JP2010081509A - Signal processor, signal processing method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact device by improving utilization efficiency of a memory. <P>SOLUTION: When an error detection part 32 for detecting an error of a carrier used in demodulating an OFDM (Orthogonal Frequency Division Multiplexing) signal executes a tracking operation for detecting only a phase error of the carrier after initial pull-in that detects both the phase error and a frequency error of the carrier, a sharing control part 41 releases a storage region of a memory 40 necessary for the initial pull-in, but unnecessary for tracking, for another process (for instance, a channel estimation process executed in an equalization part 39) that is not executed simultaneously with the process of the initial pull-in, and allows the storage region of the memory 40 to be shared by the tracking operation and the other process. This invention can be applied to, for instance, a device for demodulating an OFDM signal and the like. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a signal processing device, a signal processing method, and a program, and in particular, a signal processing device that enables, for example, a receiving device that receives an OFDM (Orthogonal Frequency Division Multiplexing) signal to be configured in a small size. , A signal processing method, and a program.

  For example, in a receiving apparatus that receives an OFDM signal, digital orthogonal demodulation of the OFDM signal is performed using the carrier of the OFDM signal.

  However, the carrier of the OFDM signal used for digital orthogonal demodulation in the receiving apparatus generally does not coincide with the carrier of the OFDM signal used in the transmitting apparatus that transmits the OFDM signal, and includes an error. That is, the frequency of the carrier of the OFDM signal used for digital quadrature demodulation is shifted from the center frequency of the OFDM signal (IF (Intermidiate Frequency) signal) received by the receiving apparatus.

  Therefore, in the receiving apparatus, error detection for detecting a carrier error of an OFDM signal used for digital quadrature demodulation and carrier error correction for correcting the carrier error are performed (see, for example, Patent Document 1).

  In addition, a receiving apparatus that receives an OFDM signal performs channel estimation processing, error correction processing, output processing, and the like.

  Here, in the channel estimation process, a transmission path characteristic that is a characteristic of a transmission path through which the OFDM signal is transmitted is estimated. In the error correction process, error correction of errors occurring on the transmission path is performed. In the output process, when a TS (Transport Stream) packet is included in the OFDM signal, a TS packet obtained after demodulation of the OFDM signal is output at a predetermined constant rate.

JP 2004-214960 Gazette

  For various types of processing such as carrier error detection processing, channel estimation processing, error correction processing, and output processing performed in the receiving device, a memory that stores data necessary for the processing is, for example, for each processing. And the processing is performed using the memory.

  As described above, when a memory for storing data necessary for the processing is provided for each process performed in the receiving apparatus, a large amount of memory (storage area) is required, and the receiving apparatus is increased in size.

  Among the processes performed in the receiving apparatus, there is a process (hereinafter also referred to as a temporary process) that is performed only temporarily. The memory (storage area) provided for temporary processing is used only while the temporary processing is being performed, and is not used while temporary processing is not being performed. From the point of view, it is not preferable.

  The present invention has been made in view of such a situation, and enables the apparatus to be configured in a small size.

  A signal processing apparatus or program according to one aspect of the present invention includes an error detection unit that detects a carrier error used when demodulating an OFDM (Orthogonal Frequency Division Multiplexing) signal, and a process that detects the carrier error. A storage unit for storing necessary data and a tracking operation for detecting only the phase error of the carrier after the error detection unit performs an initial pull-in operation for detecting both the phase error and the frequency error of the carrier. When the initial pull-in operation is performed, a storage area of the storage unit that is necessary for the initial pull-in operation process but is unnecessary for the tracking operation process is simultaneously performed with the initial pull-in operation process. To the other processing, and share the storage area of the storage means for the tracking operation processing and the other processing. Signal processing device and a shared control unit, or, as a signal processing apparatus, a program for causing a computer to function.

  A signal processing method according to one aspect of the present invention includes error detection means for detecting a carrier error used when demodulating an OFDM (Orthogonal Frequency Division Multiplexing) signal, and data necessary for the processing for detecting the carrier error. In the signal processing apparatus comprising the storage means for storing, the error detecting means performs an initial pull-in operation for detecting both the phase error and the frequency error of the carrier, and then detects only the phase error of the carrier. When performing an operation, after the initial pull-in operation is completed, the storage area of the storage unit that is necessary for the initial pull-in operation process and is unnecessary for the tracking operation process is defined as the initial pull-in process. Release to other processes that are not performed at the same time, and the storage area of the storage means for the tracking operation process and the other process A signal processing method comprising the steps of covalently.

  In one aspect as described above, the storage area of the storage means that is necessary for the process of the initial pull-in operation after the completion of the initial pull-in operation is unnecessary for the process of the tracking operation. The process is released to another process that is not performed at the same time as the process, and the storage area of the storage unit is shared by the process of the tracking operation and the other process.

  Note that the signal processing device may be an independent device or may be an internal block constituting one device.

  The program can be provided by being transmitted via a transmission medium or by being recorded on a recording medium.

  According to one aspect of the present invention, the device can be configured in a small size.

  <Overall configuration example of the receiving system>

  FIG. 1 is a diagram of a receiving system to which the present invention is applied (a system is a logical collection of a plurality of devices, regardless of whether each configuration device is in the same housing). The structural example of embodiment is shown.

  The receiving system of FIG. 1 can be applied to, for example, a TV (television receiver), a TV tuner, a recorder, or the like that receives an OFDM signal as a digital broadcast or the like.

  The receiving system can receive OFDM signals transmitted via terrestrial waves, satellite waves, and CATV (Cable Television) networks, or receive OFDM signals transmitted via networks such as the Internet. You can also

  In FIG. 1, the reception system includes an antenna 11, a demodulation processing unit 12, a decoder 16, and an output unit 17.

  The antenna 11 receives, for example, an OFDM signal transmitted from a transmission device (not shown) as digital broadcasting, and supplies an RF (Radio Frequency) signal of the OFDM signal obtained as a result to the demodulation processing unit 12.

  The demodulation processing unit 12 demodulates the OFDM signal (the RF signal) from the antenna 11 and supplies the TS packet obtained as a result to the decoder 16.

  That is, the demodulation processing unit 12 includes a demodulation unit 13, an error correction unit 14, and an output I / F (Interface).

  The demodulation unit 13 demodulates the OFDM signal supplied from the antenna 11 to the demodulation processing unit 12 and supplies the demodulated signal obtained as a result to the error correction unit 14.

  The error correction unit 14 performs error correction processing on the demodulated signal from the demodulation unit 13 and supplies the TS obtained as a result to the output I / F 15.

  Here, in the transmission device, for example, data such as an image or sound as a program is encoded by MPEG (Moving Picture Experts Group), and TS composed of TS packets including encoded data obtained as a result of the MPEG encoding. Is transmitted as an OFDM signal.

  Furthermore, in the transmission apparatus, as a countermeasure against errors occurring on the transmission path, the TS is encoded into a code such as an RS (Reed Solomon) code or an LDPC code, but the error correction unit 14 performs error correction processing. A process for decoding the code is performed.

  The output I / F 15 performs output processing for outputting TS packets constituting the TS from the error correction unit 14 to the outside at a predetermined constant rate. The TS packet output by the output I / F 15 by the output process is supplied to the decoder 16.

  The decoder 16 MPEG-decodes the encoded data included in the TS packet from the output I / F 15 and supplies image and audio data obtained as a result to the output unit 17.

  The output unit 17 includes, for example, a display, a speaker, and the like, displays an image corresponding to the image and audio data from the decoder 16, and outputs audio.

  <Configuration Example of Demodulator 13>

  FIG. 2 shows a configuration example of the demodulator 13 of FIG.

  In FIG. 2, a demodulator 13 includes a tuner 21, a BPF (band pass filter) 22, an A / D (Analog / Digital) converter 23, a clock generator 24, a DC (Direct Current) cancel unit 25, and a digital quadrature demodulator. 26, carrier error correction unit 27, FFT (Fast Fourier Transform) calculation unit 28, phase correction unit 29, timing synchronization unit 31, error detection unit 32, NCO (Numeric Control Oscillator) 37, frame synchronization unit 38, equalization unit 39 , A memory 40, a sharing control unit 41, and the like.

  The tuner 21 is supplied with the RF signal of the OFDM signal from the antenna 11.

  The tuner 21 includes a calculation unit 21A and a local oscillator 21B, and an RF signal from the antenna 11 is supplied to the calculation unit 21A.

  In the tuner 21, the local oscillator 21B oscillates a sine wave signal having a predetermined frequency and supplies the sine wave signal to the arithmetic unit 21A.

  Further, in the tuner 21, the arithmetic unit 21 </ b> A multiplies the RF signal from the antenna 11 by the signal from the local oscillator 21 </ b> B, thereby frequency-converting the RF signal into an IF (Intermidiate Frequency) signal and supplying it to the BPF 22. To do.

  The BPF 22 filters the IF signal from the tuner 21 and supplies it to the A / D converter 23.

  The A / D converter 23 A / D converts the IF signal from the BPF 22 in accordance with the sampling clock supplied from the clock generator 24 and supplies the IF signal of the digital signal obtained as a result to the DC cancel unit 25. .

