JP2006211441A - Ofdm demodulator, integrated circuit, ofdm demodulating method and receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a synchronous pull-in time in response to a transmission path environment in a carrier reproduction and a sampling clock reproduction. <P>SOLUTION: This device comprises an oscillator for outputting a signal having a given frequency; a quadrature demodulation part for performing quadrature demodulation of an OFDM signal input depending on a signal generated by the oscillator, a delay part for delaying an output of the quadrature demodulation part for a time corresponding to a period of a valid symbol, a correlative calculator for calculating a correlation between the output of the quadrature demodulation and an output of the delay part, a standardization part for standardizing an amplitude of an output signal of the correlative calculator, a section integrator for section-integrating an output of the standardization part in response to a guard interval period, a frequency error detector for detecting a frequency offset depending on an output of the section integrator, a reliability determinator for determining a reliability of the frequency offset depending on the output of the section integrator, and a control unit for controlling an oscillation frequency of the oscillator depending on outputs of the frequency error detection part and the reliability determinator. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a carrier recovery unit and a sampling clock recovery unit in an OFDM (Orthogonal Frequency Division Multiplexing) system demodulator used in domestic terrestrial digital broadcasting and the like.

  The OFDM system is adopted in the domestic terrestrial digital broadcasting system (ISDB-T: Integrated Services Digital Broadcasting-Terrestrial transmission, Non-Patent Document 1) and the European terrestrial digital broadcasting system (DVB-T: Digital Video Broadcasting, etc.). This is a multi-carrier digital transmission system. The OFDM method is a transmission method with good frequency utilization efficiency and suitable for high-speed data communication.

  First, an OFDM signal transmission symbol will be described using the ISDB-T system as an example.

  An OFDM signal is composed of a plurality of transmission symbols. Each transmission symbol is composed of an effective symbol and a guard interval as shown in FIG. The guard interval is arranged before the effective symbol, and a part of the effective symbol (the rear part in the ISDB-T system) is copied.

  Next, carrier recovery and sampling clock recovery in the OFDM method will be described.

  In general, when receiving an OFDM signal, it is necessary to reproduce and demodulate a sampling clock and a carrier wave set on the transmission side on the reception side. At this time, for example, if there is a shift (frequency offset) between the recovered carrier frequency and the carrier frequency set on the transmission side, interference (ICI: Inter Carrier Interference) occurs between the carriers of the OFDM signal. And the received signal quality is degraded. Similarly, with respect to the sampling clock, ICI is generated due to a deviation (timing offset) from the timing set on the transmission side, and the received signal quality is deteriorated. That is, in the OFDM reception / demodulation, in order to achieve better reception quality, it is necessary to set the frequency offset and timing offset to “0”. A state where the frequency offset and the timing offset are “0” on the receiving side is referred to as a “synchronization established state”.

  Here, the operation at the time of power-on or reception signal tuning will be considered. In the state immediately after the start of reception, there are a frequency offset and a timing offset. The demodulator estimates the frequency offset and timing offset values from the received signal, and controls carrier recovery and sampling clock recovery based on the estimated offset values. At this time, since the estimated offset value has an error due to the influence of the transmission path environment or the like, in general, a contrivance is made so that the control amount gradually changes using a loop filter or the like. By this action, the offset value gradually approaches “0” from the reception start time point, and reaches a synchronization establishment state. The transition time from the reception start time to the synchronization establishment state is called “synchronization pull-in time”. The synchronization pull-in time is mainly determined by the time constant of the loop filter. If the time constant is heavy, the synchronization pull-in time increases, but stable reception is possible even if the estimated value error is large.If the time constant is light, the synchronous pull-in time decreases, but the estimated value error is large. The reception becomes unstable.

  Patent Document 1 discloses a demodulator that can easily remove a timing offset and a frequency offset in a multicarrier (OFDM) communication system.

  The conventional technique described in Patent Document 1 will be described below with reference to the drawings.

  FIG. 6 shows an embodiment of a conventional OFDM demodulator in Patent Document 1. In FIG. 6, the signal input from the input terminal 701 is supplied to the frequency conversion circuit 702. The frequency conversion circuit 702 converts an input signal based on the frequency generated by the frequency generation circuit 712 into a baseband signal. The signal frequency-converted by the frequency conversion circuit 702 is supplied to the sampling means 703 and sampled at a predetermined timing. The sampled signal is supplied to a fast Fourier transform circuit (FFT circuit) 704, converted from a time domain signal to a frequency domain signal, and output from an output terminal 705. In general, a signal converted into the frequency domain is subjected to detection and error correction and reproduced as digital data, but it is not shown here.

  In the invention according to Patent Document 1, the data output from the sampling means 703 is held (delayed) by the data holding unit 706 for a time corresponding to the effective symbol period of the OFDM transmission symbol. Next, the correlation detection circuit 707 calculates the correlation between the delayed signal and the output signal of the sampling means 703. The correlation calculation can be performed by complex conjugate multiplication of the output signal of the sampling means 703 and the delayed data. Next, the interval integration circuit 708 performs interval integration on the output signal of the correlation detection circuit 707 over a time corresponding to the guard interval period of the OFDM transmission symbol. The peak detection circuit 709 detects the time when the power of the interval integration output signal is maximum. The phase detection circuit 710 determines the phase at the peak position of the interval integration output based on the output of the peak detection circuit 709. The division circuit 711 divides the output of the phase detection circuit 710 by the time length corresponding to the effective symbol period, and outputs the result to the frequency generation circuit 712. The sampling means 703 compares the output of the peak detection circuit 709 with its own sampling timing and corrects the sampling timing. The frequency generation circuit 712 corrects its own oscillation frequency based on the output of the division circuit 711.

  The principle of removing frequency offset and timing offset in the above configuration will be described.

