KR100822885B1 - Frame synchronization setting method of orthogonal frequency division multiplexing system, frame synchronization setting unit using this method, and data receiving apparatus having same - Google Patents

Abstract

The present invention relates to a frame synchronization setting method of an orthogonal frequency division multiplexing system, and more particularly, to stably detect a null symbol at a receiving end of an orthogonal frequency division multiplexing system and to check a period of an OFDM frame to achieve stable frame synchronization. It is about how to set. The frame synchronization setting method according to the present invention is a method for establishing synchronization of an OFDM frame in a process of demodulating data received in an orthogonal frequency division multiplexing (OFDM) scheme, the baseband being transmitted to demodulate data of an OFDM frame. Measures the power of the signal, generates a control signal for controlling the gain of the baseband signal in consideration of the search for the null symbol interval, holds and outputs the signal according to a predetermined period, detects the null symbol interval, and corresponds to the null Generate a symbol detection signal, generate a frame synchronization signal in consideration of the length of the null symbol detection signal and the data interval of the OFDM frame, and gain the baseband signal in consideration of the length of the OFDM frame as the null symbol interval is detected Generates a gain control signal to adjust.

Description

Method for setting up frame sync in Orthogonal Frequency Division Multiplexing system, Unit using the method, and Apparatus having the unit}

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 illustrating a structure of a transmitter / receiver in a physical layer of a general OFDM system.

2 is a diagram illustrating data symbols transmitted in a general OFDM system in units of time and frequency.

3 is a diagram illustrating a structure of a general OFDM frame.

4 is a block diagram showing the configuration of a frame synchronization detecting apparatus according to the prior art.

5 is a configuration diagram schematically showing the configuration of a data receiving apparatus according to a preferred embodiment of the present invention.

6 is a flowchart showing a procedure of a frame synchronization setting method according to a preferred embodiment of the present invention.

7 is a flowchart illustrating a detailed procedure of a process of determining null symbol detection in a frame synchronization setting method according to an exemplary embodiment of the present invention.

8 is a timing diagram illustrating a signal flow in a process of detecting a null symbol signal according to a preferred embodiment of the present invention.

9 is a flowchart illustrating a detailed procedure of generating a frame synchronization signal in the frame synchronization setting method according to an embodiment of the present invention.

10 is a timing diagram illustrating a signal flow in a process of generating a frame synchronization signal according to a preferred embodiment of the present invention.

<Description of main reference numerals in the drawings>

100 ... tuner 200 ... frame sync detection unit

210 ... A / D converter 220 ... Band converter

230 ... AGC unit 231 ... Power measurement unit

232 Gain Gain Unit 233 Constant Water Generation Unit

234 ... selection means 235 ... control signal generator

240 Null symbol detector 241 Average value calculator

242 Threshold calculator 243 Signal generator

250 ... Synchronous signal generator 300 ... OFDM demodulation unit

The present invention relates to a frame synchronization setting method of an orthogonal frequency division multiplexing system, a frame synchronization setting unit using the method, and a data receiving apparatus having the same. More particularly, the detection of a null symbol at a receiving end of an orthogonal frequency division multiplexing system. The present invention relates to a method for stably setting frame synchronization by performing interworking and gain control, checking a period of an OFDM frame, a frame synchronization setting unit using the method, and a data receiving apparatus having the same.

Orthogonal Frequency Division Multiplexing (hereinafter, referred to as OFDM) technology is a fourth generation (4G) modulation technology expected to be adopted as a digital TV standard in Europe, Japan, and Australia. It was first promoted as a wireless LAN (Local Area Network) technology in the early 1990s, and has recently been developed into a cellular system for wireless Internet service by adding mobility to the OFDM-based wireless LAN technology.

The spread spectrum technique of OFDM distributes data over a number of subcarriers spaced at regular intervals at the correct frequency. This frequency spacing provides "orthogonality" within the technique of preventing the demodulator from referring to a frequency other than its own. In addition, the OFDM technology is a kind of multicarrier modulation and shows excellent performance in a multi-path mobile reception environment. Therefore, OFDM technology has attracted attention as a modulation method suitable for terrestrial digital TV and digital voice broadcasting.

