JP2964484B2 - Image receiving method and image receiving apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image receiving method and an image receiving apparatus suitable for use in a communication system for transmitting still image data via a communication satellite, for example.

[Summary of the Invention]

The present invention relates to an image receiving method and an image receiving apparatus suitable for use in, for example, a communication system for transmitting still image data via a communication satellite, wherein the receiving side adds a packet number and error detection data from the transmitting side, respectively. Received packets are sequentially received by a predetermined number of packets, and the presence or absence of an error in the image data of each packet is determined using the error detection data added to each packet. In order to decode only the data, store the decoded image data in a predetermined area of the image memory, and collectively request retransmission of erroneous packets from a predetermined number of received packets, the image memory By transmitting the packet numbers of the packets that have not been stored to the transmitting side together, the transmission is performed in a communication system with a slow response such as satellite communication. If the error has occurred is obtained by allowing the reception of efficiently image data even.

[Conventional technology]

ISO (International Organization for Standa) as a transmission control procedure for high-speed data transmission
rdization) to control the high-level data link control procedure (H
A control procedure called igh level Data Link Control procedure (hereinafter abbreviated as HDLC) is standardized. HD
LC is a transmission control method that is capable of high-speed transmission and is also suitable for computer networks connecting computers.
It has the following features.

For example, transmission of an arbitrary bit pattern such as transmission in bit units is possible.

Frames or packetized data can be transferred continuously.

Error detection is strict and transmission reliability is high.

As described above, in HDLC, data is continuously transmitted in units of one frame or one packet. FIG. 6A shows the structure of one packet. In FIG. 6A, the packet (1) has an 8-bit head flag (2), an 8-bit address corresponding to the transmission / reception destination, and a 16-bit extension mode. The control section (3) includes an information section of an arbitrary bit string, a 16-bit error detection code (CRCC), and an 8-bit termination flag (4). As shown in FIG. 6B, the control unit (3) of the 16-bit extended mode is composed of a first octet and a second octet of 8 bits, respectively. The packet (1) includes an I packet of an information transfer method for transmitting information data, an RR packet of a monitoring format used for executing monitoring control of a communication state, and the like. The control unit (3) has a transmission sequence number N (S) of 7 pits (0 to 127), a reception sequence number N (R) of 7 bits (0 to 127), and a poll / final (P / F) bit. In response to the RR packet, the control unit (3) has a monitoring function bit S, a 7-bit reception sequence number, and a P / F bit.

A conventional information transmission / reception method using HDLC will be described with reference to FIG. 7. In FIG. 7, (5) and (6)
Are composite stations A and B each having an equivalent transmission / reception function.
It is assumed that data corresponding to 50 I packets (7) is transmitted from the composite station A (5) to the composite station B (6). In this case, the composite station A (5) transmits the transmission state variable VA
(S) and the reception state variable VA (R) are stored in the built-in RAM, and the complex station B (6) stores the transmission state variable VB (S) and the reception state VB (R) in the built-in RAM.

As shown in FIG. 7, the transmission sequence number N (S) in the I packet (7) increases by one from 0 to 49, and
The transmission state variable VA (S) of (5) becomes 1 to 50 after transmission of each I packet (7), and indicates the transmission sequence number N (S) of the I packet (7) to be transmitted next. On the other hand, the complex station B (6) detects the presence or absence of an error during transmission from the error detection code CRCC of the received I packet (7), and if there is no error, the data of the information part of the I packet (7) is detected. It is stored in the memory and the reception state variable VB (R) is incremented by one from 0. Therefore, the value of the transmission sequence number N (S) of the I packet (7) and the reception state variable VB of the complex station B (6)
The value of (R) matches in principle.

However, when a transmission error occurs as shown by the arrow (8) in FIG. 7, the composite station B (6) keeps updating the reception state variable VB (R) stopped. Further, the value of the transmission sequence number N (S) of the I packet (7) and the reception state variable of the complex station B (6)
If the value does not match the value of VB (R), the multi-station B (6) stops updating the reception state variable VB (R) similarly as the occurrence of a "transmission order error".
The value of (R) is fixed at “3”.

