DIGITAL TRANSMISSION

DIGITAL TRANSMISSION

1. Digital-to-Digital

   • Line Coding
     • • Process of converting digital data (sequence of bits)to digital sgnals
     • Characteristics
       • level representing signal and data element
         • Data element
           • The smallest entity that represent a piece of information (bit)
         • Signal element
           • The shortest unit (timewise)of a digital signa to carry data element
       • Pulse rate and bit rate
         • Bit/Data rate (bps)
           • number of data bits send in 1s
         • Pulse/Signal rate (baud)
           • number of signal elements sent in 1s
         • pulse_rate = c x bit_rate x 1/r
       • DC Componenets
         • signal that have zero frequency and the average amplitude is nonzero
           • undesirable by
             • possibilities of signal distortion
             • Omit extra energy residing on the line
       • Self-synchronization
     • Line Coding Scheme
       • Unipolar
         • • --> uses only one voltage level --> +ve = bits 1 , -ve = bits 0
       • Polar
         • NRZ(Nonreturn-to-zero)
           • NRZ-L
             • • Bit 1 = -ve , Bit 0 = +ve
           • NRZ-I
             • Bit 1 = inversion , Bit 0 = No Changes
         • RZ
           • • Bit 1 = positive to zero , Bit 0 = negative to zero
         • Biphase
           • Manchester (RZ+NRZ-L)
           • Differential Manchester(RZ+NRZ-l
       • Bipolar
         • Alternate Mark Inversion (AMI)
           • • Bit 1 = +ve & -ve alternately , Bit 0 = 0V
       • Multilevel
       • Multitransition
   • Block Coding
     • Improve line coding performance by including redundant bits to detect errors
     • steps in transformation
       • 1.Division
       • 2.Substitution
       • 3.Line Coding

2. Analog-to-Digital

   • Transmission Modes
     • Parallel Transmission
     • Serial Transmission
     • Asynchronous
     • Synchronous
   • Applicable techniques
     • Pulse Code Modulation (PCM)
       • Digitization
         • 2.quantizing
         • 3.encoding
         • 1.sampling
           • Based on Nquist theorem
             • band-limited
             • sampling rate = 2 x highest f
             • intervals = 1/sampling_rate
     • Delta Modulation

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