  As shown in FIG. 7A, an OFDM signal transmission symbol is composed of an effective symbol and a guard interval. Since the guard interval is a copy of the rear part of the effective symbol, the signal delayed in the effective symbol period (FIG. 7B) and the received signal have a high correlation. That is, as for the output of the correlation detection circuit 707, as shown in FIG.7 (c), a high correlation is observed in a guard interval area. The interval integration circuit 708 integrates this correlation signal over the guard interval interval. Therefore, the output is a triangular signal as shown in FIG. Here, paying attention to the peak of the interval integral output, the interval integral output peak just indicates a transmission symbol boundary.

  The sampling means 703 can correct the sampling timing and remove the timing offset by detecting the time error between the transmission symbol timing generated by itself and the detected transmission symbol boundary.

  It is assumed that the carrier wave frequency is fc, the frequency generated by the frequency generation circuit 712 is fc ′, and there is a frequency offset Δfc (fc ′ = fc + Δfc). At this time, the reception signal r (t) is expressed as (Equation 1) when the transmission signal s (t) is used.

  The output of the correlation detection circuit is expressed as (Equation 2).

  As shown in (Expression 2), a correlation having a constant phase (exp (j2πΔfc · Tu)) is observed in the output of the correlation detection circuit in the guard interval section.

  This signal is subjected to interval integration, and the phase of the interval integration output at the peak position has a phase rotation (exp (j2πΔfc · Tu)) due to the carrier frequency error Δfc. By controlling the frequency generated in the frequency generation circuit 712 based on this phase detection amount, the frequency offset can be removed.

  Generally, in the above-described timing offset and frequency offset removal, in order to realize stable control, the estimated offset is input to the loop filter so that the control amount changes gently.

The time constant of the loop filter is set so that the sampling clock recovery and the carrier wave recovery operate stably even in the worst situation among the receivable transmission path environments. In order to realize a more stable operation, the time constant in the synchronization pull-in time and the time constant in the synchronization establishment state can be switched.
Japanese Patent No. 3421880 Standard “Digital Terrestrial Television Broadcasting Transmission System” ARIB STD-B31

  Here, attention is focused on the synchronization pull-in time.

  If the synchronization pull-in time becomes long, for example, in television broadcasting, the time until the viewer actually views the video at power-on and channel selection increases, and the convenience is greatly impaired.

  In addition, in the DVB-H system (DVB-T: Digital Video Broadcasting-Handheld), which is a digital television broadcasting system for portable terminals that has been standardized in Europe in recent years, the synchronization pull-in time is the consumption of the demodulator. The power will be greatly affected. This is because the DVB-H system is a system in which a plurality of services are time-division multiplexed, and the demodulator is a system for reducing the power consumption of the terminal by turning on the power only when receiving a desired service. to cause. As for the power-on timing of the demodulator, it is necessary to assume the synchronization pull-in time in advance and turn on the power earlier than a desired service reception start time. That is, when the synchronization pull-in time is long, the power-on period is increased accordingly, and the power consumption is increased.

  As described above, the synchronization pull-in time is an important factor regarding not only the convenience for the user but also the power consumption of the terminal.

  However, in the prior art, in order to realize stable control even in a poor reception environment, it is usually necessary to set a heavy time constant of the loop filter. For this reason, for example, even in a good transmission path environment, there is a problem that the same synchronization pull-in time is required as in a poor situation.

  The present invention has been made in view of the above-described conventional problems, and realizes optimum synchronization pull-in according to the state of the transmission path environment and shortens the synchronization pull-in time.

  In order to solve the above-described conventional problems, an OFDM demodulator according to the present invention is an OFDM demodulator that demodulates an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals, and includes an orthogonal demodulator, a delay unit, and the like. A correlation calculation unit, an interval integration unit, a normalization unit, a reliability determination unit, a frequency error detection unit, a control unit, and an oscillation unit, the oscillation unit having a predetermined frequency The orthogonal demodulation unit orthogonally demodulates the input OFDM signal based on the signal generated by the oscillation unit, and the delay unit performs a time corresponding to the period of the effective symbol, The output is delayed, the correlation calculation unit calculates the correlation between the output of the orthogonal demodulation unit and the output of the delay unit, the normalization unit normalizes the amplitude of the output signal of the correlation calculation unit, Interval product The section integrates the output of the normalization section according to the guard interval period, the frequency error detection section detects a frequency offset based on the output of the section integration section, the reliability determination section, The reliability of the frequency offset is determined based on the output of the interval integration unit, and the control unit controls the oscillation frequency of the oscillation unit based on the outputs of the frequency error detection unit and the reliability determination unit.

  By providing the above-described configuration, the OFDM demodulator according to the present invention can determine the reliability of the frequency offset according to the transmission path environment by the reliability determination unit. Thereby, it is possible to provide an OFDM demodulator that shortens the synchronization pull-in time of the carrier recovery unit according to the transmission path environment.

  An OFDM demodulator that demodulates an OFDM signal composed of transmission symbols including effective symbols and guard intervals, a sampling unit, a delay unit, a correlation calculation unit, an interval integration unit, a normalization unit, A reliability determination unit; a timing error detection unit; a control unit; and an oscillation unit. The oscillation unit generates a signal having a predetermined frequency. The sampling unit is generated by the oscillation unit. The OFDM signal input based on the signal is sampled, the delay unit delays the output of the sampling unit for a time corresponding to the period of the effective symbol, and the correlation calculation unit includes the output of the sampling unit and the delay The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit, and the interval integration unit calculates the output of the normalization unit. Interval integration according to the guard interval period, the timing error detection unit detects a timing offset based on the output of the interval integration unit, the reliability determination unit is based on the output of the interval integration unit, The reliability of the timing offset may be determined, and the control unit may constitute an OFDM demodulator that controls the oscillation frequency of the oscillation unit based on the outputs of the timing error detection unit and the reliability determination unit.

  With the above configuration, an OFDM demodulator that shortens the synchronization pull-in time according to the transmission path environment can be provided in the sampling clock recovery unit as well.

