JP2007124416A - Ofdm demodulating device, ofdm demodulation program, and record medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve stability of a carrier frequency error correcting process as the whole OFDM demodulating device. <P>SOLUTION: The carrier frequency error is separately corrected by a narrow band carrier frequency error correcting part 5 and a wide band carrier frequency error correcting part 7. So, a narrow band carrier frequency error correction feedback loop 11 and a wide band carrier frequency error correction feedback loop 12 are independent from each other. Thus, the stability of carrier frequency error correcting process is improved as the whole of OFDM demodulating device 20. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an orthogonal frequency division multiplexing (hereinafter abbreviated as OFDM) demodulator capable of efficiently transmitting video signals and audio signals in a digital transmission scheme.

(OFDM broadcast)
In terrestrial digital broadcasting, a multicarrier OFDM modulation / demodulation method is known as a modulation method suitable for overcoming ghost interference (fading, multipath) by buildings. The OFDM modulation / demodulation method is a digital modulation / demodulation method in which a large number (about 256 to 1024) of sub-carriers are provided in one channel band and video signals and audio signals can be efficiently transmitted.

  The subcarrier information of the symbol m and the carrier number k can be described as a complex format IQ signal by the following equation (1).

  At this time, a baseband (BB) signal Z (m, n) obtained by OFDM-modulating all carriers by inverse fast Fourier transform (IFFT) can be described as the following equation (2).

  Here, N represents the number of all carriers to be multiplexed by IFFT processing.

  The frequency of each carrier is expressed by the following equation (3):

And the predetermined plane wave is expressed by the following equation (4):

And each carrier information is represented by the following equation (5):

Z (m, n) in equation (2) corresponds to superimposing and multiplexing each carrier information on the plane wave represented by equation (4) where the frequency of each carrier is equation (3). . In Equation (3), F _s is the IFFT sampling frequency.

Duration of the processing window of IFFT conversion, a valid symbol period _{t s.} The effective symbol period corresponds to N cycles of F _s clocks. The combined addition of all carriers digitally modulating the effective symbol period t _s as a basic unit, that OFDM transmission symbol.

As shown in FIG. 9, an actual transmission symbol is usually configured by adding a period tg called a guard interval (GI) 202a to an effective symbol period 201. Waveform of the GI period _t g (202a) it is adapted to a repeat of the rear 202b of the signal waveform of the effective symbol period _{t s.} The symbol period 203 of the transmission symbol is the sum of the effective symbol period 201 and the GI period 202a. For example, according to the broadcasting standard of Non-Patent Document 1, the effective symbol period length is defined as shown in the following table 1 by a parameter called MODE.

  Further, the GI period (unit: μs) is defined as shown in the following Table 2 by a parameter called GI period length (GI ratio) which is a ratio to each effective symbol period length.

When the guard interval ratio is g, GI period _{t g} is equivalent to _{N GI} period at Fs clock.

  A collection of several transmission symbols is called a transmission frame. This is a collection of about 100 information transmission symbols plus frame synchronization symbols and service identification symbols. For example, in Non-Patent Document 1, one frame is defined as 204 symbols.

  Further, according to Non-Patent Document 1, one transmission symbol that has been QPSK, 16QAM, or 64QAM modulated is arranged with carriers shown in the following table (3) per segment.

  In this table, SP means an SP (Scattered Pilot) signal. This SP signal is a pilot signal periodically inserted. For example, the SP signal is inserted once in 12 carriers in the carrier direction and once in 4 symbols in the symbol direction. TMCC means TMCC (Transmission and Multiplexing Configuration Control) signal. This TMCC signal is a signal for transmitting a frame synchronization signal and a transmission parameter. AC1 means an AC1 (Auxiliary Channel) signal. The AC1 signal is a signal for transmitting additional information. Unlike SP, TMCC and AC1 are arranged aperiodically in each carrier.

(Basic configuration of conventional OFDM demodulator)
A configuration example of a conventional OFDM demodulator is shown in Non-Patent Document 2, for example. Therefore, the OFDM demodulator disclosed in Non-Patent Document 2 will be described below.

  FIG. 10 is a block diagram showing a configuration of a conventional OFDM demodulator 100. As shown in FIG. 10, the OFDM demodulator 100 includes an antenna 101, a tuner 102, a band pass filter (BPF) 103, an A / D conversion circuit 104, a DC cancellation circuit 105, a digital orthogonal demodulation circuit 106, an FFT operation circuit 107, Frame extraction circuit 108, synchronization circuit 109, carrier demodulation circuit 110, frequency deinterleave circuit 111, time deinterleave circuit 112, demapping circuit 113, bit deinterleave circuit 114, depuncture circuit 115, Viterbi circuit 116, byte deinterleave circuit 117 A spread signal removal circuit 118, a transport stream generation circuit 119, an RS decoding circuit 120, a transmission control information decoding circuit 121, and a channel selection circuit 122.

  A broadcast wave of a digital broadcast broadcast from a broadcast station is received by the antenna 101 of the OFDM demodulator 100 and supplied to the tuner 102 as an RF signal. The tuner 102 includes a multiplier 102a and a local oscillator 102b, and frequency-converts the RF signal received through the antenna 101 into an IF signal. The tuner 102 supplies the IF signal subjected to frequency conversion to the BPF 103.

  The oscillation frequency of the reception carrier signal oscillated from the local oscillator 102 b is switched according to the channel selection signal supplied from the channel selection circuit 122. The IF signal output from the tuner 102 is filtered by the BPF 103 and then digitized by the A / D conversion circuit 104. The digitized IF signal has its DC component removed by the DC cancellation circuit 105 and is supplied to the digital quadrature demodulation circuit 106.

  The digital orthogonal demodulation circuit 106 orthogonally demodulates a 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 quadrature demodulation circuit 106 is supplied to the FFT operation circuit 107 and the synchronization circuit 109.

  The FFT operation circuit 107 performs an FFT operation on the baseband OFDM signal, and extracts and outputs a signal that is orthogonally modulated on each subcarrier. The FFT operation circuit 107 extracts a signal for an effective symbol length from one OFDM symbol, and performs an FFT operation on the extracted signal. That is, the FFT operation circuit 107 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 transmission symbol as long as the extracted signal points are continuous. That is, the start position of the extracted signal range is any position during the GI period. The signal modulated by each subcarrier extracted by the FFT operation circuit 107 is a complex signal composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The signal extracted by the FFT operation circuit 107 is supplied to the frame extraction circuit 108, the synchronization circuit 109, and the carrier demodulation circuit 110.

  The frame extraction circuit 108 extracts the boundary of the OFDM transmission frame based on the signal demodulated by the FFT operation circuit 107, and also includes pilot signals such as CP and SP, TMCC and TPC, etc. included in the OFDM transmission frame. The transmission control information is demodulated and supplied to the synchronization circuit 109 and the transmission control information decoding circuit 121.

  The synchronization circuit 109 includes a baseband OFDM signal, a signal modulated on each subcarrier after being demodulated by the FFT operation circuit 107, a pilot signal such as CP and SP detected by the frame extraction circuit 108, and a channel An OFDM symbol boundary is calculated using the channel selection signal supplied from the selection circuit 122, and the calculation start timing of the FFT calculation is set for the FFT circuit 107.

  The carrier demodulated circuit 110 is supplied with a signal demodulated from each subcarrier output from the FFT operation circuit 107. The carrier demodulation circuit 110 performs carrier demodulation on the signal. In the case of demodulating an ISDB-T standard OFDM signal, the carrier demodulation circuit 110 performs, for example, DQPSK differential demodulation or synchronous demodulation such as QPSK, 16QAM, and 64QAM.

  The carrier demodulated signal is deinterleaved in the frequency direction by the frequency deinterleave circuit 111. Subsequently, the time deinterleave circuit 112 performs deinterleave processing in the time direction and then supplies the demapper circuit 113 with it.

  The demapping circuit 113 performs data reassignment processing (demapping processing) on the carrier demodulated signal (complex signal). Thereby, the transmission data series is restored. For example, in the case of demodulating an ISDB-T standard OFDM signal, the demapping circuit 113 performs demapping processing corresponding to QPSK, 16QAM, or 64QAM.

  The transmission data series output from the demapping circuit 113 passes through the bit deinterleave circuit 114, the depuncture circuit 115, the Viterbi circuit 116, the byte deinterleave circuit 117, and the spread signal removal circuit 118. This enables deinterleaving processing corresponding to bit interleaving for error dispersion of multilevel symbols, depuncturing processing corresponding to puncturing processing for reducing transmission bits, and decoding of convolutionally encoded bit strings. Energy despreading processing corresponding to Viterbi decoding processing, deinterleaving processing in byte units, and energy diffusion processing is performed. Thereafter, the transmission data sequence is input to the transport stream generation circuit 119.

  For example, the transport stream generation circuit 119 inserts data defined by each broadcasting method such as a null packet at a predetermined position in the stream. In addition, the transport stream generation circuit 119 performs a so-called smoothing process in which the bit interval of the intermittently supplied stream is smoothed to obtain a temporally continuous stream. The transmission data sequence subjected to the smoothing process is supplied to the RS decoding circuit 120.

  The RS decoding circuit 120 performs a Reed-Solomon decoding process on the input transmission data sequence. Thereby, it outputs as a transport stream prescribed | regulated by MPEG-2 systems.

  The transmission control information decoding circuit 121 decodes transmission control information such as TMCC and TPC that is modulated at a predetermined position in the OFDM transmission frame. The decoded transmission control information is supplied to the carrier demodulation circuit 110, the time deinterleave circuit 112, the demapping circuit 113, the bit deinterleave circuit 114, and the transport stream generation circuit 119, and is used for demodulation and reproduction of each circuit. Used for control.

(Classification of carrier frequency error)
A true BB signal Z0 (m, n) at a symbol m and a sampling point n that does not have a digital carrier frequency error is expressed by the following equation (6).

Here, I ₀ is (m, n) is an in-phase component (I component: In-phase) of the BB signal Z ₀ (m, n). Q ₀ (m, n) is an orthogonal component (Q component: Quadrature-phase) of the BB signal ₀ (m, n).

  A carrier frequency error δf occurs in the DC component of the BB signal inside the OFDM demodulator. This is generally due to IF signal output specifications in the tuner, operating clock frequency error in the tuner, or Doppler effect when the receiver moves. The BB signal Z '(m, n) when an error occurs is expressed by the following equation (7) using the true BB signal Z0 (m, n).

Here, δf is a carrier frequency interval F _s / N unit. Hereinafter, in order to simplify the equation transformation, all carrier frequency errors are handled as units of the carrier interval Fs / N.

In the carrier frequency error δf, a component having an absolute value of ½ or less is described as a narrowband carrier frequency error δf _n (| δf _n | ≦ 1/2). Further, the remaining integer part, the broadband carrier frequency error _{δfw (δf w = 0, ±} 1, ± 2, ± 3 ...) to as. At this time, the following equation (8) is established.

(Conventional technology for carrier frequency error correction)
As a document disclosing a technique for correcting a carrier frequency error, there is Patent Document 1. Therefore, the OFDM demodulator of Patent Document 1 will be described below with reference to FIG.

  As shown in FIG. 11, first, the A / D converters 38 and 40 convert both IQ components of the BB signal into digital signals. A complex correlation is calculated in the correlators 53 and 54 in the symbol synchronization detection unit 50 from the I and Q components of the digitalized BB signal. Further, the carrier frequency error detection circuit 61 detects the narrow band carrier frequency error δfn.

  An FFT operation circuit (Fast Fourier Transform) 43 demodulates the orthogonal frequency division multiplex modulation signal. In addition, the carrier frequency error detection circuit 71 detects the broadband carrier frequency error δfw from the FFT operation circuit output signal.

  In the carrier frequency control circuit 62, the detected narrow band carrier frequency error δfn and the wide band carrier frequency error δfw are added. Thereby, the total carrier frequency error δf in total is calculated.

  The total carrier frequency error δf is changed to an analog signal by the D / A converter 75. Further, the analog local oscillation circuit 35 converts it into an analog sine wave. Further, analog multipliers 33 and 34 multiply the analog BB signal by an analog sine wave. As a result, the total carrier frequency error δf included in the analog BB signal is corrected. That is, the D / A converter 75, the analog local oscillation circuit 35, and the analog multipliers 33 and 34 constitute carrier frequency error correction means.

As described above, Patent Document 1 corrects the total carrier frequency error δf of the analog BB signal before being converted into a digital signal by the A / D converter by analog signal processing. On the other hand, in Patent Document 2, the total carrier frequency error δf of the digital BB signal after being converted into a digital signal by the A / D converter is corrected by digital signal processing.
"Transmission method for digital terrestrial television broadcasting ARIB STD-B31 1.5 edition", the radio industry, the first edition of May 31, 2001, revised version 1.5 on July 29, 2003 "Digital Terrestrial Audio Broadcasting Demodulator Standard (desired specification) ARIB STD-B30 version 1.2", Radio Industry, first edition of May 31, 2001, July 29, 2003 version 1.2 Revision VLSI algorithm for arithmetic operations Naofumi Takagi Corona Company 2005 Japanese Patent Laid-Open No. 7-143097 (published on June 2, 1995) JP-A-8-102771 (released on April 16, 1996)

  In the techniques of Patent Literature 1 and Patent Literature 2, the same carrier frequency error correction means corrects both the narrow-band carrier frequency error and the wide-band carrier frequency error. In such a configuration, a feedback loop with a narrow-band carrier frequency error and a feedback loop with a wide-band carrier frequency error are mixed. If the response time of each feedback loop is different, there is a high possibility that the entire carrier frequency error correction system in the entire OFDM demodulator becomes unstable.

  FFT is an algorithm that requires many addition / subtraction / division / division and complex multiplication by butterfly processing. For example, in order to demodulate the one segment area of mode 3 in the technique of Non-Patent Document 1, a 1024-point FFT operation circuit is required. Since this 1024-point FFT operation circuit needs to perform complex multiplication about 5000 times, the processing time is long. Depending on how the circuit is implemented, the processing time may require several symbol periods. In addition, the response time in the feedback loop of the wide band carrier frequency error is longer than the response time in the feedback loop of the narrow band carrier frequency error by the processing time required for the FFT operation circuit.

  For example, if the total carrier frequency error is δf = 3.5, the narrow band carrier frequency error and the wide band carrier frequency error have the following two combinations. That is, a combination of δfw = 3 and δfn = 0.5 and a combination of δfw = 4 and δfn = −0.5. Therefore, the narrow-band carrier frequency error detection unit is unstable, and if it fluctuates near δθ = π (equivalent to δθ = −π), it fluctuates near δfn = ± 0.5. Here, since the response time in the feedback loop for wideband carrier frequency error detection is long, the feedback loop for narrowband carrier frequency error and the feedback loop for wideband carrier frequency error do not work together. Therefore, there arises a problem that the carrier frequency error cannot be followed.

  When the carrier frequency error is corrected by the mixer, it is easy to correct the narrow band carrier frequency error δfn by generating a low-frequency complex plane wave. However, in order to correct the broadband carrier frequency error δfw, it becomes necessary to generate a high-frequency complex plane wave. Therefore, both the analog signal processing and the digital signal processing increase the circuit scale in order to ensure the calculation accuracy. This causes a problem of increasing power consumption.

  The case where the narrow band carrier frequency error correction system corresponds to the feedback loop has been described above, but the same problem occurs even in the case of the feed forward loop.

  An OFDM demodulator according to the present invention has been made to solve the above-described problems, and an object thereof is to provide an OFDM demodulator with improved carrier frequency error correction processing.

In order to solve the above problems, an OFDM demodulator according to the present invention provides:
Orthogonal demodulation means for obtaining a first baseband signal from an orthogonal modulation wave of an orthogonal frequency division multiplex modulation signal including a transmission symbol having an effective symbol and a guard interval obtained by copying the same content as a part of the effective symbol When,
Narrowband carrier frequency error correction means for obtaining a second baseband signal by correcting a narrowband carrier frequency error included in the first baseband signal;
Delay means for delaying the second baseband signal by an effective symbol period to obtain a third baseband signal;
Correlation calculating means for obtaining a complex correlation between the second baseband signal and the third baseband signal;
Symbol synchronization means for obtaining a symbol synchronization signal for extracting the effective symbol from the second baseband signal based on the amplitude of the complex correlation;
Narrowband carrier frequency error detection means for detecting the narrowband carrier frequency error included in the first baseband signal based on the phase of the complex correlation;
Broadband carrier frequency error correction means for obtaining a fourth baseband signal by correcting a broadband carrier frequency error included in the second baseband signal;
Guard interval removing means for outputting a fifth baseband signal by removing the guard interval from the fourth baseband signal according to the symbol synchronization signal;
Orthogonal frequency division multiplexing demodulation means for obtaining a demodulated signal by demodulating the fifth baseband signal that has been orthogonal frequency division multiplexed modulated in the effective symbol;
Broadband carrier frequency error detection means for detecting the broadband carrier frequency error from the demodulated signal;
An effective carrier extracting means for extracting effective carriers from the demodulated signal is provided.

  According to the above configuration, the narrowband carrier frequency error correction means, together with the delay means, the correlation calculation means, the symbol synchronization means, and the narrowband carrier frequency error detection means, the first band for correcting the narrowband carrier frequency error. A feedback loop is formed. On the other hand, the wideband carrier frequency error correction means forms a second feedback loop for correcting the wideband carrier frequency error together with the guard interval removal means, the orthogonal frequency division multiplexing demodulation means, and the wideband carrier frequency error detection means. Yes.

  Thus, in the OFDM demodulator, the narrow band carrier frequency error correction means and the wide band carrier frequency error correction means are separated. Thus, the narrow band carrier frequency error correction feedback loop and the wide band carrier frequency error correction feedback loop function independently. That is, for example, even if the time required for one loop process is longer than the time required for the other loop process, the other loop process is not affected. Therefore, there is an effect of improving the stability of the carrier frequency error correction process in the entire OFDM demodulator.

In order to solve the above problems, an OFDM demodulator according to the present invention provides:
Orthogonal demodulation means for obtaining a first baseband signal from an orthogonal modulation wave of an orthogonal frequency division multiplex modulation signal including a transmission symbol having an effective symbol and a guard interval obtained by copying the same content as a part of the effective symbol When,
Narrowband carrier frequency error correction means for obtaining a second baseband signal by correcting a narrowband carrier frequency error included in the first baseband signal;
Delay means for delaying the first baseband signal by an effective symbol period to obtain a third baseband signal;
Correlation calculating means for obtaining a complex correlation between the first baseband signal and the third baseband signal;
Symbol synchronization means for obtaining a symbol synchronization signal for extracting the effective symbol from the second baseband signal based on the amplitude of the complex correlation;
Narrowband carrier frequency error detection means for detecting the narrowband carrier frequency error included in the first baseband signal based on the phase of the complex correlation;
Broadband carrier frequency error correction means for obtaining a fourth baseband signal by correcting a broadband carrier frequency error included in the second baseband signal;
Guard interval removing means for outputting a fifth baseband signal by removing the guard interval from the fourth baseband signal according to the symbol synchronization signal;
Orthogonal frequency division multiplexing demodulation means for obtaining a demodulated signal by demodulating the fifth baseband signal that has been orthogonal frequency division multiplexed modulated in the effective symbol;
Broadband carrier frequency error detection means for detecting the broadband carrier frequency error from the demodulated signal;
An effective carrier extracting means for extracting effective carriers from the demodulated signal is provided.

  According to the above configuration, the narrowband carrier frequency error correction means, together with the delay means, the correlation calculation means, the symbol synchronization means, and the narrowband carrier frequency error detection means, is a feedforward A loop is formed. On the other hand, the wideband carrier frequency error correction means forms a feedback loop for correcting the wideband carrier frequency error together with the guard interval removal means, the orthogonal frequency division multiplexing demodulation means, and the wideband carrier frequency error detection means.

  Thus, in the OFDM demodulator, the narrow band carrier frequency error correction means and the wide band carrier frequency error correction means are separated. Thus, the narrowband carrier frequency error correction feedforward loop and the wideband carrier frequency error correction feedback loop function independently. That is, for example, even if the time required for one loop process is longer than the time required for the other loop process, the other loop process is not affected. Therefore, there is an effect of improving the stability of the carrier frequency error correction process in the entire OFDM demodulator.

In the OFDM demodulator according to the present invention,
The broadband carrier frequency error correction means includes:
It is a phase rotation circuit whose unit is a phase rotation amount obtained by multiplying 2π by the guard interval ratio,
The phase rotation circuit preferably changes the phase rotation amount during the guard interval of each symbol.

  According to the above configuration, the wideband carrier frequency error correction means need only perform phase rotation of a specific phase rotation amount. Therefore, the circuit scale can be reduced and the power consumption can be reduced as compared with a phase rotation circuit that performs phase rotation of an arbitrary amount of phase rotation. Furthermore, since it is only necessary to perform phase rotation of a specific phase rotation amount, it is possible to improve calculation accuracy compared to a phase rotation circuit that performs phase rotation of an arbitrary phase rotation amount.

In the OFDM demodulator according to the present invention,
The phase rotation circuit preferably further performs a phase rotation process in which the phase rotation amount is smaller than π / 4.

  According to the above configuration, the broadband carrier frequency error correction means utilizes the complex plane wave formula. Therefore, since the amount of phase rotation can be further reduced, the circuit scale can be further reduced and the power consumption can be further reduced.

In the OFDM demodulator according to the present invention,
The narrow band carrier frequency error detecting means includes:
It is preferable to obtain a specific narrowband carrier frequency error as the narrowband carrier frequency error when the absolute value of the phase of the complex correlation is π.

  Mathematically, δθ = π and δθ = −π are equivalent. However, the narrowband carrier frequency error detection means has an uncertainty that it determines that the narrowband carrier frequency error is δfn = 0.5 or δfn = −0.5, respectively. However, in this configuration, when the detected phase of the complex correlation is δθ = π, the narrowband carrier frequency error detection means outputs, for example, δfn = 0.5 as a specific narrowband carrier frequency error error. This eliminates the uncertainty. Therefore, the OFDM demodulator has an effect that the narrow band carrier frequency error correction process and the wide band carrier frequency error correction process can be performed stably. The specific narrow band carrier frequency error δfn may be −0.5.

In the OFDM demodulator according to the present invention,
It further comprises start means for starting or stopping each means described above,
The starting means is
First, after activating the narrowband carrier frequency error detecting means, narrowband carrier frequency error correcting means, and wideband carrier frequency error detecting means, and the wideband carrier frequency error detecting means once detecting the wideband carrier frequency error, Stop the broadband carrier frequency error detection means,
After the start-up means stops the wideband carrier frequency error detection means, the narrowband carrier frequency error correction means corrects the narrowband carrier frequency error, and the wideband carrier frequency error correction means detects the wideband carrier frequency error. It is preferable to correct the frequency error.

  According to the above configuration, the activation unit stops the wideband carrier frequency error detection unit after the wideband carrier frequency error is detected. Therefore, the time during which both the loop processing for correcting the narrow band carrier frequency error and the loop processing for correcting the wide band carrier frequency error are simultaneously activated can be further shortened. As a result, the probability that one loop process affects the other loop process is further reduced, so that the frequency error correction process in the entire OFDM demodulator can be made more stable.

In the OFDM demodulator according to the present invention,
The starting means is
First, the narrow-band carrier frequency error detecting means and the narrow-band carrier frequency error correcting means are activated, and then the wide-band carrier frequency error detecting means is activated when the detected narrow-band carrier frequency error satisfies a specific condition. It is preferable.

  According to the above configuration, the starting means is when the narrowband carrier frequency error detected by the narrowband carrier frequency error detecting means satisfies a specific condition, for example, when the error value is 1/100 or less of the carrier interval. The broadband carrier frequency error detecting means is activated. As a result, the wideband carrier frequency error detecting means detects the wideband carrier frequency error from the baseband signal in which the narrowband carrier frequency error correction is completely corrected. Therefore, there is an effect that the frequency error correction processing of the entire OFDM demodulator can be made more stable.

  The OFDM demodulator may be realized by a computer. In this case, an OFDM demodulation program that realizes the OFDM demodulator in the computer by operating the computer as each of the above means, and a computer-readable recording medium that records the OFDM demodulation program also fall within the scope of the present invention.

  As described above, in the OFDM demodulator according to the present invention, the narrowband carrier frequency error correction processing loop and the wideband carrier frequency error correction processing loop are independent. There is an effect of improving the stability of the correction process.

  Embodiments of the present invention will be described below.

(Basic principle: Narrowband carrier frequency error detection)
The complex correlation c (m, n) between the complex BB signal Z (m, n) at the symbol m sampling point n and the complex BB signal Z (m, n−N) at the symbol m sampling point (n−N) The following equation is satisfied.

  If the phase error per effective symbol period length (N sampling points) is δθ due to the carrier frequency error δf, the following equation is established.

  The relationship between the complex BB signal Z (m, n) and Z (m, n−N) at this time satisfies the following equation.

  Therefore, the following equation is established.

  Here, r (m, n) is the amplitude of the complex BB signal Z (m, n). If the phase of the complex correlation is detected, the phase rotation δθ generated in the symbol period length by the carrier frequency error δf, that is, the carrier frequency error δf can be detected. However, since δfw is an integer (0, ± 1, ± 2,...), The following equation is established.

  Therefore, when the formula (10) is substituted into the formula (12), the following formula is established.

  Therefore, in the carrier frequency error detection using the complex correlation, only the component of the narrow band carrier frequency error δfn can be detected.

(Basic principle: Broadband carrier frequency error detection)
Next, the basic principle of broadband carrier frequency error detection will be described.

  When the amplitude of the output signal or the square of the amplitude is calculated from the output of the FFT operation circuit, as shown in Table 3 above, the signal intensity differs in data, SP, TMCC, and AC1. Further, TMCC and AC1 are non-periodically carrier-arranged. Accordingly, the carrier arrangement of SP, TMCC, and AC1 can be detected. The difference between the detected carrier arrangement and the carrier arrangement of SP, TMCC, and AC1 when the DC component is frequency 0 corresponds to the broadband carrier frequency error δfw.

(Basic principle: carrier frequency error correction)
Next, the basic principle of carrier frequency error correction will be described. If the narrow-band carrier frequency error δfn can be detected by the narrow-band carrier frequency error detector, and the wide-band carrier frequency error δfw can be detected by the wide-band carrier frequency error detector, the entire carrier frequency error δf is also detected in the entire OFDM demodulator. It will be. Here, a complex plane wave having a frequency of −δf is expressed by the following equation (15).

  If the total carrier frequency error δf can be detected, the carrier frequency error can be obtained by multiplying the complex plane wave shown in Equation (15) by the BB signal Z ′ (m, n) in which the carrier frequency error shown in Equation (8) is δf. Can be corrected. Therefore, when the corrected BB signal is Z ″ (m, n), the following equation is established.

From equation (16), the true BB signal Z ₀ (m, n) can be extracted.

Embodiment 1
A first embodiment of the present invention will be described below with reference to FIG. One configuration example of the OFDM demodulator 20 is shown in FIG. FIG. 1 is a block diagram illustrating a configuration of a wireless communication device. As shown in this figure, an antenna 1, a tuner 2, an A / D converter 3, a digital quadrature detection unit 4 (orthogonal demodulation means), a narrow band carrier frequency error correction unit 5 (narrow band carrier frequency error correction means), a narrow band Band carrier frequency error detection unit 6 (narrow band carrier frequency error detection unit), wide band carrier frequency error correction unit 7 (wide band carrier frequency error correction unit), FFT operation circuit 8 (orthogonal frequency division multiplex demodulation unit), wide band carrier frequency error A detection unit 9 (broadband carrier frequency error detection means) and a waveform equalization unit 10 are provided.

  In this embodiment, the narrowband carrier frequency error correction unit 5 and the narrowband carrier frequency error detection unit 6 form a narrowband carrier frequency error correction feedback loop 11. This narrow band carrier frequency error correction feedback loop 11 is a feedback system. Further, the wide band carrier frequency error correction unit 7, the FFT operation circuit 8, and the narrow band carrier frequency error detection unit 6 form a wide band carrier frequency error correction feedback loop 12. The broadband carrier frequency error correction feedback loop 12 is also a feedback system. These points will be described later.

  In FIG. 1, an antenna 1 receives an OFDM signal passing through a communication path and supplies it to a tuner 2 as an RF signal. The RF signal input to the tuner 2 is frequency converted to an IF signal and supplied to the A / D converter 3. The IF signal input by the A / D converter 3 is digitized and output to the quadrature detection unit 4. The quadrature detection unit 4 converts the frequency of the input IF signal into a BB signal Z0 (m, n).

(Narrowband carrier frequency error correction unit 5)
Next, the narrowband carrier frequency error correction unit 5 corrects the narrowband carrier frequency error of the BB signal Z1 (m, n), and generates and outputs the BB signal Z2 (m, n). Thereby, the following expression (17) is established.

  As shown in Expression (17), a broadband carrier frequency error remains in the BB signal Z2 (m, n).

(Narrowband carrier frequency error detector 6)
The narrowband carrier frequency error detection unit 6 feeds back a predetermined control signal to the narrowband carrier frequency error correction unit 5. This control signal is a signal for detecting and correcting a narrow band carrier frequency error of the BB signal Z2 (m, n) using the method described above. The narrow-band carrier frequency error correction unit 5 is configured by, for example, a complex BB signal phase rotation circuit. At this time, the control signal is a phase rotation amount to be corrected. Further, the narrow band carrier frequency error correction unit 5 is constituted by, for example, a complex multiplication circuit. At this time, the control signal is a complex plane wave that vibrates at a frequency obtained by inverting the sign of the detected narrowband carrier frequency δfn, or a phase rotation factor that can be expressed by the following equation (18).

(Broadband carrier frequency error correction unit 7)
The broadband carrier frequency error correction unit 7 corrects the broadband carrier frequency error of the BB signal Z 2 (m, n), thereby generating the BB signal Z 3 (m, n) and outputs it to the FFT operation circuit 8. At this time, the following equation (19) is established.

  Thereby, the OFDM demodulator 20 can extract the true BB signal Z0 (m, n) in which the carrier frequency error is corrected.

(FFT operation circuit 8)
The FFT operation circuit 8 demodulates the OFDM modulation of the BB signal Z3 (m, n) and outputs X3 (m, k) corresponding to the carrier information.

(Broadband carrier frequency error detector 9)
The broadband carrier frequency error detection unit 9 feeds back a predetermined control signal to the broadband carrier frequency error correction unit 7. This control signal is a signal for detecting and correcting the broadband carrier frequency error of the carrier information signal X3 (m, k) by using the method described in the above (basic principle: broadband carrier frequency error detection). .

  The broadband carrier frequency error correction unit 7 is constituted by, for example, a complex BB signal phase rotation circuit. At this time, the control signal is a phase rotation amount to be corrected. The wideband carrier frequency error correction unit 7 is configured by, for example, a complex multiplication circuit. At this time, the control signal is a complex plane wave that vibrates at a frequency obtained by inverting the sign of the detected narrowband carrier frequency δfw, or a phase rotation factor represented by Expression (18).

(Waveform equalization unit 10)
The waveform equalization unit 10 outputs a carrier information signal X4 (m, k) from which the influence of fading or the like due to the communication path is removed with reference to the SP carrier or the like. The OFDM demodulator 20 can output a TSP signal by performing processing after the interleaving with the above-described frequency using the signal X4 (m, k).

(Function and effect)
In the OFDM demodulator 20 having the above configuration, as shown in FIG. 1, a narrowband frequency error correction feedback loop 11 and a wideband frequency error correction feedback loop 12 are configured independently. Therefore, even if the response time of the narrowband frequency error correction feedback loop 11 and the response time of the wideband frequency error correction feedback loop 12 are different, each feedback loop operates independently and stably. Thereby, the correction of the total carrier frequency error δf can be stably performed in the entire OFDM demodulator 20.

[Embodiment 2]
A second embodiment according to the present invention will be described below with reference to FIG.

  In the OFDM demodulator 20 shown in FIG. 2, the narrowband carrier frequency error detection unit 6 and the wideband carrier frequency error correction unit 7 form a feedforward loop 13. Except for this point, the configuration is basically the same as that shown in FIG.

  As described above, in the narrowband carrier frequency error correction feedback loop 11 shown in FIG. 1, the narrowband carrier frequency error is detected from the BB signal Z2 (m, n) output from the narrowband carrier frequency error correction unit 5. . Thereby, the BB signal Z1 (m, n) is corrected.

  On the other hand, in the narrowband carrier frequency error correction feedforward loop 13 shown in FIG. 2, the narrowband carrier frequency error correction unit 6 determines the narrowband carrier frequency error from the output BB signal Z1 (m, n) of the quadrature detection unit 4. Is detected. Thereby, the narrow band carrier frequency error detection unit 6 corrects the BB signal Z1 (m, n). Even in such a feed-forward loop, a narrow band carrier frequency error can be corrected. The processing after the BB signal is the same as that in the first embodiment.

  Also in the OFDM demodulator 20 of the present embodiment, as in the first embodiment, the narrowband frequency error correction feedforward loop 13 and the wideband frequency error correction feedback loop 12 are configured independently. . Therefore, even if the response time of the narrowband frequency error correction feedforward loop 13 and the response time of the wideband frequency error correction feedback loop 12 are different, each feedback loop operates independently and stably. Thereby, the correction of the total carrier frequency error δf can be stably performed in the OFDM demodulator 20 as a whole.

[Embodiment 3]
This embodiment according to the present invention will be described below.

  As described above, the OFDM demodulator 20 of this embodiment completely removes the phase rotation of the BB signal Z1 (m, n) due to the narrowband carrier frequency error δfn, as in the first embodiment. However, the phase rotation due to the broadband carrier frequency error δfw remaining in the BB No. Z2 (m, n) is not completely removed as in the first embodiment.

As a phase reference in the following description, it is assumed that the phase rotation due to each carrier frequency error at symbol m = 0 sampling n = 0 is zero. That is, Z ′ (0,0) = Z ₀ (0,0) is established.

(First example of correcting only narrowband carrier frequency error)
In the following, an example will be described in which a transmission symbol has no GI period and the OFDM modulated wave received by the OFDM demodulator 20 is composed of only an effective symbol period.

  As described above, the narrowband carrier frequency error correction unit 5 corrects only the narrowband carrier frequency error of the BB signal Z1 (m, n). The output signal BB signal Z2 (m, n) of the narrowband carrier frequency error correction unit 5 at this time satisfies the equation (17).

  An example of phase rotation caused by the remaining broadband carrier frequency error δfw is shown in FIG. FIG. 3 is a diagram illustrating an example of phase rotation due to a carrier frequency error in an OFDM wave in which a GI period is not inserted. In this figure, the solid line 211 indicates the phase rotation before the narrowband carrier frequency error correction. On the other hand, the solid line 212 shows the phase rotation after the narrowband carrier frequency error correction.

  However, in the solid line 212 in FIG. 3, the phase rotation amount at the head of each symbol is an integer multiple of 2π. That is, the phase rotation factor at the beginning of the symbol always satisfies the following equation (20).

  Therefore, the OFDM demodulator 20 can correctly perform OFDM demodulation. Actually, when the broadband carrier frequency error correction unit 7 does not perform any processing and inputs the BB signal Z2 (m, n) to the FFT operation circuit 8 as it is, the following equation (21) is established.

Here, X ₀ (m, k) is each carrier information of the true BB signal Z 0 (m, n). At this time, the carrier arrangement is shifted by the broadband carrier frequency error δfw. However, the original carrier information X0 (m, k) can be extracted. That is, it is not necessary to correct the total carrier frequency error as indicated by the solid line 213 in FIG. 3, and it is only necessary to correct the narrow band carrier frequency error as indicated by the solid line 212. That is, the original carrier information can be extracted by shifting the carrier number for extracting information from the output of the FFT operation circuit 8 by the wide band carrier frequency error δfw.

(Second example of correcting only narrow-band carrier frequency error)
When a GI period is inserted into a transmission symbol, phase rotation occurs even during the GI period due to the narrowband carrier frequency error δfn. The phase rotation due to the narrow band carrier frequency error of the BB signal Z2 (m, n) after the narrow band carrier frequency error correction satisfies Expression (22) instead of Expression (17).

  Further, in the equation (22), the following equation (23) is established.

  The left side in this equation represents the amount of phase rotation during the GI period (corresponding to the solid line 217 in FIG. 4).

The phase rotation in this case is shown in FIG. FIG. 4 is a diagram illustrating an example of phase rotation due to a carrier frequency error in an OFDM wave into which a GI period is inserted. The phase rotation indicated by the solid line 214 in this figure is changed to the phase rotation indicated by the solid line 215 by correcting only the narrow-band carrier frequency error. Unlike the case where there is no GI period, the phase rotation amount due to the broadband carrier frequency error at the head of each effective symbol is an integral multiple of 2πθ _GI . In this case, if the broadband carrier frequency error correction unit 7 does not perform any processing and outputs the BB signal to the FFT operation circuit 8 as it is, the FFT operation circuit 8 cannot correctly perform OFDM demodulation.

  If the BB signal Z2 (m, n) is input to the FFT operation circuit, the following equation is established.

  From this equation, it can be seen that not only the carrier number shifts, but also the phase rotates for each symbol.

  By the way, the difference between (first example in which only narrowband carrier frequency error is corrected) and (second example in which only narrowband carrier frequency error is corrected) is the presence or absence of a GI period in a transmission symbol. That is, it is different whether or not the phase rotation factor represented by the equation (20) is further added to the BB signal Z2 (m, n). Therefore, if the phase twiddle factor in equation (20) is removed from the BB signal Z2 (m, n) shown in equation (24), the method described in (first example for correcting only narrowband carrier frequency error) is used. It can be applied as it is.

Therefore, the OFDM demodulator 20 may have the following configuration. That is, the broadband carrier frequency error correction unit 7 in the broadband carrier frequency error correction feedback loop 11 rotates the phase of the BB signal Z2 (m, n) by the phase rotation amount φ (m). The phase rotation amount φ (m) of the symbol m is φ (m) = − mθ _GI . Further, the phase rotation amount φ (m) is changed during the GI period, and is always a constant value during the effective symbol period. The timing for changing the phase rotation amount may be anywhere as long as it is during the GI period.

  The phase rotation due to the broadband carrier frequency error of the BB signal Z2 (m, n) shown by the solid line 218 in FIG. 5 becomes as shown by the solid line 219 in FIG. 5 by correcting the phase rotation amount φ (m). In this solid line 219, the phase rotation amount of the BB signal Z3 (m, n) at the head of each effective symbol is an integral multiple of 2π.

  In addition, the BB signal Z3 (m, n) during the effective symbol period of each symbol completely matches the equation (17). However, during the GI period, there is a change in the amount of phase rotation, which is different from Equation (17). Note that this is not a problem because the FFT operation circuit 8 processes only the BB signal Z3 (m, n) in the effective symbol period.

  Accordingly, the FFT operation circuit 8 uses the BB signal Z3 (m, n) to convert the original carrier information X0 (m, k) from the BB signal Z3 (m, n) by the method described in (First example of correcting only the narrowband carrier frequency error). Can be extracted. In this way, the OFDM demodulator 20 corrects only the narrow-band carrier frequency error, and even if the wide-band carrier frequency error cannot be removed, the phase rotation factor whose angle is expressed by Equation (23) may be removed. Thus, the original carrier information can be extracted by shifting the carrier number for extracting information from the output of the FFT operation circuit 8 by the wide band carrier frequency error δfw.

  The broadband carrier frequency error correction unit 7 only needs to perform phase rotation in units of the phase rotation amount expressed by the following equation (25).

  For example, when the minimum value of the GI ratio g defined by a standard such as Non-Patent Document 1 is g = 1/16, the wideband carrier frequency error correction unit 7 uses the following equation (26 The phase rotation process satisfying the above may be performed.

  In this way, the broadband carrier frequency error correction unit 7 needs to perform only a specific phase rotation. Therefore, the circuit scale can be reduced as compared with the case of configuring a rotation circuit having an arbitrary phase.

  For example, Non-Patent Document 3 discloses a CORDIC (Coordinating Rotation Digital Computer) method as a method of performing arbitrary phase rotation. In this method, phase rotation is approximately performed by an arbitrary θ of the complex BB signal Z = I + jQ. In order to ensure 12-bit calculation accuracy by the CORDIC method, a full adder circuit for 12 bits is required. Further, in order to perform real-time processing on the input BB signal, the CORDIC circuit is configured by a circuit whose internal operation clock frequency is 12 times or more of the input signal rate or a circuit that performs 12-stage pipeline processing. There is a need. In particular, in order to perform 12-stage pipeline processing, at least 3 × 12 × 12≈430 flip-flops and 12 × 3 full adders are required. Thus, the arbitrary rotation circuit using the CORDIC circuit has a problem that the circuit scale becomes large.

  On the other hand, when only a specific angle θ is rotated in phase, a circuit that performs the arithmetic processing shown in the following equation (27) may be mounted.

  For example, when θ = π / 6, the following equation (28) is established.

  The 1/2 multiplication can be implemented with a 1-bit shift. On the other hand, the multiplication of √3 / 2 is an irrational number and is difficult to handle, but if approximated as in the following equation (29), a 12-bit operation is performed with only 9 bit shifters and 8 adders. Accuracy can be secured.

  Further, if the bit width of Expression (29) is increased, the calculation accuracy can be further improved. With respect to the phase rotation of Expression (26) other than θ = π / 6, phase rotators with other phase rotation amounts can be configured by the same method.

  As described above, the broadband carrier frequency error correction unit 7 can be configured by the phase rotators 311a to 311o and the selector 312 as shown in FIG. Although the circuit of FIG. 6 can perform real-time processing, it can operate with significantly lower power consumption than the CORDIC circuit. Therefore, the power consumption of the OFDM demodulator 20 can be greatly reduced.

