JP2001036495A - Ofdm digital receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely demodulate OFDM data transmitted in plural transmission modes by executing a correlation operation using correlation between a guard and data on the latter half of a valid symbol and detecting a symbol break. SOLUTION: In a correlation computing element 12, a correlation coefficient is calculated by using data obtained by delaying complex reception data on a time area, which is inputted from an A/D converter 6, by a valid symbol period. When the correlation coefficient has correlation in a guard period, a rectangular or trapezoidal waveform appears in a real symbol period in a correlation sum outputted from a correlation sum computing element 13. The mode of a transmission string, the guard period and the valid symbol period are discriminated based on the addition results of 12 ways, which are obtained by adding elements obtained by dividing the correlation sum in a real symbol period, and a symbol break is detected. When the plural elements obtained by dividing the correlation sum in the real symbol period are added, the influence of noise can be reduced and the symbol break can precisely be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM receiver for receiving and demodulating an OFDM-modulated signal having a guard interval between symbols, and more particularly to an apparatus for detecting a break between a symbol period and a guard period of a received signal.

[0002]

2. Description of the Related Art Orthogonal frequency division multiplexing (hereinafter, OFDM)
The modulation method is characterized by being resistant to multipath interference and having high frequency use efficiency, and has recently been studied for use in digital broadcasting including mobile communication. FIG. 11 is a block diagram illustrating a configuration of the OFDM receiver.

[0003] An OFDM signal in an RF frequency band input from an antenna 1 is amplified by an RF amplifier 2 and multiplied by a signal output from a voltage controlled oscillator 10 by a mixer 3 to produce an intermediate frequency signal (hereinafter, IF signal). The signal is band-limited by an IF amplifier 4, amplified to an appropriate signal level, and quadrature-demodulated by a quadrature demodulator 5. The in-phase signal component (hereinafter, I signal) and the quadrature signal component (hereinafter, Q signal) of the baseband frequency band output from the quadrature demodulator 5 are input to the A / D converter 6 and the A / D converter
The data is converted into digital data by the converter 6. The I and Q signals converted to digital data are input to a high-speed discrete Fourier transformer (hereinafter, FFT processor) 7, converted to frequency-domain complex data, input to an error corrector 8, and then subjected to error correction. The subsequent data is the digital data output terminal 9
Output to

The frequency shift detector 11 detects a frequency error between the reproduced carrier and the carrier frequency based on the output from the FFT processor 7 and performs automatic frequency control for controlling the oscillation frequency of the voltage controlled oscillator 10. As a result, the center frequency of the IF signal down-converted by the mixer 3 approaches the ideal value.

[0005] As shown in FIG. 12, in OFDM digital broadcasting, data is temporally divided and transmitted in units of symbols. One symbol and valid symbol period equal to the inverse T _s of OFDM subcarrier spacing length, composed of a guard period provided at the front. Here, in order for the above-mentioned FFT processor 7 to perform accurate demodulation, it is necessary to detect a break between a guard period and an effective symbol period (hereinafter, a symbol break). The symbol break detection unit 20 detects this symbol break by the method described below, and controls the FFT processor.

[0006] As shown in FIG.
In the transmission signal, the data in the guard period _Gn is the same as the data in the second half _Gn 'of the effective symbol period. Therefore, the number of data samples of the effective symbol period N, the number of data samples of the guard interval as M, the transmission data s (i transmit data s (i _Gn) and a guard interval G _n of the latter part G _n 'of the effective symbol period _Gn- N) satisfies the following relationship.

[0007]

(Equation 1)

In the OFDM receiver, transmission data s
When a correlation coefficient between (i) and a data sequence s (iN) obtained by delaying this from the effective symbol period N is obtained, and this is added in a period equal to the guard interval _Gn , a waveform having a peak at each symbol segment is obtained. appear. Utilizing this, a break between the guard and the effective symbol is detected, and symbol synchronization at the time of data demodulation is achieved. This method is disclosed in Japanese Patent Application Laid-Open No. 7-14309.
No. 7 is introduced.