  The clock generation unit 24 generates (generates) a sampling clock having a predetermined frequency and supplies the sampling clock to the A / D conversion unit 23. Further, the clock generation unit 24 generates a clock synchronized with the sampling clock, and supplies the clock to a necessary block configuring the demodulation unit 13.

  The DC cancellation unit 25 removes the DC component contained in the IF signal from the A / D conversion unit 23 and supplies it to the digital quadrature demodulation unit 26.

  The digital orthogonal demodulator 26 uses a carrier having a predetermined frequency (carrier frequency) (ideally, the same carrier as that used in the transmission apparatus) and a signal orthogonal to the carrier, and the DC cancellation unit 25. The IF signal is digitally quadrature demodulated, and the resulting baseband OFDM signal is output.

  Here, the OFDM signal output from the digital quadrature demodulator 26 has an IFFT (Inverse transmission symbol (data transmitted on one subcarrier) on the IQ constellation before the FFT operation is performed on the transmitter side. FFT) is a time domain signal immediately after computation, and is also referred to as an OFDM time domain signal hereinafter.

  The OFDM time domain signal is a complex signal represented by a complex number including a real axis component (I (In Phase) component) and an imaginary axis component (Q (Quadrature Phase) component).

  The OFDM time domain signal is supplied from the digital quadrature demodulation unit 26 to the carrier error correction unit 27.

  The carrier error correction unit 27 corrects a carrier error included in the OFDM time domain signal by multiplying (complex multiplication) the OFDM time domain signal from the digital quadrature demodulation unit 26 and the correction signal supplied from the NCO 37. .

  Here, the carrier error refers to an OFDM time domain signal obtained as a result of digital quadrature demodulation due to an error of the carrier used for digital quadrature demodulation by the digital quadrature demodulation unit 26 with respect to the center frequency of the IF signal of the OFDM signal. The resulting error relative to the original OFDM time domain signal.

  The OFDM time domain signal whose carrier error has been corrected by the carrier error correction unit 27 is supplied to the FFT calculation unit 28 and the guard correlation detection unit 33A included in the time domain carrier phase error detection unit 33 constituting the error detection unit 32. Is done.

  In accordance with the symbol synchronization signal supplied from the timing synchronization unit 31, the FFT operation unit 28 extracts the OFDM time domain signal (sample value) of the FFT period from the OFDM time domain signal from the carrier error correction unit 27, and outputs the DFT ( Performs FFT calculation, which is a high-speed calculation of Discrete Fourier Transform.

  That is, the FFT calculation unit 28 performs FFT calculation on a transmission symbol having an effective symbol length obtained by removing a guard interval (the transmission symbol) from a transmission symbol constituting one OFDM symbol included in the OFDM time domain signal. Is extracted as an OFDM time domain signal of the FFT interval. Then, the FFT operation unit 28 performs an FFT operation on an OFDM time domain signal (a transmission symbol having an effective symbol length (hereinafter also referred to as an effective symbol)) in the FFT interval.

  By the FFT calculation of the OFDM time domain signal in the FFT calculation unit 28, the data transmitted on the subcarrier, that is, the OFDM signal representing the transmission symbol on the IQ constellation is obtained.

  Note that the OFDM signal obtained by the FFT calculation of the OFDM time domain signal is a frequency domain signal, and is hereinafter also referred to as an OFDM frequency domain signal.

  The FFT operation unit 28 supplies the OFDM frequency domain signal obtained by the FFT operation to the phase correction unit 29.

  The phase correction unit 29 corrects the phase rotation component of the OFDM frequency domain signal from the FFT calculation unit 28 in accordance with the phase correction signal supplied from the timing synchronization unit 31, and the error detection unit 32, the frame synchronization unit 38, and the like. To the conversion unit 39.

  Here, the boundary of the FFT section that is the object of the FFT operation by the FFT operation unit 28 is deviated from the actual boundary of the OFDM symbol of the OFDM time domain signal. Since the phase of the OFDM frequency domain signal obtained by the FFT calculation unit 28 rotates by the phase rotation component as an angle corresponding to the above-described boundary shift, the phase correction unit 29 performs correction to cancel the phase rotation component. .

  In other words, the phase correction unit 29 multiplies (complex multiplication) the OFDM frequency domain signal from the FFT calculation unit 28 and the complex signal as the phase correction signal from the timing synchronization unit 31 to obtain the phase of the OFDM frequency domain signal. Are rotated in the opposite direction by the phase rotation component. As a result, the phase correction unit 29 performs phase correction to remove (cancel) the phase rotation component of the OFDM frequency domain signal.

  The timing synchronization unit 31 performs processing such as filtering of a peak timing signal representing a timing at which a guard correlation value, which will be described later, is supplied, which is supplied from a guard correlation detection unit 33A included in the time domain carrier phase error detection unit 33. Further, the timing synchronization unit 31 estimates the position of the OFDM symbol boundary (boundary position) based on the peak timing signal after processing such as filtering, and performs an FFT operation using the signal representing the boundary position as a symbol synchronization signal. Supplied to the unit 28.

  The timing synchronization unit 31 also generates a phase rotation component generated in accordance with a shift between the OFDM symbol boundary position estimated based on the peak timing signal and the FFT interval boundary position where the FFT calculation unit 28 performs the FFT calculation. Is calculated. The timing synchronization unit 31 generates a phase correction signal for removing the phase rotation component and supplies the phase correction signal to the phase correction unit 29.

  The error detection unit 32 uses the OFDM time domain signal supplied from the carrier error correction unit 27 and the OFDM frequency domain signal supplied from the phase correction unit 29 to perform carrier orthogonal demodulation on the OFDM signal. Error (carrier error) is detected. Further, the error detection unit 32 supplies a carrier error signal representing a carrier error to the NCO 37.

  That is, the error detection unit 32 includes a time domain carrier phase error detection unit 33, a frequency domain carrier phase error detection unit 34, a frequency domain carrier frequency error detection unit 35, and an addition unit 36.

  The time domain carrier phase error detection unit 33 includes a guard correlation detection unit 33A, and the guard correlation detection unit 33A obtains a guard correlation described later from the OFDM time domain signal from the carrier error correction unit 27. Further, the time-domain carrier phase error detection unit 33 uses the guard correlation value obtained by the guard correlation detection unit 33A to perform carrier orthogonal frequency shift amount (carrier frequency used for digital orthogonal demodulation and digital orthogonal demodulation). The carrier phase error, which is a narrowband component, of the amount of deviation from the center frequency of the OFDM signal to be detected) is detected. Then, the time domain carrier phase error detection unit 33 supplies the carrier phase error to the addition unit 36.

  Here, the carrier phase error, which is a narrow band component of the carrier frequency shift amount, is narrower than the range of ± 1/2 of the subcarrier frequency interval of the carrier frequency shift amount. Represents a range value.

  The guard correlation detection unit 33A obtains the autocorrelation of the OFDM time domain signal from the carrier error correction unit 27.

  That is, the guard correlation detection unit 33A has, for example, the length of the guard interval of the product of the OFDM time domain signal from the carrier error correction unit 27 and the delayed signal obtained by delaying the OFDM time domain signal by the effective symbol length. The average value (or moving average value) for the corresponding time is obtained as the autocorrelation of the OFDM time domain signal with the lag being an effective symbol length.

  Here, the autocorrelation (hereinafter also referred to as a guard correlation value) of the OFDM time domain signal obtained as described above is a signal having a peak value at the boundary of OFDM symbols.

  The phase of the guard correlation value of the peak value becomes 0 if the frequency of the carrier used for digital quadrature demodulation and the center frequency of the OFDM signal demodulated digitally match completely. However, when the carrier frequency used for digital quadrature demodulation deviates from the center frequency of the OFDM signal demodulated by digital quadrature demodulation, the phase of the guard correlation value of the peak value rotates by the amount of the deviation.

  Therefore, the phase of the guard correlation value of the peak value represents the shift amount (shift amount of the carrier frequency) between the carrier frequency used for digital quadrature demodulation and the center frequency of the OFDM signal subjected to digital quadrature demodulation.

  Since the phase of the guard correlation value of the peak value makes one rotation at the subcarrier frequency interval of the OFDM signal, the carrier frequency shift amount is narrower than the range of ± 1/2 of the subcarrier frequency interval. Represents a range value.

  The guard correlation detection unit 33A detects the peak value of the guard correlation value of the OFDM time domain signal, and supplies a peak timing signal indicating the timing to the timing synchronization unit 31.

  The frequency domain carrier phase error detector 34 uses a pilot signal subcarrier (a pilot signal transmission symbol included in an OFDM symbol) included in an OFDM frequency domain signal supplied from the phase corrector 29 to the error detector 32. The carrier phase error is detected. Then, the frequency domain carrier phase error detection unit 34 supplies the carrier phase error to the addition unit 36.

  Here, in a transmission apparatus that transmits an OFDM signal, known signals with predetermined amplitudes and phases are discretely inserted into transmission symbols (OFDM signal subcarriers) constituting the OFDM symbol. This known signal is a pilot signal.

  The frequency domain carrier frequency error detection unit 35 uses the OFDM frequency domain signal supplied from the phase correction unit 29 to the error detection unit 32 to calculate a carrier frequency error that is a broadband component of the carrier frequency deviation amount. To detect. Then, the frequency band carrier frequency error detection unit 35 supplies the carrier frequency error to the addition unit 36.

