Multiplex communications – Duplex – Transmit/receive interaction control
Reexamination Certificate
1999-02-16
2002-10-01
Nguyen, Steven (Department: 2665)
Multiplex communications
Duplex
Transmit/receive interaction control
C370S494000, C370S208000, C379S413020
Reexamination Certificate
active
06459684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to communication systems. More specifically, a multiplexed CODEC for an ADSL central office is disclosed that processes signals sent and received on multiple data lines. In addition, a multiplexed CODEC is disclosed for an ADSL remote unit that generates a data signal for sending an upstream signal to the central office as well as an echo cancellation signal that is used to process an incoming downstream signal from the central office. A multiplexed CODEC at the ADSL remote unit also is disclosed that may be used to process both ADSL signals and voice band modem POTS signals.
2. Description of the Related Art
Asymmetric Digital Subscriber Line (ADSL) technology is used to deliver high-rate digital data over existing phone lines without modification of the phone lines. A modulation scheme called Discrete Multitone (DMT) allows the transmission of high speed digital data. ADSL facilitates the simultaneous use of normal telephone services, ISDN, and high speed data transmission. ADSL allows a large bandwidth (1.104 MHz) for transmission in a downstream direction from a central office to a subscriber in a remote location and a lesser bandwidth (138 kHz) for transmission in an upstream direction from a subscriber in a remote location to a central office. ADSL systems are described further in the ADSL T1E1.413 standard, which is herein incorporated by reference for all purposes.
FIG. 1A
illustrates the architecture of an ADSL system. A digital network
100
provides data that is to be sent downstream over the ADSL line. The data is delivered to an ADSL transceiver unit in a central office (an ATU-C)
102
. The ATU-C modulates data for downstream transmission using a DMT scheme. ATU-C drives a line
104
with an analog signal. Line
104
is connected to a telephone line
110
that is part of a Public Switched Telephone Network (PSTN)
106
by a splitter
108
. ATU-C also receives data transmitted in the upstream direction on line
104
.
At the receiver end, a splitter
120
splits the signal on line
110
between a message telecommunication service (MTS)
122
(also referred to as plain old telephone service (POTS)) and an ADSL transceiver unit line for a remote unit (an ATU-R)
124
. ATU-R
124
is connected to one or more service modules (SM)
128
by a bus
126
. The ATU-R demodulates data transmitted by the ATU-C in the downstream direction and also transmits data in the upstream direction.
FIG. 1B
is a block diagram illustrating the transmission path of an ADSL system. The transmission path may be in either the upstream or the downstream direction. An encoder
150
sends digital data to a DAC
152
. The analog output of DAC
152
represents an ADSL modulated signal that is to be transmitted on an ADSL line. The analog output of DAC
152
is therefore directed to a reconstruction filter
154
. Reconstruction filter
154
reconstructs the signal that is to drive an ADSL line
156
. Usually, there is an additional line driver in the signal path. Thus, the signal that drives ADSL line
156
is first generated digitally by encoder
150
. DAC
152
converts the digital signal to an analog signal and reconstruction filter
154
drives the ADSL line.
FIG. 1C
is a block diagram illustrating an asymmetric digital subscriber line (ADSL) system that includes a central office
160
and several remote terminals
162
. Typically, the central office includes a large number of lines extending to a large number of remote terminals. For economic reasons, it is desirable that the central office be able to accommodate as many lines as possible. A number of factors limit how many lines may be supported in a central office building. A major factor is the ability of the building to dissipate sufficient heat so that the heat generated by the ADSL transceiver and modulation hardware does not cause systems to fail. Therefore, it is important to design systems so that the power dissipated per line to a remote terminal is minimized, making it possible to maximize the number of lines included in a central office building.
One approach to increasing the number of lines that can be included in a central office is to design ADSL central office chip sets with multiple line architectures. Including circuitry for more than one line on a chip may have the advantage of reducing the amount of heat generated for each line in the central office as well as reducing manufacturing costs.
FIG. 2
is a block diagram illustrating a prior art system that includes a multiple line ADSL transceiver that generates downstream transmitted ADSL signals on two ADSL lines. An ADSL transceiver
200
transmits and receives ADSL signals to and from a CODEC
202
. In the downstream direction, CODEC
202
converts a digital signal from the ADSL transceiver to an analog signal and sends the analog signal to a line driver
204
. Line driver
204
generates an analog modulation signal that can be applied to the first ADSL line supported by the ADSL transceiver. The output from the line driver is input to a hybrid
206
. Hybrid
206
is connected to the ADSL line usually through a transformer.
Incoming upstream signals from the ADSL line are transferred by hybrid
206
to a line receiver driver
205
. The analog signals from line receiver
205
in the upstream direction are converted to digital signals by CODEC
202
and those digital signals are input to the ADSL transceiver
200
. In the same manner, for the second line supported by ADSL transceiver
200
, digital signals from the ADSL transceiver are converted to analog signals in the downstream direction by a CODEC
212
. Analog signals from CODEC
212
are input to line driver
214
which drives the second ADSL line through hybrid
216
. Also, incoming upstream signals from ADSL line
2
are input to the hybrid
216
which transfers the signals to line receiver
215
so that they may be converted to digital signals by CODEC
212
. The digitized signals from CODEC
212
are input to the second ADSL port of ADSL transceiver
200
.
The benefit of this architecture is that a single ADSL transceiver may be used for two lines instead of requiring an ADSL transceiver for each line. It would also be useful if the number of other chips in the chip set could be reduced as well. For example, one line driver and CODEC is required for each ADSL line. If a system could be designed that would allow such chips to support more than one ADSL line, then further power and cost saving could be realized.
SUMMARY OF THE INVENTION
Accordingly, a system and method for sending and receiving ADSL signals for more than one ADSL line at an ATU-C is disclosed that requires only a single CODEC for multiple lines. Signals output from an ADSL transceiver are time division multiplexed and input into a single CODEC. The output of the CODEC is switched and sent to different line drivers for each of the lines associated with the transceiver. Similarly, in the upstream direction, multiple lines are connected through receivers to the CODEC and the CODEC samples each of the lines alternatively and interleaves the digitized data on a signal digital output to the transceiver. In addition, a system and method implemented at an ATU-R is disclosed that also includes a multiplexed CODEC. The multiplexed CODEC is used to receive an ADSL transmission and also process an echo canceling signal in some embodiments. The multiplexed CODEC is also used to process a modem signal from a POTS line in some embodiments.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium. Several inventive embodiments of the present invention are described below.
In one embodiment, an ADSL central office transmission system for transmitting downstream DMT signals to a plurality of remote ADSL transceiver is disclosed. The system includes a DMT digital signal transceiver that generates a time division multiplexed digital signal that in
Conroy Cormac S.
Sheng Samuel W.
Uehara Gregory T.
Lathrop & Gage L.C.
LSI Logic Corporation
Nguyen Phuongchau Ba
Nguyen Steven
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