KR100739562B1 - Apparatus for detecting sync of OFDM receiver - Google Patents

Abstract

An apparatus for detecting synchronization in an OFDM receiving system, the apparatus comprising: an I / Q separation unit for receiving a signal not including a synchronization signal and transitioning to an I, Q baseband signal; An FFT unit performing fast Fourier transform (FFT) on the I and Q baseband signals; A storage unit having a size corresponding to one symbol and storing the FFT signal; An operation unit which takes an absolute value on an output sample of the storage unit, takes an absolute value on the current sample inputted by FFT, and then obtains a difference between two absolute value values; And a synchronization detector configured to generate a complex sine wave corresponding to an offset value based on an output value of the operation unit and output the complex sine wave to the I / Q separation unit or to track the start point of each symbol to be FFTed, thereby receiving data without a synchronization signal. It is possible to detect the complex sine wave for synchronizing each symbol by using the wrong values generated while restoring the signal and to use the value to shift to the baseband.

Sync signal, OFDM, FFT

Description

Apparatus for detecting sync of OFDM receiver

1 is a block diagram of a general OFDM receiving system

2 is a block diagram illustrating an OFDM receiving system according to the present invention.

3 is a detailed block diagram of the FFT unit of FIG.

4 is a detailed block diagram of a synchronization detector of FIG. 2.

Explanation of symbols for main parts of the drawings

202: A / D conversion section 203: I / Q separation section

204: serial / parallel conversion unit 205: FFT unit

206: parallel / serial conversion unit 207: error correction unit

401: storage unit 402, 403: absolute value calculation unit

404: subtractor 405: zero detector

406: position shifter 407: offset detector

408: sin rom 409: cos rom

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital TV transmission, and more particularly, to a synchronization detection apparatus of an OFDM reception system for detecting synchronization of a signal transmitted by an orthogonal frequency division (OFDM) scheme.

In general, a transmission method of a digital TV includes a single carrier modulation method using a single carrier and a multicarrier modulation method of transmitting desired data using a plurality of multiple carriers as in the conventional transmission methods. Can be distinguished. That is, the transmission method of the digital TV is classified into a residual side band (VSB) method using one single carrier and an OFDM method using a plurality of carriers.

Among them, the OFDM scheme using a plurality of multi-carriers can easily recover damage of a signal caused by a multi-path channel, and unlike a single carrier, a single frequency network (SFN) is also possible.

In addition, such OFDM is used to map and transmit data in a manner called quadrature amplitude modulation (QAM). The modulation schemes mainly used are quadrature phase shift keying (QPSK), 16-QAM, and 64-QAM.

That is, in order to transmit desired data by the OFDM scheme, first, data is mapped by one of the three modulation methods described above, and then transmitted by performing an Inverse Fast Fourier Transform (IFFT). At this time, the number of carriers is divided into 2K mode of 1705 and 8K mode of 6817. For example, in the 2K mode, the OFDM symbol consists of 2048 samples.                         

Then, the OFDM receiving system enables fast demodulation in a general transmission scheme by fast Fourier transform (FFT) of the received signal. In this case, when the received signal is in the 2K mode, the OFDM reception system uses a 2048-point FFT. In the 8K mode, the 8192-point FFT should be used.

In addition, in order to perform FFT in the OFDM reception system, the FFT needs to be FFT from which of the digital samples of the received signal (ie, the starting point of the data sample to be FFTed) and how much (ie, the sample interval of the data to be FFTed). It is important to know how to get accurate FFT results. For this purpose, a synchronization signal must be detected.

For this purpose, the OFDM receiver generally inserts and transmits a synchronization signal.

1 is a schematic diagram of a conventional OFDM receiving system, in which an RF signal received through an antenna is converted into an intermediate frequency (IF) signal through a tuner 101 and then digitized in the A / D converter 102. The digitized signal is input to the I / Q separation unit 103, separated into an I signal and a Q signal, and then to the synchronization tracking unit 104. The sync tracking unit 104 detects a sync signal from the input I, Q signals and outputs the sync signal to the FFT unit 105. The FFT unit 105 performs FFT on the received data in synchronization with the synchronization signal and outputs the data to the error correction unit 106.

The error correcting unit 106 receives the FFT signal and divides the channel impulse response to compensate for a carrier distorted by a channel and outputs the demapped signal.

In this case, the OFDM reception system as described above is possible when the transmitter inserts and transmits a synchronization signal.

