Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Patent
1996-06-20
1999-08-17
Nguyen, Chau
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
370210, 370203, 375260, H04J 1100
Patent
active
059404060
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is based on a method of frequency correction in multicarrier transmission processes and, more particularly, to a method of frequency correction in multicarrier transmission processes, in which a multicarrier signal is subjected to bandpass filtering and then, via a frequency mixture with a predetermined frequency, shifted into a bandpass range, whereupon a discrete Fourier transform is carried out, and the Fourier-transformed signal is then subjected to a channel decoding, wherein from the Fourier transformed signal a frequency deviation is determined between a carrier signal and the frequency that is used for the frequency mixture. U.S. Pat. No. 5,228,025 has already disclosed a method for frequency correction in multicarrier transmission processes in which the received signal is bandpass-filtered and then, via a mixture having a predetermined oscillator frequency, frequency-shifted into the base band, then filtered and digitally converted. The digital signal is then subjected to a digital Fourier transformation and is output for further decoding. An accurate Fourier transform requires accurate knowledge of the transmission frequency with which the carrier signal is sent, so that the oscillator frequency can be tuned to it. The signal output by the digital Fourier transform is investigated for deviation of the carrier frequency of the carrier signal relative to the predetermined oscillator frequency, and control values are ascertained with the aid of which an automatic frequency correction of the oscillator is performed. In this way, a detectable frequency deviation in the evaluated signal between the frequency of the carrier signal and the frequency of the oscillator is corrected by the readjustment of the oscillator.
SUMMARY OF THE INVENTION
In the method for frequency correction in a multicarrier transmission process according to the invention, a multicarrier signal is subjected to bandpass filtering and then, via a frequency mixture with a predetermined frequency, shifted into a bandpass range, whereupon a discrete Fourier transform is carried out, and the Fourier-transformed signal is then subjected to a channel decoding, wherein from the Fourier transformed signal a frequency deviation is determined between a carrier signal and the frequency that is used for the frequency mixture.
The method according to the invention is characterized in that from the ascertained frequency deviation, values for a modified Fourier transform are calculated in such a way that the frequency deviation between the carrier signal and the frequency that is used for the frequency mixture is compensated for by the modified Fourier transform.
The arrangement according to the invention has the advantage over the prior art that automatic frequency correction of the oscillator frequency is unnecessary; instead, the ascertained frequency shift is taken into account directly in the Fourier transform. In this way, a simple and reliable method is assured for being able to carry out accurate-frequency demodulation in multicarrier transmission processes.
Advantageous further features of and improvements to the method according to the invention are provided in preferred embodiments of the invention. In various preferred embodiments it is especially advantageous to use a fast algorithm to calculate the modified discrete Fourier transform.
A further preferred embodiment of the method of the invention includes a readout of modified rotation factors, stored in memory in a table, from the table. In this way, the required rotation factors can be accessed quickly and without difficulty.
One advantageous application of the method of the invention is to digital radio transmission.
BRIEF DESCRIPTION OF THE DRAWING
One exemplary embodiment of the invention is shown in the drawing and described in further detail in the ensuing description, in which
FIG. 1, is a block diagram of a prior art multicarrier transmission process;
FIG. 2, is a block diagram of a receiver for a multicarrier transmission proc
REFERENCES:
patent: 5345440 (1994-09-01), Gledhil et al.
patent: 5371761 (1994-12-01), Daffara et al.
patent: 5377232 (1994-12-01), Davidov et al.
patent: 5550812 (1996-08-01), Philips
patent: 5627863 (1997-05-01), Aslanis
Nguyen Chau
Robert & Bosch GmbH
Striker Michael J.
Vanderpuye Kenneth
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