KR19990016365A - Synchronization code detection device and method - Google Patents

Abstract

The present invention relates to an apparatus and method for detecting a synchronization code of an image code string, and more particularly, to an apparatus and method for detecting a synchronization code using a GOB header pattern and a GOB number. According to the present invention, if a predetermined error correction criterion is satisfied compared to a preset error correction criterion for bit errors occurring during transmission of the compressed video information, the synchronization code is regarded as detected, and if the error correction criterion is not satisfied, It is regarded as an error occurrence. Therefore, by correcting the error position by correcting the error position when the synchronization code error occurs, the image quality of the image decoding can be improved.

Description

Synchronization code detection device and method

The present invention relates to an apparatus and method for detecting a synchronization code of an image code string, and more particularly, to an apparatus and method for detecting a synchronization code using a GOB header pattern and a GOB number.

Currently, research and development for digital video / audio services is active worldwide, and efforts are being made not only to transmit information in one direction like a conventional TV, but also to various digital video / audio services in two directions through a communication channel. Digital video / audio services over limited communication channels not only require high compression rates, but also extend to the use of noisy transmission lines such as wireless channels in urban areas. However, when an error occurs in the information with high compression rate and important information is lost, the effect is enormous, and countermeasures have emerged.

Conventionally, a sync code of an N-bit video code string is detected according to a preset sync code pattern. However, if the sync code is not detected, the received data is shifted by one bit and compared with the sync code pattern. At this time, if there is a detected synchronization code, Re-Synchronization is performed from that time. If there is no detected synchronization code, it is determined that an error has occurred.

However, the above-described method can be seen that an error has occurred, but there is a disadvantage that it is unknown from which position the error occurred. In addition, when the number of consecutive '0's defined in advance in the sync code pattern is small, it may be mistaken as a sync code even though it is not a sync code by the data value used for encoding.

Accordingly, an object of the present invention is to detect a sync code using a predetermined GOB header pattern in an input image code string, and if the sync code is not normally detected, if the error correcting criterion is satisfied compared to the preset error correcting criterion, The present invention provides a synchronization code detection apparatus that considers a synchronization code to perform decoding and regards an error occurrence if the error correction criteria are not satisfied.

In addition, another object of the present invention is to select a plurality of candidate regions that match the predetermined GOB header pattern up to a predetermined number of next GOB position and the previous GOB in the image code sequence, and then detect the final position of the synchronization code in consideration of the front and back correlation A synchronization code detection method is provided.

1 is a conceptual diagram showing the position of the GOB header in the video code sequence,

2 is a block diagram showing a synchronization code detection device of the present invention;

3 is a flow chart for explaining the operation of the apparatus of FIG.

Explanation of symbols for the main parts of the drawings

22: decoder 24: header pattern detection unit

26: synchronization code detection unit

A feature of the present invention for achieving the above object is a device for detecting a synchronization code of a video signal, a decoder for decoding the video signal in a GOB unit, the GOB header pattern is stored in advance, from the decoded previous GOB position The header pattern detection unit detects a plurality of GOBs matching the previously stored GOB header pattern, and detects a synchronization code of the current GOB among the plurality of GOBs detected by the header pattern detection unit, and if there is no detected synchronization code, preset error correction. A synchronization code detection apparatus for an image code string including a synchronization code detection unit for correcting an error based on a reference to detect a normal synchronization code.

A feature of the present invention for achieving another object of the present invention is a method for detecting a synchronization code of a video signal, a plurality of GOBs matching a predetermined GOB header pattern from a previous GOB after decoding according to a predetermined GOB header pattern Detecting a GOB by detecting a GOB by comparing the before and after correlation of the plurality of detected GOBs with a preset reference, and detecting a synchronization code by the GOB header pattern error and GOB number error if the synchronization code is not detected. And a sync code detection step of detecting a sync code by correcting an error according to a predetermined error correction criterion.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a GOB (Group of blocks) used in the present invention. GOB contains synchronization code and data. This synchronization code consists of a GOB header (A) and a GOB number (B). In an embodiment of the present invention, the synchronization code is assumed to use a pattern defined by the H.263 technique. Therefore, the synchronization code of the present invention is a 22-bit synchronization code consisting of a GOB header (17 bits) composed of 16 consecutive '0's and one' 1 'and a 5-bit GOB number.