[0009]

When detecting a symbol delimiter using the conventional apparatus, it is necessary to set an effective symbol period and a guard period of received data at the time of correlation calculation. In the OFDM transmission system, the guard period and the effective symbol period of the transmission data differ depending on the transmission mode. Therefore, the receiver must perform the correlation operation from the state where the guard period and the effective symbol period of the transmission data are unknown. In the case where a data sequence having a different guard period and effective symbol period is input depending on the transmission mode, the transmission mode is discriminated, a symbol break of the received data is detected from a state where the guard period and the effective symbol period are unknown, and demodulation is performed. No means is provided for doing so.

The OFDM receiver according to the present invention performs a correlation operation using the correlation between the guard and the data of the latter half of the effective symbol from a state where the guard period and the effective symbol period are unknown, detects symbol delimiters, and detects a plurality of symbol delimiters. An object of the present invention is to provide an OFDM receiver capable of reliably demodulating OFDM data transmitted in a transmission mode.

[0011]

In order to achieve the above object,
The OFDM digital receiver according to the present invention provides a phase relationship between a received data sequence consisting of a real symbol period composed of different effective symbol periods and guard periods according to the mode, and a data sequence obtained by delaying this data sequence by the effective symbol period. A correlation calculation means for calculating the number is provided, and a correlation coefficient corresponding to a plurality of existing modes is obtained. Subsequently, a correlation sum is obtained by adding these correlation coefficients in a period corresponding to the minimum guard period of each mode, and this correlation sum is continuously divided by a period corresponding to a real symbol period. Are added, and a break between the guard period and the symbol period is detected based on the addition result, and the received data sequence is demodulated.

The means for detecting the break between the guard period and the effective symbol period is a computing means for adding the sum of the correlation sum and a result obtained by delaying the sum by a period corresponding to a predetermined multiple of the minimum guard period, or Calculating means for integrating the addition result over an integration interval corresponding to a predetermined multiple of the minimum guard period, and determining the guard period based on the waveform whose output has the maximum peak among the waveforms represented by the outputs of these calculating units. Detects a break from the effective symbol period. The means for detecting the break detects the break between the guard period and the effective symbol period based on the height and width of the waveform represented by the sum of the correlation sums.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. Note that the same or corresponding parts as those described in the above related art are denoted by the same reference numerals, and description thereof is omitted.

Embodiment 1 FIG. 1 is a block diagram illustrating a configuration of an OFDM digital broadcast receiver according to the present embodiment. In FIG. 1, reference numeral 101 denotes a symbol break detection unit according to the present embodiment, which includes a correlation calculator 12, a correlation sum calculator 13, a correlation sum adder 14, a symbol break detector 201, and an FFT controller 15.

In the symbol delimiter detecting unit 101 according to the embodiment of the present invention, a transmission mode (hereinafter, referred to as a mode) is used.
Even when a data sequence having a different effective symbol period and guard period is received, the effective symbol period and the guard period of the received data sequence are determined from a mode whose mode is unknown at the time of reception, and a symbol delimiter for data demodulation is performed. Then, the FFT processor 7 performs control so that the FFT processor 7 performs FFT processing on the effective symbol with the correct number of points.

The operation of the symbol period detecting section 101 in the guard period in the present embodiment will be described with reference to the case where three different effective symbol periods exist depending on the transmission mode (A, B and C) as shown in FIG. explain. in this case,
In each mode, there are four more different guard periods. Here, the effective symbol period N and the guard period M are represented by the number of data samples. As shown in FIG. 2, the guard periods M ₂ , M ₃ and M ₄ of each mode are ₂ , 4, and 8 times the minimum guard period M ₁ , respectively, and there are a total of 12 actual symbol periods.

First, in the correlation calculator 12, data g (i-) obtained by delaying the complex reception data g (i) and g (i) in the time domain inputted from the A / D converter 6 by the effective symbol period N.
N), the correlation coefficient c (i) is calculated by the following equation. Here, * represents a complex conjugate.

[0018]

(Equation 2)

In this case, since there are three types of effective symbol periods N depending on the mode, three types of correlation coefficients are obtained.

