WO2004062150A1 - Ofdm復調装置 - Google Patents
Ofdm復調装置 Download PDFInfo
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- WO2004062150A1 WO2004062150A1 PCT/JP2003/016261 JP0316261W WO2004062150A1 WO 2004062150 A1 WO2004062150 A1 WO 2004062150A1 JP 0316261 W JP0316261 W JP 0316261W WO 2004062150 A1 WO2004062150 A1 WO 2004062150A1
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2602—Signal structure
- H04L27/2605—Symbol extensions, e.g. Zero Tail, Unique Word [UW]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2668—Details of algorithms
- H04L27/2673—Details of algorithms characterised by synchronisation parameters
- H04L27/2676—Blind, i.e. without using known symbols
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/02—Speed or phase control by the received code signals, the signals containing no special synchronisation information
Definitions
- the present invention relates to an OFDM demodulator that demodulates an OFDM (Orthogonal Frequency Division Multiplexing) modulated signal.
- OFDM Orthogonal Frequency Division Multiplexing
- Orthogonal frequency division multiplexing (hereinafter, referred to as OFDM) is used as a method for transmitting digital signals.
- OFDM A modulation method called Orthogonal Fre (! Return division Mul Uplexing) is used.
- a number of orthogonal sub-carriers are provided in the transmission band.
- Sub-carriers are assigned, and the amplitude and phase of each sub-carrier are assigned to the data by PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation). This is a digital modulation method.
- the transmission band is divided by a large number of subcarriers, so the band per subcarrier wave is narrowed and the modulation speed is slow, but the total transmission speed is not different from the conventional modulation system.
- data is allocated to a plurality of subcarriers, so an IFT (Inverse Fast Fourier Transform) arithmetic circuit that performs an inverse Fourier transform during modulation, and an FFT (Fast Fast) that performs a Fourier transform during demodulation.
- IFT Inverse Fast Fourier Transform
- FFT Fast Fast
- Fourier Transform By using the arithmetic circuit, it is possible to configure the transmission and reception circuit It has the characteristics of
- the OFDM method is often applied to terrestrial digital broadcasting that is strongly affected by multipath interference.
- terrestrial digital broadcasting adopting the OFDM system there are standards such as DVBT (Digital Video Broadcasting-Terrestrial) and ISDBT (Integrated Services Digital Broadcasting-Terrestrial).
- the transmission symbol of the OFDM scheme (hereinafter referred to as OFDM symbol) is an effective symbol that is a signal period during which an IF FT is performed at the time of transmission, and a part of the latter half of the effective symbol. It consists of a guard interval whose waveform is copied as it is. The guard interval is located in the first half of the OFDM symbol.
- OFDM symbol In the OFDM system, provision of such a guard-in signal allows inter-symbol interference due to multipath and improves multipath resistance.
- I SDB- T SB mode 3 standard (terrestrial digital audio broadcasting broadcasting standard adopted in Japan), in the effective Shinporu, includes a 5 12 subcarriers, the Sabukiyaria interval, 125/126 ⁇ 0.92 kHz. Also, in the mode 3 of the IS DB- T SB standard, of 5 12 subcarriers in the effective Shinporu, transmission data series 433 pieces of subcarriers is modulated. Moreover, the ISD B- T SB standard mode 3, the time length of the guard one pulse is 1/4 of the time length of the valid Shinporu, 1/8, 1/16, and either 1/32.
- a transmission unit called an OFDM transmission frame configured by a plurality of consecutive OFDM symbols is generally defined.
- pilot signals of a predetermined phase and amplitude called CP (Continual Pilot) and SP (Scattered Pilot)
- TMC C Transmission and Multi-plexing Configuration Control
- TPS Transmission Parameter Signaling
- FIG. 2 shows a block diagram of a conventional OFDM receiving apparatus.
- a conventional OFDM receiver 100 includes an antenna 101, a channel 102, a bandpass filter (BPF) 103, an A / D conversion circuit 104, DC cancel circuit 105, digital quadrature demodulation circuit 106, FFT operation circuit 107, frame extraction circuit 108, synchronization circuit 109, and carrier demodulation circuit 110
- Frequency diving leave circuit 1 1 1, time diving leave circuit 1 1 2, demapping circuit 1 1 3, bit diving leave circuit 1 14, depuncturing circuit 1 1 5, display circuit 1 16 and itinereve circuit 1 17, spread signal elimination circuit 1 18, transport stream generation circuit 1 19, RS decoding circuit 1 20, transmission control information decoding circuit 1 2 1, channel And a selection circuit 122.
- a broadcast wave of a digital broadcast broadcast from a broadcast station is received by an antenna 101 of an OFDM receiving apparatus 100 and supplied to a tuner 102 as an RF signal.
- the RF signal received by the antenna 101 is frequency-converted into an IF signal by a tuner 102 composed of a multiplier 102 a and a local oscillator 102 b, and supplied to a BPF 103.
- the oscillation frequency of the reception carrier signal oscillated from the local oscillator 102 b is switched according to the channel selection signal supplied from the channel selection circuit 122.
- the IF signal output from the tuner 102 is filtered by the BP 103 and digitized by the A / D conversion circuit 104. From the digitized IF signal, the DC component is removed by the DC cancel circuit 105 and supplied to the digital quadrature demodulation circuit 106.
- the digital quadrature demodulation circuit 106 quadrature demodulates the digitized IF signal using a carrier signal of a predetermined frequency (carrier frequency), and outputs a baseband OFDM signal.
- the baseband OFDM signal is a complex composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal) as a result of quadrature demodulation. Signal.
- the baseband OFDM signal output from the digital quadrature demodulation circuit 106 is supplied to the FFT operation circuit 107 and the synchronization circuit 109.
- the FFT operation circuit 107 performs an FFT operation on the baseband OFDM signal, and extracts and outputs a signal orthogonally modulated to each subcarrier.
- the FFT arithmetic circuit 107 extracts a signal corresponding to the effective symbol length from one OFDM symbol, and performs an FFT operation on the extracted signal. That is, the FFT operation circuit 107 removes the signal of the guard interval length from one OFDM symbol and performs the FFT operation on the remaining signal.
- the range of the signal extracted for performing the FFT operation may be any position of one OFDM symbol as long as the extracted signal points are continuous. In other words, the start position of the range of the extracted signal is, as shown in FIG. 1, from the first boundary position of the OFDM symbol (the position A in FIG. 1) to the end position of the guard interval (see FIG. 1). (Position B)).
- the signal modulated by each subcarrier extracted by the FFT operation circuit 107 is a complex signal composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal).
- the signal extracted by the FFT arithmetic circuit 107 is supplied to a frame extracting circuit 108, a synchronizing circuit 109, and a carrier demodulating circuit 110.
