JPH1070715A - Digital video communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the digital video communication system which prevents delay when an error correction code is adaptively added to a moving image to be sent. SOLUTION: A terminal 608 is provided with a frame generating means 604 which separates moving image codes in error-corrected and encoded image frame units into inspection bits of error correction codes and moving image codes and form inspection bits and moving image codes in respective packets at a request for the inspection bits that is made by a center 622 or only moving image packets unless there is the request, and a transmitting means 606 which transmits the moving image packets over individual channels and the inspection bit packets over a common channel. Then the center 622 is provided with a receiving means 611 which makes the request for the inspection bits when the reception level of packets is lower than a threshold value and a frame generating means 613 which takes the moving image information and inspection bits out of the packets of the moving image and inspection bits synchronously. Error correction codes are added adaptively over the common channel, so moving image transmission is not delayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital video communication system for wirelessly communicating moving image data.
An error correction code can be adaptively added to moving image data while suppressing transmission delay of moving image data.

[0002]

2. Description of the Related Art Conventionally, in a digital video communication system in which moving image information transmitted from a plurality of terminal devices is collected in a center device, a remote monitoring system using a wired transmission path is known. However, in a remote monitoring system using a wire, it is difficult to install the monitoring terminal device at an arbitrary position, and it is necessary to attach a wire to the monitoring terminal device, so that the installation is complicated and complicated.

As a system for solving such a point, there is a digital video communication system using a wireless transmission path. However, when moving image information is transmitted through a wireless transmission path, a measure against the transmission error is required. In general, since interframe coding is used for compressing a moving image, the effect of a transmission error on image quality is very large. This protection of image information from errors can be realized by adding redundancy using an error correction code to transmission data according to the state of the transmission path.

As shown in FIG. 10, a digital video communication system using a wireless transmission path is a center device (center device) 101 capable of receiving video data and receiving image data.
And m image data transmission capable terminal devices (terminal devices) 102, 103, and 104 for transmitting image data.
Uplink wireless channels 105, 106, 107 from each terminal device 102, 103, 104 to the center device 101 are used for image data transmission, and downlink wireless channels 108 from the center device 101 to each wireless terminal 102, 103, 104, 109 and 110 are used for transmitting control information.

[0005] Here, the operation of the system shown in Fig. 11 having three terminal devices will be described as an example. Terminal device 205
Is a moving image code input terminal 201 to which a moving image code is input,
Control signal receiving means 204 for receiving a control signal from center device 216 transmitted through downlink control channel 218
And error correction coding means 202 for performing error correction coding of a moving image code based on a control signal from the center device 216.
And the output of the error correction coding means 202 to the uplink transmission channel 2.
And transmission means 203 for transmitting the data to the center device 216 through the communication device 17. The terminal devices 206 and 207 have the same configuration.

On the other hand, the center device 216 is
Receiving means 208 for receiving the transmission data transmitted from to 207 and comparing the reception level of each channel with a threshold value Th, and an error correction code of a moving image code to be transmitted to a terminal device whose reception level is equal to or less than the threshold value Th. Control signal transmitting means 20 for instructing
9 and error correction means 210, 211, 212 for correcting errors in transmission data sent from each terminal device, and reproduction display means 213, 214, 215 for reproducing an error-corrected moving image.

In the terminal device 205 of this system, a moving image code is input from a moving image code input terminal 201. The error correction coding unit 202 performs error correction coding of the input moving image code when the center device 216 requests transmission of the error correction code through the control signal receiving unit 204. Then, the error correction code, which is the output, is transmitted to the center device 216 through the transmission means 203. When the center device 216 does not request transmission of the error correction code, the input moving image code is output to the transmitting unit 203 as it is, and the transmitting unit 203 transmits only the digital video data to the center device 216.

FIG. 12 shows the data format of the output data of the error correction encoding means 202. Whether the error correction coding is performed or not is determined by the FEC (forward
error correction) flag (for example, a flag signal composed of 5 bits).

