Telephonic communications – Centralized switching system – With generating of call associated substation signal
Reexamination Certificate
2000-02-09
2003-12-02
Tieu, Binh (Department: 2643)
Telephonic communications
Centralized switching system
With generating of call associated substation signal
C379S373010, C370S496000, C375S254000, C375S296000
Reexamination Certificate
active
06658105
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method to reduce distortion of digital data by a Plain Old Telephone Service (POTS) ringing signal and a telephone ringing generator enabling this method.
Several methods and devices to reduce distortion of digital data, e.g. transferred in accordance with the ADSL (Asymmetric Digital Subscriber Line) standard specification, by the high voltage ringing of a POTS (Plain Old Telephone Service) signal, transferred simultaneously with the digital data over a single line, are known in the art. Traditional splitters consisting of active or passive high pass and low pass filters, such as the ones described in the article ‘ADSL and VADSL Splitter Design and telephony Performance’ from the authors John Cook and Phil Sheppard that was published in IEEE Journal on Selected Areas in Communications, Vol. 13, No. 9, December 1995, separate telephony signals (including ringing) from ADSL signals at the central office and at the customer's premises thus minimising interference between the POTS and digital data transmission. These splitters however are bulky and expensive because high order (up to 7th order) operator dependent low and high pass filters are required therein.
In the full digital loop known for instance from the European Patent Application EP 0 740 451 entitled ‘Method, Interface Modules and telephone Network for Multiplexing and Demultiplexing an Analog MTS (Message Telephone Service) signal and an ADSL (Asymmetric Digital Subscriber Line) Datastream’ from applicant Alcatel Bell, mutual interference between concurrently transferred telephony signals and digital data is avoided by digitising the telephony signals and by embedding the digitised telephony signals in the digital data frames that also convey the digital data. POTS signalling such as the ringing signal and the metering pulses are replaced with digital codes, also embedded in the digital data frames. These digital codes do not distort the digital data but encoding thereof at the transmitter's side and decoding thereof at the receiver's side requires some modifications of the current xDSL implementations. Moreover, the full digital loop requires by-passing equipment to maintain telephony service even when the digital data equipment fails, which can occur for instance in case of a power supply failure at the customer's premises, and requires the presence of a ringing signal generator at the customer's premises to re-generate the high voltage ringing signal from the received codes.
A third known method to reduce interference between simultaneously transferred digital data and telephony signals, in particular ringing signals, is known as the ADSL Lite solution with microfilters. In the ADSL Lite solution, studied for instance in the presentation summary ‘Study of Non-Linear Distortion in an ADSL-Lite Environment’ written by the authors Marc Van Bladel and Gerd Vandersteen and presented on the 5th Bayona Workshop on Emerging Technologies in Telecommunications held in Bayona, Spain from 6 till 8 September 1999, microfilters in the line towards the phone separate the digital data from the telephony signals before these telephony signals are supplied to the phone. Such a microfilter for example is known from the press release ‘Orckit Announces New Dynamic Microfilter for Use with G.Lite ADSL’ from Jun. 2, 1999 that can be retrieved from the Internet via the following URL: http://www.xdsl.com
ewsreleases/xDSL/3075.asp. The telephony signals however are not separated from the digital data before the digital data are supplied to the ADSL modem so that there is distortion of digital data by the ringing signal. As a consequence, the digital data service usually goes down in the ADSL Lite solution at the moment a telephone call is set up over the same twisted pair.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and a device for reducing distortion of digital data by the POTS ringing of a telephony signal transmitted concurrently with the digital data over a single line, but which overcome the drawbacks of the above mentioned state of the art solutions, i.e. which do not require bulky splitters with 7th order filters at the central office and customer's premises, which do not require additional encoding/decoding complexity and precautions to realise a POTS life-line in case of failure of the digital data service, and which avoid that the digital data service can go down as a result of a presence of the high voltage POTS ringing signals.
According to the invention, this object is achieved by the method to reduce distortion of digital data by a Plain Old telephone Service (POTS) ringing signal defined by claim
1
, and the telephone ringing signal generator defined by claim
2
.
Indeed, by windowing a sine or cosine shaped signal, a digital data friendly ringing signal is generated. The influence of the on/off switching of this digital data friendly ringing signal on digital data concurrently transmitted over the same line is far below the transient distortion due to on/off switching of a traditional sine or cosine shaped ringing signal. When smoothly windowing a sine or cosine shaped signal to constitute a digital data friendly ringing signal, a slight increase of the peak-to-average ratio (PAR) of the ringing signal is an acceptable price paid for the obtained reduction in transient distortions.
It is to be noticed that the term ‘comprising’, used in the claims, should not be interpreted as being limitative to the means listed thereafter. Thus, the scope of the expression ‘a device comprising means A and B’ should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
An optional characteristic feature of the telephone ringing signal generator according to the present invention is defined by claim
3
.
In this way, for new operators that do not have to care about an installed base (the so called green field installation), a per-line scenario can be implemented with a universal linecard that terminates both the telephony service and the digital data service and with an intelligent switch, smoothly controlled by for example a microprocessor so that the on/off switching of the ringing signal is aligned with respectively the beginning/ending of the applied window. For this implementation of the present invention, a traditional ringing generator sourcing an analog sine or cosine shaped ringing signal can serve as input for the smoothly controlled switches on the different linecards.
An additional characteristic feature of the telephone ringing signal generator of claim
3
, is defined by claim
4
.
Thus, in order to avoid distorting the ringing signal heavily by the windowing applied to reduce the ringing signal transient distortion on digital data, the window length may be selected to be equal to the on-period of the ringing signal.
Alternatively to the telephone ringing signal generator described by claim
3
, an optional characteristic feature of the telephone ringing signal generator according to the present invention is defined by claim
5
.
In this way, for incumbent operators that offer digital data services on top of telephony services and that want to reuse to a maximum their installed infrastructure, a scenario can be implemented whereby only the ringing card is updated to a ringing card that generates the windowed digital data friendly ringing signal, and whereby all POTS linecards and switches for on/off switching the ringing signal on the different lines are reused.
An additional characteristic feature of the telephone ringing signal generator of claim
5
, is defined by claim
6
.
Thus, the reused switches for on/off switching the ringing signal are controlled, for instance by a microprocessor that communicates with the ringing card generating the windowed digital data friendly ringing signal, to switch on/off respectively aligned with the beginning/ending border of the applied s
De Clercq Luc Josephine Theoduul
Ploumen Franciscus Maria
Alcatel
Tieu Binh
LandOfFree
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