- the frame extraction circuit 108 extracts the boundaries of the OFDM transmission frame based on the signal demodulated by the FFT operation circuit 107, and extracts the CP, SP, etc. included in the OFDM transmission frame. And demodulates transmission control information such as TMCC and TMCC and TPS, and supplies them to the synchronization circuit 109 and transmission control information decoding circuit 121.
- the synchronization circuit 109 includes a baseband OFDM signal, a signal modulated on each subcarrier after demodulation by the FFT calculation circuit 107, a CP detected by the frame extraction circuit 108, Using the pilot signal such as SP and the channel selection signal supplied from the channel selection circuit 122, calculate the boundary of the OFDM symbol and set the FFT calculation circuit 107 timing to start the FFT calculation. You.
- the carrier demodulation circuit 110 is supplied with a demodulated signal from each subcarrier output from the FFT operation circuit 107 and performs carrier demodulation on the signal. For example, in the case of demodulating an OFDM signal of the ISD B- TSB standard, the carrier demodulation circuit 110 performs, for example, differential demodulation of DQP SK or QP SK: of 16 QAM, 64 QAM. Performs synchronous demodulation.
- the carrier-demodulated signal is subjected to frequency directional elimination processing by the frequency dithering circuit 111, and then to time directional diving processing by the time dithering circuit 112. Thereafter, it is supplied to the demapping circuit 113.
- the demapping circuit 113 performs de-allocation processing (demapping processing) on the carrier-demodulated signal (complex signal) to restore the transmission data sequence. For example, when demodulating an OFDM signal of the ISDB- TSB standard, the demapping circuit 113 performs a demapping process corresponding to QPSK :, 16QAM or 64QAM.
- the transmission data sequence output from the demapping circuit 113 is composed of a bit ding circuit 114, a depuncturing circuit 115, a Viterbi circuit 116, a byte ding leaving circuit 117, and a spreading signal removing circuit 111.
- the transport stream generating circuit 119 inserts data specified by each broadcasting system, such as a null packet, at a predetermined position in the stream. Further, the transport stream generating circuit 119 performs a so-called smoothing process in which the bit intervals of the intermittently supplied stream are smoothed to form a temporally continuous stream.
- the transmission data sequence subjected to the smoothing process is supplied to the RS decoding circuit 120.
- the RS decoding circuit 120 performs a Reed-Solomon decoding process on the input transmission data sequence, and outputs it as a transport stream defined by MPEG-2 Systems.
- the transmission control information decoding circuit 121 decodes transmission control information such as TMCC and TPS modulated at a predetermined position of the OFDM transmission frame.
- the decoded transmission control information is transmitted to a carrier demodulation circuit 110, a time dinning leave circuit 112, a demapping circuit 113, a bit dinning leave circuit 114, and a transport stream generation circuit 111. It is supplied to 9 and used for control of demodulation and reproduction of each circuit.
- the clock frequency error is the frequency error between the transmission clock of the received OFDM signal and the sampling clock used to quantize the received 0 FDM signal. That is, the clock frequency error is a frequency error between the reference clock on the transmitter side and the reference clock on the receiver side.
- the clock frequency error detection method includes, for example, calculating the autocorrelation of the OFDM signal, detecting the boundary position of the OFDM symbol, and converting the boundary position from the boundary interval, or calculating the zero position from the insertion position of the pilot signal.
- a method of converting the FDM symbol period may be considered, but in any case, it is difficult to accurately detect the period.
- the present invention has been proposed in view of such conventional circumstances, and has as its object to provide an OFDM demodulator capable of accurately detecting a clock frequency error.
- the OFDM demodulation device generates an effective symbol generated by time-dividing an information sequence and modulating it into a plurality of subcarriers, and a signal waveform generated by copying a part of the signal waveform of the effective symbol.
- the clock frequency error calculation means calculates the clock frequency error based on a plurality of time change rates output from each of the change rate calculation
- the OFDM demodulator according to the present invention can accurately calculate the clock frequency error even when the reception environment deteriorates.
- An OFDM demodulator is generated by copying an effective symbol generated by time-dividing an information sequence and modulating the information sequence into a plurality of subcarriers, and copying a signal waveform of a part of the effective symbol.
- An OFDM demodulator for demodulating an orthogonal frequency division multiplexing (OFDM) signal using a transmission symbol including a guard interval as a transmission unit, wherein the FDM signal is demodulated with a sampling clock of a predetermined frequency.
- Analog / digital conversion means for sampling and converting to digital data; symbol boundary measurement means for measuring a measurement value indicating the boundary of the transmission symbol of the FDM signal by the sampling clock; and a time change rate of the measurement value.
- a rate-of-change calculating means for calculating M (where M is a natural number) transmission symbol units; Histogram generation means that is input for each symbol, classifies the time change rate into classes, and generates a histogram indicating the detection frequency of the time change rate for each class; and a transmission clock for the OFDM signal based on the histogram. And a clock frequency error calculating means for calculating a clock frequency error which is an error with respect to the sampling clock.
- the 0-FDM demodulator generates an effective symbol generated by time-dividing an information sequence and modulating the information sequence into a plurality of subcarriers and copying a signal waveform of a part of the effective symbol.
- An OFDM demodulator for demodulating an orthogonal frequency division multiplexing (OFDM) signal using a transmission symbol including a guard interval as a transmission unit, wherein the OFDM demodulation device demodulates the 0 FDM signal to a sampling frequency of a predetermined frequency.
- OFDM orthogonal frequency division multiplexing
- Analog / digital conversion means for sampling with a hook and converting it to digital data
- symbol boundary measurement means for measuring a measurement value indicating a boundary of the transmission symbol of the FDM signal by the sampling clock
- M Is a natural number.
- a plurality of rate-of-change calculation means for calculating the rate of change of the measured value over time in transmission symbol units of Histogram generating means for generating a histogram as shown in the following, and clock frequency error calculating means for calculating a clock frequency error which is an error between the transmission clock of the OFDM signal and the sampling clock based on the histogram.
- a time interval for calculating the time change rate is set in multiples of the M symbols, and The interval intervals are different from each other, and the histogram generating means inputs the above-mentioned time change rates from the plurality of change rate calculation means for each of the time intervals set in the change rate means.
- the rate of change is classified into classes, and a histogram showing the detection frequency of the time rate of change for each class is generated.
- FIG. 1 is a diagram for explaining a transmission symbol of the FDM scheme.
- FIG. 2 is a block diagram of a conventional OFDM receiving apparatus.
- FIG. 3 is a block diagram of the OFDM receiving apparatus according to the embodiment of the present invention.
- FIG. 4 is a block diagram of a guard correlation / peak detection circuit.
- FIG. 5 is an evening timing chart of each signal in the guard correlation / peak detection circuit.
- FIG. 6 is a block diagram of the timing synchronization circuit.
