JP4161921B2 - OFDM signal demodulating device and OFDM signal demodulating method - Google Patents

Description

  The present invention relates to an OFDM signal demodulating apparatus and an OFDM signal demodulating method for receiving and demodulating a signal modulated by an orthogonal frequency division multiplexing modulation system.

  In terrestrial digital broadcasting, an OFDM (Orthogonal Frequency Division Multiplexing) system that can multiplex and transmit / receive a plurality of signals is used as a modulation system. In this OFDM system, a number of orthogonal subcarriers (carriers) are provided in a transmission band, data is allocated to the amplitude and phase of each carrier, and digital modulation is performed by PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation). It is a method.

  An OFDM signal modulated by the OFDM method is transmitted in a transmission unit called an OFDM symbol (hereinafter simply referred to as “symbol”). Within one symbol, an effective symbol (for example, the first symbol Sa of the A wave in FIG. 12A) that is an IFFT (Inverse Fast Fourier Transform) signal, and a signal in the latter half of the effective symbol A guard interval (for example, the A-wave guard interval GIa in FIG. 12A) is included, and the guard interval is provided in the first half of one symbol. In this way, since the guard interval is a copy of the latter half of the effective symbol, it is possible to select a signal in an arbitrary range as the effective symbol range within one symbol.

  Also, a synchronization signal (referred to as “scattered pilot signal”, hereinafter referred to as “SP signal”) having a predetermined amplitude and phase is embedded in the symbol in advance by the OFDM method. On the receiving side, the characteristics and characteristics of the transmission path are estimated by monitoring the amplitude and phase of the synchronization signal, and the waveform equivalence of the received signal is determined based on the estimated characteristics of the transmission path. ").

  FIG. 11 is a block diagram of a conventional OFDM signal demodulator 900 that receives and demodulates an OFDM signal. Hereinafter, the functional configuration of the OFDM signal demodulator 900 will be described with reference to FIG.

  As shown in the figure, an OFDM signal demodulator 900 includes a tuner unit 3 that receives an OFDM signal via an external antenna ANT, a demodulator 500, and a decoder 7.

  The demodulator 500 includes an ADC (Analog Digital Converter) circuit 10, an FFT (Fast Fourier Transform) circuit 102, a peak detection circuit 104, an FFT window pulse generation circuit 106, and a transmission line equivalent circuit 108. And a demodulation circuit 26.

  First, the tuner unit 3 receives an OFDM signal transmitted from a broadcasting station, reflected and diffracted due to obstacles such as a building or terrain, and including a delayed wave whose transmission time and phase have changed via an external antenna ANT, and is amplified, intermediate After performing conversion to a frequency signal and gain control, the signal is output to the demodulation unit 500.

  The ADC circuit 10 converts the signal output from the tuner unit 3 into a digital signal. This digital signal is a so-called symbol domain signal (OFDM time domain signal) before being subjected to FFT processing, and is converted into a carrier domain signal (OFDM frequency domain signal) by the FFT processing of the FFT circuit 102. . Specifically, a signal in a range corresponding to an effective symbol is selected from one symbol, FFT processing is performed on the selected signal, and a signal in a carrier region (hereinafter, a carrier region output from the FFT circuit 102). The signal is referred to as “FFT signal”).

  The processing range to be subjected to the FFT processing is called an FFT window. The FFT window pulse generation circuit 106 generates an FFT window pulse for designating an FFT window. Specifically, a signal converted into a digital signal by the ADC circuit 10 is subjected to FFT processing in an FFT circuit unit (not shown) included in the peak detection circuit 104 to obtain a plurality of FFT signals having different transmission times and phases. Extract. Then, the FFT signal of the maximum level is selected from the plurality of extracted FFT signals, and is output to the FFT window pulse generation circuit 106. Then, the FFT window pulse generation circuit 106 generates an FFT window pulse synchronized with the maximum level signal output from the peak detection circuit 104 and outputs the FFT window pulse to the FFT circuit 102.

  The FFT circuit 102 performs FFT processing on the OFDM signal output from the ADC circuit 10 according to the FFT window pulse synchronized with the maximum level signal output from the FFT window pulse generation circuit 106, and sends the FFT signal to the transmission line equivalent circuit 108. Output.

  For example, when the maximum level signal is the A wave shown in FIG. 12A, the FFT window pulse Pa (FIG. 12D) synchronized with the A wave is generated by the FFT window pulse generation circuit 106.

  The FFT circuit 102 performs FFT processing on the signal corresponding to the processing range represented by the FFT window pulse Pa. Specifically, the FFT processing is performed on a range R in which the FFT window pulse Pa is in a high state in the A-wave signal.

  The transmission line equivalent circuit 108 accumulates FFT signals (first to fourth FFT signals) corresponding to the number of four symbols (the number of defined symbols necessary for transmission line equivalent processing) among the FFT signals output from the FFT circuit 102. An FFT signal memory 110 for storing is provided. The FFT signal memory 110 has a function like a shift register. Whenever the FFT signal is output from the FFT circuit 102, the contents of the fourth FFT signal are deleted and the contents of the memory are shifted one by one. Then, the FFT signal newly output from the FFT circuit 102 is stored as the first FFT signal.

  The transmission path equivalent circuit 108 performs transmission path equivalent processing on the FFT signal that has been subjected to the FFT processing by the FFT circuit 102. The transmission path equivalent processing will be briefly described. First, the FFT signal output from the FFT circuit 102 is stored in the FFT signal memory 110. Then, SP signals are extracted from each stored FFT signal, and SP signals for the number of four symbols are collected. Then, the distortion amount of the collected SP signal is calculated, and the transmission characteristics of the transmission path for all subcarriers of the symbol are obtained based on the calculated distortion amount. Then, using the transfer characteristics, amplitude equivalent and phase equivalent are performed on the first FFT signal.

  Further, the transmission line equivalent circuit 108 outputs the FFT signal subjected to the transmission line equivalent processing to the demodulation circuit 26. The demodulation circuit 26 performs a predetermined error correction process and a demodulation process, and then outputs the processing result to the decoding unit 7. Then, when the decoding unit 7 performs predetermined decoding processing, display output and audio output are performed as a television broadcast by a device incorporating the OFDM signal demodulation device 900.

Here, as a technique related to the FFT processing of the OFDM signal demodulator described above, for example, the following is known. That is, the symbol period is estimated by performing a correlation operation between the received OFDM signal and a signal obtained by delaying the signal by a predetermined time, and the FFT processing of the OFDM signal in the effective symbol period is performed in synchronization with the estimated symbol period. Technology (see Patent Document 1).
JP 2002-77101 A

  Now, an actual OFDM signal received via the external antenna ANT includes not only a direct wave but also a plurality of reflected waves that have arrived after being reflected on a building or the like. This reflected wave is a signal (delayed wave) having a phase change and a delay in transmission time compared to a direct wave due to a difference in transmission distance from the broadcasting station to the external antenna ANT.

  For example, it is assumed that A wave and B wave as shown in FIGS. 12A and 12B are received. The B wave is a signal in which a slight delay occurs in the A wave due to a difference in transmission distance. Therefore, a signal actually received by the external antenna ANT is received as a composite signal ABw as shown in FIG.

  Then, due to the influence of the transmission path, the signal level of the A wave may become strong, or the signal level of the B wave may become strong. For example, when the signal level of the A wave is strong, the peak detection circuit 104 detects the A wave in the combined signal ABw, and the FFT window pulse generation circuit 106 generates the FFT window pulse Pa synchronized with the A wave. When the signal level of the B wave is strong, the peak detection circuit 104 detects the B wave in the composite signal ABw and generates an FFT window pulse Pb synchronized with the B wave. Since each FFT window pulse is a pulse signal synchronized with each signal, the FFT window pulse Pb is also delayed as shown in FIG.

