JP3115239B2 - Receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates also relates to a receiving ShinSo location of Ru used for reception, such as a digital audio broadcasting signal, further orthogonal frequency division multiplexing in particular (hereinafter referred to as OFDM) demodulation for demodulating the modulated signal The present invention relates to a receiving device provided with a receiver.

[0002]

BACKGROUND ART As receiver using a conventional demodulator of this type is shown in FIG. 2, O FDM modulated received signal is supplied to the input terminal, the received signal is frequency converted by a mixer 1, A A / D conversion is performed by the / D converter 2. A
The received signal subjected to the / D conversion is converted to a serial / parallel converter 3
Is converted into parallel data, and the output parallel data is supplied to a fast Fourier transform circuit (hereinafter, referred to as an FFT circuit) 4. The FFT circuit 4 performs a Fourier transform on the input data, converts the input time-domain signal into a frequency-domain signal, and outputs the signal. FFT circuit 4
Is supplied to the delay detection circuit 6 and the frequency offset detection circuit 17, and the delay detection circuit 6 delay-detects the input signal and sends out the demodulated data from the output terminal.

A frequency offset detecting circuit 17 detects a frequency offset amount based on a reference symbol for detecting a frequency offset in an input signal, and converts an oscillation frequency of a voltage control oscillator 9 acting as a local oscillator into a detected frequency offset amount. The output from the voltage-controlled oscillator 9 with the frequency deviation corrected is supplied to the mixer 1 and frequency-converted.

[Problems to be solved by the invention]

However, in the conventional receiver described above, in the multipath environment in JP <br/> constant, and become large frequency offset detection error, it has a problem that if occurs can no longer be received normally .

[0005] It is an object of the present invention to provide a receiving apparatus in which the detection performance of a frequency offset is prevented from being deteriorated by a receiving environment.

[0006]

SUMMARY OF THE INVENTION A receiving apparatus according to the present invention performs A / D conversion of a received signal, performs a discrete Fourier transform on the A / D-converted received signal, and performs delay detection of discrete Fourier transform output data. A first frequency offset detecting means for detecting a frequency offset value at an input of a demodulator based on a reference symbol for detecting a frequency offset in the discrete Fourier transform data; Second frequency offset detection means for detecting a frequency offset value at the input of the demodulator from the phase difference, and a frequency offset value detected by the first frequency offset detection means falls within a frequency offset detection range by the second frequency offset detection means. From the start of reception until the frequency offset detected by the first frequency offset detection means Select, and selection means for subsequently selecting a detected frequency offset value by the second frequency offset detecting means, and performs automatic frequency control on the basis of the detected frequency offset value selected.

According to the receiving apparatus of the present invention, the frequency offset value at the input of the demodulator is detected by the first frequency offset detecting means based on the reference symbol for detecting the frequency offset in the discrete Fourier transform data, The frequency offset value at the input of the demodulator is detected from the phase difference of the differential detection output data by the second frequency offset detecting means. The selection means selects the detection frequency offset value from the first frequency offset detection means from the start of reception until the detected frequency offset value by the first frequency offset detection means enters the frequency offset detection range by the second frequency offset detection means. Then, the detected frequency offset value by the second frequency offset detecting means is selected, and automatic frequency control is performed based on the detected frequency offset value selected by the selecting means.

However, since the detection of the detected frequency offset value by the second frequency offset detecting means is detected from the phase difference of the output data of the differential detector, the detection range of the detected frequency offset value is narrow, but is detected depending on the reception environment. It will not be impossible. On the other hand, since the detection of the detected frequency offset value by the first frequency offset detecting means is based on the reference symbol, it is affected by the reception environment. Therefore, the selecting means sets the detected frequency offset value by the first frequency offset detecting means from the start of reception until the detected frequency offset value by the first frequency offset detecting means enters the frequency offset detecting range by the second frequency offset detecting means. As a result, automatic frequency control is performed, and then automatic frequency control is performed based on the frequency offset value detected by the second frequency offset detection means. As a result, good reception is possible regardless of the reception environment.