- FIG. 7 is a block diagram of the clock frequency error calculation circuit.
- FIG. 8 is a diagram illustrating the output fluctuation of the free-running counter when the transmission clock of the received OFDM signal is synchronized with the clock of the receiving device.
- FIG. 9 is a diagram showing the output fluctuation of the free-running counter when the clock of the receiving device is faster than the transmission clock of the received OFDM signal.
- FIG. 10 is a diagram showing the output fluctuation of the free-running counter when the clock of the receiving device is slower than the transmission clock of the received OFDM signal.
- FIG. 11 is a diagram showing the time change rate of the output value of the self-propelled count.
- FIG. 12 is a diagram showing the output fluctuation of the free-running counter when frequency-selective fading has occurred and a clock frequency error has occurred.
- FIG. 13 is a diagram illustrating a case where a slope value can be accurately detected and a case where a slope value cannot be accurately detected in a reception environment of frequency selective fading.
- FIG. 14 is a circuit configuration diagram of the inclination detection circuit.
- FIG. 15 is a diagram illustrating an error detection histogram generated by the histogram generation circuit.
- FIG. 16 is a diagram illustrating the range of the error detection histogram.
- FIG. 17 is a diagram showing a reference histogram.
- FIG. 18 is a diagram for explaining that the reference histogram is translated.
- FIG. 19 is a block diagram of the histogram generation circuit.
- FIG. 2OA is a histogram for error detection
- FIG. 20B is a diagram showing a histogram obtained by moving-averaging the histogram for error detection.
- FIG. 21 is a diagram showing a reference histogram used for moving-averaging the histogram for error detection.
- FIG. 22 is a diagram showing a state machine for determining the convergence of the histogram for error detection.
- FIG. 3 shows a block diagram of the OFDM receiving apparatus according to the embodiment of the present invention.
- the signal shown by the double line in FIG. 3 is a complex signal.
- an OFDM receiver 1 includes an antenna 2, a tuner 3, a non-pass filter (BPF) 4, an A / D conversion circuit 5, a clock generation circuit 6, DC cancellation circuit 7, Digital quadrature demodulation circuit 8, Carrier frequency error correction circuit 9, FFT operation circuit 10, phase correction circuit 11, guard correlation / peak detection circuit 12, timing synchronization circuit 13, narrowband carrier error calculation circuit 14, wideband Carrier error calculation circuit 15, Addition circuit 16, Numerical control oscillator (NCO) 17, Frame synchronization circuit 18, Equalization circuit 19, Demapping circuit 20, Transmission path decoding circuit 21 and a transmission control information decoding circuit 22.
- BPF non-pass filter
- a broadcast wave of a digital broadcast broadcasted from a broadcasting station is received by the antenna 2 of the OFDM receiver 1 and supplied to the tuner 3 as an RF signal.
- the RF signal received by the antenna 2 is frequency-converted into an IF signal by a tuner 3 including a multiplier 3 a and a local oscillator 3, and supplied to a BPF 4.
- the IF signal output from the tuner 3 is supplied to the A / D conversion circuit 5 after being filtered by the BP F 4.
- the A / D conversion circuit 5 samples the IF signal using the clock supplied from the clock generation circuit 6 and digitizes the IF signal.
- the IF signal digitized by the A / D conversion circuit 5 is supplied to the DC cancellation circuit 7, and after the DC component is removed by the DC cancellation circuit 7, the signal is supplied to the digital quadrature demodulation circuit 8. .
- the digital quadrature demodulation circuit 8 quadrature demodulates the digitized IF signal using a two-phase carrier signal having a predetermined carrier frequency, and outputs a baseband OFDM signal.
- the OFDM time domain signal output from the digital quadrature demodulation circuit 8 is supplied to a carrier frequency error correction circuit 9.
- the present device 1 when digital quadrature demodulation is performed by the digital quadrature demodulation circuit 8, a two-phase signal of one Sin component and Cos component is required as a carrier signal. For this reason, the present device 1 generates a two-phase carrier signal to be supplied to the digital quadrature demodulation circuit 8 by setting the frequency of the sampling clock given to the A / D conversion circuit 5 to four times the center frequency f IF of the IF signal. It is possible.
- the 4 f IF clock data series is down-sampled to 1/4, and the number of effective symbol sampling points after digital quadrature demodulation is defined as the number of subcarriers (Nu).
- the clock of the data sequence after digital quadrature demodulation is set to a frequency equal to the subcarrier interval. Also, Assuming that the ratio of the downsampled after 1 digital quadrature demodulation is 1/2, the FFT operation is performed with twice the normal number of sampling points, and further 1/2 the downsample after the FFT operation.
- the frequency band of the signal that can be extracted by the FFT operation is doubled, and the circuit size of the low-pass filter circuit during digital quadrature demodulation is reduced. be able to.
- the number of effective symbol sampling points (N u) after digital quadrature demodulation is set to twice the number of subcarriers (where Where n is a natural number).
- the clock generation circuit 6 supplies the clock having the above frequency to the A / D conversion circuit 5 and also supplies the operation clock of the data series after digital quadrature demodulation (to the A / D conversion circuit 5).
- a clock divided by 14 with respect to the clock frequency for example, a clock having a frequency equal to the subcarrier interval) is supplied to each circuit in the device 1.
- the operation clock generated from the clock generation circuit 6 is a free-running clock that is asynchronous with respect to the transmission clock of the received OFDM signal. That is, the operation clock generated by the clock generation circuit 6 is not synchronized in frequency and phase with the transmission clock by PLL or the like, and operates in a free-running state. Thus, the operation clock can be set to the free running state because the timing synchronization circuit 13 detects the frequency error between the transmission clock of the OFDM signal and the operation clock, and detects the frequency error. This is because the error is removed at a later stage by feedforward processing based on the components.
- the clock generation circuit 6 is an asynchronous free-running clock as described above.
- the present invention can also be applied to a device that variably controls the operation clock frequency by feedback control. is there.
- the baseband 0 FDM signal output from the digital quadrature demodulation circuit 8 is a so-called time domain signal before the FFT operation.
- the baseband signal before the FFT operation is hereinafter referred to as an OFDM time domain signal.
- the OFDM time domain signal becomes a complex signal composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal).
- the carrier frequency error correction circuit 9 corrects the carrier frequency error of the OFDM time domain signal by performing complex multiplication of the carrier frequency error correction signal output from the NCO 17 and the 0 FDM time domain signal after digital quadrature demodulation. I do.
- the carrier frequency error correction circuit 9 corrects an error caused by a difference between the frequency of the carrier signal used at the time of digital quadrature demodulation and the center frequency of the transmitted OFDM signal (IF signal).
- the OFDM time domain signal whose carrier frequency error has been corrected by the carrier frequency error correction circuit 9 is supplied to the FFT operation circuit 10 and the guard correlation / peak detection circuit 12.
