Basics of Echo Cancellation

• Telephone network made up of two major components:

  • 4-wire or toll network
  • 2-wire or local network

• 2-wire to 4-wire conversion process (using transformers) leaks signals creating echo

• Round trip echo path delay can range from few milliseconds to hundreds of milliseconds (satellite hops)

• Echo Cancellation is required to suppress the echo and maintain a clean channel

• Echo Cancellers are adaptive filters which model the echo path to generate an estimated echo and subtract it from the real signal.

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