  Here, the carrier frequency error, which is a broadband component of the carrier frequency shift amount, represents the carrier frequency shift amount with the accuracy of the subcarrier frequency interval. Note that the value of the carrier frequency deviation amount, which is finer than the accuracy of the subcarrier frequency interval, is represented by the carrier phase error described above.

  The adder 36 includes a carrier phase error from the time domain carrier phase error detector 33, a carrier phase error from the frequency domain carrier phase error detector 34, and a carrier frequency error from the frequency domain carrier frequency error detector 35. Are added to obtain a carrier error signal representing the amount of carrier frequency deviation (total deviation). Then, the adder 36 supplies the carrier error to the NCO 37.

  The NCO 37 generates (oscillates) a signal whose frequency changes according to the carrier error signal from the adder 36 as a correction signal, and supplies the signal to the carrier error corrector 27.

  That is, for example, when the carrier error from the adder 36 is a positive value (when the carrier frequency is higher than the center frequency of the OFDM signal), the NCO 37 has a lower frequency than the current correction signal. Generate a correction signal (decrease the oscillation frequency). Further, for example, when the carrier error from the adding unit 36 is a negative value (when the carrier frequency is lower than the center frequency of the OFDM signal), the NCO 37 has a higher frequency than the current correction signal. Generate a correction signal (increase the oscillation frequency).

  The frame synchronization unit 38 detects a synchronization word inserted at a predetermined position of the OFDM transmission frame from the OFDM frequency domain signal supplied from the phase correction unit 29, and starts the OFDM transmission frame based on the synchronization word Detect the timing. Further, the frame synchronization unit 38 specifies the symbol numbers of the OFDM symbols constituting the OFDM transmission frame based on the start timing of the OFDM transmission frame, and supplies them to the equalization unit 39.

  Here, in digital broadcasting, a unit called an OFDM transmission frame is defined, and this OFDM transmission frame is composed of a plurality of OFDM symbols. For example, in the ISDB-T standard, one OFDM transmission frame is composed of 204 OFDM symbols. A position where a pilot signal is inserted is determined in advance in units of this OFDM transmission frame.

  The equalization unit 39 performs so-called equalization processing on the OFDM frequency domain signal supplied from the phase correction unit 29 using the channel characteristics estimated based on the symbol number from the frame synchronization unit 38.

  That is, the equalization unit 39 detects a pilot signal called an SP (Scattered Pilots) signal inserted in the OFDM frequency domain signal based on the symbol number supplied from the frame synchronization unit 38. Further, the equalization unit 38 performs channel estimation processing for estimating transmission path characteristics that are frequency characteristics of the transmission path on which the OFDM signal has been transmitted (transmitted) from the pilot signal. Then, the equalization unit 38 divides the OFDM frequency domain signal supplied from the phase correction unit 29 by the estimated value of the transmission path characteristic, thereby correcting distortion that the OFDM signal has received on the transmission path. Perform as an equalization process. The OFDM frequency domain signal after distortion correction is supplied from the equalization unit 39 to the error correction unit 14 (FIG. 1).

  The memory 40 is composed of, for example, a RAM or the like, and stores data necessary for processing in which the error detection unit 32 detects a carrier error (hereinafter also referred to as carrier error detection processing). Further, as described later, the memory 40 appropriately stores data necessary for other processing in accordance with the control of the sharing control unit 41.

  The sharing control unit 41 performs sharing control in which the storage area of the memory 40 is shared by the carrier error detection processing by the error detection unit 32 and other processing such as channel estimation processing performed by the equalization unit 39, for example.

  Here, the error detection unit 32 performs the initial pull-in operation for detecting both the carrier phase error and the frequency error (carrier phase error and carrier frequency error) as the carrier error detection process, and then performs only the carrier phase error. A tracking operation to detect is performed.

  That is, when the receiving system of FIG. 1 is a device that is used in a fixed manner, such as a TV (a device that is not a device that is used while moving (a device that performs fixed reception), such as a mobile terminal). There is little variation in the reception environment. For this reason, the error detection unit 32 does not always have to perform the initial pull-in operation for detecting both the carrier phase error and the carrier frequency error. Therefore, after performing the initial pull-in operation, only the carrier phase error is detected. Perform tracking operation.

  On the other hand, as described above, since the memory 40 stores data necessary for the carrier error detection process, the memory 40 has a storage capacity that can store at least data necessary for the initial pull-in operation.

  In other words, since both the carrier phase error and the carrier frequency error are detected in the initial pull-in operation, more data is required for processing than the tracking operation in which only the carrier phase error is detected. Therefore, the memory 40 has a storage capacity that can store at least data necessary for the initial pull-in operation.

  Therefore, after the completion of the initial pull-in operation, a memory area is generated in the memory 40 that is necessary (but necessary) for the initial pull-in operation, but is unnecessary for the tracking operation. That is, an empty area (hereinafter also referred to as a non-use area) is generated in the memory 40 as a storage area that is not used during the tracking operation.

  The sharing control unit 41 releases the unused area to other processing such as channel estimation processing that is not performed simultaneously with the initial pull-in operation processing, and stores the memory 40 in the tracking operation processing and other processing. The use efficiency of the memory 40 is improved by sharing the area.

  As other processing that is not performed at the same time as the initial pull-in operation, carrier error correction by the carrier error correction unit 27 functions (to some extent), and the frame synchronization unit 38 detects the start timing of the OFDM transmission frame. There are processes that can only be performed after being done.

  Specifically, as other processing that is not performed simultaneously with the initial pull-in operation processing, in addition to the above-described channel estimation processing, error correction processing performed by the error correction unit 14 (FIG. 1), output I / F 15 ( For example, the output processing performed in FIG.

  Here, the sharing of the storage area of the memory 40 with the processing of the tracking operation is performed with one other process among a plurality of other processes such as a channel estimation process, an error correction process, and an output process. In addition, if the capacity of the memory 40 permits, it can be performed between two or more other processes.

  In addition, when the reception environment of the reception system of FIG. 1 is stable, it is not necessary to perform the tracking operation process constantly (for each OFDM symbol), but intermittently (periodically) (a plurality of OFDM symbols). For each one of the OFDM symbols).

  When the tracking operation process is performed intermittently, the sharing control unit 41 stores the storage area of the memory 40 required for the tracking operation process (for the tracking operation process) when the tracking operation process is not performed. The storage area used (hereinafter also referred to as tracking storage area) can be further freed for other processing.

  In this case, the tracking storage area is shared in a time division manner between the tracking operation process and other processes.

  The other process for releasing the tracking storage area and the other process for releasing the unused area may be the same process or different processes.

  Also, when other processing for releasing the tracking storage area is different from other processing for releasing the unused area, the other processes for releasing the unused area have higher priority. Other processes that employ processing (for example, processing that must always be performed after the carrier error correction by the carrier error correction unit 27 functions) and release the tracking storage area include low-priority processing (for example, For example, a process that may be performed intermittently or temporarily).

  Here, in FIG. 2, sharing of the storage area of the memory 40 with the tracking operation process is performed between the channel estimation process performed by the equalization unit 39.

  In FIG. 2, the sharing of the storage area of the memory 40 with the tracking operation process is used, for example, to extract the OFDM time domain signal of the FFT section to be subjected to the FFT calculation by the FFT calculation unit 28. It is possible to perform the processing between the generation of the symbol synchronization signal to be generated (estimation of the boundary position of the OFDM symbol) and the like.

  <Demodulation Operation of Demodulator 13>

  With reference to FIG. 3, the demodulation operation by the demodulator 13 of FIG. 2 will be described.

  For example, when the power supply of the receiving system in FIG. 1 is turned on, in step S11, a built-in AGC (Automatic Gain Control) circuit (not shown) starts operation in a necessary block of the demodulator 13, and AGC is started. When the circuit is in a so-called locked state, the process proceeds to step S12.

  In step S12, demodulation parameters required for demodulation of the OFDM signal, such as MODE and GI (Guard interval), are estimated in the necessary blocks of the demodulator 13, and when the estimation is completed, the process proceeds to step S12. Proceed to S13.

  In step S13, carrier error correction in the initial pull-in mode is performed.

  That is, the OFDM signal received by the antenna 11 is supplied to the digital orthogonal demodulation unit 26 via the tuner 21, BPF 22, A / D conversion unit 23, and DC cancellation unit 25.

  The digital quadrature demodulating unit 26 performs digital quadrature demodulation on the OFDM signal from the DC canceling unit 25 using a carrier having a predetermined frequency, and supplies the baseband OFDM time domain signal obtained as a result to the carrier error correcting unit 27. To do.

  The carrier error correction unit 27 corrects the carrier error of the OFDM time domain signal from the digital quadrature demodulation unit 26 according to the correction signal supplied from the NCO 37, and the resulting OFDM time domain signal is converted into an FFT calculation unit 28, This is supplied to the guard correlation detection unit 33A of the time domain carrier phase error detection unit 33.

  The guard correlation detection unit 33A obtains the above-described guard correlation value from the OFDM time domain signal from the carrier error correction unit 27. Furthermore, the guard correlation detection unit 33A obtains a peak value of the guard correlation value and supplies a peak timing signal indicating the timing of the peak value to the timing synchronization unit 31.