- the FFT operation circuit 10 extracts a signal having an effective symbol length from one OFDM symbol, that is, a signal obtained by removing all guard interval samples from all samples of one ⁇ FDM symbol, and extracting the signal. FFT operation is performed on the signal.
- the timing for specifying the extraction range (the timing at which the FFT calculation starts) is set by a start flag provided from the timing synchronization circuit 13.
- the FFT operation circuit 10 performs one FFT operation on one OFDM symbol, and extracts a signal component modulated on each subcarrier in the OFDM symbol.
- the signal output from the FFT operation circuit 10 is a so-called frequency-domain signal after the FFT. For this reason, the signal after the FFT operation is hereinafter referred to as an OFDM frequency domain signal.
- the OFDM frequency domain signal output from the FFT operation circuit 10 is a complex signal composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal). It is.
- the OFDM frequency domain signal is supplied to a phase correction circuit 11.
- the phase correction circuit 11 corrects the OFDM frequency domain signal for a phase rotation component caused by a deviation between the actual boundary position of the OFDM symbol and the start timing of the FFT calculation range.
- the phase correction circuit 11 corrects the phase of a shift that occurs with an accuracy shorter than the sampling period.
- the OFDM frequency domain signal output from the FFT operation circuit 10 is complex-multiplied by the phase correction signal (complex signal) supplied from the timing synchronization circuit 13 to perform phase rotation correction. Do.
- the OFDM frequency domain signal having undergone the phase rotation correction is supplied to a wideband carrier error calculation circuit 15, a frame synchronization circuit 18, an equalization circuit 19, and a transmission control information decoding circuit 22.
- the guard correlation / peak detection circuit 12 receives an OFDM time-domain signal.
- the guard correlation / peak detection circuit 12 calculates a correlation value between the input OFDM time domain signal and the OFDM time domain signal delayed by the effective symbol.
- the time length for obtaining the correlation is set to the time length of the guard interval. Therefore, a signal indicating this correlation value (hereinafter, referred to as a guard correlation signal) is a signal that has a peak at the boundary position of the OFDM symbol.
- the guard correlation / peak detection circuit 12 detects the peak position of the guard correlation signal and outputs a value (peak timing value Np) specifying the timing of the peak position.
- the guard correlation / peak detection circuit 12 also detects a value indicating the phase of the correlation value at the peak position of the guard correlation signal.
- This phase value is 0 when the center frequency of the OFDM signal completely matches the carrier frequency after digital orthogonal decoding. However, if there is a shift, this phase value rotates by the amount of the shift. That is, this phase value indicates the amount of deviation between the center frequency of the received 0 FDM signal and the center frequency of the OFDM signal after digital orthogonal decoding.
- the phase value, the frequency interval of the subcarriers e.g., ISD B- T SB mode 3 der lever, 0. 992 kHz
- the peak timing value output from the guard correlation / peak detection circuit 12 is supplied to the timing synchronization circuit 13, and the phase of the correlation value at the boundary position of the 0 FDM symbol is calculated as a narrow-band carrier frequency error. Supplied to circuit 14. '
- the timing synchronization circuit 13 performs, for example, a filtering process on the peak timing value output from the guard correlation / peak detection circuit 12, estimates the boundary position of the OFDM symbol, and performs The operation start timing for performing the FFT operation is determined based on the estimated value of the boundary position.
- the operation start timing is supplied to the FFT operation circuit 10.
- the FFT operation circuit 10 extracts a signal in the FFT operation range from the input OFDM time domain signal and performs the FFT operation based on the operation start timing.
- the timing synchronization circuit 13 calculates a phase rotation amount that occurs due to a time lag between the estimated boundary position of the OFDM symbol and the operation start timing for performing the FFT operation, and calculates the phase rotation amount.
- Phase correction signal No. 4 (complex signal) is generated and supplied to the phase correction circuit 11.
- the narrow-band carrier error calculation circuit 14 calculates a narrow-band carrier frequency that indicates a narrow-band component of the center frequency shift amount during digital orthogonal demodulation based on the phase of the correlation value at the boundary position of the OFDM symbol. Calculate the error component. Specifically, the narrow-band carrier frequency error component is a deviation of the center frequency with an accuracy of ⁇ 1/2 or less of the subcarrier frequency interval. The narrow-band carrier frequency error component obtained by the narrow-band carrier error calculation circuit 14 is supplied to the addition circuit 16.
- the wideband carrier error calculation circuit 15 calculates the wideband carrier frequency error component indicating the wideband component of the deviation amount of the center frequency during digital orthogonal demodulation based on the OFDM frequency domain signal output from the phase correction circuit 11 I do.
- the wideband carrier frequency error component is a deviation amount of the center frequency of the subcarrier frequency interval accuracy.
- the wideband carrier frequency error component obtained by the wideband carrier error calculation circuit 15 is supplied to the addition circuit 16.
- the adding circuit 16 adds the narrow-band carrier error component calculated by the narrow-band carrier error detecting circuit 14 and the wide-band carrier error component calculated by the wide-band carrier error calculating circuit 15 to obtain a carrier frequency.
- the shift amount of the total center frequency of the baseband OFDM signal output from the error correction circuit 9 is calculated.
- the adder circuit 16 outputs the calculated total deviation amount of the center frequency as a frequency error value.
- the frequency error value output from the adder circuit 16 is supplied to NCO 17.
- N C0 17 is a so-called numerically controlled oscillator, and generates a carrier frequency error correction signal that increases or decreases according to the frequency error value output from the addition circuit 16.
- the NCO 17 reduces the oscillation frequency of the carrier frequency error correction signal if the supplied frequency error value is a positive value, and the error correction signal if the supplied carrier frequency error value is a negative value. Is controlled so as to increase the oscillation frequency.
- NC ⁇ 17 generates a carrier frequency error correction signal that stabilizes the oscillation frequency when the frequency error value becomes zero.
- the frame synchronization circuit 18 detects a synchronization word inserted at a predetermined position in the OFDM transmission frame, and detects the start timing of the FDM transmission frame.
- the frame synchronizing circuit 18 sets each OF based on 0 FDM transmission frame start timing.
- the symbol number of the DM symbol is specified and supplied to the equalizing circuit 19 and the like.
- the equalization circuit 19 performs a so-called equalization process on the OFDM frequency domain signal.
- the equalization circuit 19 detects a pilot signal called an SP (Scattered Pilots) signal inserted in the OFDM frequency domain signal based on the symbol number supplied from the frame synchronization circuit 18.
- the equalization circuit 19 estimates the frequency characteristic of the transmission line from the detected SP signal, and multiplies the OFDM frequency domain signal by the inverse characteristic of the estimated transmission line frequency characteristic. By performing such processing, the equalization circuit 19 can remove distortion due to the influence of the transmission path and restore the originally transmitted signal.
