Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-04-01
2003-02-18
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S514000, C375S365000, C714S758000, C714S776000, C714S779000, C714S798000
Reexamination Certificate
active
06522665
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data sequence generator for generating a data sequence suitable for transmission of a data sequence composed of variable length frames having information data of variable length particularly in an environment where a code error is liable to occur, a transmitter using the data sequence generator, an information data decoder for decoding information data from the data sequence, a receiver using the information data decoder, a transmitter-receiver using the data sequence generator and the information data decoder, a data sequence generating method for generating the data sequence, an information data decoding method for extracting information data from the data sequence, and a recording medium recording the data sequence.
2. Description of the Related Art
In case of transmitting a data sequence having a frame structure, detection of the synchronous position of a frame in a received signal sequence, namely, a frame synchronization is very important, and particularly in transmission of a variable length frame, since the synchronous position varies with each frame, a more highly accurate frame synchronization is required. And header information necessary for decoding data (information data) in an information data portion is also as important as the frame synchronization, and protection of the header information from a code error is also required.
As a method for realizing a frame synchronization (frame synchronization method), a method for realizing a frame synchronization by adding a unique word (UW: specific information) such as the M sequence and the like to each frame as a frame synchronization code in a transmitter side, and detecting the unique word from a received signal sequence in a receiver side (hereinafter referred to as a first frame synchronization method) is widely known. The first frame synchronization method does not limit in particular the position where a unique word is to be added, but a variable length data transmission system adopting the synchronization method often adds a unique word usually to the forefront of a frame, as shown in
FIG. 1A
, in order to simplify the process.
By the way, in the first frame synchronization method, when a unique word and information data in a frame coincide with each other in a unique word detecting process, an “erroneous synchronization” occurs which is a phenomenon in which an erroneous position results in being adopted as a frame-synchronous position. And in a unique word detecting process, when the unique word in a frame contains an error which has occurred on a transmission channel (communication channel), a “non-detection” occurs which is a phenomenon in which the unique word cannot be detected from the frame and the synchronous position cannot be determined. Both the above-mentioned phenomena each are a frame synchronization error of a kind, and when such a frame synchronization error occurs, the receiver side cannot decode the whole frame for which a correct synchronous position has not been obtained and the frame comes to be discarded. Since the discard of a frame brings about a great reduction in data transfer rate, it is desired to reduce the frame synchronization error rate in the first frame synchronization method. Particularly, since the probability of occurrence of a code error is very high in a radio transmission channel and the like, it is desirable to adopting a frame synchronization method more robust against error.
Up to now, as a method for reducing the probability of occurrence of an erroneous synchronization (hereinafter referred to as a synchronization error rate), a method of using the result of error detection of header information is known. In a frame synchronization method adopting this method (hereinafter referred to as a second frame synchronization method), when a unique word is detected in a receiver side, then an error detection decoding process of header information is performed and if the header information does not have an error, a position where the unique word has been detected is determined as a synchronous position. That is to say, since the system fails in detection of header information even if a unique word and information data in a frame coincide with each other, it is possible to avoid an erroneous synchronization which has occurred in such a case. However, in an environment where a burst error occurs (burst error environment), the probability of occurrence of non-detection cannot be reduced even by using the second frame synchronization method. The reason is that it is impossible to detect a synchronous position in case that the unique word and header information in a frame are contained in a burst error section.
As a frame synchronization method for realizing a high-accuracy frame synchronization even in a burst error environment, there is a method which disposes frame length information in a frame as shown in FIG.
1
B and detects a frame synchronization using this frame length information (hereinafter referred to as a third frame synchronization method). Since the frame length information coincides with the length from the position of the unique word of the frame to the position of the unique word of the next frame, according to the third frame synchronization method, it is possible to know in advance the position of the unique word in the next frame using the frame length information and reduce the probability of non-detection and erroneous detection of a unique word.
In the third frame synchronization method using frame length information, since the length of a frame n−1 is determined if the header information and frame length information of the frame n−1 shown in
FIG. 2
can be correctly decoded, decoding of the frame n−1 can be started without performing search of the next synchronous position (hereinafter referred to as a synchronization search). And since a synchronization search can be started at the forefront of the next frame, it is possible to reduce the probability of occurrence of an erroneous synchronization which is caused by erroneous detection of a unique word in an information data portion. In case of being not able to decode frame length information due to a burst error which has occurred over the synchronous position indicated by the frame length information in the frame n−1 as shown in the frame n, it is possible to determine a section of the frame n and take out the frame n by searching a unique word from an appropriate position (position where there can be the unique word of the frame n+1) and detecting the unique word of the frame n+1 at a correct position. Therefore, by using jointly this method and the above-mentioned second frame synchronization method using header information (a method of reducing erroneous synchronization), it is possible to realize a high-accuracy frame synchronization even in a burst error environment.
By the way, in a data transmission having a frame structure, a frame to which header information necessary for decoding information data has been added is transmitted in many cases, and in the above-mentioned second frame synchronization method it is assumed that the header information is used. As an example of a data transmission procedure for adding header information, the HDLC (High Level Data Link Control) procedure being generally used in data transmission can be mentioned. In the HDLC procedure, in case that header information cannot be correctly decoded due to a transmission channel error, the whole frame cannot be decoded in the same way as the case that a frame synchronization error has occurred. Therefore, it is necessary to strengthen protection of header information to the same degree as the frame synchronization.
As a method for protecting header information, a method of error-correction-encoding the header information is conceivable. However, in case that an error exceeding the error correcting ability of the header information has occurred in the header information portion in a frame as shown in
F
Kawahara Toshiro
Miki Toshio
Naka Nobuhiko
Suzuki Takashi
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