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.

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

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

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

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.

Parity Bit: Parity Checking:

Limitations: