Page 21 - Broadband Internet The Basics for Next Generation Networks (NGN) in Telecommunication.

ADSL Frequency

Bands and

Modulation

ADSL frequency bands ADSL Modulation

The physical layer (OSI-1) of ADSL is The band 0–4 kHz is used for POTS.
designed to be able to coexist with The band 25–160 kHz is allocated for
standard POTS spectrum. upstream data.
The two services can coexist because The band 240 kHz to 1.5MHz is used for
ADSL is using a higher frequency downstream data transmission.
spectrum than the baseband spectrum DMT (discrete multitone) modulation is
used for POTS. used in ADSL.
the frequency band dedicated for voice DMT is a method of separating a DSL signal
in POTS is 0.3–3.4 kHz, but the so that the usable frequency range is
bandwidth between 3.4 and 4.0 kHz is separated into 256 frequency bands
needed as guard band (to avoid (channels) of 4.3125 KHz each.
interference) for dial-up modem Within each channel, modulation use
communication specified in V.90 quadratude amplitude modulation (QAM).
standard. By varying the number of bits per symbol
ADSL is full duplex communication within a channel, the modem can be rate-
achieved either by FDD (Frequency adaptive.
Division Duplex), TDD (Time Division
Duplex) or ECD (Echo-Canceling Duplex).
.In this case, the ADSL uses spectrum
between 25 and 1104 kHz.
The lower band between 25 and 138 kHz
is used for upstream communication
(i.e., uplink), and the higher band
between 138 and 1104 kHz is used for
the downstream communication
(downlink).

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