JP2006074403A - Method and device for ofdm demodulation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the quality of a demodulated signal by controlling a FFT window to an optimum position even in an environment wherein the state of multipath is varied. <P>SOLUTION: An OFDM reception device includes: a FFT operation circuit 7 which specifies an operation range of an effective symbol period from one OFDM symbol of a received OFDM signal and demodulates information by Fourier transform of the specified operation range; and a symbol synchronizing circuit 9 which detects a main path from the received OFDM signal and controls the operation range on the basis of a symbol boundary position of the detected main path. The symbol synchronizing circuit 9 calculates transmission line characteristics from an SP signal and detects a plurality of paths of the OFDM signal from the calculated transmission line characteristics and selects n paths having higher signal strength out of the detected paths and takes a path having a time nearest to a preceding main path, as a main path out of selected n paths. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  In recent years, a modulation method called orthogonal frequency division multiplexing (OFDM) has been proposed as a method for transmitting digital signals. In this OFDM system, a number of orthogonal subcarriers (subcarriers) are provided in a transmission band, data is allocated to the amplitude and phase of each subcarrier, and digitally transmitted 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 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 is performed at the time of transmission, and a guard interval in which a waveform of a part of 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. The guard interval is, for example, a signal having a length of 1/4 or 1/8 of the effective symbol.

  In an OFDM receiving apparatus that receives such an OFDM signal, the received OFDM signal is demodulated by performing an FFT operation by an FFT 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.

  In this way, in a transmission path under a multipath environment, there are a plurality of symbol boundaries because there are a plurality of paths. Usually, however, the direct wave from the broadcasting station reaches the earliest, so this signal Is set as the main signal (main path), and the FFT window position is set based on the symbol boundary position of the main path 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).

  When setting the FFT window, the OFDM signal before the FFT operation is delayed to correlate the waveform of the guard interval portion with the waveform of the latter half of the OFDM symbol (that is, the signal waveform of the guard interval copy source). Find the OFDM symbol boundary. The time indicated by the peak value of the autocorrelation function is the OFDM symbol boundary of each path, and the highest peak value is the OFDM symbol boundary of the main path.

  As another method, a signal (pilot signal) having a specific level and a specific phase included in the OFDM signal is extracted, and the pilot signal is subjected to IFFT to obtain the signal strength of each path. There is also a method in which the highest path is used as the main path and the symbol boundary is obtained.

  As described above, by extracting the path with the highest received signal strength and detecting the symbol boundary using this path as the main path, the FFT calculation range is accurately determined so that there is no intersymbol interference.

JP 2002-368717 A JP 2001-292125 A

  However, when performing mobile reception, the surrounding environment such as surrounding terrain and buildings frequently fluctuates, so the multipath state of the received signal also fluctuates frequently.

  For this reason, the signal strength of the direct wave from the broadcast station may decrease instantaneously, or the signal strength of the delayed wave may increase instantaneously. In such a case, a main path detection error occurs instantaneously, and the starting point of the FFT window fluctuates greatly instantaneously, resulting in poor reproduction.

  The present invention has been made in view of such circumstances, and an OFDM that controls the FFT window to an optimal position and improves the quality of a demodulated signal even in an environment where the multipath state fluctuates. An object of the present invention is to provide a signal demodulating device and a demodulating method.

  An OFDM demodulator according to the present invention is an OFDM demodulator that demodulates an orthogonal frequency division multiplex (OFDM) signal. The OFDM signal is input via a transmission path under a multipath environment, and one of the input OFDM signals is input. A Fourier transform means for demodulating information by identifying a computation range for the effective symbol period from the transmission symbol, and a Fourier transform of the identified computation range, and detecting a main path of the input OFDM signal, and detecting the detected main path Synchronization control means for controlling the calculation range based on the symbol boundary position, and the synchronization control means detects a path included in the input OFDM signal, and has a high signal strength among the detected paths Select n paths (where n is an integer greater than or equal to 2). Among the selected n paths, select the path that is closest in time to the previous main path. Characterized in that the campus.

  An OFDM demodulator according to the present invention is an OFDM demodulator that demodulates an orthogonal frequency division multiplex (OFDM) signal. The OFDM signal is input via a transmission path under a multipath environment, and one of the input OFDM signals is input. A Fourier transform means for demodulating information by identifying a computation range for the effective symbol period from the transmission symbol, and a Fourier transform of the identified computation range, and detecting a main path of the input OFDM signal, and detecting the detected main path Synchronization control means for controlling the calculation range based on the symbol boundary position, and the synchronization control means detects a path of the input OFDM signal, and among the detected paths, a predetermined time from the previous main path. A path existing in the range is selected, and the path having the highest signal strength among the selected paths is set as the main path.

  In the OFDM demodulation method according to the present invention, an orthogonal frequency division multiplexing (OFDM) signal is input via a transmission path under a multipath environment, and the calculation range for the effective symbol period of the input OFDM signal is specified and specified. In an OFDM demodulation method for demodulating information by performing Fourier transform on an operation range, a path included in an input OFDM signal is detected, and n of the detected paths having a large signal strength (n is an integer of 2 or more) ), The path closest to the previous main path among the selected n paths is set as the main path, the symbol boundary position of the main path is detected, and the detected symbol boundary position of the main path Based on the above, the calculation range is controlled.

  In the OFDM demodulation method according to the present invention, an orthogonal frequency division multiplexing (OFDM) signal is input via a transmission path under a multipath environment, and the calculation range for the effective symbol period of the input OFDM signal is specified and specified. In an OFDM demodulation method that demodulates information by Fourier transforming the calculation range, a path included in the input OFDM signal is detected, and among the detected paths, a path that exists within a predetermined time range from the previous main path The path having the highest signal strength among the selected paths is set as the main path, the symbol boundary position of the main path is detected, and the calculation range is controlled based on the detected symbol boundary position of the main path.

  In the OFDM demodulating apparatus and method according to the present invention, n paths (n is an integer of 2 or more) with high signal strength are selected, and the path closest in time to the previous main path is selected from the selected n paths. A symbol boundary position is detected as a main path, and a Fourier transform calculation range is set based on the detected symbol boundary position of the main path.

  In the OFDM demodulating apparatus and method according to the present invention, a path included in an OFDM signal is detected, a path existing within a predetermined time range from the previous main path is selected from the detected paths, and the path among the selected paths is selected. The symbol boundary position is detected with the path having the highest signal intensity as the main path, and the calculation range of the Fourier transform is set based on the detected symbol boundary position of the main path.

  Hereinafter, an OFDM receiving apparatus to which the present invention is applied will be described.

  As shown in FIG. 1, the OFDM receiver 1 includes an antenna 2, a tuner 3, a band pass filter (BPF) 4, an A / D conversion circuit 5, a digital orthogonal demodulation circuit 6, an FFT operation circuit 7, The pilot position detection circuit 8, the symbol synchronization circuit 9, the equalization circuit 10, and the transmission path decoding circuit 11 are provided.

  A broadcast wave of a digital broadcast broadcast from a broadcast station is received by the antenna 2 of the OFDM receiver 1 and supplied to the tuner 3 as an RF signal. The received RF signal is frequency-converted into an IF signal by a tuner 3 including a multiplier and a local oscillator, and is supplied to the BPF 4. The IF signal output from the tuner 3 is filtered by the BPF 4 and then digitized by the A / D conversion circuit 5. The digitized IF signal is supplied to the digital quadrature demodulation circuit 6.

  The digital quadrature demodulation circuit 6 performs quadrature demodulation on the digitized IF signal using a carrier signal having a predetermined frequency (carrier frequency), and outputs a baseband OFDM signal. As a result of orthogonal demodulation, the baseband OFDM signal becomes a complex signal composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The baseband OFDM signal output from the digital orthogonal demodulation circuit 6 is supplied to the FFT operation circuit 7 and the symbol synchronization circuit 9.

  The FFT operation circuit 7 performs an FFT operation on the baseband OFDM signal, and extracts and outputs a signal that is orthogonally modulated on each subcarrier.

  The FFT operation circuit 7 extracts a signal corresponding to the effective symbol length from one OFDM symbol, and performs an FFT operation on the extracted signal. That is, the FFT operation circuit 7 removes a signal corresponding to the guard interval length from one OFDM symbol, and performs an FFT operation on the remaining signal. The range of the signal extracted for performing the FFT operation may be an arbitrary position of one OFDM symbol as long as the extracted signal points are continuous. That is, the start position of the extracted signal range is any position between the leading boundary position of the OFDM symbol and the end position of the guard interval. The signal extracted by the FFT operation circuit 7 is supplied to the pilot position detection circuit 8, the symbol synchronization circuit 9, and the equalization circuit 10.

  The pilot position detection circuit 8 extracts the boundary of the transmission frame based on the signal demodulated by the FFT operation circuit 7. A transmission frame is a transmission unit composed of a predetermined number of OFDM symbols. The pilot position detection circuit 8 specifies the insertion position of a scattered pilot signal (SP signal) included at a predetermined position in the transmission frame. In the OFDM signal, SP signals having a predetermined amplitude and a predetermined phase are scattered at specific positions in the OFDM symbol. The pilot position detection circuit 8 detects the insertion position of the SP signal by detecting the timing of the transmission frame. The pilot position detection circuit 8 supplies the detected position information of the SP signal to the equalization circuit 10 and the symbol synchronization circuit 9.

  The symbol synchronization circuit 9 calculates the symbol boundary of the main signal (main path) in the baseband OFDM signal output from the digital orthogonal demodulation circuit 6, and performs the FFT operation circuit 7 based on the detected symbol boundary position. Specify the FFT calculation range. The symbol synchronization circuit 9 calculates the symbol boundary of the main path using the baseband OFDM signal, the signal modulated by each subcarrier after being demodulated by the FFT operation circuit 7, and the SP signal. The symbol synchronization circuit 9 generates a trigger indicating the calculation start timing based on the FFT calculation range, and supplies the generated trigger to the FFT calculation circuit 7.

  The equalization circuit 10 performs phase equalization and amplitude equalization on the signal output from the FFT operation circuit 7 using the SP signal. The equalization circuit 10 extracts the SP signal, calculates the distortion amount of the SP signal, and performs waveform equalization. The signal subjected to waveform equalization is supplied to the transmission path decoding circuit 11.

  The transmission path decoding circuit 11 performs carrier demodulation, frequency deinterleaving, demapping, Viterbi decoding, error correction processing, and the like on the signal whose waveform has been equalized by the equalization circuit 10, and outputs a transport stream.

  In the OFDM receiver 1 as described above, an OFDM signal broadcast as a digital terrestrial broadcast is received and demodulated, the demodulated signal is subjected to transmission path decoding, and a transport stream including, for example, an audio or video signal is generated. Can be output.

  Next, the symbol synchronization circuit 9 will be described.

  As shown in FIG. 13, the symbol synchronization circuit 9 detects the boundary position of the OFDM symbol, specifies the calculation range (FFT window) having the same length as the effective symbol from the detected symbol boundary position, A trigger indicating the start timing is generated. However, in a transmission path under a multipath environment, the input OFDM signal is composed of OFDM signals that have passed through a large number of paths, and there are many symbol boundaries. Therefore, the symbol synchronization circuit 9 estimates the most stable path signal (hereinafter referred to as a main path) such as a direct wave from a broadcasting station from the OFDM signals of a large number of paths, and based on the estimated symbol boundary of the main path. An FFT window is set.

  FIG. 2 shows a configuration diagram of the symbol synchronization circuit 9.

  As shown in FIG. 2, the symbol synchronization circuit 9 includes a first synchronization detection circuit 21 that generates rough symbol synchronization timing using a baseband OFDM signal before FFT calculation, and a signal after FFT calculation. A second synchronization detection circuit 22 that generates a fine symbol synchronization timing using the detected SP signal, and a timing detected by the first synchronization detection circuit 21 or a timing detected by the second synchronization detection circuit 22 And a trigger generation circuit 23 for generating an FFT window trigger.

  In the symbol synchronization circuit 9, at the start of reception, first, the first synchronization detection circuit 21 generates a rough FFT window trigger. That is, at the start of reception, the OFDM signal is demodulated with rough symbol synchronization. When a symbol synchronization process is performed by a rough FFT window trigger and continues for a certain period of time, the symbol synchronization circuit 9 uses the second synchronization detection circuit 22 to generate an FFT window trigger. That is, after a certain degree of rough synchronization is established, more accurate symbol synchronization is performed and a stable reproduction state is achieved.

  Hereinafter, the first synchronization detection circuit 21 and the second synchronization detection circuit 22 will be described.

  First, the first synchronization detection circuit 21 will be described.

  FIG. 3 shows a circuit configuration of the first synchronization detection circuit 21.

  As shown in FIG. 3, the first synchronization detection circuit 21 includes a delay circuit 31, a correlation circuit 32, a moving average circuit 33, an integration circuit 34, and a peak detection circuit 35.

  The baseband OFDM signal (FIG. 4A) output from the digital quadrature demodulation circuit 6 is supplied to the delay circuit 31 and the correlation circuit 32. The delay circuit 31 delays the input baseband OFDM signal by an effective symbol time. The baseband OFDM signal (FIG. 4B) delayed by the effective symbol time by the delay circuit 31 is input to the correlation circuit 32.

  The correlation circuit 32 calculates a complex conjugate of the baseband OFDM signal delayed by the effective symbol period, and a complex conjugate of the undelayed baseband OFDM signal and the baseband OFDM signal delayed by the effective symbol period. The signal is multiplied every sample. The multiplication result is supplied to the moving average circuit 33.

  The moving average circuit 33 includes, for example, a shift register composed of a register group for the guard interval length and an adder that calculates the average of the values stored in each register, and is sequentially input for each sample. The moving average calculation for each sample for the guard interval is performed on the multiplication result. The value averaged by the moving average circuit 33 is input to the integrating circuit 34. The integration circuit 34 integrates the input moving average value. The value output from the integration circuit 34 is a correlation signal (FIG. 4C) indicating the correlation between the baseband OFDM signal and the baseband OFDM signal delayed by an effective symbol.

  The peak detection circuit 35 detects the peak value of the correlation signal and generates a pulse that becomes high at the peak timing (rough FFT trigger, FIG. 4D).

  As described above, the first synchronization detection circuit 21 generates symbol synchronization timing by feedforward control. The trigger generation circuit 23 supplies the trigger generated from the first synchronization detection circuit 21 to the FFT operation circuit 7 at the start of reception.

  Next, the second synchronization detection circuit 22 will be described.

  FIG. 5 shows a circuit configuration of the second synchronization detection circuit 22.

  As shown in FIG. 5, the second synchronization detection circuit 22 includes a pilot extraction circuit 41, an IFFT circuit 42, a signal strength calculation circuit 43, and a main path selection circuit 44.

  The pilot extraction circuit 41 receives a signal after the FFT calculation by the FFT calculation circuit 7. The pilot extraction circuit 41 extracts only the SP signal from the signal after the FFT calculation based on the SP signal insertion position. The SP signal extracted by the pilot extraction circuit 41 is supplied to the IFFT calculation circuit 42.

  The IFFT arithmetic circuit 42 performs inverse FFT conversion on the SP signal to generate a baseband OFDM signal composed only of the SP signal. The baseband OFDM signal configured using the SP signal is supplied to the signal strength calculation circuit 43.

  The signal strength calculation circuit 43 performs a filter operation on the baseband OFDM signal composed only of the SP signal to calculate the transmission path characteristic. Specifically, the delay time and signal strength of each path in the received signal in which a large number of delayed waves are combined are calculated. Since the SP signal is a signal whose amplitude and phase are known in advance, such transmission path characteristics can be calculated. For example, as shown in FIG. 6, the signal strength calculation circuit 43 sets the delay time of each path to the time difference between the current FFT window setting position and each path (that is, the path set as the current main path). , Time difference from other paths). The delay time and signal strength of each path calculated by the signal strength calculation circuit 43 are supplied to the main path selection circuit 44.

  The main path selection circuit 44 selects one main path from a plurality of paths based on the delay time and signal intensity of each path detected by the signal intensity calculation circuit 43. When the main path selection circuit 44 selects the main path, the main path selection circuit 44 calculates a time difference between the selected main path and the current main path, and calculates a correction amount corresponding to the time difference. The calculated correction amount is input to the trigger generation circuit 23.

  When the correction amount is input from the second synchronization detection circuit 22 described above, the trigger generation circuit 23 corrects the trigger generation timing that is currently set, and generates a trigger at the next corrected timing.

  As described above, the second synchronization detection circuit 22 obtains the time difference between the currently set FFT window timing and the main path of the received signal, and corrects the FFT window by the time difference. For this reason, the symbol synchronization circuit 9 can generate the FFT window timing following the main path even if the main path fluctuates. Therefore, it is possible to always perform correct FFT calculation.

  Next, a main path selection method by the main path selection circuit 44 will be described with reference to the flowchart of FIG.

  First, the main path selection circuit 44 acquires the signal strength and delay time of each sample calculated by the signal strength calculation circuit 43 (step S11). Subsequently, one sample is selected from the acquired samples (step S12). Subsequently, a moving average for a predetermined number of OFDM symbols is calculated for the signal strength and delay time of the selected sample (step S13).

  Subsequently, the main path selection circuit 44 determines whether or not the signal strength of the selected sample is greater than the signal strength of the lowest strength path (candidate path E) among the predetermined number of candidate paths (A to E). Judgment is made (step S14).

  If the signal intensity of the selected sample is larger, the main path selection circuit 44 removes the candidate path (candidate path E) having the lowest intensity from the candidate path and includes the selected sample in the candidate path. At the same time, the main path selection circuit 44 rearranges a predetermined number of candidate paths (A to E) in descending order of signal strength (step S15). If the signal strength of the selected path is smaller, the main path selection circuit 44 does not perform any processing.

  Subsequently, the main path selection circuit 44 determines whether or not the processing in steps S12 to S14 has been completed for all samples (step S16). If all the paths have not been processed, the process returns to step S12, and the processes from step S12 are performed on other samples.

  When the processing of steps S12 to S14 is completed for all samples, a predetermined number (for example, five) of paths are selected as candidate paths in descending order of signal strength.

  If it is determined that the processing of steps S12 to S14 has been completed for all samples, the main path selection circuit 44 refers to the delay times of a predetermined number of candidate paths (candidate paths A to E), and A path that is closest in time to the previous main path (the absolute value of the delay time is the smallest) is identified from the candidate paths (step S17).

  The main path selection circuit 44 selects the path specified in step S17 as the main path.

  The main path selection circuit 44 calculates a correction value for correcting the trigger timing of the previous FFT window based on the delay time of the main path selected as described above.

  That is, as shown in FIG. 8, the main path selection circuit 44 selects and selects n paths (n is an integer of 2 or more) having a high signal strength among paths included in the received OFDM signal. Of the n paths, the path closest to the previous main path is the main path.

  For this reason, in the OFDM receiver 1, for example, even when the signal strength of a direct wave from a broadcasting station is instantaneously reduced or the signal strength of a delayed wave is instantaneously increased, Reception can be continued stably without making a mistake in judgment.

  Next, another method (second method) of main path selection by the main path selection circuit 44 will be described with reference to the flowchart of FIG.

  First, the main path selection circuit 44 acquires the signal strength and delay time of each sample calculated by the signal strength calculation circuit 43 (step S21).

  Subsequently, one sample is selected from the acquired samples (step S22). Subsequently, it is determined whether or not the delay time of the selected sample is within a predetermined time difference from the previous main path (step S23). As a result of the determination, if it is out of the range, the process from step S24 to step S26 is not performed and the process directly proceeds to step S27. If it is within the range, the process proceeds to step S24.

  Subsequently, the main path selection circuit 44 calculates a moving average for a predetermined number of OFDM symbols with respect to the signal strength and delay time of the selected sample (step S24).

  Subsequently, the main path selection circuit 44 determines whether or not the signal strength of the selected sample is larger than the signal strength of the candidate path (A) (step S25).

  If the signal intensity of the sample selected from the candidate path A is larger than that of the candidate path A, the main path selection circuit 44 sets the selected path as a candidate path (step S26). If the signal intensity of the selected sample is smaller, the main path selection circuit 44 does not perform any processing.

  Subsequently, the main path selection circuit 44 determines whether or not the processing in steps S22 to S26 has been completed for all samples (step S27). If all the samples have not been processed, the process returns to step S22, and the processes from step S22 are performed on the other samples.

  If it is determined that the processing in steps S22 to S26 has been completed for all samples, the main path selection circuit 44 selects a candidate path (candidate path A) as the main path (S28).

  The main path selection circuit 44 calculates a correction value for correcting the trigger timing of the previous FFT window based on the delay time of the main path selected as described above.

  That is, as shown in FIG. 10, the main path selection circuit 44 selects a path existing within a predetermined time range from the previous main path from the paths included in the received OFDM signal, and selects the selected path. Of these, the path with the highest signal strength is used as the main path.

  For this reason, in the OFDM receiver 1, for example, even when the signal strength of a direct wave from a broadcasting station is instantaneously reduced or the signal strength of a delayed wave is instantaneously increased, Reception can be continued stably without making a mistake in judgment.

  Next, still another method (third method) of main path selection by the main path selection circuit 44 will be described with reference to the flowchart of FIG.

  First, the main path selection circuit 44 acquires the signal strength and delay time of each sample calculated by the signal strength calculation circuit 43 (step S31).

  Subsequently, one sample is selected from the acquired samples (step S32). Subsequently, the main path selection circuit 44 calculates a moving average for a predetermined number of OFDM symbols with respect to the signal intensity and delay time of the selected sample (step S33).

  Subsequently, the main path selection circuit 44 adds an offset to the signal intensity of the selected path (step S34).

  Here, the offset is set to a value that decreases as the delay time increases, that is, as the time difference from the previous main path increases. That is, the closer to the previous main path, the greater the offset.

  Subsequently, the main path selection circuit 44 determines whether or not the signal intensity of the selected sample after the offset is added is larger than the signal intensity of one candidate path (A) (step S35).

  If the signal intensity of the selected sample is larger than that of the candidate path (A), the main path selection circuit 44 sets the selected sample as a candidate path (step S36). If the signal intensity of the selected sample is smaller, the main path selection circuit 44 does not perform any processing.

  Subsequently, the main path selection circuit 44 determines whether or not the processing of steps S32 to S36 has been completed for all samples (step S37). If all the samples have not been processed, the process returns to step S32, and the processes from step S32 are performed on the other samples.

  If it is determined that the processing of steps S32 to S36 has been completed for all samples, the main path selection circuit 44 selects the candidate path A as the main path (S38).

  The main path selection circuit 44 calculates a correction value for correcting the trigger timing of the previous FFT window based on the delay time of the main path selected as described above.

  That is, in the main path selection circuit 44, as shown in FIG. 12, an offset that decreases as the time difference from the previous main path increases is added to the path included in the received OFDM signal. A path having a large signal intensity after correction by the above is used as a main path.

  For this reason, in the OFDM receiver 1, for example, even when the signal strength of the direct wave from the broadcasting station is instantaneously reduced or the signal strength of the delayed wave is instantaneously increased, Reception can be continued stably without making a mistake in judgment.

  Note that the third method shown in FIG. 11 may be combined with the first method or the second method described above. That is, in the first method or the second method, the signal intensity may be corrected by the offset.

It is a block diagram of an OFDM receiver to which the present invention is applied. It is a block diagram of the symbol synchronization circuit in the said OFDM receiver. It is a block diagram of the 1st synchronous detection circuit in a symbol synchronous circuit. It is a figure showing the signal currently processed with the 1st synchronous detection circuit. It is a block diagram of the 2nd synchronous detection circuit in a symbol synchronous circuit. It is a figure which shows the delay time and signal strength of the path | route of the transmission line detected by the 2nd synchronous detection circuit. It is a flowchart which shows the process sequence of the 1st method among the selection methods of a main path. It is a figure for demonstrating the processing content of the said 1st method. It is a flowchart which shows the process sequence of the 2nd method among the selection methods of a main path. It is a figure for demonstrating the processing content of the said 2nd method. It is a flowchart which shows the process sequence of the 3rd method among the selection methods of a main path. It is a figure for demonstrating the processing content of the said 3rd method. It is the figure which showed the OFDM signal, the OFDM symbol, the effective symbol, the guard interval, and the FFT window.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 OFDM receiver, 6 Digital orthogonal demodulation, 7 FFT operation circuit, 8 Pilot position detection circuit, 9 Symbol synchronous circuit, 21 1st synchronous detection circuit, 22 2nd synchronous detection circuit, 23 Trigger generation circuit