[Embodiment 4]
A fourth embodiment according to the present invention will be described below.

  The wideband carrier frequency error correction unit 7 described in the third embodiment can be configured with a smaller circuit as in this embodiment. For example, in the phase rotation of the equation (26) when the GI ratio is g = 1/16, when n = 5, the following equation (30) is established.

  Therefore, if θ = π / 8 rotation is performed, then the I component and Q component are exchanged, and the sign of the Q component is reversed, the processing of θ = 5π / 8 rotation as a whole becomes possible.

  Generalizing this specific example, the complex plane wave exp (jθ) satisfies the following expression (31).

  Therefore, the wideband carrier frequency error correction unit 7 can be configured by a phase rotator that satisfies the phase rotation amount of 0 ≦ θ ≦ π / 4, not an arbitrary phase rotator of 0 ≦ θ ≦ 2π. For example, FIG. 7 shows the broadband carrier frequency error correction unit 7 when the GI ratio is g = 1/16. FIG. 7 is a block diagram showing the broadband carrier frequency error correction unit 7 when the GI ratio is g = 1/16.

  The broadband carrier frequency error correction unit 7 shown in FIG. 7 exchanges the phase rotators 311a to 311b, the means 313 for exchanging the I component and the Q component, the means 314 for exchanging the sign of the I component, and the sign of the Q component. Means 315 and a selector 312. With this configuration, the broadband carrier frequency error correction unit 7 can perform phase rotation in which the amount of phase rotation satisfies Equation (26).

  The basic functions of the configuration of the broadband carrier frequency error correction unit 7 shown in FIG. 7 and the configuration of the broadband carrier frequency error correction unit 7 shown in FIG. 6 are the same. However, since the configuration shown in FIG. 7 includes significantly fewer phase rotators than the configuration of FIG. 6, the circuit scale is reduced and the power consumption can be further reduced.

[Embodiment 5]
As described above, the narrowband carrier frequency error can be detected from the phase of the complex correlation shown in Equation (9). By the way, for example, when the value of c (m, n) satisfies C (m, n) = − 1, it can be said that the phase of this complex correlation is φ = + π or φ = −π. Since it is an equivalent angle when considering the complex plane, there is no problem mathematically.

  However, since the narrow band carrier frequency error is detected from the equation (10), δfn = + 0.5 when φ = + π, and δfn = −0.5 when φ = −π. That is, there is a big problem that the detected carrier frequency error is different by one carrier.

  Broadband carrier frequency error correction is affected depending on which OFDM demodulator 20 employs. As described above, generally, the broadband carrier frequency error correction feedback loop includes an FFT operation circuit. This results in a longer response time than the narrow band carrier frequency error correction feedback loop. Therefore, the narrow band carrier frequency error detection unit 6 has a problem with such uncertainty of frequency error detection.

  Therefore, when the absolute value of the phase of the complex correlation is π, the narrowband carrier frequency error detection unit 6 has either δfn = + 0.5 or δfn = −0.5 as the narrowband carrier frequency error δfn. It is preferable to output one of them. This eliminates the uncertainty of the narrow band carrier frequency error. That is, the broadband carrier frequency error correction feedback loop functions stably.

[Embodiment 6]
In the configuration shown in FIG. 1, the OFDM demodulator 20 further includes an activation unit (not shown) for activating or deactivating the above-described members. Here, in the OFDM demodulator 20 of the present embodiment, the starting unit is first the tuner 2, the A / D converter 3, the quadrature detection unit 4, the narrow band carrier frequency error correction unit 5, and the narrow band carrier frequency error detection unit. 6. The broadband carrier frequency error correction unit 7, the FFT operation circuit 8, and the broadband carrier frequency error detection unit 9 are activated. Next, once the broadband carrier frequency error detection unit 9 detects the broadband carrier frequency error δfw, the broadband carrier frequency error detection unit 9 outputs the broadband carrier frequency error δfw to the broadband carrier frequency error correction unit 7. As a result, the activation unit stops the broadband carrier frequency error detection unit 9. Thereafter, the broadband carrier frequency error correction unit 7 always corrects the detected broadband carrier frequency error δfw.

  The broadband carrier frequency error correction unit 7 corrects errors, but the broadband carrier frequency error detection unit 9 does not detect errors. Thereby, the broadband carrier frequency error correction does not form a feedback loop. That is, in the narrowband carrier frequency error correction control and the wideband carrier frequency error correction control, both feedback loops are effective only when the wideband carrier frequency error detection unit 9 is activated. As a result, the time during which both of the two different feedback loops are activated is shortened, so that the carrier frequency error correction process in the entire OFDM demodulator can be performed more stably.

  By the way, in the OFDM demodulator 20, when the carrier frequency error fluctuates after stopping the wide band carrier frequency error detection unit 9, the narrow band carrier frequency error correction feedback loop 11 tracks the error. If the fluctuation of the carrier frequency error is within half of the carrier interval, it can be followed by the narrowband carrier frequency error correction feedback loop 11. Therefore, the carrier frequency error correction process can be stably performed in the entire OFDM demodulator 20.

  Furthermore, even if the fluctuation of the carrier frequency error is larger than half of the carrier interval, the narrow band carrier frequency error correction feedback loop 11 can sometimes follow. Therefore, FIG. 8 shows an example of time variation of the carrier frequency error δf. FIG. 8 is a diagram illustrating an example of the variation of the carrier frequency error.

  As indicated by a solid line 350 in FIG. 8, the change amount of the carrier frequency error exceeds half of the carrier interval in a long time. Here, the case where the amount of change per symbol period length is half or less of the carrier interval will be described below. At this time, the fluctuation of the carrier frequency error can be followed by the narrow band carrier frequency error correction feedback loop 11.

  As described above, a narrowband carrier frequency error whose absolute value is within half the carrier interval can be detected from the phase of the complex correlation. The OFDM demodulator 20 detects the complex correlation every symbol. Therefore, if the amount of change in the carrier frequency error per symbol period length is within half of the carrier interval, the fluctuation amount for each symbol can be detected correctly. Further, the narrowband carrier frequency error correction feedback loop 11 detects the narrowband carrier frequency error δfn from the BB signal Z2 (m, n) after the narrowband carrier frequency error correction. Therefore, the narrowband carrier frequency error detection unit 6 or the narrowband carrier frequency error correction unit 5 includes an integration circuit that integrates the detected narrowband carrier frequency error.

  Even if the amount of change in the carrier frequency error exceeds half of the carrier interval over a long period of time, if the amount of change is correctly detected in each symbol and the detected value is integrated, the narrowband carrier frequency error correction feedback loop 11 Can follow this change. In other words, it is possible to follow the fluctuation of the carrier frequency error closed by the solid line 350 in FIG. On the other hand, as shown by the solid line 351 in FIG. 8, when the fluctuation of the carrier frequency error exceeds half of the carrier interval per symbol period length, the narrowband carrier frequency error correction feedback loop 11 I can't follow.

  In an environment where the OFDM demodulator 20 is actually used, there are several reasons why the carrier frequency error fluctuates after the OFDM demodulator 20 is activated. For example, one reason is that the temperature inside the tuner LSI rises during startup and the frequency of the local oscillator for frequency conversion fluctuates. However, the frequency fluctuation is about several tens to several thousand ppm in a sufficiently long time as compared with one effective symbol period length on the order of milliseconds. The fluctuation of the carrier frequency error due to the fluctuation of the local oscillation frequency is smaller than half of the carrier interval per effective symbol period length. Therefore, if the narrow band carrier frequency error correction feedback loop 11 has the tracking ability of the carrier frequency error fluctuation as described above, no particular problem occurs when the OFDM demodulator 20 is actually used.

[Embodiment 7]
The OFDM demodulator 20 according to this embodiment further includes the above-described activation unit in addition to the components shown in FIG. The activation unit sets a specific convergence condition. This convergence condition takes into account the stability and responsiveness of the entire system in the OFDM demodulator 20. For example, the activation unit sets a condition that the narrowband carrier frequency error is about 1/100 or less of the carrier interval as the convergence condition.

  In the present embodiment, the activation unit first includes the tuner 2, the A / D converter 3, the quadrature detection unit 4, the narrowband carrier frequency error correction unit 5, the narrowband carrier frequency error detection unit 6, and the FFT operation circuit 8. to start.