1 is a block diagram illustrating a structure of a transmitter / receiver in a physical layer of a general OFDM system. Referring to FIG. 1, an input bit stream to be transmitted is first delivered to a serial / parallel (S / P) converter 12 via an encoder 11. The N / S symbols are then collected by the serial / parallel converter 12 and passed to an Inverse Fast Fourier Transform (IFFT) 13 to convert the transmitted symbols from the frequency domain to the time domain symbols. The parallel / serial converter 14 converts parallel time-domain symbols into serial symbols. Here, the collected N data symbols are referred to as 'OFDM symbols'. Symbols in the time domain obtained through the parallel / serial converter 14 are CP added by a CP (Cyclic Prefix: CP) adder 15 in units of OFDM symbols to remove the influence of the multipath channel. The analog converter 16 converts the signal from the digital domain into the analog domain signal, and then passes through the channel 20 to the receiver.

When the transmission signal is received through the channel 20, the receiver 30 converts the received signal from the analog domain to the digital domain signal through the analog / digital converter 31 and multiplexes through the CP remover 32. The CP is removed from the OFDM symbol contaminated by the influence of the path. The CP-received received signal is converted into a signal in the frequency domain through a fast Fourier transform (FFT) 34 via a serial / parallel converter 33. The received symbols transformed into the frequency domain are passed through an equalizer 35 to cancel the influence of channel interference, and finally passed through a decoder 37 through a parallel / serial converter 36 to output streams of the receiver. Is output.

2 is a diagram illustrating data symbols transmitted in a general OFDM system in units of time and frequency, and FIG. 3 is a diagram illustrating a structure of a typical OFDM frame.

1 to 3, in an OFDM system, data symbols in one OFDM symbol are transmitted on N carriers in units of N, respectively. N data symbols transmitted on the N carriers constitute one OFDM symbol, and the OFDM symbols are collected in M units to form one OFDM frame. In addition, the OFDM frame is composed of a null symbol interval 51 and a data interval 55. In addition, the null symbol section 51 includes a null symbol 52 having no separate data, and the data section 55 includes a reference symbol 56 including information for synchronizing an OFDM symbol with a carrier frequency; Data symbols 57 including data to be transmitted through the OFDM system.

Here, the null symbol interval 51 is an interval inserted to synchronize the OFDM frame in the receiver of the OFDM system. In the OFDM system, the receiver detects the null symbol interval 51 to synchronize the OFDM frame.

4 is a block diagram showing the configuration of a frame synchronization detecting apparatus according to the prior art.

Hereinafter, the operation of the frame synchronization detecting apparatus will be described with reference to FIG. 4. First, the signal received through the reception filter 71 is input to the AGC unit 73 via the band converter 72. The AGC unit 73 automatically adjusts the signal power to fix the received signal level constant. Then, the real part of the signal power input from the AGC unit 73 through the real detection unit 74 is detected, and the absolute value of the real part output from the real detection unit 74 is calculated through the absolute value calculation unit 75 to calculate the LPF 76. ) Then, the LPF 76 removes the noise of the high frequency band mixed with the signal and transmits the noise to the null symbol detector 77, and the null symbol detector 77 uses the power value of the received signal to determine the position of the null symbol. Detect.

However, in the above-described frame synchronization detecting apparatus, the AGC unit 73 always operates, and thus, the null symbol section determines that the strength of the received signal is weaker than the reference signal, thereby increasing the size of the null symbol. Therefore, as the strength of the received signal increases in the null symbol period, the null symbol detection unit 77 cannot accurately detect the null symbol.

As an alternative, a method of not operating the AGC 73 while searching for a null symbol is used. However, when the AGC is not operated, at the very low RF level, the power strength of the null symbol and the power strength of the data of the OFDM frame are used. The difference is not so large that it is difficult to find null symbols. In addition, in a severe fading environment, the null symbol detection unit 77 incorrectly detects a portion in which a signal has weakened due to fading as a null symbol, or fails to detect a null symbol as fading occurs in a null symbol section. Occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and a frame synchronization setting method capable of stably performing null symbol detection and gain control even in an environment in which an orthogonal frequency division multiplexing system is not in good condition, and frame synchronization using this method It is an object of the present invention to provide a setting unit and a data receiving device having the same.

In addition, a frame synchronization setting method capable of reducing the error of detecting a null symbol in an orthogonal frequency division multiplexing system and stably maintaining frame synchronization even when an error of detecting a null symbol occurs, a frame synchronization setting unit using the method, and It is another object to provide a data receiving apparatus provided.

