Source adaptive digital subscriber line and method

Details Source adaptive digital subscriber line and method Source adaptive digital subscriber line and method

2001-04-12

2004-07-13

Woo, Stella (Department: 2643)

Telephonic communications

Telephone line or system combined with diverse electrical...

Having transmission of a digital message signal over a...

C379S093280, C379S093080, C379S093140

Reexamination Certificate

active

06763097

ABSTRACT:

TECHNICAL FIELD OF INVENTION
The invention relates in general to data communication, and more particularly to Digital Subscriber Line on telephone cable.
BACKGROUND ART OF THE INVENTION
Digital Subscriber Line (DSL), a new modem technology, converts existing twisted pair telephone lines into access paths for multimedia and high speed data communications. The most successful Asymmetric Digital Subscriber Line (ADSL) transmits more than 6 Mbps to the subscriber, and as much as 640 kbps in both directions. Such rates expand existing access capacity by a factor of 50 or more without new cabling. ADSL can practically transform the existing public information network from one limited to voice, text and low resolution graphics to a powerful, ubiquitous system capable of bringing multimedia, including full motion video, to every home.
An ADSL circuit connects an ADSL modem on each end of a twisted-pair telephone line, creating three information channels—a high speed downstream channel, a medium speed duplex channel and a POTS (Plain Old Telephone Service) channel. The POTS channel is split off from the digital modem by filters, thus guaranteeing uninterrupted POTS, even if ADSL fails. The high-speed downstream channel ranges from 1.5 to 6.1 Mbps, while the duplex rate ranges from 16 to 640 kbps. Downstream data rates depend on a number of factors, including the length of the copper line, its wire gauge, the presence of bridged taps and cross-coupled interference. Line attenuation increases with line length and frequency, and decreases as wire diameter increases. Ignoring bridged taps, ADSL will perform as follows:
DATA RATE
WIRE SIZE
DISTANCE
1.5 MBPS
0.5 mm
5.5 km
1.5 MBPS
0.4 mm
4.6 km
6.1 Mbps
 
0.5 mm
3.7 km
6.1 Mbps
 
0.4 mm
2.7 km
One problem is that a real telephone cable has many bridged taps that significantly decrease line length. Another problem is that the flat telephone cable that is used for wiring buildings. Practically these problems render it impossible to provide 6.1 Mbps service to more than 30% of the subscribers. The ADSL home modem is a very complex and expensive apparatus. ADSL Central Office Equipment is very expensive too, because every subscriber line must have its own ADSL office modem. The cost of Central Office ADSL Equipment may be as high as a $300 per subscriber.
The ADSL modem was developed to maximize performance for all available lines. The result is a high performance modem which is not always the most cost-effective solution.
ADSL is not cost-effective due to the following reasons:
DLC's or remote exchanges connect customers located at distances up to 9000 ft from the exchange. Obviously, full high performance ADSL is not need for such short lines. A more economical solution is required.
Current ADSL requires one dedicated central office (C.O.) unit for every customer. This is a very inefficient concept since most of the time only part of the lines are in use so there always are many central office units that are not in use. This inefficiency increases the cost per line and the space needed for ADSL equipment installation. The same service can be provided with a smaller number of units at the C.O. side together with concentration.
ADSL was designed to maximize the data rates on the connection between the customer and the C.O. However, this is usually not the limiting factor. Current Internet communication is limited today by the Internet's back-bone so increased ADSL data rates will not be truly translated to higher end-to-end communication. This is why lately a G.lite standard defined lower targets for the data rates.
ADSL today requires very complex and expensive apparatus at both the C.O. and the customer side.
ADSL was defined to maximize data rates without taking into account the characteristics of the various applications. Some applications require a high downstream bit rate with a very small upstream bit rate e.g. high quality video. Other applications require mid range symmetric data rates like video conferencing. Current ADSL supports maximal uplink and downlink data rates both at the same time. The result is a more complex solution that supports more than what is actually needed.
From another point of view, ADSL is a very redundant system, because ADSL was developed for maximal use of bandwidth for telephone cable without considering information sources characteristics.
Another problem of existing ADSL systems is that only one subscriber computer may be connected to an Internet service at the same time.
About 15 million subscribers in the USA have at least 2 computers at home and since it is impossible to connect every home computer to the Internet by the same twisted pair, the existing ADSL service limitation is a clear drawback.
In accordance with the present invention, the disadvantages and problems associated with the ADSL system have been substantially reduced or eliminated. In particular, Source Adaptive Digital Subscriber Line (SADSL) provides data service to a subscriber in three operation modes: asymmetric mode, half-asymmetric mode and symmetric mode, according to the information source characteristics.
The SADSL uses QAM or DMT modulation for transmitting downstream and upstream data. The symbol rate of the upstream signal is several times less then the symbol rate of the downstream signal. SADSL transmits downstream and upstream data on the same twisted pair of telephone cable using time division modulation (TDM). The transmission frame of SADSL includes a downstream time interval for downstream symbols and an upstream time interval for upstream symbols. The transmission frame of SADSL has a constant duration in any operation mode but downstream and upstream time intervals have a different duration in different operation modes. Symbols of the synchronization word and symbols of the frame control word are added to downstream data symbols. Symbols of the acknowledges word are added to upstream data symbols.
In accordance with the present invention, information sources that may be connected to the subscriber end of SADSL are divided into three groups:
1. Asymmetrical information sources. These sources require a high bit rate downstream and produce only output control signals with a very low bit rate.
Downstream
Upstream
This group includes:
Digital TV
6.1 Mbps
 
16 Kbps
Digital HI FI AUDIO
1.5 MBPS
16 Kbps
Compressed Video
1.5 MBPS
16 Kbps
This group relates to the following situation: the subscriber only receives data from the network server.
2. Half-asymmetrical information sources. These sources receive high bit rate downstream data and produce upstream date with a low bit rate.
Downstream
Upstream
This group includes Internet
~
1.0 Mbps
~
100 Kbps
 This group relates to the following situation: the subscriber receives data from a network server and transmits data to a network server.
3. Symmetrical information sources. These sources require the same middle bit rate upstream data and downstream data.
Downstream
Upstream
This group includes Video Conference
384 kbps
384 kbps
and Video Phone
 This group relates to the following situation: information can be exchanged between subscribers.
Since the amount of information produced by one subscriber is significantly less than the amount of information produced by a network server, every current and future data service will be related to one of the three groups mentioned above.
The Source Adaptive Digital Subscriber Line may work in one of three operation modes, corresponding to three groups of information sources. Selection of the operation mode is implemented during an initialization phase of the communication session. A communication session means here the cycle of information exchange with the current information source. There are many communication sessions with different sources during one connection to a subscriber.
The SADSL Central Office may support communication of many different home modems located at the same house and in different houses as well. Various upstream and downstream data bit rates can be supported. The initialization proce

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