  The timing synchronization unit 31 estimates the OFDM symbol boundary position based on the peak timing signal from the guard correlation detection unit 33A, and supplies a signal representing the boundary position to the FFT calculation unit 28 as a symbol synchronization signal.

  The timing synchronization unit 31 also generates a phase rotation component generated in accordance with a shift between the OFDM symbol boundary position estimated based on the peak timing signal and the FFT section boundary position where the FFT calculation unit 28 performs the FFT calculation. calculate. Further, the timing synchronization unit 31 generates a phase correction signal for removing the phase rotation component and supplies the phase correction signal to the phase correction unit 29.

  On the other hand, the FFT calculation unit 28 extracts the OFDM time domain signal of the FFT section from the OFDM time domain signal from the carrier error correction unit 27 according to the symbol synchronization signal supplied from the timing synchronization unit 31, and the OFDM time domain signal Perform FFT calculation. Then, the FFT calculation unit 28 supplies the OFDM frequency domain signal obtained by the FFT calculation to the phase correction unit 29.

  The phase correction unit 29 corrects the phase rotation component generated by the phase rotation of the OFDM frequency domain signal from the FFT calculation unit 28 in accordance with the phase correction signal supplied from the timing synchronization unit 31. The corrected OFDM frequency domain signal is supplied to the frequency domain carrier phase error detection unit 34, the frequency domain carrier frequency error detection unit 35, the frame synchronization unit 38, and the equalization unit 39 of the error detection unit 32. Is done.

  The time domain carrier phase error detection unit 33 of the error detection unit 32 detects the carrier phase error using the guard correlation value obtained by the guard correlation detection unit 33 </ b> A and supplies the carrier phase error to the addition unit 36.

  The frequency domain carrier frequency error detection unit 35 of the error detection unit 32 detects the carrier frequency error using the OFDM frequency domain signal from the phase correction unit 29 and supplies the carrier frequency error to the addition unit 36.

  Here, the carrier phase error detected by the time domain carrier phase error detector 33 is hereinafter also referred to as a time domain carrier phase error. In addition, the carrier frequency error detected by the frequency band carrier frequency error detection unit 35 is hereinafter also referred to as a frequency band carrier frequency error.

  The adder 36 supplies a carrier error signal representing the time domain carrier phase error from the time domain carrier phase error detector 33 to the NCO 37. Further, the adder 36 supplies the NCO 37 with a carrier error signal representing the frequency domain carrier frequency error from the frequency domain carrier frequency error detector 35.

  The NCO 37 generates a correction signal according to the carrier error signal from the adder 36 and supplies it to the carrier error corrector 27.

  The carrier error correction unit 27 corrects the OFDM time domain signal supplied from the digital quadrature demodulation unit 26 according to the correction signal supplied from the NCO 37, thereby obtaining an OFDM time domain signal in which the carrier error is corrected, This is supplied to the FFT calculation unit 28 and the guard correlation detection unit 33A.

  As described above, in the carrier error correction in the initial pull-in mode, the error detection unit 32 detects the time domain carrier phase error in the time domain carrier phase error detection unit 33, and further the frequency domain carrier frequency error detection unit 35. The initial pull-in operation for detecting the frequency domain carrier frequency error is performed.

  Then, the carrier error correction unit 27 corrects the carrier error of the OFDM time domain signal based on the time domain carrier phase error and the frequency domain carrier frequency error.

  In step S13, as described above, when carrier error correction is performed in the initial pull-in mode, the error detection unit 32 ends the initial pull-in operation, and the process proceeds to step S14.

  In step S14, carrier error correction in the tracking mode is started.

  That is, in step S 14, the frequency domain carrier phase error detection unit 34 of the error detection unit 32 detects the carrier phase error using the OFDM frequency domain signal from the phase correction unit 29 and supplies it to the addition unit 36.

  Here, the carrier phase error detected by the frequency domain carrier phase error detector 34 is hereinafter also referred to as a frequency domain carrier phase error.

  The adder 36 supplies a carrier error signal representing the frequency domain carrier phase error from the frequency domain carrier phase error detector 34 to the NCO 37. The NCO 37 receives a correction signal in accordance with the carrier error signal from the adder 36. It is generated and supplied to the carrier error correction unit 27.

  The carrier error correction unit 27 corrects the OFDM time domain signal supplied from the digital quadrature demodulation unit 26 according to the correction signal supplied from the NCO 37, thereby obtaining an OFDM time domain signal in which the carrier error is corrected, This is supplied to the FFT calculation unit 28 and the guard correlation detection unit 33A.

  As described above, in the carrier error correction in the tracking mode, the error detection unit 32 performs the tracking operation process for detecting the frequency domain carrier phase error in the frequency domain carrier phase error detection unit 34.

  Then, the carrier error correction unit 27 corrects the carrier error of the OFDM time domain signal based only on the frequency domain carrier phase error.

  When the carrier error correction in the tracking mode as described above is started in step S14 (when the carrier error correction in the initial pull-in mode in step S13 is completed), in step S15, the equalization unit 39 performs channel estimation. Start processing.

  That is, the frame synchronization unit 38 specifies the symbol number of the OFDM symbol constituting the OFDM transmission frame from the OFDM frequency domain signal supplied from the phase correction unit 29 and supplies it to the equalization unit 39.

  The equalization unit 39 detects a pilot signal from the OFDM frequency domain signal from the phase correction unit 29 based on the symbol number supplied from the frame synchronization unit 38, and estimates channel characteristics from the pilot signal. I do.

  When the equalizer 39 starts the channel estimation process, the process proceeds from step S15 to step S16, and the equalizer 39 performs an equalization process for equalizing the OFDM frequency domain signal supplied from the phase correction unit 29. Start. That is, the equalization unit 39 divides the OFDM frequency domain signal supplied from the phase correction unit 29 by the estimated value of the transmission path characteristic, thereby starting distortion correction for correcting the distortion received by the OFDM signal on the transmission path. Then, the OFDM frequency domain signal after distortion correction is supplied to the error correction unit 14 (FIG. 1).

  In FIG. 3, in step S14, the frequency domain carrier phase error detection unit 34 performs the tracking operation for detecting the (frequency domain) carrier phase error. However, in step S14, the frequency domain carrier phase error is detected. Instead of the detection unit 34, the time domain carrier phase error detection unit 33 can perform a tracking operation process for detecting a (time domain) carrier phase error.

  <Share Control Operation of Demodulator 13>

  With reference to FIG. 4, the operation of sharing control of the memory 40 by the demodulator 13 of FIG. 2 will be described.

  For example, when the power supply of the receiving system in FIG. 1 is turned on, in step S21, the sharing control unit 41 performs carrier error detection processing (initial pull-in operation of the error detection unit 32) for carrier error correction in the initial pull-in mode. The storage area of the memory 40 necessary for the process is allocated.

  When the carrier error correction in the initial pull-in mode is completed, in step S22, the sharing control unit 41 releases the storage area of the memory 40 allocated for the initial pull-in operation process of the error detection unit 32 (assignment process). The process proceeds to step S23.

  In step S23, the sharing control unit 41 allocates a storage area necessary for the carrier error detection processing (the tracking operation processing of the error detection unit 32) for carrier error correction in the tracking mode, and performs processing. Advances to step S24.

  In step S <b> 24, the sharing control unit 41 starts sharing control in which the storage area of the memory 40 is shared between the tracking operation processing and other processing such as channel estimation processing performed by the equalization unit 39, for example.

  That is, the shared control unit 41 is used in the initial pull-in operation, but the unused area of the memory 40 that is a storage area that is not used in the tracking operation is used as another process, for example, a channel performed by the equalization unit 39 Release to estimation processing. Then, the sharing control unit 41 allocates the storage area of the memory 40 necessary for the channel estimation process to the channel estimation process, and thereby the storage area of the memory 40 is used for the tracking operation process and the channel estimation process. Share.

  Therefore, since it is not necessary to provide the equalizer 39 with a memory for storing data necessary for the channel estimation process, the demodulator 13 (and thus the demodulator 12 and the reception system in FIG. 1) is configured to be small. be able to.

  Further, the memory 40 needs to be a memory having a capacity capable of storing all the data necessary for the initial pull-in operation process, the data necessary for the tracking operation process, and the data necessary for the channel estimation process. There is no.

  In other words, the memory 40 has the larger data amount of the data required for the initial pull-in operation or the total of the data required for the tracking operation and the data required for the channel estimation process. It is possible to employ a memory having a capacity capable of storing the data.

  Therefore, the demodulator 13 is compared with the case where a memory for separately storing data necessary for the initial pull-in operation, data necessary for the tracking operation, and data necessary for the channel estimation process is provided. Can be made compact.

  Note that data necessary for the channel estimation process, that is, data stored in the memory 40 in the channel estimation process includes an estimated value of a transmission path characteristic at a position of a transmission symbol (subcarrier) of a pilot signal.

  That is, in the channel estimation process, first, an estimated value of the channel characteristic of the position of a transmission symbol of a pilot signal that is a known signal is obtained, and then the position of another transmission symbol is obtained by interpolation or the like using the estimated value. The transmission path characteristics are estimated. In this case, in order to use for filtering for interpolation, it is necessary to hold the estimated value of the transmission path characteristic at the position of the transmission symbol of the pilot signal, and the memory 40 is used for this holding.