In order to achieve the above object, the frame synchronization setting unit according to an aspect of the present invention receives a signal transmitted by an orthogonal frequency division multiplexing (OFDM) scheme, converts it into a baseband signal, and converts the data of the converted baseband signal. A data receiving apparatus for processing demodulation, wherein the apparatus for setting frame synchronization of the baseband signal before processing data demodulation of the baseband signal, the power of the baseband signal by measuring the power of the baseband signal An AGC unit for estimating the change and adjusting a gain of the signal by comparing the estimated power value with a reference value; A null symbol detection unit that detects a null symbol of an OFDM frame by using the power measured by the AGC unit and generates a null symbol detection signal corresponding thereto; An AGC hold unit for holding a signal output from the AGC unit differentially in a predetermined period in a section for searching for a null symbol and a section after detecting a null symbol based on an output value of the null symbol detection unit; And a synchronization signal generator configured to generate a frame synchronization signal corresponding to the length of a predetermined OFDM frame based on a null symbol detection signal output from the null symbol detection unit.

The AGC unit may generate a control signal for differentially controlling gain in a section for searching for a null symbol and a section after detecting a null symbol based on an output value of the null symbol detector.

The AGC unit comprises a power measurement unit for measuring the power of the baseband signal; A gain adjusting unit generating a gain signal by using a difference between a preset reference value and the measured power value measured by the power measuring unit; A constant generator configured to generate a constant value to be output in a current section by using the measured power value output from the power measurer and a constant value output in a previous section; A control signal generator for generating a control signal for controlling the gain of the baseband signal based on a value received from the gain adjuster or the constant generator; And selection means for selectively transferring a gain signal generated by the gain adjusting unit or a constant value generated by the constant generator with reference to the null symbol detection signal to the control signal generator.

The null symbol detector includes: an average value calculator configured to calculate an average of power values estimated by the AGC unit during a predetermined period; A threshold calculator for calculating a threshold value and outputting the threshold value for a predetermined period; And comparing the power intensity of the measured power value measured by the AGC unit with the threshold value output from the threshold calculator, and checking the null symbol interval as the result value is continuously maintained for a predetermined period, and corresponding null And a detection signal generator for generating a symbol detection signal.

An apparatus for demodulating data by receiving a signal transmitted by an orthogonal frequency division multiplexing (OFDM) scheme according to another aspect of the present invention, comprising: a tuner for extracting a signal of a specific band from a received RF signal; A band converter for digitizing the signal output through the tuner and converting the signal into a baseband signal; A data demodulator for demodulating the baseband signal output from the band converter based on an OFDM scheme; And measuring the power of the baseband signal outputted from the band converter by being connected between the band converter and the data demodulator, estimating a change in the measured power, and comparing the estimated power value with a reference value to obtain a gain of the signal. An AGC unit that adjusts a signal, a null symbol detector that detects a null symbol of an OFDM frame by using the power measured by the AGC unit, and generates a null symbol detection signal corresponding thereto, and a null based on an output value of the null symbol detector. A AGC hold unit for holding a signal output from the AGC unit differentially in a predetermined period in a section for searching for a symbol and a section after detecting a null symbol, and a null symbol detection signal output from the null symbol detection unit; In consideration of the length of a predetermined OFDM frame, a synchronization signal generator for generating a frame synchronization signal corresponding thereto is obtained. Include; for frame synchronization setting unit.

The AGC unit may generate a control signal for differentially controlling gain in a section for searching for a null symbol and a section after detecting a null symbol based on an output value of the null symbol detector.

The AGC unit comprises a power measurement unit for measuring the power of the baseband signal; A gain adjusting unit generating a gain signal by using a difference between a preset reference value and the measured power value measured by the power measuring unit; A constant generator configured to generate a constant value to be output in a current section by using the measured power value output from the power measurer and a constant value output in a previous section; A control signal generator for generating a control signal for controlling the gain of the baseband signal based on a value received from the gain adjuster or the constant generator; And selection means for selectively transferring a gain signal generated by the gain adjusting unit or a constant value generated by the constant generator with reference to the null symbol detection signal to the control signal generator.

The null symbol detector includes: an average value calculator configured to calculate an average of power values estimated by the AGC unit during a predetermined period; A threshold calculator for calculating a threshold value and outputting the threshold value for a predetermined period; And comparing the power intensity of the measured power value measured by the AGC unit with the threshold value output from the threshold calculator, and checking the null symbol interval as the result value is continuously maintained for a predetermined period, and corresponding null And a detection signal generator for generating a symbol detection signal.

According to another aspect of the present invention, there is provided a frame synchronization setting method according to a method of setting synchronization of an OFDM frame in a process of receiving data transmitted by an orthogonal frequency division multiplexing (OFDM) scheme and processing data demodulation. Measuring the power of the baseband signal transmitted to demodulate the data of the OFDM frame; (20) generating a control signal for controlling the gain of the baseband signal in consideration of searching for a null symbol section, and holding and outputting the generated control signal at a predetermined period; (30) detecting a null symbol period and generating a corresponding null symbol detection signal; Generating a frame synchronization signal in consideration of the null symbol detection signal output in step 30 and the length of a data interval of an OFDM frame; And (45) proceeding in parallel with step (40), and generating a gain control signal for adjusting the gain of the baseband signal in consideration of the length of the OFDM frame as a null symbol interval is detected. And, steps (30), (40), and (45) are repeatedly performed.

