JP2007202082A - Ofdm demodulating device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM demodulating device and method thereof in which immunity to CW (Continuous Wave) disturbance is strengthened. <P>SOLUTION: A CW disturbance detection circuit 19 calculates a power for each sub carrier of an OFDM frequency domain signal and detects a sub carrier in which the CW disturbance is present. A data extraction circuit 20 extracts data in a part of transmission line characteristics estimated by a transmission line characteristic estimation circuit 18 and supplies the extracted transmission characteristics to an IFFT operation circuit 21. In particular, if CW disturbance is present, data are extracted from a range avoiding the sub carrier in which the CW disturbance is present. The IFFT operation circuit 21 performs IFFT operation on the transmission line characteristics supplied from the data extraction circuit 20 to generate a delay profile representing a signal strength of each path. A window reproduction circuit 22 uses the delay profile to detect a symbol contour of a first reached path and specifies an FFT operation range for an FFT operation circuit 17. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an OFDM demodulator and method for demodulating an Orthogonal Frequency Division Multiplex (OFDM) signal.

  In recent years, a modulation scheme called an orthogonal frequency division multiplexing (OFDM) scheme (hereinafter referred to as an OFDM scheme) has been proposed as a scheme for modulating digital data. In this OFDM system, a number of orthogonal subcarriers (subcarriers) are provided in a transmission band, and data is allocated to the amplitude and phase of each subcarrier by PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation) Modulation method.

The OFDM system is widely studied to be applied to terrestrial digital broadcasting that is strongly affected by multipath interference. As terrestrial digital broadcasting adopting the OFDM system, for example, there are standards such as DVB-T (Digital Video Broadcasting-Terrestrial), ISDB-T (Integrated Services Digital Broadcasting-Terrestrial), ISDB- _TSB (ISDB-T Sound Broadcasting). is there.

  As shown in FIG. 13, a transmission signal by the OFDM scheme is transmitted in symbol units called OFDM symbols. This OFDM symbol is composed of an effective symbol that is a signal period during which IFFT (Inverse Fast Fourier Transform) calculation is performed at the time of transmission, and a guard interval in which a waveform in the latter half of the effective symbol is copied as it is. This guard interval is provided in the first half of the OFDM symbol, and is, for example, a signal having a time length of 1/4 or 1/8 of the effective symbol.

  In an OFDM receiver that receives such an OFDM signal, the received OFDM signal is demodulated by performing an FFT operation by an FFT (Fast Fourier Transform) operation circuit. The OFDM receiver detects an OFDM symbol boundary position with respect to an OFDM symbol composed of an effective symbol and a guard interval, and an operation range (FFT window) having the same length as the effective symbol from the detected symbol boundary position And the FFT operation is performed by specifying the data of the portion determined by the FFT window from the OFDM symbol.

  By the way, terrestrial broadcasting is a transmission path under a multipath environment. That is, the signal received by the OFDM receiver is strongly combined with a plurality of delayed waves due to strong interference from delayed waves depending on the surrounding terrain around the reception position and surrounding environment such as a building.

  Thus, in a transmission path under a multipath environment, there are a plurality of symbol boundaries because there are a plurality of paths. Usually, the FFT window position is based on the symbol boundary position of the path that has arrived first. Is set so that there is no intersymbol interference.

  Here, a method for setting the position of the FFT window for determining the FFT calculation position will be described (see Patent Documents 1 and 2).

  As a first method for setting the FFT window, the OFDM signal before the FFT operation is delayed, and the waveform of the guard interval portion and the latter half of the OFDM symbol (that is, the signal waveform of the guard interval copy source) There is a method for obtaining the correlation between the symbol boundary position and detecting the symbol boundary position. In this method, the time indicated by the peak value of the autocorrelation function is the boundary between the OFDM symbols of each path. Therefore, an FFT window trigger is generated based on the symbol boundary position of the path that has arrived first, and symbol synchronization is achieved.

  As a second method, there is a method of using a scattered pilot signal (SP signal) having a specific power and a specific phase scattered at specific positions of the OFDM symbol. In this method, the SP signal is extracted from the OFDM signal, the modulation component is removed, and then the channel characteristics of all subcarriers in the OFDM symbol are estimated by interpolation using a time direction interpolation filter and a frequency direction interpolation filter. . Then, IFFT calculation is performed on the estimated transmission path characteristics to generate a delay profile indicating the signal strength of each path, and an OFDM symbol boundary is obtained based on the path that has arrived first. Then, an FFT window trigger is generated based on the symbol boundary position to achieve symbol synchronization.

