Digital communication

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Digital communication
H V KUMARASWAMY
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Topics to be covered in this session
I Minimum shift keying II M-ary FSK III
M-ary PSK
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Minimum shift keying
Proper utilization of phase during detection, for
improving noise performance Complexity
increases CPFSK (Continuous-phase frequency-shift
keying)
.
?(0) denotes the value of the phase at time t0
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An angle-modulated wave

?(t) is the phase of s(t), continuous function of
time.
Carrier frequency
Phase
Deviation ratio
Measured with respect to bit rate 1/Tb
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At time tTb

Phase Tree
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Phase Trellis, for sequence 1101000
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In terms of In phase and Quadrature Component

h1/2
Sign corresponds to symbol 1 - Sign corresponds
to symbol 0
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In phase components
For the interval of

Half cosine pulse
Sign corresponds to ?(0) 0 - Sign corresponds
to ?(0) ?
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Quadrature components

Sign corresponds to ?(Tb) ?/2 - Sign
corresponds to ?(Tb) -?/2
Half sine pulse
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• Four possibilities

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Basic functions

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coefficients

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Signal Space Characterization of MSK

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MSK receiver

Q-channel
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Sketch the waveform of the MSK signal for the
sequence for the 101101.Assume that the carrier
frequencya) Is 1.25 times the bit rate. b) Equal
to the bit Solution (a) fc (f1f2)/2 1.25/ Tb
OR f1f22.5/Tb Also f1-f21/(2Tb) Solving
f11.5/Tb f21/Tb (b) fc1/Tb
f1f22/Tb f1-f21/(2Tb)\
Solving f11.25/Tb f20.75/Tb
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conclusion