JP5395368B2 - OFDM receiver - Google Patents

Description

  The present invention relates to an OFDM receiver that receives segment-type OFDM signals.

  In Japanese digital terrestrial television broadcasting, an OFDM (Orthogonal Frequency Division Multiplexing) system is adopted as a transmission system. In digital terrestrial television broadcasting, one channel (6 MHz) is divided into 13 segments. Of the 13 segments, 12 segments are used for broadcasting for fixed receivers (12 segment broadcasting), and the remaining 1 segment is used for broadcasting for mobile receivers such as mobile phones (1 segment broadcasting).

  In 1-segment broadcasting, transmission parameters different from those in 12-segment broadcasting are used to enable viewing in an environment where reception conditions are not good. For example, in 12 segment broadcasting, 64QAM having a high coding rate is used as a modulation method, whereas in 1 segment broadcasting, QPSK is used.

JP 2006-310948 A

  Patent Document 1 discloses a television receiving system that supports both 12-segment broadcasting and 1-segment broadcasting. The television receiving system according to Patent Document 1 includes a receiver that supports 12-segment broadcasting and a receiver that supports 1-segment broadcasting. Depending on the broadcast wave reception status, video data of either 12-segment broadcast or 1-segment broadcast is output to the liquid crystal display. Parameters such as C / N (Carrier to Noise) and BER (Bit Error Rate) are used to determine the reception status.

  However, in the television reception system according to Patent Document 1, a receiver that supports 12-segment broadcasting and a receiver that supports 1-segment broadcasting perform reception processing such as OFDM demodulation processing in parallel. For example, even when the user is watching 1-segment broadcast, reception processing corresponding to 12-segment broadcast is performed in the background. For this reason, the television reception system according to Patent Document 1 has a problem that the amount of power consumption is larger than that of a normal terrestrial digital broadcast receiver.

  Therefore, in view of the above problems, an object of the present invention is to provide an OFDM receiving apparatus that can cope with both 12-segment broadcasting and 1-segment broadcasting and can suppress power consumption.

In order to solve the above-mentioned problems, an invention according to claim 1 is an OFDM receiver, which receives a segmented OFDM (orthogonal frequency division multiplexing) signal and demodulates the OFDM signal into a frequency domain signal. and parts, as the quality information indicating the reception quality of said OFDM signal, instructs the quality information detection unit for detecting the Doppler shift value from a signal of the frequency domain, the segments to be demodulated on the basis of the Doppler shift value to the OFDM demodulator And a demodulating segment instruction section.

According to a second aspect of the invention, in the OFDM receiving apparatus according to claim 1, further the frequency of the system clock for operating the OFD M demodulation unit, a clock generator, which changes depending on the segment to the demodulation It is characterized by providing.

  The invention according to claim 3 is the OFDM receiver according to claim 2, wherein the OFDM demodulator converts the OFDM signal into a digital signal based on a first sampling clock; A fast Fourier transform unit that performs a fast Fourier transform based on a second sampling clock and converts the digital signal into a signal in the frequency domain, and the OFDM receiver further includes a predetermined clock for the system clock. A sampling clock generation for generating the first sampling clock by dividing by a first dividing ratio and generating the second sampling clock by dividing the system clock by a predetermined second dividing ratio Part.

In order to solve the above-mentioned problem, an invention according to claim 1 is an OFDM receiver for receiving a segmented OFDM (orthogonal frequency division multiplexing) signal and demodulating the OFDM signal into a frequency domain signal. A quality information detection unit that detects a Doppler shift value from a symbol included in the frequency domain signal , and a segment that is demodulated based on the Doppler shift value as the quality information indicating reception quality of the OFDM signal. A demodulating segment instruction unit for instructing the demodulating unit.

  According to a fifth aspect of the present invention, in the OFDM receiver according to the third or fourth aspect, the fast Fourier transform unit includes a first arithmetic unit that performs a fast Fourier transform on the digital signal corresponding to one segment. A second arithmetic unit that performs a fast Fourier transform on the digital signal corresponding to a plurality of segments, and the second arithmetic unit according to the segment to be demodulated, the first arithmetic unit and the second arithmetic unit And a control unit for supplying to any of the above.

A sixth aspect of the present invention is the OFDM receiving apparatus according to any one of the first to fifth aspects, wherein the quality information detecting unit detects C / N from the signal in the frequency domain. .

A seventh aspect of the present invention is the OFDM receiver according to any one of the first to fifth aspects, further comprising: a decoding unit that decodes the frequency domain signal to generate a data signal; The information detection unit detects a BER obtained based on error correction of the data signal.

According to an eighth aspect of the present invention, in the OFDM receiver according to any one of the first to seventh aspects, the demodulation segment instruction unit detects a control signal included in the OFDM signal from the signal in the frequency domain. And a demodulating segment instruction unit that determines whether or not the demodulated segment can be changed based on the control signal .

According to a ninth aspect of the present invention, in the OFDM receiver according to the second aspect , the demodulating segment instruction unit instructs the OFDM demodulating unit to demodulate the segment to be demodulated at a timing of receiving a guard interval included in the OFDM signal. The clock generator may change the frequency of the system clock at the timing.

  The OFDM receiver according to the present invention demodulates the received OFDM signal into a frequency domain signal, and determines a demodulated segment based on quality information detected from the frequency domain signal. Thereby, since the segment to demodulate can be changed according to the reception condition of the OFDM signal, the power consumption can be reduced.

  The OFDM receiver according to the present invention changes the frequency of the system clock of the OFDM demodulator according to the segment to be demodulated. As a result, since the OFDM receiver can operate at a processing speed corresponding to the segment to be demodulated, the power consumption can be reduced.

  In addition, the OFDM receiving apparatus according to the present invention switches the arithmetic unit used for the fast Fourier transform according to the segment to be demodulated. Thereby, power consumption can further be reduced.

{Overall configuration of OFDM receiver}
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of OFDM receiving apparatus 1 according to the present embodiment. The OFDM receiver 1 includes an antenna 2, a tuner 3, a baseband processing unit 4, a source decoder 5, and a D / A conversion unit 6.

  The antenna 2 receives an RF (Radio Frequency) signal 100 transmitted from an OFDM transmitter (not shown). The RF signal 100 is a signal corresponding to terrestrial digital television broadcasting. The tuner 3 converts the frequency of the RF signal 100 received by the antenna 2 into an IF (Intermediate Frequency) signal. A high frequency component is removed from the IF signal, and the IF signal is output from the tuner 3.

  The baseband processing unit 4 performs OFDM demodulation processing, demapping processing, error correction processing, and the like on the IF signal, and demodulates the IF signal into a data signal. The baseband processing unit 4 will be described later, but is a characteristic part of the present invention.

  The source decoder 5 converts the data signal output from the baseband processing unit 4 into MPEG (Moving Picture Experts Group) -2 or H.264 format. The decoding is performed based on the H.264 system. The D / A converter 6 converts the decoded digital signal into an analog signal and outputs it to a liquid crystal display (not shown) or the like.

{Configuration of baseband processing unit}
Next, the configuration of the baseband processing unit 4 will be described in detail. As shown in FIG. 1, the baseband processing unit 4 includes an A / D converter 41, a baseband converter 42, a digital filter 43, a resampler 44, and an FFT (Fast Fourier Transform) processing unit. 45, an equalizer 46, a channel decoder 47, a determination unit 48, and a clock generation unit 49.

  The baseband processing unit 4 executes either narrowband demodulation processing or wideband demodulation processing. Narrowband demodulation processing refers to processing for demodulating a data signal using a segment corresponding to one-segment broadcasting. The broadband demodulation process refers to a process of demodulating a data signal using 13 segments, and is executed when the OFDM receiver 1 receives a 12-segment broadcast. The baseband processing unit 4 can change the segment to be demodulated according to the reception status of the RF signal 100.

  The A / D converter 41 converts the analog IF signal output from the tuner 3 into a digital signal (symbol signal) based on the sampling clock 71. The baseband converter 42 converts the symbol signal into a baseband band complex signal. The symbol signal is converted into a complex signal by being multiplied by the local oscillation signal output from the local oscillator 421 and the mixer 422. The local oscillation signal is generated based on the sampling clock 72 input to the local oscillator 421.

  The digital filter 43 is an adaptive filter, and extracts a complex signal in the frequency band designated by the determination unit 48. The resampler 44 outputs a complex signal based on the sampling clock 71 to the FFT processing unit 45 in accordance with the sampling clock 73 used in the FFT operation. The FFT processing unit 45 converts the complex signal in the time domain into a complex signal in the frequency domain (hereinafter referred to as “received OFDM signal”) by performing a fast Fourier transform process.

  The equalizer 46 estimates the transmission path of the RF signal 100 and equalizes the received OFDM signal. The channel decoder 47 decodes the equalized received OFDM signal into a data signal by performing various processes such as demapping, Viterbi decoding, and Reed-Solomon decoding.

  The determination unit 48 determines whether to perform wideband demodulation processing or narrowband demodulation processing based on fading information extracted from the received OFDM signal.

  The clock generation unit 49 generates sampling clocks 71 to 73 and an operation clock used in each block according to the determination result of the determination unit 48. The clock generation unit 49 includes a PLL (Phased Lock Loop) circuit 491, a sampling clock generation unit 492, and an operation clock generation unit 493. The PLL circuit 491 generates a system clock 70 used in the baseband processing unit 4. The sampling clock generation unit 492 divides the system clock 70 to generate sampling clocks 71 to 73 having different frequencies. The operation clock generation unit 493 divides the system clock 70 to generate an operation clock for each functional block.

{Configuration of determination unit}
Next, the configuration of the determination unit 48 will be described. FIG. 2 is a block diagram illustrating a configuration of the determination unit 48. The determination unit 48 includes a fading detection unit 481, a TMCC (Transmission and Multiplexing Configuration Control) demodulation unit 482, and a demodulation segment instruction unit 483.

  The fading detection unit 481 detects the Doppler shift value from the received OFDM signal as fading information. TMCC demodulation section 482 demodulates TMCC information included in the received OFDM signal. The TMCC information is control information used when a data signal is demodulated from the received OFDM signal. Demodulation segment instruction unit 483 determines the reception status of RF signal 100 based on the fading information, and determines a segment to be demodulated according to the reception status of RF signal 100.

{Configuration of FFT processing unit}
Next, the configuration of the FFT processing unit 45 will be described. FIG. 3 is a block diagram illustrating a configuration of the FFT processing unit 45. The FFT processing unit 45 includes a narrowband computing unit 451, a wideband computing unit 452, and a control unit 453. The narrowband calculation unit 451 executes an FFT calculation based on the number of points corresponding to one segment. The broadband operation unit 452 performs an FFT operation based on the number of points corresponding to 13 segments. The control unit 453 controls the narrowband computing unit 451 and the wideband computing unit 452.

{Demodulation segment change processing flow}
Next, the flow of demodulated segment change processing performed in the OFDM receiver 1 will be described. The demodulating segment changing process is a process of changing from the wideband demodulating process to the narrowband demodulating process or from the narrowband demodulating process to the wideband demodulating process depending on the reception status of the RF signal 100.

  Here, the operation of the OFDM receiver 1 when switching from wideband demodulation processing to narrowband demodulation processing will be described as an example. It is assumed that the OFDM receiver 1 is mounted on an automobile and performs wideband demodulation processing in a stationary state. In such a state, the OFDM receiver 1 operates as follows.

  Each functional block of the OFDM receiver 1 operates with an operation clock corresponding to wideband demodulation processing. Specifically, the PLL circuit 491 generates a system clock 70 of f1 (Hz) corresponding to wideband demodulation processing. The operation clock generation unit 493 divides the system clock 70 of f1 (Hz) by a division ratio determined for each functional block, and generates an operation clock corresponding to each functional block.

  The sampling clock generation unit 492 generates sampling clocks 71 to 73 from the system clock 70 of f1 (Hz). Similarly to the operation clock, each frequency division ratio between the system clock 70 and the sampling clocks 71 to 73 is determined. Sampling clocks 71 to 73 are generated by dividing system clock 70 by each division ratio. For example, the frequency of the sampling clock 71 in the wideband demodulation process is 8.127 (MHz).

  The digital filter 43 extracts a complex signal in a frequency band corresponding to 13 segments. The resampler 44 serial-parallel converts the complex signal input from the digital filter 43 at 8.127 (MHz), and outputs the complex signal to the FFT processing unit 45 based on the frequency of the sampling clock 73.

  In the FFT processing unit 45, the broadband calculation unit 452 performs an FFT calculation of the complex signal input from the resampler 44. At this time, the control unit 453 outputs the sampling clock 73 and the operation clock to the wideband calculation unit 452. The sampling clock 73 or the like is not input to the narrowband calculation unit 451.

  In the determination unit 48, the fading detection unit 481 continuously detects the Doppler shift value from the received OFDM signal. The Doppler shift value can be estimated from the rate of change of the power of pilot symbols such as SP (Scattered Pilot). For example, fading detection section 481 calculates the average power of pilot symbols from each symbol of the received OFDM signal, obtains the rate of change of average power of pilot symbols over a plurality of symbols, and estimates the Doppler shift value from this rate of change. . Here, since it is assumed that the OFDM receiver 1 is in a stationary state, the Doppler shift value is zero. For this reason, the demodulation segment instruction | indication part 483 determines with the reception condition of the RF signal 100 being favorable, and continues a wideband demodulation process.

  Next, consider a case where the OFDM receiver 1 starts moving from a stationary state. That is, as the automobile accelerates, a Doppler shift based on Rayleigh fading occurs in the received OFDM signal.

  FIG. 4 is a diagram showing the relationship between the Doppler shift value and the frequency of the system clock 70. As shown in FIG. As shown in FIG. 4, the Doppler shift value increases from time t1, and at time t2, the Doppler shift value is greater than Δf1 (Hz). Further, at time t2, the demodulation segment changing process is performed, and the frequency of the system clock 70 is changed from f1 (Hz) to f2 (Hz) corresponding to the narrowband demodulation process. Note that f1 = 8 × f2 (Hz). The demodulated segment instruction unit 483 holds a Doppler shift value Δf1 (Hz) as a threshold value for determining whether to execute the demodulated segment change process.

  Specifically, when a Doppler shift value exceeding Δf1 (Hz) is detected, the demodulation segment instruction unit 483 has moved the OFDM receiver 1 and stably decodes the OFDM reception signal in the wideband demodulation process. It is determined that this is not possible, and it is determined to switch to narrowband reception processing. Demodulation segment instruction unit 483 confirms whether the partial reception flag recorded in the TMCC information is “1”. The partial reception flag is information indicating whether 1-segment broadcasting is being performed.

  When the partial reception flag is not “1”, the demodulation segment instruction unit 483 continues the wideband demodulation processing. On the other hand, when the partial reception flag is “1”, the demodulation segment instruction unit 483 determines that one-segment broadcasting can be received, and switches to narrowband demodulation processing.

  Specifically, demodulation segment instruction unit 483 outputs clock switching signal 81 to clock generation unit 49. The clock switching signal 81 is a signal that instructs to change the frequency of the system clock 70. The PLL circuit 491 generates a system clock 70 of f2 (Hz) based on the clock switching signal 81 and supplies the system clock 70 to the sampling clock generation unit 492 and the operation clock generation unit 493.

  The sampling clock generation unit 492 generates sampling clocks 71 to 73 from the system clock 70 of f2 (Hz). For this reason, each frequency of the sampling clocks 71 to 73 in the narrowband demodulation processing is 1/8 of the frequency in the wideband demodulation processing. For example, in the narrowband demodulation process, the frequency of the sampling clock 71 is 1.016 (MHz). Similarly, the frequency of the operation clock output from the operation clock generation unit 493 is also 比較 compared to that during the wideband demodulation process.

  The demodulation segment instruction unit 483 outputs the filter control signal 82 to the digital filter 43. The filter control signal 82 is a signal that instructs to change the frequency band extracted by the digital filter 43. The digital filter 43 changes the frequency band corresponding to the narrowband demodulation process by changing the tap coefficient based on the filter control signal 82.

