Line Coding

Introduction

The process of converting digital data to digital signals. Digital data – sequences of bits.

Characteristics

• Data rate vs. signal rate
  • Data rate (bit rate) – the number of data elements in a unit time (bps).
  • Signal rate (pulse, modulation rate, baud rate) – the number of signal element in a unit time (baud).
  • 
• No. of Signal Levels
  • Two data levels,
    Two Signal levels
    
  • Two data levels
    Three signal levels
    
• DC components
  • It is the mean value of the waveform. If the mean amplitude is zero, there is no DC offset.
  • unable to pass a low-pass filter or Over one cycle period if all positive voltage are cancelled by negative volatge then the DC component of the waveform is zero.
  • In line coding, the signal with non-zero dc component is treated as distorted one and it can create errors in the received signal.
• Bandwidth
  • Although the actual bandwidth of a digital signal is infinite, the effective bandwidth is finite.
• Self synchronization
  • the clocks at the sender and the receiver must have the same bit interval. If the receiver clock is faster or slower it will misinterpret the incoming bit stream.