- the OFDM frequency domain signal that has been equalized by the equalization circuit 19 is supplied to a demapping circuit 20.
- the demapping circuit 20 reallocates data (demodulation data) corresponding to the modulation method (for example, QP SK, 16 QAM, or 64 QAM) to the equalized OFDM frequency domain signal (complex signal). Mapping processing) to restore the transmission data sequence.
- the transmission data sequence output from the demapping circuit 20 is supplied to the transmission path decoding circuit 21.
- the transmission line decoding circuit 21 performs a transmission line decoding process corresponding to the broadcast system on the input transmission data sequence. For example, in the transmission line decoding circuit 21, time din / leave processing corresponding to time-direction interleaving, frequency ding / leave processing corresponding to frequency-direction interleaving, and bit interleaving for error dispersion of multi-valued symbols are performed. Dinterleaving processing for puncturing processing to reduce transmission bits, Viterbi decoding processing for decoding convolutionally encoded bit strings, Dinari processing in byte units It performs the energy despreading process corresponding to the power process, the energy spreading process, and the error correction process corresponding to the RS coding process.
- the transmission data sequence decoded in this way is output, for example, as a transport stream defined in MPEG-2 Systems.
- the transmission control information decoding circuit 22 decodes transmission control information such as TMCC and TPS modulated at a predetermined position of the OFDM transmission frame.
- Guard correlation / peak detection circuit 6 Next, a detailed configuration of the guard correlation / peak detection circuit 12 will be described.
- constants Nu, Ng, and Ns (Nu, Ng, and Ns are natural numbers) are used.
- Nu is the number of samples in one valid symbol.
- FIG. 4 shows a block diagram of the guard correlation / peak detection circuit 12.
- FIG. 5 shows a timing chart of each signal in the guard correlation / peak detection circuit 12.
- the guard correlation / peak detection circuit 12 includes a delay circuit 31, a complex conjugate circuit 32, a multiplication circuit 33, a moving sum circuit 34, an amplitude calculation circuit 35, and an angle.
- a conversion circuit 36, a free-running counter 37, a peak detection circuit 38, and an output circuit 39 are provided.
- the FDM time domain signal (FIG. 5 (A)) output from the carrier frequency error correction circuit 9 is supplied to the delay circuit 31 and the multiplication circuit 33.
- the delay circuit 31 is a shift register composed of Nu register groups, and delays the input OFDM time domain signal by an effective symbol time.
- the OFDM time domain signal (FIG. 5 (B)) delayed by the effective symbol time by the delay circuit 31 is input to the complex conjugate circuit 32.
- the complex conjugate circuit 32 calculates the complex conjugate of the OFDM time-domain signal delayed by the effective symbol period and supplies it to the multiplication circuit 33.
- the multiplication circuit 33 converts the non-delayed OFDM time-domain signal (FIG. 5 (A)) and the complex conjugate signal of the OFDM time-domain signal (FIG. 5 (B)) delayed by the effective symbol period. Multiply every sample.
- the result of the multiplication is input to the moving sum circuit 34.
- the moving sum circuit 34 is composed of, for example, a shift register composed of Ng register groups and an adder for calculating the sum of the values stored in each register, and is sequentially input for each sample. A moving sum operation is performed for each of the N g samples on the multiplied result.
- the value output from the moving sum circuit 34 is the correlation between the OFDM time-domain signal and the OFDM time-domain signal delayed by the effective symbol (Nu samples).
- the guard correlation signal output from the moving sum circuit 34 is supplied to an amplitude calculation circuit 35 and an angle conversion circuit 36.
- the amplitude calculation circuit 35 calculates the amplitude component of the guard correlation signal by squaring the real part and the imaginary part of the guard correlation signal, adding them, and taking the square root of the addition result.
- the amplitude component of the guard correlation signal is supplied to a peak detection circuit 38.
- the angle conversion circuit 36 calculates T an-1 for the real part and the imaginary part of the guard correlation signal to obtain the phase component of the guard correlation signal.
- the phase component of the guard correlation signal is supplied to a peak detection circuit 38.
- the self-running counter 37 is a counter for counting the operation clock.
- the count value N of the self-propelled counter 37 is incremented by 1 from 0 to N s -1 and returns to 0 when it exceeds N s -1 (Fig. 5 (D)).
- the self-propelled counter 37 is a cyclic count which has one cycle in the number of samples in the OFDM symbol period.
- the count value N of the free-running counter 37 is supplied to a peak detection circuit 38.
- the peak detection circuit 38 detects a point having the highest amplitude value of the guard correlation signal within one cycle (0 to Ns-1) of the free-running counter 37, and detects a count value at the point. When the count value of the free-running counter 37 shifts to the next period, the peak detection circuit 38 newly detects a point where the amplitude value of the guard correlation signal is high. The count value detected by the peak detection circuit 38 becomes the peak timing value Np indicating the peak time of the guard correlation signal. Further, the peak detection circuit 38 also detects the phase component of the guard correlation signal at the peak time, and outputs the detected phase component to the output circuit 39.
- the output circuit 39 captures the count value output from the peak detection circuit 38 and stores it in the internal register when the count value N of the self-running counter 37 becomes 0, and stores the count value in the external register. Is set to be ready for output (Fig. 5 (E)).
- the count value stored in the register is output to the subsequent timing synchronization circuit 13 as information (peak timing value Np) indicating the peak time of the guard correlation signal.
- the output circuit 39 also takes in the phase component output from the peak detection circuit 38 at the timing when the count value N of the self-running counter 37 becomes 0, and internally outputs the same. Stored in the 8th register, and set the phase component so that it can be output to outside.
- the phase component stored in the register is output to the subsequent narrow-band carrier frequency error calculation circuit 14.
- the self-running counter 37 issues a valid flag that becomes high when the count value N becomes 0 (FIG. 5 (F)). This valid flag indicates the peak timing value Np and the phase value issue timing value for the subsequent circuit.
- the circulation timing of the self-running counter 37 is adjusted so as to deviate from the OFDM symbol period by about half a cycle. That is, the peak timing value Np is adjusted so as to be about 1/2 of the maximum value of the count value (Ns-1).
- the peak detection cycle of the peak detection circuit 38 is from the timing when the count value of the self-running counter 37 becomes 0 to the time when it becomes N s -1.
- the peak detection circuit 38 outputs the count value when the amplitude value of the guard correlation signal becomes the maximum during the period as the peak evening value Np.
- the timing at which the cycle of the self-running counter 37 is updated that is, the timing at which the count value becomes 0
- the timing at which the amplitude value of the guard correlation signal becomes maximum are close in time
- a part having a high correlation that is, a mountain-shaped part
- the peak value of the gar correlation signal may not always be constant due to various noises and errors and may fluctuate for each symbol, so the peak value is generated by the guard interval of the previous OFDM symbol.
