JPH0575655A - Data regenerating device - Google Patents

Abstract

PURPOSE:To improve the error correction capability at data transmission and to enhance the reliability at data transmission in the data regenerating device in the data transmission system in which deep fading takes place such as mobile band communication especially. CONSTITUTION:This device is provided with a demodulation means 7 demodulating input digital data modulated by the modulation system such as the MSK, a level detection means 9 detecting an output signal level of the demodulation means 7 and a means 12 generating an error flag when the output signal level is not within a prescribed range. That is, the level detection means 9 uses an output of the demodulation means 7 to detect a carrier level and when the carrier level is a prescribed value or below, an error flag is generated. When error correction processing is implemented, the error flag is referenced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data reproducing apparatus suitable for use in mobile communication such as digital automobile / portable telephone and MCA communication.

[0002]

2. Description of the Related Art Mobile communication systems for performing data communication between mobiles or between a mobile station and a fixed station, such as digital automobiles, mobile phones and MCA communication, are becoming popular. In mobile communication, the baseband signal is FSK (Frequency Shred).
It is modulated by a modulation method such as ift Keying) or PSK (Phase Shift Keying) and transmitted / received.

FIG. 3 shows an example of a conventional receiving apparatus used for such mobile communication. In FIG. 3, the reception output of the antenna 51 is supplied to the reception circuit 52. The reception circuit 52 selects a desired reception signal and converts this reception signal into a predetermined intermediate frequency signal. The output of the receiving circuit 52 is supplied to the IF circuit 53. IF circuit 53
Is provided with an AGC circuit 54. The AGC circuit 54 sets the gain so that the received signal level becomes constant. The output of the AGC circuit 54 is the demodulation circuit 55.
Is supplied to. The demodulation circuit 55 demodulates the baseband signal from the received signal. The output of the demodulation circuit 55 is supplied to the error correction circuit 56. The error correction circuit 56 performs error correction processing. The data decoded by the error correction circuit 56 is output from the output terminal 57.

[0004]

In mobile communication such as an automobile, the position of the mobile communication is constantly changing, so that the signal level is not stable and deep fading occurs. Therefore, the reception output is stabilized by using a means such as antenna diversity. In addition, an error correction code is added to the transmission data so that the data transmission can be performed reliably.

In mobile band communication, however, a car may be located in the shadow of a building, for example, and communication may not be performed at all. Therefore, errors in transmission may be caused only by such antenna diversity and error correction code. Is difficult to completely remove. Further, if an error correction code having a strong error correction capability is added, the redundancy of data increases, the hardware scale increases, and the cost increases.

Therefore, it is an object of the present invention to provide a data reproducing apparatus which has a simple structure and can improve reliability during data transmission, particularly when mobile band communication is performed.

[0007]

The present invention is directed to a demodulation means for demodulating input digital data modulated by a predetermined modulation method, a level detection means for detecting an output signal level of the demodulation means, and an output signal of the demodulation means. And a means for generating an error flag if the level of the output signal of the demodulation means is not within the predetermined range. The data reproducing device is characterized in that it is sent to a correction circuit.

[0008]

For example, MSK-modulated data is characterized by a constant envelope. Therefore, MS
In the case of transmission using K modulation, the received data level is substantially constant, and when the received data level is significantly lower than the average level, the received data is highly likely to be in error. So the received data level is detected,
When the received data level is equal to or lower than the predetermined value, an error flag is generated and this error flag is sent to the error correction circuit. The error correction circuit refers to this error flag to perform error correction processing.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. This invention is, for example, MSK (Minimum
Shift keying) is used for mobile band communication that modulates and transmits baseband signals.

FIG. 1 shows an example of a mobile band communication receiver to which the present invention is applied. In FIG. 1, the reception signal from the antenna 1 is supplied to the reception circuit 2. The reception circuit 2 selects a desired reception signal and converts the reception signal into a predetermined intermediate frequency signal. The output of the receiving circuit 2 is supplied to the IF circuit 3. The IF circuit 3 is provided with an AGC circuit 4, and the gain of the AGC circuit 4 is set so that the received signal level becomes constant. The output of the AGC circuit 4 is supplied to the A / D conversion circuit 5. In the A / D conversion circuit 5, the received signal is digitized for each sample. This digitized received signal is supplied to a DSP (Digital Signal Processor) 6 surrounded by a broken line.

The DSP 6 can realize various digital signal processing circuits by setting a program. DSP6 is
It is versatile for various digital circuits and has the advantage that the circuit configuration can be simplified. The DSP 6 realizes a demodulator and a circuit for detecting a received data level and generating an error flag if the received data level is not within a predetermined range.

