KR100820315B1 - Method for demodulating ofdm signal and apparatus therefor - Google Patents

Abstract

A method for demodulating an OFDM signal and a receiving apparatus for the same are provided to set sampling clock synchronization with a sample structure without separate hardware for checking an offset of a sampling clock. A method for demodulating an OFDM signal includes the steps of: converting a received OFDM signal to a baseband signal(S25); converting the baseband signal to a sampled signal(S35); setting symbol synchronization by using an offset of a symbol timing detected from the sampled signal(S43); performing a Fourier transform of the sampled signal considering the symbol synchronization(S45); and demodulating the Fourier transformed signal with an OFDM method(S55). The step of converting the received OFDM signal to the baseband signal sets local carrier wave frequency synchronization by using the Fourier transformed signal considering the symbol synchronization(S23). The step of converting the baseband signal to the sampled signal sets sampling frequency synchronization by using the offset value of the symbol detected from the sampled signal(S33).

Description

ODFM signal demodulation method and receiving apparatus for the same {Method for demodulating OFDM signal and Apparatus therefor}

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to

1 is a block diagram showing an OFDM signal receiving apparatus according to the prior art.

2 is a diagram illustrating a frame structure of a general OFDM signal.

3 is a block diagram showing an OFDM signal receiving apparatus according to a preferred embodiment of the present invention.

4 is a flowchart illustrating a procedure of a received OFDM signal processing method according to a preferred embodiment of the present invention.

5 is a flowchart illustrating a procedure of setting a symbol synchronization and a synchronization of a sampling clock according to an exemplary embodiment of the present invention.

<Description of main reference numerals in the drawings>

100 Orthogonal detection means 130 Symbol synchronization means

131 Frame Sync Settings 135 Symbol Sync Settings

150 ... sampling frequency control means 155 ... clock generating means

200 Fourier transform means 250 Carrier frequency control means

300 ... OFDM demodulation means

The present invention relates to an OFDM signal demodulation method and a receiver for the same. More particularly, the present invention relates to an OFDM signal demodulation method and a reception device for implementing the same.

OFDM transmission is a technique of dividing a channel having a given bandwidth into a plurality of subchannels and transmitting a signal through subcarriers orthogonal to each other in each subchannel, so that bands between adjacent channels overlap each other using orthogonality of subcarriers. Therefore, the inter-symbol interference (ISI) shown in the frequency division multiplexing scheme can be effectively removed. Due to these advantages, the recent OFDM transmission scheme has been used as a standard transmission scheme of various high speed data transmission systems such as digital audio broadcasting (DAB), digital video broadcasting (DVB), and wireless LAN.

In order to accurately demodulate a signal transmitted over a wireless channel through an OFDM scheme, a reception apparatus must accurately match the reception timing of the signal. When the clock generated by the receiver is unstable or the Doppler frequency shift causes an offset between the carrier frequency of the transmitter and the carrier frequency of the receiver, the orthogonality of the subcarriers is broken and inter-channel interference (ICI) is lost. Occurs and distortion of the received signal occurs. In addition, the OFDM symbol is transmitted in an IFFT-processed state at the transmitting end, and subjected to FFT processing at the receiving end to demodulate the symbols. If the symbol is not synchronized correctly, inter-symbol interference (ISI) is obtained. May occur. As a result, in the OFDM scheme, the process of setting the synchronization of the carrier frequency and the synchronization of the OFDM symbol must be performed.

1 is a block diagram illustrating a signal receiving apparatus of an OFDM system according to the prior art, and FIG. 2 is a diagram illustrating a frame structure of a general OFDM signal.

The conventional OFDM signal receiving apparatus converts the received signal into a baseband signal having orthogonality through the orthogonal detection means 10, and converts the received signal into an OFDM signal sampled through the sampling unit 41. The output OFDM signal is transmitted to the FFT 30 after the synchronization of each symbol is set through the symbol synchronization setting unit 20. Here, the symbol synchronization setting unit 20 correlates the guard interval (GI) of each symbol included in each frame with respect to the time domain in the sampled OFDM signal output from the orthogonal detection unit 10. Set symbol synchronization by using

The sampled OFDM signal is converted into a signal in the frequency domain through the FFT 30, and transferred to the OFDM demodulation means 70 and finally output as bit streamed data.