JP 2002-368717 A JP 2001-292125 A

  However, in such a conventional OFDM receiving apparatus, when the SP signal is disturbed by a continuous wave having a constant frequency and no modulation (hereinafter referred to as CW interference), estimation of transmission path characteristics is performed. Since the accuracy is degraded, the equalization performance is degraded, and further, the estimation accuracy of the delay profile generated from the estimated transmission path characteristics is also degraded.

  The present invention has been proposed in view of such a conventional situation, and an object of the present invention is to provide an OFDM demodulator and method for enhancing resistance against CW interference.

  In order to achieve the above-described object, the OFDM demodulator according to the present invention uses transmission symbols generated by dividing and orthogonally modulating information for a plurality of subcarriers within a predetermined band as transmission units. An OFDM demodulator for demodulating an orthogonal frequency division multiplexing (OFDM) signal in which a pilot signal having a specific power and a specific phase is discretely inserted into predetermined subcarriers in the transmission symbol, The calculation range for the effective symbol period is set from each transmission symbol of the OFDM signal, the Fourier transform means for Fourier transforming the set computation range, and the power for each subcarrier of the signal Fourier transformed by the Fourier transform means Based on the above, it is determined whether or not there is interference by a constant frequency and unmodulated continuous wave. The interference detection means for detecting the subcarrier, the pilot signal is extracted for each transmission symbol from the signal Fourier-transformed by the Fourier transform means, and the transmission is performed by interpolating the extracted pilot signal in the time direction and the frequency direction. Transmission line characteristic estimation means for estimating transmission line characteristics of all subcarriers in the symbol, data extraction means for extracting a part of the transmission line characteristic data estimated by the transmission line characteristic estimation means, and the data An inverse Fourier transform unit that generates a delay profile by performing an inverse Fourier transform on the transmission path characteristics extracted by the extraction unit for each transmission symbol, and the calculation based on the delay profile generated by the inverse Fourier transform unit. Window reproducing means for controlling the range, and the data extracting means comprises If it is determined that the interference by the interference detecting means are present, and extracts the data from the subcarriers other than subcarriers interference is present.

  In addition, the OFDM demodulation method according to the present invention uses a transmission symbol generated by dividing and orthogonally modulating information for a plurality of subcarriers within a predetermined band as a transmission unit, and has a specific power. An OFDM demodulation method for demodulating an Orthogonal Frequency Division Multiplex (OFDM) signal in which a pilot signal having a specific phase is discretely inserted into predetermined subcarriers in the transmission symbol, wherein each transmission of the OFDM signal is performed. Based on the Fourier transform step of Fourier transforming the set computation range for the effective symbol period from the symbol, and the Fourier transform of the signal subjected to Fourier transform in the Fourier transform step, a constant frequency and Judgment to detect the presence of disturbances due to unmodulated continuous waves and to detect subcarriers with disturbances, if any And extracting the pilot signal for each transmission symbol from the signal subjected to Fourier transformation in the Fourier transform step, and interpolating the extracted pilot signal in the time direction and the frequency direction to A transmission line characteristic estimation step for estimating the transmission line characteristic of the subcarrier, a data extraction step for extracting a part of the transmission line characteristic data estimated in the transmission line characteristic estimation step, and the data extraction step. Inverse Fourier transform process for generating a delay profile by performing inverse Fourier transform on the transmission path characteristics extracted for each transmission symbol, and the calculation range based on the delay profile generated in the inverse Fourier transform process A window reproduction process for controlling the disturbance, and in the data extraction process, there is a disturbance in the disturbance detection process. If it is determined that that, and extracts the data from the subcarriers other than subcarriers interference is present.

  Also, the OFDM demodulator according to the present invention uses a transmission symbol generated by dividing and orthogonally modulating information for a plurality of subcarriers within a predetermined band as a transmission unit, and has a specific power. An OFDM demodulator for demodulating an orthogonal frequency division multiplexing (OFDM) signal in which a pilot signal having a specific phase is discretely inserted into predetermined subcarriers in the transmission symbol, the OFDM signal being transmitted Based on the Fourier transform means that performs Fourier transform in symbol units, and the power for each subcarrier of the signal Fourier-transformed by the Fourier transform means, the presence / absence of interference due to a constant frequency and unmodulated continuous wave is determined, and interference exists. If there is a disturbance by the interference detection means for detecting the subcarrier in which the interference exists, and the interference detection means, If it is a constant, among the OFDM signals, characterized in that it comprises a interference removing means for removing a signal of a frequency of the subcarrier interference is present.