  FIG. 13 is a diagram for explaining the operation of the transmission line equivalent circuit 108 when the FFT circuit 102 performs FFT processing on the received composite signal ABw and stores the result in the FFT signal memory 110. In the figure, “An” (n is an integer) represents an FFT signal obtained by performing FFT processing on an A-wave symbol having a symbol number “n” with an FFT window pulse Pa synchronized with the A-wave, and “Bn” represents a symbol number. It represents an FFT signal obtained by performing FFT processing on an “n” B wave symbol with an FFT window pulse Pb synchronized with the B wave.

  First, when the composite signal ABw (symbol number “0”) when the signal level of the A wave is stronger than the B wave is received, the FFT window pulse generation circuit 106 generates the FFT window pulse Pa, and the FFT circuit 102 according to the pulse. Performs FFT processing and outputs an FFT signal “A0”. The transmission line equivalent circuit 108 stores the FFT signal “A0” in the FFT signal memory 110 as the first FFT signal.

  During a period when the signal level of the A wave is strong (symbol numbers “0” to “3”), the FFT circuit 102 performs FFT processing according to the FFT window pulse Pa, and the FFT signals “A0” to “A3” are sent to the FFT signal memory 110. Store it. At the time of the symbol number “3”, the FFT signal memory 110 stores the A-wave FFT signals “A0”, “A1”, “A2”, and “A3”, which are transmitted by these four FFT signals. A path equivalent process is performed.

  In the following description, a combination of signal waves that are the basis of an FFT signal to be subjected to transmission line equivalent processing is referred to as “symbol classification”. For example, in the symbol number “3”, the transmission line equivalent processing is performed only with the A-wave FFT signal (the FFT signal subjected to the FFT processing with the FFT window pulse Pa synchronized with the A-wave). The classification is A wave.

  Then, at a certain timing, the signal level of the B wave becomes stronger than that of the A wave, and when the composite signal ABw (symbol number “4”) at this time is received, the FFT window pulse generation circuit 106 generates the FFT window pulse Pb, In accordance with the pulse, the FFT circuit 102 performs FFT processing and outputs an FFT signal “B4”. The transmission line equivalent circuit 108 stores the FFT signal “B4” in the first FFT signal memory of the FFT signal memory 110.

  At this time, the FFT signal memory 110 stores A-wave FFT signals “A1”, “A2”, and “A3”, and a B-wave FFT signal “B4”. Transmission path equivalent processing is performed using these four FFT signals. Therefore, the symbol classification is A wave and B wave (FFT signal processed with FFT signal pulse FFT pulse Pa synchronized with A wave and FFT signal processed with FFT window pulse Pb synchronized with B wave) Thus, the transmission path equivalent processing is performed in a state where the A-wave and B-wave FFT signals are mixed.

  Then, during a period in which the B wave signal level from symbol numbers “4” to “6” is strong, the symbol division is A wave and B wave. If the signal level of the B wave continues to be strong for a certain period, the symbol division is only the B wave as in the symbol number “7”, but if the signal level of the A wave is temporarily increased, As in the symbol number “9”, the symbol division is A wave and B wave.

  As described above, since the signal levels of a plurality of signals (delayed waves) such as A wave and B wave may vary with time, the number of defined symbols required for transmission line equivalent processing (for example, 4 symbols) The transmission path equivalent processing is performed in a state where a plurality of delayed wave FFT signals having different transmission times and phases are mixed in a number of FFT signals. In this case, when the A-wave FFT signal is subjected to transmission path equivalent processing, the characteristics of the A-wave transmission path are estimated by the B-wave SP signal, and the amplitude equivalent and the phase equivalent are caused. Since the FFT signal output from the transmission line equivalent circuit 108 includes not only distortion (noise) on the actual transmission line but also inconvenience due to symbol division of the transmission line equivalent processing, an error of the demodulation circuit 26 occurs. There is a possibility that the processing capacity of the correction process will be exceeded and an error of the demodulation circuit 26 may be caused.

  Also, the OFDM signal demodulator disclosed in Patent Document 1 performs FFT processing with a signal wave having a stronger signal level, similar to the conventional OFDM signal demodulator 900, when receiving a plurality of signals whose signal levels vary. Therefore, in the end, demodulation processing was performed with a plurality of FFT signals mixed.

  The present invention has been made in view of the above-described problems, and the object of the present invention is appropriate when receiving and demodulating an OFDM signal including delayed waves received via a plurality of transmission paths. It is to improve the reception performance of the OFDM signal demodulator by performing simple waveform equalization.

In order to solve the above problems, an OFDM signal demodulator according to claim 1 demodulates a plurality of OFDM signals including delay waves received from a receiver through a plurality of transmission paths. In (for example, the OFDM signal demodulator 1 in FIG. 1),
Peak detection means (for example, peak detection circuit 18-1 and peak detection circuit 18-2 in FIG. 1) for detecting the peak value of each OFDM signal for the plurality of OFDM signals including the received delayed wave, Based on the peak value detected by the peak detecting means, the window pulse generating means (for example, the FFT window pulse generating circuit 20 in FIG. 1) that generates an FFT window pulse synchronized with each of the OFDM signals of the maximum level and the second level and thereafter . -1, FFT window pulse generation circuit 20-2), and FFT processing for extracting the FFT signal by performing FFT processing on the plurality of OFDM signals including the received delay wave according to the FFT window pulse generated by the window pulse generation means and extraction means (e.g., FFT circuit 14-1 of FIG. 1, FFT circuit 14-2), the maximum record extracted by the FFT extracting means Storage means (for example, the maximum memory 16-1 and the second memory 16-2 in FIG. 1) for storing FFT signals based on the OFDM signals based on the OFDM level and the second and subsequent levels while sequentially shifting each symbol, and this storage The selection means (for example, the switching circuit 22 in FIG. 1) for selecting the FFT signal necessary for waveform equalization for each symbol from the FFT signals stored by the means , and the waveform of the FFT signal selected by the selection means Equivalent waveform equivalent means (for example, the transmission line equivalent circuit 24 in FIG. 1), and demodulation means (for example, the demodulator circuit 26 in FIG. 1) for performing demodulation processing on the FFT signal waveform-equalized by the waveform equivalent means , wherein the selecting means, other thin already stored in the FFT signal and said storage means based on the maximum level of the OFDM signal newly stored in the storage means When the FFT signal extracted according to the FFT window pulse synchronized with the FFT signal based on the OFDM signal of the maximum level of the signal is the FFT signal based on the OFDM signal of the maximum level newly stored in the storage means and the storage means The FFT signal based on the OFDM signal of the maximum level of the other symbols already stored in is selected as the FFT signal necessary for waveform equivalence .