In the center device 216, the receiving means 208 receives the data multiplexed and transmitted from each of the terminal devices 205, 206 and 207, and separates the data into data corresponding to each terminal. At this time, the receiving means 208 determines the reception level of each channel, and notifies the control signal transmitting means 209 of a terminal device whose reception level is equal to or less than the threshold Th. The control signal transmitting unit 209 transmits a control signal for instructing the terminal device whose reception level is equal to or less than the threshold Th to perform error correction encoding of a moving image code to the downlink control channel
8. Transmit via 219, 220 (eg, with signal level set to 1). In addition, for terminal devices whose reception level is equal to or higher than Th, it is notified through the downlink control channels 218 to 220 that error correction coding is not necessary (for example, when the signal level is 0).
Set to notify.

[0010] The data, which is an output signal of the receiving means 208 and is separated for each terminal, is output to error correcting means 210, 211, 212 corresponding to each terminal. Error correction means 210-21
2 indicates whether or not error correction coding has been performed.
Judgment is made by the C flag. If the FEC flag indicates that error correction coding has been performed, error correction processing is performed. If the FEC flag indicates that error correction coding has not been performed, the input signal is output as it is.

The outputs of the error correction means 210 to 212 are input to the reproduction display means 213, 214, 215 corresponding to each terminal and displayed as a moving image.

As described above, even when the transmission quality of the radio channel is deteriorated, good image quality is maintained by adaptively adding an error correction code to the transmission data.

[0013]

However, since the addition of the redundant bits (check bits of the error correction code) leads to an increase in the data transmitted by each terminal, transmission of the information in the originally allocated transmission bandwidth is performed. However, there is a problem that the delay of data transmission is increased when the above is performed.

In order to prevent the occurrence of this delay, a method of (1) reducing the image code amount by the increased redundant bits and (2) statically allocating a transmission band increased by the maximum redundant bits is conceivable. However, when the method (1) is adopted, there is a problem that code amount control for controlling the generated code amounts of the error correction code and the moving image code is required, and the system configuration is complicated. Further, when the method (2) is adopted, the transmission band is always secured in consideration of the maximum number of redundant bits of the error correction code, so that a delay is generated for the adaptively increased redundant bits. However, there is a problem that an unnecessarily large transmission bandwidth is required for the entire system.

SUMMARY OF THE INVENTION The present invention solves such a conventional problem, and does not significantly increase the transmission bandwidth of a system when adaptively adding an error correction code to moving image data to be transmitted. It is another object of the present invention to provide a digital video communication system capable of preventing an increase in data transmission delay.

[0016]

Therefore, in a digital video communication system according to the present invention, a terminal device capable of transmitting image data transmits a moving image code for each image frame, which has been subjected to error correction coding, to a check bit of an error correction code and a moving image code. If the center device capable of receiving image data requests transmission of the check bit, the check bit and the moving image code are respectively formed in a packet. If the transmission of the check bit is not requested, the transmission frame creating means for forming only the moving image code packet, and the moving image code packet are transmitted through the dedicated channel allocated to the terminal device capable of transmitting image data, and the check bit packet is transmitted. Multiplex transmission means for selecting and transmitting one of the shared channels is provided; Receives moving image code packets and check bit packets sent from several image data transmittable terminal devices, separates them for each image data transmittable terminal device, and if the reception level is equal to or lower than the threshold level Demultiplexing receiving means for requesting the terminal capable of transmitting image data to transmit a check bit of an error correction code, and synchronizing moving image information and a check bit of the same image frame from the moving image code packet and the check bit packet. FEC
Frame creating means.

In this system, when the transmission quality of the radio channel is degraded, the error correction code is adaptively added using the shared channel, so that the transmission of the moving picture code is not delayed. At this time, since the shared channel is used, the increase in the wireless transmission bandwidth of the entire system is small.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a digital video communication system comprising a terminal device capable of transmitting image data and a center device capable of receiving image data, wherein a terminal device capable of transmitting image data has an error. If the correction-encoded moving image code in units of image frames is separated into a check bit and a moving image code of an error correction code, and the center device capable of receiving image data requests to transmit the check bit, the moving image The code and the check bit are output as a packet together with the image frame number, and unless the image data receivable center device requests transmission of the check bit, only the moving image code is output as a packet together with the image frame number. The transmission frame generating means and the video code packet output from the transmission frame generating means are transmitted to the Multiplexing transmission means for transmitting a check bit packet to a dedicated channel assigned to the terminal device capable of transmitting data, and selecting and transmitting one of the shared channels commonly used among the plurality of terminal devices capable of transmitting image data. The center device capable of receiving image data receives the moving image code packet and the check bit packet sent from the plurality of terminal devices capable of transmitting image data, and separates each of the terminal devices capable of transmitting image data. If the reception level at that time is equal to or less than the threshold level, a demultiplexing receiving means for requesting the terminal device capable of transmitting image data to transmit a check bit of an error correction code, and a moving image which is an output signal of the demultiplexing receiving means FE that extracts moving image information and an inspection bit having the same image frame number from an image code packet and an inspection bit packet and outputs them in synchronization Are those in which a frame creation unit, if the transmission quality of the radio channel is degraded, without transmission delay of video information, adaptively can for adding an error correction code.

According to a second aspect of the present invention, the image data transmittable terminal device is provided with a parity adding means for adding a parity bit for error detection to a check bit packet to be transmitted. Device F
An error is detected by the parity bit with respect to the check bit packet output from the demultiplexing reception means in the EC frame creation means, and if the error and the reception of the moving picture code packet having the same frame number are not completed, the check is performed. An error detection unit for requesting retransmission of a bit packet is provided, and the multiplex transmission unit of the terminal device capable of transmitting image data performs retransmission when a retransmission request of a check bit packet is received from the center device capable of receiving image data. The center device capable of receiving image data can obtain inspection bits without bit errors and reproduce a high-quality moving image.

According to a third aspect of the present invention, the multiplexing transmitting means of the terminal device capable of transmitting image data performs carrier sense on the selected shared channel and transmits a check bit packet when it is determined that the channel is free. Thus, collision of the check bit packet on the shared channel can be avoided, and reliability in transmission of the check bit packet can be improved.

According to a fourth aspect of the present invention, when requesting a terminal device capable of transmitting image data to transmit a check bit of an error correction code to the terminal device capable of receiving image data, the terminal device searches for a vacant channel of a shared channel, and A shared channel allocating means for notifying the identifier to the terminal capable of transmitting image data is provided. By designating a shared channel to be selected from the terminal capable of receiving image data, collision of the check bit packet on the shared channel can be achieved. And reliability in transmission of the check bit packet can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) As shown in FIG. 1, a digital video communication system according to a first embodiment is a terminal device (terminal device) 608, 609, 610 capable of transmitting image data.
And a center device capable of receiving image data (center device)
622, the terminal device comprises a moving picture code input terminal 601 to which a moving picture code is inputted, and an error correction coding means 60 for performing error correction coding of the inputted moving picture code in image frame units.
3, an image frame number input terminal 602 for inputting an image frame number, and a transmission frame generation for dividing a video code and an error correction code check bit into packets to generate a video code packet and a check bit packet. Means604
A parity adding unit 605 for adding a parity bit for error detection to a check bit packet output from the transmission frame generating unit 604, and a video code packet output from the transmission frame generating unit 604 are allocated to each terminal device. Multiplexing means 606 for transmitting the check bit packet output from the parity adding means 605 to the shared channel between the terminal devices of the system, and control signals from the center device 622 requesting the transmission of the check bits. And control signal receiving means 607 for receiving the control signal.

Further, the center device 622 receives the moving picture code packet and the check bit packet transmitted from the plurality of terminal devices 608 to 610, and separates and outputs them for each terminal device. If the level is equal to or less than the threshold level, the demultiplexing receiving means 611 requesting the terminal device to transmit the check bit of the error correction code, and the corresponding terminal device receives the request of the demultiplexing receiving means 611 and transmits the error correction code to the corresponding terminal device. A control signal transmitting unit 612 for outputting a control signal for instructing transmission of check bits, and a moving image having the same image frame number from a moving image code packet and a check bit packet which are output signals of the demultiplexing receiving unit 611. FEC frame creating means 613 for taking out image information and inspection bits and outputting them in synchronization
And error correction means 616, 617, and 618 for performing error correction on transmission data transmitted from each terminal device, and reproduction display means 619, 620, and 621 for reproducing an error-corrected moving image.

FIG. 3 shows that the digital video communication system is "TDMA (Time Division Multiple Access) / FDD".
(Frequency Division Duplex)
13 shows a configuration example of a channel in the embodiment. Also,
FIG. 4 shows that the digital video communication system is “TDMA /
The first in the case of adopting the “TDD (Time Division Duplex)” system
13 shows a configuration example of a channel in the embodiment.

As shown in FIGS. 3 and 4B, a channel corresponding to each terminal device for transmitting image data and a redundant bit (check bit) of an error correction code are transmitted on the uplink. And a plurality of shared channels are provided. As shown in FIG. 3 and FIG. 4 (c), a channel corresponding to each terminal for transmitting a control signal from the center apparatus to each terminal is prepared in the downlink.

The TDMA / TDD and the TDMA / FDD differ only in whether the uplink and downlink channel settings are time division or frequency division, as shown in FIGS. 3 and 4 (a). , Because there is no difference in its operation and operation,
Hereinafter, the operation will be described collectively.

In the system shown in FIG.
Since 09 and 610 all have the same configuration, the operation of this system will be described using the configuration of the terminal device 608.

In the terminal device 608, the moving image code is input from the moving image code input terminal 601 and the error correction coding means 603
This moving image code is subjected to error correction coding in image frame units. FE which is an output signal of the error correction encoding means 603
The C frame is shown in FIG.

From the image frame number input terminal 602, an image frame number corresponding to the moving image code input from the moving image code input terminal 601 is input. This image frame number is required to establish a correspondence between the divided moving image code and the check bit.

The output signal of the error correction coding means 603 and the image frame number input from the image frame number input terminal 602 are input to the transmission frame generation means 604, and the transmission frame generation means 604 transmits the error correction code from the center device 622. When the request for transmission of the check bit is received through the control signal receiving means 607, a video code packet and a check bit packet are created.

As shown in FIG. 5 (b-1), the moving picture code packet created at this time includes an FEC flag indicating that a check bit packet is present, an image frame number, image data of the FEC frame, and The inspection bit packet includes the length information of the image data, and the check bit packet specifies the center ID for specifying the destination center device 622 and the source terminal device 608 as shown in FIG. 5C. It consists of a terminal ID, an image frame number, an error correction code check bit of the FEC frame, and length information of the check bit.

When there is no check bit transmission request from the center device 622, the transmission frame creating means 604 does not create a check bit packet, but (b) of FIG.
2), only the video code packet shown in FIG.
The EC flag indicates that there is no corresponding check bit packet.

The check bit packet created by the transmission frame creating means 604 is sent to the parity adding means 605,
The parity adding unit 605 adds a parity bit for error detection for the check bit packet to the check bit packet. By the addition of the parity bit, when a collision occurs on a shared channel with another terminal device and when the check bit packet includes a transmission error, the center device 622 detects the bit error and replaces the check bit. This can be discarded, and incorrect error correction can be prevented.

The moving picture code packet (FIGS. 5 (b-1) and 5 (b-2)) created by the transmission frame creating means 604 and the check bit packet output from the parity adding means 605 are input to the multiplex transmitting means 606. The multiplexing transmission means 606 transmits the moving image code packet to the channel allocated to the terminal device 608, and when a request for transmitting a check bit is received from the center device 622 through the control signal receiving means 607, The check bit packet is transmitted according to the procedure shown in FIG.

Step 1001: Check bit packet is 1
After inputting the packets, the transmission process is started.

Step 1002: First, a transmission channel is randomly selected from a plurality of shared channels.

