JP2007208856A - Ofdm demodulation apparatus, method of operating ofdm demodulation apparatus, program, and computer-readable recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM demodulation apparatus with reduced circuit scale and power consumption. <P>SOLUTION: An OFDM demodulation apparatus 1 comprises demodulation units 2a, 2b, with each of the demodulation units 2a, 2b includes antennas 3a, 3b, tuners 4a, 4b, baseband signal processing sections 5a, 5b and error correction processing sections 6a, 6b; the baseband signal processing sections 5a, 5b that include quadrature detection circuits 8a, 8b, waveform equalization circuits 15a, 15b and diversity composition circuits 16a, 16b; and the error correction processing sections 6a, 6b that include error correction processing memories 21a, 21b, 22a, 22b. For a baseband signal from the waveform equalization circuit 15a, the timing with the baseband signal, from the waveform equalization circuit 15b, is adjusted by the error correction processing memory 21a; and the diversity composing circuit 16b combines the baseband signal of which the timing is adjusted by the error correction processing memory 21a with the baseband signal from the waveform equalization circuit 15b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an Orthogonal Frequency Division Multiplex (hereinafter abbreviated as OFDM) demodulator capable of efficiently transmitting video signals and audio signals in a digital transmission scheme, an operation method of the OFDM demodulator, a program, and a computer The present invention relates to a readable recording medium.

(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. A baseband (BB) signal in which all the carriers are OFDM-modulated by an inverse fast Fourier transform (IFFT) is generated.

FIG. 7 is a diagram illustrating an example of transmission symbols of an OFDM modulated wave. The period of the IFFT conversion processing window is an effective symbol period ts. The effective symbol period corresponds to N cycles of F _s clocks. The sum of all digitally modulated carriers with the effective symbol period ts as a basic unit is called an OFDM transmission symbol.

  As shown in FIG. 7, an actual transmission symbol is usually configured by adding a period tg called a guard interval (GI) 202a to an effective symbol period 201. The waveform of the GI period tg (202a) is obtained by repeating the signal waveform of the rear part 202b of the effective symbol period ts. 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.

  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, a carrier shown in the following table 3 is arranged for one segment in one transmission symbol subjected to QPSK, 16QAM, or 64QAM modulation.

  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. This 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)
An example of a configuration of a conventional OFDM demodulator is shown in FIG. FIG. 8 is a block diagram showing a configuration of a conventional OFDM demodulator 91. The OFDM demodulator 91 includes two demodulation units 92a and 92b for space diversity.

  Diversity is a technique for providing means for obtaining a plurality of received signals and improving reception performance such as fading resistance by selection or synthesis. Diversity includes spatial diversity, which is received by multiple antennas and combined with multiple received signals by the receiver, frequency diversity that places the same information on different frequencies (TMCC / AC1), and the difference in transmission characteristics in polarization , Polarization diversity that puts the same information on vertically polarized waves, parallel polarized waves or right-handed circularly polarized waves, left-handed circularly polarized waves, and time diversity that transmits the same information at time intervals, There is path diversity in which each wave is separated by using the difference in delay and the delay is adjusted and combined.

  The spatial diversity combining method includes a selective combining method for switching the two demodulation units to the one with the better reception status, an equal gain combining method for combining the signals of the two demodulation units by adjusting only the phase, and two There is a maximum ratio combining method in which both the amplitude and phase of the signal of the demodulation unit are adjusted and combined.

  The demodulation unit 92a is configured in a single chip and includes an antenna 93a, a tuner 94a, a baseband signal processing unit 95a, and an error correction processing unit 96a. The baseband signal processing unit 95a includes an analog-to-digital converter (ADC) 97a, an orthogonal detection circuit 98a, a narrowband carrier frequency error correction circuit 99a, a symbol synchronization circuit 80a, and an AGC (Auto Gain Control). ) Circuit 81a, FFT operation circuit 82a, broadband carrier frequency error correction circuit 83a, TMCC decoding circuit 84a, waveform equalization circuit 85a, timing adjustment RAM 87a, and diversity combining circuit 86a. The error correction processing unit 96a includes a demapping circuit 89a, a deinterleave circuit 70a, deinterleave RAMs 71a and 72a, and a Reed-Solomon (RS) decoding circuit 73a.

  The demodulation unit 92b is also configured in common with the demodulation unit 92a. The demodulating unit 92b is configured as a single chip, and includes an antenna 93b, a tuner 94b, a baseband signal processing unit 95b, and an error correction processing unit 96b. The baseband signal processing unit 95b includes an analog-to-digital converter (ADC) 97b, an orthogonal detection circuit 98b, a narrowband carrier frequency error correction circuit 99b, a symbol synchronization circuit 80b, an AGC circuit 81b, and an FFT operation circuit 82b. A broadband carrier frequency error correction circuit 83b, a TMCC decoding circuit 84b, a waveform equalization circuit 85b, a timing adjustment RAM 87b, and a diversity combining circuit 86b. The error correction processing unit 96b includes a demapping circuit 89b, a deinterleave circuit 70b, deinterleave RAMs 71b and 72b, and a Reed-Solomon (RS) decoding circuit 73b.

  Broadcast waves of digital broadcasting broadcast from a broadcasting station are received by the antennas 93a and 93b of the OFDM demodulator 91, and supplied to the tuners 94a and 94b as RF signals, respectively. The tuners 94a and 94b frequency-convert RF (high frequency) signals received through the antennas 93a and 93b, respectively, into IF (intermediate frequency) signals. The tuners 94a and 94b supply the IF signals subjected to frequency conversion to the ADCs 97a and 97b provided in the baseband signal processing units 95a and 95b, respectively.

  The IF signals output from the tuners 94a and 94b are digitized by the ADCs 97a and 97b. The digitized IF signal is supplied to quadrature detection circuits 98a and 98b, respectively.

  The quadrature detection circuits 98a and 98b perform quadrature demodulation on the digitized IF signal using a carrier signal having a predetermined frequency (carrier frequency), and output 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). Baseband OFDM signals output from the quadrature detection circuits 98a and 98b are supplied to narrowband carrier frequency error correction circuits 99a and 99b.

  The narrowband carrier frequency error correction circuits 99a and 99b correct the narrowband carrier frequency error of the baseband OFDM signal supplied from the quadrature detection circuits 98a and 98b, and perform symbol synchronization circuits 80a and 80b and FFT operation circuits 82a and 82a. 82b.

  The symbol synchronization circuits 80a and 80b execute symbol synchronization processing for extracting transmission parameters such as a transmission mode and a guard interval ratio from the baseband OFDM signal.

  The broadband carrier frequency error correction circuits 83a and 83b correct the broadband carrier frequency error of the baseband OFDM signal supplied by the FFT calculation circuits 82a and 82b, and supply the corrected error to the FFT calculation circuits 82a and 82b.

  The FFT operation circuits 82a and 82b perform an FFT operation on the baseband OFDM signal, and extract and output a signal that is orthogonally modulated on each subcarrier. The FFT operation circuits 82a and 82b extract a signal corresponding to the effective symbol length from one OFDM symbol, and perform an FFT operation on the extracted signal. That is, the FFT operation circuits 82a and 82b remove a signal corresponding to the guard interval length from one OFDM symbol, and perform an FFT operation on the remaining signals. 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 circuits 82a and 82b is a complex signal composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The signals extracted by the FFT operation circuits 82a and 82b are supplied to the TMCC decoding circuits 84a and 84b and the waveform equivalent circuits 85a and 85b.

  Signals demodulated from the subcarriers output from the FFT operation circuits 82a and 82b are supplied to the waveform equivalent circuits 85a and 85b. In a communication path such as in the air, frequency selective fading, Rayleigh fading, etc. occur, and the baseband signal is distorted. The waveform equivalent circuits 85a and 85b are blocks that correct this distortion with reference to the SP carrier included in the subcarrier.

  The TMCC decoding circuits 84a and 84b decode transmission control information such as TMCC that is modulated at a predetermined position in the OFDM transmission frame.

  Consider a case where diversity combining is performed on two signals respectively received by two antennas 93a and 93b. In any of the above-described spatial diversity selection combining method, equal gain combining method, and maximum ratio combining method, the diversity effect cannot be obtained unless the FFT output and waveform equalization output of the same carrier number are selected and combined. However, since separate tuners 94a and 94b are connected to the respective antennas 93a and 93b, the demodulation side independently performs carrier frequency synchronization and symbol synchronization. Therefore, even if the information has the same carrier number on the transmission side, the timings at which the corresponding data are output in the two reception side FFTs or waveform equalization outputs are different from each other.

  Therefore, the signal output from the waveform equivalent circuit 85a is stored in the timing adjustment RAM 87a, and the signal output from the waveform equivalent circuit 85b is stored in the timing adjustment RAM 87b. Then, the diversity combining circuit 86b combines the signal stored in the timing adjustment RAM 87a and the signal stored in the timing adjustment RAM 87b by adjusting the timing, and a demapping circuit 89b provided in the error correction processing unit 96b. To supply.

  The demapping circuit 89b performs data reassignment processing (demapping processing) on the carrier demodulated signal (complex signal). Thereby, the transmission data series is restored.

  The deinterleave circuit 70b deinterleaves the carrier demodulated signal along the frequency axis direction by the deinterleave RAM 71b, deinterleaves along the time axis direction by the deinterleave RAM 72b, and then performs an RS decoding circuit 73b. To supply.

  The RS decoding circuit 73b performs a Reed-Solomon decoding process on the input transmission data series. As a result, the transmission data sequence is output as a transport stream defined by MPEG-2 Systems.

  Diversity combining circuit 86a, demapping circuit 89a, deinterleaving circuit 70a, deinterleaving RAMs 71a and 72a, and RS decoding circuit 73a are not used.

The OFDM demodulator having a two-chip diversity configuration configured as described above has a demodulating function of one system per chip. From the viewpoint of cost, both chips need to be a common LSI, but diversity is performed. If not, a module is configured with one chip, and when performing diversity, the module may be configured with two chips, and a lean configuration is possible by changing the number of chips according to the system.
"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 Japanese Patent Laying-Open No. 2003-333012 (published November 21, 2003 (2003.11.21)), FIG.

  However, in the conventional configuration shown in FIG. 8, two timing adjustment RAMs must be added in order to adjust the timing shift in the space diversity, which makes it difficult to reduce the circuit scale and power consumption. This causes a problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an OFDM demodulator capable of reducing the number of memories and reducing the circuit scale and power consumption.

  In order to solve the above problems, an OFDM demodulator according to the present invention includes a plurality of demodulation units for spatial diversity, each demodulation unit including an antenna that receives a high frequency signal, and the high frequency signal as an intermediate frequency signal. A baseband signal processing unit for extracting a baseband signal from the intermediate frequency signal and processing the digital signal, and correcting an error in the baseband signal digitally processed by the baseband signal processing unit An error correction processing unit provided, wherein the baseband signal processing unit includes a quadrature detection circuit that extracts a baseband signal from the intermediate frequency signal, a waveform equalization circuit that equalizes the waveform of the baseband signal, and a space A diversity combining circuit for diversity combining, and the error correction processing unit includes an error correcting circuit. An error correction processing memory provided for processing, and a first baseband signal output from one waveform equalization circuit of the plurality of demodulation units is received by one error correction processing memory of the demodulation unit. The timing of the second baseband signal output from the other waveform equalization circuit of the demodulation unit is adjusted, and the other diversity combining circuit of the demodulation unit provides one error correction of the demodulation unit. The first baseband signal whose timing is adjusted with the second baseband signal by a processing memory and the second baseband signal are synthesized.

  According to the above feature, the first baseband signal output from one waveform equalization circuit of the plurality of demodulation units is transmitted to another one of the demodulation units by one error correction processing memory of the demodulation unit. The timing of the second baseband signal output from the waveform equalization circuit is adjusted, and the other diversity combining circuit of the demodulation unit is connected to the second baseband signal by one error correction processing memory of the demodulation unit. The first baseband signal whose timing is adjusted and the second baseband signal are synthesized. For this reason, in the spatial diversity demodulation circuit having a plurality of chips, the error correction processing memory provided in the error correction processing unit can be used as a memory for adjusting a difference in timing in the spatial diversity. Therefore, it is not necessary to add a new memory to adjust the difference in timing of space diversity, and as a result, the number of memories can be reduced, and an OFDM demodulator with reduced circuit scale and power consumption is provided. can do.

  In the OFDM demodulator according to the present invention, it is preferable that the error correction processing memory is a RAM for a deinterleave circuit that performs a deinterleave process on the baseband signal.

  According to the above configuration, a large-capacity RAM of the order of several megabits necessary for the deinterleaving process can be used for the timing adjustment of space diversity.

  In the OFDM demodulator according to the present invention, the plurality of demodulation units are preferably a pair of demodulation units.

  According to the above configuration, the error correction processing memory can be utilized as a spatial diversity timing adjustment memory in a two-chip spatial diversity demodulation circuit.

  In the OFDM demodulator according to the present invention, each of the plurality of demodulation units is preferably configured in a chip shape.

  According to the above configuration, when space diversity is not performed, a module can be configured by one chip, and when space diversity is performed, a module can be configured by a plurality of chips, and the number of chips can be changed according to the system. The demodulator can be configured flexibly.

  In the OFDM demodulator according to the present invention, the baseband signal processing unit preferably includes a symbol synchronization circuit that performs symbol synchronization processing of the baseband signal.

  According to the above configuration, the symbol synchronization shift caused by the symbol synchronization circuit can be adjusted using the error correction processing memory, and it is not necessary to add a new memory to adjust the symbol synchronization shift.

  In the OFDM demodulator according to the present invention, the baseband signal processing unit includes a symbol synchronization circuit that performs symbol synchronization processing of the baseband signal, and a broadband carrier frequency error correction circuit that corrects a broadband carrier frequency error of the baseband signal. And a timing adjustment circuit provided for adjusting a timing difference in space diversity, wherein the timing adjustment circuit provided in one of the plurality of demodulation units is configured to synchronize one symbol of the demodulation unit. Difference in symbol synchronization timing between the circuit and one other symbol synchronization circuit of the demodulation unit, one broadband carrier frequency error correction circuit of the demodulation unit and another broadband carrier frequency error correction of the demodulation unit Wideband carrier frequency error correction difference with the circuit Preferably generates a control signal for adjusting by a single error correction memory demodulation unit.

  According to the above configuration, the symbol synchronization shift by the symbol synchronization circuit and the difference in broadband carrier frequency error correction can be adjusted with a simple configuration.

  In order to solve the above problems, an operating method of an OFDM demodulator according to the present invention includes a plurality of demodulation units for spatial diversity, each demodulation unit including an antenna for receiving a high-frequency signal, and the high-frequency signal. A tuner for converting to an intermediate frequency signal, a baseband signal processing unit for extracting a baseband signal from the intermediate frequency signal and processing the digital signal, and correcting errors in the baseband signal digitally processed by the baseband signal processing unit An error correction processing unit provided to perform the detection, wherein the baseband signal processing unit includes a quadrature detection circuit that extracts a baseband signal from the intermediate frequency signal, and a waveform equalization circuit that equalizes the waveform of the baseband signal And a diversity combining circuit for space diversity combining, the error correction processing unit An OFDM demodulator operating method having an error correction processing memory provided for error correction processing, the first baseband signal output from one waveform equalization circuit of the plurality of demodulation units, The timing between the second baseband signal output from one other waveform equalization circuit of the demodulation unit is adjusted by one error correction processing memory of the demodulation unit, and one error correction processing of the demodulation unit The first baseband signal whose timing is adjusted with the second baseband signal by a memory and the second baseband signal are synthesized by another diversity synthesis circuit of the demodulation unit. .

  According to the above feature, the first baseband signal output from one waveform equalization circuit of the plurality of demodulation units and the second baseband output from another waveform equalization circuit of the demodulation unit. A first baseband signal whose timing with the second baseband signal is adjusted by one error correction processing memory of the demodulation unit And the second baseband signal are combined by another diversity combining circuit of the demodulation unit. For this reason, in the spatial diversity demodulation circuit having a plurality of chips, the error correction processing memory provided in the error correction processing unit can be used as a memory for adjusting a difference in timing in the spatial diversity. Therefore, there is no need to add a new memory to adjust the difference in spatial diversity timing, and as a result, the number of memories can be reduced, and an OFDM demodulation method with reduced circuit scale and power consumption is provided. can do.

  In order to solve the above problems, a program according to the present invention includes a plurality of demodulation units for spatial diversity, each demodulation unit converting an antenna for receiving a high-frequency signal and the high-frequency signal into an intermediate frequency signal. A baseband signal processing unit for extracting a baseband signal from the intermediate frequency signal and processing the digital signal, and for correcting an error in the baseband signal digitally processed by the baseband signal processing unit. The baseband signal processing unit includes a quadrature detection circuit that extracts a baseband signal from the intermediate frequency signal, a waveform equalization circuit that equalizes the waveform of the baseband signal, and spatial diversity synthesis A diversity combining circuit, and the error correction processing unit includes error correction processing A program for executing an OFDM demodulation method by an OFDM demodulator having an error correction processing memory provided for a first baseband output from a waveform equalization circuit of the plurality of demodulation units to a computer Adjusting a timing between the signal and a second baseband signal output from another waveform equalization circuit of the demodulation unit by one error correction processing memory of the demodulation unit; The first baseband signal whose timing with the second baseband signal is adjusted by one error correction processing memory and the second baseband signal are combined by another diversity combining circuit of the demodulation unit. And a procedure is executed.

  In order to solve the above problems, a computer-readable recording medium according to the present invention includes a plurality of demodulation units for spatial diversity, each demodulation unit including an antenna that receives a high-frequency signal, and the high-frequency signal. A tuner for converting to an intermediate frequency signal, a baseband signal processing unit for extracting a baseband signal from the intermediate frequency signal and processing the digital signal, and correcting errors in the baseband signal digitally processed by the baseband signal processing unit An error correction processing unit provided to perform the detection, wherein the baseband signal processing unit includes a quadrature detection circuit that extracts a baseband signal from the intermediate frequency signal, and a waveform equalization circuit that equalizes the waveform of the baseband signal And a diversity combining circuit for space diversity combining, the error correction The processing unit is a computer-readable recording medium in which a program for executing an OFDM demodulation method by an OFDM demodulator having an error correction processing memory provided for error correction processing is recorded. The timing between the first baseband signal output from one waveform equalization circuit of the demodulation unit and the second baseband signal output from one other waveform equalization circuit of the demodulation unit is the demodulation unit. The first baseband signal whose timing is adjusted with the second baseband signal by one error correction processing memory of the demodulation unit, and the second baseband signal. And a procedure for synthesizing the same by another diversity synthesis circuit of the demodulation unit. And characterized by recording a program for.

  In the OFDM demodulator according to the present invention, as described above, the first baseband signal output from one waveform equalization circuit of the plurality of demodulation units is received by one error correction processing memory of the demodulation unit. The timing with the second baseband signal output from the other waveform equalization circuit of the demodulation unit is adjusted, and the other diversity combining circuit of the demodulation unit provides an error correction process of the demodulation unit. Since the first baseband signal whose timing with the second baseband signal is adjusted by the memory and the second baseband signal are synthesized, the number of memories can be reduced, and the circuit scale and power consumption can be reduced. It is possible to provide an OFDM demodulator with reduced noise.

  The operation method of the OFDM demodulator according to the present invention, as described above, the first baseband signal output from one waveform equalization circuit of the plurality of demodulation units, the other waveform of the demodulation unit, etc. The timing between the second baseband signal output from the conversion circuit and the second baseband signal is adjusted by one error correction processing memory of the demodulation unit, and the second baseband signal is adjusted by one error correction processing memory of the demodulation unit. Since the timing-adjusted first baseband signal and the second baseband signal are combined by another diversity combining circuit of the demodulation unit, the circuit scale and power consumption of the OFDM demodulator are reduced. There is an effect that can be.

  An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an embodiment of the present invention and is a block diagram showing a configuration of an OFDM demodulator 1. The OFDM demodulator 1 according to the present embodiment improves reception performance by spatial diversity. The OFDM demodulator 1 includes two demodulation units 2a and 2b for spatial diversity.

  As described above, the spatial diversity combining method includes a selective combining method for switching between two demodulating units to the better receiving state, and equal gain combining for adjusting only the phase of the signals of the two demodulating units. And a maximum ratio combining method in which both amplitude and phase of signals of two demodulation units are adjusted and combined.

  The demodulation unit 2a is configured in one chip, and includes an antenna 3a, a tuner 4a, a baseband signal processing unit 5a, and an error correction processing unit 6a. The baseband signal processing unit 5a includes an analog-digital converter (ADC) 7a, an orthogonal detection circuit 8a, a narrowband carrier frequency error correction circuit 9a, a symbol synchronization circuit 10a, an AGC circuit 11a, and an FFT operation circuit 12a. And a broadband carrier frequency error correction circuit 13a, a TMCC decoding circuit 14a, a waveform equalization circuit 15a, a timing adjustment circuit 18a, and a diversity combining circuit 16a. The error correction processing unit 6a includes a demapping circuit 19a, a deinterleave circuit 20a, deinterleave RAMs 21a and 22a, and a Reed-Solomon (RS) decoding circuit 23a.

  The demodulation unit 2b is also configured in common with the demodulation unit 2a. The demodulating unit 2b is configured as a single chip, and includes an antenna 3b, a tuner 4b, a baseband signal processing unit 5b, and an error correction processing unit 6b. The baseband signal processing unit 5b includes an analog-to-digital converter (ADC) 7b, an orthogonal detection circuit 8b, a narrowband carrier frequency error correction circuit 9b, a symbol synchronization circuit 10b, an AGC circuit 11b, and an FFT operation circuit 12b. And a broadband carrier frequency error correction circuit 13b, a TMCC decoding circuit 14b, a waveform equalization circuit 15b, a timing adjustment circuit 18b, and a diversity combining circuit 16b. The error correction processing unit 6b includes a demapping circuit 19b, a deinterleave circuit 20b, deinterleave RAMs 21b and 22b, and a Reed-Solomon (RS) decoding circuit 23b.

  Broadcast waves of digital broadcasting broadcast from a broadcasting station are received by the antennas 3a and 3b of the OFDM demodulator 1 and supplied to the tuners 4a and 4b as RF signals, respectively. The tuners 4a and 4b frequency-convert RF (high frequency) signals received through the antennas 3a and 3b, respectively, into IF (intermediate frequency) signals. The tuners 4a and 4b supply the IF signals subjected to frequency conversion to the ADCs 7a and 7b provided in the baseband signal processing units 5a and 5b, respectively.

  The IF signals output from the tuners 4a and 4b are digitized by the ADCs 7a and 7b. The digitized IF signal is supplied to the quadrature detection circuits 8a and 8b, respectively.

  The quadrature detection circuits 8a and 8b perform quadrature demodulation on the digitized IF signal using a carrier signal having a predetermined frequency (carrier frequency), and output 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). Baseband OFDM signals output from the quadrature detection circuits 8a and 8b are supplied to narrowband carrier frequency error correction circuits 9a and 9b.

  The narrowband carrier frequency error correction circuits 9a and 9b correct the narrowband carrier frequency error of the baseband OFDM signal supplied from the quadrature detection circuits 8a and 8b, and the symbol synchronization circuits 10a and 10b and the FFT calculation circuit 12a 12b.

  The symbol synchronization circuits 10a and 10b execute symbol synchronization processing for extracting transmission parameters such as a transmission mode and a guard interval ratio from the baseband OFDM signal.

  The FFT operation circuits 12a and 12b perform an FFT operation on the baseband OFDM signal, and extract and output a signal that is orthogonally modulated on each subcarrier. The FFT operation circuits 12a and 12b extract an effective symbol length signal from one OFDM symbol, and perform an FFT operation on the extracted signal. That is, the FFT operation circuits 12a and 12b remove the signal corresponding to the guard interval length from one OFDM symbol and perform the 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 arithmetic circuits 12a and 12b is a complex signal composed of a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The signals extracted by the FFT operation circuits 12a and 12b are supplied to the TMCC decoding circuits 14a and 14b, the broadband carrier frequency error correction circuits 13a and 13b, and the waveform equivalent circuits 15a and 15b.

  The broadband carrier frequency error correction circuits 13a and 13b correct the broadband carrier frequency error of the baseband OFDM signal supplied by the FFT calculation circuits 12a and 12b, and supply the corrected error to the FFT calculation circuits 12a and 12b.

  Signals demodulated from the subcarriers output from the FFT operation circuits 12a and 12b are supplied to the waveform equivalent circuits 15a and 15b. In a communication path such as in the air, frequency selective fading, Rayleigh fading, etc. occur, and the baseband signal is distorted. The waveform equivalent circuits 15a and 15b are blocks for correcting this distortion with reference to the SP carrier included in the subcarrier.

  The TMCC decoding circuits 14a and 14b decode transmission control information such as TMCC that is modulated at a predetermined position in the OFDM transmission frame.

  Consider a case where two signals received by two antennas 3a and 3b are diversity combined. In any of the above-described spatial diversity selection combining method, equal gain combining method, and maximum ratio combining method, the diversity effect cannot be obtained unless the FFT output and waveform equalization output of the same carrier number are selected and combined. However, since separate tuners 4a and 4b are connected to the antennas 3a and 3b, the demodulation side independently performs carrier frequency synchronization and symbol synchronization. Therefore, even if the information has the same carrier number on the transmission side, the timings at which the corresponding data are output in the two reception side FFTs or waveform equalization outputs are different from each other.

  Therefore, in the present embodiment, the signal output from the waveform equivalent circuit 15a is stored in the deinterleave RAM 21a, and the signal output from the waveform equivalent circuit 15b is stored in the deinterleave RAM 22a.

  The timing adjustment circuit 18a includes a difference in symbol synchronization timing between the symbol synchronization circuit 10a and the symbol synchronization circuit 10b, and a broadband carrier frequency error correction between the broadband carrier frequency error correction circuit 13a and the broadband carrier frequency error correction circuit 13b. A control signal is generated for adjusting the difference between the deinterleave RAMs 21a and 22a.