  <Detailed examples of carrier error detection and correction>

  With reference to FIG. 5, the details of the carrier error detection performed by the error detection unit 32 (FIG. 2) and the carrier error correction performed by the carrier error correction unit 27 (FIG. 2) will be described.

  FIG. 5 shows the OFDM time domain signal with the horizontal axis as frequency f.

  That is, FIG. 5A shows an ideal OFDM time domain signal.

  An OFDM time domain signal includes a plurality of subcarriers c # 0, c # 1, c # 2, c # 3, c # 4, c # 5, c # 6, c # 7,. In such an OFDM time domain signal, the frequency (position) of each subcarrier c # i matches a frequency (hereinafter also referred to as a set frequency) f # i determined in advance for the subcarrier c # i.

  FIG. 5B shows an example of an actual OFDM time domain signal supplied from the digital quadrature demodulation unit 26 of FIG. 2 to the carrier error correction unit 27.

  In an actual OFDM time domain signal, the frequency of each subcarrier c # i is shifted from the set frequency f # i.

  Here, the frequency shift amount of the subcarrier c # i from the set frequency f # i is the above-described carrier frequency shift amount.

  The error detector 32 detects the carrier frequency shift amount as a carrier error.

  In the carrier error correction in the initial pull-in mode, first, based on the time domain carrier phase error detected by the time domain carrier phase error detector 33 (FIG. 2), the frequency of the subcarrier c # i is closer to the set frequency. The OFDM time domain signal is corrected so as to coincide with f # i ′.

  FIG. 5C shows the corrected OFDM time domain signal obtained by correcting the OFDM time domain signal so that the frequency of the subcarrier c # i matches the set frequency f # i ′ closer to the current frequency. ing.

  In FIG. 5C, the OFDM time domain signal is corrected so that the frequency of the subcarrier c # i matches the other set frequency f # i + 2 that is not the set frequency f # i for the subcarrier c # i. ing.

  After the OFDM time domain signal is corrected so that the frequency of the subcarrier c # i matches the closer set frequency f # i ′, the subcarrier c # The OFDM time domain signal is corrected so that the frequency of i matches the set frequency f # i for the subcarrier c # i.

  That is, after the OFDM time domain signal is corrected so that the frequency of the subcarrier c # i matches the closer set frequency f # i ′, the frequency domain carrier frequency error detection unit 35 (FIG. 2) Is corrected so that the frequency of the subcarrier c # i matches the set frequency f # i for the subcarrier c # i.

  FIG. 5D shows the corrected OFDM time domain signal obtained by correcting the OFDM time domain signal so that the frequency of subcarrier c # i matches the set frequency f # i for subcarrier c # i. Yes.

  When the reception environment is stable, after the carrier error correction in the initial pull-in mode as described above, the frequency of the subcarrier c # i is the set frequency f for the subcarrier c # i. From #i, due to the temperature characteristics of each block constituting the demodulator 13, etc., there is only a slight deviation.

  That is, after the carrier error correction in the initial pull-in mode, the reception environment may be greatly deteriorated, for example, the S / N (Signal to Noise ratio) of the OFDM signal suddenly decreases. Otherwise, the frequency of the subcarrier c # i does not vary so much from the set frequency f # i for the subcarrier c # i (for example, it does not vary as much as the frequency interval of the subcarriers).

  Therefore, after the carrier error correction in the initial pull-in mode is performed, the carrier error correction in the tracking mode is performed.

  That is, FIG. 5E shows OFDM in which the frequency of the subcarrier c # i is slightly shifted from the set frequency f # i for the subcarrier c # i after the carrier error correction in the initial pull-in mode is performed. A time domain signal is shown.

  In the carrier error correction in the tracking mode, for example, the subcarrier c # i slightly deviated from the set frequency f # i based on the frequency domain carrier phase error detected by the frequency domain carrier phase error detector 34 (FIG. 2). The OFDM time domain signal is corrected so that the frequency of the frequency coincides with the set frequency f # i.

  <Description of Detection of Time Domain Carrier Phase Error by Time Domain Carrier Phase Error Detection Unit 33>

  A method of detecting the time domain carrier phase error by the time domain carrier phase error detection unit 33 of FIG. 2 will be described with reference to FIGS.

  In the time domain carrier phase error detection unit 33, the guard correlation detection unit 33A calculates a guard correlation value, and cumulatively adds the guard correlation value for a plurality of OFDM symbol sections. Further, the time domain carrier phase error detection unit 33 detects the peak (value) of the cumulative addition value of the guard correlation value, and based on the phase component of the guard correlation value at the timing of the peak of the cumulative addition value of the guard correlation value, A carrier phase error (time domain carrier phase error) is detected.

  FIG. 6 shows an OFDM signal in the time domain.

  An OFDM signal is a series of OFDM symbols, and an OFDM symbol is a valid symbol that is a signal interval in which IFFT is performed during modulation, and a waveform in the latter half of the valid symbol is copied as it is to the beginning of the valid symbol. Guard interval.

  The effective symbol length of the OFDM symbols is called effective symbol length Tu [seconds].

  Assuming that an OFDM signal (OFDM time domain signal) that does not include a carrier error is represented as r (t) (t represents a time (time) based on the timing of the beginning of an effective symbol of an OFDM symbol). ), An OFDM signal s () including a certain carrier error Δf (the amount of deviation between the frequency of the subcarrier c # i and the set frequency f # i for the subcarrier c # i shown in FIGS. 5B and 5E). t) is expressed by the following equation.

s (t) = r (t) e ^j2πΔft
... (1)

  Note that e is the Napier's constant, and j is an imaginary unit.

  On the other hand, in the OFDM symbol of the OFDM signal r (t) that does not include a carrier error, as described above, a partial copy of the latter half of the effective symbol is a guard interval.

  That is, if the guard interval length (guard interval length) of OFDM symbols is expressed as Tg [seconds], the last OFDM symbol of the OFDM signal r (t) that does not include a carrier error is the last effective symbol. The length Tg and the guard interval coincide with each other. For example, in FIG. 6, the OFDM signal r (t) from time t = -Tg to time t = 0 and the OFDM signal (guard interval) from time t = Tu-Tg to time t = Tu match. .

  Therefore, the OFDM signal r (t) that does not include a carrier error satisfies the following expression for the portion of the OFDM symbol effective symbol Tg from the end, that is, for the time t that satisfies the expression Tu-Tg ≦ t ≦ Tu. .

r (t-Tu) = r (t) where Tu-Tg ≦ t ≦ Tu
... (2)

  Note that the length of the OFDM symbol is represented by Tg + Tu.

  As described above, the time domain carrier phase error detection unit 33 obtains a guard correlation value by the guard correlation detection unit 33A, and cumulatively adds the guard correlation value for a plurality of OFDM symbol sections.

  Here, with reference to FIG. 7, the guard correlation value calculated | required by the guard correlation detection part 33A is demonstrated.

  The guard correlation detection unit 33A obtains, as a guard correlation value, an autocorrelation having an effective symbol length Tu of a lag of an OFDM time domain signal corresponding to the guard interval length Tg. The guard correlation value is an average (or moving average) of the product of the OFDM time-domain signal and a delayed signal obtained by delaying the OFDM time-domain signal by the effective symbol length Tu by the guard interval length Tg. Can be obtained.

  FIG. 7A shows an OFDM signal s (t) including a carrier error Δf and a delayed signal s (t-Tu) obtained by delaying the OFDM signal s (t) by an effective symbol length Tu.

A multiplication value s (t) s ^* (t-Tu) of the OFDM signal s (t) and the delayed signal s (t-Tu) (a complex conjugate thereof) is expressed by the following equation from the equation (1). . The superscript asterisk (*) represents a complex conjugate.

s (t) s ^* (t-Tu) = r (t) e ^j2πΔft r (t-Tu) e ^{-j2πΔf (t-Tu)}
= r (t) r (t-Tu) e ^j2πΔfTu
... (3)

However, for the time t satisfying the expression Tu−Tg ≦ t ≦ Tu, the multiplication value s (t) s ^* (t−Tu) in the expression (3) is expressed by the following expression from the expression (2).

s (t) s ^* (t-Tu) = | r (t) | ² e ^j2πΔfTu
... (4)

Furthermore, for the time t satisfying the expression Tu-Tg ≦ t ≦ Tu, the argument Arg [s (t) s ^* (t-Tu)] of the multiplication value s (t) s ^* (t-Tu) is From (4), it is expressed by the following equation.

Arg [s (t) s ^* (t-Tu)] = Arg [| r (t) | ² e ^j2πΔfTu ]
= 2πΔfTu
... (5)

  Since the declination can be obtained in the range of −π to + π, according to the equation (5), the range satisfying the equation −π ≦ 2πΔfTu <+ π, that is, the equation −1 / (2Tu) ≦ Δf < The carrier error Δf in the range satisfying + 1 / (2Tu) can be detected.

  However, in order to detect the carrier error Δf based on the equation (5), it is necessary to recognize the timing of the time t that satisfies the equation Tu−Tg ≦ t ≦ Tu.

