JP2009284436A - Ofdm receiving apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM receiving apparatus simplifying setting for channel selection by automatically detecting a PRBS initial value when receiving a link-transmitted digital terrestrial signal. <P>SOLUTION: A pilot signal extraction means 104 extracts a pilot signal from an output of an FFT means 102 for converting a received signal into a frequency area signal. A PRBS generation means 109 generates any one of a plurality of PRBS according to a selection signal. A BPSK modulation removal means 108 performs BPSK modulation removal of an output from the pilot signal extraction means 104 by using an output from a PRBS generation means 109. A data demodulation means 103 equalizes an output from the FFT means 102 by an output from the BPSK modulation removal means 108 and obtains modulation data. A detection means 108 obtains a detection signal concerned with the quality of modulation data which is an output from the data demodulation means 103. A determination means 110 outputs a selection signal for selecting an optimum PRBS in the plurality of PRBSs, based on a criterion for obtaining the best detection signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an OFDM receiver that receives a part of a terrestrial digital signal that is concatenated and transmitted, and more particularly to an OFDM receiver that receives a scattered pilot (hereinafter referred to as SP) signal.

  In recent years, digital transmission systems using OFDM signals have been put into practical use in the field of terrestrial digital broadcasting. In Japan, ISDB-T standard terrestrial digital television broadcasting is started in the UHF band, and ISDB-TSB standard terrestrial digital audio broadcasting is started in the VHF band. In the future, terrestrial digital mobile multimedia broadcasting of ISDB-Tmm standard is scheduled to start.

  In this OFDM system, a large number of subcarriers orthogonal to each other are modulated by digital data to be transmitted, and these modulated waves are multiplexed and transmitted. This method has a feature that the number of subcarriers used is from several hundred to several thousand and is not easily affected by multipath interference.

  In terrestrial digital broadcasting, a transmission method has been developed in which a plurality of segments (one or more predetermined number of segments) of each program provider are concatenated and transmitted as one OFDM signal, and one of the concatenated terrestrial digital signals is transmitted. Digital terrestrial receivers that receive the signal have appeared.

  In addition, scattered pilot (SP) signals are sparsely inserted into the terrestrial digital signal in the frequency direction and time direction, and the receiver demodulates the data by correcting the transmission path distortion based on the SP signal. I do. The SP signal is BPSK (Binary Phase Shift Keying) modulated by a known pseudo-random code sequence (PRBS) in the frequency direction and transmitted. In the receiving apparatus, BPSK modulation is removed from the BPSK-modulated SP signal using the same PRBS as that on the transmission side. However, in the case of concatenated transmission, the initial value of PRBS differs depending on the position (center subchannel number) of the concatenated segments (see Non-Patent Document 1, for example).

The conventional OFDM receiver is configured to perform data demodulation by correcting transmission path distortion with reference to the SP signal after selecting a segment by a tuner (see, for example, Patent Documents 1 and 2). ).
In such a conventional OFDM receiver, the position of the segment (center subchannel number) of the concatenated signal to be received is grasped in advance, and the corresponding segment position (center subchannel number) is received. It is necessary to perform BPSK removal of the SP signal using the initial value of PRBS (see FIG. 10 described later). Therefore, in the conventional receiving apparatus, it is necessary to supply frequency information for channel selection to the tuner of the receiving apparatus at the time of channel selection. On the other hand, the SP signal serving as a reference signal for the subsequent equalization circuit that is a demodulator Also when reproducing, information on the center subchannel number or the PRBS initial value is required to remove the BPSK modulation. Thus, it is necessary to supply the channel selection information to different circuit units of the receiving apparatus. For this reason, a wiring for supplying tuning information on the tuner side to the demodulating part at the subsequent stage is necessary, or the tuning side tuning information must be taken into account in manufacturing the demodulating part. A circuit configuration that does not require information could not be achieved.
"Transmission method of digital terrestrial audio broadcasting", Japan Radio Industry Association, ARIB STD-B29 Chapter 3 JP 2003-259244 A JP 2005-191801 A

  In view of the above problems, the present invention automatically detects the PRBS initial value when receiving a part of the concatenated terrestrial digital signal, and uses the PRBS initial value to remove the BPSK modulation of the SP signal. By selecting the OFDM receiver, it is not necessary to input the center subchannel number or the PRBS initial value from the microcomputer side that performs channel selection control in the demodulation part during channel selection, and the setting at the time of channel selection is simplified. It is intended to provide.

  According to one aspect of the present invention, a pilot signal is multiplexed and transmitted in a predetermined arrangement pattern in the frequency direction and the time direction, and the pilot signal is BPSK modulated with one of a plurality of PRBSs in the frequency direction. In an OFDM receiver for receiving an OFDM signal to be transmitted, fast discrete Fourier transform means for transforming the received signal into a frequency domain signal by fast discrete Fourier transform, and a pilot signal for extracting a pilot signal from the output of the fast discrete Fourier transform means Extracting means; PRBS generating means for generating any one of the plurality of PRBSs according to a selection signal; and BPSK modulation removing means for removing BPSK modulation from the output of the pilot signal extracting means using the output of the PRBS generating means And the fast discrete Fourier transform using the output of the BPSK modulation removing means. A data demodulating means for equalizing the output of the means to obtain demodulated data, a detecting means for obtaining a detection signal relating to the quality of the demodulated data which is the output of the data demodulating means, and the detection signal are inputted, the detection signal being Determining means for outputting an optimum selection signal for selecting an optimal PRBS from among the plurality of PRBSs based on the determination criterion, wherein the determination unit tries the plurality of PRBSs to determine the determination criterion. An OFDM receiving apparatus is provided.

ADVANTAGE OF THE INVENTION According to this invention, the OFDM receiver which makes the setting at the time of channel selection simple can be provided by automatically detecting the PRBS initial value when receiving the terrestrial digital signal that is transmitted concatenated.

Embodiments of the invention will be described with reference to the drawings.
Prior to describing the embodiments of the present invention with reference to FIGS. 1 to 4, related techniques of the present invention will be described with reference to FIGS. 5 to 10.
FIG. 5 shows an OFDM signal of 6 MHz band that is divided into 14 segments and concatenated for transmission. Note that one segment includes, for example, 432 subcarriers.

  FIG. 6 shows central subchannel numbers 0 to 41 of one segment obtained by dividing a 6 MHz band of a certain frequency band into 41 parts. Normally, a broadcasting station has one of the subchannel numbers 0 to 41 in the center subchannel number 0 to 41 of a certain frequency band shown in FIG. 6 (for example, subchannel number 2 as shown in the second row of the number row in FIG. , 3 or 4), for example, the frequency is set so as to match the center frequency f1 of the first segment (the left end in the figure) of the 14 segments shown in FIG. This frequency setting is fixed once set, but when the frequency band of the broadcast channel must be moved or changed for the purpose of effective use of the frequency, the center frequency f1 of the first segment (the left end in the figure) Can be set to any one of the subchannel numbers 0 to 41. For example, as shown in the 14th row of the number row in FIG. 10, it is possible to set the subchannel numbers 38, 39, or 40.

  FIG. 7 is a diagram illustrating an arrangement example of SP signals in the OFDM transmission scheme. The vertical axis in FIG. 7 is the time direction (corresponding to the number of symbols), and the horizontal axis is the frequency direction (corresponding to the number of subcarriers). In the OFDM transmission system (ISDB-T) used for terrestrial digital broadcasting and the like, a known SP signal having a constant amplitude and phase is previously stored in a data signal sequence at a predetermined position on the frequency axis and time axis on the transmission side. Are inserted regularly. It is inserted once every 12 carriers in the frequency direction and once every 4 symbols in the time direction. In FIG. 7, ● is an SP carrier, and ○ is a data carrier. On the reception side, data demodulation is performed by correcting transmission path distortion based on the SP signal. The SP signal is BPSK-modulated and transmitted by a PRBS (pseudo random code sequence) known in the frequency direction on the transmission side.

  For example, as shown in FIG. 7, 1 or 0 is randomly assigned in accordance with a pseudo-random code sequence (PRBS) with respect to subcarriers (hereinafter simply referred to as carriers) constituting the symbols in the first row (first), thereby SP. The signal is BPSK modulated and transmitted. In FIG. 7, when looking at the PRBS (1011010111010101...) Assigned to the carrier constituting the first symbol, the first SP carrier ● constituting the first symbol is “1” and the next SP carrier. ● is assigned '0'. As a result, as shown in FIG. 8, 1 or 0 is randomly assigned according to PRBS for each SP carrier, and if “1” is assigned, the phase of point a on the I axis of the IQ plane is If it is transmitted and “0” is assigned, it is transmitted at the phase of point b, which is 180 degrees different from the phase of point a on the I axis. The reason why the SP signal is BPSK modulated by using PRBS '1' and '0' in this way is that there is a demerit in signal transmission (interference with other signals, etc.) if the signal is sent with only one phase. This is to avoid the problem.

On the receiving side, the same PRBS as that on the transmitting side is used to remove the BPSK modulation. That is, it is possible to generate the same PRBS on the transmission / reception side by having the same PRBS generation circuit on the transmission / reception side and giving the PRBS initial value to a predetermined number of registers constituting the PRBS generation circuit at the same timing.
In OFDM transmission, data is allocated to a plurality of carriers orthogonal to each other to perform modulation and demodulation. This is realized by performing inverse fast Fourier transform (hereinafter IFFT) processing on a plurality of symbol data on the transmission side, and performing fast Fourier transform (hereinafter FFT) processing on the reception data on the reception side.

Further, as shown in FIG. 7, SP signals are inserted at a rate of 1/12 in the frequency direction and 1/4 in the time direction on the transmission side, and the SP signal is detected on the reception side to detect the error of each carrier. Thus, synchronous detection is realized by performing amplitude equalization and phase equalization. That is, since the SP signals are arranged in the time direction with a 4-symbol period, an SP signal with a 3-carrier interval is obtained by interpolating the SP signal with a 4-symbol period in the time direction to obtain a 4-symbol SP signal. Here, as described above, BPSK modulation is removed using the same PRBS as that on the transmission side. By the BPSK modulation removal, all SP signals that are randomly BPSK modulated in the phase of either point a or point b in FIG. 8 are returned to the original SP signal only in the phase a. Next, the SP signal from which the BPSK modulation has been removed is interpolated in the frequency direction to obtain an SP signal as a reference signal over all carriers.
The SP signals of all carriers interpolated in this way in the time direction and frequency direction are sent to an equalization circuit that performs amplitude equalization and phase equalization.

  FIG. 8 shows the QPSK (Quadrature Phase Shift Keying) modulated I-axis and Q-axis complex data amplitude / phase characteristics (hereinafter referred to as constellation) and the BPSK-modulated complex SP signal constellation. Four small white circles are QPSK-modulated data signals, and two small black circles on the I axis indicate BPSK-modulated SP signals a and b. In the state shown in the figure, neither the QPSK signal nor the SP signal is subjected to any distortion, but when receiving interference such as multipath on the transmission path to be transmitted, the phase of the SP signal at point a is set to point a ′ on the receiving side. Similarly, the phase of the QPSK signal at point c is also shifted to point c ′ with the same amount of deviation. This causes the same amount of deviation in the phase of the SP signal at point b and the phase of the QPSK signal at the other three points. In the receiving apparatus, an equalizer circuit (see reference numeral 103 in FIG. 1) restores the phase shift amount (that is, phase rotation) and amplitude displacement.

FIG. 9 shows a configuration example of a PRBS generation circuit used for BPSK modulation of an SP signal with a terrestrial digital signal. In the PRBS generation circuit, 11 registers D1, D2, D3,..., D10, D11 capable of latching (delaying) bit by bit are connected in series, and the output signal of the register D9 and the output signal of the register D11 are connected. The exclusive OR (referred to as EXOR) circuit 21 is inputted to two input terminals, the output signal of the EXOR circuit 21 is inputted to the register D1, and the signal from the register D11 is outputted from the output terminal 22. Each of the registers D1 to D11 is composed of a flip-flop as a latch circuit capable of latching one bit for each clock.
The eleven registers D1 to D11 constituting the EXOR circuit 21 can be set by selecting from the table showing "PRBS register initial values" in FIG. 10 as initial values.

  However, in the case of concatenated transmission, the initial value of PRBS differs depending on the position of the concatenated segments (center subchannel number) as shown in FIG. As shown in FIG. 10, there are three central subchannel numbers that can be set in one segment, and 42 central subchannel numbers are predetermined for all 14 segments. In other words, on the transmission side, the segment is shifted in units of subchannels for each segment. For example, “2, 3, 4” of “center subchannel number of one segment” in the second row of the number row in FIG. 10 is 2, 3 of the subchannel numbers from 0 to 41 shown in FIG. , 4 means that the segment is shifted so that the center frequency f1 of the segment becomes the center frequency f1. Note that modes 1, 2, and 3 in FIG. 10 indicate differences in modes that are distinguished by transmission parameters of terrestrial digital broadcasting, and the numbers of subcarriers in one segment correspond to 108, 216, and 432, respectively. is there. The terrestrial digital signal and the transmission method of concatenated transmission are described in detail in Non-Patent Document 1.

  The conventional OFDM receiver knows in advance which segment (center subchannel number) the segment of the concatenated signal is received, and the initial value of PRBS according to the received segment position (center subchannel number) The BPSK modulation removal of the SP signal was performed using the. Therefore, in the conventional receiving apparatus, it is necessary to supply the center subchannel number or the PRBS initial value information to the tuner at the time of channel selection, and also to the demodulation IC constituting the demodulation portion.

  Therefore, in the embodiment of the present invention, in the demodulation IC of the receiving apparatus, the initial values of a plurality of PRBS necessary for demodulation are switched, and detection signals (for example, S / N ratio and error rate) relating to the quality of the demodulated data are switched. By automatically detecting the best time, it is possible to detect the optimum initial value of PRBS.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an OFDM receiving apparatus according to the first embodiment of the present invention.

  An OFDM receiver 100 shown in FIG. 1 includes a tuner (not shown) that selects a terrestrial digital broadcast signal, a quadrature detection circuit (not shown) that generates a terrestrial digital signal in a time domain by converting it into a baseband complex signal, An FFT circuit 102 that converts a received signal into a frequency domain signal by FFT, an SP extraction circuit 104 that serves as a pilot signal extraction unit that extracts an SP signal from the output of the FFT circuit 102, and an SP extraction circuit 104 that extracts the signal. An SP time axis interpolation circuit 105 that interpolates the SP signal in the time direction, a PRBS generation circuit 109 that generates one of a plurality of PRBSs according to the selection signal, and an output of the SP time axis interpolation circuit 105 is used as the PRBS generation circuit 109. BPSK modulation removing circuit 106 for removing BPSK modulation using the output of the BPSK, and this BPSK modulation The SP frequency axis interpolation circuit 107 that performs interpolation in the frequency direction on the SP signal from which the BPSK modulation has been removed by the last circuit 106, and the output of the FFT circuit 102 are equalized by the SP output of the SP frequency axis interpolation circuit 107 to obtain demodulated data. An equalization circuit 103 as data demodulating means, an S / N detection circuit 108 that detects a received S / N using demodulated data that is output from the equalization circuit 103, and a detected received S / N signal are input. And a determination circuit 110 that outputs a selection signal for selecting an optimum PRBS among a plurality of PRBSs based on a determination criterion that provides the best received S / N signal, an output terminal 111 for demodulated data, and a PRBS search. And a mode signal input terminal 112.

When a search mode signal is input from a control means (not shown), the determination circuit 110 gives a PRBS switching signal to the PRBS generation circuit 109 and causes the PRBS generation circuit 109 to try a plurality of PRBSs, so that the received S / N signal is the best. By obtaining the determination criterion, the optimum PRBS is automatically found and the demodulation operation is executed.
As the PRBS generation circuit 109, the configuration shown in FIG. 9 can be used.

The operation will be described below with reference to FIG.
A terrestrial digital signal in the time domain, which is selected by a tuner (not shown) and converted to a baseband complex signal by a quadrature detection circuit (not shown), is input to the input terminal 101. The input signal of the FFT circuit 102 is a partial segment signal of the terrestrial digital signal that is concatenated and transmitted. Note that the tuner can receive a predetermined number of segments. The partial segment signal of the terrestrial digital signal is a signal of a predetermined number of segments constituting one symbol. This input signal is supplied to the FFT circuit 102 and converted into a frequency domain signal by a fast Fourier transform (FFT) operation. The output of the FFT circuit 102 is branched into two, one being supplied to the equalization circuit 103 and the other being supplied to the SP extraction circuit 104.

  The SP extraction circuit 104 extracts only SP signals sparsely multiplexed in the frequency direction and the time direction as shown in FIG. 7 and supplies them to the SP time axis interpolation circuit 105. The SP signal interpolated in the time direction by the SP time axis interpolation circuit 105 is supplied to the BPSK modulation removal circuit 106. By this time axis interpolation, the SP signal is inserted once every three carriers in the frequency direction. That is, the SP signal is inserted at a rate of 1/3 in the frequency direction.