- the highly correlated part that was previously determined will be the boundary position of the next OFDM symbol. Therefore, by adjusting the peak timing value Np in advance so as to be approximately 1/2 of the maximum value of the count value (Ns-1), the guardinterpulse of the previous OFDM symbol can be adjusted.
- the part with high correlation (crest-like part) caused by the above can be excluded from the judgment of the next OFDM symbol, and stable 9 The peak position can be detected.
- the guard correlation / peak detection circuit 12 has a configuration in which the peak timing value N is generated in one OFDM symbol period. However, instead of one OFDM symbol period, M (M is a natural number) .) The configuration may be such that the peak timing value Np is generated in the OFDM symbol period. However, in this case, the valid flag is configured to be High (1) only once in the M OFDM symbol periods.
- FIG. 6 shows an internal configuration diagram of the timing synchronization circuit 13.
- the timing synchronization circuit 13 includes a clock frequency error calculation circuit 41, an initial value calculation circuit 42, a symbol boundary calculation circuit 43, a symbol boundary correction circuit 44, and a start flag. And a generation circuit 45.
- the timing synchronization circuit 13 receives the peak timing value Np from the guard correlation / peak detection circuit 12 for each of the M OFDM symbols (M is a natural number). The operation of each circuit in the timing synchronization circuit 13 is controlled in the input timing period (M symbol period) of the peak evening value Np.
- the clock frequency error calculating circuit 41 calculates the clock frequency error based on the peak timing values Np input at the M OFDM symbol periods, and calculates the calculated clock frequency error as a symbol boundary calculating circuit 4 3 To enter.
- the internal configuration of the clock frequency error calculation circuit 41 will be described later in detail.
- the initial value calculation circuit 42 calculates an initial value of the peak timing value Np based on the peak timing value Np input at the M symbol period. This initial value is input to the symbol boundary calculation circuit 43.
- the symbol boundary calculating circuit 43 performs a filtering process on the peak evening value Np input at the M symbol period, and calculates a symbol boundary position Nx indicating a boundary position of 0 FDM symbol.
- the symbol boundary position Nx is a value expressed in the range of 0 to Ns, which is the period of the free-running counter 37 in the guard correlation / peak detection circuit 12.
- the symbol boundary position NX is a value with a precision below the decimal point, while the self-propelled counter 37 and the peaking value Np are values with an integer precision.
- the symbol boundary calculation circuit 43 calculates the phase error between the output value (symbol boundary position N x) and the input value (peak timing value N p), and calculates the output value (symbol boundary position NX) based on the phase error component. Filtering processing for stabilization is performed.
- the initial value output from the initial value calculation circuit 42 is an initial output value at the start of the filtering process, for example.
- the symbol boundary calculating circuit 43 adds the clock frequency error calculated by the clock frequency error calculating circuit 41 to the phase error component, thereby obtaining an output value based on the clock frequency error ( The fluctuations of the symbol boundary position N x) are also corrected. By obtaining the symbol boundary position including the clock frequency error in this way, it is possible to specify the symbol boundary position with higher accuracy.
- the symbol boundary position Nx output from the symbol boundary calculation circuit 43 is input to the symbol boundary correction circuit 44.
- the symbol boundary correction circuit 44 detects an integer component of the symbol boundary position N X input to the M symbol ⁇ and calculates a start time for the FFT calculation. The calculated start time is supplied to the start flag generation circuit 45. Further, the symbol boundary correction circuit 44 detects a component that is smaller than or equal to the fraction of the symbol boundary position Nx, and obtains a time lag between the symbol boundary time and the FFT operation start time with an accuracy equal to or less than the sampling clock cycle. The phase rotation amount of the signal component included in each subcarrier after the FFT calculation is calculated based on the time shift amount. The calculated amount of phase rotation is supplied to the phase correction circuit 11 after being converted into a complex signal.
- the start flag generation circuit 45 generates a start flag for specifying a signal cutout timing for FFT calculation (that is, FFT calculation start timing) based on the set time supplied from the symbol boundary correction circuit 44. .
- This star The two flags are generated for each OFDM symbol.
- the start flag may be generated after being delayed by a predetermined margin time from the input symbol boundary position NX. However, this margin time should not exceed at least the length of the guard interval.
- FIG. 7 shows an internal configuration diagram of the clock frequency error calculation circuit 41.
- the clock frequency error calculation circuit 41 includes a slope detection circuit 51, a histogram generation circuit 52, and an output circuit 53.
- the inclination detection circuit 51 is a circuit that detects the temporal change rate of the peak timing value Np input from the guard correlation / peak detection circuit 12. That is, it is a circuit that detects the amount of slope S of the peak timing value Np.
- the inclination detection circuit 51 is provided with a plurality of detection paths having different detection periods for detecting the amount of inclination, and outputs a plurality of inclination amounts S obtained in each of the detection paths.
- the histogram generation circuit 52 classifies the amount of inclination S output from the inclination detection circuit 51 at that level and generates a histogram indicating the frequency of detection of the amount of inclination S.
- the histogram generation circuit 52 detects the mode of the generated histogram, and outputs the mode to the output circuit 53.
- the output circuit 53 determines whether or not the mode value is output stably based on the input mode value, and generates a synchronization establishment flag when it is determined that the mode value is stable. At the same time, the mode value is output to the outside as a clock frequency error.
- the slope detection circuit 51 detects the time change rate (slope amount S) of the peak timing value Np, and the slope amount S is a value proportional to the clock frequency error. First, the reason is explained.
- the peak timing value Np output from the guard correlation / peak detection circuit 12 is the value of the self-running counter 37 at the peak time of the guard planning signal.
- the self-propelled counter 37 is a cyclic counting circuit, but the count number in one cycle is set in advance to the sampling number of 1 OFDM symbol.
- the peak evening value Np gradually increases as shown in FIG. If the cycle of the free-running counter 37 is longer than the symbol cycle of the received ⁇ FDM signal, that is, the operating clock of the free-running counter 37 is longer than the transmission clock of the received OFDM signal. When is slow, the peak timing value Np gradually decreases as shown in FIG.
- the time rate of change of the peak timing value Np is a value proportional to the clock frequency error, which is the error between the transmission clock of the received OFDM signal and the sampling clock of the receiving side. Therefore, as shown in Fig. 11, the clock frequency error is obtained by detecting the peak timing value Np at every fixed detection period (T), and detecting the peak timing value at an arbitrary time ( ⁇ ) (or an integer). Calculate the time change rate ( ⁇ ) based on the difference value X between the value ⁇ ⁇ and the peak timing value ⁇ ⁇ detected at the sample time ((1 1) ⁇ ) immediately before that time. Can be. That is, if the slope amount S of the peak timing value ⁇ is obtained, the clock frequency error can be obtained. In addition, it can be said that the slope amount S of the peak timing value Np is, in other words, a value obtained by measuring the symbol interval of the received OFDM symbol with the operation clock of the reception side.
- a reception environment called frequency selective fading (a state where multipath reception is performed and fading occurs in each received wave (main wave and a plurality of delayed waves)) may occur.
- OF in frequency selective fading environment When a DM signal is received, the reception levels of the main wave and the delayed wave fluctuate periodically. Therefore, when the peak position of the guard correlation signal is detected, the symbol boundary position indicated by the peak position is periodically switched between the main wave and the delayed wave. That is, if the reception level of the main wave is higher, the boundary position of the symbol of the main wave is detected, and if the reception level of the delay wave is higher, the boundary position of the symbol is detected.
- the peak timing value N p in the frequency selective fading state and in the state where the clock frequency error is generated is determined by the main cycle at a substantially constant period (fading period).
- the increase and decrease of the time difference between the wave and the delayed wave are alternately repeated.
- the cycle at which the main wave reception level and the delayed wave reception level are switched by frequency selective fusing differs depending on the reception environment and becomes longer or shorter.
- the present inventor has provided in the inclination detection circuit 51 a plurality of inclination detection paths each having a different detection period T for detecting the amount of inclination S of the peak timing value Np.
- the clock frequency error is measured comprehensively based on the amount of slope S detected by. For example, based on a plurality of inclination amounts having different detection periods T, the detection results are averaged or converted into a histogram, for example, so that the clock frequency error can be estimated.
- FIG. 14 shows a specific circuit configuration diagram of the inclination detection circuit 51.
- the inclination detection circuit 51 includes first to fifth five inclination detection paths 61-1 to 61-5 that output the amount of inclination S.
- the first to fifth tilt detection paths 61-1-61-5 have M OFDM symbols In synchronization with the valid flag set to high (1), the peak timing value Np is input. In the first to fifth inclination detection paths 61-1 to 61-5, the operation is performed in synchronization with the valid flag (for each of M OFDM symbols), and the inclination amount S i S g is output. Power.
- different inclination detection periods T are set.
- ⁇ is a parameter (natural number) for setting the detection period ⁇ , and has a different value for each inclination detection path.
- the third tilt detection path is set.
- the first to fifth slope detection paths 6 1-1 to 6 1-5 are respectively a delay unit 62-1 to 62-5, a subtractor 63-1 to 63-5, and a multiplier. 64-1 to 64-5, and the initial mask circuit 65- :! to 65-5.
- Delay unit 62- :! 62 to 62-5 are shift registers which are composed of ⁇ -stage registers and which shift data to the next register in synchronization with a valid flag.
- the delay unit 62-1 of the first slope detection path is composed of 16-stage shift registers
- the delay unit 62-2 of the second slope detection path is composed of an 8-stage shift register.
- the delay device 62-3 of the third slope detection path is composed of four stages of shift registers
- the delay device 62-4 of the fourth gradient detection path is composed of two stages of shift registers.
- the delay device 6 2-5 of the slope detection path is composed of a one-stage shift register.
- the subsequent peak timing value Np is input.
- the subtractor 6 3-1 -6 3-5 subtracts the delayed peak timing value N p from the undelayed peak timing value N p. Therefore, the amount of change in the peak timing value Np detected in the detection period T is output from the subtractors 63-1 to 63-5.
- the multipliers 64-1 to 64-5 multiply the amount of change in the peaking value Np output from the subtractor 63-1-6-3-5 by the reciprocal of the parameter n to obtain the peak value. Calculate the amount of slope S to 5 indicating the slope of the timing value Np.
- the multipliers 64-1 to 64-5 output the inclination amounts S i to S 5 to the outside via the initial mask circuits 64-;! To 64-5.
- the initial mask circuit 65-1-65-5 is used between the time when the detection of the slope S is stopped and the time when a valid value is output from the multipliers 64-1 to 64-5.
- a process of stopping the output of the inclination amounts S i to S 5 is performed. That is, the initial mask circuit 6 5-1 to 65-5 stops the output of the slope amount S while the invalid value is output from the register at the last stage of each delay unit 62-1-62-5. Circuit.
- the initial mask circuit 64-1 of the first slope detection path outputs the output of the slope amount S from when the detection operation of the slope amount S1 is started until the valid flag is counted 16 times. stop, initial mask circuit 64 2 of the second inclination detection path, stops the output of the inclination amount S 2 of until valid flag is 8 counts after the detection of the gradient S 2 is started and, initial mask circuit 64 3 of the third gradient detection path, stops the output of the inclination amount S 3 until the valid flag is four counts since the detection of the gradient S 3 is started, initial mask circuit 64 4 of the fourth gradient detection path, stops the output of the inclination amount S 4 until the effective flag since the detection of the gradient S 4 is started is 2 counts, the inclination detection path initial mask circuit 64-5 of 5, effective since the detection of the gradient S 5 is scan evening Ichito off Grayed stops the output of the inclination amount S 5 of until it is one count.
- the inclination amounts S i to S 5 output from the initial mask circuit 65-1-65-5 are supplied to the histogram generation circuit 52.
- the amount of inclination S (S i to S 5 ) is input from the inclination detection circuit 51 to the histogram generation circuit 52 at every input interval TX of the peak timing value N.
- the histogram generation circuit 52 classifies the input gradient amount S into classes divided by the magnitude (level) of the gradient amount S, and shows the frequency of detection of the gradient amount S for each classified class. Generate a histogram as shown in Fig.5. This histogram is hereinafter referred to as an error detection histogram. Then, the histogram generation circuit 52 accumulates the detection frequency of the slope amount S in the error detection histogram, and calculates the error detection histogram. Output the mode (the class value of the most frequent class).
- the histogram referred to in the present specification does not show the figure itself, but refers to a data group showing a frequency distribution in which the frequency is described for each class.
- the histograms shown in Figure 15 and the following figures are provided to make the data group visually easy to understand.
- a plurality of gradient amounts S having different detection periods T are input at every input interval TX of the peak timing value Np. The longer is assumed to be higher. Therefore, in the histogram generation circuit 52, as shown in FIG. 17, a reference histogram having different weights is set for each time length of the detection interval T (that is, for the slope detection path 61-1 to 61-5 ⁇ ). Keep it. Then, when the slope amount S detected at a certain detection interval T is input, a reference histogram corresponding to the detection interval T is selected, and the class of the slope amount S is the maximum as shown in FIG. The reference histogram is translated so as to match the frequent value, and the translated reference histogram is added to the error detection histogram.
- the weight of each reference histogram is set, for example, as follows.