  Next, unlike the sixth embodiment, the activation unit does not activate the broadband carrier frequency error correction unit 7 and the broadband carrier frequency error detection unit 9 at this stage. After the narrow-band carrier frequency error correction feedback loop 11 is activated, the detected narrow-band carrier frequency error δfn is always monitored. At this time, the activation unit determines that the narrowband carrier frequency error correction feedback loop 11 has become stable when the narrowband carrier frequency error δfn satisfies the convergence condition described above. Therefore, the activation unit of the OFDM demodulator 20 activates the broadband carrier frequency error correction unit 7 and the broadband carrier frequency error detection unit 9.

  Next, once the broadband carrier frequency error detection unit 9 detects the broadband carrier frequency error δfw, it outputs the broadband carrier frequency error δfw to the broadband carrier frequency error correction unit 7. Further, the OFDM demodulator 20 stops the broadband carrier frequency error detector 9. Thereafter, the broadband carrier frequency error correction unit 7 always corrects the detected broadband carrier frequency error δfw.

  In the control method described in the sixth embodiment, there is a possibility that the wideband carrier frequency error detection unit 9 is activated in a state where the narrowband carrier frequency error remains in the BB signal Z2 (m, n). At this time, a problem remains in the stability of the carrier frequency error correction of the entire OFDM demodulator 20. However, if the wideband carrier frequency error detector 9 is activated in a state where the narrowband carrier frequency error can be regarded as almost zero as in the present embodiment, the stability problem can be completely eliminated.

  As described above, the OFDM demodulator 20 stably corrects the carrier frequency error as a whole. This eliminates errors caused by instability when processing the BB signal. Therefore, for example, it is possible to stably demodulate a television broadcast by the OFDM modulation method as in Non-Patent Document 1.

  In addition, this invention is not limited to embodiment mentioned above, A various change is possible in the range shown to the claim. In other words, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

(Other configurations)
In addition, this invention can also be set as the structure shown below.

(First configuration)
An orthogonal modulation wave of an orthogonal frequency division multiplex modulation signal including a transmission symbol having an effective symbol and a guard interval obtained by copying the same content as a part of the effective symbol is input,
Orthogonal demodulation means for obtaining a baseband signal 1 from the orthogonal modulation wave;
Narrowband carrier frequency correction means 1 for correcting the narrowband carrier frequency error of the baseband signal 1 and outputting the baseband signal 2 based on the narrowband carrier frequency error;
Delay means for delaying the baseband signal 2 by an effective symbol period and outputting the baseband signal 3;
Correlation calculating means for obtaining a complex correlation between the baseband signal 2 and the baseband signal 3;
A symbol synchronization unit for generating a symbol synchronization signal for extracting the effective symbol based on the amplitude of the complex correlation;
Narrowband carrier frequency error detection means for detecting a narrowband carrier frequency error of the baseband signal 2 based on the phase of the complex correlation;
Means for removing a guard interval from the baseband signal 2 according to the symbol synchronization signal and extracting a valid symbol for outputting a baseband signal 4;
Orthogonal frequency division multiplexing demodulating means for demodulating the baseband signal 4 which has been orthogonal frequency division multiplexed modulated in the effective symbol and outputting a demodulated signal;
A broadband carrier frequency error detecting means for detecting a broadband carrier frequency error from the demodulated signal;
An OFDM demodulator comprising: means for removing a carrier component outside a desired band based on the broadband carrier frequency error and extracting an effective carrier.

(Second configuration)
An orthogonal modulation wave of an orthogonal frequency division multiplex modulation signal including a transmission symbol having an effective symbol and a guard interval obtained by copying the same content as a part of the effective symbol is input,
Orthogonal demodulation means for obtaining a baseband signal 1 from the orthogonal modulation wave;
Narrowband carrier frequency correction means 1 for correcting the narrowband carrier frequency error of the baseband signal 1 and outputting the baseband signal 2 based on the narrowband carrier frequency error;
Delay means for delaying the baseband signal 1 by an effective symbol period and outputting a baseband signal 3;
Correlation calculating means for obtaining a complex correlation between the baseband signal 1 and the baseband signal 3;
A symbol synchronization unit for generating a symbol synchronization signal for extracting the effective symbol based on the amplitude of the complex correlation;
Narrowband carrier frequency error detecting means for detecting a narrowband carrier frequency error of the baseband signal 1 based on the phase of the complex correlation;
Means for removing a guard interval from the baseband signal 2 according to the symbol synchronization signal and extracting a valid symbol for outputting a baseband signal 4;
Orthogonal frequency division multiplexing demodulating means for demodulating the baseband signal 4 which has been orthogonal frequency division multiplexed modulated in the effective symbol and outputting a demodulated signal;
A broadband carrier frequency error detecting means for detecting a broadband carrier frequency error from the demodulated signal;
An OFDM demodulator comprising: means for removing a carrier component outside a desired band based on the broadband carrier frequency error and extracting an effective carrier.

(Third configuration)
An OFDM demodulator according to the first to second configurations,
The carrier frequency correction means 2 is a phase rotation circuit whose unit is a phase rotation amount obtained by multiplying the guard interval ratio by 2π.
The OFDM demodulator characterized in that the phase rotation circuit changes a phase rotation amount during a guard interval period of each symbol.

(Fourth configuration)
A third configuration OFDM demodulator, comprising:
2. The OFDM demodulator according to claim 1, wherein the phase rotation circuit comprises a phase rotator that performs a phase rotation process in which a phase rotation amount obtained by multiplying 2π by a guard interval ratio is a unit and the phase rotation amount is smaller than π / 4.

(Fifth configuration)
An OFDM demodulator according to any one of the first to fourth configurations,
The narrow band carrier frequency error detecting means is provided to output a specific narrow band carrier frequency error 1 as a narrow band carrier frequency error when the detected absolute value of the phase of the complex correlation is π. The OFDM demodulator according to claim 1 to 4.

(Sixth configuration)
An OFDM demodulator according to any one of the first to fourth configurations,
Activating the narrowband carrier frequency error detecting means, the carrier frequency correcting means 1 and the wideband carrier frequency error detecting means,
After detecting the broadband carrier frequency error once, stop the broadband carrier frequency error detection means,
The carrier frequency correction means 1 corrects the narrow band carrier frequency error detected by the narrow band carrier frequency error detection means,
An OFDM demodulator for correcting the broadband carrier frequency error detected by the carrier frequency correcting means (2).

(Seventh configuration)
An OFDM demodulator according to a sixth configuration,
First, the narrow band carrier frequency error detecting means and the carrier frequency correcting means 1 are activated,
An OFDM demodulator characterized in that, when the detected narrow band carrier frequency error satisfies condition 1, the broadband carrier frequency error detecting means is activated.

(Program and recording medium)
Finally, each block included in the OFDM demodulator 20 may be configured by hardware logic. Alternatively, it may be realized by software using a CPU (Central Processing Unit) as follows.

  `In other words, the OFDM demodulator 20 develops a CPU that executes an OFDM demodulation program instruction for realizing each function, a ROM (Read Only Memory) that stores the OFDM demodulation program, and a format that can execute the OFDM demodulation program. A random access memory (RAM) and a storage device (recording medium) such as a memory for storing the OFDM demodulation program and various data are provided. With this configuration, the object of the present invention can be achieved by a predetermined recording medium.

This recording medium only needs to record the program code (execution format program, intermediate code program, source program) of the OFDM demodulation program of the OFDM demodulator 20 which is software that realizes the above-described functions so that it can be read by a computer. This recording medium is supplied to the OFDM demodulator 20. Thereby, the OFDM demodulator 20 (or CPU or MPU) as a computer may read and execute the program code recorded on the supplied recording medium.
`The recording medium for supplying the program code to the OFDM demodulator 20 is not limited to a specific structure or type. That is, the recording medium includes, for example, a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. A disk system, a card system such as an IC card (including a memory card) / optical card, or a semiconductor memory system such as a mask ROM / EPROM / EEPROM / flash ROM can be used.

  Moreover, even if the OFDM demodulator 20 is configured to be connectable to a communication network, the object of the present invention can be achieved. In this case, the above program code is supplied to the OFDM demodulator 20 via the communication network. The communication network is not limited to a specific type or form as long as it can supply a program code to the OFDM demodulator 20. For example, the Internet, an intranet, an extranet, a LAN, an ISDN, a VAN, a CATV communication network, a virtual private network, a telephone line network, a mobile communication network, a satellite communication network, or the like may be used.

