JP2000151551A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a null symbol from a strong input electric field strength to a weak input electric field strength in an OFDM receiver. SOLUTION: This receiver is provided with a reception means 2 that receives a signal, a signal processing means 4 that applies prescribed processing to a received signal by the reception means, a synchronizing signal extract means 7 that extracts a synchronizing signal from the signal received by the reception means 2, a threshold setting means 11 that sets a threshold value for detecting the synchronizing signal, a comparison means 9 that compares a level of the synchronizing signal extracted by the synchronizing signal extract means 7 with a threshold set by the threshold setting means 11 and allows the signal processing means 4 to conduct processing, based on the comparison result, and an electric field strength detection means 10 that detects the electric field strength of the reception signal by the reception means 2 and an output of the electric field strength detection means 10 changes a threshold of the threshold setting means 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DAB (Digital
TAL Audio Broadcasting) OFDM (Orthogonal F) used for receivers and the like.
frequencyDivision Multiple
The present invention relates to a receiver of the x) system, and particularly to detection of a null symbol used for synchronization and mode detection.

[0002]

2. Description of the Related Art OF transmitted according to the DAB standard
As shown in FIG. 4, the DM modulated signal has a portion without a signal (t2 to t3, t4 to t5) and a portion with a signal (t1 to t1).
t2, t3 to t4, and t5 to t6) are transmitted alternately.
The part without this signal is called a null symbol. The null symbol detection circuit is a circuit that detects a null symbol portion from a DAB signal as shown in FIG. 4 and binarizes and outputs it.

The DAB has four modes, and the length of a null symbol differs depending on each mode as shown in FIG. Therefore, it is possible to determine each mode by accurately extracting the length of the null symbol. Further, since the null symbol also serves as a synchronization signal, no temporal delay is allowed in the extraction. If the null symbol cannot be accurately extracted, the DAB receiver does not operate normally.

[0004] An example of the configuration of a conventional receiving apparatus will be described with reference to FIG. FIG. 6 shows a configuration example of a receiving apparatus that receives an OFDM modulated signal transmitted according to the DAB standard, for example. The radio wave captured by the receiving antenna 1 is input to the tuner 2. The OFDM signal input to the tuner 2 is subjected to frequency conversion and high gain amplification in the tuner 2. Frequency conversion, high gain amplified OF
The DM signal is output from the tuner 2 and the A / D converter 3
Is input to The OFDM signal input to the A / D converter 3 is converted from an analog signal to a digital signal. The OFDM signal converted to a digital signal is output to a signal processing circuit 4.
Is demodulated. The signal demodulated by the signal processing circuit 4 is subjected to audio processing by the audio processing circuit 5 and
Output. The operation of the signal processing circuit 4 requires synchronization detection. Further, since there are four modes in the DAB, it is necessary to detect the modes. Therefore, a null symbol is detected from the OFDM signal output from the tuner 2,
Input to the signal processing circuit 4.

The detection of a null symbol as a synchronization signal
As shown in FIG. 7, OFDM output from tuner 2
After the signal is detected by a detection circuit 7 which is a null symbol extraction means, the signal is amplified by an amplification circuit 8 and compared with a threshold by a comparator 9. In the signal detected by the detection circuit 7 (see FIGS. 7A and 7A), the potential difference between the null symbol portion (no signal portion) and the other portion (signal portion) is not large. Therefore, the signal detected by the detection circuit 7 is amplified by the amplification circuit 8, and the difference between the null symbol portion and the other portions is sharpened.

[0006] The signal amplified by the amplifier circuit 8 is input to a comparator 9. The comparator 9 is a circuit that compares the input of two systems of a threshold value and a detection signal, which will be described later, and outputs a binary value. The signal amplified by the amplifying circuit 8 input to the comparator 9 is compared with the output of the threshold setting circuit 11 and converted into a binary value higher or lower than the threshold voltage. The binary signal output from the comparator 9 is input to the signal processing circuit 4 as a null symbol, and is used for mode determination and synchronization detection. In the case of FIG. 7, if the voltage of the detected signal is higher than the threshold, it is determined to be a null symbol, and if the voltage of the detected signal is lower than the threshold,
It is determined that it is not a null symbol. OFDM as above
A null symbol is detected from the signal.

Next, the operation of the conventional example will be described with reference to FIG. In the prior art, as shown in FIG. 7, a detection circuit detects an OFDM signal (step 101), and detects the level of the detected signal and a threshold value of a certain value (v in FIG. 7).
1, v2) by the comparator (step 102),
The null symbol has been detected (steps 103 and 104).