Step 1003: Next, a check bit packet is transmitted to the selected transmission channel, and Step 1004: the transmission processing ends.

When there is no request for transmission of a check bit from the center device 622, no check bit packet is created by the transmission frame creation means 604, so there is no output from the parity addition means 605, and the multiplex transmission means 606 Only the moving picture code packet is transmitted.

On the other hand, in the center device 622, the demultiplexing reception means 611 separates the moving picture code packet multiplexed and transmitted by each of the terminal devices 608 to 610 into data for each terminal device. At this time, the demultiplexing receiving means 611
The reception level of each channel is determined, and a control signal is transmitted through the control signal transmission unit 612 so that a check bit of an error correction code is transmitted to a terminal device whose level is equal to or less than a threshold value.

The demultiplexing reception means 611 converts the data of the shared channel into all FEC frame creation means 613,6.
Output to 14,615.

The FEC frame creation means 613 to 615 correspond to FIG.
As shown in the figure, a moving image code packet storage means 70 for storing moving image code packets transmitted from a corresponding terminal device.
1; a check bit storage means 702 for storing a check bit packet having a terminal ID of the terminal device; an error detection means 703 for detecting an error in the check bit packet and requesting retransmission of the check bit packet having the error; An FEC framing unit 704 for reproducing an FEC frame by combining moving image data having the same image frame number and error-free check bits is provided.

The moving picture code packet storage means 701 of the FEC frame creation means 613 to 615 includes a demultiplexing reception means 611.
The check bit storage unit 702 stores the moving image code packet output from the unit for each packet. The check bit packet having the corresponding terminal ID is selected from the check bit packets output from the demultiplexing reception unit 611. Is stored for each packet.

The check bit packet stored in the check bit storage means 702 may cause packet collision in the shared channel or may include a transmission error.
The error detecting means 703 detects an error of the check bit packet by using the parity bit added to the check bit packet (a packet collision can be detected by detecting a bit error). As a result, the check bit packet determined to have no error is output to the FEC framing unit 704.

If the error detecting means 703 determines that the check bit packet has an error, the moving picture code packet having the picture frame number of the check bit packet is stored in the moving picture code packet storing means 701. After confirming that there is (the reception of the moving image code packet is not completed), the control signal transmitting unit 612 retransmits the check bit packet of the corresponding image frame number to the transmitting terminal device 608. Request to do so.
The control signal for the retransmission request is sent to the control signal receiving means 607 of the terminal device 608 through the downlink channel 624, and the multiplex transmitting means 606 receiving the retransmission request notification from the control signal receiving means 607.
Retransmits the check bit packet of the designated image frame number.

When an error correction code for a normal wireless channel is considered, the length of the check bit is shorter than the length of the information to be protected. It takes a short time. Therefore, it is possible to retransmit the check bit packet a plurality of times until the reception of the video code packet having the same image frame number is completed, and the transmission of the video code data is delayed even if the check bit packet is retransmitted. It does not mean that In other words, by retransmitting the check bit packet, it is possible to increase the probability of receiving a check bit having no bit error without increasing the delay time of moving image transmission.

The moving picture code packet stored in the moving picture code packet storing means 701 is output to the FEC framing means 704 after one packet of data is stored.
When the FEC flag of the video code packet indicates that the corresponding check bit exists, the FEC framing unit 704 extracts the video data from the video code packet and outputs the same video data output from the error detection unit 703. The check bits are extracted from the check bit packet having the image frame number, synchronized with the check bit presence flag and the corresponding error correction means 616 to synchronize the flag (with the FEC frame in FIG. 5A). 618
Output to

When the FEC flag of the video code packet indicates that there is no corresponding check bit, the video data extracted from the video code packet and the flag without the check bit are sent to the error correction means 616 to 618. Output.

The error correction means 616 to 618 perform an error correction process when the FEC flag of the frame output from the FEC frame creation means 613 to 615 indicates that a check bit is present. In the case shown, the input signal is output as it is.

The outputs of the error correction means 616 to 618 are input to the reproduction display means 619 to 621 corresponding to each terminal and displayed as a moving image.