Claims (8)

In an OFDM demodulator for demodulating an Orthogonal Frequency Division Multiplex (OFDM) signal,
The OFDM signal is input via a transmission path in a multipath environment, and the calculation range for the effective symbol period is specified from one transmission symbol of the input OFDM signal, and information is obtained by performing Fourier transform on the specified calculation range. Fourier transform means for demodulating,
Synchronization control means for detecting a main path in the input OFDM signal and controlling the calculation range based on a symbol boundary position of the detected main path;
The synchronization control means detects a path included in the input OFDM signal,
Among the detected paths, select n paths (n is an integer of 2 or more) with high signal strength,
An OFDM demodulator characterized in that, among the selected n paths, the path closest to the previous main path is the main path. The synchronization control means gives an offset such that the value decreases as the time difference from the previous main path increases, to the detected signal strength of the path,
2. The OFDM demodulator according to claim 1, wherein n paths having a large signal strength after giving an offset are selected. In an OFDM demodulator for demodulating an Orthogonal Frequency Division Multiplex (OFDM) signal,
The OFDM signal is input via a transmission path in a multipath environment, and the calculation range for the effective symbol period is specified from one transmission symbol of the input OFDM signal, and information is obtained by performing Fourier transform on the specified calculation range. Fourier transform means for demodulating,
Synchronization control means for detecting a main path in the input OFDM signal and controlling the calculation range based on a symbol boundary position of the detected main path;
The synchronization control means detects the path of the input OFDM signal,
Among the detected paths, select a path that exists within a predetermined time range from the previous main path,
An OFDM demodulator characterized in that, among the selected paths, the path with the highest signal strength is used as the main path. The synchronization control means gives an offset such that the value decreases as the time difference from the previous main path increases, to the signal strength of the path existing within a predetermined time range from the previous main path,
The OFDM demodulator according to claim 3, wherein a path having the largest signal strength after giving an offset is set as a main path. An orthogonal frequency division multiplex (OFDM) signal is input via a transmission path in a multipath environment, the calculation range for the effective symbol period of the input OFDM signal is specified, and information is obtained by performing Fourier transform on the specified calculation range. In an OFDM demodulation method for demodulating,
Detect the path included in the input OFDM signal,
Among the detected paths, select n paths (n is an integer of 2 or more) with high signal strength,
Of the n selected paths, the path that is closest in time to the previous main path is the main path,
An OFDM demodulation method comprising: detecting a symbol boundary position of the main path, and controlling the calculation range based on the detected symbol boundary position of the main path. An offset is given to the signal strength of the detected path so that the value decreases as the time difference from the previous main path increases.
6. The OFDM demodulation method according to claim 5, wherein n paths having a large signal strength after giving an offset are selected. An orthogonal frequency division multiplex (OFDM) signal is input via a transmission path in a multipath environment, the calculation range for the effective symbol period of the input OFDM signal is specified, and information is obtained by performing Fourier transform on the specified calculation range. In an OFDM demodulation method for demodulating,
Detect the path included in the input OFDM signal,
Among the detected paths, select a path that exists within a predetermined time range from the previous main path,
Of the selected paths, the path with the highest signal strength is the main path,
An OFDM demodulation method comprising: detecting a symbol boundary position of the main path, and controlling the calculation range based on the detected symbol boundary position of the main path. An offset is given to the signal strength of a path existing within a predetermined time range from the previous main path so that the value decreases as the time difference from the previous main path increases.
8. The OFDM demodulation method according to claim 7, wherein a path having the largest signal intensity after giving an offset is set as a main path.

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