  An OFDM demodulator that demodulates an OFDM signal composed of a transmission symbol composed of a valid symbol and a guard interval, comprising: an orthogonal demodulator, a delay unit, a correlation calculator, a first interval integrator, 2 interval integration unit, normalization unit, reliability determination unit, frequency error detection unit, control unit, and oscillation unit, the oscillation unit generates a signal having a predetermined frequency, The orthogonal demodulation unit orthogonally demodulates an input OFDM signal based on the signal generated by the oscillation unit, and the delay unit delays the output of the orthogonal demodulation unit for a time corresponding to the period of the effective symbol. The correlation calculation unit calculates a correlation between the output of the orthogonal demodulation unit and the output of the delay unit, the normalization unit normalizes the amplitude of the output signal of the correlation calculation unit, and the first interval The integration unit is the correlation calculation The second interval integration unit integrates the output of the normalization unit according to the guard interval period, and the frequency error detection unit A frequency offset is detected based on the output of the first interval integration unit, the reliability determination unit determines the reliability of the frequency offset based on the output of the second interval integration unit, and the control unit includes: An OFDM demodulator that controls the oscillation frequency of the oscillation unit based on the outputs of the frequency error detection unit and the reliability determination unit may be configured.

  With the above configuration, it is possible to improve error detection accuracy in the frequency error detection unit.

  An OFDM demodulator that demodulates an OFDM signal composed of a transmission symbol composed of a valid symbol and a guard interval, the sampling unit, a delay unit, a correlation calculation unit, a first interval integration unit, a second An interval integration unit, a normalization unit, a reliability determination unit, a timing error detection unit, a control unit, and an oscillation unit, the oscillation unit generates a signal having a predetermined frequency, The sampling unit samples the input OFDM signal based on the signal generated by the oscillation unit, the delay unit delays the output of the sampling unit for a time corresponding to the period of the effective symbol, and the correlation calculation The unit calculates a correlation between the output of the sampling unit and the output of the delay unit, and the normalization unit normalizes the amplitude of the output signal of the correlation calculation unit, and the first section The integration unit integrates the output of the correlation calculation unit according to the guard interval period, and the second interval integration unit integrates the output of the normalization unit according to the guard interval period, The timing error detection unit detects a timing offset based on the output of the first interval integration unit, and the reliability determination unit determines the reliability of the timing offset based on the output of the second interval integration unit. The control unit may configure an OFDM demodulator that controls an oscillation frequency of the oscillation unit based on outputs of the timing error detection unit and the reliability determination unit.

  With the above configuration, the error detection accuracy in the timing error detection unit can be improved.

  In the OFDM demodulator according to the present invention, in the conventional OFDM demodulator, means for determining the reliability of the detected offset amount in the carrier recovery unit and the sampling clock recovery unit that performed constant control regardless of the transmission path environment. Is provided. By performing the control based on the reliability, for example, it is possible to control the OFDM demodulator so that it can shift to the synchronization establishment state more quickly in a good transmission path environment.

  That is, it is possible to provide an OFDM demodulator that shortens the synchronization pull-in time of the carrier recovery unit according to the transmission path environment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment)
FIG. 1 shows a configuration of a digital television receiver using an OFDM demodulator according to an embodiment of the present invention. In the embodiment of the present invention, a digital television receiver is taken as an example, but the OFDM demodulator according to the present invention can be applied to other communication devices using the OFDM system.

  The signal received by the antenna 1 is selected by the tuner 2. The A / D conversion unit 3 samples the selected signal and converts it into digital data. The orthogonal demodulator 4 performs frequency conversion on the digital data and outputs a baseband signal. The baseband signal is input to the FFT unit 5 and converted from a time domain signal to a frequency domain signal. The frequency domain signal is subjected to removal of distortion due to the transmission path by the detection unit 6 and is reproduced as digital data by the error correction unit 7. The reproduced digital data is converted into a video / audio signal by the decoder unit 8 and provided to the viewer by the audio output device 9 and the video output device 10. The sampling clock reproduction unit 11 reproduces the sampling frequency set on the transmission side from the output of the quadrature demodulation unit 4 and outputs it to the A / D conversion unit 3. The carrier recovery unit 12 recovers the carrier frequency set on the transmission side from the output of the orthogonal demodulation unit 4 and outputs the carrier frequency to the orthogonal demodulation unit 4.

  Next, the carrier recovery unit 12 will be described with reference to FIG. The delay unit 13 delays the output of the orthogonal demodulation unit 4 by a time corresponding to the effective symbol period of the OFDM transmission symbol. The correlation calculation unit 14 calculates the correlation between the output of the delay unit 13 and the output of the orthogonal demodulation unit 4. The correlation calculation can be realized by, for example, complex conjugate multiplication. The normalization unit 15 normalizes so that the amplitude of the output of the correlation calculation unit 14 is constant. Normalization can be realized, for example, by dividing the real component and the imaginary component by the amplitude of the signal. The interval integration unit 16 integrates the output of the normalization unit 15 over an interval corresponding to the guard interval period of the OFDM transmission symbol. The error detection unit 18 detects a carrier frequency offset from the signal of the interval integration unit 16. The carrier frequency offset detection can be detected based on the phase at the maximum power point as described in the prior art. Alternatively, for example, the center of gravity of the waveform of the interval integral output (a point where the power of the interval integral output is equally divided) can be used regardless of the maximum power point. The reliability determination unit 17 determines the reliability of the frequency offset output from the error detection unit 18 based on the power of the interval integration unit output. The reliability can be, for example, the maximum power of the interval integration output. Or it is good also as average electric power of an interval integration part output. Or it can also be made into the electric power in the gravity center point of an interval integration part output. The loop filter unit 19 controls the time constant of the frequency offset output from the error detection unit 18 based on the reliability signal output from the reliability determination unit 17 and controls the oscillation frequency of the oscillator 20.