  In addition, the OFDM demodulation method according to the present invention uses a transmission symbol generated by dividing and orthogonally modulating information for a plurality of subcarriers within a predetermined band as a transmission unit, and has a specific power. An OFDM demodulation method for demodulating an orthogonal frequency division multiplexing (OFDM) signal in which a pilot signal having a specific phase is discretely inserted into predetermined subcarriers in the transmission symbol, the OFDM signal being transmitted Based on the Fourier transform step of performing Fourier transform in symbol units and the power of each subcarrier of the signal Fourier-transformed in the Fourier transform step, the presence or absence of interference by a continuous wave of a constant frequency and unmodulated is determined. If present, the interference detection step for detecting the subcarrier in which the interference is present, and the interference detection step determines that the interference is present If it, among the OFDM signal, and having an interference removing step of removing a signal of a frequency of the subcarrier interference is present.

  According to the OFDM demodulating apparatus and method according to the present invention, it is possible to prevent the estimation accuracy of transmission path characteristics and the estimation accuracy of delay profiles from deteriorating even when CW interference exists.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

  First, FIG. 1 shows a block diagram of an OFDM receiving apparatus according to the first embodiment.

  As shown in FIG. 1, the OFDM receiver 10 in the first embodiment includes an antenna 11, a tuner 12, a bandpass filter (BPF) 13, an A / D converter circuit 14, and a DC cancel circuit 15. Digital quadrature demodulation circuit 16, FFT operation circuit 17, transmission line characteristic estimation circuit 18, CW interference detection circuit 19, data extraction circuit 20, IFFT operation circuit 21, window reproduction circuit 22, transmission line characteristic A compensation circuit 23 and a transmission path decoding circuit 24 are provided.

  A transmission wave transmitted from the OFDM transmitter is received by the antenna 11 of the OFDM receiver 10 and supplied to the tuner 12 as an RF signal.

  The RF signal received by the antenna 11 is frequency-converted into an IF signal by a tuner 12 including a multiplier 12a and a local oscillator 12b, and is supplied to the BPF 13.

  The IF signal output from the tuner 12 is filtered by the BPF 13 and then digitized by the A / D conversion circuit 14. The digitized IF signal has its DC component removed by the DC cancellation circuit 15 and is supplied to the digital quadrature demodulation circuit 16.

  The digital orthogonal demodulation circuit 16 orthogonally demodulates the digitized IF signal using a carrier signal having a predetermined frequency (carrier frequency), and outputs a baseband OFDM signal. The baseband OFDM signal output from the digital quadrature demodulation circuit 16 is a so-called time domain signal before the FFT operation is performed. Therefore, hereinafter, a baseband signal after orthogonal demodulation and before FFT calculation is referred to as an OFDM time domain signal. As a result of orthogonal demodulation, the OFDM time domain signal becomes a complex signal including a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The OFDM time domain signal output from the digital quadrature demodulation circuit 16 is supplied to the FFT operation circuit 17.

  The FFT operation circuit 17 performs an FFT operation on the OFDM time domain signal, and extracts and outputs data that is orthogonally modulated on each subcarrier. The signal output from the FFT operation circuit 17 is a so-called frequency domain signal after the FFT operation. Therefore, hereinafter, the signal after the FFT operation is referred to as an OFDM frequency domain signal.

  The FFT operation circuit 17 extracts a signal in the effective symbol length range (for example, 2048 samples) from one OFDM symbol, that is, removes a range corresponding to the guard interval from one OFDM symbol, and extracts an OFDM time domain signal of 2048 samples. An FFT operation is performed on. Specifically, the calculation start position is any position between the boundary of the OFDM symbol and the end position of the guard interval. This calculation range is called an FFT window.

  As described above, the OFDM frequency domain signal output from the FFT operation circuit 17 is a complex signal composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal), like the OFDM time domain signal. It has become. This complex signal is, for example, a signal subjected to quadrature amplitude modulation by the 16QAM system, the 64QAM system, or the like. The OFDM frequency domain signal is supplied to the transmission line characteristic estimation circuit 18, the CW disturbance detection circuit 19, and the transmission line characteristic compensation circuit 23.

  The transmission path characteristic estimation circuit 18 estimates transmission path characteristics based on the SP signal extracted from the OFDM frequency domain signal.