  The BPSK modulation removal circuit 106 also receives the PRBS signal from the PRBS generation circuit 109, and the BPSK modulation of the SP signal is removed based on the PRBS signal. The output of the BPSK modulation removal circuit 106 is supplied to the SP frequency axis interpolation circuit 107, interpolated by a frequency interpolation filter in the frequency direction, and the interpolation output is supplied to the equalization circuit 103. By this time axis interpolation, reference signals for all carriers are obtained.

In the equalizing circuit 103, the data carrier from the FFT circuit 102 is corrected for transmission line distortion based on the SP signals of all the carriers from the SP frequency axis interpolation circuit 107, and is output as demodulated data from the output terminal 111 to a subsequent error correction circuit (not shown). Supplied with.
The output of the equalization circuit 103 is also supplied to the S / N detection circuit 108, and the received S / N is detected using the demodulated data. The received S / N signal as the detection result is supplied to the determination circuit 110. The determination circuit 110 receives a PRBS search mode signal and switches between the PRBS search mode and the normal reception mode.

  In the PRBS search mode, a PRBS initial value switching signal is supplied from the determination circuit 110 to the PRBS generation circuit 109, and the determination circuit 110 monitors the received S / N signal while sequentially switching the PRBS initial value. Then, the PRBS initial value with the best received S / N signal is selected, the PRBS search mode is terminated, and the normal reception mode is switched. If the PRBS initial value does not match the input signal, the BPSK modulation removal of the SP signal is not performed correctly, and the BPSK modulation component becomes a high-frequency component on the frequency axis, causing a failure in the frequency interpolation filter, and the received S / N Deteriorate. Therefore, since the received S / N signal is the best when the correct PRBS initial value is used, it can be used as a criterion for detecting the optimal PRBS initial value. The PRBS search mode may be executed once, for example, immediately after the 4-symbol period of the SP signal is established or immediately after frame synchronization is established.

  As described above, according to the first embodiment, the PRBS initial value can be automatically detected by using the received S / N signal as a determination criterion while switching the PRBS initial value. There is no need to set.

[Second Embodiment]
FIG. 2 is a block diagram showing a configuration of an OFDM receiving apparatus according to the second embodiment of the present invention.
An OFDM receiver 200 shown in FIG. 2 includes a tuner (not shown) that selects a terrestrial digital broadcast signal, a quadrature detection circuit (not shown) that generates a terrestrial digital signal in a time domain by converting it into a baseband complex signal, An FFT circuit 202 that converts a received signal into a frequency domain signal by FFT, an SP extraction circuit 204 as a pilot signal extraction means that extracts an SP signal from the output of the FFT circuit 202, and an SP extraction circuit 204 An SP time axis interpolation circuit 205 that interpolates the SP signal in the time direction, a PRBS generation circuit 209 that generates one of a plurality of PRBSs according to the selection signal, and an output of the SP time axis interpolation circuit 205 is used as the PRBS generation circuit 209. BPSK modulation removing circuit 206 for removing BPSK modulation using the output of the BPSK, and this BPSK modulation An SP frequency axis interpolation circuit 207 that performs interpolation in the frequency direction on the SP signal from which BPSK modulation has been removed by the last circuit 206, and the output of the FFT circuit 202 is equalized with the SP output of the SP frequency axis interpolation circuit 207 to obtain demodulated data. An error having a function of detecting an error rate while inputting an equalization circuit 203 as data demodulating means and demodulating data output from the equalization circuit 203 to perform error correction and output to the output terminal 211 A correction circuit 208, a determination circuit 210 that inputs the detected error rate, and outputs a selection signal for selecting an optimum PRBS among a plurality of PRBSs based on a determination criterion that provides the best error rate; and TS A data output terminal 211 and a PRBS search mode signal input terminal 212 are provided.

  When a search mode signal is input from a control means (not shown), this determination circuit 210 gives a PRBS switching signal to the PRBS generation circuit 209 and causes the PRBS generation circuit 209 to try a plurality of PRBS, thereby determining the best error rate. By obtaining the reference, the optimum PRBS is automatically found and the demodulation operation is performed.

The operation will be described below with reference to FIG.
A terrestrial digital signal in the time domain, which is selected by a tuner (not shown) and then converted to a baseband complex signal by an orthogonal detector (not shown), is input to the input terminal 201. The input signal of the FFT circuit 202 is a segment signal that is a part of the terrestrial digital signal that is concatenated and transmitted. Note that the tuner can receive a predetermined number of segments. The partial segment signal of the terrestrial digital signal is a signal of a predetermined number of segments constituting one symbol. This input signal is supplied to the FFT circuit 202 and converted into a frequency domain signal by FFT calculation. The output of the FFT circuit 202 is branched into two, one being supplied to the equalization circuit 203 and the other being supplied to the SP extraction circuit 204.

  As shown in FIG. 7, the SP extraction circuit 204 extracts only SP signals that are sparsely multiplexed in the frequency direction and the time direction and supplies them to the SP time axis interpolation circuit 205. The SP signal interpolated in the time axis direction by the SP time axis interpolation circuit 205 is supplied to the BPSK modulation removal circuit 206. By this time axis interpolation, the SP signal is inserted once every three carriers in the frequency direction. That is, the SP signal is inserted at a rate of 1/3 in the frequency direction.

  The BPSK modulation removal circuit 206 also receives the PRBS signal from the PRBS (pseudo random code sequence) generation circuit 209 and removes the BPSK modulation of the SP signal based on the PRBS signal. The output of the BPSK modulation removal circuit 206 is supplied to the SP frequency axis interpolation circuit 207, interpolated by the frequency interpolation filter in the frequency axis direction, and the interpolation output is supplied to the equalization circuit 203. By this time axis interpolation, reference signals for all carriers are obtained.

In the equalizing circuit 203, the data carrier from the FFT circuit 202 is corrected for the transmission path distortion based on the SP signals of all the carriers from the SP frequency axis interpolation circuit 207, and is supplied to the error correction circuit 208 as demodulated data. The error correction circuit 208 performs error correction calculation processing, and outputs it to the output terminal 211 as TS data.
Further, error information indicating an error rate is supplied from the error correction circuit 208 to the determination circuit 210. The determination circuit 210 receives a PRBS search mode signal and switches between the PRBS search mode and the normal reception mode.

  In the PRBS search mode, a PRBS initial value switching signal is supplied from the determination circuit 210 to the PRBS generation circuit 209, and the determination circuit 210 monitors error information while sequentially switching the PRBS initial value. Then, the PRBS initial value with the best error rate is selected, the PRBS search mode is terminated, and the normal reception mode is switched. If the PRBS initial value does not match the input signal, the BPSK modulation removal of the SP signal is not performed correctly, and the error correction circuit 208 cannot perform error correction and degrades the error rate. Therefore, since the error rate is the best when the correct PRBS initial value is used, it can be used as a criterion for detecting the optimal PRBS initial value. It should be noted that the PRBS search mode may be executed once, for example, immediately after the 4-symbol period of the SP signal is established or immediately after frame synchronization is established.

  As described above, according to the second embodiment, the PRBS initial value can be automatically detected by using error information indicating the error rate state as a criterion while switching the PRBS initial value. There is no need to set an initial value.

[Third Embodiment]
FIG. 3 is a block diagram showing a configuration of an OFDM receiving apparatus according to the third embodiment of the present invention.
An OFDM receiver 300 shown in FIG. 3 includes a tuner (not shown) that selects a terrestrial digital broadcast signal, a quadrature detection circuit (not shown) that converts a baseband complex signal into a time-domain digital signal, An FFT circuit 302 that converts a received signal into a frequency domain signal by FFT, an SP extraction circuit 304 as a pilot signal extraction unit that extracts an SP signal from the output of the FFT circuit 302, and the SP extraction circuit 304 An SP time axis interpolation circuit 305 that interpolates the SP signal in the time direction, a PRBS generation circuit 309 that generates one of a plurality of PRBSs according to the selection signal, and an output of the SP time axis interpolation circuit 305 is used as the PRBS generation circuit 309. BPSK modulation removing circuit 306 for removing BPSK modulation using the output of the BPSK, and this BPSK modulation An SP frequency axis interpolation circuit 307 that performs interpolation in the frequency direction on the SP signal from which BPSK modulation has been removed by the leaving circuit 306, and the output of the FFT circuit 302 is equalized with the SP output of the SP frequency axis interpolation circuit 307 to obtain demodulated data. An equalization circuit 303 as data demodulating means, an SP signal output from the BPSK modulation removal circuit 306, and a differential error detection circuit 311 for detecting a component that has not been subjected to BPSK modulation removal as a differential error signal; A decision circuit 310 that inputs the differential error signal, outputs a selection signal for selecting an optimum PRBS among a plurality of PRBSs based on a decision criterion that minimizes the differential error signal, and an output terminal for demodulated data 312 and a PRBS search mode signal input terminal 313.