  The transmission medium constituting the communication network may be any medium that can transmit the program code, and is not limited to a specific configuration or type. For example, in the case of wired communication such as IEEE 1394, USB (Universal Serial Bus), power line carrier, cable TV line, telephone line, ADSL (Asymmetric Digital Subscriber Line) line, etc., infrared rays such as IrDA and remote control, Bluetooth (registered trademark), 802. 11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, etc. can also be used. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  INDUSTRIAL APPLICABILITY The present invention can be widely used as an OFDM demodulator that demodulates an OFDM wave transmitted by the OFDM method to obtain a television signal or the like.

It is a block diagram which shows the structure of the OFDM demodulation apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the OFDM demodulation apparatus which concerns on other embodiment of this invention. It is a figure which shows an example of the phase rotation by a carrier frequency error in the OFDM wave by which GI period is not inserted. It is a figure which shows an example of the phase rotation by the carrier frequency error in the OFDM wave in which GI is inserted. It is a figure which shows an example of a broadband carrier frequency error correction process. It is a figure which shows an example of a broadband carrier frequency error correction | amendment part. It is a block diagram which shows the broadband carrier frequency error correction | amendment part 7 in case GI ratio is g = 1/16. It is a figure which shows an example of the fluctuation | variation of a carrier frequency error. It is a figure which shows an example of the transmission symbol of an OFDM modulation wave. It is a block diagram which shows the structure of the OFDM demodulation apparatus in a nonpatent literature 2. It is a block diagram which shows the OFDM demodulation apparatus in patent document 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 Tuner 3 A / D converter 4 Digital quadrature detection part (orthogonal demodulation means)
5 Narrowband carrier frequency error correction unit (Narrowband carrier frequency error correction means)
6 Narrowband carrier frequency error detector (Narrowband carrier frequency error detection means)
7 Broadband carrier frequency error correction unit (Wideband carrier frequency error correction means)
8 FFT operation circuit (orthogonal frequency division multiplexing demodulation means)
9 Broadband carrier frequency error detector (Wideband carrier frequency error detection means)
10 Waveform Equalization 11 Narrowband Carrier Frequency Error Correction Feedback Loop 12 Wideband Carrier Frequency Error Correction Feedback Loop 13 Narrowband Carrier Frequency Error Correction Feedforward Loop 32 BPF
33, 34 Multiplier 35 Local oscillator 36 90 ° phase shifter 37, 39 LPF
38, 40 A / D converter 41 Guard period removal circuit 45 OFDM demodulation unit 50 Symbol synchronization detection unit 51, 52 Delay circuit 53, 54 Correlator 55 Guard timing detection circuit 60 Carrier synchronization detection unit 61, 71, 72 Carrier frequency error Detection circuit 62, 73 Carrier frequency control circuit 74 Adder 75 D / A converter 76 Clock error detection circuit 77 Clock control circuit 79 Local oscillator 80 Timing circuit
100 Conventional OFDM demodulator,
DESCRIPTION OF SYMBOLS 101 Antenna 102 Tuner 103 Band pass filter 104 A / D conversion circuit 105 DC cancellation circuit 106 Digital orthogonal demodulation circuit 107 FFT operation circuit 108 Frame extraction circuit 109 Synchronous circuit 110 Carrier demodulation circuit 111 Frequency deinterleave circuit 112 Time deinterleave circuit 113 De Mapping circuit 114 Bit deinterleave circuit 115 Depuncture circuit 116 Viterbi circuit 117 Byte deinterleave 118 118 Spread signal elimination circuit 119 Stream generation circuit 120 RS composite circuit 121 Transmission control information decoding circuit 122 Channel selection circuit 201 Effective symbol period 202 Guard interval period 203 Symbol Period 211 to 216 Phase rotation due to carrier frequency error 217 Phase rotation amount during GI period 18 to 219 Phase rotation due to carrier frequency error 311a to 311o Phase rotator 312 Selector 313 I component Q component exchanging means 314 I component code inversion 315 Q component code inversion means 350 Example of variation in carrier frequency error 351 Variation in carrier frequency error One case

Claims (9)

Orthogonal demodulation means for obtaining a first baseband signal from an orthogonal modulation wave of an orthogonal frequency division multiplex modulation signal including a transmission symbol having an effective symbol and a guard interval obtained by copying the same content as a part of the effective symbol When,
Narrowband carrier frequency error correction means for obtaining a second baseband signal by correcting a narrowband carrier frequency error included in the first baseband signal;
Delay means for delaying the second baseband signal by an effective symbol period to obtain a third baseband signal;
Correlation calculating means for obtaining a complex correlation between the second baseband signal and the third baseband signal;
Symbol synchronization means for obtaining a symbol synchronization signal for extracting the effective symbol from the second baseband signal based on the amplitude of the complex correlation;
Narrowband carrier frequency error detection means for detecting the narrowband carrier frequency error included in the first baseband signal based on the phase of the complex correlation;
Broadband carrier frequency error correction means for obtaining a fourth baseband signal by correcting a broadband carrier frequency error included in the second baseband signal;
Guard interval removing means for outputting a fifth baseband signal by removing the guard interval from the fourth baseband signal according to the symbol synchronization signal;
Orthogonal frequency division multiplexing demodulation means for obtaining a demodulated signal by demodulating the fifth baseband signal that has been orthogonal frequency division multiplexed modulated in the effective symbol;
Broadband carrier frequency error detection means for detecting the broadband carrier frequency error from the demodulated signal;
An OFDM demodulator comprising: effective carrier extraction means for extracting effective carriers from the demodulated signal. Orthogonal demodulation means for obtaining a first baseband signal from an orthogonal modulation wave of an orthogonal frequency division multiplex modulation signal including a transmission symbol having an effective symbol and a guard interval obtained by copying the same content as a part of the effective symbol When,
Narrowband carrier frequency error correction means for obtaining a second baseband signal by correcting a narrowband carrier frequency error included in the first baseband signal;
Delay means for delaying the first baseband signal by an effective symbol period to obtain a third baseband signal;
Correlation calculating means for obtaining a complex correlation between the first baseband signal and the third baseband signal;
Symbol synchronization means for obtaining a symbol synchronization signal for extracting the effective symbol from the second baseband signal based on the amplitude of the complex correlation;
Narrowband carrier frequency error detection means for detecting the narrowband carrier frequency error included in the first baseband signal based on the phase of the complex correlation;
Broadband carrier frequency error correction means for obtaining a fourth baseband signal by correcting a broadband carrier frequency error included in the second baseband signal;
Guard interval removing means for outputting a fifth baseband signal by removing the guard interval from the fourth baseband signal according to the symbol synchronization signal;
Orthogonal frequency division multiplexing demodulation means for obtaining a demodulated signal by demodulating the fifth baseband signal that has been orthogonal frequency division multiplexed modulated in the effective symbol;
Broadband carrier frequency error detection means for detecting the broadband carrier frequency error from the demodulated signal;
An OFDM demodulator comprising: effective carrier extraction means for extracting effective carriers from the demodulated signal. The broadband carrier frequency error correction means includes:
It is a phase rotation circuit whose unit is a phase rotation amount obtained by multiplying 2π by the guard interval ratio,
The phase rotation circuit is
3. The OFDM demodulator according to claim 1, wherein the phase rotation amount is changed during a guard interval period of each symbol. The phase rotation circuit is
4. The OFDM demodulator according to claim 3, further comprising a phase rotation process in which the phase rotation amount is smaller than π / 4. The narrow band carrier frequency error detecting means includes:
3. The OFDM demodulator according to claim 1, wherein a specific narrow band carrier frequency error is obtained as the narrow band carrier frequency error when the absolute value of the phase of the complex correlation is π. It further comprises start means for starting or stopping each means described above,
The activation means is
First, after activating the narrowband carrier frequency error detecting means, narrowband carrier frequency error correcting means, and wideband carrier frequency error detecting means, and the wideband carrier frequency error detecting means once detecting the wideband carrier frequency error, Stop the broadband carrier frequency error detection means,
After the start-up means stops the wideband carrier frequency error detection means, the narrowband carrier frequency error correction means corrects the narrowband carrier frequency error, and the wideband carrier frequency error correction means detects the wideband carrier frequency error. The OFDM demodulator according to claim 1 or 2, wherein a frequency error is corrected. The starting means is
First, the narrowband carrier frequency error detection means and the narrowband carrier frequency error correction means are activated, and then when the detected narrowband carrier frequency error satisfies a specific condition,
7. The OFDM demodulator according to claim 6, wherein the broadband carrier frequency error detecting means is activated.   8. An OFDM demodulation program for operating the OFDM demodulator according to claim 1, for causing a computer to function as each of the above means. A computer-readable recording medium in which the OFDM demodulation program according to claim 8 is recorded.

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