  Here, FIG. 2 shows an arrangement pattern in the OFDM symbol of the SP signal adopted in the ISDB-T standard.

  In the ISDB-T standard, an SP signal that is BPSK modulated at a ratio of 1 to 12 subcarriers is inserted in the subcarrier direction (frequency direction). Further, in the ISDB-T standard, the SP signal insertion position is shifted in the frequency direction by 3 subcarriers for each OFDM symbol. As a result, the SP signal is inserted once every 4 OFDM symbols with respect to the same subcarrier in the OFDM symbol direction (time direction). As described above, in the ISDB-T standard, SP signals are inserted into OFDM symbols in a spatially dispersed state, thereby reducing the redundancy of the SP signal with respect to the original information.

  The transmission path characteristic estimation circuit 18 removes the information component from the OFDM frequency domain signal, extracts only the SP signal, and obtains the difference between the extracted SP signal and the reference SP signal, thereby removing the modulation component. The SP signal from which the modulation component has been removed represents the transmission path characteristics of the subcarrier into which the SP signal is inserted. Then, the transmission path characteristic estimation circuit 18 performs time direction interpolation processing on the SP signal from which the modulation component is removed, and estimates the transmission path characteristic of the subcarrier in which the SP signal is arranged for each OFDM symbol. As a result, as shown in FIG. 3, the transmission path characteristics can be estimated every three subcarriers in the frequency direction for all OFDM symbols. Subsequently, as shown in FIG. 4, the transmission path characteristic estimation circuit 18 performs frequency direction interpolation processing by oversampling the SP signal interpolated in the time direction three times, and transmits all subcarriers in the OFDM symbol. Estimate road characteristics.

  The transmission line characteristic estimation circuit 18 supplies the transmission line characteristic thus estimated to the data extraction circuit 20 and the transmission line characteristic compensation circuit 23.

  The CW interference detection circuit 19 calculates power for each subcarrier of the OFDM frequency domain signal, and detects a subcarrier in which CW interference exists based on the power for each subcarrier. Then, the CW interference detection circuit 19 supplies a CW interference detection flag indicating the presence or absence of CW interference and a maximum power subcarrier number to the data extraction circuit 20. Details of the CW interference detection circuit 19 will be described later.

  The data extraction circuit 20 extracts some data from the transmission path characteristics estimated by the transmission path characteristic estimation circuit 18 and supplies the extracted transmission path characteristics to the IFFT calculation circuit 21. Usually, as shown in FIG. 5, the data extraction circuit 20 extracts 2 to the power of every 3 subcarriers including the central subcarrier. However, when there is CW interference, the data extraction circuit 20 extracts data from a range that avoids subcarriers with CW interference in order to prevent deterioration of delay profile estimation accuracy in the subsequent stage. Details of the data extraction circuit 20 will be described later.

  The IFFT operation circuit 21 performs an IFFT operation on the transmission line characteristics supplied from the data extraction circuit 20, thereby generating a delay profile indicating the signal strength of each path, and the generated delay profile is displayed as a window reproduction circuit. 22 is supplied.

  The window recovery circuit 22 detects the symbol boundary of the path that has arrived first in the OFDM frequency domain signal, and specifies the FFT calculation range for the FFT calculation circuit 17 based on the detected symbol boundary position. The window reproduction circuit 22 uses the delay profile supplied from the IFFT arithmetic circuit 21 to detect the symbol boundary of the path that has arrived first. Then, the window reproduction circuit 22 generates a trigger indicating the calculation start timing based on the FFT calculation range, and supplies the generated trigger to the FFT calculation circuit 17.

  The transmission line characteristic compensation circuit 23 performs phase equalization and amplitude equalization of the OFDM frequency domain signal using the transmission line characteristic estimated by the transmission line characteristic estimation circuit 18. The transmission path characteristic compensation circuit 23 supplies an OFDM frequency domain signal subjected to phase equalization and amplitude equalization to the transmission path decoding circuit 24.

  The transmission path decoding circuit 24 performs carrier demodulation, deinterleaving, demapping, depuncturing, Viterbi decoding, error correction processing, etc. on the OFDM frequency domain signal subjected to phase equalization and amplitude equalization, Output.

  The OFDM receiver 10 as described above receives and demodulates an OFDM signal broadcast as a terrestrial digital broadcast, decodes the demodulated signal through a transmission path, and outputs a transport stream including, for example, audio and video signals. be able to.

