Pulse or digital communications – Cable systems and components
Reexamination Certificate
1998-06-09
2001-11-13
Pham, Chi (Department: 2631)
Pulse or digital communications
Cable systems and components
C375S258000
Reexamination Certificate
active
06317464
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of data transmission. More specifically, it pertains to a method and a device for transmitting digital data signals over analog channels in telecommunication networks, for instance the analog loop connecting the central office of the Public Switched Telephone Network (PSTN) to the subscribers' Customer Premises Equipment (CPE).
BACKGROUND OF THE INVENTION
With the arrival and expansion of the Information Highway the quantity and speed of data transmission continues to grow. Telephone networks have being slowly converted from an all analog environment to a virtually all-digital network. Within these networks, the trunks and switches have been virtually 100 percent converted, while the local loops leading to the customer remain largely analog, other than in those environments where Integrated Services Digital Network (ISDN) technology has managed to gain a foothold.
This evolution towards a completely digital network brings many advantages, including the ability to provide a broader and more diverse range of services, a less error-prone network, the ability to achieve both physical and logical integration of applications, and an enhanced ability to deliver the higher bandwidth services requested by many customers.
Unfortunately, this deployment of higher bandwidth services must overcome a large issue, notably the fact that the traditional telephone network is designed to transport voice and relatively low-speed data, as opposed to high-speed digital data. It has also been designed around the known behavior patterns of typical telephony users, with well-understood calling patterns and hold times. The growth in Internet access has had an important, even negative effect on the ability of the local switching infrastructure to handle the requested load, since most users log on and stay connected much longer that the typical telephone call, which is what the switches were designed to handle.
Solutions to the bandwidth bottleneck problem faced by the telecommunications networks include massive switch capacity retrofits, construction of overlay networks for Internet traffic, as well as schemes designed to limit customers' connect time. A particularly promising solution is of a technological nature, specifically the use of Asymmetric Digital Subscriber Line (ADSL) in the networks' analog local loops. ADSL is a technology that offers the subscribers enormous bandwidth, engineered to overlay the existing analog Plain Old Telephone Service (POTS) and basic rate ISDN service. The term“asymmetric” arises from the fact that the system offers as much as 6 Mbps toward the customer, as compared to 384 Kbps from the customer.
Within traditional telephone networks, a copper loop (or two-conductor cable) connecting the central office and the CPE is used to provide the POTS, whose signals are Voice Frequency (VF) signals in the frequency range of 0-4 KHz. These cables are capable of carrying signals up to several MHz, depending on their length and type. ADSL takes advantage of the unused frequency band above 4 KHz and uses the copper loop as its transmission medium, transporting voice in the traditional 4 KHz channel bandwidth where it has always been, while higher bandwidth digital services are relegated to higher frequency domains.
In order to overlay the existing analog POTS, the ADSL system includes, among others, two circuits: a POTS Splitter circuit and a 2-4 W (2 wire to 4 wire) Hybrid circuit. These two circuits are used to combine and separate the POTS and ADSL signals, and are needed at both the CPE and central office ends of the copper analog loop. Unfortunately, the typical ADSL POTS Splitter and 2-4 W Hybrid circuitry is not only expensive, large and very power inefficient, but also produces important distortion which limits the cable range between CPE and central office in certain cases.
OBJECTS AND STATEMENT OF THE INVENTION
An object of the present invention is to provide a device for separating signals transported over a common conductor.
Another object is to provide a method for separating signals transported over a common conductor.
As embodied and broadly described herein, the invention provides a signal separation device, comprising:
a terminal for coupling to a conductor transporting simultaneously a first and a second signal having different frequency ranges, said second signal being characterized by a transmit component and by a receive component;
a first filter coupled to said terminal for extracting said first signal;
a second filter coupled to said terminal for rejecting said first signal;
a transformer having a first winding and a second winding magnetically coupled to one another, said first winding being electrically coupled to said terminal and forming part of said second filter;
a junction circuit, including:
a) a transmit component output electrically coupled to said second winding for impressing at said first winding the transmit component of the second signal;
b) a composite signal input electrically coupled to said second winding for receiving a composite signal being a combination of the transmit component and the receive component of the second signal;
c) processing means for receiving the transmit component of the second signal and the composite signal and generating the receive component of the second signal;
d) a receive component output coupled to said processing means for issuing the receive component of the second signal.
In a most preferred embodiment of this invention, the signal separation device as defined above is used in a telephone network environment to split the analog voice signal from a high-speed data signal carried over the analog loop connecting the central office of the PSTN to the CPE. Two such devices are required for each analog loop, one at each end of the loop. Accordingly, one device resides in the central office, while the other resides at the CPE.
Since the analog voice signal and the high-speed data signal reside in different frequency domains they can be separated by filtering. More particularly, the analog voice signal propagating on the analog loop is extracted by a low pass filter while the high-speed digital signal is extracted by a high pass filter.
The signal separation device includes a transformer having two windings, namely a first winding and a second winding. The first winding includes first and second balanced sections connected to the tip and ring conductors of the analog loop, respectively. The first winding forms part of the high pass filter. More specifically, the primary magnetizing inductance of the transformer (resulting from the balanced first and second sections) can be used together with an input capacitance to provide the functionality of a high pass filter. The second winding connects to a junction circuit that acts as a 2-4 W hybrid permitting to separate the receive and the transmit components of the digital high-speed data signal. The terms “receive component” and “transmit component” are relative to one another and indicate components of the signal traveling in opposite directions. The “receive component” is data usually issued from the signal separation device and forwarded toward a remote location, while the “transmit component” is data issued from a remote location and directed toward the signal separation device. In a situation where a signal separation device is placed at each end of an analog loop, the “transmit component” for one of the signal separation devices forms the “receive component” of the other signal separation device, and vice-versa.
Most preferably, the winding of the transformer connecting to the junction circuit (second winding) includes two separate sections. One section is connected to a transmit component output of the junction circuit on which is impressed the transmit component of the second signal. That transmit component is obtained locally through a transmit component input. The transmit component injected at the transmit component input is processed with amplifiers and then presented to the tra
Jakab Gyula
Le Minh
Bayard Emmanuel
Nortel Networks Limited
Pham Chi
LandOfFree
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