  Next, the sampling clock recovery unit 11 will be described with reference to FIG.

  The AD conversion unit 3 samples the input signal based on the signal output from the oscillator 23, and converts analog data into digital data. The orthogonal demodulator 4 converts the input signal into a baseband signal. In addition, the delay unit 13, the correlation calculation unit 14, the normalization unit 15, and the interval integration unit 16 can have the same configuration as the above-described carrier recovery unit. The error detection unit 21 estimates a timing offset from the output of the interval integration unit 16. As described in the above-mentioned prior art, the timing offset can be calculated from the time error between the time timing at the maximum power point and the symbol timing generated by an internal counter or the like. Further, for example, the center of gravity of the waveform of the interval integral output (the point at which the power of the interval integral output is equally divided) can be used regardless of the maximum power point. Similar to the carrier wave recovery unit, the reliability determination unit 17 determines the reliability of the timing offset output from the error detection unit 21 based on the power of the interval integration unit output. The reliability can be, for example, the maximum power of the interval integration output. Or it is good also as average electric power of an interval integration part output. Or it can also be made into the electric power in the gravity center point of an interval integration part output. The loop filter unit 22 controls the time offset of the timing offset output from the error detection unit 21 based on the reliability signal output from the reliability determination unit 17, and controls the oscillation frequency of the oscillator 23.

  In the embodiment of the present invention, each element of the carrier wave recovery unit and the sampling clock recovery unit is illustrated separately, but these blocks can be mounted in parallel in the OFDM demodulator. At that time, the delay unit 13, the correlation calculation unit 14, the normalization unit 15, the interval integration unit 16, and the reliability determination unit 17 can reduce the circuit scale by using a common circuit.

  In the embodiment of the present invention, A / D conversion is used as the sampling means. However, digital data after A / D conversion may be resampled. In this configuration, the sampling means can be arranged after the orthogonal demodulator.

  The operation principle and effect of the OFDM demodulator shown in the embodiment of the present invention will be described below.

  FIG. 8A shows the output of the correlation calculation unit 14 in the embodiment of the present invention. In the OFDM transmission symbol, since the rear data of the effective symbol is copied in the guard interval, high correlation is observed in this interval. In the guard interval section, since the correlation is with the same signal, the phase is “0” in a state where there is no frequency offset. In the prior art, the frequency offset and the timing offset are calculated by integrating the correlation calculation output. However, as shown in FIG. 8A, since the correlation signal amplitude in the guard interval section is not constant, for example, even in a situation where the transmission path environment is bad, almost no change is observed in the maximum power of the section integral output. Therefore, the normalization unit 15 is provided in the embodiment of the present invention. The normalizing unit 15 normalizes the amplitude of the correlation calculation output. FIG. 8B shows the output of the normalization unit 15. As shown in FIG. 8B, when there is no disturbance, the normalized correlation calculation output is a signal indicating a constant phase in the guard interval section and a random phase in the other portions. When there is a disturbance due to the transmission path environment, the phase is dispersed according to the disturbance from a certain phase in the guard interval section. FIG. 8C shows the result of interval integration of the above normalized signal. The maximum power of the normalized signal is Tg (guard interval section) when there is no disturbance and when the power of the normalized correlation signal is 1. When there is a disturbance due to the transmission path environment, the maximum power is reduced because the correlation signal is dispersed in the guard interval section without a constant phase.

  FIG. 9 shows a relationship diagram between the transmission path environment and the maximum power of the interval integral output in the embodiment of the present invention. In FIG. 9, additive white Gaussian noise (AWGN) is assumed as a transmission path environment. As shown in the figure, the maximum power of the interval integral output decreases under a situation where the transmission path environment is poor, and the maximum power increases when the transmission environment is good.

  FIG. 10 shows an error from the original offset value of the transmission path environment and the detected frequency offset in the embodiment of the present invention. As shown in FIG. 10, it can be seen that the error of the frequency offset detection value increases and the reliability of the estimated frequency offset is low in a situation where the transmission path environment is poor as shown in the figure. As for the timing offset, similarly to the frequency offset, the error in the detected value increases when the transmission path environment is poor.

  9 and 10, there is a correlation between the maximum power of the interval integral output and the frequency offset detection value, and it can be said that the higher the maximum power of the interval integral output, the higher the reliability of the detection value.

  As described above, the reliability determination unit 17 in the embodiment of the present invention outputs the maximum power of the interval integral output as the reliability of the frequency offset detection value or the timing offset detection value.

  Alternatively, the average power of the interval integration output can be used. This is because the average power of the interval integral power decreases as the maximum power decreases. By setting the average power, the maximum value detection circuit becomes unnecessary and the circuit scale can be reduced.

  Or it can also be set as the electric power in the gravity center point (electric power bisection point) of an interval integration output. Under a transmission path environment such as multipath, the waveform of the interval integration output is not triangular, and the position indicating the maximum power frequently fluctuates. By detecting the power at the center of gravity of the interval integral output, it is possible to observe the power at a fixed position regardless of the transmission path environment.

  Next, the operation of the loop filter unit (19, 22) will be described. The loop filter unit (19, 22) determines a time constant based on the output of the reliability determination unit 17. Generally, by increasing the gain of the loop filter, the time constant becomes light and the synchronization pull-in time can be shortened. Therefore, when the reliability is high based on the output to the reliability determination unit 17, the loop gain is increased to shorten the synchronization pull-in time. Further, when the reliability is low, stable control is realized by reducing the loop gain.

  In the conventional technique, since the loop gain at the time of synchronous pull-in is constant, the time constant is usually set so that the control is stable even in the worst transmission path environment. For this reason, even when the transmission path environment is good, the same synchronization pull-in time as in the worst transmission path environment is required. In the OFDM demodulator according to the embodiment of the present invention, since the time constant can be controlled according to the transmission path environment, the synchronization pull-in time can be shortened according to the transmission path environment.