In step (20), in order to search for a null symbol interval, the measured power value is compared with the constant value output in the previous section, and a constant value to be output in the current section is generated to control the gain of the baseband signal. Generate a control signal.

In step (20), the generated control signal may be held and output according to a period corresponding to the length of the fading period.

In step 45, the generated control signal may be held for a null symbol period in consideration of the length of an OFDM frame.

In step (40), a final value equal to the length of the OFDM frame and an intermediate value calculated through the final value are set in advance, and the count is started based on the intermediate value at the time when the null symbol detection signal is received. After reaching, the count starts again from the initial value and when the intermediate value is reached, the confirmation of the length of the OFDM frame is completed.

The length of the predetermined OFDM frame further includes a length of an error tolerance section based on the intermediate value, and outputs a frame synchronization signal limitedly only when a point where a frame synchronization signal is generated exists within the error tolerance interval. .

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.

5 is a configuration diagram schematically showing the configuration of a data receiving apparatus according to a preferred embodiment of the present invention.

A data receiving apparatus according to an embodiment of the present invention includes a tuner 100, a frame sync detection unit 200, and an OFDM demodulation unit 300.

The tuner 100 extracts a signal of a specific frequency band from the RF signal received through the antenna, and removes a signal of noise component from the extracted signal.

The frame synchronization detecting unit 200 is a unit for detecting frame synchronization in a signal transmitted from the tuner 100 to the OFDM demodulation unit 300, and includes an A / D converter 210, a band converter 220, and an AGC unit. 230, a null symbol detector 240, an AGC hold unit 260, and a synchronization signal generator 260.

The A / D converter 210 converts a signal transmitted from the tuner 100 into a digital signal, and the band converter 220 converts a high frequency carrier into a baseband signal.

The AGC unit 230 is a means for maintaining a constant gain of the signal input to the A / D converter 210 before setting the synchronization of the carrier and the synchronization of the symbol in the received analog signal, the power measuring unit 231 ), A gain control unit 232, a constant generator 233, a selection means 234, and a control signal generator 235.

The power measuring unit 231 is connected between the band converter 220 and the OFDM demodulation unit 300, and continuously measures the power of the signal output from the band converter 220 to output a measured power value. .

The gain adjusting unit 232 compares the measured power value continuously applied from the power measuring unit 231 with the reference power value applied from the outside, generates a difference value, and calculates the generated value to calculate the gain. The gain signal for generating the control signal is provided to the control signal generator 235.

Like the gain adjuster 232, the constant generator 233 is a means for providing the control signal generator 235 with a reference value necessary for generating a control signal for gain control. The constant generator 233 calculates a power value for each section by using the value output from the power measuring unit 231, compares the calculated value with a constant value output in the previous section, and calculates a value calculated in the current section. If the value is larger, the constant value is reduced by the size of a predetermined step. If the value calculated in the current interval is smaller, the constant value is increased by the size of the predetermined step and the output is maintained by one section. Here, if each period is relatively longer than the fading period, fading may affect the delay of the AGC. If the interval is relatively shorter than the null symbol period, the null symbol may be affected by the AGC. Therefore, the interval should be relatively shorter than the fading period according to the RF frequency and relatively longer than the null symbol interval.

The selecting means 234 has an input terminal connected to an output terminal of the gain control unit 232 and the constant generator 233 and an output terminal connected to an input terminal of the control signal generator 235, and selected from the null symbol detector 240. Receive a signal and selectively connect one of the two input terminals to the output terminal. Specifically, the selecting means 234 connects the constant generator 233 to the control signal generator 235 in a section (null symbol search section) where the data receiving apparatus starts to search for a null symbol. In the section after receiving the null symbol detection signal from the detector 240 (the AGC normal operation section), the gain control unit 232 and the control signal generator 235 are connected.

The control signal generator 235 generates a PWM signal using a reference value input through the selection means.

The PWM signal generated by the control signal generator 235 is transmitted to the AGC of the tuner 100 to control the magnitude of the signal input to the frame synchronization detection unit 200 and the OFDM demodulation unit 300.

The null symbol detector 240 is a means for detecting a null symbol of a signal by using the power value measured by the AGC unit 230. The null symbol detector 240, the threshold calculator 242, and the detection signal generator ( 243).