  Hereinafter, the CW disturbance detection circuit 19 and the data extraction circuit 20 described above will be described in detail.

  First, a first example of a block configuration diagram of the CW interference detection circuit 19 is shown in FIG.

  In the CW disturbance detection circuit 19 shown in FIG. 6, the power calculation circuit 31 includes a conjugate complex calculator 31a and a complex multiplier 31b, and calculates power for each subcarrier. The 1-symbol integrator 32 integrates the power for each subcarrier with respect to all subcarriers of one symbol, and obtains the total power for one symbol. The scaling circuit 33 supplies a value obtained by scaling the total power to the comparator 35 as a CW interference determination threshold value. The maximum power subcarrier search circuit 34 searches for a subcarrier having the maximum power, supplies the maximum power to the comparator 35, and supplies the maximum power subcarrier number to the data extraction circuit 20 (FIG. 1). The comparator 35 compares the maximum power with the CW interference determination threshold value to determine the presence or absence of CW interference, and supplies a CW interference detection flag indicating the presence or absence of CW interference to the data extraction circuit 20 (FIG. 1).

  As described above, the CW interference detection circuit 19 shown in FIG. 6 compares the maximum power in the subcarrier having the maximum power in one symbol with the CW interference determination threshold value calculated based on the total power for one symbol. Then, the presence / absence of CW interference is determined.

  Next, a second example of a block configuration diagram of the CW interference detection circuit 19 is shown in FIG. In FIG. 7, the same components as those in FIG. 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the CW disturbance detection circuit 19 shown in FIG. 7, the N symbol period determination circuit 36 accumulates the comparison result of one symbol supplied from the comparator 35 for N symbols (N is an integer of 2 or more), and for N symbols. The presence / absence of CW interference is determined based on the comparison result. For example, the N symbol period determination circuit 36 determines that CW interference exists when the maximum power exceeds the CW interference determination threshold value for N symbols in succession. The N symbol period determination circuit 36 supplies a CW interference detection flag indicating the presence or absence of CW interference and a maximum power subcarrier number to the data extraction circuit 20 (FIG. 1).

  As described above, the CW interference detection circuit 19 shown in FIG. 7 compares the maximum power in the subcarrier having the maximum power in one symbol with the CW interference determination threshold value calculated based on the total power for one symbol. Then, the presence / absence of CW interference is determined based on the comparison result for N symbols. In this way, in FIG. 7, since the presence / absence of CW interference is determined using the comparison result for N symbols, the reliability of CW interference detection can be improved as compared with FIG.

  Next, a third example of a block configuration diagram of the CW interference detection circuit 19 is shown in FIG. In FIG. 8, the same components as those in FIG. 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the CW disturbance detection circuit 19 shown in FIG. 8, the N symbol integrator 37 integrates the power for each subcarrier for all subcarriers of one symbol, and further integrates it for N symbols (N is an integer of 2 or more). By integrating, the total power for N symbols is obtained. The subcarrier power integrator 38 integrates the power for each subcarrier for N symbols, and supplies the power for N symbols and the subcarrier number to the maximum power subcarrier search circuit 34.

  As described above, the CW interference detection circuit 19 shown in FIG. 8 compares the maximum power in the subcarrier having the maximum power in N symbols with the CW interference determination threshold value calculated based on the total power for N symbols. Then, the presence / absence of CW interference is determined. In this way, in FIG. 8, since the presence or absence of CW interference is determined based on the power for N symbols, the reliability of CW interference detection can be improved as compared with FIG.

  Next, a block diagram of the data extraction circuit 20 is shown in FIG.

  In the data extraction circuit 20 shown in FIG. 9, the extraction start position determination circuit 41 determines the extraction start position when extracting a part of the data of the transmission path characteristics based on the CW interference detection flag and the maximum power subcarrier number. decide. Normally, as shown in FIG. 5, the data extraction circuit 20 extracts 2 to the power of every 3 subcarriers including the central subcarrier, but when CW interference exists, the extraction starts. The position determination circuit 41 determines an extraction start position so that data can be extracted from a range avoiding subcarriers (maximum power subcarriers) in which CW interference exists. The selection circuit 42 extracts transmission path characteristic data at predetermined intervals (every 3 subcarriers) from the determined extraction start position, and supplies the extracted transmission path characteristics to the IFFT arithmetic circuit 21 (FIG. 1).