However, this method adds additional synchronization signals at the transmitting side, which increases bandwidth and consumes a lot of power. In order to solve this problem, there is a method of transmitting only data without information on a synchronization signal at a transmitting side. However, even at this time, the receiving side must synchronize each symbol when restoring the data, or the restoring of the data will not be performed properly.

In addition, there is a problem in that an additional loop is required to capture complex sinusoids Sin (wt) and Cos (wt) for transitioning a pass band signal to a base band signal.

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 synchronization detection apparatus of an OFDM receiving system that synchronizes for each symbol when restoring data received without information of a synchronization signal.

Another object of the present invention is to provide a synchronization detection apparatus of an OFDM reception system for detecting a complex sine wave for transitioning to baseband with data for symbol synchronization.

In accordance with another aspect of the present invention, there is provided a synchronization detection apparatus of an OFDM reception system, including: an I / Q separation unit that receives a signal that does not include a synchronization signal and transitions to an I, Q baseband signal; An FFT unit performing fast Fourier transform (FFT) on the I and Q baseband signals; A storage unit having a size corresponding to one symbol and storing the FFT signal; An operation unit which takes an absolute value on an output sample of the storage unit, takes an absolute value on the current sample inputted by FFT, and then obtains a difference between two absolute value values; And a synchronization detector for generating a complex sine wave corresponding to an offset value based on the output value of the calculator and outputting the complex sine wave to the I / Q separator or tracking the starting point of each symbol to be FFTed.

If there is zero in the output of the calculator, the sync detector moves the position of the symbol to FFT from that point.

The synchronization detection apparatus of the OFDM receiving system according to the present invention may generate an offset detection unit for outputting an offset corresponding to an output value of the operation unit when the output of the operation unit is zero, and generate a complex sine wave corresponding to the offset value of the offset detection unit. It further comprises a ROM table output to the I / Q separator.

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.

2 is a block diagram of an OFDM receiving system according to the present invention, which includes an A / D converter 202, an I / Q separator 203, a serial / parallel converter 204, an FFT unit 205, and a bottle. The / serial converting section 207 and the error correcting section 208 are connected in sequence. At this time, the output of the FFT unit 205 is input to the synchronization detection unit 206, the synchronization detection unit 206 detects the synchronization signal from the data without the synchronization signal information and outputs to the FFT, and at the same time transition to the baseband A complex sine wave (Cos (wt), Sin (wt)) for outputting is output to the I / Q separator 203.

That is, the passband signal digitized by the A / D converter 202 is input to the I / Q separator 203, and the I / Q separator 203 is synchronized with the passband digital signal. Multiply the complex sine wave (Cos (wt), Sin (wt)) provided by to transition the passband digital signal to the baseband digital signal and simultaneously separate it into I and Q signals.

3 is a detailed block diagram of the FFT 205 of FIG. 2, and FIG. 4 is a detailed block diagram of the synchronization detector 206 of FIG. 2.

The synchronization detector 206 has a size corresponding to one symbol and stores the FFT sample signal, and a first absolute value calculator 402 which takes an absolute value on the sample signal output from the storage unit 401. ), From the output of the subtractor 404 and the subtractor 404 for obtaining the difference between the second absolute value calculating unit 403 which takes an absolute value on the sample signal output from the FFT unit 205, and the first and second absolute value calculating units. A zero detector 405 for detecting zero, a sync detector 406 for finding synchronization from the output of the zero detector 405, an offset detector 407 for detecting an offset from the output of the zero detector 405, and the offset A sinusoidal ROM 408 for outputting a corresponding sinusoidal sin (wt) to the I / Q separation unit 203, and a cosine wave Cos (wt) corresponding to the offset to the I / Q separation unit 203. It is composed of cosine wave ROM (409).

In the present invention configured as described above, the A / D converter 202 converts an IF analog signal of an input passband into a digital signal and outputs the digital signal to the I / Q separator 203. The I / Q separator 203 multiplies the passband digital signal by a complex sine wave (Cos (wt), Sin (wt)) provided by the synchronization detector 206 to transition the passband digital signal to a baseband digital signal. At the same time, the signal is separated into I and Q signals and output to the serial / parallel converter 204. The serial / parallel converter 204 converts the baseband digital signal into a parallel signal and outputs the parallel-band signal to the FFT unit 205.

The FFT unit 205 is an equivalent circuit of a portion multiplying multicarriers as shown in FIG. 3.

The signal S (t) generated by the FFTQN 205 is expressed by Equation 1 below.

Where N is the number of unit-level symbols and f _k is the k-th carrier frequency.

And, if the equation (1) is expressed by the complex analysis, it is as shown in the following equation (2).

