 106 multiplexes the pilot symbols and the data symbols modulated from the modulator 104 into one signal and outputs the multiplexed signal to the multiplexer 108.

The multiplexer 108 multiplexes the preamble signal and the signal output from the multiplexer 106 into a single signal and outputs the signal to the serial / parallel converter 110.

The serial / parallel converter 110 converts the signals output from the multiplexer 108 in parallel and outputs them to the inverse fast Fourier transformer 112.

The inverse fast Fourier transform unit 112 performs inverse fast Fourier transform on the parallel signal output from the serial / parallel converter 110 and outputs the parallel signal to the parallel / serial converter 114. That is, the inverse fast Fourier transform unit 112 outputs the inverse fast Fourier transform of the parallel signal in the frequency domain as a parallel signal in the time domain.

The parallel / serial converter 114 converts the parallel signal output from the inverse fast Fourier transform unit 112 into a serial section and outputs it to the guard section insertion unit 116.

The guard interval inserting unit 116 inserts a guard interval in front of the data symbol modulated from the serial signal output from the parallel / serial converter 114. At this time, the guard period and the modulated data symbol are summed to be called an OFDM symbol.

That is, referring to FIG. 2, one frame includes a preamble and valid data. The preamble is a guard interval (GI2) located between the short training symbol (t ₁ -t ₁₀ ), the long training symbol (T _11- T ₁₂ ), and the short training symbol (t ₁₀ ) and the long training symbol (T ₁₁ ) having repetitive characteristics. ). In this case, the short training symbols t _{1 to} t ₁₀ have a characteristic that a predetermined number of sample signals are repeated. In FIG. 2, the short training symbols t _1- t ₁₀ are illustrated as 16 sample signals are repeated 10 times. In addition, the long training symbols T ₁₁ and T ₁₂ may have 64 sample signals. In addition, the valid data includes a plurality of OFDM symbols, and each of the OFDM symbols includes a data symbol DATA and a guard period GI.

Referring back to FIG. 1, the digital-analog converter 118 converts a signal having a guard interval into an analog wireless signal and transmits the signal to the receiving apparatus 200 through a channel.

Next, the receiver 200 includes an analog-digital converter 202, a time synchronization detector 204, a frequency synchronization detector 206, a guard interval elimination unit 208, a serial / parallel conversion unit 210, a high speed. Fourier transform unit 212, parallel / serial converter 214, channel estimation and equalization unit 216, a demodulator 218 and a channel decoder 220.

The analog-digital converter 202 converts the analog radio signal received through the channel into a digital signal and outputs the digital signal to the time synchronization detector 204.

The time synchronization detector 204 acquires time synchronization by performing time synchronization using a preamble signal stored from the digital signal output from the analog-digital converter 202. The time synchronization includes initial synchronization for detecting a start point of a frame from a received signal and symbol synchronization for detecting a start position of an OFDM symbol for fast Fourier transform.

After acquiring time synchronization, the frequency synchronization detector 206 performs frequency synchronization using a preamble signal to estimate a carrier frequency offset, compensates it, and outputs the compensation to the guard interval remover 208.

The guard interval remover 208 removes the guard interval from the signal output from the frequency synchronization detector 206 and outputs the guard interval to the serial / parallel converter 210.

The serial / parallel converter 210 converts the signal from which the guard interval is removed into a parallel signal and outputs the parallel signal to the fast Fourier transform unit 212.

The fast Fourier transform unit 212 performs fast Fourier transform on the parallel signal output from the serial / parallel converter 210 and outputs the parallel signal to the parallel / serial converter 214. That is, the fast Fourier transform unit 212 performs fast Fourier transform on the parallel signal in the time domain and outputs the parallel signal in the frequency domain.

The parallel / serial converter 214 converts the parallel signals output from the fast Fourier transform unit 212 into serial and outputs them to the channel estimation and equalizer 216.

The channel estimator and equalizer 216 separates the data symbols and the pilot symbols from the signals output from the parallel / serial converter 214, estimates the channels using the pilot symbols, and equalizes the data symbols based on the channel estimates. Output to demodulator 218.

The demodulator 218 demodulates the equalized data using the same method as the modulation method used by the transmission apparatus 100 using the channel estimate value.

The channel decoder 220 decodes the demodulated data by a predetermined decoding method to generate data.

3 is a block diagram of a time synchronization detector shown in FIG. 1, and FIG. 4 is a flowchart illustrating an operation of the time synchronization detector shown in FIG. 3.

Referring to FIG. 3, the time synchronization detector 204 includes a correlator 10, a comparator 20, a maximum value detector 30, and a synchronization detector 40.

