What is equalisation? Why do we need it?

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What is equalisation? Why do we need it?..

Answer / debasis gayen

Adaptive equalization is a
solution
specifically designed to
counteract
the problem of time
dispersion. It
works as follows:
1. A set of predefined
known bit
patterns exist, known as
training
sequences. These are known
to the
BTS and the MS (programmed
at
manufacture). The BTS
instructs the
MS to include one of these
in its
transmissions to the BTS.
2. The MS includes the
training
sequence in its
transmissions to the
BTS. However, due to the
problems
over the radio path, some
bits may be
distorted.
3. The BTS receives the
transmission
from the MS and examines the
training sequence within
it. The BTS
compares the received
training
sequence with the training
sequence
which it had instructed the
MS to use.
If there are differences
between the
two, it can be assumed that
the
problems in the radio path
affected
these bits must have had a
similar
affect on the non-training
sequence
bits.
4. The BTS begins a
process in which it
uses its knowledge of what
happened
the training sequence to
correct the
other bits of the
transmission.