1. Why to Apply Digital Transmission?
Digital transmission system
Why to Apply Digital Transmission?
Advantages of Digital Communication Over Analog Modulation:            There are many advantages of using Digital Communication over Analog Communication. Some of them are listed as below: The digital communication has mostly common structure of encoding a signal so devices used are mostly similar.
The Digital Communication's main advantage is that it provides us added security to our information signal.
The digital Communication system has more immunity to noise and external interference.
Digital information can be saved and retrieved when necessary while it is not possible in analog.
Digital Communication is cheaper than Analog Communication.
The configuring process of digital communication system is simple as compared to analog communication system. Although, they are complex.
In Digital Communication System, the error correction and detection techniques can be implemented easily.

2. Transmitted power;
bandpass/baseband signal BW
Digital Transmission
Information:
- analog:BW & dynamic range
- digital:bit rate
Information
source
Message
estimate
Message
Information
sink
Source
encoder
Maximization of information transferred
Source
decoder
In baseband systems
these blocks are missing
Channel
Encoder
Channel
decoder
Message protection & channel adaptation;
convolution, block coding
Interleaving
Deinterleaving
Modulator
Demodulator
Fights against burst errors
Received signal (may contain errors)
Transmitted
signal
Channel
M-PSK/FSK/ASK..., depends on channel BW & characteristics
wireline/wireless
constant/variable
linear/nonlinear
Noise
Interference
‘Baseband’ means that no carrier wave modulation is used for transmission

4. Intersymbol Interference
Intersymbol interference (ISI) occurs when a pulse spreads out in such a way that it interferes with adjacent pulses at the sample instant.
Example: assume polar NRZ line code. The channel outputs are shown as spreaded (width Tb becomes 2Tb) pulses shown (Spreading due to bandlimited channel characteristics).
Channel Input
Pulse width Tb
Channel Output
Pulse width Tb
Data 1
Data 0

5. Intersymbol Interference
For the input data stream:
The channel output is the superposition of each bit’s output: 1
Resultant Channel Output Waveform 1

6. Band Width
The numerical difference between the upper and lower frequencies of a band of electromagnetic radiation, especially an assigned range of radio frequencies is called Band Width.

9. Parity Bit:
Parity Checking:

10. Limitations: