JP3363465B2 - Data transmission apparatus and method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a data transmission device and method.
Concerning the law .

[0002]

2. Description of the Related Art There is known a transmission system in which quantized image information data is variable-length coded according to a transmission rate, phase-amplitude modulated, and sent to a transmission medium. For example, it is used for image communication via a communication satellite. FIG. 4 shows a block diagram of a configuration on the transmission side of a conventional example using the 4-phase modulation method.

An image signal is input to the input terminal 10, and the image coding device 12 performs quantization, variable length coding according to the transmission rate, and further adds P, the image information data to which error correction coding is added. Output in two phases of Q. Four-phase modulator 1
4, the output of the image coding device 12 is first filtered by the roll-off filters 16a and 16b, and the modulation circuit 18
4 phase modulation. The carrier wave subjected to the four-phase modulation is output from the output terminal 20 to the transmission medium. The pass frequency band and the roll-off coefficient α of the roll-off filters 16a and 16b are determined in advance by the transmission rate, the transmission frequency occupied band, the error correction capability, and the like.

Generally, if the transmission speed is high, it is necessary to widen the pass frequency band. Also, if the transmission line condition is poor,
As the roll-off coefficient α becomes smaller, Eb /
No deteriorates, leading to an increase in decoding error rate. On the contrary, when the coefficient α is increased, the decoding error rate is reduced, but the transmission frequency occupied band is widened.

[0005]

When the transmission line condition deteriorates in the above-mentioned transmission system, in order to suppress an increase in the decoding error rate, the redundancy is increased to enhance the error correction capability, and the roll-off coefficient α is increased. Although such methods are conceivable, these methods are not realistic because they involve changes in the transmission format and changes in the transmission frequency occupied band.

It is an object of the present invention to provide a data transmission device and method that suppress an increase in decoding error rate with respect to deterioration of the transmission line condition.

[0007]

In order to achieve the above object, a data transmitting apparatus of the present invention comprises an encoding means for encoding input information data and a waveform shaping filter.
And a carrier wave according to the encoded information data.
Modulating means for modulating the
Transmission means for transmitting information data to a transmission line, and the transmission line
Receiving means for receiving the information data via the detecting means, detecting means for detecting an error state of the information data received by the receiving means, and a transmission rate and a forward speed according to the output of the detecting means.
And a control means for controlling the characteristics of the filter . In addition, in order to achieve the above object, the data transmission method of the present invention uses an encoding step of encoding input information data and a filter for waveform shaping.
The carrier wave according to the coded information data
And the information data modulated in the modulation step
And a transmission step of transmitting the transmission path, a reception step of receiving information data via the transmission path, a detection step of detecting an error condition of the received information data, depending on the detection result of the detecting step The method further comprises a control step of controlling the transmission rate and the characteristics of the filter .

[0008]

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a basic configuration diagram of an embodiment of the present invention using a satellite communication line as a transmission medium. Reference numeral 30 is an input terminal of an image signal to be transmitted, 32 is an image encoding circuit for encoding the image signal from the input terminal 30, 34 is a phase modulation circuit for phase modulating the output code of the image encoding circuit 32, and 36.
Transmits the output of the phase modulation circuit 34 to the communication satellite 38,
A transmitting / receiving circuit for receiving signals from the communication satellite 38, 40
Is a phase demodulation circuit for phase demodulating the signal received by the transmission / reception circuit 36, 42 is an image decoding circuit for decoding the demodulated signal by the phase demodulation circuit 40, and 44 is an output terminal for the received image signal.

Reference numerals 36R, 40R, and 42R denote a transmission / reception circuit, a phase demodulation circuit, and an image decoding circuit of the receiving station, which have the same circuit configuration as the circuits 36, 40, and 42. 44R is an output terminal of the image signal decoded by the image decoding circuit 42R.

