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Digital communication (Optimum reception of digital data (Optimum filter…
Digital communication
Optimum reception of digital data
Probability of error
Optimum filter
Polar non-return zero signal
Matched filter
Probability of error for ASK
Probability of error for BPSK
Probability of error for BFSK
Pulse modulation system
Sampling
Instantaneous sampling
Natural sampling
Flat top sampling
Modulation system
Pulse amplitude modulation
Sample and hold circuit is used for generation
Pulse width modulation
Comparator is used for generation
Pulse position modulation
Comparator along with monostable multivibrator is used for generation
Quantization
Companding
Micro law companding
A law companding
Time division multiplexing
Consists
LPF
Commutator
Pulse modulator
Communication channel
Pulse demodulator
Decommutator
Principle of digital data transmission
Line coding
Types
Unipolar non return to zero signaling.
Polar non- return- to -zero signaling.
Unipolar return- to -zero signaling
Bipolar return-to-zero signaling
Split-phase (manchester code)
Pulse shaping
Necessary to limit the bandwidth of signal before transmission.
Scrambling
Helpful in timing extraction by removing long string of zeros in binary data.
It consist of a feedback shift register and the matching descrambler has a feed forward shift register.
Regenerative repeater
Consists
Transmission medium
Preamplifier and equalizer
Sampler and decision
Timing extraction
Regenerator
Eye daigram
It is a pattern displayed on the screen of CRO.
To study the inter symbol interference and it's effect on a PCM .
Eye pattern obtained by applying the received signal to vertical deflection plates of CRO and a sawtooth wave at transmission symbol rate to the horizontal deflection plates.
Digital transmission of analog data
Pulse code modulation
No. Of bit = 4,8 or 16.
Quantization error depend on no. Of bits.
Highest transmission bandwidth .
No feedback.
Complex system
Delta modulation
Use only one bit .
Granular noise are present.
Lowest bandwidth.
Feedback exist.
Simple construction.
Adaptive delta modulation
One bit is present.
Noise is present.
Lowest bandwidth.
Feedback exists.
Simple in construction
Differential code modulation
More than one bit is used but less than pcm.
Noise is present.
Bandwidth required.
Feedback exists.
Simple in construction.
Digital modulation techniques
Coherent digital modulation techniques
Binary
Amplitude shift(on-off keying)
Variable characteristics- amplitude
Bandwidth- 2f
Noise immunity low
Error probability high
Keying -ASK
Frequency shift
Variable characteristics-frequency
Bandwidth- 4f
Noise immunity high
Error probability low
Keying-FSK
Phase shift
Variable characteristics-phase
Bandwidth-2f
Noise immunity low
Error probability low
Keying-PSK
M-ary
M-ary ASK
M-ary FSK
M-ary PSK
Bandwidth increase with no. Of bits
Probability of error increase with bits
M-ary amplitude phase keying - QAM
Non-coherent digital modulation techniques
Binary
Non-coherent ASK
Non-coherent FSK
DPSK
Variable characteristics phase
Bandwidth f
Error probability higher
Noise effect high
M-ary
M-ary non-coherent ASK
M-ary non-coherent FSK