ADSL: DMT OR CAP

There are two main modulation methods that can be used with the ADSL technology , the first one is the DMT and the second is CAP - carrierless Amplitude Phase modulation which is a multilevel multiphase encoding method . The CAP algorithm's give the data bit combinations a form of both Amplitude and phase and in this way creates a number of signals to be send over the Twisted pair lines . Not like the DMT , CAP uses the whole frequency range from 4KHz up to 1.1MHz as one channel.CAP is used today in some of the modem communication standards like V.32/V.32bis.

The number of signals that the CAP can generate depends on the amount of information bits we want to send over the line , by using different algorithm's CAP can adjust the bit rate of the ADSL session in real-time.

Main advantages of CAP are:

* Lower cost.
* Lower latency.
* Rate adaptivty.

On the other hand DMT is considered a more reliable and sophisticated technology and meny believe it will dominate the future communication world.

The ITU/TSS ADSL standard defines the DMT as the modulation method to be used in ADSL communication equipment but some of the manufacturers are working on a different standard which will use the CAP technology.