In place of the selecting means, there is provided a synthesizing means for synthesizing a detected frequency offset value detected by the first frequency offset detecting means and a frequency offset detected value detected by the second frequency offset detecting means at a predetermined ratio. The same applies to the case where automatic frequency control is performed based on the synthesized frequency offset value. In this case, the combining ratio in the combining means may be changed based on the error correction rate obtained from the error correcting means.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A receiving apparatus according to the present invention will be described with reference to an embodiment. FIG. 1 is a block diagram showing a configuration of a main part of a receiving apparatus according to one embodiment of the present invention.

In the receiving apparatus according to one embodiment of the present invention, the received signal is frequency-converted by the mixer 1 in cooperation with the voltage-controlled oscillator 9 acting as a local oscillator, and is converted into an intermediate frequency signal. The intermediate frequency signal is supplied to the A / D converter 2 and is converted into a digital signal. The intermediate frequency signal converted into the digital signal is supplied to the serial / parallel converter 3 and converted into parallel data, and the output parallel data is supplied to the FFT circuit 4.

In the FFT circuit 4, the input parallel data is windowed in accordance with the number of FFT points, Fourier-transformed in units of the window, and the input signal in the time domain is input in the frequency domain. The signal is converted and output. The output from the FFT circuit 4 is supplied to the delay detection circuit 6 to be subjected to delay detection, and the demodulated data subjected to the delay detection is transmitted from an output terminal. The output from the FFT circuit 4 is also sent to the frequency offset detection circuit 7, and the demodulated data subjected to the delay detection is also sent to the frequency offset detection circuit 8.

The frequency offset detection circuit 7 receiving the output from the FFT circuit 4 detects a frequency offset amount based on a reference symbol for frequency offset detection in the input signal. In the frequency offset detection circuit 8 receiving the demodulated data from the delay detection circuit 6, the difference between the phase value obtained by obtaining the phase of the input demodulated data and the phase without the frequency offset is obtained. An offset amount is detected.

A signal based on the frequency offset amount detected by the frequency offset detection circuit 7 and a signal based on the frequency offset amount detected by the frequency offset detection circuit 8 are sent to the switch circuit 10. On the other hand, the changeover switch circuit 10 selects a signal based on the frequency offset amount output from the frequency offset detection circuit 7 until the frequency offset value detected by the frequency offset detection circuit 7 falls within the frequency offset detectable range by the frequency offset detection circuit 8. When the frequency offset value detected by the frequency offset detection circuit 7 falls within the frequency offset detectable range by the frequency offset detection circuit 8, a signal based on the frequency offset amount output from the frequency offset detection circuit 8 is selected by the changeover switch circuit 10. The switching signal to be transmitted is transmitted from the frequency offset detection circuit 7 to the switching circuit 10.

A signal based on the detected frequency amount selected in the switching circuit 10 is supplied to a voltage-controlled oscillator 9 acting as a local oscillator, and the oscillation frequency of the voltage-controlled oscillator 9 is detected by the detection signal transmitted from the switching circuit 10. By controlling based on the frequency offset amount, the frequency deviation is corrected. In this case, when the frequency control voltage of the voltage controlled oscillator 9 is an analog voltage, a signal based on the detected frequency offset amount is converted into an analog voltage by a converter (not shown) and supplied to the voltage controlled oscillator 9. As a result, the oscillation output from the voltage controlled oscillator 9 in which the frequency deviation has been corrected is supplied to the mixer 1 and the received signal inputted is frequency-converted to perform automatic frequency control.

Regarding the frequency offset detection in frequency offset detection circuit 7 and frequency offset detection circuit 8 in the receiving apparatus according to an embodiment of the present invention configured as described above, the transmission mode of the digital audio broadcast signal of the European standard is used. The case of 1 will be described as an example.

