Interactive video distribution systems – Video distribution system with upstream communication – Transmission network
Reexamination Certificate
1997-11-13
2004-02-17
Faile, Andrew (Department: 2611)
Interactive video distribution systems
Video distribution system with upstream communication
Transmission network
C725S126000, C725S130000, C725S131000, C725S107000
Reexamination Certificate
active
06694516
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a method used in a telecommunication network, a termination unit realizing the latter, and a telecommunication network including such a termination unit.
2. Discussion of Related Art
Such a termination unit is already known in the art, e.g. from the article “CATV Return Path Characterization for Reliable Communications” of Charles A. Eldering, Nageen Himayat and Floyd M. Gardner, published in the IEEE communications Magazine of August 1995 from page 62 to page 69. As described in the abstract of the article, there is a tremendous need for equipment to support bidirectional communications over a hybrid fiber coax HFC network shown on FIG. 1 of page 63. The HFC network is a tree branch network emanating from a central office and terminating at the subscriber residences in termination units which are called in the article coaxial termination units. Additional splitting of the downstream signal takes place in the residences in order to terminate in the subscriber terminals, e.g. personal computer, videophone, set-top box and TV.
It has to be remarked that the signal power attenuation of a transmission line between two points refers in this invention to the global attenuation of the transmission line taking into account the following parameters:
the attenuation of the transmission line proportional to the distance and the number of splittings along the line between the two points; and
the included amplifiers along the transmission line between the two points in the transmission direction.
A portion of the downstream signal power is provided to each subscriber terminal. Due to the attenuation along the network links, i.e. external signal power attenuation, and the attenuation of the growing in-house network in the residences, i.e. internal signal power attenuation, the portion of the power level of the downstream signal received in each of the subscriber terminals becomes low compared with the power level of the upstream signal generated by the subscriber terminal. This difference in power level makes the region of the internal network near the subscriber terminal very sensitive to cross-talk which influences the downstream signal.
This phenomenon is described in the book “Digital, Analog, and Data Communication, Second Edition” of William Sinnema with reference number ISBN 0-8359-1313-9, published in 1986 by Prentice-Hall, Inc., a division of Simon & Schuster, Englewood Cliffs, N.J. 07632, and more particularly on pages 115 to 117 thereof. On page 115 cross-talk is defined as induced signals into neighbouring pairs by either capacitive or inductive coupling because of the close proximity of adjacent wire pairs in a cable. As described on page 116 the crosstalk can be reduced by physically separating the downstream and upstream signals with a screened cable e.g. coaxial cable.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a termination unit such as the above known ones but which is suited to further reduce the cross-talk in the region of the internal transmission line at the subscriber terminal.
According to a first aspect of the present invention, a method for use in a telecommunication network wherein a central station is coupled to a plurality of residences, one of said residences including a termination unit coupled to said central station via a first port, said residence including at least one subscriber terminal coupled to said termination unit via a second port, is characterized in that said method includes the steps of amplifying an upstream signal applied to said second port with an upstream gain value by means of an upstream signal amplifier included in said termination unit and generating an amplified upstream signal provided to said first port and that said upstream gain value is for compensating any of an upstream signal power attenuation of an internal transmission line coupled between said termination unit and any of said subscriber terminals, and a downstream signal power attenuation of said internal transmission line.
According to a second aspect of the present invention, a method for use in a telecommunication network wherein a central station is coupled to a plurality of residences, one of said residences including a termination unit coupled to said central station via a first port, said residence including at least one subscriber terminal coupled to said termination unit via a second port, is characterized in that said method includes the steps of amplifying a downstream signal applied to said first port with a downstream gain value by means of a downstream signal amplifier included in said termination unit and generating an amplified downstream-signal provided to said second port and that said downstream gain value is for compensating any of an upstream signal power attenuation of the internal transmission line coupled between said termination unit and any of said subscriber terminals, and a downstream signal power attenuation of said internal transmission line.
According to a third aspect of the present invention, a termination unit for inclusion in a telecommunication network wherein a central station is coupled to a plurality of residences, one of said residences including said termination unit coupled to said central station via a first port of said termination unit, said residence including at least one subscriber terminal coupled to said termination unit via a second port, is characterized in that said termination unit includes an upstream signal amplifier to amplify an upstream signal applied to said second port with an upstream gain value and to thereby generate an amplified upstream signal provided to said first port and that said downstream gain value compensates any of the upstream signal power attenuation of the internal transmission line coupled between said termination unit and any of said subscriber terminals, and the downstream signal power attenuation of said internal transmission line.
According to a fourth aspect of the present invention, a telecommunication network is characterized in that said telecommunication network includes at least one termination unit according to the third aspect of the present invention.
By including an upstream signal amplifier in the termination unit to amplify the upstream signal, according to the first, second and third aspects of the present invention, the required power level of the upstream signal generated by the subscriber terminal is allowed to be smaller.
Indeed, the subscriber terminal sends a less powerful upstream signal which is amplified in the termination unit in order to receive there the required powerbudget needed for a signal to be transmitted from the residence to the central station. The upstream gain value of the upstream signal amplifier is in fact a compensation for the upstream signal power attenuation of the internal transmission line coupled between the subscriber terminal and the termination unit.
In this way, at the region of the internal transmission line at the subscriber terminal, the difference in power level of the received downstream signal and of the transmitted upstream signal is smaller which makes this region less sensitive to cross-talk.
It also has to be remarked that in a totally symmetrical network the attenuation in upstream and downstream direction is identical, however e.g. the usable downstream and upstream frequency band for transmission in HFC networks are not the same. This makes for a situation in which the equipment to support bi-directional transmission e.g. the position of taps along the transmission line are optimized in one direction but not necessarily in the other direction. The following article, dealing with this problem can be mentioned as technical background: “Designing the Return System for Full Digital Services” written by Dean A. Stoneback and William F. Beck and published in the proceedings manual of “1996 Conference on Emerging Technologies, Jan. 8-10, 1996, San Francisco Hilton and Towers”, by the Society of Cable Telecommunications Enginee
Beller Dieter
Vandenabeele Peter
Alcatel Alsthom Compagnie Generale d'Electricite
Brown Reuben M.
Faile Andrew
Ware, Fressola VanDer Sluys & Adolphson LLP
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