2 is a block diagram showing a synchronization code detection device of the present invention. The apparatus of the present invention includes a decoder 22 for receiving and decoding a video code string. The header pattern detection unit 24 stores the GOB header pattern (17 bits) in advance, and temporarily searches for three target areas matching the GOB header pattern from the beginning of the decoded GOB. That is, as shown in FIG. 1, the GOB header patterns GOB-1, GOB, GOB + 1 are found. At this time, in a normal case, GOB-1 is the header pattern of the last GOB, GOB is the header pattern of the GOB to be searched for now, and GOB + 1 is the header pattern of the next GOB. If the synchronization code detection unit 26 has a synchronization code in which the 22 bits including the 17-bit header pattern and the GOB number match the GOB to be searched among the three GOB header patterns, the decoder 22 performs a normal decoding. Output a control signal. However, if the 22-bit sync code including the 17-bit GOB header pattern and the GOB number does not match the GOB to be searched for, the error is detected by dividing the 22-bit sync code into the GOB header pattern and the GOB number. If a normal sync code is detected according to a preset error correction criterion, the sync code detector 26 outputs a control signal to the decoder 22 to perform normal decoding, and if the normal sync code is not detected, skips the current GOB ( skip) and output a control signal to decode the next target GOB.

3 is a flowchart for describing an operation of the apparatus of FIG. 2.

First, the decoder 22 performs GOB decoding (step 310). The decoder 22 determines whether the decoding process of one GOB is finished (step 315), and if decoding of one GOB is not finished, the process returns to step 310 and repeats the steps. When the GOB decoding is finished, the header pattern detection unit 24 detects three GOB header patterns having a predetermined header pattern (step 320). The error discrimination unit 26 determines whether the expected GOB number is detected in the GOB that is currently decoded (step 325). If the expected GOB number is detected, a normal sync code is found, and the flow proceeds to step 310. However, if the expected GOB number is not detected, the 22-bit sync code is divided into a header pattern (17 bits) and a GOB number (5 bits) for error discrimination. In order to divide the error occurrence position in detail, it is determined whether GOB-1 and GOB + 1 exist continuously (step 330). Here, the reason for determining whether GOB-1 and GOB + 1 exist continuously is as follows. For example, if there is data with GOB number 11 (GOB-1) and GOB number 13 (GOB + 1), the GOB number 12 is not detected. Can be determined by That is, if the GOB numbers should be detected in the order of 11, 12, and 13, but 11 and 13 are detected continuously, since the GOB number 12 is not detected, it is not considered that the GOB header pattern is normally detected. However, if GOB-1 and GOB + 1 do not exist continuously and other GOBs are inserted in the middle, for example, GOB numbers 11, 15 and 13, the GOB header pattern is normally detected and the GOB number An error has occurred.

Therefore, if GOB-1 and GOB + 1 are continuously present in step 330, it is determined as a GOB header pattern detection error (step 325), and the predetermined 22 bits are shifted by one bit from GOB-1 to GOB + 1. In step 345, it is checked whether there is a synchronization pattern and a Hamming distance, i.e., a position where the number of bits having a difference is less than or equal to '1'. If a position where the hamming distance is equal to or less than '1' is detected, it is set that a normal sync code is detected, and the flow returns to step 310. However, if the position where the hamming distance is less than '1' is not detected, it is determined as a GOB error (step 355), the current GOB is skipped, and the next GOB is passed (step 360).