The composite station A (5) sets the poll (P) bit of the 50th I packet (7) to "1" and requests the response of the composite station B (6). ) Indicates the value “3” of the reception state variable VB (R) as the reception sequence number N (R).
The monitor packet (RR packet) (9) having the value of (1) is transmitted to the composite station A (5). The multi-station A (5) generates a transmission error due to the difference between the value "3" of the reception sequence number N (R) of the RR packet (9) and the value "50" of its own transmission state variable VA (S). And the value of the transmission sequence number N (S) “3”
The remaining 47 I-packets are sequentially transmitted to the composite station B (6) again from the I-packet (10).

When no transmission error occurs, the composite station B
The RR packet (1) transmitted from (6) to the composite station A (5)
The value “50” of the reception sequence number N (R) of 1) is
Since the value matches the value “50” of the transmission state variable VA (S) in (5), the data transmission is completed.

[Problems to be solved by the invention]

According to the conventional HDLC shown in FIG. 7, data can be transmitted without error. However, in the conventional HDLCD, when a transmission error occurs, a series of subsequent I packets must be transmitted again, and the communication time becomes longer, resulting in poor communication efficiency.

However, in a communication system in which a full-duplex communication is performed using a terrestrial high-speed digital circuit network, the efficiency is inconspicuous because the response is fast. However,
In the case where data is transmitted in half-duplex through a communication satellite with a response as slow as about 1 second and the data is still image data containing a huge amount of information, the conventional The inefficient communication of HDLC has been a major problem.

In view of the above, an object of the present invention is to propose an image receiving method and an image receiving apparatus capable of efficiently receiving data even when a transmission error occurs in a communication system having a slow response such as satellite communication. .

[Means for solving the problem]

The image receiving method according to the present invention is an image receiving method for receiving a packet composed of encoded image data sent from a transmitting side, for example, as shown in FIG. 1 and FIG. ) Sequentially receives a predetermined number of packets (34) to which the packet number N (S) and the error detection data from the transmission side (12) are added, and outputs the error detection data added to each packet (34). Is used to determine the presence or absence of an error in the image data of each packet (34), and based on the determination result, only the image data of the packet (34) having no error is decoded. Packets (38) and (39) not stored in the image memory are stored in a predetermined area of the memory, and in order to collectively request a retransmission of packets having an error from the received predetermined number of packets. packet The number N (S) is collectively transmitted to the transmitting side (12).

Further, the image receiving apparatus according to the present invention, in an image receiving apparatus that receives a packet composed of encoded image data sent from the transmitting side, a transmitting and receiving unit that transmits and receives image data to and from the transmitting side , An image memory for storing image data, and a control unit for controlling writing and reading operations of the image data to and from the image memory, wherein the transmitting and receiving unit transmits a packet to which a packet number and error detection data from the transmitting side are respectively added. A predetermined number of packets are sequentially received, and the control unit determines the presence or absence of an error in the image data of each packet using the error detection data added to each packet, and based on the determination result, determines whether or not there is no error in the packet. Decoding only the image data, controlling the writing operation of the image data to store the decoded image data in a predetermined area of the image memory, The receiving unit collectively sends the packet numbers of the packets that are not stored in the image memory to the transmitting side in order to collectively request a retransmission of the erroneous packets from the received predetermined number of packets. I have.

[Action]

According to the present invention, the transmitting side (12) is switched from the receiving side (1) to the receiving side (1).
In step 3), the occurrence of an error in the transmission stage is detected from the error detection data of a predetermined number of packets (34) in succession, and only the image data of the packet (34) transmitted without error is decoded, respectively. Are sequentially stored in a predetermined area. Further, the receiving side (13) transmits packets (38), (3) not stored in the image memory.
By transmitting the packet number N (S) of (9) collectively to the transmission side (12), packets erroneous (38), (3)
Since the retransmission request of (9) is performed collectively, the transmitting side (12) only receives the unstored packets (38) and (39) on the receiving side (13).
Can be resent to Therefore, the communication efficiency is greatly improved as compared with the conventional case where all packets after the packet having a transmission error are uniformly retransmitted.

