Telephonic communications – Subscriber line or transmission line interface – Network interface device
Reexamination Certificate
1998-02-23
2001-07-17
Chan, Wing F. (Department: 2643)
Telephonic communications
Subscriber line or transmission line interface
Network interface device
C379S093280, C375S222000
Reexamination Certificate
active
06263077
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to communication systems. More particularly, the present invention relates to a system for and a method of reducing noise on a subscriber line.
BACKGROUND OF THE INVENTION
Explosive growth of the internet and the worldwide web is driving a need for increased communication data rates. In the corporate world, the need for high-speed access or data rates is met by dedicated high-speed links (perhaps T
1
/E
1
frame relays or OC
1
ATM systems) from the company to an internet access provider. Users in the company utilize a local area network (LAN) to gain access to an internet access router, which is attached to the high-speed link. Unfortunately, home-users of the internet do not often have a high-speed link and must rely on standard analog or plain old telephone service (POTS) line.
The need for high-speed access to the home is ever increasing due to the availability of information, data, programs, entertainment, and other computer applications on the worldwide web and on the internet. For example, designers of web technology are constantly developing new ways to provide sensory experiences, including audio and video, to users of the web (web surfers). Higher-speed modems will be required so the home-user can fully interact with incoming web and communication technologies.
Although designers of modems are continuously attempting to increase data rates, analog or POTS line modems are presently only able to reach data rates of up to 56 kilobits per second (Kbps). These conventional analog modems transmit and receive information on POTS subscriber lines through the public-switched telephone network. The internet access provider is also coupled to the switched telephone network and transmits and receives information through it to the subscriber line.
Some home-users have utilized integrated digital services network (ISDN) equipment and subscriptions to obtain up to 128 Kbps access or data rates by the use of 2 B channels. ISDN equipment and subscriptions can be expensive and require a dedicated subscriber line. Heretofore, neither ISDN modems nor analog modems are capable of providing 256 Kbps or higher access between the home and the internet. Over one megabit per second (Mbps) data rates with analog modems or ISDN equipment do not seem feasible at this time.
A variety of communication technologies are competing to provide high-speed access to the home. For example, asymmetric digital subscriber lines (ADSL), cable modems, satellite broadcast, wireless LANs, and direct fiber connections to the home have all been suggested. Of these technologies, the asymmetric digital subscriber line can utilize the POTS subscriber line (the wire currently being utilized for POTS) between the home-user (the residence) and the telephone company (the central office).
ADSL networks and protocols were developed in the early 1990's to allow telephone companies to provide video-on-demand service over the same wires which were being used to provide POTS. ADSL technologies include discrete multitone (DMT), carrierless amplitude and phase modulation (CAP), VHDL, and other technologies. Although the video-on-demand market has been less than originally expected, telephone companies have recognized the potential application of ADSL technology for internet access and have begun limited offerings.
ADSL technology allows telephone companies to offer high-speed internet access, while removing internet traffic from the telephone switch network. Telephone companies cannot significantly profit from internet traffic in the telephone switch network due to regulatory considerations. However, the telephone company can charge a separate access fee for ADSL services. The separate fee is not as restricted by regulatory considerations.
With reference to
FIG. 1
, a conventional asymmetric ADSL (ADSL) system
10
includes a copper twisted pair analog subscriber line
12
, an ADSL modem
14
, an ADSL modem
16
, a band splitter
18
, and a band splitter
20
. Line
12
is a POTS local loop or wire connecting a central office
32
of the telephone company to a user's residence
22
.
ADSL modem
14
is located in user's residence
22
and provides data to and from subscriber line
12
. The data can be provided from line
12
through modem
14
to various equipment (not shown) coupled to modem
14
. Equipment, such as, computers, network devices, servers, or other devices, can be attached to modem
14
. Modem
14
communicates with a data network (not shown) coupled to modem
16
across line
12
. ADSL modem
16
receives and transmits signals from and to line
12
to modem
14
. The data network can be coupled to other networks (not shown), including the internet.
At least one analog telephone
26
, located in residence
22
, can be coupled to subscriber line
12
through splitter
20
for communication across line
12
with telephone switch network
28
. Telephone
26
and telephone switch network
28
(e.g., public-switched telephone (PST) network) are conventional systems well-known in the art. Alternatively, other analog equipment, such as, facsimile machines, POTS modems, answering machines, and other telephonic equipment, can be coupled to line
12
in user's residence
22
.
System
10
requires that band splitter
18
and band splitter
20
be utilized to separate higher frequency ADSL signals and lower frequency POTS signals. For example, when the user makes a call from residence
22
on telephone
26
, lower frequency signals (under 4 kilohertz (kHz)) are provided through band splitter
20
to subscriber line
12
and through band splitter
18
to telephone switch network
28
in central office
32
. Band splitter
18
prevents the lower frequency POTS signals from reaching ADSL modem
16
. Similarly, band splitter
20
prevents any of the POTS signals from reaching modem
14
.
ADSL modem
16
and ADSL modem
14
communicate higher frequency ADSL signals across subscriber line
12
. The higher frequency ADSL signals are prevented from reaching telephone
26
and telephone switch network
28
by band splitters
20
and
18
, respectively. Splitters
18
and
20
can be passive analog filters or other devices which separate lower frequency POTS signals (below 4 kHz) from higher frequency ADSL signals (above 50 kHz).
The separation of the POTS signals and the ADSL signals by splitters
18
and
20
is necessary to preserve POTS voice and data traffic and ADSL data traffic. More particularly, splitters
18
and
20
can eliminate various effects associated with POTS equipment which may affect the transmission of ADSL signals on subscriber line
12
. For example, the impedance of subscriber line
12
can vary greatly as at least one telephone
26
is placed on-hook or off-hook. Additionally, the changes in impedance of subscriber line
12
can change the ADSL channel characteristics associated with subscriber line
12
. These changes in characteristics can be particularly destructive at the higher frequencies associated with ADSL signals (e.g., from 30 kHz to 1 megahertz (MHz) or more).
Additionally, splitters
18
and
20
isolate subscriber line wiring within residence
22
. The impedance of such wiring is difficult to predict. Further still, the POTS equipment, such as, telephone
26
, provides a source of noise and nonlinear distortion. Noise can be caused by POTS voice traffic (e.g., shouting, loud laughter, etc.) and by POTS protocol, such as, the ringing signal. The nonlinear distortion is due to the nonlinear devices included in conventional telephones. For example, transistor and diode circuits in telephone
26
can add nonlinear distortion and cause hard clipping of ADSL signals. Telephone
26
can further generate harmonics which can reach the frequency ranges associated with the ADSL signals. The nonlinear components can also demodulate ADSL signals to cause a hiss in the audio range which affects the POTS.
Conventional ADSL technology has several significant drawbacks. First, the costs associated with ADSL services can be quite h
Haque Jamal
Ko Kenneth D.
Patravali Shrenik P.
Rodriguez Manuel I.
Souders Keith A.
Chan Wing F.
Conexant Systems Inc.
Foley & Lardner
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