Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1999-03-22
2002-08-27
Vo, Don N. (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S262000
Reexamination Certificate
active
06442211
ABSTRACT:
BACKGROUND OF THE INVENTION
Filed of the Invention
The invention relates to a system for digital information transmission, to a method and to a device for producing a transmission signal, to a demodulation method and to a receiver for receiving a transmission signal.
A multicarrier transmission method for transmitting digital data is generally known in information technology, which method uses a discrete Fourier transform for signal synthesis. Multicarrier transmission methods are described, for example, by John Bingham in “Multicarrier Modulation for Data Transmission: An Idea Whose Time Has Come,” IEEE Communications Magazine, May 1990, pages 5-14.
One specific method in this context is, for example, the so-called OFDM method (OFDM=orthogonal frequency division multiplexing), also referred to as the DMT method (DMT=discrete multitone), which is described by Weinstein and Ebert in “Data Transmission By Frequency-Division Multiplexing Using The Discrete Fourier Transform,” IEEE Transactions on Communication Technology, vol. COM-19, no. 5, October 1971, pages 628-34. The action of pulse interference between successive symbols is solved using the already known method of inserting a guard interval.
U.S. Pat. No. 5,345,439 to Marston discloses a signal processing apparatus, in which one appliance uses various modulation formats for universal application. U.S. Pat. No. 4,313,197 to Maxemchuk discloses a device for multiplexing and demultiplexing signals, in particular voice signals. Fourier transformation is used in that case. One application of the OFDM method for optical transmission is known from Olofsson et al.: “Design of OFDM Systems at High Power Levels,” 17 Journal of Optical Communications, 1996, 3, pages 95-97.
German Patent Application No. 43 10 031 discloses a method for correcting the phase amplitude of a broadband received signal, in which the individual carrier frequencies that are used are phase modulated using the COFDM method. In that method, the data blocks are synchronized to one another in the time domain.
Fundamental principles relating to these techniques and methods can be found in the textbook “Nachrichtenubertragung” [Information transmission] by Karl Dirk Kammermeyer, Teubner Verlag, Stuttgart, 1992, in particular on pages 68-70, 372, 378, 379 and 606-613.
The most recent advance in the art is described in the international PCT publication WO 91/14316. Of similar interest is a published article by Paul Moose: “Differentially Coded Multi-Frequency Modulation For Digital Communications,” FIFTH EUROPEAN SIGNAL PROCESSING CONFERENCE, Sep. 18-21, 1990, Amsterdam, Netherlands, pages 1807-10. These publications provide so-called baud synchronization, in which a number of blocks of code symbols are preceded by a common synchronization baud.
Error coding for the so-called PSK method with an RF modem is known from Gene Porter: “Error Distribution And Diversity Performance Of A Frequency-Differential PSK HF Modem,” IEEE TRANSACTIONS ON COMMUNICATION TECHNOLOGY, Vol. 16, No. 4, August 1996, New York, pages 567-75.
A further method and arrangement for differential modulation of signals in a multichannel transmission system is known from international PCT publication WO 92/20179.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a system with associated methods and devices for digital information transmission for channels with dispersive distortion, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which avoids complex carrier phase and sampling phase synchronization, with high bandwidth efficiency and a low error rate.
With the foregoing and other objects in view there is provided, in accordance with the invention, an improved method of producing a transmission signal for digital information transmission, wherein, for multicarrier transmission, subcarriers are modulated with channel coded parallel code symbols of an input signal by means of differential coding in the frequency domain, and synchronization information is added to the transmission signal. The improvement comprises:
prior to the differential coding, error coding and/or interleaving;
after the differential coding, producing a serial output signal by means of parallel/serial conversion;
assigning each block of code symbols, as synchronization information, a preamble for block synchronization; and
adding to each block of code symbols a transmission pause after the differential coding.
In accordance with an added feature of the invention, the serial output signal is subjected to digital/analog conversion.
In accordance with an additional feature of the invention, the serial output signal is transmitted in transmission blocks transmitted with time discontinuities and/or in burst mode.
In accordance with another feature of the invention, after the differential coding, there is added to each block of code symbols at a start thereof, a periodic continuation as a guard interval.
In accordance with a further feature of the invention, prior to the differential coding, the code symbols are assigned to a signal space by means of a PSK or QAM method.
In accordance with again a further feature of the invention, after the differential coding, the signal is subjected to an inverse discrete Fourier transform (IDFT).
With the above and other objects in view there is also provided, in accordance with the invention, a device for producing a transmission signal for digital information transmission with a multicarrier transmission method, comprising:
a module for carrier modulation receiving channel coded, parallel code symbols of an input signal and adding code symbols to subcarriers by means of differential coding in a frequency domain, wherein the transmission signal contains synchronization information;
a module for at least one of error coding and interleaving connected upstream of the module for carrier modulation in a signal flow direction;
a parallel/serial converter connected downstream of the module for carrier modulation in the signal flow direction;
a synchronization device for producing synchronization information, the synchronization device producing a preamble for each produced block of code symbols for block synchronization; and
an element for producing a transmission pause between successive blocks.
There is also provided, in accordance with the invention, an n improved demodulation method for a received multicarrier transmission signal, wherein code symbols are modulated onto subcarriers by means of differential coding in the frequency domain, and wherein blocks follow one another with time discontinuities, and a phase of complex subcarrier coefficients is distinguished and blocks of code symbols are synchronized. The improvement comprises the following steps:
prior to differentiation, subjecting the received transmission signal to analog/digital conversion with subsequent serial/parallel conversion;
prior to differentiation, removing any transmission pause between adjacent blocks;
subsequent to differentiation, carrying out one of error detecting respective preambles assigned to the blocks, and synchronizing each of the blocks.
There is furthermore provided, in accordance with the invention, a receiving device for a received multicarrier transmission signal, wherein code symbols are modulated onto subcarriers by means of differential coding in a frequency domain, and wherein blocks follow one another with time discontinuities, comprising:
an analog/digital converter receiving a transmission signal;
a serial/parallel converter connected downstream of the analog/digital converter in a signal flow direction;
a demodulator for differentiating a phase of complex subcarrier coefficients and for synchronizing blocks connected downstream of the serial/parallel converter in the signal flow direction;
an error decoding and/or deinterleaving module connected downstream of the demodulator in the signal flow direction;
means for removing a transmission pause between the blocks; and
a synchronization
Hampel Herrmann
Huber Johannes
Lehmann Klaus
Wagner Thomas
Greenberg Laurence A.
IAD Gesellschaft für Informatik, Automatisierung und Datenverarb
Mayback Gregory L.
Stemer Werner H.
Vo Don N.
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