〔Example〕

Hereinafter, an embodiment of an image receiving method and an image receiving apparatus according to the present invention will be described with reference to FIGS.
In this embodiment, the present invention is applied to a satellite communication system. In FIGS. 3 and 5, parts corresponding to FIGS. 6 and 7 are denoted by the same or similar reference numerals, and detailed description is omitted. I do.

FIG. 1 shows the satellite communication system of the present embodiment. In FIG. 1, (12) is a mobile station, (13) is a broadcasting center,
(14) indicates a communication satellite, and it is assumed that still image data is transmitted from the mobile station (12) to the broadcasting center (13) via the communication satellite (14). At the mobile station (12)
(15) Central processing unit (CPU) (16), ROM (17) and RAM
A computer comprising (18), (19) a system bus of a CPU (16) comprising a data bus, an address bus, a control bus, etc., and a ROM (17) and a RAM (18) connected to the system bus (19) The computer (15) controls transmission and reception of still image data of the mobile station (12) via the system bus (19).

(20) is a frame memory capable of storing image data of 768 × 480 pixels, (21) is a write / read control circuit,
Reference numeral (22) denotes an address signal generation circuit, which connects the input / output port of the frame memory (20) to the system bus (19) and outputs a write / read pulse generated by the write / read control circuit (21). An address signal input terminal of the frame memory (20) supplies a write enable terminal of the frame memory (20) to the write enable terminal of the frame memory (20) and supplies a signal generated by the address signal generation circuit (22) and indicating an address of each pixel for writing or reading. To supply. Further, (23) shows a timing circuit for forming a timing pulse by separating the vertical synchronizing signal and the horizontal synchronizing signal from the video signal, and supplies this timing pulse to the address signal generating circuit (22).

Reference numeral (24) denotes a still image signal input / output source such as a video tape recorder, and the video signal output from the input / output source (24) is separated into, for example, a Y signal, an RY signal, and a BY signal. Digitizing with an analog / digital (A / D) converter (25) according to the so-called 4: 2: 2 standard and supplying the digitized image data for one frame to the input port of the frame memory (20) Thus, the image data of one frame of the still image stored in the input / output source (24) is written to the frame memory (20). (26) denotes a digital / analog (D / A) converter, which inputs the image data in the frame memory (20) to the still image via the system bus (19) and the D / A converter (26). It can also be stored in the output source (24).

The image data of the frame memory (20) is supplied to a D / A converter (27), and the obtained analog video signal is supplied to a monitor (28A) or a video printer (29). And a still image corresponding to the image can be displayed or printed out.

The computer (15) divides the image data of the frame memory (20) into blocks, for example, an ABTC (Adaptive Block).
Truncation Coding: Block coding method or ADCT (A
After performing high-efficiency compression coding by a daptive Discrete Cosine Transform (Adaptive Discrete Cosine Transform) method or the like, the data is supplied to the communication control device (31). The communication control device (31) performs satellite communication protocol processing and modulation on the image data, and then transmits the image data to the broadcast center (13) via the transmission / reception antenna (32A). The broadcast center (13) also has an element corresponding to the request of the mobile station (12) for transmission and reception, and the letter A is used for the element corresponding to the element of the mobile station (12) on the broadcast center (13). The reference numerals are replaced with B and shown.

The operation of this example will be described with reference to FIGS. 2 to 4. As shown in FIG. 2, a monitor (28) on the mobile station (12) side is used.
A) Image data corresponding to a screen (33A) consisting of 768 dots in the horizontal direction × 480 lines in the vertical direction is divided into 240 blocks PA0, PA1,... PA239 each consisting of 192 dots × 8 lines. The transmission order numbers N (S) shown in FIG.
Compression-encoded and written in the information section (see FIG. 6A) of the packet (I packet) (34) in the information transfer format as the packet of (1). In this example, since the number of I-packets (34) as packets is 240, the control unit (3) shown in FIG. 6B has one more bit for both the transmission sequence number N (S) and the reception sequence number N (R). The number N (S) and N (R) may be recorded in the information section as data, although they need to be increased to 8 bits (0 to 255) each.