Here, g (i) and g (i−N) * are s (i) for the transmission signal, Δf for the frequency error on the receiving side, θ for the phase difference between the carriers of the transmission and reception signals, and the effective symbol The duration of T _S
Is expressed as follows. Here, j represents an imaginary unit.

[0021]

(Equation 3)

From the above equation, the correlation coefficient c (i) can be expressed as follows.

[0023]

(Equation 4)

Here, s (i) = s (i-N) in a region having a correlation according to the relationship of Equation 1, so that s (i) s (i-N) * is equal to s (i).
(i) It can be expressed as s (i) *. Where s (i) s (i) * is i
It is a real number irrespective of this, and is specifically the square of the amplitude of s (i). Therefore, the correlation coefficient c (i) in the guard period is as follows.

[0025]

(Equation 5)

The correlation coefficient c (i) in the case of having a correlation as shown in Equation 5 is obtained by calculating the square of the amplitude of the transmission signal s (i) by the frequency error Δ
The phase is rotated by f, and the phase can be regarded as a fixed value regardless of i. On the other hand, in a region having no correlation, s (i)) s (i−N), so that s (i) s (i−N) * varies in phase and amplitude depending on i.

As shown in FIG. 3, since the correlation coefficients c (i) have the same phase in a region where s (i) and s (i-N) have a correlation, the correlation coefficient c (i) By adding
The start point and end point of the correlated area can be detected. In the present embodiment, utilizing the correlation, the correlation sum calculator 103 calculates the correlation sum obtained by adding the correlation coefficient c (i) in the minimum guard period M ₁ , so that the start point and the end point can be determined. Ask.

[0028] The correlation sum obtained by adding the correlation coefficient when the correlation of the guard period has taken c (i) with a minimum guard period M ₁ C (i) is shown schematically is Figure 4. Figure 4-a is a correlation sum when the guard period of the transmission data sequence is the minimum value M _1, FIG. 4-b, c and d are each twice the guard period of the transmitted data sequence minimize the guard period M _1, This is the correlation sum when it is 4 times and 8 times (M ₂ , M ₃ , M ₄ ).

As shown in FIG. 4, when the correlation coefficient c (i) has a correlation in the guard period, that is, in the calculation of the correlation coefficient shown in Equation 2, the delay amount N is equal to the effective symbol period of the transmission data sequence. If they match, a triangular or trapezoidal waveform appears in the correlation sum C (i) output from the correlation sum calculator 13 at the actual symbol period. Accordingly, the mode, guard period, and effective symbol period of the transmission data sequence are determined based on 12 addition results obtained by adding the elements obtained by dividing the correlation sum C (i) by each real symbol period, and the symbol separation is performed. Can be detected. Further, by adding a plurality of elements obtained by dividing the correlation sum by the actual symbol period as described above, the influence of noise can be reduced, and the symbol break can be detected accurately.

The calculation method for adding the correlation sum and the elements obtained by dividing the correlation sum by the actual symbol period will be described below.

The equation for calculating the correlation sum C (i) can be expressed by the following equation.

[0032]

(Equation 6)

Based on the above equation, the correlation sum calculator 13 calculates 3 for each mode using the equation 2 in the correlation calculator 12.
Based on the correlation coefficient as obtained correlation sum of three ways as the minimum guard period corresponding to M ₁ in each mode. These correlation sums are input to the correlation sum adder 14.

In the correlation sum adder 14, the correlation sum C (i)
Is calculated by adding the elements obtained by dividing the real symbol periods by L ₁ , L ₂ ,
The sum of the L ₃ and L ₄ correlation sums is calculated as S _C1 (i ′), S _C2 (i ′), S
_{If C3} (i ') and S _C4 (i') are expressed as follows.

