Encoding Neil Tang 9142009

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Encoding Neil Tang9/14/2009
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Outline

• Encoding/Decoding
• Non-Return to Zero (NRZ)
• Non-Return to Zero Inverted (NRZI)
• Manchester
• 4B/5B

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Encoding

• Signals Different signals correspond to
  different power levels, frequencies and so on.
• Encoding/Decoding the procedure to transfer
  binary data (the signals) to the signals (binary
  data).

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NRZ

• 1 ? High Signal
• 0 ? Low Signal

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Problems

• Cause long strings of 1s and 0s
• Baseline Wander Too many consecutive 1s or 0s
  cause the average signal strength to change,
  making it more difficult to detect a significant
  change in the signal.
• Clock Drift A long period of time without a
  transition leads to clock drift.

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NRZI and Manchester

• NRZI
• 1 ? a transition from the current signal
• 0 ? stay at the current signal
• Manchester
• 1 ? high-to-low transition
• 0 ? low-to-high transition
• Differential Manchester
• 1 ? the first half signal equals to the last half
  of the previous bits signal
• 0 ? the first half signal is opposite to the last
  half of the previous bits
• signal

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NRZI and Manchester
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Problems

• NRZI consecutive 0s
• Manchester inefficient because link bit rate is
  half of the baud rate.
• Baud Rate (symbol rate) the number of distinct
  symbolic changes (signaling events) per second.

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4B/5B

• Basic Idea
• Every 4 bits of actual data are encoded in a
  5-bit code that is transmitted using NRZI.
• No more than one leading 0 and no more than two
  trailing 0s in a 5-bit code, i.e., no more than 3
  consecutive 0s.