  As described above, the data extraction circuit 20 extracts data of transmission path characteristics from a range avoiding a subcarrier (maximum power subcarrier) in which CW interference is present when CW interference is present. Thereby, it is possible to prevent the estimation accuracy of the delay profile from deteriorating due to CW interference.

  Next, FIG. 10 shows a block configuration diagram of an OFDM receiving apparatus according to the second embodiment. In FIG. 10, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 10, the OFDM receiver 50 in the second embodiment includes an antenna 11, a tuner 12, a bandpass filter (BPF) 13, an A / D converter circuit 14, and a DC cancel circuit 15. Digital quadrature demodulation circuit 16, CW disturbance removal circuit 52, FFT operation circuit 17, CW disturbance detection circuit 51, transmission line characteristic estimation circuit 18, synchronization circuit 53, transmission line characteristic compensation circuit 23, transmission And a path decoding circuit 24.

  The CW interference detection circuit 51 calculates power for each subcarrier of the OFDM frequency domain signal and detects a subcarrier in which CW interference exists based on the power for each subcarrier. Then, the CW interference detection circuit 51 supplies a CW interference detection flag indicating the presence or absence of CW interference and the frequency of the maximum power subcarrier to the CW interference removal circuit 52. Details of the CW interference detection circuit 51 will be described later.

  When there is CW interference, the CW interference removal circuit 52 removes the signal of the subcarrier in which CW interference exists in order to prevent the estimation accuracy of the transmission path characteristics from deteriorating. Details of the CW interference removal circuit 52 will be described later.

  The synchronization circuit 53 detects the OFDM symbol boundary position using the OFDM time domain signal or the OFDM frequency domain signal, and generates a trigger indicating the calculation start timing of the FFT operation based on the detected symbol boundary position. The trigger is supplied to the FFT operation circuit 17. The synchronization circuit 53 also performs carrier reproduction and timing reproduction. The synchronization circuit 53 can perform symbol boundary position detection, carrier recovery, and timing recovery from the correlation of the waveform of the guard interval portion when the OFDM time domain signal is delayed. The synchronization circuit 53 can also extract the SP signal from the OFDM frequency domain signal and perform carrier recovery and timing recovery from the phase difference between the symbols of the SP signal.

  In the OFDM receiver 50 as described above, an OFDM signal broadcast as terrestrial digital broadcasting is received and demodulated, the demodulated signal is subjected to transmission path decoding, and a transport stream including, for example, audio and video signals is output. be able to.

  Hereinafter, the CW interference detection circuit 51 and the CW interference removal circuit 52 described above will be described in detail.

  First, an example of a block diagram of the CW interference detection circuit 51 is shown in FIG.

  In the CW disturbance detection circuit 51 shown in FIG. 11, the power calculation circuit 61 includes a conjugate complex calculator 61a and a complex multiplier 61b, and calculates the power for each subcarrier. The 1-symbol integrator 62 integrates the power for each subcarrier with respect to all the subcarriers of one symbol, and obtains the total power for one symbol. The scaling circuit 63 supplies a value obtained by scaling the total power to the comparator 66 as a CW disturbance determination threshold value. The maximum power subcarrier search circuit 64 searches for a subcarrier having the maximum power, supplies the maximum power to the comparator 66, and supplies the maximum power subcarrier number to the frequency converter 65. The frequency converter 65 converts the maximum power subcarrier number into a frequency and supplies the frequency of the maximum power subcarrier to the CW interference elimination circuit 52 (FIG. 10). The comparator 66 compares the maximum power with the CW interference determination threshold value to determine the presence or absence of CW interference, and supplies a CW interference detection flag indicating the presence or absence of CW interference to the CW interference removal circuit 52 (FIG. 10).

  As described above, the CW interference detection circuit 51 shown in FIG. 11 compares the maximum power in the subcarrier having the maximum power within one symbol with the CW interference determination threshold value calculated based on the total power for one symbol. Then, the presence / absence of CW interference is determined.

  Note that the CW interference detection circuit 51 shown in FIG. 11 has the same configuration as that of FIG. 6 as an example, but the configuration of FIG. 7 and FIG.

  Next, an example of a block configuration diagram of the CW interference removal circuit 52 is shown in FIG.

  In the CW interference removal circuit 52 shown in FIG. 12, the frequency variable notch filter 71 removes the signal at the frequency of the maximum power subcarrier from the OFDM time domain signal and supplies the removed OFDM time domain signal to the selector 72. . The selector 72 selects an OFDM time domain signal that has not passed through the frequency variable notch filter 71 according to the CW interference detection flag when there is no CW interference, and selects the frequency variable notch filter 71 when there is CW interference. The passed OFDM time domain signal is selected and supplied to the FFT operation circuit 17 (FIG. 10).