On the other hand, if GOB-1 and GOB + 1 do not exist continuously in step 330, and if any value exists between GOB-1 and GOB + 1, it is determined as an GOB number error (step 340). Therefore, the GOB header pattern is normal, so compare the 5 bits representing the expected GOB number that should exist between GOB-1 and GOB + 1 and the 5 bits representing the GOB number currently existing between GOB-1 and GOB + 1. It is determined whether the hamming distance is 1 or less (step 350). If the hamming distance is '1' or less, go to step 310 to perform decoding, and if the hamming distance is not '1' or less, it is determined as a GOB error (step 355) and the current GOB is skipped and the next GOB is passed ( Step 360).

As described above, according to the present invention, when an error occurs, an error position is determined in detail when an error occurs, and when a predetermined error correction criterion is satisfied by comparing with a preset error correction criterion according to the position where the error occurs, If it is detected and does not satisfy the error correction criteria, it is regarded as an error occurrence. Therefore, by correcting the error position by correcting the error position when the synchronization code error occurs, the image quality of the image decoding can be improved.

Claims (8)

An apparatus for detecting a synchronization code of a video signal, comprising: a decoder for decoding the video signal in GOB units; A header pattern detection unit which pre-stores a GOB header pattern and detects a plurality of GOBs matching the pre-stored GOB header pattern from the decoded previous GOB position; And a synchronization code detection unit that detects a synchronization code of the current GOB among the plurality of GOBs detected by the header pattern detection unit, and if there is no detected synchronization code, corrects an error by a predetermined error correction criterion to detect a normal synchronization code. An apparatus for detecting a synchronization code of an image code string comprising: 2. The apparatus of claim 1, wherein the sync code detector pre-stores a sync pattern including a header pattern and a GOB number of a GOB, and if the current GOB matches a pre-stored sync code pattern, a control signal is transmitted to the decoder to perform normal decoding. Outputting a signal, and if the current GOB does not match the synchronization code pattern, it is regarded as an error occurrence and the error identification is divided into a GOB header pattern error and a GOB number error. The method according to claim 2, wherein if the GOB-1 and GOB + 1 are continuously detected by the header pattern detection unit, the synchronization code detection unit determines that a GOB header pattern detection error occurs, and GOB-1 and GOB + 1 are not continuously detected. And a GOB number error. The method of claim 3, wherein the synchronization code detection unit considers that the synchronization code is detected when the predetermined error correction criterion is compared with the predetermined error correction criterion according to the determined error occurrence position, and does not satisfy the error correction criterion. Otherwise, it is regarded as an error occurrence. A method for detecting a synchronization code of a video signal, the method comprising: a GOB detection step of detecting a plurality of GOBs matching a predetermined GOB header pattern from a previous GOB after decoding according to a predetermined GOB header pattern; The synchronization code is detected by comparing the detected correlations between the plurality of GOBs with a preset reference. If the synchronization code is not detected, the error is detected by dividing the error of the synchronization code into a GOB header pattern error and a GOB number error. Error detection step; And a sync code detecting step of detecting a sync code by correcting an error according to a preset error correction criterion. 6. The error detection step of claim 5, wherein the error detection step for each region is determined by a GOB header pattern detection error when the relationship between the GOBs is in the order of GOB-1 and GOB + 1, and the GOB before and after relationship is GOB. A method of detecting a sync code of a video code string, characterized in that it is discriminated by a GOB number error unless it is a sequence of -1, G0B + 1. 6. The synchronization code detecting method of claim 5, wherein the detecting of the synchronization code comprises determining that the GOB-1 pattern has a hamming distance of less than or equal to '1' in the interval from GOB-1 to G0B + 1. If the position of Hamming distance is less than or equal to '1' does not exist, GOB error is detected. The method of claim 7, wherein the detecting of the synchronization code comprises determining that the synchronization code is detected when the relationship between the predetermined GOB number and the current GOB number is equal to or less than '1' when the GOB number error is determined. Is not equal to or less than '1', it is determined by an error.