Multiband detector

Details Multiband detector Multiband detector

1998-10-26

2002-06-04

Pham, Chi (Department: 2631)

Pulse or digital communications

Receivers

Interference or noise reduction

Reexamination Certificate

active

06400781

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a multiband detector used to generate a plurality of sub-band symbols from a distored multiband signal applied to a detector input thereof.
BACKGROUND OF THE INVENTION
Such a multiband detector is already known in the art, e.g. from the article ‘
A Multicorrier E
1-
HDSL Transceiver System with Coded Modulation’
from the authors Peter S. Chow, Noofal Al-Dhchir, John M. Cioffi and John A. C. Bingham. This article was published in the issue N° 3, May/June 1993 of the
Journal of European Transactions on Telecommunications and Related Technologies
(
ETT
), pages 257-266.
Therein, the multiband detector, named DMT (Discrete Multi Tone) receiver and drawn in
FIG. 5
of that article, contains an arrangement which reconstructs the individual carrier signals of an incoming multicarrier signal and which compensates for distortion of the incoming multicarrier signal due to transmission over a transmission line in between a DMT transmitter drawn in
FIG. 4
of that article and the DMT receiver drawn in
FIG. 5
of that article. This arrangement consists of the cascade connection of a time domain equalizer, a serial to parallel converter with cyclic prefix stripper, a fast fourier transformer and a frequency domain equalizer. The time domain equalizer is a short adaptive finite impulse response filter which aims to reduce the cyclic prefix of multicarrier symbols by shortening the impulse response length of the transmission line. The time domain equalizer so helps to reduce intersymbol interference with an acceptable cyclic prefix length. Samples of a single multicarrier symbol in the incoming multicarrier signal are then paralleled by the serial to parallel converter and applied to the fast fourier transformer to be transformed from time domain to frequency domain. Since the equalized channel, i.e. the combination of transmission line and time domain equalizer, is not yet flattened, a frequency domain equalizer is included in the arrangement to compensate for phase and amplitude distortions of individual carriers. The frequency domain equalizer thereto consists of a parallel structure of one-tap filters, adaptive via a least mean square technique. The arrangement of time domain equalizer, serial to parallel converter, fast fourier transformer and frequency domain equalizer is followed by what is called a decoder in the cited article but is named a decision unit in this document. This decoder or decision unit compares the single carrier signals at the outputs of the frequency domain equalizer with the constellation schemes used to modulate the respective carriers and derives therefrom the symbols modulated on the different carriers.
An arrangement which compensates for distortion in a discrete wavelet multitone signal, i.e. another kind of multiband signal, and which reconstructs the different wavelet bands from the distorted wavelet multitone signal is known from the article ‘
Overlapped Discrete Multitone Modulation for High Speed Copper Wire Communications’
from the authors Stuart D. Sandberg and Michael A. Tzonnes. This article was published in the
IEEE Journal on selected Areas in Communications,
Vol. 13, N° 9 of December 1995, and the arrangement described therein and drawn partially in
FIG. 1
has an architecture similar to the above described one. A pre-detection equalizer suppresses intersymbol interference by digitally filtering the incoming discrete wavelet multitone signal, a wavelet transformer generates the wavelet sub-band signals and applies these wavelet sub-band signals in parallel to a post-detection equalizer which again consists of a parallel structure of single band equalizers adapted via a least mean square technique. The arrangement, except for the length in taps of the pre-detection equalizer and post-detection equalizer and the nature of the transformation used to reconstruct the sub-bands from the multiband signal, does not differ significantly from the above described arrangement with time domain equalizer, fast fourier transformer and frequency domain equalizer. The arrangement in the article from Stuart D. Sandberg and Michael A. Tzonnes further is coupled to a so called constellation symbol decision unit comparable to the decoder in the article from Peter S. Chow et al.
In a more general article ‘
Multicarrier Modulation for Data Transmission: An Idea Whose Time Has Come’,
the author John A. C. Bingham proposes a structure with a simple equalizer which performs a time domain convolution, a transformer which reconstructs orthogonal sub-bands from a multiband signal, and a set of parallel single band equalizers. The article from John A. C. Bingham was published in
IEEE Communications
magazine of May 1990 and obviously suggests to use, whatever the nature of the multiband to sub-band transformation, a detector with an architecture similarly to that of the above cited articles.
The architecture of a detector for sub-band reconstruction and distortion compensation, known from the above reference articles, has the disadvantage that it is insufficiently flexible vis a vis changes in the distortion of the multiband signal on the transmission line. Narrowband distortions for instance, which affect only a few sub-bands and which are likely to occur as can be derived from the articles of John A. C. Bingham (see page 12, paragraph entitled “Single-Frequency Interference”) and Peter S. Chow et al (see page 259; right-hand column, lines 28-29), can be compensated for by adapting the taps of the pre-detection equalizer or by enlarging the number of taps in the pre-detection equalizer but these solutions obviously have an influence on the detection of other sub-bands which are not affected by the norrowband distortions. This solution consequently is not very effective which explains why Peter S. Chow and John A. C. Bingham propose to either update the bit allocations or to avoid using affected carriers in their respective articles in response to narrowband distortions.
The known architecture moreover limits the applicability of the multiband detector to environments wherein one and the some kind of multiband signal is transferred. By the choice of the sub-band reconstructor in between the pre-detection equalizer and the post-detection equalizer, the multiband detector becomes able to either receive DMT (Discrete Multi Tone) signals whose sub-bands are reconstructed via a fast fourier transformation, DWMT (Discrete Wavelet Multi Tone) signals whose sub-bands are reconstructed via a wavelet transformation, or another kind of multiband signal whose orthogonal sub-bands are reconstructed via yet another transformation. Receiving another kind of multiband signal with a detector having the known architecture requires replacement of components therein. For evident reasons (complexity of interfacing) this is not done.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a multiband detector of the above known type, but which is more flexibly adaptive to distortion changes on the transmission line, even if these changes in distortion affect only a few sub-bands, and which is suitable for detection of different kinds of multiband signals.
This object is realised by a multiband detector used to generate a plurality of sub-band symbols from a distorted multiband signal applied to a detector input thereof, the multiband detector comprising the cascade connection of: a sub-band reconstruction and distortion compensation arrangement whose arrangement input is coupled to the detector input and which is adapted to compensate for distortion in the distorted multiband signal and to reconstruct a plurality of sub-band signals from the distorted multiband signal, and to source each sub-band signal amongst the plurality of sub-band signals via a respective arrangement output amongst a plurality of arrangement outputs; and a decision unit with a plurality of unit inputs coupled one by one to the plurality of arrangement outputs and a plurality of associated unit outputs, the decision unit including between each unit

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