<Modification 1>
FIG. 4 shows a modification of the carrier recovery unit in the embodiment of the OFDM demodulator according to the present invention.

  The delay unit 13 delays the output of the orthogonal demodulation unit 4 by a time corresponding to the effective symbol period of the OFDM transmission symbol. The correlation calculation unit 14 calculates the correlation between the output of the delay unit 13 and the output of the orthogonal demodulation unit 4. The correlation calculation can be realized by, for example, complex conjugate multiplication. The normalization unit 15 normalizes the output of the correlation calculation unit 14 so that the amplitude is constant. Normalization can be realized, for example, by dividing the real component and the imaginary component by the amplitude of the signal. The interval integrator 161 integrates the output of the correlation calculator 14 over an interval corresponding to the guard interval period of the OFDM transmission symbol. The interval integration unit 162 integrates the output of the normalization unit 15 over an interval corresponding to the guard interval period of the OFDM transmission symbol. The error detection unit 18 detects an offset of the carrier frequency from the output of the interval integration unit 161. The carrier frequency offset detection can be detected based on the phase at the maximum power point as described in the prior art. Further, for example, the center of gravity of the waveform of the interval integral output (the point at which the power of the interval integral output is equally divided) can be used regardless of the maximum power point. The reliability determination unit 17 determines the reliability of the frequency offset output from the error detection unit 18 based on the output power of the interval integration unit 162. The reliability can be, for example, the maximum power of the interval integration output. Or it is good also as average electric power of an interval integration part output. The loop filter unit 19 changes the time constant of the frequency offset output from the error detection unit 18 based on the reliability signal output from the reliability determination unit 17 and controls the oscillation frequency of the oscillator 20.

  The effect in the above structure is demonstrated. Modification 1 of the embodiment of the present invention is characterized in that an interval integration unit 161 for calculating a frequency offset and an interval integration unit 162 for calculating reliability are provided in parallel. A signal not subjected to normalization processing is input to the interval integration unit 161 for frequency offset calculation, and a signal after normalization processing is input to the interval integration unit 162 for reliability calculation.

  In the normalization process, the amplitude of the portion where the correlation is inherently low is increased, and as a result, a phenomenon in which the frequency offset detection accuracy deteriorates occurs. Modification 1 of the embodiment of the present invention is characterized in that a signal that is not subjected to normalization processing is used for frequency offset detection in order to prevent deterioration in frequency offset detection accuracy. With the above configuration, it is possible to improve the frequency offset detection accuracy compared to the configuration of FIG.

<Modification 2>
FIG. 5 shows a modification of the sampling clock recovery unit in the embodiment of the OFDM demodulator according to the present invention.

  The delay unit 13 delays the output of the orthogonal demodulation unit 4 by a time corresponding to the effective symbol period of the OFDM transmission symbol. The correlation calculation unit 14 calculates the correlation between the output of the delay unit 13 and the output of the orthogonal demodulation unit 4. The correlation calculation can be realized by, for example, complex conjugate multiplication. The normalization unit 15 normalizes the output of the correlation calculation unit 14 so that the amplitude is constant. Normalization can be realized, for example, by dividing the real component and the imaginary component by the amplitude of the signal. The interval integrator 161 integrates the output of the correlation calculator 14 over an interval corresponding to the guard interval period of the OFDM transmission symbol. The interval integration unit 162 integrates the output of the normalization unit 15 over an interval corresponding to the guard interval period of the OFDM transmission symbol. The error detection unit 21 estimates the timing offset from the output of the interval integration unit 161. As described in the above-mentioned prior art, the timing offset can be calculated from the time error between the time timing at the maximum power point and the symbol timing generated by an internal counter or the like. Further, for example, the center of gravity of the waveform of the interval integral output (the point at which the power of the interval integral output is equally divided) can be used regardless of the maximum power point. The reliability calculation unit 17 determines the reliability of the timing offset output from the error detection unit 21 based on the power output from the interval integration unit 162. The reliability can be, for example, the maximum power of the interval integration output. Or it is good also as average electric power of an interval integration part output. The loop filter unit 22 controls the time offset of the timing offset output from the error detection unit 21 based on the reliability signal output from the reliability determination unit 17, and controls the oscillation frequency of the oscillator 23.

  The effect in the above structure is demonstrated. The second modification of the embodiment of the present invention is characterized in that an interval integration unit 161 for calculating a timing offset and an interval integration unit 162 for calculating reliability are provided in parallel. A signal not subjected to normalization processing is input to the interval integration unit 161 for timing offset calculation, and a signal after normalization processing is input to the interval integration unit 162 for reliability calculation.

  In the normalization process, the amplitude of the portion where the correlation is inherently low is increased, and as a result, a phenomenon that the timing offset detection accuracy deteriorates occurs. Modification 2 of the embodiment of the present invention is characterized in that a signal that is not subjected to normalization processing is used for frequency offset detection in order to prevent deterioration in frequency offset detection accuracy. As described above, the timing offset detection accuracy can be increased as compared with the configuration of FIG.

  Note that the OFDM demodulator described above is typically realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include all or part thereof.

  The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

  Further, the method of circuit integration is not limited to LSI, and implementation with a dedicated circuit or a general-purpose processor is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

  Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Biotechnology can be applied.

  The OFDM demodulator according to the present invention has a carrier recovery unit and a sampling clock recovery unit capable of shortening the synchronization pull-in time according to the transmission path environment, and is useful as an OFDM demodulator for domestic terrestrial digital broadcasting. Also, it can be applied to the use of a transmission type demodulator employing the OFDM system such as European terrestrial digital broadcasting.

Configuration diagram of an OFDM demodulator according to an embodiment of the present invention Configuration diagram of a carrier recovery unit in an embodiment of the present invention Configuration diagram of sampling clock recovery unit in an embodiment of the present invention The figure explaining the modification of the carrier wave reproduction | regeneration part in embodiment of this invention The figure explaining the modification of the sampling clock reproduction | regeneration part in embodiment of this invention Configuration diagram of conventional OFDM demodulator Principle of offset calculation The figure explaining the example of the output signal of the OFDM demodulation apparatus in embodiment of this invention Relationship diagram between transmission line environment and maximum power Relationship diagram between transmission path environment and frequency offset detection error

Explanation of symbols

1 Antenna 2 Tuner 3 A / D Converter 4 Orthogonal Demodulator 5 FFT
DESCRIPTION OF SYMBOLS 6 Detection part 7 Error correction part 8 Decoder 9 Audio | voice output apparatus 10 Video | video output apparatus 11 Sampling clock reproduction | regeneration part 12 Carrier wave reproduction | regeneration part 13 Delay part 14 Correlation calculation part 15 Normalization part 16,161,162 Section integration part 17 Reliability determination part 18 Frequency error detection unit 19, 22 Loop filter unit 20, 23 Oscillator 21 Timing error detection unit 701 Input terminal 702 Frequency conversion circuit 703 Sampling means 704 FFT circuit 705 Output terminal 706 Data holding unit 707 Correlation detection circuit 708 Section integration circuit 709 Peak Detection circuit 710 Phase detection circuit 711 Division circuit 712 Frequency generation circuit

Claims (24)