As described above, in the digital video communication system of the first embodiment, when the transmission quality of the radio channel is deteriorated, the error correction code is adaptively added using the common channel in order to maintain the image quality. Is performed. At this time, since the transmission of the error correction code is performed on the common channel, the transmission bandwidth of the image data is unchanged, and the transmission delay of the image data does not occur. Further, since the common channel is used, the increase in the wireless transmission bandwidth of the entire system is small.

Further, in this system, an error of a check bit of an error correction code is detected, and when an error is included, a correct check bit reaches the center device by retransmitting the check bit. Therefore, the center device can reproduce the moving image without error.

(Second Embodiment) The digital video communication system according to the second embodiment has improved reliability in transmission of check bit packets.

The configuration of this system is the same as that of the first embodiment (FIG. 1), and its operation is the same except for the operation of the multiplex transmission means 606 of the terminal device 608.

When transmitting the check bit packet to the shared channel, the multiplexing transmission means 606 in the terminal device 608 of this system performs the transmission according to the procedure shown in FIG.

Step 1101: Check bit packet is 1
When the number of packets has been input, the transmission process starts.

Step 1102: First, a transmission channel is randomly selected from a plurality of shared channels. Step 1103: Carrier sense of the next selected transmission channel is performed, and it is checked whether the channel is being used by another terminal device.
Return to 02 and select a channel. If not in use, Step 1104: Transmit the check bit packet to the selected transmission channel, and Step 1105: End the transmission process.

By doing so, collision of check bit packets on the shared channel can be avoided, reliability of check bit packet transmission can be improved, and effective use of the line can be achieved.

(Third Embodiment) In the digital video communication system according to the third embodiment, the transmission channel of the check bit packet is designated from the center device side.

As shown in FIG. 8, the center device of this system includes shared channel allocating means 822 for allocating a shared channel to terminal devices 808 to 810. Other configurations are the same as those of the first embodiment (FIG. 1).

In this system, the demultiplexing reception means 611 of the center device 823 determines the reception level of the moving picture code packet transmitted from each of the terminal devices 808 to 810, and determines the reception level for the terminal device whose level is equal to or less than the threshold. Then, when a transmission request for a check bit of an error correction code is output, the shared channel allocating means 822 that has received the output searches the shared channel for a free channel that is not used by another terminal device.
The shared channel ID is output to the terminal device 808 through the control signal transmission unit 812.

In response to this, multiplex transmission means 806 of terminal apparatus 808 transmits a check bit packet in the procedure shown in FIG.

Step 1201: Check bit packet is 1
After inputting the packets, the transmission process is started.

Step 1202: Select a shared channel having an ID specified by the center device 823 as a transmission channel. Step 1203: Transmit a check bit packet to the selected transmission channel. Step 1204: End transmission processing.

By doing so, collision of check bit packets on the shared channel can be avoided, reliability of check bit packet transmission can be improved, and effective use of the line can be achieved.

[0066]

As is apparent from the above description, the digital video communication system according to the present invention is capable of reducing the transmission quality of a radio channel without causing a transmission delay of image data.
An error correction code for maintaining image quality can be adaptively added, and the use of the common channel can suppress an increase in the wireless transmission bandwidth of the entire system at that time.

Further, by detecting the error of the check bit, a highly reliable moving image can be reproduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a digital video communication system according to first and second embodiments of the present invention;

FIG. 2 is a block diagram showing a configuration of an FEC frame creation unit in the digital video communication systems of the first and second embodiments;

FIG. 3 is a diagram showing a configuration of a wireless channel when a TDMA / FDD scheme is adopted in the digital video communication system according to the first embodiment;

FIG. 4 is a diagram showing a configuration of a wireless channel when the TDMA / TDD scheme is adopted in the digital video communication system according to the first embodiment;

FIG. 5 is a diagram showing a configuration of a processing frame in the digital video communication system according to the first embodiment;

FIG. 6 is a flowchart showing an operation procedure of a multiplex transmission unit in the digital video communication system according to the first embodiment;

