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Digital & analog transmission

Fundamentals in digital transmission

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Digital & analog transmission

  1. 1. INFORMATION TRANSMISSION(DIGITAL AND ANALOG TRANSMISSION)  Digital-to-Digital Conversion  Analog-to-Digital Conversion  Transmission Modes  Digital-to-Analog Conversion  Analog-to-Analog Conversion
  2. 2. DIGITAL TO DIGITAL CONVERSION • The three conversion from digital to digital conversion includes: • Line codding, • block codding and scrambling • Line Codding is the process of converting digital data to digital signals
  3. 3. THE FOLLOWING ARE LINE CODING SCHEMES: • Unipolar, Polar, Bipolar, Multilevel and Multitransition • Block coding is normally referred to as mBlnB coding; • it replaces each m~bit group with an n~bit group.(Block coding)
  4. 4. T • The slash in block encoding (for example, 4B/5B) distinguishes block encoding • from multilevel encoding (for example, 8B6T), which is written without a slash. Block • coding normally involves three steps: division, substitution, and combination.
  5. 5. ANALOG TO DIGITAL CONVERSION • This another technique that covert digital data to digital signal • Pulse code modulation (PCM) and delta modulation. • PCM is the process of digitization. It’s encoder has three process: • 1. Sampling ( 1st step, analog sig is sampled T s where T s is the sample interval or period and its inverse is called sampling rate or frequency. There are 3 sampling methods: ideal(pulses from analog sign. Sampled),natural(high switched is turned on for small period of time) and flattop • 2.
  6. 6. DELTA MODULATION • Is a simplex technique • Difference is the PCM finds the value of the signal amplitude for each sample and DM finds the change from previous sample. • The modulator is used at the sender site to create a stream of bits from an analog signal. The process records the small positive or negative changes, called delta ð. If positive delta records 1 and 0 vice versa
  8. 8. DIGITAL TO ANALOG CONVERSION • The transmission of binary data across a link can be accomplished in either serial or parallel mode. • In parallel mode multiple bits are sent with each clock tick and serial 1 bit is sent in each clock tick. There is only one way to send parallel data and three sub class of serial transmission. • Asynchronous, synchronous and isochronous
  10. 10. PARALLEL & SERIAL • Parallel transmission by grouping, we can send data n bits at a time instead of 1. • Its advantage over serial transmission is in terms of speed. • Serial transmission one bit follows another • It advantage over parallel transmission is that it reduces cost of transmission. But communication with device is parallel hence conversion devices are required at the interface between the sender and the line (p to S) and between the line and receiver (S to P)
  13. 13. ASYNCHRONOUS, SYNCHRONOUS AND ISOCHRONOUS • In Asynchronous is received and translated by agreed upon patterns. Usually 8bits is sent along the link as a unit. • In asynchronous transmission, we send 1 start bit (0) at the beginning and 1 or more • stop bits (Is) at the end of each byte. There may be a gap between each byte. • In synchronous transmission, we send bits one after another without start or stop bits or gaps. It is the responsibility of the receiver to group the bits • In Isochronous transmission , uneven delays between frames are not acceptable. ( TV images -30 ps)
  17. 17. AM • Analog modulation is the representation of analog information by analog signal. • You will ask why modulate to analog signal; it is already analog. • Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is available to us.
  18. 18. AMPLITUDE MODULATION 5-23 • The total bandwidth required for AM can be determined from the bandwidth of the audio signal: BAM = 2B.
  19. 19. FREQUENCY MODULATION 5-24 • The total bandwidth required for FM can be determined from the bandwidth of the audio signal: BFM = 2(1 + β)B.
  20. 20. PHASE MODULATION 5-25 • The total bandwidth required for PM can be determined from the bandwidth and maximum amplitude of the modulating signal: BPM = 2(1 + β)B.