[0008]

In the above-mentioned conventional null symbol detection circuit, when the input electric field strength is weak, the signal shown in FIG.
As shown in (a), the detection signal becomes less clear. Therefore, in the case of a weak electric field, it is necessary to lower the threshold value in order to accurately binarize the detected signal. However, when the electric field is strong, as shown in FIG. 7A, the voltage of the non-null symbol fluctuates and rises, so that if the threshold value is lowered, the null symbol cannot be detected normally. Thus, it is difficult to make the input electric field strength compatible with both the strong electric field and the weak electric field at a fixed threshold.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a receiving apparatus capable of detecting a null symbol more accurately regardless of the electric field intensity.

[0010]

A receiving apparatus according to the present invention comprises: a receiving means for receiving a signal; a signal processing means for performing predetermined processing on a signal received by the receiving means; Synchronization signal extracting means for extracting a signal,
Threshold value setting means for setting a threshold value for detecting a synchronization signal; comparing the magnitude of the synchronization signal extracted by the synchronization signal extraction means with the threshold value set by the threshold value setting means; Comparing means for performing the processing of the signal processing means based on the result, and electric field intensity detecting means for detecting the electric field intensity of the reception signal of the receiving means, wherein the threshold value setting means is provided by the output of the electric field intensity detecting means Is changed.

In addition, there is provided amplification means for amplifying the synchronization signal extracted by the synchronization signal extraction means at a predetermined rate and supplying the amplified synchronization signal to the comparison means, and based on the magnitude of the electric field strength detected by the electric field strength detection means, amplification of the amplification means The rate is changed.

Further, the signal received by the receiving means is a digital signal.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG.
1 shows a configuration example of a receiving apparatus that receives an OFDM modulated signal transmitted in accordance with the AB standard. Receiving antenna 1
The radio wave captured at is input to the tuner 2. The OFDM signal input to the tuner 2 is subjected to frequency conversion and high gain amplification in the tuner 2. The frequency-converted and high-gain amplified OFDM signal is output from tuner 2,
The signal is input to the A / D converter 3. The OFDM signal input to the A / D converter 3 is converted from an analog signal to a digital signal. The OFDM signal converted to a digital signal is demodulated by the signal processing circuit 4. The signal demodulated by the signal processing circuit 4 is subjected to audio processing such as D / A conversion and amplification by an audio processing circuit 5 and output from a speaker 6.
The operation of the signal processing circuit 4 requires synchronization detection. Further, since there are four modes in the DAB, it is necessary to detect the modes. Therefore, OF output from tuner 2
A null symbol is detected from the DM signal and input to the signal processing circuit 4.

The detection of a null symbol as a synchronization signal
As shown in FIG. 7 described above, the OFDM signal output from the tuner 2 is detected by a detection circuit 7 which is a null symbol extraction means, then amplified by an amplification circuit 8 and compared with a threshold value by a comparator 9. It is done by doing. The signal detected by the detection circuit 7 is a null symbol part (no signal part).
And the other part (signal part) does not have a large potential difference. Therefore, the signal detected by the detection circuit 7 is amplified by the amplification circuit 8, and the difference between the null symbol portion and the other portions is sharpened.

The signal amplified by the amplifier circuit 8 is input to a comparator 9. The comparator 9 is a circuit that compares an output of a threshold value setting circuit 11 described later and two inputs of a detection signal, and outputs a binary value. The signal amplified by the amplifier 8 input to the comparator 9 is applied to a threshold setting circuit 11.
, And is converted to a binary value that is higher or lower than the threshold voltage. The binary signal output from the comparator 9 is input to the signal processing circuit 4 as a null symbol, and is used for mode determination and synchronization detection. In the case of FIG. 7, when the voltage of the detected signal is higher than the thresholds (v1, v2), it is determined to be a null symbol, and when the voltage of the detected signal is lower than the threshold, it is determined to be other than the null symbol. Is determined. As described above, a null symbol is detected from the OFDM signal.

At this time, the output of the threshold value setting circuit 11 input to the comparator 9 is determined by the input electric field strength determining circuit 10 and is changed by the obtained value. For example, when the input electric field strength is −50 dBm or more, the threshold value is changed to 3 V, and when the input electric field strength is −50 dBm or less, the threshold value is changed to 2 V. This makes it possible to accurately detect a null symbol from a weak electric field to a strong electric field.

Further, by changing the amplification factor of the detection signal by the amplifier circuit 8 between a weak electric field and a strong electric field, the range in which the threshold can be taken can be widened. Therefore, by changing the amplification factor of the detection signal amplifier circuit 8 at the time of the weak electric field and at the time of the strong electric field, it is possible to reduce the possibility of the malfunction at the time of the weak electric field and at the time of the strong electric field. Can be detected.

As described above, by changing the threshold value and the amplification factor of the amplifier circuit according to the input electric field strength, it is possible to more accurately detect a null symbol from a weak electric field to a strong electric field.