- the range of the variable (the width from the class value of the lowermost class to the class value of the uppermost class of the histogram) becomes longer according to the detection interval T, and the range of the variable becomes the other reference histogram.
- the range of the variables in the reference histogram is set to 15/1/6, etc. I have.
- the mode is set so that the mode becomes smaller in accordance with the detection interval T, and the mode is different from the other reference histograms.
- the detection interval T 4
- the mode of the XT X reference histogram is set to 8
- the detection interval T 2
- the mode of the XTx reference histogram 4
- the detection interval T 1
- the mode of the XTx reference histogram is set to 2, and so on. ing.
- Each reference histogram has the same total frequency. That is, when the reference histogram is shown in the figure, the area is the same. For example, as shown in Fig. 17, the total frequency is set to 32.
- Each reference histogram is set so that the mode and the median match, and the median is located in the middle of the variable range.
- each reference histogram is set so that the frequency of the upper class and the frequency of the lower class match.
- Each reference histogram is set so that the frequency of the class near the center of the range of the variate is higher than the frequency of the class closer to the end of the class.
- FIG. 19 shows a specific circuit configuration of the histogram generation circuit 52, and its operation will be described.
- the histogram generation circuit 52 includes first to fifth reference histogram generation circuits 71-1 to 71-5, and a histogram addition / normalization circuit 72. .
- the first to fifth reference histogram generating circuits 71-1 to 71-5 hold differently weighted reference histograms.
- the first to fifth reference histogram generation circuits 7 1-1-7 1-5 are provided with the slope amounts S ⁇ ⁇ from the corresponding first to fifth slope detection paths 6 1-1-6 1-5.
- inclination amount S 5 is input to each input interval TX.
- the first to fifth reference histogram generation circuits 7 1-1-7 1-5 classify the input slope amount S into classes and store the internally stored values so that the mode value is in that class. Translate the quasi-histogram parallel. Then, the parallel-shifted reference histogram is supplied to the histogram addition / normalization circuit 72. The first to fifth reference histogram generation circuits 71-1-7 1-5 output reference histograms at each input interval Tx.
- the histogram addition / normalization circuit 72 internally stores an error detection histogram.
- the histogram addition / normalization circuit 72 adds all the input reference histograms to the error detection histogram.
- the histogram for error detection is generated by adding all five reference histograms and accumulatively adding the reference histograms input for each input interval ⁇ X.
- the histogram addition / normalization circuit 72 calculates the mode of the error detection histogram. The calculated mode value is supplied to a subsequent output circuit 53 at, for example, every input interval ⁇ .
- the histogram addition / normalization circuit 72 normalizes the error detection histogram when the frequency of the mode of the error detection histogram stored therein exceeds a certain threshold value. . That is, if the frequency of the mode exceeds a certain threshold value, data cannot be managed in a memory or the like, so that a process for reducing the data amount of the entire error detection histogram is performed.
- a normalization processing method for example, a method of dividing the whole by a certain value may be applied, but in this example, the most frequent value in the histogram for error detection is a particularly important value. Classes with low frequency have low importance.
- normalization is performed by subtracting a constant value from the frequency of the class of the entire histogram for error detection.
- the histogram addition / normalization circuit 72 may calculate the mode value after moving and adding the frequency of the generated error detection histogram in the class direction. For example, the histogram addition / normalization circuit 72 adds the frequency of each class to the histogram for error detection as shown in FIG. The moving averaged error detection histogram as shown in Fig. 20 (B) is regenerated. Then, the histogram addition / normalization circuit 72 calculates the mode value based on the moving averaged error detection histogram. By calculating the moving average of the error detection histogram in this way; f, the error can be removed.
- each of the reference histogram generating circuits 71-1-71-5 may hold a moving averaged reference histogram.
- a moving averaged reference histogram as shown in FIG. 21 may be held for the reference histogram shown in FIG.
- the histogram addition / normalization circuit 72 can perform the processing without performing the averaging processing.
- the output circuit 53 determines the convergence state of the histogram generated by the histogram generation circuit 52, and outputs the input mode as a clock frequency error when it is determined that the histogram has sufficiently converged and stabilized. I do. . At the same time, the output circuit 53 generates a synchronization establishment flag indicating that synchronization using the clock frequency error has been established.
- the output circuit 53 is connected to a state machine 75 composed of three states, a standby state St1, an asynchronous state St2, and a synchronous state St3, as shown in FIG. Therefore, the output control of the clock frequency error and the output control of the synchronization establishment flag are performed.
- the state machine 75 shown in FIG. 22 will be described.
- the state machine 75 When the reset operation is performed, the state machine 75 first transitions to the standby state St1. In the standby state St1, the clock frequency error and the synchronization establishment flag are not output. After 1 XT x time has passed since the reset operation, the state machine The pin 75 transitions from the standby state St1 to the asynchronous state St2.
- the meaning of 1 XTX time is a time interval from when the reset operation is performed to when the slope detection circuit 51 outputs at least one effective slope amount S.
- the standby state St1 is set for the shortest detection period among the detection periods T of the plurality of different inclination amounts S, and after that period, Transition to the asynchronous state St2.
- the state machine 75 observes the fluctuation state of the input mode, and the histogram converges sufficiently and becomes stable (that is, the clock frequency). Judgment is made whether the synchronization using the error is established) or the histogram is not converged and unstable (that is, the synchronization using the clock frequency error is not established).
- the mode input continuously every Tx time is j times (j is a natural number. For example, 100).
- j is a natural number. For example, 100).
- a transition is made from the asynchronous state St2 to the synchronous state St3. That is, if the same value is continuously output from the histogram generation circuit 52, it is determined that the operation is stable.
- the mode that is continuously input at every Tx time is k times (k is a natural number; for example, 10) continuously different values.
- k is a natural number; for example, 10.
- the state is shifted from the synchronization state St 3 to the synchronization state St 2. That is, if the value output from the histogram generation circuit 52 continues to fluctuate, it is determined that the value is unstable.
- the state machine 75 does not output the clock frequency error and the synchronization establishment flag in the standby state St 1 and the asynchronous state St 2, and outputs the clock frequency error and the synchronization establishment only in the asynchronous state St 3. Output a flag.
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EP03780894A EP1578045A1 (en) | 2002-12-27 | 2003-12-18 | Ofdm demodulation device |
US10/504,341 US7447277B2 (en) | 2002-12-27 | 2003-12-18 | Ofdm demodulation device |
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JP2002382213A JP2004214962A (ja) | 2002-12-27 | 2002-12-27 | Ofdm復調装置 |
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US20050117667A1 (en) | 2005-06-02 |
CN1692587A (zh) | 2005-11-02 |
EP1578045A1 (en) | 2005-09-21 |
US7447277B2 (en) | 2008-11-04 |
JP2004214962A (ja) | 2004-07-29 |
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