An OFDM demodulator for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
An orthogonal demodulation unit, a delay unit, a correlation calculation unit, an interval integration unit, a normalization unit, a reliability determination unit, a frequency error detection unit, a control unit, and an oscillation unit,
The oscillation unit generates a signal having a predetermined frequency,
The orthogonal demodulator performs orthogonal demodulation on the input OFDM signal based on the signal generated by the oscillator,
The delay unit delays the output of the orthogonal demodulation unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the orthogonal demodulation unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The interval integration unit integrates the output of the normalization unit according to the guard interval period,
The frequency error detection unit detects a frequency offset based on the output of the interval integration unit,
The reliability determination unit determines the reliability of the frequency offset based on the output of the interval integration unit,
The said demodulation part is an OFDM demodulator which controls the oscillation frequency of the said oscillation part based on the output of the said frequency error detection part and the said reliability determination part. An OFDM demodulator for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
A sampling unit, a delay unit, a correlation calculation unit, an interval integration unit, a normalization unit, a reliability determination unit, a timing error detection unit, a control unit, and an oscillation unit,
The oscillation unit generates a signal having a predetermined frequency,
The sampling unit samples the input OFDM signal based on the signal generated by the oscillation unit,
The delay unit delays the output of the sampling unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the sampling unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The interval integration unit integrates the output of the normalization unit according to the guard interval period,
The timing error detection unit detects a timing offset based on the output of the interval integration unit,
The reliability determination unit determines the reliability of the timing error detection unit output based on the output of the interval integration unit,
The said demodulation part is an OFDM demodulator which controls the oscillation frequency of the said oscillation part based on the output of the said timing error detection part and the said reliability determination part. An OFDM demodulator for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
An orthogonal demodulation unit, a delay unit, a correlation calculation unit, a first interval integration unit, a second interval integration unit, a normalization unit, a reliability determination unit, a frequency error detection unit, a control unit, An oscillation unit,
The oscillation unit generates a signal having a predetermined frequency,
The orthogonal demodulator performs orthogonal demodulation on the input OFDM signal based on the signal generated by the oscillator,
The delay unit delays the output of the orthogonal demodulation unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates the correlation between the output of the orthogonal demodulation unit and the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The first interval integration unit integrates the output of the correlation calculation unit according to the guard interval period,
The second interval integration unit integrates the output of the normalization unit according to the guard interval period,
The frequency error detection unit detects a frequency offset based on the output of the first interval integration unit,
The reliability determination unit determines the reliability of the frequency offset based on the output of the second interval integration unit,
The said demodulation part is an OFDM demodulator which controls the oscillation frequency of the said oscillation part based on the output of the said frequency error detection part and the said reliability determination part. An OFDM demodulator for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
A sampling unit, a delay unit, a correlation calculation unit, a first interval integration unit, a second interval integration unit, a normalization unit, a reliability determination unit, a timing error detection unit, a control unit, An oscillation unit,
The oscillation unit generates a signal having a predetermined frequency,
The sampling unit samples the input OFDM signal based on the signal generated by the oscillation unit,
The delay unit delays the output of the sampling unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the sampling unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The first interval integration unit integrates the output of the correlation calculation unit according to the guard interval period,
The second interval integration unit integrates the output of the normalization unit according to the guard interval period,
The timing error detection unit detects a timing offset based on the output of the first interval integration unit,
The reliability determination unit determines the reliability of the timing offset based on the output of the second interval integration unit,
The said demodulation part is an OFDM demodulator which controls the oscillation frequency of the said oscillation part based on the output of the said timing error detection part and the said reliability determination part. The OFDM demodulator according to any one of claims 1 to 4, wherein the reliability determination unit outputs maximum power of a signal input to the reliability determination unit as reliability information. The OFDM demodulator according to any one of claims 1 to 4, wherein the reliability determination unit outputs average power of a signal input to the reliability determination unit as reliability information. The said reliability determination part detects the point which bisects the electric power of the signal input into the said reliability determination part (centroid point), and outputs the electric power in the said centroid point as reliability information. The OFDM demodulator according to any one of claims. The OFDM demodulator according to any one of claims 1 to 4, wherein the control unit includes a loop filter, and changes a time constant of the loop filter in accordance with an output of the reliability determination unit. 4. The OFDM demodulator according to claim 1, wherein the frequency error detection unit detects a frequency error from a phase of a signal having a maximum power among signals input to the frequency error detection unit. 4. The OFDM demodulator according to claim 1, wherein the frequency error detection unit detects a frequency error from a phase of a signal at a point at which the power of an input signal is divided into two equal parts among signals detected by the frequency error. The timing error detection unit detects a timing error from a time error between a time of a signal having the maximum power among signals input to the timing error detection unit and a time by an internal counter. The OFDM demodulator according to claim 2 or claim 4. The timing error detection unit detects a timing error from a time error between a time at which the power of an input signal is divided into two equal parts and a time by an internal counter among signals detected from the timing error. The OFDM demodulator according to claim 2 or 4. An integrated circuit for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
An orthogonal demodulation unit, a delay unit, a correlation calculation unit, an interval integration unit, a normalization unit, a reliability determination unit, a frequency error detection unit, a control unit, and an oscillation unit,
The oscillation unit outputs a signal having a predetermined frequency,
The orthogonal demodulator performs orthogonal demodulation on the input OFDM signal based on the signal generated by the oscillator,
The delay unit delays the output of the orthogonal demodulation unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the orthogonal demodulation unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The interval integration unit integrates the output of the normalization unit according to the guard interval period,
The frequency error detection unit detects a frequency offset based on the output of the interval integration unit,
The reliability determination unit determines the reliability of the frequency offset based on the output of the interval integration unit,
The said control part is an integrated circuit which controls the oscillation frequency of the said oscillation part based on the output of the said frequency error detection part and the said reliability determination part. An integrated circuit for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
A sampling unit, a delay unit, a correlation calculation unit, an interval integration unit, a normalization unit, a reliability determination unit, a timing error detection unit, a control unit, and an oscillation unit,
The oscillation unit outputs a signal having a predetermined frequency,
The sampling unit samples the input OFDM signal based on the signal generated by the oscillation unit,
The delay unit delays the output of the sampling unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the sampling unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The interval integration unit integrates the output of the normalization unit according to the guard interval period,
The timing error detection unit detects a timing offset based on the output of the interval integration unit,
The reliability determination unit determines the reliability of the timing offset based on the output of the interval integration unit,
The said control part is an integrated circuit which controls the oscillation frequency of the said oscillation part based on the output of the said timing error detection part and the said reliability determination part. An integrated circuit for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
An orthogonal demodulation unit, a delay unit, a correlation calculation unit, a first interval integration unit, a second interval integration unit, a normalization unit, a reliability determination unit, a frequency error detection unit, a control unit, An oscillation unit,
The oscillation unit generates a signal having a predetermined frequency,
The orthogonal demodulator performs orthogonal demodulation on the input OFDM signal based on the signal generated by the oscillator,
The delay unit delays the output of the orthogonal demodulation unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the orthogonal demodulation unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The first interval integration unit integrates the output of the correlation calculation unit according to the guard interval period,
The second interval integration unit integrates the output of the normalization unit according to the guard interval period,
The frequency error detection unit detects a frequency offset based on the output of the first interval integration unit,
The reliability determination unit determines the reliability of the frequency offset based on the output of the second interval integration unit,
The said control part is an integrated circuit which controls the oscillation frequency of the said oscillation part based on the output of the said frequency error detection part and the said reliability determination part. An integrated circuit for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
A sampling unit, a delay unit, a correlation calculation unit, a first interval integration unit, a second interval integration unit, a normalization unit, a reliability determination unit, a timing error detection unit, a control unit, An oscillation unit,
The oscillation unit generates a signal having a predetermined frequency,