First, detection of the frequency offset amount in the frequency offset detection circuit 7 will be described. In the case of a digital audio broadcast signal, a phase reference symbol (PRS) which is a reference symbol is included in the transmitted signal. The 1536 QSPK symbol used for this PRS is composed of 48 blocks of 32 QPSK symbols, and each block has a phase-shifted C
AZC (Constanto Amplitude Zero AutoCorrelation)
A code sequence obtained by differentially coding the code sequence is used. The CAZAC code sequence used in all blocks is the same, and the phase to be shifted is every π / 2.

The frequency offset detecting circuit 7 of the receiving apparatus detects the frequency offset amount using this property of the PRS. Upon receiving the output of the FFT circuit 4,
The RS is differentially detected between QPSK symbols. The differentially detected QPSK symbol becomes a phase-shifted CAZAC code sequence including a frequency offset, and is divided into 48 blocks. Thereafter, in order to reduce interference between blocks, only 16 QPSK symbols are extracted per block, and a 16 × 48 QPSK symbol is phase-shifted for each block, so that all blocks have the same CAZAC.
After a code sequence is obtained and combined, a correlation is obtained with a CAZAC code sequence prepared in advance.

Here, if the position is changed when 16QPSK symbols are extracted, the effect is the same as offsetting the frequency at the carrier frequency interval.
The autocorrelation of the code sequence has almost no correlation when shifted by one or more symbols, as in the case of the M sequence. By utilizing this property, the position of extracting the 16QPSK symbol is shifted and the correlation is made with the previously prepared CAZAC code sequence, and the amount of shift that maximizes the correlation coefficient is obtained to detect the frequency offset amount. The resolution in this detection is the carrier frequency interval, which is 1 kHz.

Therefore, the following operation is performed in order to obtain the frequency offset amount with a resolution equal to or less than the carrier frequency interval.
After obtaining the shift amount at which the correlation coefficient becomes maximum, the correlation coefficient at that point and the correlation coefficient at the point where the shift amount is changed by ± 1 symbol are obtained. In addition, delay detection between 2QPSK symbols is also performed to obtain correlation coefficients at the same shift amount and at a point changed by one symbol, and the frequency offset amount is obtained from the five types of correlation coefficients.

Next, in the frequency offset detection circuit 8,
The frequency offset is estimated from the phase of the QPSK symbol after differential detection in the differential detection circuit 6. Delay detection is performed at 1.246 ms (OF) in each QPSK symbol.
Since the phase difference per DM symbol length is obtained, if the frequency is shifted, the delay detection output from the delay detection circuit 6 includes a phase offset corresponding to the frequency shift, and the phase offset amount , The frequency offset amount is detected.

Each carrier of OFDM is π / 4-QPSK
Modulated. In this case, the phase of the data output from the delay detection circuit 6 is ± without a frequency offset.
There are four values of 45 degrees and ± 135 degrees. When there is a frequency offset, a data phase shift occurs according to the frequency offset amount. However, the deviation can be normally detected within the range of ± 45 degrees, and if the deviation is longer than that, it is detected as different data. Therefore, the frequency offset detection circuit 8 can detect the frequency offset within a narrow range.

In the frequency offset detection circuit 7,
Although the frequency offset amount is detected based on the frequency offset detected reference symbol subjected to the FFT, a large error occurs in the detected value depending on the state of the multipath.
On the other hand, the detection of the frequency offset by the frequency offset detection circuit 8 is limited to the frequency offset amount in a narrow range, but the detection is performed such that data cannot be reproduced in a multipath state within the detectable range. There is no error.

Here, a signal based on the frequency offset amount output from the frequency offset detection circuit 7 at the start of reception is selected in the changeover switch circuit 10 by the selection signal from the frequency offset detection circuit 7, and is output from the frequency offset detection circuit 7. The oscillation frequency of the voltage controlled oscillator 9 is controlled by a signal based on the frequency offset amount thus set.

During this time, when the frequency offset amount output from the frequency offset detection circuit 7 falls within the frequency offset detectable range by the frequency offset detection circuit 8, the changeover switch circuit 10 switches according to the selection signal from the frequency offset detection circuit 7. Then, a signal based on the frequency offset amount output from the frequency offset detection circuit 8 is selected, and the oscillation frequency of the voltage control oscillator 9 is controlled by the signal based on the frequency offset amount output from the frequency offset detection circuit 8.

As a result, once the oscillation frequency of the voltage controlled oscillator 9 is controlled by the signal based on the frequency offset amount output from the frequency offset detection circuit 8 and the reception frequency is pulled in, the multipath or the like is used. As a result, the frequency offset amount is not erroneously detected, and the detection performance of the frequency offset is not deteriorated by the reception environment, so that stable reception can be performed.

Further, instead of the changeover switch circuit 10,
A synthesizing circuit for synthesizing a signal based on the frequency offset amount output from the frequency offset detection circuit 7 and a signal based on the frequency offset amount output from the frequency offset detection circuit 8 is provided. The oscillation frequency of the voltage controlled oscillator 9 may be controlled by increasing the synthesis ratio of the signal based on the frequency offset amount output from the detection circuit 7.

In this case, the change of the combination ratio may be the output frequency offset amount from the frequency offset detection circuit 7 or 8, or the correction rate of the data obtained from the error correction circuit.

[0029]

As described above, according to the receiving apparatus of the present invention, it is possible to prevent the detection performance of the frequency offset from deteriorating due to the receiving environment, and to obtain an effect that normal reception can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a main part of a receiving device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a main part of a conventional receiving apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mixer 2 A / D converter 3 serial / parallel converter 4 FFT circuit 6 delay detection circuit 7 and 8 frequency offset detection circuit 9 voltage controlled oscillator 10 switch circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-312627 (JP, A) JP-A-9-275385 (JP, A) JP-A-7-95175 (JP, A) JP-A 8- 265293 (JP, A) JP-A-10-51418 (JP, A) JP-A-9-130362 (JP, A) JP-A-9-307526 (JP, A) JP-A-56-158545 (JP, A) Technical Report of the Institute of Television Engineers of Japan, Vol. 19, NO. 38, p. 7-12 (58) Field surveyed (Int. Cl. ⁷ , DB name) H04J 11/00

Claims (3)

(57) [Claims] An A / D-converted received signal, a discrete Fourier transform of the A / D-converted received signal, and a demodulator for delay-detecting discrete Fourier-transformed output data are provided. First frequency offset detection means for detecting a frequency offset value at the input of the demodulator based on a reference symbol for detecting a frequency offset in the medium, and a frequency offset value at the input of the demodulator from the phase difference of the differential detection output data. A second frequency offset detecting means for detecting, and a first frequency offset detecting means from the start of reception until the detected frequency offset value detected by the first frequency offset detecting means enters a frequency offset detecting range detected by the second frequency offset detecting means. The detected frequency offset value based on the second frequency offset detection value. And selecting means for selecting a detected frequency offset value by means receiving apparatus and performs automatic frequency control on the basis of the detected frequency offset value selected. 2. A receiving apparatus comprising a demodulator for performing A / D conversion of a received signal, performing a discrete Fourier transform on the A / D-converted received signal, and delay-detecting the output data of the discrete Fourier transform. First frequency offset detection means for detecting a frequency offset value at the input of the demodulator based on a reference symbol for detecting a frequency offset in the medium, and a frequency offset value at the input of the demodulator from the phase difference of the differential detection output data. A second frequency offset detecting means for detecting, and a synthesizing means for synthesizing a detected frequency offset value obtained by the first frequency offset detecting means and a frequency offset detected value obtained by the second frequency offset detecting means at a predetermined ratio; Automatic frequency control is performed based on the frequency offset value synthesized by the means. Receiver that. 3. The receiving apparatus according to claim 2, wherein the combining ratio in the combining means is changed based on the error correction rate obtained from the error correcting means.