  When a search mode signal is input from a control means (not shown), this determination circuit 310 gives a PRBS switching signal to the PRBS generation circuit 309 and causes the PRBS generation circuit 309 to try a plurality of PRBSs to obtain the best differential error signal. By obtaining the criterion, the optimum PRBS is automatically found and the demodulation operation is executed.

FIG. 4 shows a block diagram of a configuration example of the differential error detection circuit 311 in FIG.
The differential error detection circuit 311 shown in FIG. 4 includes a register 311-1 for delaying the output of the BPSK modulation removal circuit 306, an SP output of the BPSK modulation removal circuit 306, and an SP signal (register 311) adjacent to the output in the frequency direction. -1 output) difference calculation circuit 311-2, an absolute value detection circuit 311-3 for detecting the absolute value of the difference calculation circuit, and the differential value obtained by integrating the output of the absolute value detection circuit for a predetermined interval. An integration circuit 311-4 that outputs an error signal is provided, and a PRBS that minimizes the output of the integration circuit is selected using the output of the integration circuit as a criterion.

The operation will be described below with reference to FIGS.
The input terminal 301 receives a terrestrial digital signal in the time domain that is selected by a tuner (not shown) and then converted to a baseband complex signal by a quadrature detection circuit (not shown). The input signal of the FFT circuit 302 is a partial segment signal of the terrestrial digital signal that is concatenated and transmitted. Note that the tuner can receive a predetermined number of segments. The partial segment signal of the terrestrial digital signal is a signal of a predetermined number of segments constituting one symbol. This input signal is supplied to the FFT circuit 302 and converted into a frequency domain signal by FFT calculation. The output of the FFT circuit 302 is branched into two, one being supplied to the equalization circuit 303 and the other being supplied to the SP extraction circuit 304.

  As shown in FIG. 7, the SP extraction circuit 304 extracts only SP signals that are sparsely multiplexed in the frequency direction and the time direction and supplies them to the SP time axis interpolation circuit 305. The SP signal interpolated in the time axis direction by the SP time axis interpolation circuit 305 is supplied to the BPSK modulation removal circuit 306. By this time axis interpolation, the SP signal is inserted once every three carriers in the frequency direction. That is, the SP signal is inserted at a rate of 1/3 in the frequency direction.

  The BPSK modulation removal circuit 306 also receives a PRBS signal from a PRBS (pseudo random code sequence) generation circuit 309, and the BPSK modulation of the SP signal is removed based on the PRBS signal. The output of the BPSK modulation removal circuit 306 is supplied to the SP frequency axis interpolation circuit 307, is interpolated by the frequency interpolation filter in the frequency direction, and the interpolation output is supplied to the equalization circuit 303. By this time axis interpolation, reference signals for all carriers are obtained.

  In the equalization circuit 303, the data carrier from the FFT circuit 302 is corrected on the basis of the SP signals of all carriers from the SP frequency axis interpolation circuit 307, and is supplied to the error correction circuit 308 as demodulated data. Error correction processing is performed by the error correction circuit 308 and output to the output terminal 312 as TS data.

  The output of the BPSK modulation removal circuit 306 is also supplied to the differential error detection circuit 311. As shown in FIG. 4, the differential error detection circuit 311 performs a difference operation on the SP signal in the frequency direction and integrates the absolute value for a certain period. The integration calculation result is supplied to the determination circuit 310 as a differential error signal. Further, a PRBS search mode signal is input to the determination circuit 310, and the PRBS search mode and the normal reception mode are switched.

  In the PRBS search mode, the PRBS initial value switching signal is supplied from the determination circuit 310 to the PRBS generation circuit 309, and the determination circuit 310 monitors the differential error signal while sequentially switching the PRBS initial value. Then, the PRBS initial value that minimizes the differential error signal is selected, the PRBS search mode is terminated, and the normal reception mode is switched. If the PRBS initial value does not match the input signal, the BPSK modulation removal of the SP signal is not performed correctly, and the differential error signal becomes large because the BPSK modulation component exists. Therefore, since the differential error signal is minimized when the correct PRBS initial value is used, it can be used as a determination criterion for detecting an optimal PRBS initial value. The PRBS search mode may be executed once, for example, immediately after the 4-symbol period of the SP signal is established or immediately after frame synchronization is established.

  As described above, according to the third embodiment, the PRBS initial value can be automatically detected using the differential error signal as a criterion while switching the PRBS initial value, so the user sets the PRBS initial value. There is no need.