The OFDM signal demodulation method according to claim 5 is an OFDM signal demodulation method for demodulating a plurality of OFDM signals including delayed waves received from a receiving unit via a plurality of transmission paths (for example, the OFDM signal demodulation method shown in FIG. 1). A demodulation method of the signal demodulator 1),
A peak detection step (for example, peak detection circuit 18-1 and peak detection circuit 18-2 in FIG. 1) for detecting a peak value of each OFDM signal for the plurality of OFDM signals including the received delayed wave, and this Based on the peak value detected in the peak detection step, a window pulse generation step (for example, FFT window pulse generation circuit 20 in FIG. 1) that generates an FFT window pulse synchronized with each of the OFDM signal of the maximum level and the second level or later . -1, FFT window pulse generation circuit 20-2), and FFT processing for extracting the FFT signal by performing FFT processing on the plurality of OFDM signals including the received delay wave according to the FFT window pulse generated in this window pulse generation step an extraction step (e.g., FFT circuit 14-1 of FIG. 1, FFT circuit 14-2), the FFT extracted stearate Storing step (for example, the maximum memory 16-1 and the second memory 16- in FIG. 1) while storing the FFT signal based on the OFDM signal of the maximum level extracted from the second level and the second and subsequent levels while sequentially shifting each symbol. 2), a selection step (for example, switching circuit 22 in FIG. 1) for selecting an FFT signal necessary for waveform equalization for each symbol from the FFT signals stored in this storage step, and selection in this selection step A waveform equivalent step (for example, the transmission line equivalent circuit 24 in FIG. 1) that performs waveform equivalent to the FFT signal that has been converted, and a demodulation step that performs demodulation processing on the FFT signal that has been waveform equivalent in the waveform equivalent step (for example, FIG. 1) wherein the demodulation circuit 26), the said selection step, OFD maximum level newly stored in the storing step When the FFT signal based on the signal and the FFT signal based on the FFT signal based on the OFDM signal of the maximum level of the other symbols already stored in the storing step are the FFT signals extracted according to the synchronized FFT window pulse, the FFT is newly performed in the storing step. Selecting an FFT signal based on the stored OFDM signal of the maximum level and an FFT signal based on the OFDM signal of the maximum level of another symbol already stored in the storing step as an FFT signal necessary for waveform equivalence. To do.

The invention according to claim 2 is the OFDM signal demodulator according to claim 1 , wherein the selection means (the switching circuit 22 in FIG. 1 and the switching circuit 22a in FIG. 7) is newly stored in the storage means. If the FFT signal based on the OFDM signal of the maximum level and the FFT signal based on the OFDM signal of the maximum level of another symbol already stored in the storage means are not FFT signals extracted according to the FFT window pulse synchronized, and selects a waveform equivalently FFT signals required power sale by FFT signal extracted increases according FFT window pulses.

The invention according to claim 3 is the OFDM signal demodulator according to claim 1 , wherein the selection means (the switching circuit 22 in FIG. 1, the switching circuit 22a in FIG. 7) is newly stored in the storage means. If the FFT signal based on the OFDM signal of the maximum level and the FFT signal based on the OFDM signal of the maximum level of another symbol already stored in the storage means are not FFT signals extracted in accordance with the synchronized FFT window pulse, An FFT signal based on an OFDM signal of the maximum level of another symbol already stored in the storage means and an FFT signal newly extracted and stored in the storage means in accordance with an FFT window pulse synchronized with the OFDM signal of the maximum level of the other symbol characterized by select and as FFT signal waveform equivalent subject.

The invention according to claim 4 is the OFDM signal demodulator according to claim 1 , wherein the average peak value of each OFDM signal is calculated based on the peak values of the plurality of OFDM signals detected by the peak detecting means. Mean peak value calculating means for calculating (for example, maximum level signal wave system 12-1, second to sixth level signal wave systems 12-2 to 12-6 in FIG. 7),
The selection means (for example, the switching circuit 22a in FIG. 7) detects the OFDM signal having the maximum average peak value calculated by the average peak value calculation means, and receives the reception according to the FFT window pulse synchronized with the OFDM signal. It is characterized in that an FFT signal necessary for waveform equivalence is selected from FFT signals extracted by performing FFT processing on the OFDM signal.

According to the first and fifth aspects of the present invention, when demodulating a plurality of OFDM signals including delay waves received via a plurality of transmission paths, the signals are continuously transmitted via the same transmission path. the FFT signal extracted by FFT processing the maximum level of the OFDM signal is selected as a waveform equivalently necessary F FT signal and waveform equalization demodulates the selected FFT signal.
This makes it possible to perform appropriate waveform equivalent processing, improve the correction processing capability of error correction processing after waveform equivalent processing, and perform demodulation processing and the like more accurately. Therefore, the device performance of the OFDM signal demodulator can be improved.

According to the invention described in claim 2, OFDM signal that has reached through the same transmission path, i.e. as transmission time becomes much FFT signals FFT processed according FFT window pulses synchronized to the OFDM signal having the same An FFT signal necessary for waveform equalization is selected.
This makes it possible to perform appropriate waveform equivalent processing, improve the correction processing capability of error correction processing after waveform equivalent processing, and perform demodulation processing and the like more accurately. Furthermore, it is possible to reduce the influence due to the deterioration of the reception state based on the obstacle such as a building or terrain, and to improve the device performance of the OFDM signal demodulator.

According to the invention described in claim 3, you select only the same OFDM signals propagated through the transmission path, i.e. FFT signal transmission time has been FFT processed according FFT window pulses synchronized to the OFDM signal having the same .
This makes it possible to perform appropriate waveform equivalent processing, improve the correction processing capability of error correction processing after waveform equivalent processing, and perform demodulation processing and the like more accurately. Furthermore, it is possible to reduce the influence due to the deterioration of the reception state based on the obstacle such as a building or terrain, and to improve the device performance of the OFDM signal demodulator.

According to the fourth aspect of the present invention, from the FFT signal obtained by performing the FFT process on the OFDM signal received according to the FFT window pulse synchronized with the OFDM signal received from the receiving unit via the same transmission path , the signal level It becomes possible to select the FFT signal having the maximum average value as a waveform equivalent target.
Thus, it is possible to select an FFT signal more suitable for processing of waveform equalization, improves the correction capability of the error correction processing after waveform equalization, it is possible to perform demodulation processing and the like more accurately. Furthermore, it is possible to reduce the influence due to the deterioration of the reception state based on the obstacle such as a building or terrain, and to improve the device performance of the OFDM signal demodulator.

  Hereinafter, an embodiment in which the OFDM signal demodulator of the present invention is applied to an OFDM signal demodulator 1 for terrestrial digital television broadcasting will be described with reference to FIGS. In the background art, the same components as those of the OFDM signal demodulator 900 shown in FIG. 11 and described are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 1 is a block diagram showing a functional configuration of the OFDM signal demodulator 1. As shown in FIG. 1, the OFDM signal demodulator 1 includes a tuner unit 3, a demodulation unit 5, and a decoding unit 7.

  The tuner unit 3 amplifies an OFDM signal including a delayed wave (a signal whose transmission time is delayed compared to a direct wave and whose phase has changed compared to a direct wave) received via the external antenna ANT, conversion to an intermediate frequency signal, and gain control. The processed signal is output to the demodulator 5.

  The demodulator 5 includes an ADC circuit 10, a maximum level signal wave system block 12-1 that performs signal processing on a maximum level signal, and a second level signal wave system block 12 that performs signal processing on a second level signal. -2, switching circuit 22, transmission line equivalent circuit 24, and demodulation circuit 26. The maximum level signal wave system block 12-1 includes an FFT circuit 14-1, a peak detection circuit 18-1, and an FFT window pulse generation circuit 20-1, and a second level signal wave system block 12-2. Includes an FFT circuit 14-2, a peak detection circuit 18-2, and an FFT window pulse generation circuit 20-2.

  The FFT circuit 14-1 of the maximum level signal wave block 12-1 includes a maximum memory 16-1, and the FFT circuit 14-2 of the second level signal wave block 12-2 includes a second memory. 16-2. FIG. 2 is a diagram illustrating the configuration of the maximum memory 16-1 and the second memory 16-2.