Where S (k) = A (k) + jB (k).

In addition, if the OFDM signal of Equation 2 is sampled at intervals of Ts, and this is represented as a complex number as in Equation 3 below.                     

Where Ts is a symbol interval and t = mTs.

As described above, the FFT unit 205 exhibits a strong characteristic against distortion of a signal by multipath by using a multicarrier.

That is, the present invention can prevent the signal distortion due to the multipath that may occur while the cable modem is wireless by using the multiplier multiplying the multi-frequency, which is a strong OFDM signal processing method.

The sample signal FFT by the FFT unit 205 is converted into a serial signal by the parallel / serial converter 207 and output to the error correcting unit 208 and to the synchronization detector 206 for symbol recovery.

The synchronization detector 206 performs signal tracking to capture the correct FFT position. Here, the FFT position refers to finding the starting point of each symbol to be FFTed. The synchronization detector 206 also tracks the complex sine wave Cos (wt), Sin (wt) for looping the passband signal to the baseband signal.

The sample signal output from the FFT unit 205 is stored in the storage unit 401 and input to the second absolute value calculator 403. The storage unit 401 has a size capable of storing one symbol, and the output of the storage unit 401 is input to the first absolute value calculator 402.                     

In other words, the FFT signals absoluteized by the first and second absolute value calculators 402 and 403 have a difference of one symbol, and the outputs of the first and second absolute value calculators 402 and 403 are input to the subtractor 404. The difference value is detected. The output of the subtractor 404 is input to the zero detector 405.

If the FFT unit 205 FFTs the start point of each symbol, each data of the FFT symbol has only values of +1 and -1. In this case, if the absolute value is taken out and subtracted, the output of the subtractor 404 becomes zero. Therefore, finding this point finds motivation. In addition, if the FFT unit 205 does not FFT the start point of each symbol, that is, if the synchronization is not correct, each data of the FFT symbol may have a value other than +1, -1, so the output of the subtractor 404 Outputs a value that is proportional to the wrong degree.

Accordingly, the zero detector 405 determines whether the output of the subtractor 404 is zero or not zero, and the position shifter 406 generates a position shift signal or a synchronization signal according to the output of the zero detector 405. Output to the FFT unit 205.

That is, the position detector 406 outputs a signal for shifting the position of the symbol to the FFT unit 205 so as to FFT from the point when there is a zero value.

On the other hand, if the zero value is not detected by the zero detector 405, the value of the complex sine wave (Cos (wt), Sin (wt)) for transitioning to the baseband signal is wrong. The offset is generated according to the SIN ROM 408 for outputting the sine wave signal and output to the COS ROM 409 for outputting the cosine wave signal. The SIN and COS ROMs 408 and 409 read the values corresponding to the offsets and output them to the I / Q separator 203. That is, the offset detector 407 finds an accurate complex sine wave (Cos (wt), Sin (wt)) value by changing w while looping to transition to a baseband signal.

As described above, according to the synchronization detection apparatus of the OFDM reception system according to the present invention, the synchronization of each symbol using the wrong values generated while recovering the data received without the synchronization signal, and using the value to the baseband By detecting the complex sinusoids (Cos (wt), Sin (wt)) for transition, the transmitter does not need to insert a synchronization signal to reduce bandwidth and eliminate power waste, and to pass the passband signal to the baseband. The circuit can be simplified by eliminating the necessary complex sinusoidal (Cos (wt), Sin (wt)) generation circuits.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (3)

An I / Q separation unit for receiving a signal not including a synchronization signal and transitioning to an I, Q baseband signal; An FFT unit performing fast Fourier transform (FFT) on the I and Q baseband signals; A storage unit having a size corresponding to one symbol and storing the FFT signal; An operation unit which takes an absolute value on an output sample of the storage unit, takes an absolute value on the current sample inputted by FFT, and then obtains a difference between two absolute value values; And OFDM reception, characterized in that it comprises a synchronization detector for generating a complex sine wave corresponding to an offset value based on the output value of the operation unit and outputs to the I / Q separation unit or to track the starting point of each symbol to be FFT Synchronous detection device of the system. The method of claim 1, wherein the sync detection unit And a zero position at the output of the arithmetic unit to shift the position of the symbol to FFT from that point. The method of claim 1, wherein the sync detection unit An offset detector for outputting an offset corresponding to an output value of the calculator when the output of the calculator is not zero; And a ROM table generating a complex sine wave corresponding to an offset value of the offset detector and outputting the complex sine wave to the I / Q separator.

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