JPH1198105A - Receiver for digital broadcast - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a digital audio broadcast DAB receiver to surely detect identification information of a transmission station regardless of a simple configuration. SOLUTION: The receiver is provided with a differential circuit 33 that extracts a difference between a signal for a null symbol period of a one- preceding frame and a signal for a null symbol period of a current frame, with a discrimination circuit 34 that discriminates identification information from the difference and with a discrimination circuit 35 that discriminates a frame in which the identification information is included from the polarity of an output of the differential circuit 33.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast receiver suitable for use in a digital audio broadcast receiver.

[0002]

2. Description of the Related Art In Europe, DAB according to the EUREKA 147 standard is implemented as digital audio broadcasting. In this DAB, various encoding processes are performed on a plurality of digital data, and
An FDM signal (orthogonal frequency division multiplexed signal)
An FDM signal is transmitted. In that case, digital data such as digital audio data can be simultaneously broadcast in up to 64 channels. In general, even if there is only one provider (a radio wave provider), the OFDM signal is transmitted or broadcast to the service area SA by a plurality of transmitting stations # 1 to #N, for example, as shown in FIG. .

FIG. 5 shows a frame configuration of data subjected to OFDM processing, that is, baseband data. In this case, the DAB has four operation modes.
Is mainly the case of Mode II for terrestrial broadcasting. One frame of this data has a time length of 24 ms, and is divided into a synchronization channel SC, a high-speed information channel FIC, and a main service channel MSC in order from the beginning.

[0004] The synchronization channel SC is used for processing such as frame synchronization and AFC, and is composed of two symbols, the first symbol of which is a null symbol NULL, and the second symbol of which is a symbol for phase reference. It is TFPR. Further, in this case, the null symbol NULL in every other frame includes identification information TII for identifying the transmitting stations # 1 to #N, and the remaining every other null symbol NULL
Nothing is sent during the period.

[0005] The high-speed information channel FIC is for providing data and the like relating to the main service channel MSC. In mode II, the high-speed information block FIB is divided into three high-speed information blocks FIB. Data such as date, type, data array, and traffic message control are arranged. Further, data called a CIF counter is prepared in the high-speed information block FIB, and the remainder of the value 8 of the CIF counter is 0, 1, 2, 3 (in the case of mode I) The remainder of 2 of the value of the CIF counter is 0. (In the case of Modes II and III) When the remainder of 4 of the value of the CIF counter is 0 or 1 (in the case of Mode IV), the frames in which the CIF counters are prepared are every other frame described above, Contains identification information TII.

Further, the main service channel MSC
Is divided into a number of CI frames CIF determined according to the mode, and digital audio data as main data and various data are arranged. In addition, CIF
The value of the counter is the count result of the CI frame CIF.

[0007] In the case of mode II, the OFDM signal is
Since 384 carrier signals are distributed every 4 kHz, the power spectrum is as shown in FIG. The identification information TII is also expressed by transmitting only the carrier signal of the number corresponding to the transmitting station out of the 384 carrier signals. For example, in the case of mode II, the carrier signal transmitted from the transmitting station having the main identification value of 16 and the sub identification value of 4 is as shown in FIG.

[0008]

By the way, in the DAB receiver, in order to obtain the identification information TII of the transmitter from the received signal, it is necessary to determine and process a null symbol NULL including the identification information TII. For this purpose, the high-speed information block FIB is decoded, and the identification information TI is converted from the remainder of the CIF counter to the null symbol NULL of the corresponding frame.
It is necessary to determine whether or not I is included. As a result, a decoder circuit for decoding the high-speed information block FIB is required, and the circuit scale becomes large.

It is also conceivable to take out the null symbol NULL from the synchronization channel SC as it is, determine the presence or absence of the identification information TII, and obtain the identification information TII. However, since noise due to a clock or the like is constantly generated inside the receiver, the noise may affect the extraction of the correct identification information TII in some cases.

