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o Based
on the above
two facts, instead
of utilizing only
two variations of a
signal,
each representing one bit, we can use four variations and let each phase
shift
represent two bits
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4PSK
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BW for PSK
o Minimum bandwidth required for PSK
transmission is the same
as
ASK
o As we have seen max bit rate in PSK is
much greater than that
of
ASK
o So
while max baud
rate of ASK
and PSK are
the same for
a
given
BW, PSK bit rate using the same BW can be two or more
times
greater
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8 PSKK_
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ƒ QAM
•
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Limitations of
PSK:
-PSK is
limited by the
ability of the
equipment to distinguish
small
differences
in phase
-This factor
limits its potential bit rate
-So far
we have been
changing only of
the characteristics of
the sine
wave,
But what if we alter two
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o What should these two characteristics be?
o BW limitations make combination of FSK
with other changes practically useless
o Why not combine ASK and PSK?
o 'x'
variation in phase
and 'y variations
in amplitude result
into a total
of x * y
variations
and corresponding no. of bits per variation
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