Therefore, the time domain carrier phase error detection unit 33, during the initial pull-in operation, calculates the average value of the multiplication value s (t) s ^* (t-Tu) corresponding to the guard interval length Tg (from the current time t to the guard interval length Tg). An OFDM signal for one OFDM symbol, that is, a length Tg + Tu (hereinafter referred to as an OFDM symbol length Tg + Tu), from the time t-Tg that is traced back to the current time t. (Also referred to as OFDM signal) at each time t.

Here, FIG. 7B shows a vector as the multiplication value s (t) s ^* (t-Tu).

  Now, focusing on one OFDM symbol from time t = -Tg to time t = Tu, the interval from time t = -Tg to time t = 0 is the guard interval, and from time t = 0 The interval up to time t = Tu is the effective symbol interval. A section from time t = Tu-Tg to time t = Tu is a guard interval copy source section (also referred to as a copy source section).

  In one OFDM symbol from time t = -Tg to time t = Tu, a section from time t = -Tg at the beginning of the OFDM symbol to time t = Tu-Tg at which the copy source section starts (FIG. 7B In the section A), there is no correlation between the OFDM signal s (t) and the delayed signal s (t-Tu) obtained by delaying the OFDM signal s (t) by the effective symbol length Tu.

Therefore, a vector as a multiplication value s (t) s ^* (t-Tu) at each time t in the section A from time t = -Tg to time t = Tu-Tg is a vector directed in various directions. .

  On the other hand, in the copy source section (section B in FIG. 7B) from time t = Tu-Tg to time t = Tu, the OFDM signal s (t) and the OFDM signal s (t) are delayed by the effective symbol length Tu. Since there is a match with the delayed signal s (t-Tu) if there is no carrier error Δf, there is a strong correlation between the OFDM signal s (t) and the delayed signal s (t-Tu).

That is, in the section B from time t = Tu-Tg to time t = Tu, the argument Arg [s (t) s ^* (t-Tu)] of the multiplication value s (t) s ^* (t-Tu) is As shown in the equation (5), 2πΔfTu.

Therefore, the vector as the multiplication value s (t) s ^* (t-Tu) at each time t in the section B from the time t = Tu-Tg to the time t = Tu is oriented in the direction in which the declination is 2πΔfTu. It becomes a vector.

From the above, the guard correlation value that is the average value of the multiplication value s (t) s ^* (t−Tu) for the guard interval length Tg is as shown in FIG. 7C.

  That is, FIG. 7C shows the guard correlation value.

The magnitude of the vector as the guard correlation value obtained at each time t in the section A is different from the vector as the multiplication value s (t) s ^* (t-Tu) used for obtaining the guard correlation value. Since it faces the direction, it is close to 0.

On the other hand, the magnitude of the vector as the guard correlation value obtained at each time t in the section B is the vector as the multiplication value s (t) s ^* (t-Tu) used to obtain the guard correlation value. Since it is facing almost a constant direction, the value is somewhat large.

That is, from the time t = Tu-Tg at which the section B starts, a multiplication value as a vector (hereinafter also referred to as a constant direction multiplication value) s (t) s ^* (t-Tu) is directed in a substantially constant direction. Start to get the average value. Then, as time t elapses, the constant direction multiplication value s (t) s ^* (t-Tu) for which the average value is obtained increases, and the average value is obtained at time t = Tu when section B ends. The number of constant direction multiplication values s (t) s ^* (t-Tu) as a target becomes the maximum.

Therefore, the guard correlation that is the average value of the multiplication values s (t) s ^* (t−Tu) has a peak (maximum value) at the time t = Tu when the section B ends.

  From the above, by detecting the peak of the guard correlation value, it is possible to recognize the timing at time t that satisfies the formula Tu−Tg ≦ t ≦ Tu, that is, the timing at time t = Tu at which the section B ends.

  The time domain carrier phase error detector 33 recognizes the timing at time t = Tu as described above. Then, the time domain carrier phase error detector 33 determines the carrier phase error (time domain carrier phase error) Δ based on the timing t = Tu timing, that is, the phase component of the guard correlation value at the peak timing of the guard correlation value. Detect f.

  That is, if the phase component of the guard correlation value at the peak timing is expressed as θ [radian], the time domain carrier phase error detection unit 33 follows the equation (5) and the phase component of the guard correlation value at the peak timing. The carrier error Δf is detected based on the deviation angle θ = 2πΔfTu.

  As described above, the carrier phase error Δf is a value in a range that satisfies the equation −1 / (2Tu) ≦ Δf <+ 1 / (2Tu).

  On the other hand, when the frequency interval between OFDM subcarriers is expressed as Fc [Hz], the frequency interval Fc is expressed by the equation Fc = 1 / Tu.

  Therefore, as described above, the carrier phase error Δf is a range narrower than the range of ± 1/2 of the subcarrier frequency interval Fc = 1 / Tu in the carrier frequency deviation amount (carrier error). (The following range) value.

  In the above case, the time domain carrier phase error detector 33 detects the peak of the guard correlation value, and detects the carrier phase error Δf based on the phase component of the guard correlation value at the timing of the peak. In addition, for example, the guard correlation value is cumulatively added for a plurality of OFDM symbol sections, and the guard correlation value at the peak timing of the cumulative addition value (or the cumulative addition value of the guard correlation value). The carrier phase error Δf can be detected based on the phase component.

  That is, the peak appears more prominently in the cumulative addition value obtained by cumulatively adding a plurality of guard correlation values for a plurality of OFDM symbol sections than only one guard correlation value.

  Therefore, the accuracy of detection of the carrier phase error Δf is detected by detecting the peak of the cumulative addition value of the guard correlation value and detecting the carrier phase error Δf based on the phase component of the guard correlation value at the timing of the peak. Can be improved.

  Note that details of a method for improving the detection accuracy of the carrier phase error Δf by accumulating the guard correlation values in this way are described in, for example, Patent Document 1.

The time domain carrier phase error detection unit 33 detects the carrier phase error as described above. At this time, at each time t of the OFDM signal s (t) with the OFDM symbol length Tg + Tu, the guard correlation value is calculated. The multiplication value s (t) s ^* (t−Tu) (intermediate result of the calculation of the average) used for the determination is temporarily stored (stored) in the memory 40 (FIG. 2).

  Further, when the time domain carrier phase error detection unit 33 cumulatively adds the guard correlation value for a plurality of OFDM symbol sections, the time domain carrier phase error detection unit 33 stores the guard correlation value (the intermediate result of the cumulative addition) in the memory 40. Temporary storage.

  <Description of Detection of Frequency Domain Carrier Frequency Error by Frequency Domain Carrier Frequency Error Detection Unit 35>

  With reference to FIG. 8 and FIG. 9, a method of detecting the frequency domain carrier frequency error by the frequency domain carrier frequency error detection unit 35 of FIG. 2 will be described.

  The frequency band carrier frequency error detection unit 35 assumes that the pilot signal exists at a shift position shifted from a predetermined pilot signal position by a shift amount of a predetermined number of subcarriers (for transmission symbols). The phase difference between the frequency domain OFDM signal (OFDM frequency domain signal) and the pilot signal is obtained. Then, the frequency-domain carrier frequency error detection unit 35 cumulatively adds the vectors having the direction of the phase difference as the direction, and based on the shift amount that maximizes the cumulative addition value of the vectors, the carrier error (carrier frequency error) Is detected.

  FIG. 8 shows the position of the pilot signal determined in advance by the amount of shift for the OFDM frequency domain signal supplied from the phase correction unit 29 (FIG. 2) to the frequency domain carrier frequency error detection unit 35 and a predetermined number of subcarriers. 2 shows an OFDM frequency domain signal (hereinafter also referred to as an assumed signal) on the assumption that a pilot signal is present at a shifted position deviated from.

  In FIG. 8, the horizontal axis represents the frequency f, and the circles (white circles (◯) and black circles (●)) represent transmission symbols (or subcarriers). Of the circle marks, a black circle mark represents a transmission symbol of a pilot signal (hereinafter also referred to as a pilot symbol), and a white circle mark represents a transmission symbol of data such as an image (hereinafter also referred to as a data symbol).

  FIG. 8A shows an OFDM frequency domain signal with no carrier error (for 0 transmission symbols (subcarriers)) and an OFDM frequency domain signal with a carrier error of 4 transmission symbols.

  In the OFDM frequency domain signal, the pilot symbols are arranged at predetermined positions.

  Therefore, in an OFDM frequency domain signal having a carrier error of 4 transmission symbols, the position of the pilot symbol is shifted by 4 transmission symbols from the position of the pilot symbol of the OFDM frequency domain signal having no carrier error.

  In FIG. 8, the first transmission symbol, the fifth transmission symbol, the eighth transmission symbol, the thirteenth transmission symbol, the fifteenth transmission symbol,... .

  FIG. 8B shows an OFDM frequency domain signal (assumed signal) on the assumption that there are carrier errors corresponding to a predetermined number of transmission symbols (subcarriers).

  An OFDM frequency domain signal obtained by shifting an OFDM frequency domain signal with no carrier error in the frequency direction by i transmission symbols is an assumed signal (hereinafter referred to as a shift amount) assuming that there is a carrier error by i transmission symbols. i is also referred to as an assumed signal of transmission symbols).