Next, a method of setting the output of the threshold value setting circuit 11 input to the comparator 9 and the amplification factor of the amplifier circuit 8 will be described with reference to FIG.
This will be described with reference to FIG. First, the input electric field intensity is judged by the electric field intensity judgment circuit 10 such as an internal circuit of the tuner 2 (step 201). Next, the input electric field strength is compared with a certain value A (for example, -50 dBm) (step 20).
2) If the electric field strength is large, the threshold value input to the comparator 9 is set for a strong electric field (step 203). If the electric field strength is small, the threshold value input to the comparator 9 is set for a weak electric field (step 203). 204). Next, the electric field intensity is compared with a certain value B (step 205). If the electric field intensity is high, the amplification factor of the amplifier circuit 8 is set for a strong electric field (step 206). (Step 207). By repeating such processing, the output of the threshold setting circuit 11 of the comparator 9 of the null symbol detection circuit and the amplification factor of the amplifier circuit 8 are changed according to the electric field strength.

Next, how the receiving apparatus uses the null symbols obtained as described above will be described with reference to FIG. The signal obtained from the comparator 9 of the null symbol detection circuit is input to the signal processing circuit 4. The null symbol input to the signal processing circuit 4 is used in step 301 for synchronization detection. Next, in step 302, mode detection is performed based on the length of the null symbol. After the mode detection, in step 303, a demodulation process is performed. The demodulated signal is output as voice or data. Further, the above-described electric field strength determination processing is repeatedly performed during reception of the OFDM broadcast, and always detects a null symbol stably.

Embodiment 2 FIG. In the receiving apparatus according to the first embodiment, by continuously changing the amplification factor of the amplifier circuit 8 and the threshold value applied to the comparator 9 according to the electric field strength, without performing the electric field strength determination stepwise, It is also possible to always use the optimum amplification factor of the amplifier circuit 8 and the threshold value given to the comparator 9. For example, the threshold voltage is increased when the input electric field intensity is high, and the threshold voltage is decreased when the input electric field intensity is low.

In the first and second embodiments, the threshold value and the amplification factor of the amplifier circuit may be changed based on the error rate obtained from the signal processing circuit 4.

The same effect can be obtained when the above-mentioned receiving apparatus is used not only for a DAB receiving apparatus but also for a digital broadcasting receiving apparatus such as an RDS or a digital TV.

The same effect can be obtained by using the above-mentioned receiving apparatus not only for a digital broadcasting receiving apparatus but also for a receiving apparatus of a broadcasting system requiring synchronization (for example, an analog TV).

In the above-described receiving apparatus, the electric field strength determination processing does not have to be repeatedly performed during the reception of the OFDM broadcast.

[0026]

According to the present invention, by changing the threshold value input to the comparator for inputting the detection signal in accordance with the electric field intensity, the input electric field intensity can be accurately changed from a strong electric field to a weak electric field. Since the detection becomes possible, the sensitivity of the receiving device is improved.

Further, by changing the amplification factor of the detection signal obtained by detecting the OFDM signal and the threshold value input to the comparator for inputting the detection signal in accordance with the electric field intensity, the input electric field intensity changes from a strong electric field to a weak electric field. , A null symbol can be detected accurately.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a receiving apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a flowchart illustrating the operation of the first embodiment.

FIG. 3 is a flowchart illustrating an operation up to audio output according to the first embodiment;

FIG. 4 is an explanatory diagram of a DAB broadcast wave.

FIG. 5 is a diagram showing a pattern of the length of a null symbol of DAB broadcasting.

FIG. 6 is a block circuit diagram showing a conventional receiving device.

FIG. 7 is an explanatory diagram of a signal obtained by detecting a DAB signal.

FIG. 8 is a flowchart illustrating an operation of detecting a null symbol from a detected signal in a conventional receiving apparatus.

[Explanation of symbols]

1 antenna, 2 tuner,
3 A / D converter, 4 signal processing circuit, 5 audio processing circuit, 6 speaker, 7 detection circuit, 8 amplification circuit, 9 comparator, 10 electric field strength judgment circuit, 11 threshold value setting circuit.

Claims (3)

[Claims] A receiving means for receiving a signal; a signal processing means for performing predetermined processing on the received signal of the receiving means; a synchronizing signal extracting means for extracting a synchronizing signal from the received signal of the receiving means; Threshold value setting means for setting a threshold value for the threshold value, comparing the magnitude of the synchronization signal extracted by the synchronization signal extraction means with the threshold value set by the threshold value setting means, and based on the comparison result. Comparing means for performing the processing of the signal processing means, and electric field strength detection means for detecting the electric field strength of the received signal of the receiving means,
A receiving apparatus, wherein a threshold value of said threshold value setting means is changed by an output of said electric field strength detecting means. And amplifying means for amplifying the synchronization signal extracted by the synchronization signal extraction means at a predetermined rate and supplying the amplified amplification signal to the comparison means, based on the magnitude of the electric field strength detected by the electric field strength detection means.
2. The receiving device according to claim 1, wherein an amplification factor of said amplification means is changed. 3. The receiving device according to claim 1, wherein the signal received by the receiving means is a digital signal.