Then, the mobile station (12), as shown in FIG.
The image data of PA0 is compression-encoded, and a 16-bit error detection code CRCC (see FIG. 6A) is added, and the transmission sequence number N
An I packet (34) having the value (S) of 0 is formed, and this I packet (34) is transmitted to the broadcasting center (13). Subsequently, the image data of the order blocks PA1, PA2,... Are compression-encoded, and the I packets (34) whose transmission order numbers N (S) are 1, 2,.
Is transmitted to the broadcast center (13), and the poll (P) bit of the last I packet whose transmission sequence number N (S) is 239 is set to “1” to request a response from the broadcast center (13).

On the other hand, the broadcasting center (13) stores the auxiliary variable XB (R) in the auxiliary RAM (30B), and the value of the auxiliary variable XB (R) is transmitted by one I packet (34) from the mobile station (12). Each time it is performed, it is mechanically incremented by one from 0. The updating of the value of the reception state variable VB (R) is stopped when a transmission error occurs as in the conventional case. The updating of the value of the reception state variable VB (R) is stopped when a transmission error occurs as in the conventional case. If it is confirmed from the error detection code CRCC of the received I packet (34) that there is no transmission error in the I packet (34), the broadcast center (13)
The side decodes the compression-encoded image data of the I packet (34) and writes it in a predetermined area of the frame memory, and assists the transmission order number N (S) of the I packet (34).
Write to RAM (30B). If there is a transmission error in the received I packet (34), the broadcast center (1
On the 3) side, the image data of the I packet (34) is ignored, and the recording of the transmission sequence number N (S) is omitted.

In this example, assuming that a transmission error occurs at the time indicated by arrows (35) and (36) in FIG. 3, the value of the reception state variable VB (R) on the broadcast center (13) side remains "2". While the value of the auxiliary variable XB (R) is always 1
Is incremented by one. The auxiliary variable XB (R) is used for detecting a "transmission order error" which is an error in the value of the transmission sequence number N (S). Then, the values of the transmission sequence number N (S) are 2 and 9
Since only the image data of the I packet is ignored,
As shown in FIG. 4, the monitor (28B) of the broadcast center (13) is in a state where only the blocks PB2 and PB9 corresponding to the I packets whose numbers N (S) are 2 and 9, respectively, are missing. The screen (38B) is displayed.

After receiving the I packet whose poll (P) bit is “1”, the broadcast center (13) sets the reception state variable VB
(R) with the value “2” as the value of the reception sequence number N (R)
The packet (37) is transmitted to the mobile station (12). In the information section of the I packet (37), the transmission order numbers (2 and 9 in this example) of the I packet (34) in which the transmission error has occurred are written as number information. The mobile station (12) that has received the I packet (37) determines a transmission error due to a mismatch between the value “2” of the reception sequence number N (R) and the value “240” of its own transmission state variable VA (S). When the occurrence is recognized, the number information (2 and 9) of the I packet (37) is written into the auxiliary RAM (30A).

Thereafter, the mobile station (12) retransmits only the I packets (38) and (39) whose transmission sequence numbers N (S) are 2 and 9, respectively, to the broadcast center (13) in order. Transmission state variable VA (S) of mobile station (12) at the stage of retransmitting I packet (39)
Is 10 (= 9 + 1). In response, the broadcast center (13) receives the I packet (38), (39)
The presence / absence of a transmission error is checked from each error detection code CRCC, and if there is no transmission error, each image data is decoded and written in a predetermined area of the frame memory. In this case, as the value of the reception state variable VB (R) and the value of the auxiliary variable XB (R), the I packet (3
The value of the transmission sequence number N (S) of 4) is sequentially set.
The value of the number N (S) corresponds to the missing number in the transmission order number N (S) written in the auxiliary RAM (30B). Further, the value of the reception state variable VB (R) is fixed to the value at the time when a transmission error occurs.