[0035]

(Equation 7)

Here, k is the number of additions, and i _o is the addition start point. This calculation method is shown in FIG. Since addition of the correlation sum is performed for each real symbol period i 'returns to 0 when the value reaches the respective real symbol sample number L ₁ ~L _4. Here, S _C1 (i ′) calculated by equation 7-1 is the correlation sum C (i)
The a sum when the sum separated by a minimum real symbol period L _1, is calculated by the equation 7-2,3,4, S
_C2 (i '), S _C3 (i') and S _C4 (i ') are respectively the correlation sum C (i)
Are divided by the actual symbol periods L ₂ , L ₃ , and L ₄ .

The correlation sum adder 14 calculates the value of 3 for each mode in the correlation sum calculator 13 based on the equations 7-1 to 4-1.
Based on the correlation sum of the street, the mode 4 kinds of L ₁ ~L ₄ as an actual symbol periods for each mode, and calculates the data string of kinds total 12.

The twelve data strings calculated by the correlation sum adder 14 are input to the symbol segment detection unit 201. At this time, among the twelve calculation results of the correlation sum adder 14, as described above, in the correlation coefficient calculation by Equation 2, only the triangular wave whose delay amount N matches the effective symbol period of the received data sequence is arranged. Or a trapezoidal wave appears. The symbol break detector detects the mode, guard period, and symbol break based on the waveforms represented by these twelve data strings, and outputs the result to the FFT processor 7.
Give to. The FFT controller 15 generates the number of points of the FFT operation in the FFT processor 7 and the timing of a real symbol portion to be selected from the input mode, guard period and symbol delimiter position, and controls the FFT processor 7. .

Since the data string resulting from the correlation sum addition has a length of only one real symbol, a peak may appear at the end of the data string. In such a case, peak detection may be performed as a cyclic data sequence in which each data sequence is connected in a ring shape. Further, the processing inside the symbol break detection unit 101 according to the present embodiment can be configured as a program processing using a digital signal processor (DSP) or the like.

Embodiment 2 The present embodiment relates to a means for detecting a symbol break.

FIG. 6 shows the inside of the symbol break detector 201 in the present embodiment.
6 and a peak detector 17. The peak generator 16 performs an operation of generating a triangular wave having a peak at a position corresponding to a symbol break. The peak detector detects a symbol break based on an output from the peak generator. Hereinafter, the operation of the symbol break detector according to the present embodiment will be described.

The twelve data strings calculated by the correlation sum adder 14 shown in FIG. 1 are input to the peak generator 16. Of these data strings, the correlation sum addition result S _C1 (i ′) whose data length is the minimum real symbol period L ₁ is:
When the correlation coefficient c (i) is correlated in the guard period, a triangular wave having a peak is detected at a position corresponding to the symbol delimiter, so that the triangular wave is output to the peak detector 17 without performing any processing. .

[0043] Of the output data of the correlation sum adder 14, the data length is the actual symbol period L ₂ correlation sum sum S
_{C2 'for, S C2 (i (i)} ' and), the peak generation operation by calculating the sum of the minimum guard period M ₁ only previous data sequence S _C2 (i'-M _1), this result Is output to the peak detector 17. However, the data sequence is operated as a cyclic data sequence. This calculation method is shown in FIG. The arithmetic expression for obtaining the result shown in FIG. 7A is expressed as follows, where the peak generation result is C _P2 (i ′).

[0044]

(Equation 8)

The calculation shown in Equation 8 is performed using M ₂ and L ₂ as a guard period and an actual symbol period corresponding to each mode, and three types of peak generation results are obtained.

[0046] Of the output data of the correlation sum adder 14, the data length is the actual symbol period L ₃ correlation sum sum S
_{For C3} (i '), S _C3 (i') and the minimum guard period M ₁ ,
Twice the M ₁ and 3 times only before the data sequence _{S C3 (i'-M 1)} ,
A peak generation operation is performed by calculating the sum of S _C3 (i'-2M ₁ ) and S _C3 (i'-3M ₁ ).
Output to However, the data sequence is operated as a cyclic data sequence. This calculation method is shown in FIG. The arithmetic expression for obtaining the result shown in FIG. 7B is obtained by calculating the peak generation result as C _P3 (i ′).
Then, it is expressed as follows.

