JP2835270B2 - Image transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image transmission apparatus capable of selecting a transmission system according to a transmission line to be used.

[0002]

2. Description of the Related Art In current data communication, digital communication means is used which is less susceptible to noise on a transmission line than analog communication means. In this digital communication means, data exchanged is a symbol or a number, and if an error occurs in bit information due to noise, a serious accident may occur. Therefore, a highly reliable transmission line with few information errors is required. However, considering the versatility and cost as a data transmission line, it is not possible to pursue only high reliability,
It is generally considered that a bit error of about 10 ^-5 to 10 ^-6 cannot be avoided in a normal transmission line. Therefore, in order to improve the reliability of data transmission in digital communication, replace data with an appropriate code having redundancy.
A means called error correction coding is used. By performing the error correction coding, a bit error occurring in the transmission line can be detected. As a method of generating this code, a Hamming code method or Bose-Chaudhu
There is an ri-Hocquenghen (hereinafter abbreviated as BCH) coding scheme and the like.

A bit error of transmission data detected by the error correction coding is naturally corrected by some method. As a method of correcting transmission data, there is a method of correcting a bit error by a logical method on a data receiving side, but generally, frame information having a transmission data bit error is transmitted from a receiving side to a transmitting side. A retransmission correction method in which feedback is performed and the frame is retransmitted again is often used. If the reliability of the transmission line is high and the occurrence of bit errors is small, every time a bit error is detected on the receiving side, even if the data frame with the bit error is retransmitted, the data transmission efficiency will not greatly decrease. There is no.

However, if the reliability of the transmission line is low and the occurrence of bit errors is large, the number of retransmissions of data is increased accordingly, and the data transmission efficiency is greatly reduced. Also, the transmitted data is usually divided into several frames,
In normal data communication, when one block is transmitted by the transmitting side, the receiving side detects a bit error in the data, and if there is a bit error, a retransmission instruction for the frame is transmitted. Outputs the command to the sender. The time required for exchanging commands between transmitted frames also contributes to a reduction in transmission efficiency. If the number of retransmissions increases, the transmission efficiency naturally decreases.

[0005] In order to improve the data transmission efficiency of this low-reliability transmission line, the Hihg-Level Data
a Link Control (hereinafter abbreviated as HDLC) method will be used. In the HDLC system, the transmission side transmits a plurality of frames at a time, the reception side detects a bit error of received data, and issues a retransmission instruction only for the frame having the bit error, thereby improving transmission efficiency. Can be. Also, in the HDLC system, since there is no dummy data in the data in a frame to make the data amount constant, the data amount is small, and the average transmission rate can be suppressed lower than that in real-time transmission. Data transmission efficiency can be improved.

[0006]

When image information is handled as information to be transmitted, a function of real-time transmission of image data is often required, for example, in a videophone or a video conference system. In this case, the image data is transmitted by the BCH code transmission method using the error correction coding means based on the BCH coding method. If the reliability of the transmission line is high, there is no particular problem in transmitting image data using this BCH code method. However, if the reliability of the transmission line is low, as described above, the number of retransmissions of the data frame increases, and the transmission efficiency deteriorates. Since the use fee of the transmission line for digital communication is high, the adoption of the BCH code system in the transmission line with low reliability has many technical problems.

Therefore, for data communication using a transmission line with low reliability, an HDLC transmission system using HDLC means will be adopted. When the HDLC system is adopted, real-time transmission cannot be performed, but the average data transmission rate can be suppressed lower than that of the BCH code system, and the transmission efficiency increases. In addition, even if an accident such as an instantaneous interruption occurs in the transmission line, there is an advantage that the transmission efficiency is not significantly reduced by retransmission. However, in this HDLC system, it is necessary to occupy the back channel for the retransmission command from the receiving side to the transmitting side. Depending on the transmission line used, the back channel may not be occupied or the back channel may not exist. In this case, there is a problem that the HDLC system cannot be adopted. Therefore, an object of the present invention is to provide an image transmission apparatus that can select a data transmission method according to the reliability and state of a transmission line used.