Then, after the broadcast center (13) has successfully received the I packet (39), the value of the reception state variable VB (R) is changed to 10 (=
9 + 1) and the monitoring format packet (RR packet) (40) with the value of the reception sequence number N (R) being 10 is transmitted to the mobile station (12).
To be transmitted. The mobile station (12) receives the value "10" of the reception order N (R) of the RR packet (40) and its own transmission state variable VA.
When the value of (S) matches "10", it can be known that all the I packets have been transmitted normally, and the transmission of the still image data for one frame is completed.

According to this example, 240 I packets (34) are transmitted to the broadcast center (13) side in advance, and the value of each transmission sequence number N (S) of the I packet (34) in which a transmission error has occurred is calculated. It is transmitted from the broadcasting center (13) to the mobile station (12). Thereafter, since the mobile station (12) transmits only the I packets (38) and (39) in which the transmission error has occurred to the broadcast center (13), the normally transmitted I packets overlap. There is an advantage that communication efficiency is good without being transmitted.

In the above embodiment, the second stage I packet (3
If an error occurs in the transmission process of (8) and (39), the broadcasting center (13) collects the values of the transmission sequence number N (S) of the I packet in which the transmission error has occurred in the mobile station (12). After the transmission, the mobile station (12) transmits the I packet requested to be retransmitted again to the broadcasting center (13), and the same procedure is repeated until all the I packets are transmitted without error.

Also, the transmission state variable N (S) in the first stage shown in FIG.
May be transmitted as time series data Q0, Q1,... Q239, as shown in FIG.
In FIG. 5, FS corresponds to the 8-bit head flag (2), A corresponds to the 8-bit address, and FE corresponds to the termination flag (4) in FIG. 6A. Further, F1 is also used as the front end flag (2) and the end flag (4) in FIG. 6A.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

〔The invention's effect〕

According to the present invention, the receiving side decodes only an error-free packet and stores the decoded packet in the image memory, and requests retransmission of the unstored packets (errored packets) of the image memory collectively. In addition, there is an advantage that still image data can be efficiently transmitted even when a transmission error occurs in a communication system having a slow response such as satellite communication.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 4 are diagrams showing screen configurations of monitors on a transmitting side and a receiving side of the embodiment, respectively, and FIG. 3 is an operation of the embodiment. , FIG. 5 is a diagram for explaining a modification of the embodiment, FIG. 6 is a diagram showing the configuration of a conventional packet, and FIG. 7 is a conventional HD
FIG. 3 is a diagram showing transmission and reception of information by LC. (12) is a mobile station, (13) is a broadcasting center, (20) is a frame memory, (28A) and (28B) are monitors, (30)
A) and (30B) are auxiliary RAMs respectively, (34), (38) and (39)
Are I packets as packets.

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 7/24-7/68 H04N 7/10 H04N 7/14-7/173 H04L 12/00-13 / 18

Claims (2)

(57) [Claims] 1. An image receiving method for receiving a packet comprising coded image data sent from a transmitting side, wherein said packet to which a packet number and error detection data from said transmitting side are respectively added is sequentially determined. The received packet number is used to determine whether there is an error in the image data of each packet using the error detection data added to each packet, and based on the determination result, only the image data of the packet without errors is decoded. In order to store the decoded image data in a predetermined area of the image memory and collectively request retransmission of erroneous packets from the predetermined number of received packets, the image data is not stored in the image memory. An image receiving method, wherein the packet numbers of the packets are transmitted together to the transmitting side. 2. An image receiving apparatus for receiving a packet comprising encoded image data sent from a transmitting side, comprising: a transmitting / receiving unit for transmitting / receiving image data to / from the transmitting side; and storing the image data. An image memory, and a control unit that controls writing and reading operations of image data to and from the image memory. The transmitting and receiving unit sequentially transmits the packets to which packet numbers and error detection data from the transmitting side are respectively added. The control unit receives a predetermined number of packets, and determines whether or not there is an error in the image data of each packet by using the error detection data added to each packet. An operation of writing image data so that only the image data is decoded and the decoded image data is stored in a predetermined area of the image memory. The transmitting and receiving unit collects the packet numbers of the packets not stored in the image memory in order to collectively request a retransmission of packets having an error from the predetermined number of packets received. An image receiving apparatus characterized in that the image is sent to a user.