  Demodulation segment instruction unit 483 outputs point number change signal 83 to FFT processing unit 45. The point number change signal 83 is a signal for instructing switching of the FFT point number in accordance with the change of the demodulated segment. Based on the point number change signal 83, the control unit 453 changes the supply destination of the sampling clock 73 and the operation clock from the wideband operation unit 452 to the narrowband operation unit 451.

  By performing the demodulation segment change process in this way, the OFDM receiver 1 can switch the operation state according to the reception status of the RF signal 100. The demodulated segment change process is executed during a period when the IF signal corresponding to the guard interval is input to the baseband processing unit 4. Demodulation segment instruction unit 483 can specify the timing for executing the demodulated segment change process using the symbol timing specified by the symbol synchronization unit (not shown).

  Further, the demodulated segment changing process for switching from the narrowband demodulating process to the wideband demodulating process is performed in the same manner as described above. Here, consider a case where the automobile decelerates and the Doppler shift becomes small. As shown in FIG. 4, as the automobile decelerates from time t3, the Doppler shift value also decreases. Then, at time t4 when the Doppler shift value becomes equal to or less than Δf1 (Hz), the demodulation segment instruction unit 483 executes demodulation segment change processing for switching from narrowband demodulation processing to wideband demodulation processing. Note that at time t4, the demodulation segment instruction unit 483 does not check the partial reception flag of the TMCC information.

  Specifically, when the clock switching signal 81 is input to the clock generation unit 49, the frequency of the system clock 70 is changed from f2 (Hz) to f1 (Hz). Thereby, each clock output from the sampling clock generation unit 492 and the operation clock generation unit 493 has a frequency corresponding to the wideband demodulation process. Further, the digital filter 43 makes the frequency band for extracting the complex signal correspond to 13 segments in accordance with the input of the filter control signal 82. In the FFT processing unit 45, the supply destination of the sampling clock 73 and the operation clock is changed to the broadband operation unit 452. In this way, the narrowband demodulation process is switched to the wideband demodulation process.

  As described above, OFDM receiving apparatus 1 according to the present embodiment determines a segment to be demodulated based on fading information detected from the received OFDM signal. As a result, either one of the narrowband demodulation processing and the wideband demodulation processing is processed, so that power consumption can be suppressed.

  Also, the OFDM receiver 1 switches the frequency of the system clock 70 according to the number of segments to be demodulated. Thereby, since the OFDM receiver 1 can change the processing speed according to the number of segments to be demodulated, the power consumption can be suppressed.

  In addition, when performing an FFT operation on a complex signal, the OFDM receiver 1 determines which of the narrowband operation unit 451 and the wideband operation unit 452 to use based on the number of segments to be demodulated. Thus, since the OFDM receiver 1 switches the circuit to be used according to the segment to be demodulated, the power consumption can be further suppressed.

  In the present embodiment, the example in which the determination unit 48 determines the reception status of the RF signal 100 based on the fading information has been described, but the present invention is not limited to this. For example, the determination unit 48 may detect C / N from the received OFDM signal and confirm the reception status of the RF signal 100 based on the detected C / N. Further, the determination unit 48 may acquire a BER (Bit Error Rate) detected at the time of error correction processing from the channel decoder 47 and confirm the reception status of the RF signal 100 based on the acquired BER. Further, the determination unit 48 may check the reception status of the RF signal 100 by appropriately combining C / N, BER, and fading information.

  In the present embodiment, the example in which the FFT processing unit 45 includes the narrowband computing unit 451 and the wideband computing unit 452 has been described, but is not limited thereto. The FFT processing unit 45 may include an FFT operation unit that can switch the number of points. For example, the FFT operation unit performs an FFT operation with the number of points corresponding to 13 segments in the wideband demodulation process, and performs an FFT operation with the number of points corresponding to one segment in the narrowband demodulation process. The FFT operation unit can reduce the power consumption in the narrowband demodulation process by not supplying the sampling clock 73 to the circuit unit that is not used in the narrowband demodulation process.