[0008]

According to the present invention, there is provided an image transmission apparatus for digitally encoding an image input signal.
11 and an audio encoder that digitally encodes the audio input signal
12, a multiplexer 13 for multiplexing the image data from the image encoder 11 and the audio data from the audio encoder 12, and an error correction code for encoding the output data of the multiplexer 13 by the BCH code method. , A buffer memory 15 for temporarily storing output data of the error correction encoder 14 and transmitting the data to the transmission line at a constant transmission rate, an image memory 16 for recording data, a multiplexer 13 or Correction encoder 14
A switch 21 for selecting any one of the output data and adding the output data to the image memory 16;
An error correction encoder 17 that encodes the data by a system and sends the data to the transmission line.
14. A first transmission output in which data is sent out on a transmission line in real time through a path of a buffer memory 15, and an HDLC through a path of a multiplexer 13 to an image memory 16 and an error correction encoder 17.
The data encoded in the second method is transmitted to the transmission line.
And a third output in which data is transmitted to the transmission line through a path from the multiplexer 13 to the error correction encoder 14 and the image memory 16.
Is characterized in that any one of the transmission outputs can be selected.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a system configuration of an image transmission apparatus according to the present invention in which a data transmission method can be selected according to a transmission line to be used. In FIG. 1, an image signal and an audio signal from an external camera or the like are taken into the apparatus from an image input terminal 1 and an audio input terminal 2, respectively. Then, the captured image signal and audio signal are converted into digital codes by an image encoder 11 and an audio encoder 12, respectively, and the digitally encoded image data and audio data are converted into one digital signal by a multiplexer 13. It is multiplexed and combined with transmission data. Here, the multiplexed transmission data is normally output to the transmission line through the following three paths by the switching operation of the first switch 21 and the second switch 22.

First, as a first path, the transmission data output from the multiplexer 13 is input to an error correction encoder 14, which has redundancy in the transmission data according to the BCH coding method. Let The transmission data having the redundancy is temporarily recorded in the buffer memory 15 and transmitted to the transmission line for each frame. (Hereinafter, this output data is referred to as transmission output 1 for convenience.) As a second path, the transmission data output from the multiplexer 13 is input to the image memory 16 via the first switch 21. . The image memory 16 records the transmission data, and outputs the recorded transmission data to the error correction encoder 17. The transmission data has redundancy in the data in the error correction encoder 17, and is transmitted to the transmission line for each of a plurality of frames according to the HDLC procedure. (Hereinafter, this output data is referred to as transmission output 2.) As a third path, the transmission data output from the multiplexer 13 is input to the error correction encoder 14 and has redundancy according to the BCH coding method. Can be The transmission data having the redundancy is recorded in the image memory 16, and is transmitted from the image memory 16 to the transmission line as needed via the second switch 22. (Hereinafter, this output data is referred to as transmission output 3.)

In the transmission data transmitted to the transmission line through the above-described path, the transmission output 1 is of the BCH code transmission system, and the transmission rate of the data transmitted to the transmission line is as shown in FIG. Become. The transmission output 1 of the BCH code system is used to encode the image and audio signals generated within the same time interval as the frame in order to make the data amount of the transmission data frame time-divided at equal intervals constant. With dummy data,
The fixed amount of frames is transmitted to the transmission line at a predetermined transmission rate (64 kbps in FIG. 2) for each frame. This transmission output 1 also enables real-time transmission, and is an effective transmission method when the reliability of the transmission line is sufficiently high.

The transmission output 2 is of the HDLC transmission system, and the transmission rate of data transmitted to the transmission line is as shown in FIG. The transmission output 2 of the HDLC system forms one frame with the coded data of the image and audio signals generated at a predetermined time, and transfers the transmission data frame to a transmission line at a predetermined transmission rate (64 kbps in FIG. 3). Sending out. With this transmission output 2, since the transmission data is once recorded in the image memory 16 and a plurality of frames of the transmission data are transmitted at once to the transmission line, real-time transmission becomes impossible. However, this transmission output 2 is HD
Since the LC system is employed, the transmission efficiency is high, and the transmission system is effective in a low-reliability transmission line. (However, as described above, this HDLC system is limited to the case where the back channel is occupied as the transmission line to be used.)