  According to FIG. 5A, the maximum memory 16-1 stores the first FFT signal 161a to the fourth FFT signal 161d. The first FFT signal 161a to the fourth FFT signal 161d are FFT signals subjected to FFT processing by the FFT circuit 14-1, and are waveform identifiers (transmissions received via different transmission paths) output from the peak detection circuit 18-1. And symbols attached to signals having different time and phase.

  Similarly to the FFT signal memory 240 of the conventional OFDM signal demodulator 900, the maximum memory 16-1 has a function like a shift register, and associates the FFT signal with the waveform identifier to the first FFT signal. When storing as 161a, the memory contents are shifted one by one before storing. Specifically, after shifting the memory content of the third FFT signal 161c as the fourth FFT signal 161d, the memory content of the second FFT signal 161b as the third FFT signal 161c, and the memory content of the first FFT signal 161a as the second FFT signal 161b, The FFT identifier processed by the FFT circuit 14-1 is associated with the waveform identifier output from the peak detection circuit 18-1, and stored as the first FFT signal 161a.

  Further, according to FIG. 5B, the second memory 16-2 stores the first FFT signal 162a to the fourth FFT signal 162d. The first FFT signal 162a to the fourth FFT signal 162d are FFT signals subjected to FFT processing by the FFT circuit 14-2, and are associated with waveform identifiers output from the peak detection circuit 18-2. Similar to the maximum memory 16-1, the second memory 16-2 has a function like a shift register, and stores the FFT signal subjected to the FFT processing by the FFT circuit 14-2 as the first FFT signal 162a. In doing so, the memory contents are shifted one by one, and then the FFT signal is stored as the first FFT signal 162a.

  The transmission line equivalent circuit 24 includes an FFT signal memory 240. The FFT signal memory 240 is a memory area for storing the FFT signal output from the switching circuit 22 as a first FFT signal to a fourth FFT signal.

  Next, a specific operation of the demodulation unit 5 will be described. The ADC circuit 10 of the demodulating unit 5 performs A / D conversion on the OFDM signal output from the tuner unit 3, and performs an FFT circuit 14-1 and a peak detection circuit 18-1 of the maximum level signal wave system block 12-1, The signal is output to the FFT circuit 14-2 and the peak detection circuit 18-2 of the second level signal wave system block 12-2.

  In the maximum level signal wave system block 12-1, the peak detection circuit 18-1 detects a signal having the maximum signal level from a plurality of OFDM signals including the delayed wave output from the ADC circuit 10, and performs FFT. Output to the window pulse generation circuit 20-1. The peak detection circuit 18-1 generates a waveform identifier for each signal having a different transmission time and phase, which is output from the ADC circuit 10 and received via different transmission paths, and corresponds to the signal of the maximum level. The waveform identifier is output to the FFT circuit 14-1. Specifically, the signal output from the ADC circuit 10 is subjected to FFT processing in an FFT circuit unit (not shown) included in the peak detection circuit 18-1 for each of a plurality of FFT signals having different transmission times and phases. FFT processing is performed. Of the plurality of FFT signals with different transmission times and phases subjected to the FFT processing, the signal at the maximum level is set as the A wave, and the signal having the second highest level with respect to the A wave is set as the B wave and the third level. Are identified as C waves,... And the waveform identifier of the signal corresponding to the maximum level signal is output to the FFT circuit 14-1.

  FIG. 4 is a diagram illustrating the relationship between the signal level of the direct wave and the delayed wave (a plurality of FFT signals having different transmission times and phases) detected by the peak detection circuit 18-1, and the waveform identifier. For example, the bar line R1 indicates that it has been identified as an A wave because it is the maximum level signal. Also, the bar line R2 indicates that it is identified as a B wave because it is the second highest level signal.

  For example, it is assumed that five signal waveforms are subjected to FFT processing by the peak detection circuit 18-1. Based on the transmission time of each signal or the phase difference between the signals, the peak detection circuit 18-1 performs “A wave”, “B” in order of the signal level with respect to the received signal as shown in FIG. “Wave”, “C wave”..., “E wave” and a waveform identifier are added. In FIG. 6A, since the signal at the maximum level is an A wave, the peak detection circuit 18-1 outputs an A wave waveform identifier to the FFT circuit 14-1, and the A wave from a plurality of signals. Are extracted and output to the FFT window pulse generation circuit 20-1.

  The FFT window pulse generation circuit 20-1, which is a window pulse generation means, generates a first FFT window pulse synchronized with the maximum level signal output from the peak detection circuit 18-1, and sends it to the FFT circuit 14-1. Output.

  The FFT circuit 14-1 as the FFT extraction means performs an FFT process on the OFDM signal output from the ADC circuit 10 in accordance with the FFT window pulse output from the FFT window pulse generation circuit 20-1. And the FFT signal derived | led-out by the said process and the waveform identifier output from the peak detection circuit 18-1 are matched, and it stores in the memory 16-1 for the maximum as the 1st FFT signal 161a.

  In the second level signal wave system block 12-2, the peak detection circuit 18-2 is the second signal next to the signal having the maximum signal level among the plurality of signals including the delayed wave output from the ADC circuit 10. (Second level signal) is detected and output to the FFT window pulse generation circuit 20-2. Further, the peak detection circuit 18-2 generates a waveform identifier for each signal having a different transmission time and phase, which is output from the ADC circuit 10 and received via different transmission paths, and corresponds to the second level signal. The waveform identifier to be output is output to the FFT circuit 14-2. Specifically, the signal output from the ADC circuit 10 is subjected to FFT processing in an FFT circuit unit (not shown) included in the peak detection circuit 18-2 for each of a plurality of FFT signals having different transmission times and phases. FFT processing is performed. Of the plurality of FFT signals with different transmission times and phases subjected to the FFT processing, the signal at the maximum level is set as the A wave, and the signal having the second highest level with respect to the A wave is set as the B wave and the third level. Is identified as a C wave, and the waveform identifier of the signal having the second highest level is output to the FFT circuit 14-2. For example, in FIG. 4A, since the second level signal is a B wave, the peak detection circuit 18-2 outputs a waveform identifier of the B wave to the FFT circuit 14-2 and includes a plurality of signals. The B wave signal is extracted from the signal and output to the FFT window pulse generation circuit 20-2.

  The functions and operations of the FFT circuit 14-2 and the FFT window pulse generation circuit 20-2 are the same as those of the FFT circuit 14-1 and the FFT window pulse generation circuit 20-1 of the maximum level signal wave system block 12-1. The description is omitted.

  The peak detection circuit 18-1 and the peak detection circuit 18-2 store the phase difference between the maximum level signal and the second level signal detected at the start of reception. And the signal of the maximum level and the 2nd level is judged for two signals which have this phase difference. For example, when the A wave and the B wave are received as the maximum level signal and the second level signal at the start of reception, the phase difference between the A wave and the B wave is stored. Thereafter, as shown in FIG. 4B, when the signal level of the C wave (third signal) is higher than that of the A wave, the maximum level signal is the C wave, and the second level signal is the C level. Processing is performed as a signal (A wave) at a level next to the wave.

  Based on the waveform identifiers associated with the FFT signals stored in the maximum memory 16-1 and the second memory 16-2, the switching circuit 22 determines the number of defined symbols necessary for the transmission path equivalent processing (for example, 4 symbols) of FFT signals are selected from the maximum memory 16-1 and the second memory 16-2 and output to the transmission line equivalent circuit 24. In the initial state, the FFT signal having the waveform identifier associated with the first FFT value 161a of the maximum memory 16-1 is selected.

The switching circuit 22 receives either the first FFT signal 161a or the first FFT signal 162a, the second FFT signal 161b, or the second FFT signal 162b from the maximum memory 16-1 or the second memory 16-2. Either one of the 3FFT signal 161c and the third FFT signal 162c, or one of the fourth FFT signal 161d and the fourth FFT signal 162d is selected based on the waveform identifier associated with each FFT signal. Specifically, FFT signals having the same waveform identifier or FFT signals having the same waveform identifier are selected so as to increase.
For example, when three A-wave FFT signals and one B-wave FFT signal are stored in the maximum memory 16-1, as in the case of the symbol number “4” in FIG. By selecting the three A-wave FFT signals (A3, A2, A1) stored in 16-1 and the A-wave FFT signal (A4) stored in the second memory 16-2. Only the A-wave FFT signal is selected or the A-wave FFT signal is increased.

  The switching circuit 22 refers to the memory contents of the maximum memory 16-1, and all the waveform identifiers of the second FFT signal 161b to the fourth FFT signal 161d, which are the previous FFT signals, are the same as the waveform identifier of the first FFT signal 161a. It is determined whether or not. Only when it is determined that all the waveform identifiers of the second FFT signal 161b to the fourth FFT signal 161d, which are the previous FFT signals, are the same as the waveform identifiers of the first FFT signal 161a, the FFT selected as the transmission path equivalent processing target The signal is switched to the same FFT signal as the waveform identifier of the first FFT signal 161a. If it is determined that the waveform identifier is not the same as the waveform identifier of the first FFT signal 161a, the FFT signal having the previously selected waveform identifier is selected from the maximum memory 16-1 and the second memory 16-2.

  This will be described in detail with a specific example. FIG. 3 is a diagram for explaining the operation of the switching circuit 22 when an OFDM signal including a delayed wave is received. In the figure, the shaded portion represents the FFT signal selected by the switching circuit 22 from the maximum memory 16-1 and the second memory 16-2.

  First, when a plurality of OFDM signals including delayed waves are received, the peak detection circuit 18-1 of the maximum level signal wave system block 12-1 and the peak detection circuit 18-2 of the second level signal wave system block 12-2. The FFT processing is performed on a plurality of FFT signals having different transmission times or phases, and the maximum level signal for each of the FFT processed FFT signals is A wave, the second highest level signal is B wave, and so on. Waveform identifiers are assigned as follows.

  In the figure, when the OFDM signal with the symbol number “0” is received, the first received signal, that is, the signal level of the A wave is detected by the peak detection circuit 18-1 as the maximum level signal. . Then, the FFT window pulse synchronized with the A wave is generated by the FFT window pulse generation circuit 20-1, and the FFT process according to the pulse is performed on the signal output from the ADC circuit 10 by the FFT circuit 14-1. In FIG. 3, the FFT signal “A0”, which is the result of the FFT process, is stored in the maximum memory 16-1 as the first FFT signal 161a.

  Also, in the figure, the signal with the second highest level, that is, the B wave signal level is detected by the peak detection circuit 18-2 as the second level signal. Then, an FFT window pulse synchronized with the B wave is generated by the FFT window pulse generation circuit 20-2, and an FFT process according to the pulse is performed on the signal output from the ADC circuit 10 by the FFT circuit 14-2. The FFT signal “B0”, which is the processing result of the FFT processing, is stored as the first FFT signal 162a of the second memory 16-2.

  In the symbol numbers “1” to “3”, the same processing as that in the symbol number “0” is performed, and the maximum memory 16-1 and the second memory 16-2 are sequentially subjected to FFT as shown in FIG. The signal is stored. Then, the switching circuit 22 selects the FFT signals stored in the maximum memory 16-1 and the second memory 16-2 so that the same FFT signal as the A wave that is the waveform identifier of the first FFT signal 161a increases. To the transmission line equivalent circuit 24. Therefore, between symbol numbers “0” to “3”, the symbol division is A wave.

  In the figure, when the OFDM signal of symbol number “4” is received, the signal having the second highest level, that is, the signal level of the B wave is detected by the peak detection circuit 18-1 as the current maximum level signal, The FFT signal “B4” output from the FFT circuit 14-1 is stored as the first FFT signal 161a of the maximum memory 16-1.

  Further, the peak level detection circuit 18-2 detects the signal at the maximum level, that is, the signal level of the A wave as the current second level signal, and the FFT signal “A4” output from the FFT circuit 14-2 is the second level signal. Stored as the first FFT signal 162a of the memory 16-2.

  At this time, the switching circuit 22 determines that the waveform identifier of the first FFT signal 161a of the maximum memory 16-1 is not the same as the waveform identifier of the second FFT signal 161b to the fourth FFT signal 161d, and has previously selected it. The FFT signal of “A wave” that is the waveform identifier is selected from the maximum memory 16-1 and the second memory 16-2. Therefore, in the symbol number “4”, the symbol division is an A wave, and the transmission path equivalent processing is not performed in a state where the A wave and the B wave are mixed, unlike the conventional OFDM signal demodulator 900.

  In symbol numbers “5” and “6”, it is detected that the current (first FFT signal) B wave is the maximum level signal and the A wave is the second level signal. The FFT process is performed in the same manner as in. Also at this time, the switching circuit 22 selects the waveform identifier of the first FFT signal 161a of the maximum memory 16-1 and all the waveform identifiers of the second FFT signal 161b to the fourth FFT signal 161d, so that the selection is performed previously. The FFT signal of “A wave” which is the waveform identifier that has been selected is selected. Therefore, in the symbol numbers “5” and “6”, the symbol division is A wave.

  In the symbol number “7”, it is currently detected that the B wave is the maximum level signal and the A wave is the second level signal. At this time, the switching circuit 22 determines that the waveform identifier of the first FFT signal 161a is the same as the waveform identifiers of the second FFT signal 161b to the fourth FFT signal 161d, and the FFT signal is the same as the waveform identifier of the first FFT signal 161a. Are selected from the maximum memory 16-1 and the second memory 16-2. Therefore, in the symbol number “7”, the symbol division is a B wave. As described above, when the B wave is detected four times consecutively as the maximum level signal, the switching circuit 22 selects the B wave FFT signal as the target of the transmission line equivalent processing.

In the symbol number “9”, the signal level of the A wave is detected as being temporarily the maximum level at present, but the switching circuit 22 detects the waveform identifier of the first FFT signal 161a and the second FFT signal 161b˜ Since all the waveform identifiers of the fourth FFT signal 161d are not the same, the B-wave FFT signal that has been selected before is selected. Therefore, in the symbol number “ 9 ”, the symbol division is a B wave.

  Furthermore, in the symbol number “10”, when the C wave is currently detected as the maximum level signal and the A wave is detected as the second level signal, the first FFT signal 161a of the maximum memory 16-1 is “C10”. " In this case, there are only three B-wave FFT signals that have been selected in the memory, and the number of FFT signals in the memory is larger than that of the B-wave FFT signal. The symbol classification is A wave.

  An FFT signal associated with the same waveform identifier selected by the switching circuit 22, that is, an FFT window pulse output from the FFT window pulse generation circuit 20-1, or an output from the FFT window pulse generation circuit 20-2 Of the FFT window pulses, FFT signals extracted by performing FFT processing on signals having different transmission times and phases output from the ADC circuit 10 in accordance with either one of the FFT window pulses are signals that have passed through the same transmission path. It is.