Referring to FIG. 4, the correlator 10 calculates a correlation value through cross-correlation between a received signal and a short training symbol known in advance by the receiver 200 (S410-S420), and compares the comparator 20 and the maximum detector. Output to (30).

The comparator 20 compares the correlation value calculated from the correlator 10 with a predetermined threshold value and outputs it to the synchronization detector 40 (S430). At the same time, the maximum value detector 30 is calculated from the correlator 10. The maximum value of the correlation value is detected and output to the synchronization detector 40 (S440).

When the correlation value exceeds the predetermined threshold, the synchronization detector 40 determines that the start of the frame is determined, and determines that the correlation value exceeds the threshold value as the start point of the frame. In addition, the synchronization detector 40 determines the start position of the OFDM symbol in the frame detected from the position of the maximum value detected by the maximum value detector 30 (S450).

In this way, since initial synchronization and symbol synchronization can be obtained together using one correlator, hardware complexity can be reduced.

FIG. 5 is a diagram illustrating the structure of the correlator illustrated in FIG. 3.

Referring to FIG. 5, the correlator 10 includes a plurality of delayers 11a-11n, a plurality of multipliers 12a-12n, and a summer 13.

Each of the plurality of retarders 11a-11n has an input terminal and an output terminal, and the output terminal of the preceding delay unit is connected to the input terminal of the rear stage delay unit. The plurality of delayers 11a-11n sequentially delay the received signal by the sampling period of the digital-to-analog converter 118 from the transmitter 100 and output the received signal to the corresponding multipliers 12a-12n. Here, n is the number of sample signals of the short training symbol. Referring to FIG. 2, n may be 16.

The plurality of multipliers 12a-12n multiply the output signals of the corresponding delayers 11a-11n by the conjugate complex numbers of the short training symbols and output them to the summer 13.

The summer 13 sums and outputs the signals output from the multipliers 12a-12n, and the output value of the summer 13 becomes a correlation value of the correlator 10. In this case, the starting point of the frame may be determined from a time point when the correlation value of the correlator 10 exceeds a threshold value. In addition, referring to FIG. 2, since a short training symbol has a characteristic of repeating 10 times of 16 sample signals, 10 correlation values may be calculated in one frame, and the maximum length of the OFDM symbols may be calculated from the maximum of 10 correlation values. The starting position can be determined.

An embodiment of the present invention is not implemented only through the above-described apparatus and / or method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. Such an implementation can be easily implemented by those skilled in the art to which the present invention pertains based on the description of the above-described embodiments.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 is a block diagram schematically illustrating an OFDM system according to an embodiment of the present invention;

2 is a view showing a frame structure of an OFDM system,

3 is a block diagram of a time synchronization detector shown in FIG. 1;

4 is a flowchart illustrating an operation of a time synchronization detector shown in FIG. 3;

FIG. 5 is a diagram illustrating the structure of the correlator illustrated in FIG. 3.

Claims (5)

A method of detecting time synchronization of a received signal in an orthogonal frequency division multiplexing (OFDM) system, Obtaining a correlation value through cross correlation between the received signal and a preamble signal stored in advance; Comparing the correlation value with a preset threshold value; Detecting a starting point of a frame in the received signal by comparing the correlation value with the threshold value, Detecting a maximum value of the correlation value, and Detecting a position of a symbol in the frame from the detected position of the maximum value Time synchronization detection method comprising a. The method of claim 1, The preamble signal includes a training symbol having a property of repeating a plurality of sample signals. The obtaining step, Sequentially delaying and outputting the received signal by a predetermined interval; Outputting a plurality of first signals obtained by multiplying the received signal and a signal sequentially delayed and output by the predetermined interval with the conjugate complex number of the training symbol; And summing and outputting all of the plurality of first signals. The method of claim 1, And said comparing and detecting said maximum value are performed simultaneously. An apparatus for detecting time synchronization of a received signal in an orthogonal frequency division multiplexing (OFDM) system, A correlator for obtaining a correlation value through cross correlation between the received signal and a preamble signal stored in advance; A comparator for comparing the correlation value with a preset threshold value, A maximum value detector for detecting a maximum value of the correlation value, and A synchronization detector for detecting a starting point of a frame from a time point at which the correlation value exceeds the threshold value, and detecting a position of a symbol in the frame from the position of the detected maximum value Time synchronization detection device comprising a. The method of claim 4, wherein The preamble signal includes a training symbol having a property of repeating a plurality of sample signals. The correlator, A plurality of delayers sequentially delaying the received signal by a predetermined interval; A plurality of multipliers for multiplying each of the received signals and output signals of the plurality of delayers by the conjugate complex number of the training symbol, and And a summer for adding up signals output from the plurality of multipliers.

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