On the other hand, the signal of the frequency domain output from the FFT 30 is input to the sampling offset estimator 43 and the carrier frequency control means 50 included in the sampling frequency control means 40. Accordingly, the sampling offset estimation unit 43 included in the sampling frequency control means 40 estimates the offset of the sampling frequency by checking the phase difference between two or more Fourier transformed signals among subcarriers having different frequencies, and sampling frequency. The sampling control unit 45 provided in the control unit 40 controls the frequency of the sampling unit 41 with reference to the offset of the sampling frequency. Then, the carrier frequency control means 50 estimates the offset of the frequency of the carrier signal with respect to the orthogonal detection generated by the orthogonal detection means 10, generates a control signal for setting the synchronization of the carrier frequency, and generates the clock generation means ( 60). As a result, the clock generating means 60 resets the clock frequency based on the control signal and transmits the clock frequency to the orthogonal detection means 10.

In order to set the synchronization of the sampling frequency, the above-described data receiving apparatus should have a separate means for estimating the offset of the sampling frequency of the Fourier transformed signal. In addition, since the offset of the sampling clock is detected using the signal converted into the frequency domain, and the synchronization of the sampling clock generated in the time domain is set by using the offset of the detected sampling clock. It takes time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an OFDM signal demodulation method and a receiving apparatus for implementing the synchronization of a sampling clock by using data generated when setting symbol synchronization in a time domain. The purpose is.

In order to achieve the above object, the OFDM signal demodulation method according to an aspect of the present invention is a method for processing data demodulation by receiving a signal transmitted by the OFDM method, (1) the received OFDM signal is a baseband signal Converting to; (2) converting the baseband signal into a sampled signal; (3) detecting an offset of symbol timing in the sampled signal and setting synchronization of symbols using the detected offset of the symbol timing; (4) performing Fourier transform of the sampled signal in consideration of synchronization of the symbols; And (5) demodulating the Fourier transformed signal by the OFDM scheme, wherein step (1) includes synchronizing the local carrier frequency using the Fourier transformed signal outputted through step (4). In step (2), the synchronization of the sampling frequency is set with reference to the symbol offset value detected in step (3).

In step (3), it is preferable to measure an offset of a symbol by using a correlation of a guard interval (GI) included in each symbol.

An OFDM signal receiving apparatus according to another aspect of the present invention is a device for demodulating data by receiving a signal transmitted by an OFDM method, and detecting orthogonality using a local carrier signal generated therein, and considering the orthogonality. Orthogonal detection means for converting the received OFDM signal into a baseband signal; Sampling frequency control means for converting the signal output from the orthogonal detection means into a sampled signal and outputting the sampled signal; Symbol synchronization setting means for detecting an offset of symbol timing in the sampled signal and setting and outputting symbol synchronization of the sampled signal; Fourier transform means for performing a Fourier transform process on the signal output from the symbol synchronization setting means; OFDM demodulation means for demodulating a signal in a frequency region output from said Fourier transform means based on an OFDM scheme; Carrier frequency control means for estimating the offset of the carrier frequency in the frequency domain signal output from the Fourier transform means and outputting a control signal for setting synchronization; And clock generation means for generating a clock corresponding to the control signal output from the carrier frequency control means and providing the clock signal to the quadrature detection means, wherein the sampling frequency control means refers to the offset range of the symbol output from the symbol synchronization setting means. To set the synchronization of the sampling frequency.

The symbol synchronization setting means preferably measures an offset of a symbol using correlation of a guard interval (GI) included in each symbol.

Sampling frequency control means includes a sampling unit for converting the signal output from the orthogonal detection means into a sampled signal; And a sampling controller configured to control the sampling frequency set by the sampling unit by referring to the symbol offset value received from the symbol synchronization setting unit.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

3 is a block diagram showing a signal receiving apparatus of an OFDM system according to a preferred embodiment of the present invention.

3, an OFDM signal receiving apparatus according to an embodiment of the present invention includes orthogonal detection means 100, sampling frequency control means 130, symbol synchronization setting means 150, Fourier transform means 200, carrier frequency Control means 230, clock generation means 250, and OFDM demodulation means 300.

Orthogonal detection means 100 has a circuit for generating a local carrier signal, detects the orthogonal based on the local carrier signal generated therein, and based on the detected orthogonal OFDM signal transmitted from the OFDM transmitter Convert to a band signal.

The sampling frequency control means 130 converts the baseband signal received from the orthogonal detection means 100 into a sampled signal with reference to the sampling clock pulse.

The symbol synchronization setting unit 130 is a means for receiving the sampled signals and setting the synchronization of each symbol. The symbol synchronization setting unit 130 delays the received sampled signals by one symbol period using a delay unit, and receives the delayed signals and the signals received in real time. An offset of each valid symbol is extracted by checking the correlation generated by the guard interval of GI. A symbol synchronization setting signal for setting the synchronization of each valid symbol is generated using the offset and output to the Fourier transform unit 200.