That is, in FIG. 1, the DS surrounded by the broken line is shown.
The processing in P6 is shown as a functional block. DS
The demodulator 7 in P6 demodulates the received signal and reproduces the baseband signal. The demodulator 7 is, for example, an MS
The demodulation of K is performed. As shown in FIG. 2, the MSK modulation is such that, for example, when the transmission digital signal is "0", the signal point is counterclockwise and when the transmission digital signal is "1", the signal point is clockwise, and the length of one bit of the digital signal is Sa T
Then, the signal point moves 180 degrees on the arc during the time T while maintaining a constant angular velocity. In MSK modulation, since the signal point rotates at a constant speed, FSK (Freqency Shift Key)
ing) is a special case of modulation. This MSK modulation has a characteristic that the envelope is constant. In the demodulator 7, for example, the received data is processed for each predetermined unit (block) and demodulated.

The demodulation output of the demodulator 7 is an output of the normalization circuit 8.
And the data taken in by the demodulator 7 are also supplied to the level detection circuit 9. In the level detection circuit 9,
The data level of the received data is detected. In the embodiment of the present invention, since the demodulator 7 is realized by the DSP 6, the received data level can be detected for each sample in this way. The output of the level detection circuit 9 is supplied to the averaging circuit 10 and the comparison circuit 11. The averaging circuit 10 averages the data levels detected by the level detecting circuit 9 for each block, for example. The output of the averaging circuit 10 is supplied to the comparing circuit 11 and the normalizing circuit 8.

The normalization circuit 8 normalizes the demodulation data level using the data level averaged by the averaging circuit 10. Further, the comparison circuit 11 compares the data level currently detected by the level detection circuit 9 with the average value of the data levels output from the averaging circuit 10.

As described above, in one embodiment of the present invention, MSK modulation is used as the modulation method. The MSK modulation is characterized by a constant envelope. Therefore, in the case of MSK modulation, the reception data level should be substantially constant, and when the reception data level is significantly lower than the average level, the reception data is highly likely to be in error.

The output of the comparison circuit 11 is the flag generation circuit 12
When the difference between the input demodulated signal level compared by the comparator circuit 11 and the average value of the demodulated signal level is equal to or more than a predetermined level, the flag generation circuit 13 generates an error flag. The output of the flag generation circuit 12 is supplied to the flag memory 13.

The data demodulated by the demodulator 7 of the DSP 6 is normalized by the normalization circuit 8 and sent to the error correction circuit 14. The error correction circuit 14 performs error correction processing and the like to decode the received data. At this time, the error flag stored in the flag memory 13 is referred to. When a Hamming code, for example, is used as the error correction code, the error location is obtained by using the error flag output from the flag memory 12, so the error correction capability is improved. As the error correction method, various methods such as Viterbi code can be considered in addition to the Hamming code. The reception data thus error-corrected is output from the output terminal 15.

As described above, in the embodiment of the present invention, the comparison circuit 11 compares the received data level with the average value of the data levels, detects whether the comparison output is within a predetermined range, and outputs the demodulation output. If the level is not within the predetermined range, a flag is generated from the flag generation circuit 11 and stored in the flag memory 13. In mobile band communication, errors due to deep fading may occur. Since the error information generated by such deep fading is stored in the flag memory 13, the ability to correct such an error is improved.

In the above embodiment, the demodulator and the circuit for detecting the received data level and generating an error flag if the received data level is not within the predetermined range are
Although it is realized in the DSP 6, it goes without saying that dedicated hardware may be individually configured. Further, it may be configured by a DSP including an error correction circuit.

The use of the DSP improves the versatility and simplifies the circuit as described above, but the DSP generally has a slower processing speed than dedicated hardware. Therefore, it is desirable to decide whether to configure dedicated hardware or implement the processing circuit in the DSP in consideration of the data transfer rate.

Further, in the embodiment of the present invention, MSK is used as the modulation system, but the modulation system is not limited to this. The same can be achieved by using a modulation method (CPFSK, GMSK, etc.) in which the envelope level is constant or substantially constant.

[0022]

According to the present invention, the comparison circuit 11 compares the received data level with the average value of the data levels, detects whether the comparison output is within a predetermined range, and determines the demodulation output level as a predetermined value. If it is not within the range, a flag is generated from the flag generation circuit 11, this error flag is stored in the flag memory 13, and this error flag is referred to in the error correction process. Therefore, the error correction processing capability is improved especially when an error due to deep fading occurs, such as mobile band communication.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a signal point arrangement of MSK.

FIG. 3 is a block diagram of an example of a conventional data receiving device.

[Explanation of Codes] 6 DSP 7 Demodulator 9 Level detection circuit 11 Comparison circuit 12 Flag generation circuit 14 Error correction circuit

Claims (1)

[Claims] 1. A demodulation means for demodulating input digital data modulated by a predetermined modulation method, a level detection means for detecting an output signal level of the demodulation means, and an output signal level of the demodulation means within a predetermined range. If the output signal level of the demodulating means is not within a predetermined range, it is provided with means for generating an error flag, and the error flag is sent to the error correction circuit together with the demodulated data from the demodulating means. A data reproducing device characterized by being sent.