[0047]

(Equation 9)

The calculation shown in Equation 9 is performed by using M ₁ and L ₃ as the minimum guard period and the actual symbol period corresponding to each mode, respectively, to obtain three kinds of peak generation results.

[0049] Of the output data of the correlation sum adder 14, the data length is the actual symbol period L ₄ correlation sum sum S
_{For C4} (i '), S _C4 (i') and the minimum guard period M ₁ ,
2 times M _1, 3, 4, 5, data sequence S _C4 (i'-qM ₁₎ in 6-fold and 7-fold before (q = 1,2, ... .7) calculating the sum of the values of Then, a peak generation operation is performed, and the result is output to the peak detector 17. However, the data sequence is operated as a cyclic data sequence. This calculation method is shown in FIG. An arithmetic expression for obtaining the result shown in FIG. 7C is expressed as follows, where the output after peak generation is C _P4 (i ′).

[0050]

(Equation 10)

The operation shown in Expression 10 is performed by using M ₁ and L ₄ as the minimum guard period and the actual symbol period corresponding to each mode, respectively, to obtain three types of peak generator outputs.

The calculation for obtaining the peak generation result shown in Expression 9 can also be performed as follows.

[0053]

[Equation 11]

In the calculation according to the above equation, first, the sum S _C3 (i ′) of the data string S _{C 3} (i′−M ₁ ) preceding the minimum guard period M ₁ by S _C3 (i ′).
_C3 ′ (i ′) is obtained (Equation 11-1), and then the data string S _C3 ′ (i′−2M) two times before S _C3 ′ (i ′) and the minimum guard period M _1.
The peak generation result C _P4 (i ′) is obtained by calculating the sum of ₁ ) (Equation 11-2).

In the case of calculating the peak generation result C _P4 (i ′) in Equation 9, the number of additions is three, whereas this calculation can be performed by adding two times.

The calculation for obtaining the peak generation result shown in Expression 10 can also be performed as follows.

[0057]

(Equation 12)

[0058] First, in operation by the above equation, S _C4 and (i '), the sum S of the minimum guard period M ₁ only previous data sequence _{S C 4 (i'-M 1} )
_C4 ′ (i ′) is obtained (Equation 12-1), and then the data sequence S _C4 ′ (i′−2M) two times before S _C4 ′ (i ′) and the minimum guard period M _1.
The sum S _C4 ″ (i ′) of ₁ ) is calculated (Equation 12-2).
_The peak generation result C _P4 (i ′) is obtained by calculating the sum of _{C 4} ″ (i ′) and the data string S _C4 ″ (i′−4M ₁ ) four times before the minimum guard period M ₁ (equation 12-3).

In Equation 10, when the peak generation result C _P4 (i ′) is obtained, the number of additions is seven, whereas this calculation can be performed by adding three times.

By the above operation, the data sequence of 12 actual symbol periods output from the peak generator 16 is given to the peak detector 17. Of these twelve data strings, a triangular wave having a clear peak is detected only in the data string in which the delay amount N matches the actual symbol period of the transmission data string in the correlation coefficient calculation by Expression 2. The peak detector 17 extracts a data sequence having a triangular wave having a maximum peak from the 12 data sequences, detects a guard period, a symbol length, and a symbol delimiter position based on the waveform and the peak position. Controller 1
Give 5

The FFT controller 15 performs FFT based on the given guard period, symbol length and symbol delimiter.
The number of points of the FFT operation of the FT processor 7 and the timing of the real symbol part are generated.

The output 12 from the peak generator 16
Since each data sequence has a length of one real symbol, a peak may appear at the end of the data sequence. In such a case, peak detection may be performed as a cyclic data string by connecting the data strings in a ring shape. Further, the processing of the symbol break detection unit 101 in the present embodiment can be configured as a program processing using a digital signal processor (DSP) or the like.

Embodiment 3 The present embodiment relates to a means for detecting a symbol break.

FIG. 8 shows the inside of the symbol break detector 201 in the present embodiment.
And a peak detector 17. The operation of the area calculator 18 will be described below.

