Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1998-10-29
2003-10-28
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C375S222000, C379S093090
Reexamination Certificate
active
06639911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to data communication systems and, more particularly, to data communication systems that provide different services over a common channel.
2. Description of the Related Art
Often, with conventional communications systems, communication channels are shared by different devices that operate on the same channel. In conventional Asymmetric Digital Subscriber Line (“ADSL”) transceivers (i.e., modems) it is common to use two pairs of “splitter” filters to separate Plain Old Telephone Service (POTS) and ADSL services that operate on the same line. One pair of the splitter filters is provided at the central side and the other pair is provided at the remote side. Each pair of splitter filters includes a low pass filter that passes signals to the POTS and a high-pass filter that passes signals to the ADSL services.
FIG. 1
is a block diagram of a data communication system
10
in which a communication channel (i.e., line) supports both POTS and ADSL services. The data communication system
10
includes a central side
12
and a remote side
14
. The central side
12
is, for example, a central office, and the remote side
14
is, for example, associated with a customer's premises (e.g., business or residential premises).
The central side
12
includes a DMT transceiver
16
and a telephone network
18
. The DMT transceiver
16
includes a DMT transmitter
20
, a DMT receiver
22
, and a hybrid circuit
24
. The DMT transmitter
20
operates to transmit data over the channel through the hybrid circuit
24
. The DMT receiver
22
operates to receive data that has been transmitted over the channel and received through the hybrid circuit
24
. The central side
12
also includes a splitter
26
(i.e., pair of splitter filters) that passes lower frequency signals incoming over a line
28
to the telephone network
18
and passes higher frequency signals incoming over the line
28
to the hybrid circuit
24
.
The remote side
14
includes a DMT transceiver
30
and a customer telephone service
32
. The DMT transceiver
30
includes a DMT receiver
34
, a DMT transmitter
36
and a hybrid circuit
38
. The remote side
14
also includes a splitter
40
(i.e., pair of splitter filters) that is coupled to the line
28
as well as to the customer telephone service
32
and the hybrid circuit
38
. The splitter
40
operates to pass incoming signals from the line
28
to either the hybrid circuit
38
or the customer telephone service
32
. If the incoming signals over the line
28
are low frequency signals, then the splitter
40
forwards the signals to the customer telephone service
32
. On the other hand, if the incoming signals over the line
28
are higher frequency signals, the splitter
40
forwards the signals to the hybrid circuit
38
of the transceiver
30
.
Accordingly, the data communications system
10
is able to provide ADSL and POTS services over the same line (i.e., the line
28
). The splitters
26
and
40
operate to filter the differing services appropriately so as to direct signals to the proper service. Additional details on ADSL can be found in American Nationals Standard Institution (ANSI) published standard ANSI T1.413-1995 pertaining to Network and Customer Installation Interfaces—Asymmetric Digital Subscriber Lines (ADSL) Metallic Interface, which is hereby incorporated by reference.
There are, however, several problems associated with the conventional design of the data communication systems supporting multiple services over a common communication channel. One problem of a remote ADSL transceiver (such as the remote transceiver
30
illustrated in
FIG. 1
) is that a low-pass filter associated with the splitter (e.g., the splitter
40
) needs to be installed near the entrance of the line (e.g., the line
28
) to the customer's premises. As noted above, the design of the splitter includes two filters (i.e., splitter filters), one filter (high-pass filter) is formed in or coupled to the transceiver (i.e., the transceiver
30
) and the other filter (low-pass filter) is installed at the entrance of the line to the customer's premises. The installation of such a filter (i.e., low-pass filter) at the customer's premises is inconvenient and burdensome to both customers and telephone service providers.
Some data communication systems have tried to remove the low-pass filter associated with the splitter at the remote side. While this avoids the inconvenience and burden of having to install the low-pass filter at the customer's premises, doing so causes high levels of noise to be generated at the telephone at the customer's premise which impedes its use and is otherwise unsatisfactory to users. More particularly, in the case of ADSL transceivers using discrete multi-tone (DMT) modulation, when a customer transmits data upstream (i.e., toward a central office) using a DMT modulation technique without having a low-pass filter of the splitter at the customer's premises, non-linearities in the circuitry of many telephones can cause intolerably high levels of noise to be generated by the telephone's speaker and heard in the telephone's earpiece.
Another approach that has been proposed to solve the noise problem that results in an ADSL system without the low-pass filter associated with the splitter at the customer's premises is to transmit at lower power levels or use a less effective modulation technique. Transmitting at lower power levels significant drops the available data rates that can be supported. While DMT modulation does (at high power levels) provided high data rates, it uses high frequency signals that have high signal strengths. These resulting high signal strengths, as noted above, give rise to the undesired noise at the customer's telephones. A less effective modulation technique would use signals that have lower signal strengths or frequencies and thus produce less noise. However, the use of a less effective modulation technique in place of DMT also reduces the performance of the system in terms of its available data rate.
Thus, there is a need for improved techniques that allow telephone service and ADSL service to operate on the same line without requiring a low-pass filter portion of a splitter at a customer location.
SUMMARY OF THE INVENTION
The invention relates to a data communication system that provides different types of service to a remote site even when the remote site lacks a splitter. A central site (e.g., central office) is able to communicate with at least two different types of remote sites. One type of remote site includes a full splitter (i.e., both low-pass and high-pass filters), and the other type of remote site has only a partial splitter (i.e., includes high-pass filter but lacks a low-pass filter). Although conventionally the transceivers (e.g., ADSL transceivers) at these remote sites would be of the same design and use the same modulation technique for upstream as for downstream transmissions, here the remote site that lacks a low-pass filter (i.e., partial splitter type remote site) uses a different modulation technique for upstream transmissions. As an example, the remote site without a complete splitter could use continuous phase modulation (CPM) for upstream transmissions and discrete multi-tone (DMT) for downstream transmissions. More generally, while a high peak-average-ratio (PAR) technique like DMT can be used on downstream transmissions that do not lead to noise at the telephone service even in the splitterless design, a lower PAR technique (e.g., CPM, QAM, FSK, etc.) can be used on the upstream transmissions so that the noise levels produced at the telephone service are vastly reduced. The central site is able to communicate with both the different types of remote sites. The central site selects from various receiver units depending on the type of modulation (e.g., low PAR technique) used by the remote sites.
The invention can be implemented in numerous ways, including as an apparatus, system
Brady III W. James
Hsu Alpus H.
Stevens Roberta
Telecky , Jr. Frederick J.
Williams Tammy L.
LandOfFree
Data communications system with splitterless operation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Data communications system with splitterless operation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Data communications system with splitterless operation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3138079