[0010] The present invention is to solve the above problems.

[0011]

According to the present invention, digital data is framed,
In a digital broadcast receiver in which auxiliary data is included in a part of every other frame and a part corresponding to the part of the remaining frame is broadcast without including the auxiliary data, A differential circuit for extracting a difference between the signal of the partial section of the previous frame and the signal of the partial section of the current frame among the received frames, and the auxiliary circuit based on an output of the differential circuit. And a judgment circuit for judging a frame including the auxiliary data from the polarity of the output of the difference circuit. Therefore, data with reduced noise is extracted from the difference circuit, and the target data is determined from the data.

[0012]

In FIG. 1, a broadcast wave signal of DAB is received by an antenna 11, and the received signal is supplied to a front end circuit 12 configured in a superheterodyne format and converted into an intermediate frequency signal. This intermediate frequency signal is supplied to the A / D converter circuit 13 and converted into a digital signal.

The digital signal is supplied to a quadrature demodulation circuit 14 to demodulate baseband I-component and Q-component data, and these data are supplied to an FFT circuit 15 for OFDM demodulation. The data is supplied to the Viterbi decoder circuit 16 where deinterleaving and error correction are performed, and a program (channel) is selected to select digital audio data of a target program.

Subsequently, the selected data is supplied to a data decompression circuit 17 to perform MPEG data decompression.
From the data decompression circuit 17, digital audio data of a target program is decompressed into data of the original data length and extracted, and the extracted digital audio data is supplied to a D / A converter circuit 18 to be analogized. The signal is D / A converted into an audio signal, and this signal is taken out to a terminal 19.

Further, a part of the data is supplied from the Viterbi decoder circuit 16 to the RDI circuit 21 to be converted into data of a predetermined transfer format, and this data is output to a terminal 29. Further, for example, the synchronization circuit 22 is configured by a DSP, AFC of the front end circuit 12 is performed, and processing such as synchronization in the FFT circuit 15 is executed.

Further, the data from the FFT circuit 15 is supplied to a power spectrum calculation circuit 31, where P = I ** 2 + Q ** 2 (I ** 2 and Q ** 2 are the squares of the values I and Q, respectively) Is obtained. However, at this time,
A signal indicating the period of the null symbol NULL is supplied from the synchronization circuit 22 to the calculation circuit 31. The calculation circuit 31 executes the calculation of the data P only during the period of the first null symbol NULL of each frame, and performs the calculation. The result data P is retrieved.

FIG. 2 shows a frequency spectrum when the extracted data P includes a null symbol NULL including identification information TII (in the case of mode I). The line spectrum component having a large level is a component distributed according to the identification information TII, and the low-level component distributed almost uniformly is a noise component. The line spectrum components marked with x are noises that are constantly generated inside the receiver. Although not shown, the calculation circuit 3
When the data P extracted from 1 has a null symbol NULL that does not include the identification information TII, the frequency spectrum includes only the low-level noise component and the X-marked noise in FIG.

The data P thus extracted from the calculation circuit 31 is supplied to the memory 32, and a predetermined control signal is supplied from the synchronization circuit 22 so that the data P is delayed by one frame period in the memory 32. Then, the data PDL one frame period before is taken out from the memory 32. Then, the data PDL one frame period before and the current data P from the calculation circuit 31 are supplied to the difference circuit 33, and the difference DD = PDL-P between the data PDL and P is extracted.

In this case, as shown in FIG. 5, the null symbol NULL of the data PDL one frame period earlier is used as the identification information TII.
, The data P of the current frame period
Does not include anything, so that D> 0 and D = PDL. Conversely, when the null symbol NULL of the data PDL of one frame period before contains nothing, the null symbol NULL of the data P of the current frame period contains the identification information TII, so that D <0 and D = -P.

Then, the data D is supplied to the discriminating circuit 34, and the identification information TII of the transmitting station is analyzed from the frequency at which the peak of the absolute value of the data D is present. It is.

Further, the data D from the difference circuit 33 is supplied to a determination circuit 35, and the polarity of the data D is determined.
If 0, it is determined that the identification information TII has been received one frame period ago, and this determination result is also taken out to the terminal 39. Further, when there are a plurality of peaks in the determination circuit 35 and the sign varies between positive and negative depending on the peak, it is determined that the identification information TII has not been transmitted, and this determination result is also taken out to the terminal 39.

Thus, according to this DAB receiver, the identification information TII of the transmitting station can be obtained.
In particular, according to the above-described receiver, it is not necessary to decode the high-speed information block FIB to determine whether or not the frame includes the identification information TII.Therefore, a decoder circuit for the high-speed information block is not required. can do.

When the difference circuit 33 obtains the difference data D between the data PDL one frame period before and the data P of the current frame period, the difference data D
The noise components are canceled out, for example, as shown in FIG.
The noise component is reduced as compared with the case of. In particular, noise (indicated by a cross) constantly generated inside the receiver is greatly reduced. Since the identification information TII and the like are obtained from such data D, it is less susceptible to noise.

Further, the determination as to whether or not the frame includes the identification information TII may be made by determining the polarity of the data D. This can be done simply by looking at the sign bit of the data D, so that the determination is simple. .

The processes of the circuits 31 to 35 can be executed by a microcomputer or a DSP, and the execution is easy. Further, when a microcomputer or DSP is used, it is possible to determine whether or not the identification information TII is included by the microcomputer or DSP, and it is not necessary to determine by an external circuit. Therefore, it is necessary to have an interface with the external circuit. And the hardware can be simplified.

In the above description, the intermediate frequency signal from the front end circuit 12 is subjected to quadrature demodulation to obtain the I component
After obtaining the components and A / D converting them, the FFT circuit 15
Can be supplied to

[0027]

According to the present invention, in a DAB receiver, identification information of a transmitting station can be obtained, and the circuit scale can be reduced. In addition, noise components in the received data are reduced, and particularly noise that is constantly generated inside the receiver is greatly reduced, and is less affected by the noise.

Further, it can be easily determined whether or not the frame includes the identification information. Further, the processing can be easily executed by a microcomputer or a DSP, and the hardware can be simplified.

[Brief description of the drawings]

FIG. 1 is a system diagram illustrating one embodiment of the present invention.

FIG. 2 is a frequency spectrum diagram for explaining the present invention.

FIG. 3 is a frequency spectrum diagram for explaining the present invention.

FIG. 4 is a diagram for explaining the present invention.

FIG. 5 is a format diagram for explaining the present invention.

FIG. 6 is a frequency spectrum diagram for explaining the present invention.

FIG. 7 is a diagram for explaining the present invention.

[Explanation of symbols]

11: antenna, 12: front-end circuit, 13: A
/ D converter circuit, 14: orthogonal demodulation circuit, 15: FF
T circuit, 16 Viterbi decoder circuit, 17 data expansion circuit, 18 D / A converter circuit, 21 RDI circuit, 22 synchronization circuit, 31 power spectrum calculation circuit, 32 memory, 33 difference circuit, 34 … Discriminating circuit,
35 ... judgment circuit

Claims (2)

[Claims] The digital data is framed and auxiliary data is included in a partial section of every other frame, and the auxiliary data is included in a section corresponding to the partial section of the remaining frame. In a digital broadcast receiver that is broadcasted without including, a difference between a signal of the partial section of the previous frame and a signal of the partial section of the current frame among the received frames. A differential circuit for extracting the auxiliary data from an output of the differential circuit; and a determination circuit for determining a frame including the auxiliary data from the polarity of the output of the differential circuit. Receiving machine. 2. The digital broadcast receiver according to claim 1, wherein the auxiliary data is identification information of a transmitting station, and a signal of the one section of the immediately preceding frame is formed by a memory. Digital broadcast receiver.