  In the present embodiment, the example in which the determination unit 48 determines whether or not the narrowband demodulation process can be performed using the partial reception flag recorded in the TMCC information has been described. However, the present invention is not limited to this. For example, the determination unit 48 may perform the demodulation segment change process based on other information recorded in the TMCC information. For example, the demodulated segment instruction unit 483 may execute the demodulated segment change process when a modulation scheme or the like that cannot be handled by the wideband demodulating process is indicated by the TMCC information.

It is a block diagram which shows the structure of the OFDM receiver which concerns on embodiment of this invention. It is a block diagram which shows the structure of a determination part. It is a block diagram which shows the structure of a FFT process part. It is a figure which shows the relationship between a Doppler shift value and the frequency of a system clock.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 OFDM receiver 2 Antenna 3 Tuner 4 Baseband processing part 5 Source decoder 41 A / D converter 42 Baseband converter 43 Digital filter 45 FFT processing part 47 Channel decoder 48 Judgment part 49 Clock generation part 481 Fading detection 482 TMCC demodulation unit 483 Demodulation segment instruction unit

Claims (9)

An OFDM demodulator that receives a segmented OFDM (Orthogonal Frequency Division Multiplex) signal and demodulates the OFDM signal into a frequency domain signal;
As quality information indicating the reception quality of the OFDM signal, a quality information detection unit that detects a Doppler shift value from a symbol included in the frequency domain signal;
A demodulating segment instruction unit that instructs the OFDM demodulating unit to demodulate a segment based on the Doppler shift value;
An OFDM receiving apparatus comprising: The OFDM receiver according to claim 1, further comprising:
A clock generator for changing a frequency of a system clock for operating the OFDM demodulator according to the segment to be demodulated;
An OFDM receiving apparatus comprising: The OFDM receiver according to claim 2,
The OFDM demodulator includes:
An A / D converter that converts the OFDM signal into a digital signal based on a first sampling clock;
A fast Fourier transform unit that performs a fast Fourier transform based on a second sampling clock to convert the digital signal into a signal in the frequency domain;
Including
The OFDM receiver further includes:
The system clock is divided by a predetermined first division ratio to generate the first sampling clock, and the system clock is divided by a predetermined second division ratio to generate the second sampling clock. A sampling clock generator for generating
An OFDM receiving apparatus comprising: The OFDM receiver according to claim 3,
The OFDM demodulator further comprises:
A frequency converter for down-converting the digital signal;
An adaptive filter that extracts a signal corresponding to the segment to be demodulated from the down-converted digital signal based on an instruction of the demodulation segment instruction unit;
Including
The OFDM receiver further includes:
A frequency conversion clock generation unit configured to divide the system clock by a predetermined third division ratio to generate a clock used for down-conversion of the digital signal;
An OFDM receiving apparatus comprising: In the OFDM receiver according to claim 3 or 4,
The fast Fourier transform unit includes:
A first arithmetic unit that performs a fast Fourier transform on the digital signal corresponding to one segment;
A second arithmetic unit for fast Fourier transforming the digital signals corresponding to a plurality of segments;
A control unit that supplies the second sampling clock to either the first calculation unit or the second calculation unit according to the segment to be demodulated;
An OFDM receiving apparatus comprising: In the OFDM receiver according to any one of claims 1 to 5,
The OFDM information receiving apparatus, wherein the quality information detecting unit detects C / N from the frequency domain signal. The OFDM receiver according to any one of claims 1 to 5, further comprising:
A decoding unit for decoding the frequency domain signal to generate a data signal;
With
The OFDM information receiving apparatus, wherein the quality information detecting unit detects a BER obtained based on error correction of the data signal. The OFDM receiver according to any one of claims 1 to 7,
The demodulation segment instruction unit
A control signal detector for detecting a control signal included in the OFDM signal from the signal in the frequency domain;
Including
The OFDM receiving apparatus, wherein the demodulating segment instruction unit determines whether the demodulated segment can be changed based on the control signal. The OFDM receiver according to claim 2,
The demodulating segment instruction unit instructs the OFDM demodulating unit to demodulate the segment to be demodulated at a timing of receiving a guard interval included in the OFDM signal;
The OFDM receiver according to claim 1, wherein the clock generator changes the frequency of the system clock at the timing.

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