  In the above description of the first to third embodiments, the BPSK modulation removal circuit is located at the subsequent stage of the SP time axis interpolation circuit, but may be at the preceding stage. Furthermore, in the first to third embodiments, it has been described that the search is performed while sequentially switching the PRBS initial value. However, it goes without saying that the same effect can be obtained even if parallel processing is performed using a plurality of circuits. Yes.

  As described above, according to the present invention, the PRBS initial value for removing the BPSK modulation by the PRBS applied to the SP signal in the OFDM receiver that receives a part of the concatenated terrestrial digital signal is obtained. Since automatic detection is performed, it is not necessary to set the center subchannel number and the PRBS initial value for demodulation during tuning, and a simple tuning operation is possible.

The block diagram which shows the structure of the OFDM receiver of the 1st Embodiment of this invention. The block diagram which shows the structure of the OFDM receiver of the 2nd Embodiment of this invention. The block diagram which shows the structure of the OFDM receiver of the 3rd Embodiment of this invention. FIG. 4 is a block diagram illustrating a configuration example of a differential error detection circuit in FIG. 3. The figure which shows the OFDM signal divided | segmented into a segment and transmitted concatenatedly. The figure which shows center subchannel number 0-41 of 1 segment. The figure which shows the multiplexing example of SP signal in an OFDM transmission system. The figure which shows the constellation of the complex data of the complex data of the QPSK modulated I-axis and Q-axis complex data, and the BPSK modulation. The block diagram of the PRBS generation circuit used in order to carry out BPSK modulation of SP signal. The figure which shows the list of the register initial value in a PRBS generating circuit.

Explanation of symbols

102, 202, 302 ... FFT circuit 103, 203, 303 ... Equalization circuit 104, 204, 304 ... SP extraction circuit 105, 205, 305 ... SP time axis interpolation circuit 106, 206, 306 ... BPSK modulation removal circuit 107, 207 , 307 ... SP frequency axis interpolation circuit 108 ... S / N detection circuit 109, 209, 309 ... PRBS generation circuit 110, 210, 310 ... determination circuit 208 ... error correction circuit 311 ... differential error detection circuit

Claims (5)

A pilot signal is multiplexed and transmitted in a predetermined arrangement pattern in the frequency direction and the time direction, and the pilot signal is transmitted after being BPSK-modulated in one of a plurality of pseudo-random code sequences (hereinafter referred to as PRBS) in the frequency direction. In an OFDM receiver that receives an orthogonal frequency division multiplexing (hereinafter referred to as OFDM) signal,
Fast discrete Fourier transform means for transforming the received signal into a frequency domain signal by fast discrete Fourier transform;
Pilot signal extraction means for extracting a pilot signal from the output of the fast discrete Fourier transform means;
PRBS generating means for generating any of the plurality of PRBS in response to a selection signal;
BPSK modulation removing means for removing the BPSK modulation from the output of the pilot signal extracting means using the output of the PRBS generating means;
A data demodulating means for equalizing the output of the fast discrete Fourier transform means with the output of the BPSK modulation removing means to obtain demodulated data;
Detecting means for obtaining a detection signal relating to the quality of the demodulated data which is an output of the data demodulating means;
Determining means for inputting the detection signal and outputting the selection signal for selecting an optimal PRBS among the plurality of PRBSs based on a determination criterion that the detection signal is best;
The OFDM receiver according to claim 1, wherein the determination means tries the plurality of PRBSs to obtain the determination criterion.   The detection means is an S / N detection means for detecting a reception S / N from an output of the data demodulation means, and a PRBS with the best reception S / N with the output of the S / N detection means as the determination criterion. The OFDM receiving apparatus according to claim 1, wherein: Further comprising error correction means for correcting the output of the data demodulation means;
The detection means is an error rate detection means for detecting an error rate from the output of the error correction means, and selects a PRBS with the best error rate using the output of the error rate detection means as the determination criterion. The OFDM receiver according to claim 1.    4. The OFDM receiver according to claim 3, wherein the error correction means includes the error rate detection means. The detection means includes
Difference calculating means for obtaining a difference value between pilot signals adjacent in the frequency direction from the output of the BPSK modulation removing means;
Absolute value detecting means for detecting the absolute value of the difference calculating means;
Integration means for integrating the output of the absolute value detection means for a predetermined interval,
2. The OFDM receiving apparatus according to claim 1, wherein a PRBS having a minimum integration means output is selected using the output of the integration means as the determination criterion.

Images