Further, as for the transmission output 3, the transmission rate of the data to be transmitted to the transmission line is as shown in FIG.
The transmission output 3 records the generated transmission data of the encoded data of the image and audio signals in the image memory 16,
Transmission data is transmitted from the image memory 16 to the transmission line at any time. For this reason, real-time transmission is not possible, but the average transmission rate is kept low, and the transmission efficiency can be improved as compared with the case of transmission output 1. Further, since the transmission output 3 does not need to occupy the back channel, the transmission output 3 is not reliable enough to employ the transmission output 1, and is an effective transmission method in a transmission line in which the occupation of the back channel is not allowed.

Although the transmitter of the image transmission device has been described above, the present invention, which switches the transmission method according to the state of the transmission line, naturally converts the image data received according to the transmission method of the transmitter. The processing also applies to the receiver of the image transmission device. In this case, in the system configuration diagram of FIG. 1, each output terminal 3, 4, 5 of the transmitter is an input terminal of the receiver, and each input terminal 1, of the transmitter,
2 becomes an output terminal in the receiver, and the data flow is reversed. Further, the buffer memory 15 of the transmitter becomes unnecessary in the receiver, the error correction encoders 14 and 16 become error correction detectors, the multiplexer 13 becomes a demultiplexer, and the image encoder 11 becomes empty.
Can be replaced by an image decoder and the audio encoder 12 can be replaced by an audio decoder, respectively, to constitute a receiver. As described above, the present invention provides the first
Transmission output, second transmission output by HDLC system, BC
Three transmission outputs of a third transmission output having improved transmission efficiency of the H-code system are provided in the image transmission device, and three transmission outputs are provided according to the state of the transmission line such as high reliability and the presence or absence of a back channel. In this configuration, an optimum transmission output can be selected from the outputs.

[0015]

According to the present invention, an optimum transmission system can be selected according to a transmission line to be used, and efficient data transmission can be performed. Further, since some of the components are used in common to obtain the first, second, and third transmission outputs, the number of components is smaller than that of separately providing image transmission devices of three transmission methods. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a system configuration of an image transmission apparatus according to the present invention.

FIG. 2 is a diagram showing a transmission rate of a first transmission output.

FIG. 3 is a diagram showing a transmission rate of a second transmission output.

FIG. 4 is a diagram showing a transmission rate of a third transmission output.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Image encoder 12 Audio encoder 13 Multiplexer 14 1st error correction encoder 15 Buffer memory 16 Image memory 17 2nd error correction encoder

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 7/24-7/68 H03M 13/00 H04L 1/00

Claims (1)

(57) [Claims] 1. A picture encoder for digitally encoding an image input signal (11), the speech encoder for digitally encoding a voice input signal (12), the image data from the image encoder (11) A multiplexer (13) for multiplexing audio data from the audio encoder (12), and an error correction encoder (14) for encoding output data of the multiplexer (13) by the BCH code method. A buffer memory (15) for temporarily storing output data of the error correction encoder (14) and sending data to the transmission line at a constant transmission rate, an image memory (16) for recording data, and a multiplexer ( 13) Or error correction encoder
Select one of the output data (14) and image memory
A switch (21) added to (16), an error correction encoder output data and sends the data to the encoding and transmission line HDLC method of the image memory (16) (17); and a, multiplexer (13 ) To error correction encoder (14), buffer
A first transmission output, the image memory from the multiplexer (13) which data path of the memory (15) is transmitted to the transmission line in real time (16), error correction coding
Vessel (17) and a second transmission output coded data is sent to the transmission line in HDLC mode in a path, the error correction encoder from multiplexer (13) (14), the image memo
An image transmission transmission device , wherein any one of the third transmission outputs from which data is transmitted to the transmission line through the path of (16) can be selected.