Furthermore, the aforementioned sampling frequency control means 130 includes a sampling unit 131 and a sampling control unit 135. In detail, the sampling unit 131 performs sampling with reference to the sampling clock pulse of the baseband signal received from the orthogonal detection means 100. The sampling control unit 135 receives the offset of the valid symbol extracted by the symbol synchronization setting unit 130, and controls the sampling unit 131 for acquiring a portion of the offset size to set the synchronization of the sampling clock. Here, a part of the offset size obtained by the sampling frequency control unit 130 is a size for setting sampling synchronization and may be determined experimentally.

As a result, the sampling frequency control means 130 according to the embodiment of the present invention does not estimate a separate sampling offset from the Fourier transformed signal, and easily performs sampling using the offset of the symbol generated in the process of setting the symbol synchronization setting. Synchronization can be set.

The Fourier transforming means 200 extracts the OFDM signal sampled during each valid symbol period by using the symbol synchronization setting signal received from the symbol synchronization setting means 150, and Fourier transforms the extracted signal.

The carrier frequency control means 230 extracts two or more converted signals from subcarriers having different frequencies output from the Fourier transform means 200, and detects a frequency offset of the local carrier signal according to the phase rotation of the converted signals. . Then, the carrier frequency control means 230 generates a carrier frequency control signal for setting the frequency synchronization of the local carrier signal generated by the orthogonal detection means 100 by using the detected frequency offset of the carrier signal.

The clock generating means 250 is a means for providing a clock necessary for the orthogonal detection means 100 to generate a carrier frequency, and the frequency of the clock based on the carrier frequency control signal received from the carrier frequency control means 230. Decide

As a result, the orthogonal detection means 100 controls the local carrier frequency generated therein in consideration of the period of the clock received from the clock generation means 250, and generates an orthogonal reference based on the controlled local carrier frequency. The sampling frequency control unit 130 sets a sampling period using the symbol offset value received from the symbol synchronization setting unit 135, and converts the baseband signal into a sampled signal based on the set sampling period. Output In addition, the Fourier transform means 200 performs a Fourier transform process on the sampled signal based on the symbol synchronization detection signal output from the symbol synchronization setting means 150.

The OFDM demodulation means 300 decodes the Fourier transformed transform signal and finally outputs it as a bit streamed signal.

Through the above configuration, the OFDM signal receiving apparatus according to the embodiment of the present invention sets the carrier frequency synchronization, the sampling clock synchronization, and the symbol synchronization to stably process demodulation by the OFDM scheme of the received signal. have.

Hereinafter, an OFDM signal demodulation method according to an embodiment of the present invention will be described by explaining an operation of an OFDM signal receiving apparatus according to an embodiment of the present invention with reference to the above-described components, and FIGS. 4 and 5.

First, when receiving an OFDM signal from the outside (S10), the orthogonal detection means 100 generates a local carrier signal with reference to the clock received from the clock generating means 250 (S21), and generates the generated local carrier signal Orthogonality is detected as a reference, and the OFDM signal of the signal received from the outside is converted into a baseband signal based on the detected orthogonality (S25).

In addition, the sampling frequency control unit 130 converts the baseband signal into a sampled signal (S35) and outputs the converted signal. The output sampled signal is transmitted to the symbol synchronizing means 150.

Upon receiving the sampled signal (S431), the symbol synchronizing unit 130 confirms that the received signal is a valid symbol period (S432), and delays the sampled signal by a sampling clock corresponding to one symbol period using a delay unit. The correlation generated by the guard interval (GI) of the delayed signal and the signal received in real time is checked (S433), and an offset of each valid symbol is extracted (S434). The symbol synchronization setting signal for setting the synchronization of each valid symbol is generated using the extracted offset (S435) and input to the Fourier transform means 200. Then, the Fourier transforming means 200 extracts the OFDM signal sampled during each valid symbol period based on the symbol synchronization setting signal and performs Fourier transform (S45).

Finally, the Fourier transformed signal is input to the OFDM demodulation means 300 and finally converted into a bit stream signal and outputted (S55).

On the other hand, in order to convert the signal received by the orthogonal detection means 100 into a baseband signal (S25), the carrier frequency of the output signal must be accurately synchronized, and convert the baseband signal into a sampled signal (S35). The sampling clock of the output signal must be synchronized correctly. Therefore, the step S23 of setting the frequency synchronization of the local carrier should be performed before the step S25, and the step S33 of setting the synchronization of the sampling clock should be performed before the step S35.