  As described above, in the CW interference removal circuit 52 shown in FIG. 12, when CW interference is present, the signal of the subcarrier frequency (maximum power subcarrier frequency) where the CW interference is present is removed from the OFDM time domain signal. To do. Thereby, it is possible to prevent the estimation accuracy of the transmission path characteristics from deteriorating.

  Although the best mode for carrying out the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. Of course.

  For example, in the first embodiment described above, when CW interference exists, the transmission path characteristic data is extracted from the range avoiding the subcarrier in which CW interference exists, and the delay profile is generated. In the second embodiment, when CW interference is present, the subcarrier signal in which CW interference is present is removed from the OFDM time domain signal, but these may be combined.

It is a block block diagram of the OFDM receiver in 1st Embodiment. It is a figure for demonstrating the insertion position of SP signal of an OFDM signal. It is a figure for demonstrating the subcarrier by which the channel characteristic was estimated by the time direction interpolation. It is a figure for demonstrating the frequency direction interpolation process at the time of estimating a transmission line characteristic. It is a figure for demonstrating the transmission line characteristic extracted by the data extraction circuit in the said OFDM receiver. It is a 1st example of the block block diagram of the CW disturbance detection circuit in the said OFDM receiver. It is a 2nd example of the block block diagram of the said CW disturbance detection circuit. It is a 3rd example of the block block diagram of the said CW disturbance detection circuit. It is an example of a block configuration diagram of the data extraction circuit. It is a block block diagram of the OFDM receiver in 2nd Embodiment. It is an example of the block block diagram of the CW disturbance detection circuit in the said OFDM receiver. It is an example of the block block diagram of the CW disturbance removal circuit in the said OFDM receiver. It is a figure for demonstrating an OFDM signal, an OFDM symbol, an effective symbol, and a guard interval.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 OFDM receiver, 17 FFT operation circuit, 18 Transmission path characteristic estimation circuit, 19 CW disturbance detection circuit, 20 Data extraction circuit, 21 IFFT calculation circuit, 22 Window reproduction circuit, 23 Transmission path characteristic compensation circuit, 50 OFDM reception apparatus, 51 CW interference detection circuit, 52 CW interference removal circuit, 53 synchronization circuit

Claims (10)

