Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
2000-08-17
2004-05-18
Ton, Dang (Department: 2666)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S503000, C370S476000, C370S498000, C375S292000
Reexamination Certificate
active
06738394
ABSTRACT:
The invention relates to a method for the unidirectional and interference-safe transmission of digital data via radio waves, wherein the data which are composed of data packets each comprising a defined number of bytes and of at least one synchronization packet are transmitted from a transmitter to a receiver, a device for carrying out this method as well as a protocol for the unidirectional and interference-safe transmission of digital data via radio waves from a transmitter to a receiver, wherein the data are composed of data packets each comprising a defined number of bytes and of at least one synchronization packet.
The invention, in particular, refers to a protocol for the transmission of digital data, which is immune against bursty interferences, e.g. GSM signals in the 900 MHz frequency band, and which requires a minimum of hardware for the transmitter and the receiver in order to thereby guarantee interference-free transmission.
Such a protocol is used for the transmission of data packets of determined and limited lengths for signaling and controlling automatic procedures. A data packet, as a rule, contains usable information transmitted either encoded or nonencoded and optionally further information regarding data integrity. In addition, also channel coding information and synchronization information data are transmitted in order to ensure the optimum transmission via a radio channel.
Applications of such data transmission systems include remote keyless entry systems, identification systems for vehicles or persons, or machine commands operable by remote control.
In the transmission of data via radio channels, sufficient safety measures against interferences have to be taken, in particular where the frequency band used for transmission, or an adjacent frequency band, is used also by other services. This applies, for instance, to the transmission of data via the frequency band (868 MHz) released for ISM (Industrial Scientific and Medical) services, which transmission is disturbed by interferences with the signal packets of the 900 MHz GSM band.
In order to enhance the immunity against interferences both for data transmissions in which transmission errors of the individual bits occur independently of one another and for communication channels in which transmission errors occur by the splitting of clusters into bursts, the following systems are presently known:
A forward error correction system (FEC), which disregards the burst structure of the interferer. In order to ensure interference-free transmission, this system requires a great number of additional information, though. Besides, this method involves considerable decoding work.
An automatic request system (ARQ) presupposes a feedback channel, which is not available in most cases. Systems comprising a feedback channel call for a more complex hardware, requiring two transmitters/receivers and also time duplex or frequency multiplex system. When using frequency multiplex, the required band width will simultaneously increase.
The known ARQ and FEC systems offer insufficient error correction performances in the event of persistent interference bursts. Channel coding with FEC systems is feasible by one of the following methods:
Block codes offer an error detection capability just sufficient to detect random errors at individual bits. The encoder for a block code divides the information sequence into message blocks each having k information bits which are coded on n bits by the aid of block codes, block coders thus constituting systems without memory. Block codes require only simple circuits, yet are not suitable to prevent transmission errors caused by whole data packets of an interfering transmitter (burst errors).
Convolution codes differ from block codes in that the encoder includes a memory and outputs data at a given time not only as a function of the data inputs effected at that time, but also as a function of previous input blocks. A convolution coder, thus, is a system with a finite memory. Convolution codes, which were developed by Elias, Wozenkraft or Massey, are designed for the recognition of random errors. Convolution codes that are suitable for recovering burst errors, such as those developed by Berlekamp-Preparata or Iwadare-Massey, or interleaved convolution codes involve considerable decoding work. Convolution codes are primarily used for the continuous data transmission and not for the transmission of data packets. Convolution codes also call for long code sequences in order to be immune against burst errors.
Cyclic codes are suitable for both recognizing and recovering burst errors. Fire discovered a large class of cyclic codes correcting burst errors. Fire codes may be decoded by means of simple circuits. Yet, even Fire codes are designed for the continuous transmission of data, but not for the transmission of data packets.
It hence follows that the known codes either are unsuitable for recovering burst errors as is the case, for instance, with block codes or some types of convolution codes, or involve considerable decoding procedures as, e.g., for convolution codes. Cyclic codes and convolution codes, in turn, are suitable only for the continuous data transmission, but not for the transmission of individual data packets as would be of interest for applications such as, e.g., telecommanded locks.
The present invention aims to provide an interference-safe data transmission method which avoids the afore-mentioned drawbacks, which will do with a low-expense hardware both for the transmitter and for the receiver and which, moreover, keeps the power consumption of the receiver low. To solve this object, the initially described method essentially consists in that each byte is transmitted in a manner comprised of flag bits as start bits, information-representing information bits and identification bits encoding the number of the respective byte and carrying the parity information, and that the flag bits and the information bits are inverted in every second byte. The flag bits of each individual byte and the changing identification bits of the byte number prevent the formation of long sequences of 0 or 1. Because of that, the direct current (DC) components of the transmitted signal are kept as low as possible in order to thereby reduce the susceptibility to failures of the transmission. Inverting of the flag bits and of the information bits in every second byte appears like a simple encoding process, thus likewise reducing the direct current (DC) components of the signal. High DC-components in the baseband range during demodulation, i.e., in the merger lead to an offset and hence to information losses. During frequency modulation, carrier frequency shifts may occur, in particular. In order to further enhance the safety of data transmission against interferences, it is advantageously proceeded in a manner that the identification bits are arranged to be distributed within the information bits. The flag bits and the identification bits of all bytes received are known in the receiver on account of their positions within the received data flow such that, due to the distribution of the identification bits within the information bits, error signals will be recognized merely by checking the flag bits and the identification bits. The content of a byte, moreover, is provided with a parity information in one of the identification bits such that even a single error will be recognized. An even number of errors within a byte will be recognized by the additional parity information of the remaining identification bits.
Advantageously, each byte is composed of 3 bits as the start flag, 8 information bits and 3 identification bits, and each data packet is composed of 16 bytes. In this case, the DC-components of the transmitted signal are further reduced in that an unambiguous identification of 16 bytes will be enabled by the aid of the 3 identification bits, if the information bits and the flag bits of every second transmitted byte are inverted. The identification bits representing the byte number are not inverted such that wit
Kreuzgruber Peter
Löw Christian
Schultes Gerhard
Austria Mikro Systeme International Aktiengesellschaft
Joyce Kevin E.
Scheibel Robert C
Ton Dang
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