  As described above, the switching circuit 22 selects only the FFT signal associated with the same waveform identifier or the number of FFT signals associated with the same waveform identifier, that is, the same FFT. Only FFT signals obtained by performing FFT processing on signals having different transmission times and phases output from the ADC circuit 10 according to the window pulse, or FFT processing on signals having different transmission times and phases output from the ADC circuit 10 according to the same FFT window pulse By selecting the number of FFT signals to be increased, it is possible to select an FFT signal suitable for transmission path equivalent processing, that is, a signal that has passed through the same transmission path.

  Thereby, only the FFT signal subjected to the FFT process according to the FFT window pulse synchronized with the signal having the same transmission time and phase among the signals output from the ADC circuit 10 is selected as the FFT signal of the transmission path equivalent. Alternatively, among the signals output from the ADC circuit 10, the FFT signal subject to transmission line equivalence is selected so that the number of FFT signals subjected to FFT processing increases according to the FFT window pulse synchronized with the signal having the same transmission time and phase. It becomes possible. Therefore, an FFT signal suitable for transmission line equivalent processing can be selected.

The transmission line equivalent circuit 24 stores the FFT signal output from the switching circuit 22 in the FFT signal memory 240 for every four symbols (the number of defined symbols necessary for transmission line equivalent processing), and performs transmission line equivalent processing. That is, the transmission line equivalent circuit 24 is based on only the FFT signal extracted according to the FFT window pulse synchronized with the signal having the same transmission time and phase with respect to the FFT signal of the specified number of symbols necessary for transmission line equivalent. The transmission path equivalent processing is performed, or the transmission path equivalent processing is performed so that the number of FFT signals extracted according to the FFT window pulse synchronized with the signal having the same transmission time and phase increases. Then, the FFT signal subjected to the transmission line equivalent processing is output to the demodulation circuit 26.

  That is, the transmission line equivalent circuit 24 extracts an FFT signal extracted according to an FFT window pulse synchronized with a signal (delayed wave) having the same transmission time and phase with respect to an FFT signal having a specified number of symbols necessary for transmission line equivalent processing. Of the signals, only the FFT signal having the maximum signal level or the FFT signal having the maximum signal level is selected as appropriate so that the transmission path equivalent processing is performed.

  The demodulation circuit 26 performs predetermined error correction processing and demodulation processing on the FFT signal output from the transmission path equivalent circuit 24, and then outputs it to the decoding unit 7.

  As described above, according to the present embodiment, the maximum level signal is detected from the received OFDM signal including the delayed wave, and FFT processing is performed according to the FFT window pulse synchronized with the signal, and the waveform identifier of the maximum level signal is obtained. Are stored in association with each other. Further, a second level signal is detected, and a predetermined number of FFT signals subjected to FFT processing in accordance with the FFT window pulse synchronized with the signal and the waveform identifier of the second level signal are stored in association with each other. Thereafter, a signal to be subjected to transmission line equivalent processing is selected from the FFT signals based on the waveform identifier corresponding to each FFT signal.

  This selection is made so that the number of FFT signals having the same waveform identifier is selected or the number of FFT signals having the same waveform identifier is increased within the prescribed number of symbols (for example, the number of 4 symbols) required for the transmission path equivalent processing. To do. That is, only the FFT signal obtained by performing the FFT process on the OFDM signal output from the ADC circuit 10 according to the FFT window pulse synchronized with the signal having the same transmission time and phase, or the FFT synchronizing with the signal having the same transmission time and phase. According to the window pulse, the OFDM signal output from the ADC circuit 10 is selected so as to increase the number of FFT signals obtained by performing FFT processing. Accordingly, the transmission line equivalent circuit 24 performs the processing on the FFT signals for the specified number of symbols necessary for the transmission line equivalent processing by using the FFT signals based on the OFDM signals (the same delay wave) that have passed through the same transmission line. be able to.

  As a result, the correction processing capability in error correction processing, which is processing subsequent to the transmission line equivalent circuit 24, is improved, and demodulation processing and the like can be performed more accurately. Therefore, it is possible to reduce the influence due to the deterioration of the reception state based on the obstacle such as the building or the terrain. When receiving an OFDM signal including a delayed wave, select an FFT signal (an FFT signal having the same waveform identifier) extracted based on an FFT window pulse signal synchronized with a signal having the same transmission time and phase As a result, appropriate transmission path equivalent processing can be performed, and the reception performance of the OFDM signal demodulator can be improved.

[Modification]
The control content of the switching circuit 22 described above is described as an example, and the control content can be appropriately changed without departing from the gist of the present invention.

  For example, the peak detection circuit 18-1 and the peak detection circuit 18-2 store the phase difference between the maximum level signal and the second level signal detected at the start of reception. Then, the signal of the maximum level and the second level may be determined only for two signals having this phase difference. For example, when the A wave and the B wave are received as the maximum level signal and the second level signal at the start of reception, the phase difference between the A wave and the B wave is stored. Thereafter, as shown in FIG. 4B, even if the signal level of the C wave (third signal) is higher than that of the A wave, the C wave is Not subject to detection. Thereby, it is possible to prevent the FFT signals other than the A wave and the B wave from being stored in the maximum memory 16-1 and the second memory 16-2. , A-wave or B-wave FFT signal.

  In addition, for example, when a signal having the same waveform identifier is detected as a signal having the maximum level four times in succession, the signal is switched to be a target of transmission line equivalent processing. When it is the same continuously, it is good also as switching, and when it is the same 3 times continuously, it is good also as switching. Thereby, for example, when the waveform identifier of the signal of the maximum level is the same twice as shown in FIG. 5A, a B-wave FFT signal is selected, or as shown in FIG. When the waveform identifier is the same three times in succession, it is possible to realize control for selecting a B-wave FFT signal.

  Also, the FFT signal to be subjected to transmission line equalization processing is switched depending on whether or not a predetermined number of waveform identifiers are continuous, but the FFT signal is simply selected so that the number of FFT signals having the same waveform identifier increases. It is good as well. Specifically, referring to the memory contents of the maximum memory 16-1, the largest waveform identifier is selected, and the FFT signal of the waveform identifier is selected as a transmission path equivalent process target. For example, as shown in FIG. 5B, in the symbol number “6”, the signal having the largest waveform identifier in the maximum memory 16-1 is the B wave, and therefore, the B wave FFT signal is selected. Also good.

  The demodulator 5 has been described as including two blocks, the maximum level signal wave system block 12-1 and the second level signal wave system block 12-2. However, as shown in FIG. It is good also as comprising as the demodulation part 5a provided. The same components as those of the OFDM signal demodulator 1 shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted below.

  The demodulator 5a includes an ADC circuit 10, a maximum level signal wave system block 12-1, a second level signal wave system block 12-2, a third level signal wave system block 12-3,. The signal wave block 12-6, a switching circuit 22a, a transmission line equivalent circuit 24, and a demodulation circuit 26 are provided.

  The maximum level signal wave system block 12-1, the second level signal wave system block 12-2 to the sixth level signal wave system block 12-6 are the maximum level signal waveform block 12-1 and the second level signal shown in FIG. Similar to the wave system block 12-2, it includes an FFT circuit, a peak detection circuit, and an FFT window pulse generation circuit.

  The third level signal wave system block 12-3 detects the third level signal from the signal output from the ADC circuit 10, generates an FFT window pulse synchronized with the signal, and then outputs it from the ADC circuit 10. The processed signal is subjected to FFT processing according to the FFT window pulse, and stored in a third memory (not shown). Similarly, the fourth level signal wave system block 12-4 to the sixth level signal wave system block 12-6 detect the signals of the fourth level to the sixth level, and the third level signal wave system block 12-3. The same processing is performed.