In this embodiment, in order to check the state of the communication line via the communication satellite 38, the signal transmitted from the transmission / reception circuit 36 to the communication line 38 is the communication satellite 38.
From the same to the same transmitting / receiving circuit 36. Then, it is demodulated and decoded by the phase demodulation circuit 40 and the image decoding circuit 42, and the image decoding circuit 42 supplies the information of the transmission error rate to the image coding circuit 32 and the phase modulation circuit 34. The image coding circuit 32 and the four-phase phase modulation circuit 34 will be described in detail later, but the quantization characteristic and the coefficient α of the roll-off filter are determined according to the transmission error rate information from the image decoding circuit 42.
To optimize.

FIG. 2 shows a detailed block diagram of the image coding device 32 and the phase modulation circuit 34, and FIG. 3 shows a detailed block diagram of the phase demodulation circuit 40 and the image decoding circuit 42.

First, the operation of the transmitting side will be described in detail with reference to FIG. The image signal from the input terminal 30 is input to the input terminal 50 of the image encoding circuit 32, and the transmission error rate information from the image decoding circuit 42 is input to the input terminal 52. The transmission rate selection circuit 54 determines an appropriate transmission rate in accordance with the transmission error rate information from the input terminal 52, and outputs the information regarding the determined transmission rate to the quantization circuit 56, the variable length coding circuit 58, the data synthesis circuit 62, the clock. Generation circuit 64,
And the control terminals of the variable roll-off filters 66, 68. Needless to say, the transmission speed selection circuit 54
Selects a default value as the transmission rate when the transmission error rate information is not input from the input terminal 52.

The quantization circuit 56 quantizes the image signal from the input terminal 50. However, the quantization coefficient is determined by the control signal from the transmission rate selection circuit 56 and the amount of coded information from the variable length coding circuit 58 in the subsequent stage. The variable length coding circuit 58 performs variable length coding on the output of the quantization circuit 56. At the output stage of the variable length coding circuit 58, the image signal is coded into a predetermined amount of information. The error correction code generation circuit 60 generates an error correction code for a predetermined amount of codes output from the variable length coding circuit 58. The data synthesizing circuit 62 adds the error correction code from the error correction code generating circuit 60 to the output code of the predetermined amount of the variable length coding circuit 58 to form a block, and the transmission rate determined by the transmission rate selecting circuit 54. It is divided into two phases of P and Q at a speed of ½ of the above, and is output to the four-phase modulation circuit 34.

In the 4-phase modulation circuit 34, the P signal and the Q signal are applied to variable roll-off filters 66 and 68, respectively. The variable roll-off filters 66 and 68 are non-recursive or recursive digital filters, and transmit filter coefficients obtained from the transmission rate information from the transmission rate selection circuit 54 and a predetermined transmission occupied frequency band. By properly setting, the pass frequency band and the roll-off coefficient α can be changed, and the amplitude frequency characteristic is adjusted to be optimum. The P signal and the Q signal are waveform-shaped by the variable roll-off filters 66 and 68, respectively, and are applied to the modulation circuit 70. The modulation circuit 70 is
The carrier wave is modulated by the waveform-shaped P signal and Q signal, and the modulated wave is supplied from the output terminal 72 to the transmission / reception circuit 36.

The transmission / reception circuit 36 is a four-phase phase modulation circuit 3
4, the frequency of the modulated wave from the modulation circuit 70 is converted,
The amplified signal is transmitted to the communication satellite 38.

Next, the operation of the receiving side will be described in detail with reference to FIG. The transmission / reception circuit 36 (or 36R) receives the transmission wave from the communication satellite 38, amplifies and frequency-converts it, and outputs it to the four-phase phase demodulation circuit 40 (or 40R).
In FIG. 3, a reception wave from the transmission / reception circuit 36 (or 36R) is input to the input terminal 74. The demodulation circuit 76
The internal clock recovery circuit knows the transmission speed, demodulates the signal from the input terminal 74 into four-phase phase, and adjusts the amplitude frequency characteristics of the variable roll-off filters 78 and 80 to optimum values. The two outputs of the demodulation circuit 76 are passed through the variable roll-off filters 78 and 80, respectively, to the decision circuit 8
2 and is demodulated into P signal and Q signal.

