ADSL & PPPoE & RADIUS

what the receiver received would not be the original signals any more.
3,3 Proposed modulation formats for ADSL
Modulation is a technique that converts the digital signal (binary 0 and 1)
to analogy signal (such as the sine curve). The signal, that is modulated, is
consist of a whole RF carrier. The modulation is the process of varying the
amplitude, frequency, or phase of an RF carrier wave, the process whereby
some characteristic of one wave is varied in accordance with some
characteristic of another wave. The basic types of modulation are angle
modulation, including the special cases of frequency modulation, amplitude
modulation and phase modulation. The next part is the introduction of different
modulation techniques, which are used in ADSL.
3,3,1 The modulation technique
3,3,1,1 Frequency modulation
Frequency modulation is the simplest modulation. The definition of
frequency is that the number of times an electromagnetic signal repeats an
identical cycle (sine curve) in a unit of time, usually one second. The unit of
frequency is Hz. One Hertz (Hz) is one cycle per second.
There is a simple sample: if on a simple 300 band modem, 1070 Hz stands
for binary value 0 and 1270 Hz stands for binary 1. Then we can transmit the
binary values 0 and 1 by using these 2 frequencies. Of course, we can use
more frequencies to transmit more signals. We can use A, B, C, D four
frequencies to stand for 00, 01, 10, 11 four different signals. This makes the
speed of transmit more quick. And we also transmit 3 bit information at same
time when we use different 8 frequencies.
3,3,1,2 Amplitude modulation
After we know the principle of the frequency modulation, it is easier to
understand the amplitude and phase modulation. In the amplitude modulation,
we distinguish the different information via changing the amplitude,which is
the height of the amplitude. The principle is same as the frequency modulation.
3,3,1,3 Phase modulation
To change the phase of cycle (sine curve) in a specific period, then we
should send a new sine curve when stop to send the old sine curve in the
sender. The new sine curve has the same frequency and the amplitude as the
old sine curve. If we stop the old sine curve and start the new sine curve at the
same, then there will not any difference between the new signal and the old
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