The average value calculator 241 calculates the average value by summing the measured power values output from the power measuring unit 231 of the AGC unit 230 for a predetermined period (eg, about 1/2 times the length of the fading period).

The threshold calculator 242 calculates a threshold for estimating a null symbol using the average value, and maintains and outputs the calculated threshold until the average value of the next section is input. Here, the threshold value may be a value calculated by dividing the average value calculated by the average value calculator 241 by 1/4.

The detection signal generator 243 compares the threshold value input from the threshold calculator 242 and the measured power value measured by the power measurement unit 231 and continuously inputs the signal to determine a null symbol section or data section of the OFDM frame. In addition, a corresponding null symbol detection signal is generated and transmitted.

In detail, when the detection signal generator 243 receives a measurement power value relatively smaller than the threshold value from the power measurement unit 231, the detection signal generator 243 operates a first counter (not shown) to count a predetermined time. In addition, the detection signal generator 243 continuously determines that the null symbol section is started when the measured power value is relatively smaller than the threshold value during the operation time of the first counter, and the measured power value is thresholded. Wait for it to be larger than its value. In the state where the null symbol interval is maintained, the magnitude of the measured power value input from the power measurement unit 231 is equal to the threshold value by continuously comparing the measured power value input from the power measurement unit 231 with the magnitude of the threshold value. When it is relatively larger, the second counter (not shown) is operated to count a predetermined time. In addition, the detection signal generator 243 determines that the null symbol section is terminated and the data section is started when the measured power value is relatively larger than the threshold value for the duration of the operation of the second counter. As a result, the detection signal generator 243 transmits a null detection signal to the synchronization signal generator 260.

On the other hand, the detection signal generator 243 stops the counting operation of the first counter when the measured power value that is relatively larger than the magnitude of the threshold value is input from the power measuring unit 231 during the operation time of the first counter. Set to a value. As a result, it is possible to prevent the measurement power value from rising temporarily due to fading and an error occurs in the detection of the null symbol section.

Furthermore, the AGC hold unit 250 is a means for holding and outputting the control signal output from the AGC unit 240 in a predetermined period unit, and the period and length for holding the control signal in the null symbol search section and the AGC normal operation section. Set differently. In detail, the AGC hold unit 250 holds the gain control signal generated based on the signal output from the constant generator 233 in a period unit corresponding to the length of the fading period during the null symbol search period, and normal AGC hold. During the operation period, the gain control signal generated based on the signal output from the gain control unit 232 is held in each period in which the null symbol is positioned in a period corresponding to the length of the ODM frame, and finally transmitted to the tuner 100.

As a result, the AGC unit 230 and the AGC hold unit 250 adjust the signal size by gradually increasing or decreasing the gain level in predetermined intervals during the null symbol search period, and adjusting the OFDM during the AGC normal operation period. The null symbol detection error of the null symbol detector 240 may be reduced by holding the output signal without adjusting the gain of the signal during the null symbol period of the frame.

Accordingly, the AGC unit 230 and the AGC hold unit 250 may stably adjust the gain in consideration of the interval for searching for a null symbol and the normal operation period for AGC, and further, as the gain is stably adjusted, the null symbol interval or The detection of the data section can also proceed stably.

The synchronization signal generator 260 generates a frame synchronization signal in consideration of the null symbol detection signal received from the null symbol detector 240 and the length of the OFDM frame. In detail, when the synchronization signal generator 260 receives a null symbol detection signal, the synchronization signal generator 260 operates a frame counter that repeatedly counts a length of a preset OFDM frame. When the frame counter counts as much as the length of the OFDM frame, the counter starts from the middle value of the length of the OFDM frame set in the frame counter and is reset when the count is completed by the set length. . In addition, since the null symbol detection signal is generated after the second counter is operated at the start of the data period of the OFDM frame, the frame synchronization signal is generated when the length of the operation period of the second counter is subtracted from the length of the data period of the OFDM frame. do. In addition, since the frequency of the clock for operating the frame counter may be changed when the frame counter counts as much as the length of the OFDM frame, the frame counter is initialized based on the timing at which the null symbol detection signal is generated.

In addition, the time point at which the second counter completes the operation may be generated differently according to the change of the channel environment. For this reason, when the second counter is terminated early, the time at which the operation of the frame counter starts is advanced, and as a result, the time at which the frame synchronization signal is generated is advanced. Accordingly, the synchronization signal generator 260 sets an error tolerance interval based on the intermediate value in consideration of the error range at the completion time of the counter of the second counter generated according to the change in the channel environment, and counts the frame counter. The frame counter is initialized by checking whether a value belongs to the error tolerance interval. That is, the synchronization signal generator 260 first checks whether the counted value of the frame counter is within an error allowable range before initializing the frame counter upon receiving a null symbol detection signal, and thus falls within an error allowable range. Only initialize the frame counter.