  The switching circuit 22a refers to the FFT signals in the maximum memory 16-1 to the sixth memory (not shown), and has the same waveform identifier, that is, the same transmission time and phase. An FFT signal obtained by performing FFT processing on the OFDM signal output from the ADC circuit 10 in accordance with the FFT window pulse synchronized with the signal and having a stable signal level is selected and output to the transmission line equivalent circuit 24. . For example, A-wave to E-wave signals are irregularly detected in any one of the maximum level signal wave system block 12-1 to the fifth level signal wave system block 12-5, and the F wave is the sixth level signal wave. When the detection is continuously performed a predetermined number of times in the system block 12-6, the switching circuit 22a selects the FFT signal of the F wave as the target of the transmission path equivalent process.

  According to the OFDM signal demodulator 1a in FIG. 7, delay waves having different transmission times and phases are detected in descending order from the received OFDM signals including delay waves having different transmission times and phases, and synchronized with the delay waves. The FFT signal subjected to the FFT processing according to the FFT window pulse and the waveform identifier of the delayed wave are stored in association with each other. Thereafter, a signal to be subjected to transmission path equivalent processing is selected from the stored FFT signals.

  This selection is made so that the number of FFT signals having the same waveform identifier is selected or the number of FFT signals having the same waveform identifier is increased within the prescribed number of symbols (for example, the number of 4 symbols) required for the transmission path equivalent processing. To do. That is, only an FFT signal obtained by performing an FFT process on an OFDM signal output from the ADC circuit 10 according to an FFT window pulse synchronized with a signal (delayed wave) having the same transmission time and phase, or a signal having the same transmission time and phase. In accordance with the FFT window pulse synchronized with (delayed wave), the number of FFT signals obtained by performing FFT processing on the OFDM signal output from the ADC circuit 10 is selected.

  As a result, the correction processing capability in error correction processing is improved in processing subsequent to the transmission line equivalent circuit 24, and demodulation processing and the like can be performed more accurately. Therefore, it is possible to reduce the influence due to the deterioration of the reception state based on the obstacle such as the building or the terrain.

  In addition, when an OFDM signal including a delay wave is received, an appropriate FFT signal extracted based on an FFT window pulse signal synchronized with a signal (delay wave) having the same transmission time and phase can be appropriately selected. Transmission line equivalent processing can be performed, and the reception performance of the OFDM signal demodulator can be improved.

  Further, the FFT signal is selected based on the waveform identifier, but may be selected based on the signal level, for example. Specifically, the peak detection circuit 18-1 is configured to output the signal level of the signal to the FFT circuit 14-1 in addition to the waveform identifier of the signal of the maximum level, and the peak detection circuit 18- 2 is configured to output the signal level of the signal to the FFT circuit 14-2 in addition to the waveform identifier of the signal of the second level. Further, the maximum memory 16-1 and the second memory 16-2 shown in FIG. 1 are replaced with the maximum memory 16-3 and the second memory 16-4 shown in FIG. 6, respectively.

  FIG. 6 is a diagram showing the configuration of the maximum memory 16-3 and the second memory 16-4. According to FIG. 11A, the maximum memory 16-3 includes a first signal level 163a for the first FFT signal 161a, a second signal level 163b for the second FFT signal 161b, and a third signal level for the third FFT signal 161c. 163c is stored by associating the fourth signal level 163d with the fourth FFT signal 161d. The first signal level 163a to the fourth signal level 163d are signal levels output from the peak detection circuit 18-1.

  According to FIG. 5B, the second memory 16-4 has the first signal level 164a for the first FFT signal 162a, the second signal level 164b for the second FFT signal 162b, and the third signal for the third FFT signal 162c. The level 164c is stored in association with the fourth FFT signal 162d and the fourth signal level 164d. The first signal level 164a to the fourth signal level 164d are signal levels output from the peak detection circuit 18-2.

  The FFT circuit 14-1 stores the waveform identifier and the FFT signal in association with each other as the first FFT signal 161a, and stores the signal level output from the peak detection circuit 18-1 as the first signal level 163a. The FFT circuit 14-2 associates the waveform identifier with the FFT signal and stores it as the first FFT signal 162a, and stores the signal level output from the peak detection circuit 18-2 as the first signal level 164a. The switching circuit 22 refers to the maximum memory 16-3 and the second memory 16-4, and calculates an average value of signal levels associated with FFT signals having the same waveform identifier. Then, an FFT signal associated with the waveform identifier having the maximum calculated average value is selected as a transmission path equivalent process target.

  Although the selection of the FFT signal based on the signal level has been described with reference to FIG. 1, the OFDM signal demodulating apparatus 1a shown in FIG. 7 also uses the FFT signal based on the signal level as in FIG. It is possible to perform processing by selecting. The description is omitted below.

As described above, the switching circuit 22 and the switching circuit 22a convert the FFT signal associated with the waveform identifier having the maximum signal level associated with the FFT signal having the same waveform identifier to the transmission path equivalent process. Select as target.
That is, an FFT signal having an average signal level of the FFT signal obtained by performing FFT processing on the OFDM signal output from the ADC circuit 10 in accordance with an FFT window pulse synchronized with a signal (delayed wave) having the same transmission time and phase is maximized. It is possible to select the transmission line equivalent processing target, and it is possible to generate an FFT signal more suitable for the transmission line equivalent processing.

  The transmission line equivalent circuit 24 stores the FFT signals output from the switching circuit 22 and the switching circuit 22a in the FFT signal memory 240 for every four symbols (the number of defined symbols necessary for transmission line equivalent processing), and is equivalent to the transmission line equivalent. Process. That is, the transmission line equivalent circuit 24 extracts an FFT signal extracted according to an FFT window pulse synchronized with a signal (delayed wave) having the same transmission time and phase with respect to an FFT signal having a predetermined number of symbols necessary for transmission line equivalent. Of these, the transmission line equivalent processing is performed based on the FFT signal having the maximum signal level average value.

  The peak detection circuit has been described as detecting the maximum level signal and the second level signal by the two circuits of the peak detection circuit 18-1 and the peak detection circuit 18-2. It is good as well. That is, as shown in FIG. 8, the demodulator 5b includes one peak detection circuit 19, a maximum level signal waveform block 12-3, a second level signal wave system block 12-4, a switching circuit 22, and a transmission path. An equivalent circuit 24 and a demodulation circuit 26 are provided. The same components as those of the OFDM signal demodulator 1 shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted below.

  The peak detection circuit 19 detects the signal of the maximum level among the plurality of signals output from the ADC circuit 10 and outputs it to the FFT window pulse generation circuit 20-1, and also detects the second level signal. Output to FFT window pulse generation circuit 20-2. The waveform identifier of the maximum level signal is output to the FFT circuit 16-1, and the waveform identifier of the second level signal is output to the FFT circuit 16-2. The FFT circuit 14-1 and the FFT circuit 14-2 perform FFT processing according to the FFT window pulse, and store the FFT signal and the waveform identifier in association with each other in the same manner as in the present embodiment described above. Thereby, the same effect as that of the present embodiment described above can be obtained by one peak detection circuit 19.

  In addition, although it has been described that FFT signals corresponding to the number of four symbols are selected, any number can be appropriately changed as long as the number is suitable for transmission line equivalent processing. For example, since the SP signal is inserted every 4 symbols, an FFT signal for 8 symbols that is a multiple of “4” may be selected. In this case, the maximum memory 16-1 and the second memory 16-2 in FIG. 1 are replaced with the maximum memory 16-5 and the second memory 16-6 in FIG. 9, and the FFT signal memory of the transmission line equivalent circuit 24 is replaced. 240 is configured to store the first to eighth FFT signals.