Hereinafter, a process of setting frequency synchronization of a local carrier (S23) will be described in detail. The carrier frequency control means 250 extracts a converted signal output from the Fourier transform means 200, extracts two or more converted signals from subcarriers having different frequencies, and local carrier signals according to the phase rotation of the converted signal. Detect the frequency offset. The carrier frequency control unit 250 generates a carrier frequency control signal using the detected frequency offset of the carrier signal to control the clock generation period of the clock generator 250. Then, the orthogonal detection means 100 sets the frequency of the local carrier signal based on the clock received from the clock generation means 250.

The process of setting the synchronization of the sampling clock (S33) is performed using the offset size of the symbol extracted in step S434 (see Fig. 5). In detail, the sampling frequency control unit 130 converts the magnitude of the offset extracted in operation S434 (S331 of FIG. 5), and sets a sampling frequency control signal for setting sampling synchronization through the offset value of which the magnitude is converted. It generates and controls the sampling unit 131 for sampling the baseband signal.

As described above, the OFDM signal demodulation method and the reception device therefor set the carrier frequency synchronization, the sampling clock synchronization, and the symbol synchronization to stably process the demodulation by the OFDM scheme of the received signal. Can be. Further, by processing the synchronization of the sampling clock using a signal generated at the time of symbol synchronization setting, the synchronization of the sampling clock can be set with a relatively simple configuration without providing any additional hardware for setting the synchronization of the sampling clock. In addition, by processing the synchronization of the sampling clock in the time domain, the synchronization of the sampling clock can be set relatively quickly compared to the method of setting the synchronization of the sampling clock using the signal converted into the frequency domain.

Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto and will be described below by the person skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of the claims.

According to the OFDM signal demodulation method of the present invention and a receiving apparatus therefor, the following effects are obtained.

First, by setting the synchronization of the sampling clock using a signal generated at the time of symbol synchronization setting, it is possible to set the synchronization of the sampling clock with a relatively simple configuration without providing any additional hardware for checking the offset of the sampling clock.

Second, by processing the synchronization of the sampling clock in the time domain, it is possible to set the synchronization of the sampling clock relatively quickly compared to the method of setting the synchronization of the sampling clock using the signal converted into the frequency domain.

Claims (5)

In the method for receiving data transmitted by the OFDM method and processing data demodulation, (1) converting the received OFDM signal into a baseband signal; (2) converting the baseband signal into a sampled signal; (3) detecting an offset of symbol timing in the sampled signal and setting synchronization of symbols using the detected offset of the symbol timing; (4) performing Fourier transform of the sampled signal in consideration of synchronization of the symbols; And (5) demodulating the Fourier transformed signal by the OFDM method; Step (1) is to set the synchronization of the local carrier frequency using the Fourier transformed signal output through the step (4), The method of claim 2, wherein the step of setting the synchronization of the sampling frequency with reference to the symbol offset value detected in the step (3). The method of claim 1, Step (3), OFDM signal demodulation method characterized by measuring the offset of the symbol using the correlation of the guard interval (GI) included in each symbol. An apparatus for demodulating data by receiving a signal transmitted by an OFDM method, Orthogonal detection means for detecting orthogonality using a local carrier signal generated therein and converting the received OFDM signal into a baseband signal in consideration of the orthogonality; Sampling frequency control means for converting the signal output from the orthogonal detection means into a sampled signal and outputting the sampled signal; Symbol synchronization setting means for detecting an offset of symbol timing in the sampled signal and setting and outputting symbol synchronization of the sampled signal; Fourier transform means for performing a Fourier transform process on the signal output from the symbol synchronization setting means; OFDM demodulation means for demodulating the frequency domain signal output from the Fourier transform means based on the OFDM scheme; Carrier frequency control means for estimating the offset of the carrier frequency in the frequency domain signal output from the Fourier transform means and outputting a control signal for setting synchronization; And And clock generation means for generating a clock corresponding to the control signal output from the carrier frequency control means and providing the clock signal to the quadrature detection means. And the sampling frequency control means sets the synchronization of the sampling frequency with reference to the offset range of the symbols output from the symbol synchronization setting means. The method of claim 3, wherein The symbol synchronization setting means includes: OFDM signal receiving apparatus characterized in that for measuring the offset of the symbol by using the correlation of the guard interval (GI) included in each symbol. The method of claim 3, wherein Sampling frequency control means, A sampling unit converting the signal output from the orthogonal detection means into a sampled signal; And And a sampling controller configured to control a sampling frequency set by a sampling unit by referring to a symbol offset value received from the symbol synchronization setting unit.

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