In this way, the synchronization signal generator 260 can stably initialize the frame counter even when receiving the wrongly generated null symbol detection signal from the detection signal generator 243, and stably generate the frame synchronization signal of the next OFDM frame. can do.

The OFDM demodulation unit 300 receives a baseband signal output from the band converter 220, removes a cyclic prefix (CP) or guard interval (GI) present in the signal, and removes the signal from the fast fourier. The transform is transformed into the frequency domain through the transform, and the interference between the channels of the transformed signal through equalization is eliminated, and finally, the signal is output as a bit stream through decoding.

Hereinafter, the operation of the data receiving apparatus of the OFDM system according to the preferred embodiment of the present invention with reference to the above-described components and FIGS. 6 to 10, the data receiving method of the OFDM system according to the preferred embodiment of the present invention Explain.

First, a signal having a frequency of a specific band received through an antenna (S11) is amplified and filtered through the tuner 100, and the gain is adjusted and output through the AGC. The signal output through the tuner 100 is converted into a baseband signal through the A / D converter 210 and the band converter 220 (S12).

The converted baseband signal is transmitted to the OFDM demodulation unit 300 (S13).

In addition, the frame synchronization detecting unit 200 is connected between the band converter 220 and the OFDM demodulation unit 300 to estimate the synchronization of the baseband signal transmitted to the OFDM demodulation unit 300. First, the power measuring unit 211 continuously measures and provides the power strength of the baseband signal (S21).

The null symbol detection unit 240 searches for a null symbol section using the power value measured in step S21 (S31), and detects a null symbol (S41).

When the null symbol is not detected in step S41 (S41-N), that is, after the operation of the data receiving apparatus starts, the selecting means 234 does not receive a separate null symbol detection signal from the detection signal generator 243. If not, the selecting means 234 connects the constant generator 233 and the control signal generator 235 and calls the constant generator 233. Then, the constant generator 233 generates a predetermined initial constant value and outputs it (S51), integrates the power value received from the power measuring unit 231 for a predetermined period, and calculates an average value (S52). In addition, the calculated average value is compared with the constant value output in the previous section, and if the current average value is relatively larger than the constant value output in the previous section, the size of the constant value is decreased by the size of a predetermined step. When the current average value is relatively smaller than the constant value output in the previous section, the constant value is increased by the predetermined step size and output. The constant value output from the constant generator 233 is transferred to the AGC hold unit 260 through the control signal generator 235, and the AGC hold unit 260 controls the PWM received from the control signal generator 235. The signal is held during the fading period to adjust the gain of the signal output from the tuner 100 (S54).

When a null symbol is detected in step S41 (S41-Y), the selecting means 234 connects the gain control unit 232 and the control signal generator 235 and calls the gain control unit 232. Then, the gain adjusting unit 232 generates and outputs a gain signal having a magnitude necessary for gain control by comparing the measured power value with a reference power value (S61). The gain signal output from the gain control unit 232 is transmitted to the AGC hold unit 260 through the control signal generator 235, the AGC hold unit 260 is controlled during the data period in consideration of the length of the OFDM frame The gain of the signal output from the tuner 100 is adjusted using the PWM control signal received from the signal generator 235, and during the null symbol period, the PWM control signal received from the control signal generator 235 is used. The gain of the signal output from the tuner 100 is adjusted (S62).

When a null symbol is detected in step S41 (S41-Y), the synchronization signal generator 260 generates a frame synchronization signal using the null symbol detection signal in parallel with steps S61 through S62 (S65). .

Finally, the OFDM demodulation unit 300 performs data demodulation of the OFDM frame in consideration of the frame synchronization signal input from the synchronization signal generator 260 (S71).

7 is a flowchart illustrating a detailed procedure of a process of determining null symbol detection in a frame synchronization setting method according to a preferred embodiment of the present invention, and FIG. 8 is a process of detecting a null symbol signal according to a preferred embodiment of the present invention. This is a timing chart showing the signal flow of.

Hereinafter, operation S41 will be described in detail with reference to FIGS. 7 and 8.