  FIG. 9 is a diagram showing the configuration of the maximum memory 16-5 and the second memory 16-6. According to FIG. 6A, the maximum memory 16-5 stores the first FFT signal 161a to the eighth FFT signal 161h. Further, according to FIG. 6B, the second memory 16-6 stores the first FFT signal 162a to the eighth FFT signal 162h. Thereby, it is possible to select the FFT signal for 8 symbols and perform the transmission line equivalent processing.

  The switching circuit 22 has been described as selecting the FFT signal with reference to the memory contents of the maximum memory 16-1 and the second memory 16-2. For example, the function of the switching circuit 22 is changed to the transmission path. The equivalent circuit 24 may be designed to have. Specifically, the switching circuit 22 and the transmission line equivalent circuit 24 in FIG. 1 are replaced with a transmission line equivalent circuit 24c as shown in FIG. The transmission line equivalent circuit 24c refers to the memory contents of the maximum memory 16-1 and the second memory 16-2, and based on the waveform identifier associated with the FFT signal, the transmission path equivalent processing target FFT Select a signal. Then, transmission path equivalent processing is performed with the selected FFT signal.

The block diagram which shows the function structure of the OFDM signal demodulation apparatus of embodiment in this invention. (A) of the embodiment in the present invention is a diagram showing an example of the configuration of the maximum memory, (b) is a diagram showing an example of the configuration of the second memory. The figure for demonstrating operation | movement of the switching circuit of embodiment in this invention. The figure which shows the relationship between the signal level and transmission time of the signal output from the ADC circuit. The figure for demonstrating an example of the modification of the operation | movement of the switching circuit in this invention. The figure which shows the 1st example of a structure of the memory for maximum of the modification in this invention, and the memory for 2nd. The block diagram which shows the 1st functional structure of the demodulation apparatus of the modification in this invention. The block diagram which shows the 2nd function structure of the demodulator of the modification in this invention. The figure which shows the 2nd example of the structure of the memory for maximum of the modification in this invention, and the memory for 2nd. The block diagram which shows the 3rd function structure of the demodulator of the modification in this invention. The block diagram which shows the function structure of the conventional OFDM signal demodulation apparatus. The conceptual diagram of a received signal and an FFT window pulse. The figure for demonstrating an example of the processing content of the conventional transmission line equivalent process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 OFDM signal demodulator ANT External antenna 3 Tuner part 5 Demodulator part
10 ADC circuit
12-1 Maximum level signal wave system block
14-1 FFT circuit
16-1 Maximum memory
18-1 Peak detection circuit
20-1 FFT window pulse generation circuit
12-2 Second level signal wave system block
14-2 FFT circuit
16-2 Maximum memory
18-2 Peak detection circuit
20-2 FFT window pulse generation circuit
22 Switching circuit
24 Transmission line equivalent circuit
26 Demodulator 7 Decoder

Claims (5)

In an OFDM signal demodulating device that demodulates a plurality of OFDM signals including delay waves received from a receiving unit via a plurality of transmission paths,
Peak detecting means for detecting a peak value of each OFDM signal for a plurality of OFDM signals including the received delayed wave;
Based on the peak value detected by the peak detection means, a window pulse generation means for generating an FFT window pulse synchronized with each of the OFDM signal of the maximum level and the second level and thereafter ;
FFT extraction means for extracting an FFT signal by performing FFT processing on the plurality of OFDM signals including the received delayed wave according to the FFT window pulse generated by the window pulse generation means;
Storage means for storing the FFT signal based on the OFDM signal of the maximum level and the second and subsequent levels extracted by the FFT extraction means while sequentially shifting for each symbol;
A selection means for selecting an FFT signal necessary for waveform equalization for each symbol from the FFT signals stored by the storage means ;
Waveform equivalent means for waveform equalizing the FFT signal selected by the selection means;
Demodulation means for performing demodulation processing on the FFT signal waveform-equalized by the waveform equivalent means ,
The selecting means synchronizes the FFT signal based on the OFDM signal of the maximum level newly stored in the storage means and the FFT signal based on the OFDM signal of the maximum level of another symbol already stored in the storage means. In the case of the FFT signal extracted according to the window pulse, it is based on the FFT signal based on the OFDM signal at the maximum level newly stored in the storage means and the OFDM signal at the maximum level of other symbols already stored in the storage means. An OFDM signal demodulating apparatus, wherein an FFT signal is selected as an FFT signal necessary for waveform equalization . The selecting means synchronizes the FFT signal based on the OFDM signal of the maximum level newly stored in the storage means and the FFT signal based on the OFDM signal of the maximum level of another symbol already stored in the storage means. If not FFT signal extracted according to the window pulse, OFDM signal demodulation according to claim 1, wherein the selecting a waveform equivalently FFT signals required to FFT signal extracted according to the FFT window pulses synchronized increases apparatus. The selecting means synchronizes the FFT signal based on the OFDM signal of the maximum level newly stored in the storage means and the FFT signal based on the OFDM signal of the maximum level of another symbol already stored in the storage means. If it is not an FFT signal extracted according to the window pulse, it is extracted according to an FFT signal based on the OFDM signal of the maximum level of the other symbol already stored in the storage means and the FFT window pulse synchronized with the OFDM signal of the maximum level of the other symbol. by OFDM signal demodulating apparatus according to claim 1, wherein the selecting as a new stored FFT signal and a waveform equivalently required FFT signal in the memory means. An average peak value calculating means for calculating an average peak value of each OFDM signal based on the peak values of a plurality of OFDM signals detected by the peak detecting means;
It said selecting means, by the average peak value calculated by the average peak value calculation means detects the OFDM signal becomes maximum, and FFT processing the received OFDM signal in accordance with the FFT window pulses synchronized to the OFDM signal from the extracted FFT signal, OFDM signal demodulating apparatus according to claim 1, wherein the selecting a waveform equivalently F FT signals necessary. An OFDM signal demodulation method for demodulating a plurality of OFDM signals including delayed waves received from a receiver via a plurality of transmission paths,
A peak detecting step of detecting a peak value of each OFDM signal for a plurality of OFDM signals including the received delayed wave;
Based on the peak value detected in this peak detection step, a window pulse generation step for generating an FFT window pulse synchronized with each of the OFDM signal of the maximum level and the second level and thereafter ,
An FFT extraction step of extracting an FFT signal by performing FFT processing on the plurality of OFDM signals including the received delayed wave according to the FFT window pulse generated in the window pulse generation step;
A storage step of storing the FFT signal based on the maximum level extracted by the FFT extraction step and the OFDM signal of the second and subsequent levels while sequentially shifting each symbol;
A selection step of selecting an FFT signal necessary for waveform equalization for each symbol from the FFT signals stored in the storage step ;
A waveform equivalent step for waveform equalizing the FFT signal selected in this selection step;
A demodulation step for performing a demodulation process on the FFT signal having the waveform equivalent in the waveform equivalent step ,
In the selecting step, the FFT signal based on the OFDM signal of the maximum level newly stored in the storing step and the FFT signal based on the OFDM signal of the maximum level of another symbol already stored in the storing step are synchronized. In the case of the FFT signal extracted according to the window pulse, based on the FFT signal based on the OFDM signal at the maximum level newly stored in the storing step and the OFDM signal at the maximum level of other symbols already stored in the storing step. An OFDM signal demodulation method, wherein an FFT signal is selected as an FFT signal necessary for waveform equalization .

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