  The frequency band carrier frequency error detecting unit 35 is a pilot symbol of the assumed signal of the i transmission symbol and the OFDM frequency domain signal from the phase correcting unit 29 at the position of the pilot symbol (hereinafter also referred to as a target OFDM signal). ) For all pilot symbols of the hypothetical signal.

  Further, the frequency band carrier frequency error detection unit 35 is directed to the phase difference direction obtained with respect to the pilot symbol of the assumed signal of the i transmission symbol, for example, a vector having a magnitude of 1 (hereinafter referred to as a phase difference vector). Are also cumulatively added to all pilot symbols of the hypothetical signal having a transmission amount of i transmission symbols, and a vector as a cumulative addition value (hereinafter also referred to as a cumulative addition vector) is obtained.

  The frequency band carrier frequency error detection unit 35 changes the shift amount to the number of transmission symbols such as, for example, −1 transmission symbol, 0 transmission symbol, 1 transmission symbol,. Find the cumulative addition vector.

  Further, the frequency band carrier frequency error detection unit 35 obtains a cumulative addition vector having the maximum size from the cumulative addition vectors obtained for a plurality of shift amounts. Then, the frequency domain carrier frequency error detection unit 35 determines the carrier error of the focused OFDM signal (the OFDM frequency domain signal from the phase correction unit 29) based on the shift amount when the maximum cumulative addition vector is obtained. (Carrier frequency error) is detected.

  That is, FIG. 9 shows a phase difference vector.

  FIG. 9A shows a phase difference vector in the case where the transmission symbol of the target OFDM signal is a data symbol for which the phase difference from the pilot symbol of the hypothetical signal is obtained.

  As the phase difference vector whose direction is the direction of the phase difference between the pilot symbol of the hypothetical signal and the data symbol of the target OFDM signal, vectors of various directions are obtained.

  Therefore, for the shift amount in which the pilot symbol position of the hypothetical signal does not match the pilot symbol position of the target OFDM signal, the cumulative addition vector is the result of cumulative addition of phase difference vectors in various directions. This is a small vector.

  FIG. 9B shows a phase difference vector in the case where the transmission symbol of the target OFDM signal is a pilot symbol from which the phase difference between the hypothetical signal and the pilot symbol is obtained.

  As a phase difference vector whose direction is the direction of the phase difference between the pilot symbol of the hypothetical signal and the pilot symbol of the target OFDM signal, a (substantially) constant vector (direction of the direction of the angle corresponding to the carrier phase error) vector Is obtained.

  Therefore, for the shift amount where the pilot symbol position of the hypothetical signal matches the pilot symbol position of the target OFDM signal, the cumulative addition vector is the result of cumulative addition of phase difference vectors in a fixed direction. This is a vector with a large size.

  From the above, in the attention OFDM signal, there is a pilot symbol at a position that is shifted from the position of the pilot symbol of the OFDM frequency domain signal with no carrier error by the shift amount when the maximum accumulated addition vector is obtained. A carrier frequency error corresponding to the shift amount is included.

  The carrier frequency error can be obtained by multiplying the shift amount by the transmission symbol interval (subcarrier frequency interval) Fc.

  Thus, since the carrier frequency error is obtained by multiplying the shift amount by the transmission symbol interval (subcarrier frequency interval) Fc, as described above, the accuracy of the subcarrier frequency interval Fc is improved. Value.

  The frequency band carrier frequency error detection unit 35 detects the carrier frequency error as described above. At this time, in order to obtain a cumulative addition vector by accumulating the phase difference vector, The phase difference between the OFDM symbol of interest and the transmission symbol is temporarily stored in the memory 40 (FIG. 2).

  Further, the frequency domain carrier frequency error detection unit 35 temporarily stores the cumulative addition vector obtained for each shift amount in the memory 40 in order to obtain the cumulative addition vector having the maximum magnitude.

  <Description of Detection of Frequency Domain Carrier Phase Error by Frequency Domain Carrier Phase Error Detection Unit 34>

  With reference to FIG. 10, a method of detecting the frequency domain carrier phase error by the frequency domain carrier phase error detector 34 of FIG. 2 will be described.

  The frequency domain carrier phase error detection unit 34 performs pilot processing for one OFDM symbol of the OFDM frequency domain signal (frequency domain OFDM signal) from the phase correction unit 29 (FIG. 2) and another OFDM symbol. A phase difference of a signal subcarrier (subcarrier modulated with a pilot signal) is detected, and a carrier error (carrier phase error) is detected based on the phase difference.

  FIG. 10 shows an OFDM frequency domain signal supplied from the phase correction unit 29 to the frequency domain carrier phase error detection unit 34.

  In FIG. 10, the horizontal axis represents the frequency f, and the vertical axis represents the time t. In FIG. 10, as in FIG. 8, circles represent transmission symbols (or subcarriers). Further, of the circles, black circles represent transmission symbols (pilot symbols) of pilot signals, and white circles represent transmission symbols (data symbols) of data such as images.

  The frequency domain carrier phase error detector 34 detects a carrier phase error as a tracking operation process after the initial pull-in operation process is completed.

  Therefore, when the frequency domain carrier phase error detector 34 detects the carrier phase error, the carrier error of the OFDM frequency domain signal from the phase corrector 29 is ± 1/1 / of the subcarrier frequency interval Fc = 1 / Tu. It is within the range of 2.

  As described above, the carrier error of the OFDM frequency domain signal from the phase correction unit 29 is within the range of ± 1/2 of the subcarrier frequency interval Fc = 1 / Tu. An OFDM symbol can be identified (almost), and pilot symbols within the OFDM symbol can also be identified.

  The frequency domain carrier phase error detection unit 34 includes the current OFDM symbol as the OFDM frequency domain signal supplied from the phase correction unit 29 and, for example, the OFDM symbol supplied immediately before the current OFDM symbol (hereinafter referred to as the previous OFDM symbol). Phase difference between pilot symbols (pilot signal subcarriers) at the same position.

  Then, the frequency domain carrier phase error detector 34 obtains the average value av of the phase differences obtained for the current OFDM symbol and the immediately preceding OFDM symbol, and the carrier phase error (frequency domain carrier phase error) Δ from the average value av. Find f.

  Here, the average value av of the pilot symbol phase difference between the two OFDM symbols can be expressed as 2πΔf (Tu + Tg), and the carrier phase error Δf is expressed by the equation Δf = av / (2π (Tu + Tg)).

  The frequency domain carrier phase error detector 34 detects the carrier phase error as described above. At this time, in order to obtain the phase difference between the pilot symbols of the current OFDM symbol and the immediately preceding OFDM symbol, the immediately preceding OFDM is detected. The phase of the pilot symbol (pilot signal subcarrier) of the symbol is temporarily stored in the memory 40 (FIG. 2).

  As described with reference to FIGS. 5 to 10, in the error detection unit 32 (FIG. 2) for detecting the carrier error, the time domain carrier phase error detection unit 33 detects the time domain carrier phase error in the initial pull-in operation. Then, the frequency domain carrier phase error detector 35 detects the frequency domain carrier frequency error. In the initial pull-in operation, the memory 40 detects the guard correlation value (autocorrelation of the OFDM time domain signal) or the frequency domain carrier frequency error as data necessary for detecting the time domain carrier phase error. For example, the phase difference between the pilot symbol of the hypothetical signal and the transmission symbol of the OFDM signal of interest at the position of the pilot symbol is stored as necessary data.

  In the tracking operation performed after the completion of the initial pull-in operation, the frequency domain carrier phase error detector 34 detects the frequency domain carrier phase error (or the time domain carrier phase error detector 33 detects the time domain carrier. Detect phase error). In the tracking operation, the memory 40 stores the phase of the pilot symbol of the immediately preceding OFDM symbol (or data necessary for detecting the time domain carrier phase error) as data necessary for detecting the frequency domain carrier phase error. As a guard correlation value) or the like.

  Further, in the tracking operation, the channel estimation is performed as another process that is necessary for the initial pull-in operation, but does not need to be performed simultaneously with the initial pull-in operation. The storage area of the memory 40 is shared between the tracking operation process and the channel estimation process.

  Therefore, it is not necessary to separately provide a memory for storing data necessary for other processing such as channel estimation processing, so that the demodulating unit 13 (and thus the demodulating processing unit 12 and the receiving system in FIG. 1) is configured to be small. Can do.

  <Description of computer>

  Next, all or a part of the series of processes described above can be performed by hardware or can be performed by software. When all or part of the series of processing is performed by software, a program constituting the software is installed in a microcomputer or the like.

  Therefore, FIG. 11 shows a configuration example of an embodiment of a computer in which a program for executing the series of processes described above is installed.

  The program can be recorded in advance on a hard disk 105 or a ROM 103 as a recording medium built in the computer.

  Alternatively, the program is stored temporarily on a removable recording medium 111 such as a flexible disk, a CD-ROM (Compact Disc Read Only Memory), a MO (Magneto Optical) disk, a DVD (Digital Versatile Disc), a magnetic disk, or a semiconductor memory. It can be stored permanently (recorded). Such a removable recording medium 111 can be provided as so-called package software.

  The program is installed in the computer from the removable recording medium 111 as described above, or transferred from the download site to the computer wirelessly via a digital satellite broadcasting artificial satellite, LAN (Local Area Network), The program can be transferred to a computer via a network such as the Internet, and the computer can receive the program transferred in this way by the communication unit 108 and install it in the built-in hard disk 105.