The measured power value output from the power measuring unit 211 is provided to the average value calculating unit 241 and the detection signal generator 243. The power value transmitted to the average value calculator 241 is calculated and output by the average value calculator 241 as the average power value for a predetermined period (eg, about 1/2 times the length of the fading period) (S411). The average power value is calculated as a threshold value (eg, 1/4 of the average power value) through the threshold calculator 242 and transmitted to the detection signal generator 243 (S412). Accordingly, the detection signal generator 243 uses the measured power value received from the power measurement unit 211 and the signal for instructing null symbol detection using the threshold value received from the threshold calculator 242 (null symbol). Detection signal). In detail, the detection signal generator 243 compares the measured power value with a threshold value (S413) so that a state in which the measured power value is relatively smaller than the magnitude of the threshold value is determined for a predetermined period (first counter operation period 511). If it is continued (S414, S415, S416), it is determined (S416-Y) that the null symbol interval is started. In addition, the detection signal generator 243 waits in the state where the null symbol period is started (S417) and compares the measured power value with a threshold value (S418) so that the measured power value is relatively larger than the magnitude of the threshold value. If the duration (S419, S420, S421) is continued for a predetermined period (second counter operation period 513), it is determined that the null symbol interval is terminated and the data interval starts (S421-Y). Accordingly, the detection signal generator 243 outputs a null symbol detection signal (S422).

9 is a flowchart illustrating a detailed procedure of generating a frame synchronization signal in a frame synchronization setting method according to an embodiment of the present invention, and FIG. 10 is a process of generating a frame synchronization signal according to an embodiment of the present invention. This is a timing chart showing the signal flow of.

Hereinafter, step S65 will be described in detail with reference to FIGS. 9 and 10.

Initially, as the synchronization signal generator 260 receives a null symbol detection signal from the null symbol detector 240 (S651), the frame counter starts counting from the median of the OFDM frame length (S652), and sets the length. When the count is completed, the count is reset, and the count proceeds from 0 to the intermediate value again (S653). When the frame counter proceeds to count, a point at which a frame synchronization is to be generated (that is, a point at which the data period of the OFDM frame starts, calculated from the intermediate value in consideration of the second counter operation period) is reached (S654). Then, the synchronization signal generation unit 260 checks whether the count of the frame counter reaches the error tolerance section (S655). If the number of counts of the frame counter exists within the error tolerance interval (S655-Y), the synchronization signal generator 260 generates a frame synchronization signal (S656). On the other hand, if the number of counts of the frame counter does not exist within the error tolerance period (S655-N), counting continues without generating a frame synchronization signal (S653).

As described above, according to the present invention, the AGC is controlled in consideration of the null symbol interval or the data interval, so that the gain can be stably adjusted, and the null symbol detection can be stably performed as the gain is stably adjusted. In addition, even when the null symbol detection position is found incorrectly or not, the frame synchronization can be stably detected.

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 frame synchronization setting method of the present invention, a frame synchronization setting unit using the method, and a data receiving apparatus having the same, a null symbol can be stably detected at a low RF level or in an environment with heavy fading, Frame synchronization can be stably generated even when the data section is incorrectly detected or failed to be detected.

Claims (14)