A pilot symbol having a specific power and a specific phase is a transmission symbol generated by dividing the information for a plurality of subcarriers within a predetermined band and orthogonally modulated. An OFDM demodulator for demodulating an orthogonal frequency division multiplexing (OFDM) signal discretely inserted into predetermined subcarriers in a transmission symbol,
Fourier transform means for setting a computation range for the effective symbol period from each transmission symbol of the OFDM signal, and Fourier transforming the set computation range;
Based on the power of each subcarrier of the signal subjected to Fourier transform by the Fourier transform means, it is determined whether or not there is interference due to a constant frequency and unmodulated continuous wave, and if there is interference, the subcarrier where the interference exists Interference detection means for detecting
The pilot signal is extracted for each transmission symbol from the signal Fourier-transformed by the Fourier transform means, and transmission of all subcarriers in the transmission symbol is performed by interpolating the extracted pilot signal in the time direction and the frequency direction. Transmission path characteristic estimation means for estimating the path characteristics;
Data extraction means for extracting a part of the data of the transmission line characteristic estimated by the transmission line characteristic estimation means;
An inverse Fourier transform unit that generates a delay profile by performing an inverse Fourier transform on the transmission path characteristics extracted by the data extraction unit for each transmission symbol;
Window reproducing means for controlling the calculation range based on the delay profile generated by the inverse Fourier transform means,
The OFDM demodulator according to claim 1, wherein the data extraction means extracts data from subcarriers other than the subcarrier in which interference is present when the interference detection means determines that interference exists.   2. The OFDM according to claim 1, further comprising waveform equalizing means for equalizing the waveform of the signal Fourier-transformed by the Fourier transforming means based on the transmission line characteristic estimated by the transmission line characteristic estimating means. Demodulator.   The interference detection means integrates the power of each subcarrier of the signal Fourier-transformed by the Fourier transform means for N transmission symbols (N is a positive integer), and the obtained power for each subcarrier, 2. The OFDM demodulator according to claim 1, wherein the presence or absence of interference is determined by comparing with a threshold value calculated from the total power of all subcarriers in the N transmission symbols.   The disturbance detection means compares the power of each subcarrier of the signal Fourier-transformed by the Fourier transform means with a threshold value calculated from the total power of all subcarriers in the transmission symbol, and compares N 2. The OFDM demodulator according to claim 1, wherein presence or absence of interference is determined based on a comparison result of the transmission symbols (N is an integer of 2 or more).   The interference removal means according to claim 1, further comprising: an interference removal means for removing a signal having a frequency of a subcarrier in which interference exists in the OFDM signal when the interference detection means determines that interference exists. OFDM demodulator. A pilot symbol having a specific power and a specific phase is a transmission symbol generated by dividing the information for a plurality of subcarriers within a predetermined band and orthogonally modulated. An OFDM demodulation method for demodulating an Orthogonal Frequency Division Multiplexing (OFDM) signal discretely inserted into predetermined subcarriers within a transmission symbol, comprising:
A Fourier transform step of setting a computation range for an effective symbol period from each transmission symbol of the OFDM signal, and Fourier transforming the set computation range;
Based on the power of each subcarrier of the signal subjected to the Fourier transform in the Fourier transform process, it is determined whether or not there is interference by a continuous wave having a constant frequency and no modulation. A jamming detection process for detecting carriers;
The pilot signal is extracted for each transmission symbol from the signal subjected to Fourier transform in the Fourier transform step, and all the subcarriers in the transmission symbol are interpolated in the time direction and the frequency direction by extracting the pilot signal. A transmission line characteristic estimation step for estimating the transmission line characteristic;
A data extraction step of extracting a part of the data of the transmission line characteristic estimated in the transmission line characteristic estimation step;
An inverse Fourier transform step of generating a delay profile by performing an inverse Fourier transform on the transmission path characteristics extracted in the data extraction step for each transmission symbol;
A window reproduction step for controlling the calculation range based on the delay profile generated in the inverse Fourier transform step;
In the data extraction step, when it is determined that interference exists in the interference detection step, data is extracted from subcarriers other than the subcarrier in which interference exists.   7. The method according to claim 6, further comprising: a jamming removal step of removing, from the OFDM signal, a signal having a frequency of a subcarrier in which the jamming exists when the jamming detection step determines that the jamming exists. OFDM demodulation method. A pilot symbol having a specific power and a specific phase is a transmission symbol generated by dividing the information for a plurality of subcarriers within a predetermined band and orthogonally modulated. An OFDM demodulator for demodulating an orthogonal frequency division multiplexing (OFDM) signal discretely inserted into predetermined subcarriers in a transmission symbol,
Fourier transform means for Fourier transforming the OFDM signal in units of the transmission symbols;
Based on the power of each subcarrier of the signal subjected to Fourier transform by the Fourier transform means, it is determined whether or not there is interference due to a constant frequency and unmodulated continuous wave, and if there is interference, the subcarrier where the interference exists Interference detection means for detecting
An OFDM demodulator comprising: an interference removal means for removing, from the OFDM signal, a signal having a frequency of a subcarrier in which interference exists when the interference detection means determines that interference exists. The pilot signal is extracted for each transmission symbol from the signal Fourier-transformed by the Fourier transform means, and the transmission of all subcarriers in the transmission symbol is performed by interpolating the extracted pilot signal in the time direction and the frequency direction. Transmission path characteristic estimation means for estimating the path characteristics;
The waveform equalization means for equalizing the waveform of the signal Fourier-transformed by the Fourier transform means based on the transmission line characteristic estimated by the transmission path characteristic estimation means, further comprising: OFDM demodulator. A pilot signal having a specific power and a specific phase is obtained with a transmission symbol generated by dividing and orthogonally modulating information on a plurality of subcarriers within a predetermined band. An OFDM demodulation method for demodulating an Orthogonal Frequency Division Multiplexing (OFDM) signal discretely inserted into predetermined subcarriers within a transmission symbol, comprising:
A Fourier transform step of Fourier transforming the OFDM signal in units of the transmission symbols;
Based on the power of each subcarrier of the signal subjected to the Fourier transform in the Fourier transform step, the presence / absence of interference by a continuous wave having a constant frequency and no modulation is determined. A jamming detection process for detecting carriers;
An OFDM demodulation method, comprising: a disturbance removal step of removing, from the OFDM signal, a signal of a subcarrier frequency in which interference exists when it is determined in the interference detection step that interference exists.

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