Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Reexamination Certificate
1998-01-15
2002-02-26
Olms, Douglas (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
C370S529000
Reexamination Certificate
active
06351473
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method to allocate data bits of digital data packet to a set of carriers in a multicarrier transmission system wherein a set of carriers, after being modulated with the data bits, is transmitted from a transmitter from a transmitter to a receiver via a transmission link, a subset of the set of carriers having frequencies within predetermined frequency ranges (Amateur Radio Band) with high probability for being affected by narrowbanded interference compared to carriers having frequencies outside the predetermined frequency ranges (Amateur Radio Band). It is also directed to a multicarrier transmitter adapted to transform a sequence of digital data packets into multicarrier data symbols and to apply the multicarrier data symbols via an output terminal to a transmission link to be transmitted thereover. It is also direct to a multicarrier receiver adapted to transform multicarrier data symbols received from a transmission link via an input terminal into a sequence of digital data packets. It is still further directed to an allocation message generator adapted to generate an allocation message to be communicated between a multicarrier transmitter and a multicarrier receiver in a multicarrier transmission system wherein digital data packets are transmitted between the multicarrier transmitter and the multicarrier receiver via a transmission link after being modulated on a set of carriers, a subset of carriers constituting the set of carriers having frequencies within frequency ranges (Amateur Radio Band) with high probability for being affected by narrowband interference (RFI) compared to carriers having frequencies outside these frequency ranges (Amateur Radio Band), said allocation message.
BACKGROUND OF THE INVENTION
Such a method to allocate data bits and equipment adopted to perform such a method are already known in the art, e.g. from the article ‘A Multicarrier E1-HDSL Transceiver System with Coded Modulation’ from the authors Peter S. Chow, Naofal Al-Dhahir, John M. Cioffi and John A. C. Bingham. This article was published in the issue No. 3, May/June 1993 of the
Journal of European Transactions on Telecommunications and Related Technologies
(ETT), pages 257-266. Therein, a multicarrier transceiver system is described wherein digital data are modulated via Discrete Multi Tone (DMT) modulation on a set of carriers to be transmitted from a DMT transmitter to a DMT receiver via copper telephone lines. The block schemes of the DMT transmitter and DMT receiver are drawn in FIG. 4 and FIG. 5 on page 261 of the cited article respectively. In the DMT transmitter a bit allocation means, called a data bit encoder, allocates data bits of a digital data packet, called a block symbol, to the different carriers. The data bit encoder thereto uses formula (7) on page 260 of the article. A modulation means, i.e. the inverse fast Fourier transformer of FIG. 4, then modulates the data on the carriers where they are allocated to, to constitute the multicarrier symbols that are transmitted over the copper telephone line. FIG. 4A illustrates a possible constellation of data bits amongst carriers obtained by applying the known method. At the receiver's side, a fast Fourier transformer demodulates these multicarrier symbols, and the decoder which forms part of the DMT receiver drawn in FIG. 5 of the above mentioned article, retrieves from each carrier the exact amount of data bits modulated thereon and thus performs the role of bit de-allocation means. This de-allocation means obviously has to know how many bits are modulated on each one of the carriers so that it can easily retrieve the exact amount of data bits from each carrier. In the known system, the bit de-allocation means gets this knowledge during initialisation of the transceiver system. Indeed, as is stated on page 263, in lines 22-30 of the left column, the DMT transmitter and DMT receiver negotiate with respect to bit and energy allocation during initialisation. As is understood from paragraph 2.2 of the article of Peter S. Chow et al., more particularly from lines 28-34 in the right column on page 259, certain carrier frequencies may be plagued by narrowbanded or single-frequency disturbances. In FIG. 4A such a disturbance is represented by RFI. Forward error correction techniques, well-known in the art, can reduce the effect of such disturbances. Nevertheless, unrecoverable errors may still appear at the receiver's side. Thereto, Peter S. Chow et al. propose in their article the bitswapping solution: bit- and energy allocations are updated so that data bits are no longer transmitted via affected carriers. Such a re-allocation of data bits requires an additional communication between the DMT transmitter and DMT receiver, similar to the communication performed during initialisation, since both have to get aware of the new bit-allocations. Such a communication may be time-consuming and data bits may already be lost before the bits are swapped to less noisy carriers. Bitswapping thus may imply unrecoverable loss of information if it is seen as a solution for narrowbanded interference.
A problem similar to the just described one 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, an article which is published in the ‘
IEEE Journal on Selected Areas in Communications
’, Vol. 73, No. 9, December 1995 on pages 1571-1585 thereof. This article also describes a Discrete Multi Tone (DMT) modulation system which differs from the system described by Peter S. Chow et al. in that wavelet modulation and demodulation techniques are used instead of Fourier transforms. The wavelet transformation is, similar to the Fourier transformation, a linear transformation which transforms a time domain vector into a vector in another domain. This other domain is defined by its base functions which are complex exponentials for the Fourier transformation, and which can be more complex functions, implemented by means of general filter banks such as the cosine modulated filter bank, of another wavelet transformation. More details with respect to the wavelet transformation are found in the book ‘
Numerical Recipes in C
’, written by William H. Press, Saul A Teukolsky, William T. Vetterling and Brian P. Flannery and published by the Cambridge University Press, in paragraph 13.10 on pages 591-606 entitled ‘
Wavelet Transforms
’. As mentioned in the left column on page 1583 of the article of Sandberg and Tzannes, their multicarrier system may be disturbed by narrowbanded interference due to the presence of radio frequency signals. In other words, the transmission line may pick up signals broadcasted by radio amateur transmitters as a result of which some carriers in the multicarrier data symbols transported by this transmission line may be damaged. In their article, Sandberg and Tzannes prove that their system, thanks to the wavelet modulation and demodulation techniques, has an improved immunity for such narrowbanded interference compared to multicarrier systems using Fourier transform modulation and demodulation methods, due to the intrinsic better spectral containment of the carrier waveforms. Nevertheless, also in the system of Sandberg and Tzannes, unrecoverable errors still have to be solved by re-allocation of data bits.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for allocating data bits to a set of carriers and related equipment of the above known type, but wherein unrecoverable loss of information due to narrowbanded interference and time-consuming communications of the above described type are avoided.
According to the invention, this object is achieved by a method to allocate data bits of digital data packets to a set of carriers in a multicarrier transmission system wherein the set of carriers, after being modulated with the data bits, is transmitted from a transmitter to a receiver via a transmission link, a subset of the set of carriers h
Reusens Peter Paul Frans
van de Wiel Olivier
Alcatel
Olms Douglas
Vanderpute Ken
Ware Fressola Van Der Sluys & Adolphson LLP
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