The twelve data strings output from the correlation sum adder 14 are input to the area calculator 18. Of these 12 data strings, S _C1 (i ′) whose data length is the minimum actual symbol period L ₁ is output to the peak detector 17 without any processing.

Of the output data of the correlation sum adder 14,
Correlation sum addition result S whose data length is the actual symbol period L ₂
If the trapezoidal wave shown a correlation in _C2 (i ') is detected, since the upper base of the trapezoidal wave is minimized guard period M _1, which the symbol breakpoint by integrating equal interval to the minimum guard period M ₁ A triangular wave having a peak at the corresponding position is generated. Accordingly, performs integration to the integration interval minimum guard period M ₁ while shifting one sample at a time the data for the data stream.

The output data of the correlation sum adder 14
Where the data length is the actual symbol period L _ThreeCorrelation sum addition
Result S_C3When a trapezoidal wave showing a correlation is detected in (i ')
In this case, the upper base of this trapezoidal wave is the minimum guard period M₁Three times
Therefore, this is defined as the minimum guard period M₁Interval equal to three times
Integrating with
A triangular wave having a peak is generated. Therefore, this data
For columns, shift data one sample at a time and minimize
Guard period M₁Performs integration with an interval of three times as large as
U.

The output data of the correlation sum adder 14
Where the data length is the actual symbol period L _FourCorrelation sum addition
Result S_C4When a trapezoidal wave showing a correlation is detected in (i ')
In this case, the upper base of this trapezoidal wave is the minimum guard period M₁7 times
Therefore, this is set to an interval equal to seven times the minimum guard period M1.
Integrating with
A triangular wave having a peak is generated. Therefore, this data
For columns, shift data one sample at a time and minimize
Guard period M₁Perform integration with a section 7 times as large as the integration section
U.

However, all of the above operations (1) to (5) are performed using a data string as a cyclic data string.

The twelve data strings output from the area calculator 18 are input to the peak detector 17. The peak detector 17 extracts a data sequence having a triangular wave having a maximum peak from the 12 data sequences, detects a guard period, a symbol length, and a symbol delimiter position based on the waveform and the peak position. Controller 15
Give to.

The FFT controller 15 calculates FFT based on the given guard period, symbol length and symbol delimiter.
The number of points of the FFT operation of the FT processor 7 and the timing of the real symbol part are generated.

It should be noted that 12 output from the peak generator 16
Since each data sequence has a length of one real symbol, a peak may appear at the end of the data sequence. In such a case, peak detection may be performed as a cyclic data string by connecting the data strings in a ring shape. Further, the processing of the symbol break detector in the present embodiment can be configured as a program processing using a digital signal processor (DSP) or the like.

Embodiment 4 The present embodiment relates to a means for detecting a symbol break.

FIG. 9 shows the inside of the symbol break detector 201 according to the present embodiment.
It consists of. In the second and third embodiments, the guard period, the symbol length, and the symbol delimiter are obtained by generating a triangular wave having a peak at the symbol delimiter. In the present embodiment, the width and height of the output waveform of the correlation sum adder are determined. The guard period, the symbol length, and the symbol delimiter are obtained based on this.

The 1 output from the correlation sum adder 14 in FIG.
The two data strings are input to the section width detector 19.
As shown in FIG. 10, the section width detector 19 obtains the width of the waveform based on the rise and fall of the waveform of the input data sequence, and detects the height of the waveform.
At this time, the level at which the height of the waveform is set (for example, 80% of the theoretical maximum value; this level may be obtained experimentally)
The above section is detected as the width of the waveform, and when the width of the detected waveform is close to the theoretical value of the width of the waveform indicating the correlation detected in the data string, the guard period is determined based on the theoretical waveform. , Valid symbol period and symbol break.

The guard period, symbol length and symbol delimiter obtained by the section width detector 19 by the above-described method are input to the FFT controller 15. Subsequent operations are the same as those in the above-described embodiments, and a description thereof will not be repeated.

The output 12 from the peak generator 16
Since each data sequence has a length of one real symbol, a peak may appear at the end of the data sequence. In such a case, peak detection may be performed as a cyclic data string by connecting the data strings in a ring shape. Further, the processing of the symbol break detection unit 101 in the present embodiment can be configured as a program processing using a digital signal processor (DSP) or the like.

[0078]

According to the configuration of the OFDM receiver according to the present invention, OFDM transmitted in a plurality of transmission modes is provided.
Data can be reliably demodulated.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an OFDM receiver according to Embodiment 1.

FIG. 2 is an example of a symbol configuration of OFDM transmission data according to the first embodiment.

FIG. 3 is an explanatory diagram showing a correlation in a guard area.

FIG. 4 is an explanatory diagram showing a relationship among symbol division, correlation coefficient, and correlation sum.

FIG. 5 is an explanatory diagram showing a method of adding a correlation sum.

FIG. 6 is a block diagram of a symbol break detection unit according to the second embodiment.

FIG. 7 is an explanatory diagram showing a peak generation method according to the second embodiment.

FIG. 8 is a block diagram of a symbol break detection unit according to the third embodiment.

FIG. 9 is a block diagram of a symbol break detection unit according to the fourth embodiment.

FIG. 10 is an explanatory diagram showing a section width detection method according to a fifth embodiment.

FIG. 11 is a block diagram showing a configuration of a conventional OFDM receiver.

FIG. 12 shows a symbol configuration in the OFDM system.

[Explanation of symbols]

1 antenna, 2 RF amplifier, 3 mixer,
4 IF amplifier, 5 quadrature demodulator, 6 A / D converter,
7 FFT processor, 8 error corrector, 9 digital data output terminal, 10 voltage controlled oscillator, 11 frequency shift detector, 12 correlation operator, 13 correlation sum operator, 14
Correlation sum adder, 15 FFT controller, 16 peak generator, 17 peak detector, 18 area calculator, 19 section width detector, 20 symbol break detector, 101 symbol break detector, 201 symbol break detector.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Taura 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Masayuki Ishida 2-3-2 Marunouchi, Chiyoda-ku, Tokyo 3 F term in Ryo Denki Co., Ltd. (reference) 5K022 DD00 DD13 DD17 DD19 DD42

Claims (5)

[Claims] An effective symbol period and a real symbol period comprising a guard period having the same signal as a signal in the latter half of the effective symbol period are data strings in the time domain, each of which is a constituent element. A receiver for receiving the data sequence having a different guard period according to a mode, a correlation operation means for calculating a correlation coefficient between the data sequence and a data sequence obtained by delaying the data sequence by an effective symbol period; and A correlation sum calculating means for obtaining a correlation sum of the correlation coefficients within a period equal to a minimum guard period in which the period is the minimum, and a correlation sum calculation means for calculating the correlation sum of the correlation coefficients in the continuous real symbol period by the correlation sum calculation means. A correlation sum addition unit for adding the correlation sum, and the guard period and a previous period based on an output of the correlation sum addition unit. Detecting means for detecting a break in the effective symbol period, the digital receiver characterized by comprising a demodulation means for demodulating the data sequence based on the separator which is obtained by the detection means. 2. An arithmetic unit according to claim 1, further comprising arithmetic means for delaying the output of the correlation sum addition means by a predetermined multiple of the minimum guard period and adding the delayed output to the output, wherein a peak of a waveform represented by the output of the arithmetic means has a peak. A digital receiver for detecting a break between a guard period and an effective symbol period based on the largest one. 3. The digital receiver according to claim 2, wherein the output of the calculating means is delayed by a predetermined multiple of the minimum guard period and added to the output. 4. An arithmetic unit for integrating the output of the correlation sum adding unit with a predetermined multiple of the minimum guard period as an integration interval, wherein a peak of a waveform represented by the output of the arithmetic unit is obtained. A digital receiver for detecting a break of a guard period and an effective symbol period based on a maximum one. 5. The apparatus according to claim 1, further comprising detecting means for detecting a height and a width of a waveform represented by an output of the correlation sum adding means, and dividing a guard period and an effective symbol period based on the output of said detecting means. A digital receiver characterized by detecting the following.