  The computer includes a CPU (Central Processing Unit) 102. An input / output interface 110 is connected to the CPU 102 via the bus 101, and the CPU 102 operates an input unit 107 including a keyboard, a mouse, a microphone, and the like by the user via the input / output interface 110. When a command is input by the equalization, a program stored in a ROM (Read Only Memory) 103 is executed accordingly. Alternatively, the CPU 102 also transfers from a program stored in the hard disk 105, a program transferred from a satellite or a network, received by the communication unit 108 and installed in the hard disk 105, or a removable recording medium 111 attached to the drive 109. The program read and installed in the hard disk 105 is loaded into a RAM (Random Access Memory) 104 and executed. Thus, the CPU 102 performs processing according to the above-described flowchart or processing performed by the configuration of the above-described block diagram. Then, the CPU 102 outputs the processing result from the output unit 106 configured with an LCD (Liquid Crystal Display), a speaker, or the like, for example, via the input / output interface 110, or from the communication unit 108 as necessary. Transmission and further recording on the hard disk 105 are performed.

  Here, in the present specification, the processing steps for describing a program for causing the computer to perform various processes do not necessarily have to be processed in time series in the order described in the flowcharts, but in parallel or individually. This includes processing to be executed (for example, parallel processing or processing by an object).

  Further, the program may be processed by one computer or may be distributedly processed by a plurality of computers. Furthermore, the program may be transferred to a remote computer and executed.

  The embodiment of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

It is a block diagram which shows the structural example of one Embodiment of the receiving system to which this invention is applied. 3 is a block diagram illustrating a configuration example of a demodulation unit 13. FIG. 4 is a flowchart for explaining demodulation processing by a demodulation unit 13; 4 is a flowchart for explaining a process of sharing control of a memory 40 by a demodulator 13. It is a figure explaining the detection of a carrier error, and correction | amendment of a carrier error. It is a figure which shows the OFDM signal (OFDM time domain signal) in a time domain. It is a figure explaining a guard correlation value. It is a figure which shows an OFDM frequency domain signal. It is a figure which shows a phase difference vector. It is a figure which shows an OFDM frequency domain signal. It is a block diagram which shows the structural example of one Embodiment of the computer to which this invention is applied.

Explanation of symbols

  11 antenna, 12 demodulation processing unit, 13 demodulation unit, 14 error correction unit, 15 output I / F, 16 decoder, 17 output unit, 21 tuner, 21A arithmetic unit, 21B local oscillator, 22 BPF, 23 A / D conversion unit , 24 clock generation unit, 25 DC cancellation unit, 26 digital quadrature demodulation unit, 27 carrier error correction unit, 28 FFT operation unit, 29 phase correction unit, 31 timing synchronization unit, 32 error detection unit, 33 time domain carrier phase error detection Unit, 33A guard correlation detection unit, 34 frequency band carrier frequency error detection unit, 35 frequency band carrier phase error detection unit, 36 addition unit, 37 NCO, 38 frame synchronization unit, 39 equalization unit, 40 memory, 41 shared control unit , 101 bus, 102 CPU, 103 ROM, 104 RAM, 05 hard disk, 106 output unit, 107 input unit, 108 communication unit, 109 drive, 110 input-output interface, 111 removable recording medium

Claims (9)

Error detection means for detecting an error of a carrier used when demodulating an OFDM (Orthogonal Frequency Division Multiplexing) signal;
Storage means for storing data necessary for processing for detecting the carrier error;
When the error detection means performs an initial pull-in operation for detecting both the phase error and the frequency error of the carrier and then performs a tracking operation for detecting only the phase error of the carrier, the initial pull-in operation ends. Thereafter, the storage area of the storage means that is necessary for the process of the initial pull-in operation but is not necessary for the process of the tracking operation is released to another process that is not performed simultaneously with the process of the initial pull-in operation, A signal processing apparatus comprising: a tracking control process; and a sharing control unit that causes the other process to share a storage area of the storage unit. The OFDM signal includes a pilot signal that is a known signal;
The error detecting means includes
Obtain the autocorrelation of the OFDM signal in the time domain, cumulatively add for a plurality of OFDM symbol sections,
Detecting a peak of the cumulative addition value of the autocorrelation;
A time domain carrier phase error detection means for detecting a phase error of the carrier based on the phase component of the autocorrelation at the peak timing of the cumulative addition value of the autocorrelation;
Assuming that the pilot signal is at a shift position shifted from a predetermined position of the pilot signal by a shift amount corresponding to a predetermined number of subcarriers, the OFDM signal in the frequency domain, and the pilot signal at the shift position Find the phase difference of
Cumulatively adding vectors with the direction of the phase difference as a direction,
A frequency domain carrier frequency error detecting means for detecting a frequency error of the carrier based on the shift amount at which a cumulative addition value of the vector is maximized;
Detecting a phase difference of subcarriers of the pilot signal for one OFDM symbol of the OFDM signal in the frequency domain and another OFDM symbol;
A frequency domain carrier phase error detecting means for detecting a phase error of the carrier based on the phase difference, and
In the initial pull-in operation,
The time domain carrier phase error detection means detects the phase error of the carrier;
The frequency band carrier frequency error detecting means detects the frequency error of the carrier;
The storage means stores the autocorrelation and the phase difference between the OFDM signal in the frequency domain and the pilot signal at the shifted position,
In the tracking operation,
The frequency domain carrier phase error detection means or the time domain carrier phase error detection means detects the phase error of the carrier,
The signal processing apparatus according to claim 1, wherein the storage section stores a phase of a subcarrier of the pilot signal of the one OFDM symbol or a moving average value of the autocorrelation. In the case where the tracking operation is performed intermittently,
2. The storage control unit according to claim 1, wherein the sharing control unit further releases a storage area of the storage unit necessary for the tracking operation processing to the other processing when the tracking operation processing is not performed. 3. Signal processing device. The other processing includes channel estimation processing for estimating transmission channel characteristics, which are transmission channel characteristics for transmitting the OFDM signal, error correction processing for error correction, and TS (Transport Stream) packet for the OFDM signal. 2. The signal processing device according to claim 1, wherein the signal processing apparatus includes at least one of output processes for outputting the TS packet obtained after demodulation of the OFDM signal. The error detecting means includes
Obtain the autocorrelation of the OFDM signal in the time domain, cumulatively add for a plurality of OFDM symbol sections,
Detecting a peak of the cumulative addition value of the autocorrelation;
A time domain carrier phase error detection means for detecting a phase error of the carrier based on the phase component of the autocorrelation at the peak timing of the cumulative addition value of the autocorrelation;
The signal processing apparatus according to claim 1, wherein at least the autocorrelation is stored in the storage unit. The OFDM signal includes a pilot signal that is a known signal;
The error detecting means includes
Assuming that the pilot signal is at a shift position shifted from a predetermined position of the pilot signal by a shift amount corresponding to a predetermined number of subcarriers, the OFDM signal in the frequency domain, and the pilot signal at the shift position Find the phase difference of
Cumulatively adding vectors with the direction of the phase difference as a direction,
A frequency domain carrier frequency error detecting means for detecting a frequency error of the carrier based on the shift amount at which the cumulative addition value of the vector is maximized;
The signal processing apparatus according to claim 1, wherein at least a phase difference between the OFDM signal in the frequency domain and the pilot signal at the shifted position is stored in the storage unit. The OFDM signal includes a pilot signal that is a known signal;
The error detecting means includes
Detecting a phase difference of subcarriers of the pilot signal for one OFDM symbol of the OFDM signal in the frequency domain and another OFDM symbol;
A frequency domain carrier phase error detecting means for detecting a phase error of the carrier based on the phase difference;
The signal processing apparatus according to claim 1, wherein at least a phase of a subcarrier of the pilot signal of the one OFDM symbol is stored in the storage unit. Error detection means for detecting an error of a carrier used when demodulating an OFDM (Orthogonal Frequency Division Multiplexing) signal;
A signal processing apparatus comprising: storage means for storing data necessary for processing for detecting the carrier error;
When the error detection means performs an initial pull-in operation for detecting both the phase error and the frequency error of the carrier and then performs a tracking operation for detecting only the phase error of the carrier, the initial pull-in operation ends. Thereafter, the storage area of the storage means that is necessary for the process of the initial pull-in operation but is not necessary for the process of the tracking operation is released to another process that is not performed simultaneously with the process of the initial pull-in operation, A signal processing method including a step of sharing a storage area of the storage unit between a tracking operation process and the other process. Error detection means for detecting an error of a carrier used when demodulating an OFDM (Orthogonal Frequency Division Multiplexing) signal;
Storage means for storing data necessary for processing for detecting the carrier error;
When the error detection means performs an initial pull-in operation for detecting both the phase error and the frequency error of the carrier and then performs a tracking operation for detecting only the phase error of the carrier, the initial pull-in operation ends. Thereafter, the storage area of the storage means that is necessary for the process of the initial pull-in operation but is not necessary for the process of the tracking operation is released to another process that is not performed simultaneously with the process of the initial pull-in operation, A program for causing a computer to function as sharing control means for sharing a storage area of the storage means for tracking operation processing and the other processing.

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