2 of the 4-phase phase demodulation circuit 40 (or 40R)
The output of the phase is supplied to the error correction circuit 84 of the image decoding circuit 42 (or 42R). The error correction circuit 84 error-corrects the output of the 4-phase phase demodulation circuit 40 in accordance with the transmission rate information from the demodulation circuit 76, outputs the error-corrected reception signal to the variable length decoding circuit 86, and outputs the transmission error rate information to the output terminal. 92
Output to. On the transmitting station side, the transmission error rate information of the output terminal 92 is supplied from the input terminal 52 of the image encoding circuit 32 to the transmission rate selection circuit 54, as described above.

The variable length decoding circuit 86 variable length decodes the received signal from the error correction circuit 84 according to the transmission rate information from the demodulation circuit 76, and the dequantization circuit 88 follows the transmission rate information from the demodulation circuit 76. The output of the variable length decoding circuit 86 is inversely quantized by the quantized coefficient. That is, the variable length decoding circuit 86 and the dequantization circuit 88 perform the processing opposite to the encoding of the variable length coding circuit 58 and the quantization of the quantization circuit 56, respectively, and the original processing is performed by these processings. The image information is restored and output to the output terminal 44 via the output terminal 90.

In summary, in the present embodiment, when the transmission line condition deteriorates, the transmission speed is reduced, the pass frequency band of the roll-off filter of the modulation / demodulation circuit is narrowed, and the roll-off coefficient α is increased. . If the transmission line condition improves, reverse this. In either case, the occupied bandwidth of the transmission frequency should be constant.

Although the four-phase modulation is applied in the above embodiment, it goes without saying that other phase amplitude modulation methods can also be applied.

[0023]

As can be easily understood from the above description, according to the present invention, the transmission mode is changed and adjusted according to the transmission line status information obtained in the own station. Even in a transmission medium whose line condition is easily affected by the weather, stable data transmission can always be performed easily.

[Brief description of drawings]

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

FIG. 2 is a configuration block diagram of a main part on the transmission side of the present embodiment.

FIG. 3 is a configuration block diagram of a main part on the receiving side of the present embodiment.

FIG. 4 is a block diagram showing the configuration of a conventional transmission device.

[Explanation of symbols]

10: input terminal 12: image coding device 14: four-phase modulation device 16a, 16b: roll-off filter
18: Modulation circuit 20: Output terminal 30: Input terminal 3
2: Image encoding circuit 34: Phase modulation circuit 36, 36
R: Transmission / reception circuit 38: Communication satellite 40, 40R: Phase demodulation circuit 42,
42R: image decoding circuit 44, 44R: output terminal 50, 52: input terminal 5
4: Transmission rate selection circuit 56: Quantization circuit 58: Variable length coding circuit 60: Error correction code generation circuit 62: Data synthesis circuit 64: Clock generation circuit 66, 68: Variable roll-off filter 70: Modulation circuit 72: Output terminal 74: Input terminal 76: Demodulation circuit 78, 80: Variable roll-off filter 82: Judgment circuit 84: Error correction circuit 86: Variable length decoding circuit 8
8: Dequantization circuit 90, 92: Output terminal

Claims (2)

(57) [Claims] 1. Encoding input information dataSign to
Means of conversion, The coded signal is provided with a filter for waveform shaping.
Modulation means for modulating a carrier wave according to information data, The information data modulated by the modulating means is transmitted to the transmission line.
Transmission means for sending, Receiving means for receiving information data via the transmission path, Error state of information data received by the receiving means
Detecting means for detecting According to the output of the detection meansTransmission rate and the filter
CharacteristicAnd a control means for controlling
Data transmission device. 2. Encoding the input information dataSign
Process, Is encoded using a filter for waveform shaping
A modulation step of modulating a carrier wave according to the information data, The information data modulated in the modulation step is transmitted to the transmission line.
Transmission process, Receives information data via the transmission pathReceiving step, The above Detects error state of received information dataDetector
And The aboveDetection processAccording to the detection result ofTransmission rate and the fill
CharacteristicsAnd a control step for controlling
Data transmission method.