FIG. 7 is a flowchart showing an operation procedure of a multiplex transmission unit in the digital video communication system according to the second embodiment;

FIG. 8 is a block diagram showing a configuration of a digital video communication system according to a third embodiment of the present invention;

FIG. 9 is a flowchart showing an operation procedure of a multiplex transmission unit in the digital video communication system according to the third embodiment;

FIG. 10 is a schematic diagram of a digital video communication system;

FIG. 11 is a block diagram showing a configuration of a conventional digital video communication system;

FIG. 12 is a diagram showing an uplink transmission frame in a conventional digital video communication system.

[Explanation of symbols]

101, 216, 622, 823 Center equipment 102-104, 205-207, 608-610, 808-810 Terminal equipment 105-107, 217, 623, 824 Uplink transmission channels 108-110, 218-220, 624-626, 825 to 827 Downlink control channels 201, 601, 801 Video code input terminals 202, 603, 803 Error correction coding means 203 Transmitting means 204, 607, 807 Control signal receiving means 208 Receiving means 209, 612, 812 Control signal transmitting means 210-212, 616-618, 816-818 Error correction means 213-215, 619-621, 819-821 Playback display means 602, 802 Image frame number input terminal 604, 804 Transmission frame creation means 605, 805 Parity addition means 606 806, multiplex transmission means 611, 811 demultiplex reception means 613-615, 705, 813-815 FEC frame creation means 701 video code packet storage means 702 check bit packet storage means 703 error detection means 704 FEC framing means 822 Shared channel allocation means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H04N 5/00 H04N 5/00 B 7/173 7/173

Claims (4)

[Claims] In a digital video communication system including a terminal device capable of transmitting image data and a center device capable of receiving image data, a terminal device capable of transmitting image data transmits an error-corrected coded moving image code for each image frame. If the center device capable of receiving image data requests to transmit the check bit, the moving image code and the check bit are packetized together with the image frame number. If the center device capable of receiving image data does not request transmission of check bits, only a moving image code is output as a packet together with its image frame number as a packet. The output video code packet is allocated to the terminal device capable of transmitting the video data. Multiplex transmission means for transmitting the check bit packet to one of the shared channels used in common among a plurality of image data transmission capable terminal devices, and transmitting the selected check channel packet to the dedicated channel. Receiving the moving image code packet and the check bit packet transmitted from the plurality of image data transmitting capable terminal devices, separating and outputting each of the image data transmitting capable terminal devices, Demultiplexing receiving means for requesting the image data transmittable terminal device to transmit a check bit of an error correction code if the reception level of the video signal is equal to or less than the threshold level, and a moving picture code which is an output signal of the demultiplexing receiving means. FEC frame that extracts moving image information and the inspection bit having the same image frame number from the packet and the inspection bit packet and outputs them in synchronization Digital video communication system characterized by comprising the creation means. 2. The image data transmittable terminal device further includes a parity adding unit that adds a parity bit for error detection to the transmitted check bit packet, and generates an FEC frame of the image data receivable center device. Means for performing error detection on the check bit packet output from the demultiplexing reception means by using a parity bit, and if the error and the reception of the video code packet having the same frame number are not completed, the check is performed. Error detecting means for requesting retransmission of a bit packet is provided, and the multiplexing transmission means of the image data receivable terminal device retransmits a check bit packet when a retransmission request of a check bit packet is received from the image data receivable center device. The digital video communication system according to claim 1, wherein: 3. The multiplexing transmission means of the terminal device capable of transmitting image data performs carrier sense on the selected shared channel, and transmits the check bit packet when it is determined that the channel is free. The digital video communication system according to claim 1 or 2, wherein 4. When requesting the image data receivable terminal device to transmit a check bit of an error correction code to the image data receivable terminal device, the image data receivable terminal device searches for a free channel of the shared channel and sets a channel identifier thereof to the image data. 3. The digital video communication system according to claim 1, further comprising a shared channel allocating unit for notifying the terminal capable of transmitting data.