  Then, diversity combining circuit 16b adjusts the timing and combines the signal stored in deinterleave RAM 21a and the signal stored in deinterleave RAM 22a based on the control signal generated by timing adjustment circuit 18a. , And supplied to a demapping circuit 19b provided in the error correction processing unit 6b.

  The demapping circuit 19b performs data reassignment processing (demapping processing) on the carrier demodulated signal (complex signal). Thereby, the transmission data series is restored.

  The deinterleave circuit 20b deinterleaves the carrier demodulated signal along the frequency axis direction by the deinterleave RAM 21b, deinterleaves along the time axis direction by the deinterleave RAM 22b, and then performs the RS decoding circuit 23b. To supply.

  The RS decoding circuit 23b performs Reed-Solomon decoding processing on the input transmission data sequence. As a result, the transmission data sequence is output as a transport stream defined by MPEG-2 Systems.

  Diversity combining circuit 16a, demapping circuit 19a, deinterleave circuit 20a, and RS decoding circuit 23a are not used.

  The thus configured two-chip diversity OFDM demodulator 1 utilizes the deinterleave RAMs 21a and 22a provided in the error correction processing unit 6a as a spatial diversity timing adjustment RAM. For this reason, it is not necessary to add a timing adjustment RAM to adjust the timing shift in the space diversity as in the configuration of the prior art, and the circuit scale can be reduced and the power consumption can be reduced.

  The RAM capacity required for the deinterleaving process in “Transfer method ARIB STD-B31 1.5 edition of digital terrestrial television broadcasting” of Non-Patent Document 1 is on the order of several megabits, so deinterleaving having such a capacity. The RAMs 21a and 22a can be utilized as a space diversity timing adjustment RAM.

  FIG. 2 is a diagram for explaining symbol synchronization timing of the OFDM demodulator 1. In order to perform symbol synchronization in the OFDM demodulator, synchronization timing is detected based on the strength of the complex correlation in the output signals from the narrowband carrier frequency error correction circuits 9a and 9b. In an ideal communication channel in which only one wave is transmitted, as shown in FIG. 2, the peak of the complex correlation intensity is present only at one point of time t1 corresponding to the boundary between the effective symbol period ts and the guard interval (GI) period tg. Therefore, symbol synchronization may be taken at time t1 of this peak timing.

  FIG. 3 is a diagram for explaining a shift in symbol synchronization timing of the OFDM demodulator 1. FIG. 4 is a diagram for explaining a shift in FFT output timing caused by the shift in symbol synchronization timing. In the case of a communication path that transmits a two-wave multipath of a preceding wave and a delayed wave, the sum of the preceding wave and the delayed wave is received as shown in FIG. The intensity of the complex correlation of the received signal is the sum of the complex correlations of the individual waves. In diversity reception, since the spatial reception environments of the two antennas 3a and 3b are different, the intensity ratio between the preceding wave and the delayed wave in the received radio wave is different.

  In the demodulation unit 2a, the intensity of the preceding wave is larger than the intensity of the delayed wave, and the complex correlation intensity S1 corresponding to the received signal based on the preceding wave and the complex correlation intensity S2 corresponding to the received signal based on the delayed wave Received as the sum S3. At this intensity S3, a peak timing appears at time t1 corresponding to the boundary between the effective symbol period of the preceding wave and the guard interval (GI) period. In the demodulation unit 2b, the intensity of the delayed wave is greater than the intensity of the preceding wave, and the complex correlation intensity S4 corresponding to the received signal based on the preceding wave and the complex correlation intensity S5 corresponding to the received signal based on the delayed wave Received as the sum S6. At this intensity S6, a peak timing appears at time t2 corresponding to the boundary between the effective symbol period of the delayed wave and the guard interval (GI) period.

  The baseband signal processing units 5a and 5b perform processing at times t1 and t2 indicating the symbol synchronization timing, respectively.

  Thus, if the timing of the symbol synchronization signal differs between the demodulation units 2a and 2b, as shown in FIG. 4, the output timing between the FFTs 12a and 12b and the output timing between the waveform equalization circuits 15a and 15b also have a time difference t3. It shifts by (= time t2−time t1).

  FIG. 5 is a diagram for explaining a shift in FFT output timing caused by a difference in carrier frequency due to frequency conversion of each of the tuners 4a and 4b of the OFDM demodulator 1. FIG. The demodulation units 2a and 2b have different tuners 4a and 4b, respectively. Each tuner 4a and 4b converts an RF signal of several hundred MHz into an IF signal of several MHz. The frequency conversion by the tuners 4a and 4b causes a difference of about the FFT carrier interval.

  In order to simplify the discussion, it is assumed that there is no deviation in symbol synchronization. However, if there is a difference between the frequency of the IF signal converted by the tuner 4a and the frequency of the IF signal converted by the tuner 4b, the carrier number of the output signal from the FFTs 12a and 12b as shown in FIG. The same difference t4 also occurs in the carrier numbers of the output signals from the waveform equalization circuits 15a and 15b. The FFT circuits 12a and 12b and the waveform equalization circuits 15a and 15b output the BB signal of each carrier in the order of the carrier number with reference to the symbol synchronization signal. Therefore, the carrier frequency error between the tuners 4a and 4b is a difference in output timing between the FFT circuits 12a and 12b and the waveform equalization circuits 15a and 15b.

