Research About Splitterless Adsl

RESEARCH ABOUT SPLITTERLESS ADSL

Zeyu Li

ABSTRACT

Splitterless ADSL is also known as ADSL Lite or G. Lite. It is a variant of ADSL that doesn’t require splitters to separate voice from data. So splitterless ADSL is easy to install at the customer’s premise. Without splitters, it should use some other technologies such as called in-line low pass filter (distributed microfilters) with each telephone or improved or modified ADSL modem to avoid the interference between voice and data. This research paper shall introduce the background of splitterless ADSL, problem with splitterless ADSL and technologies used in splitterless ADSL in details. In the end, make a conclusion about splitterless ADSL technology.

BACKGROUND OF SPLITTERLESS ADSL

Classical ADSL use a splitter at customer’s premise to separate low-frequency voice signals from high-frequency ADSL signal. However, splitterless ADSL is a lite version of ADSL. It eliminates the splitter and ADSL modem directly link to the telephone line. Figure 1 and 2 show the difference between splittered ADSL and splitterless ADSL.

[pic 1]

figure 1. splittered ADSL

[pic 2]

figure 2. splitterless ADSL

In the figure 2, it shows that teplephone and ADSL modem are linked in to one shared telephone line.

By eliminating the splitter, it can reduce the cost of installation and enable easier installation of ADSL. Also it is convenient to realise data communication.

PROGRAM WITH SPLITTERLESS ADSL

Without splitters in the customer’s premise, it is obviously that POTS service can easily leak into ADSL data transimission and ADSL signals also leak into POTS signals.

Splitterless ADSL encounters  an interesting problem. When telephones go on-hook and off-hook, transients can be occurred which will cause ADSL modem to lose synchronization and reduce the quality of voice.

For example, when all telephone are on-hook, data can transmit correctly and successfully between computers and Internet, But when one or more

[pic 3]

figure 3. all telephone are on-hook

telephones change their state from on-hook to off-hook, meanwhile, the computer is using ADSL modem to connect to the Internet, the data traffic and interference will happen. Although the period is short and qucik, it can be enough to bring some data transmission errors. We can analysis this interesting situation in details.

The input impedance of an telephone is different because the different state of  telephone. Suppose when all telephone are on-hook, the input impedance is Zon and suppose the input impedance of the telephone line and ADSL modem are Z0 and Zmod respectively. When one or more telephone become off-hook state, it will induce a new input impedance from this telephone which supposed to be Zoff. Because the change of input impedance of telephone from Zon to Zoff will cause the change of input impedance of telephone line from Z0 to Z0’, a part of energy of the transmitted data signal transits through the upper branch in figure 4 and reduce the quality of voice.