A data receiving apparatus for receiving a signal transmitted by an orthogonal frequency division multiplexing (OFDM) scheme, converting the signal into a baseband signal, and processing data demodulation of the converted baseband signal, and processes data demodulation of the baseband signal. In the apparatus for setting the frame synchronization of the baseband signal, An AGC unit for measuring the power of the baseband signal, estimating a change in the measured power, and adjusting a gain of the signal by comparing the estimated power value with a reference value; A null symbol detection unit that detects a null symbol of an OFDM frame by using the power measured by the AGC unit and generates a null symbol detection signal corresponding thereto; An AGC hold unit for holding a signal output from the AGC unit differentially in a predetermined period in a section for searching for a null symbol and a section after detecting a null symbol based on an output value of the null symbol detection unit; And And a synchronization signal generator for generating a frame synchronization signal corresponding to a predetermined OFDM frame length based on a null symbol detection signal output from the null symbol detection unit. . The method of claim 1, And the AGC unit generates a control signal for differentially controlling gain in a section for searching for a null symbol and a section after detecting a null symbol based on an output value of the null symbol detection unit. The method of claim 2, The AGC unit, A power measuring unit measuring power of the baseband signal; A gain adjusting unit generating a gain signal by using a difference between a preset reference value and the measured power value measured by the power measuring unit; A constant generator configured to generate a constant value to be output in a current section by using the measured power value output from the power measurer and a constant value output in a previous section; A control signal generator for generating a control signal for controlling the gain of the baseband signal based on a value received from the gain adjuster or the constant generator; And And selecting means for selectively transmitting a gain signal generated by a gain control unit or a constant value generated by a constant generator to a control signal generator with reference to the null symbol detection signal. The method according to any one of claims 1 to 3, The null symbol detection unit, An average value calculator for calculating an average of power values estimated by the AGC unit for a predetermined period; A threshold calculator for calculating a threshold value and outputting the threshold value for a predetermined period; And Comparing the power intensity of the measured power value measured by the AGC unit with the threshold value output from the threshold calculator, and checks the null symbol interval as the result value is continuously maintained for a certain period, and corresponding null symbol And a detection signal generator for generating a detection signal. An apparatus for demodulating data by receiving a signal transmitted by an orthogonal frequency division multiplexing (OFDM) scheme, A tuner for extracting a signal of a specific band from the received RF signal; A band converter for digitizing the signal output through the tuner and converting the signal into a baseband signal; A data demodulator for demodulating the baseband signal output from the band converter based on an OFDM scheme; And The power of the baseband signal connected between the band converter and the data demodulator is measured to estimate the change of the measured power, and the gain of the signal is compared with the estimated power and the reference value. A null symbol detection unit for detecting a null symbol of an OFDM frame and generating a null symbol detection signal corresponding thereto by using an AGC unit for adjusting, a power measured by the AGC unit, and a null symbol based on an output value of the null symbol detection unit Based on the AGC hold unit for holding a signal output from the AGC unit in a predetermined period unit in a section for searching for and a section after detecting a null symbol, and a null symbol detection signal output from the null symbol detection unit And a synchronization signal generator for generating a frame synchronization signal corresponding thereto in consideration of the predetermined length of the OFDM frame. And a frame synchronization setting unit. The method of claim 5, And the AGC unit generates a control signal for differentially controlling gain in a section for searching for a null symbol and a section after detecting a null symbol based on an output value of the null symbol detection unit. The method of claim 6, The AGC unit, A power measuring unit measuring power of the baseband signal; A gain adjusting unit generating a gain signal by using a difference between a preset reference value and the measured power value measured by the power measuring unit; A constant generator configured to generate a constant value to be output in a current section by using the measured power value output from the power measurer and a constant value output in a previous section; A control signal generator for generating a control signal for controlling the gain of the baseband signal based on a value received from the gain adjuster or the constant generator; And And a selection unit for selectively transmitting a gain signal generated by a gain control unit or a constant value generated by a constant generator to a control signal generator with reference to the null symbol detection signal. The method according to any one of claims 5 to 7, The null symbol detection unit, An average value calculator for calculating an average of power values estimated by the AGC unit for a predetermined period; A threshold calculator for calculating a threshold value and outputting the threshold value for a predetermined period; And Comparing the power intensity of the measured power value measured by the AGC unit with the threshold value output from the threshold calculator, and checks the null symbol interval as the result value is continuously maintained for a certain period, and corresponding null symbol And a detection signal generator for generating a detection signal. In the method of setting the synchronization of the OFDM frame in the process of receiving the signal transmitted by the orthogonal frequency division multiplexing (OFDM) method and processing data demodulation, (10) measuring the power of the baseband signal transmitted to demodulate the data in the OFDM frame; (20) generating a control signal for controlling the gain of the baseband signal in consideration of searching for a null symbol section, and holding and outputting the generated control signal at a predetermined period; (30) detecting a null symbol period and generating a corresponding null symbol detection signal; Generating a frame synchronization signal in consideration of the null symbol detection signal output in step 30 and the length of a data interval of an OFDM frame; And (45) proceeding in parallel with step (40), and generating a gain control signal for adjusting the gain of the baseband signal in consideration of the length of the OFDM frame as a null symbol interval is detected; , And (30), (40), and (45) are repeatedly performed. The method of claim 9, Step (20) is In order to search for a null symbol section, comparing the measured power value with the constant value output in the previous section to generate a constant value to be output in the current section to generate a control signal for controlling the gain of the baseband signal. A frame synchronization setting method characterized by the above-mentioned. The method according to claim 9 or 10, Step (20) is And generating and holding the generated control signal according to a period corresponding to the length of a fading period. The method of claim 11, Step 45 is And holding the generated control signal during a null symbol period in consideration of the length of an OFDM frame. The method of claim 9, Step (40), The final value as long as the length of the OFDM frame and the intermediate value calculated through the final value are set in advance, and when the null symbol detection signal is received, counting is started based on the intermediate value to reach the final value and then again. And checking the length of the OFDM frame when the count starts from the initial value and reaches the intermediate value. The method of claim 13, The length of the predetermined OFDM frame further includes a length of an error tolerance section based on the intermediate value, and outputs a frame synchronization signal limitedly only when the point where the frame synchronization signal is generated is within the error tolerance interval. Frame synchronization setting method, characterized in that.

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