  When the OFDM demodulator 1 is actually used, both the symbol synchronization shift in the demodulation units 2a and 2b and the carrier frequency error between the tuners 4a and 4b occur simultaneously. That is, the sum (t3 + t4) of the deviations of the two timings is the output timing difference between the waveform equalization circuits 15a and 15b that actually occurs. The timing adjustment circuits 18a and 18b of the present invention adjust the timing difference (t3 + t4).

  As described above, the spatial diversity combining method includes the selective combining method for switching the two demodulation units to the one with the better reception condition, and equal gain generation for combining the signals of the two demodulation units by adjusting only the phase. Method and a maximum ratio combining method in which both amplitudes and phases of signals of two demodulation units are adjusted and combined, the present invention can be applied to any combining method.

  In the present embodiment, the OFDM demodulator includes two demodulation units 2a and 2b. However, the present invention is not limited to this. The present invention can be applied to a configuration including three or more demodulation units.

  FIG. 6 is a block diagram showing a configuration of a variation of the OFDM demodulator according to the present embodiment. The same reference numerals are given to the same components as those described above. Therefore, detailed description of these components is omitted.

  As shown in FIG. 6, the deinterleave RAM 22a may not be used, and the baseband signal output from the waveform equalization circuit 15b may be directly supplied to the diversity combining circuit 16b. The diversity combining circuit 16b combines the baseband signal whose timing is adjusted by the deinterleave RAM 21a and the baseband signal output from the waveform equalization circuit 15b.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, 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.

  Note that in each part and each processing step of the OFDM demodulator according to the above-described embodiment, a calculation unit such as a CPU executes a program stored in a storage unit such as a ROM (Read Only Memory) or a RAM, and a communication such as an interface circuit. This can be realized by controlling the means. Therefore, various functions and various processes of the OFDM demodulator according to the present embodiment can be realized simply by a computer having these means reading the recording medium storing the program and executing the program. In addition, by recording the program on a removable recording medium, the various functions and various processes described above can be realized on an arbitrary computer.

  As this recording medium, a program medium such as a memory (not shown) such as a ROM may be used for processing by the microcomputer, or a program reader is provided as an external storage device (not shown). It may be a program medium that can be read by inserting a recording medium therein.

  In any case, the stored program is preferably configured to be accessed and executed by the microprocessor. Furthermore, it is preferable that the program is read out, and the read program is downloaded to a program storage area of the microcomputer and the program is executed. It is assumed that this download program is stored in advance in the main unit.

  The program medium is a recording medium configured to be separable from the main body, such as a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a flexible disk or a hard disk, or a disk such as a CD / MO / MD / DVD. Fixed disk, IC card (including memory card), etc., or semiconductor ROM such as mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash ROM, etc. In particular, there are recording media that carry programs.

  In addition, if the system configuration is capable of connecting to a communication network including the Internet, the recording medium is preferably a recording medium that fluidly carries the program so as to download the program from the communication network.

  Further, when the program is downloaded from the communication network as described above, it is preferable that the download program is stored in the main device in advance or installed from another recording medium.

  The present invention can be applied to an OFDM demodulator capable of efficiently transmitting a video signal and an audio signal by a digital transmission method, and a device for receiving a signal according to the OFDM method, for example, a demodulation for a wireless LAN The present invention can also be applied to a device, a demodulator for receiving BS digital broadcast and CS digital broadcast, and a demodulator for cable television.

1, showing an embodiment of the present invention, is a block diagram showing a configuration of an OFDM demodulator. FIG. It is a figure for demonstrating the symbol synchronization timing of the said OFDM demodulator. It is a figure for demonstrating the shift | offset | difference of the symbol synchronization timing of the said OFDM demodulator. It is a figure for demonstrating the shift | offset | difference of the FFT output timing produced by the shift | offset | difference of the symbol synchronization timing of the said OFDM demodulator. It is a figure for demonstrating the shift | offset | difference of the FFT output timing produced by the difference in the carrier frequency by the frequency conversion of each tuner of the said OFDM demodulator. It is a block diagram which shows the structure of the modification of the OFDM demodulation apparatus which concerns on this Embodiment. It is a figure which shows an example of the transmission symbol of an OFDM modulation wave. It is a block diagram which shows a prior art and shows the structure of an OFDM demodulation apparatus.

Explanation of symbols

1 OFDM demodulator 2a, 2b Demodulation unit 3a, 3b Antenna 4a, 4b Tuner 5a, 5b Baseband signal processing unit 6a, 6b Error correction processing unit 8a, 8b Quadrature detection circuit 10a, 10b Symbol synchronization circuit 13a, 13b Broadband carrier frequency Error correction circuit 16a, 16b Diversity combining circuit 18a, 18b Timing adjustment circuit 21a, 21b, 22a, 22b Deinterleave RAM (error correction processing memory, deinterleave circuit RAM)

Claims (9)