The sampling unit samples the input OFDM signal based on the signal generated by the oscillation unit,
The delay unit delays the output of the sampling unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the sampling unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The first interval integration unit integrates the output of the correlation calculation unit according to the guard interval period,
The second interval integration unit integrates the output of the normalization unit according to the guard interval period,
The timing error detection unit detects a timing offset based on the output of the first interval integration unit,
The reliability determination unit determines the reliability of the timing offset based on the output of the second interval integration unit,
The said control part is an integrated circuit which controls the oscillation frequency of the said oscillation part based on the output of the said timing error detection part and the said reliability determination part. An OFDM demodulation method for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
OFDM signal is orthogonally demodulated based on a predetermined frequency,
Delaying the quadrature demodulated signal for the effective symbol period;
Calculating a correlation between the quadrature demodulated signal and the delayed signal;
Normalizing the amplitude of the correlated signal;
Interval integrating the normalized signal according to the guard interval period;
Based on the interval integrated signal, a frequency offset is detected,
Based on the interval-integrated signal, the reliability of the frequency offset is detected,
An OFDM demodulation method for controlling a value of the predetermined frequency based on the frequency offset and the reliability information. An OFDM demodulation method for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
Sampling an OFDM signal based on a predetermined frequency;
Delay the sampled signal for the effective symbol period;
Calculating a correlation between the delayed signal and the sampled signal;
Normalizing the amplitude of the correlated signal;
Interval integrating the normalized signal according to the guard interval period;
Based on the interval integrated signal, a timing offset is detected,
Based on the interval integrated signal, the reliability of the timing offset is detected,
An OFDM demodulation method for controlling a value of the predetermined frequency based on the timing offset and the reliability information. An OFDM demodulation method for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
OFDM signal is orthogonally demodulated based on a predetermined frequency,
Calculating a correlation between the quadrature demodulated signal and the delayed signal;
Normalizing the amplitude of the correlated signal;
Integrating the correlation-calculated signal according to the guard interval period to generate a first interval integrated signal,
Integrating the normalized signal according to the guard interval period to generate a second interval integrated signal;
Detecting a frequency offset based on the first interval integral signal;
Detecting the reliability of the frequency offset based on the second interval integral signal;
An OFDM demodulation method for controlling a value of the determined frequency based on the frequency offset and the reliability information. An OFDM demodulation method for demodulating an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
Sampling an OFDM signal based on a predetermined frequency;
Calculating a correlation between the sampled signal and the delayed signal;
Normalizing the amplitude of the correlated signal;
Integrating the correlation-calculated signal according to the guard interval period to generate a first interval integrated signal,
Integrating the normalized signal according to the guard interval period to generate a second interval integrated signal;
Detecting a timing offset based on the first interval integral signal;
Detecting the reliability of the timing offset based on the second interval integral signal;
An OFDM demodulation method for controlling a value of the predetermined frequency based on the timing offset and the reliability information. A receiving apparatus that receives and demodulates an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
A tuner, an OFDM demodulator, a decoder, a video output unit, and an audio output unit;
The tuner selects the received OFDM signal;
The OFDM demodulator converts the selected OFDM signal into digital data according to a predetermined method,
The decoder unit converts the digital data into a video signal and an audio signal according to a predetermined method,
The video output unit outputs the video signal as a video,
The audio output unit outputs the audio signal as audio,
The OFDM demodulator includes an orthogonal demodulator, a delay unit, a correlation calculation unit, an interval integration unit, a normalization unit, a reliability determination unit, a frequency error detection unit, a control unit, and an oscillation unit. Equipped,
The oscillation unit generates a signal having a predetermined frequency,
The orthogonal demodulation unit orthogonally demodulates the tuner OFDM signal input based on the signal generated by the oscillation unit,
The delay unit delays the output of the orthogonal demodulation unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the orthogonal demodulation unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The interval integration unit integrates the output of the normalization unit according to the guard interval period,
The frequency error detection unit detects a frequency offset based on the output of the interval integration unit,
The reliability determination unit determines the reliability of the frequency offset based on the output of the interval integration unit,
The control unit is a receiving device that controls an oscillation frequency of the oscillation unit based on outputs of the frequency error detection unit and the reliability determination unit. A receiving apparatus that receives and demodulates an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
A tuner, an OFDM demodulator, a decoder, a video output unit, and an audio output unit;
The tuner selects the received OFDM signal;
The OFDM demodulator converts the selected OFDM signal into digital data according to a predetermined method,
The decoder unit converts the digital data into a video signal and an audio signal according to a predetermined method,
The video output unit outputs the video signal as a video,
The audio output unit outputs the audio signal as audio,
The OFDM demodulator includes a sampling unit, a delay unit, a correlation calculation unit, an interval integration unit, a normalization unit, a reliability determination unit, a timing error detection unit, a control unit, and an oscillation unit. And
The oscillation unit generates a signal having a predetermined frequency,
The sampling unit samples the input OFDM signal based on the signal generated by the oscillation unit,
The delay unit delays the output of the sampling unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the sampling unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The interval integration unit integrates the output of the normalization unit according to the guard interval period,
The timing error detection unit detects a timing offset based on the output of the interval integration unit,
The reliability determination unit determines the reliability of the timing error detection unit output based on the output of the interval integration unit,
The control unit is a receiving device that controls an oscillation frequency of the oscillation unit based on outputs of the timing error detection unit and the reliability determination unit. A receiving apparatus that receives and demodulates an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
A tuner, an OFDM demodulator, a decoder, a video output unit, and an audio output unit;
The tuner selects the received OFDM signal;
The OFDM demodulator converts the selected OFDM signal into digital data according to a predetermined method,
The decoder unit converts the digital data into a video signal and an audio signal according to a predetermined method,
The video output unit outputs the video signal as a video,
The audio output unit outputs the audio signal as audio,
The OFDM demodulator includes:
An orthogonal demodulation unit, a delay unit, a correlation calculation unit, a first interval integration unit, a second interval integration unit, a normalization unit, a reliability determination unit, a frequency error detection unit, a control unit, An oscillation unit,
The oscillation unit generates a signal having a predetermined frequency,
The orthogonal demodulator performs orthogonal demodulation on the input OFDM signal based on the signal generated by the oscillator,
The delay unit delays the output of the orthogonal demodulation unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates the correlation between the output of the orthogonal demodulation unit and the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The first interval integration unit integrates the output of the correlation calculation unit according to the guard interval period,
The second interval integration unit integrates the output of the normalization unit according to the guard interval period,
The frequency error detection unit detects a frequency offset based on the output of the first interval integration unit,
The reliability determination unit determines the reliability of the frequency offset based on the output of the second interval integration unit,
The control unit is a receiving device that controls an oscillation frequency of the oscillation unit based on outputs of the frequency error detection unit and the reliability determination unit. A receiving apparatus that receives and demodulates an OFDM signal composed of transmission symbols composed of effective symbols and guard intervals,
A tuner, an OFDM demodulator, a decoder, a video output unit, and an audio output unit;
The tuner selects the received OFDM signal;
The OFDM demodulator converts the selected OFDM signal into digital data according to a predetermined method,
The decoder unit converts the digital data into a video signal and an audio signal according to a predetermined method,
The video output unit outputs the video signal as a video,
The audio output unit outputs the audio signal as audio,
The OFDM demodulator includes:
A sampling unit, a delay unit, a correlation calculation unit, a first interval integration unit, a second interval integration unit, a normalization unit, a reliability determination unit, a timing error detection unit, a control unit, An oscillation unit,
The oscillation unit generates a signal having a predetermined frequency,
The sampling unit samples the input OFDM signal based on the signal generated by the oscillation unit,
The delay unit delays the output of the sampling unit for a time corresponding to the period of the effective symbol,
The correlation calculation unit calculates a correlation between the output of the sampling unit and the output of the delay unit,
The normalization unit normalizes the amplitude of the output signal of the correlation calculation unit,
The first interval integration unit integrates the output of the correlation calculation unit according to the guard interval period,
The second interval integration unit integrates the output of the normalization unit according to the guard interval period,
The timing error detection unit detects a timing offset based on the output of the first interval integration unit,
The reliability determination unit determines the reliability of the timing offset based on the output of the second interval integration unit,
The control unit is a receiving device that controls an oscillation frequency of the oscillation unit based on outputs of the timing error detection unit and the reliability determination unit.

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