Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Reexamination Certificate
1999-06-04
2001-05-22
Chin, Wellington (Department: 2735)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
C370S352000, C370S356000
Reexamination Certificate
active
06236664
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to telecommunication systems, and more particularly to ADSL (Asymmetrical Digital Subscriber Line) transmission systems in access network.
Telephone customers are moving in an evolutionary way to higher bandwidths, from sharing POTS (Plain Old Telephone Service) and modem on one line to dedicated analog modem line at 56 kbps (kilo-bits per second) and to ISDN BA (Basic Access). Now, ADSL has been introduced and become proven technology. ADSL refers to a high-speed transmission technology using existing twisted pair of wires that permits simultaneous POTS and high-speed data communication. Generally, a higher data rate is employed downstream than upstream. Ordinary twisted pair equipped with ADSL modems can transmit movies, television, dense graphics, and very high speed data. For all its capacity, ADSL leaves POTS undisturbed. A single ADSL line therefore offers simultaneous channels for personal computers, televisions, and telephones. With ADSL, telephone companies can connect homes and businesses to exciting new interactive broadband services.
The ADSL services are different from ISDN services. ISDN provides two 64 kbps channels for voice or data, while ADSL is predominantly a data pipe providing an asymmetrical bandwidth of up to 9 Mbps downstream and 800 kbps upstream. The customers for ADSL most likely already have a dedicated modem line or ISDN.
FIG. 1
shows a conventional way of implementing ADSL over a pair gain system. A pair gain system is a system which typically includes a central office terminal (COT) located in a central office (CO) of a telephone company and a remote terminal (RT) located in a customer premises. The COT may have two or more line cards, each for connecting to a pair of wires from a telephone exchange in the CO. The COT of a pair gain system multiplexes signals received from the multiple pairs connected to its line cards, over a single pair connecting between the COT and the RT of the pair gain system. The COT also demultiplexes signals received from the RT via the single pair and provides them to the telephone exchange via the multiple pairs connected to its line cards. The RT demultiplexes signals received from the single pair and provides them to a subscriber at the customer premises over the same number of pairs. The RT also multiplexes signals received from the multiple pairs at the customer premises, over the single pair connecting to the COT. Thus, a pair gain system allows a subscriber at the customer premises to have two or more telephone lines without requiring the expense of installing additional pairs between the CO and the customer premises. An example of a pair gain system is the Miniplex® 2N1, which multiplexes two pairs over a single pair. Miniplex® 2N1 is commercially available from Raychem Corporation, Menlo Park, Calif.
As illustrated in
FIG. 1
, at a CO
10
of a telephone company, a telephone exchange
12
provides two analog POTS lines L
1
and L
2
in the form of two twisted pairs of wires to a COT
15
of a pair gain system. COT
15
multiplexes L
1
and L
2
over a single twisted pair
13
and converts the analog signals from L
1
and L
2
into DSL (Digital Subscriber Line) signals, such as ISDN signals, on pair
13
. An ADSL DSLAM (DSL Access Multiplexer)
18
receives broadband data from the Internet, for example and provides high-speed data transmission in the form of ADSL signals. The DSL and ADSL signals provided respectively from COT
15
and ADSL DSLAM
18
are fed to splitter
16
. Splitter
16
combines the DSL and ADSL signals for transmission to a customer premises
20
over a single twisted pair
19
. Splitter
16
also receives the DSL signals and ADSL signals from splitter
32
and separates the DSL signal from the ADSL signal for transmission to COT
15
and ADSL DSLAM
18
, respectively.
At customer premises
20
, splitter
32
separates the DSL signal from the ADSL signal. The DSL signal is provided, via a pair
33
, to a RT
34
of the pair gain system, which demultiplexes the DSL signal into analog signals on two analog POTS lines L
1
and L
2
. Each of lines L
1
and L
2
at customer premises
20
is for connecting to a telecommunication device (not shown), such as a telephone or a fax machine. The ADSL signal is provided to an ADSL modem
36
, which is connected to either ATM
25
(asynchronous transfer mode 25 Mbps) or Ethernet. RT
34
also multiplexes analog signals from analog lines L
1
and L
2
into a DSL signal over pair
33
for transmission to CO
10
. Splitter
32
also receives DSL and ADSL signals from RT
34
and ADSL modem
36
respectively, and combines them for transmission to CO
10
over twisted pair
19
. In the case of implementing ADSL over ISDN BA (basic access), an ISDN NT
1
(network termination
1
) can be used as RT
34
.
One of the main limitations of ADSL is the loop length which is the distance between the CO or DSLAM and the customer premises. For service with a downstream speed of 5 to 6 Mbps (mega-bits per second), the loop length is limited to less than 12 kft, in order not to sacrifice the transmission quality. At the present time, telecom operators use very conservative installation rules to ensure that the service will always be properly delivered. However, they will soon receive requests for service from people living farther away from the central office where a DSLAM is located. At present, it is estimated that about 60% of the subscribers can be potentially reached and receive high-speed data services. This leaves the other 40% with only low-speed data services.
Of course, there are several solutions for delivering high bandwidth services over longer distances (e.g. fiber optics). One solution is the use of a repeater for the ADSL signal. However, ADSL repeaters face a specific issue with power feeding as the ADSL signal is usually transmitted simultaneously with POTS on a copper pair. In order that a repeater be practical in the field, it will need to receive remote power feeding. This is very difficult and may be impossible if ADSL is implemented with POTS on the same copper pair.
An easy solution is to run POTS and ADSL on different pairs. Several POTS lines can be multiplexed over one copper pair using subscriber line multiplexers. The copper pair used for ADSL can carry a DC current for remote power feeding an ADSL repeater. However in this case telecom operators must install two copper pairs in order to provide one or more POTS lines and an ADSL. Therefore, substantial additional expenses will be incurred by telecom operators for installing a second copper pair whenever ADSL service is requested to be delivered over longer distances.
Accordingly, there is a need for implementing ADSL over POTS over longer distances without requiring an additional copper pair for transmitting an ADSL signal along with a DC current to a customer premises.
SUMMARY OF THE INVENTION
The present invention provides an efficient way to transmit ADSL and multiple POTS signals over long distances by combining a repeater for ADSL with a pair gain system, whereby the pair gain system remotely provides DC power to the repeater over the same pair as that for transmission of DSL and ADSL signals.
According to one embodiment of the invention, a telecommunication system is provided. The telecommunication system comprises a first transmission/receiving system, located at a first location, that provides and receives a first type of signal in a first frequency spectrum and a second type of signal in a second frequency spectrum over a first pair of wires; a second transmission/receiving system, located at a second location, that receives and sends the first and second types of signals over a second pair of wires; and a repeater unit, coupled between the first and second pairs of wires, for receiving a second type of signal from the first transmission/receiving system via the first pair and providing a repeated second type of signal to the second transmission/receiving system via the second pair, the repeater unit also receiving a sec
Chin Wellington
Jones Prenell
Terayon Communications Systems, Inc.
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