With multiple demodulation units for spatial diversity,
Each demodulation unit includes an antenna for receiving a high frequency signal,
A tuner for converting the high frequency signal into an intermediate frequency signal;
A baseband signal processing unit that extracts a baseband signal from the intermediate frequency signal and performs digital signal processing;
An error correction processing unit provided to correct an error of the baseband signal digitally processed by the baseband signal processing unit,
The baseband signal processing unit includes a quadrature detection circuit that extracts a baseband signal from the intermediate frequency signal;
A waveform equalization circuit for waveform equalizing the baseband signal;
A diversity combining circuit for space diversity combining;
The error correction processing unit includes an error correction processing memory provided for error correction processing;
The first baseband signal output from one waveform equalization circuit of the plurality of demodulation units is output from one other waveform equalization circuit of the demodulation unit by one error correction processing memory of the demodulation unit. Adjusted timing with the second baseband signal,
The other diversity combining circuit of the demodulation unit includes a first baseband signal whose timing is adjusted with the second baseband signal by one error correction processing memory of the demodulation unit, and the second baseband signal. And an OFDM demodulator characterized by the above-mentioned.   2. The OFDM demodulator according to claim 1, wherein the error correction processing memory is a RAM for a deinterleave circuit that performs a deinterleave process on the baseband signal.   2. The OFDM demodulator according to claim 1, wherein the plurality of demodulation units are a pair of demodulation units.   2. The OFDM demodulator according to claim 1, wherein each of the plurality of demodulation units is configured in a chip shape.   The OFDM demodulator according to claim 1, wherein the baseband signal processing unit includes a symbol synchronization circuit that performs symbol synchronization processing of the baseband signal. The baseband signal processing unit includes a symbol synchronization circuit that performs symbol synchronization processing of the baseband signal;
A broadband carrier frequency error correction circuit for correcting a broadband carrier frequency error of the baseband signal;
A timing adjustment circuit provided to adjust a difference in timing in space diversity,
A timing adjustment circuit provided in one of the plurality of demodulation units includes a difference in symbol synchronization timing between one symbol synchronization circuit of the demodulation unit and another symbol synchronization circuit of the demodulation unit; The difference of the broadband carrier frequency error correction between one broadband carrier frequency error correction circuit of the demodulation unit and the other broadband carrier frequency error correction circuit of the demodulation unit is converted into one error correction process of the demodulation unit. 2. The OFDM demodulator according to claim 1, wherein a control signal for adjustment by a memory is generated. A plurality of demodulation units for spatial diversity, each demodulation unit taking out a baseband signal from the intermediate frequency signal, an antenna that receives a high frequency signal, a tuner that converts the high frequency signal into an intermediate frequency signal, and A baseband signal processing unit for digital signal processing; and an error correction processing unit provided for correcting an error in the baseband signal digitally processed by the baseband signal processing unit, the baseband signal processing unit Comprises a quadrature detection circuit that extracts a baseband signal from the intermediate frequency signal, a waveform equalization circuit that equalizes the waveform of the baseband signal, and a diversity combining circuit for spatial diversity combining, and the error correction processing The unit includes an OFDM having an error correction processing memory provided for error correction processing. A method of operating a control apparatus,
Timing between a first baseband signal output from one waveform equalization circuit of the plurality of demodulation units and a second baseband signal output from another waveform equalization circuit of the demodulation unit Is adjusted by one error correction processing memory of the demodulation unit,
The first baseband signal whose timing with the second baseband signal is adjusted by one error correction processing memory of the demodulation unit and the second baseband signal are combined with another diversity combination of the demodulation unit. An operation method of an OFDM demodulator characterized by combining by a circuit. A plurality of demodulation units for spatial diversity, each demodulation unit taking out a baseband signal from the intermediate frequency signal, an antenna that receives a high frequency signal, a tuner that converts the high frequency signal into an intermediate frequency signal, and A baseband signal processing unit for digital signal processing; and an error correction processing unit provided for correcting an error in the baseband signal digitally processed by the baseband signal processing unit, the baseband signal processing unit Comprises a quadrature detection circuit that extracts a baseband signal from the intermediate frequency signal, a waveform equalization circuit that equalizes the waveform of the baseband signal, and a diversity combining circuit for spatial diversity combining, and the error correction processing The unit includes an OFDM having an error correction processing memory provided for error correction processing. A program that performs OFDM demodulation method according to tone device,
The computer includes a first baseband signal output from one waveform equalization circuit of the plurality of demodulation units and a second baseband signal output from another waveform equalization circuit of the demodulation unit. Adjusting the timing between them by one error correction processing memory of the demodulation unit;
The first baseband signal whose timing with the second baseband signal is adjusted by one error correction processing memory of the demodulation unit and the second baseband signal are combined with another diversity combination of the demodulation unit. A program for executing a procedure of synthesis by a circuit. A plurality of demodulation units for spatial diversity, each demodulation unit taking out a baseband signal from the intermediate frequency signal, an antenna that receives a high frequency signal, a tuner that converts the high frequency signal into an intermediate frequency signal, and A baseband signal processing unit for digital signal processing; and an error correction processing unit provided for correcting an error in the baseband signal digitally processed by the baseband signal processing unit, the baseband signal processing unit Comprises a quadrature detection circuit that extracts a baseband signal from the intermediate frequency signal, a waveform equalization circuit that equalizes the waveform of the baseband signal, and a diversity combining circuit for spatial diversity combining, and the error correction processing The unit includes an OFDM having an error correction processing memory provided for error correction processing. A computer-readable recording medium recording a program for executing the OFDM demodulation method according to tone device,
The computer includes a first baseband signal output from one waveform equalization circuit of the plurality of demodulation units and a second baseband signal output from another waveform equalization circuit of the demodulation unit. Adjusting the timing between them by one error correction processing memory of the demodulation unit;
The first baseband signal whose timing with the second baseband signal is adjusted by one error correction processing memory of the demodulation unit and the second baseband signal are combined with another diversity combination of the demodulation unit. A computer-readable recording medium having recorded thereon a program for executing a procedure of synthesis by a circuit.

Images