Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-08-19
2001-04-03
Moise, Emmanuel L. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S776000, C370S469000, C370S473000, C370S476000
Reexamination Certificate
active
06212660
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and apparatuses for identification of the position of data packets which are located in a serial received data stream.
2. Description of Related Art
Data packets in the transmission system used as the basis here contain a part of fixed length and a part of variable length. The part of fixed length may be called a check field and contains information about the length of the part of variable length.
If the data packets are transmitted via a channel which is noisy, then they can be interfered with on the transmission path, for example in the case of packet-oriented digital radio transmission. Even entire packets may be lost.
However, within the data stream, the starting points and end points of the respective data packets are intended to be detected at the receiver end. In order to make it possible to identify a data packet at the receiver end, that is to say to identify a packet position, a known bit sequence is normally introduced into the data stream at the transmitter end. At the same time, a logic device ensures that bit sequences which are identical to this are eliminated from the data stream. This is normally achieved by means of additional symbols which, admittedly, change the word but leave the useful information to be transmitted otherwise unchanged.
Another option would be to transmit ancillary information as well in the bundle structure of the system which is transmitting the data.
In the case of conventional data transmission, it is furthermore known for the transmission to be checked for errors by inserting a check sum into the data packet to be transmitted, which check sum is formed on the basis of check data which are located in a check field. At the receiver end, a new check sum is then formed in the same manner on the received check data and is compared with the received check sum. If this comparison produces a match, the transmission was error-free.
BRIEF SUMMARY OF THE INVENTION
The invention is based on the object of developing a method and apparatuses of the type mentioned initially such that the position of a data packet in a continuous data stream can be determined more easily.
In the case of the method according to the invention for identification of the position of data packets which are located in a serial received data stream and each has check data in a check field and a check sum which is formed using the check data, the received data stream is passed in serial form through at least one comparison unit which forms a new check sum with each received symbol to be newly added and compares this new check sum with data which are looked at for the associated received check sum, in which case, furthermore, during the comparison, the influence of all data is eliminated which do not belong to the check data and the check sum. A data stream bit which is in each case is to be newly added may be regarded, for example, as a received symbol. Alternatively, the received symbol may be a group with a predetermined number of bits.
Thus, according to the invention, the serial data stream is continually examined for valid code words at the receiver end, to which code words the data in the check field and the data in the check sum belong. Only when the received check sum and the check sum formed at the receiver end from the received check data match has a valid code word been found, and the position of the data packet in the data stream thus identified. At the same time, the data in the check field have then also been received without any errors, so that reliable information is now available, for example about the length of the overall data packet. Since, according to the invention, the received data stream is continually examined for code words, it is necessary to ensure that data and the bits located outside the code words have no influence on the abovementioned comparison.
The influence of these data and bits on the comparison is therefore eliminated in order to achieve correct position identification.
The solution according to the invention has the following advantages over the previously known solutions:
1. The method according to the invention is superior to simple insertion of a known bit sequence for identification of the position of data packets, since, in the case of the invention, the inserted bit sequence can be identified correctly by the receiver only if not only the bit sequence itself but also a fixed length part of the packet has been received without errors. For this reason, the invention not only assists with frame synchronization but also helps to ensure that valuable data located in the check field, for example length information, are received correctly.
2. The invention places no requirements on the fundamental transmission scheme and does not demand that the packets must be inserted in a specific manner into a bundle which is just about to be transmitted. This therefore means that the absolute position of data fields in the data packets is not specified. Furthermore, for example, the field for the check sum on the check field itself, on the basis of whose data the check sum has been formed, do not need to follow one another directly.
3. The invention can furthermore be implemented at low cost and on a small area as hardware in a digital integrated circuit.
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B-ISDN user-network interface-Physical layer specification: General characteristics, pp 1-16.
Joeressen Olaf J.
Schneider Gregor
Zwickler Uwe
Moise Emmanuel L.
Nokia Mobile Phones Limited
Perman & Green LLP
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