How Spreading & Dispreading in WCDMA-3G ?

  • Traditional radio communication systems transmit data using the minimum bandwidth required to carry it as a narrowband signal. CDMA system mix their input data with a fast spreading sequence and transmit a wideband signal.
  • The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original data. The dispreading gives substantial gain proportional to the bandwidth of the spread-spectrum signal. 
  • The gain can be used to increase system performance and range, or allow multiple coded users, or both. A digital bit stream sent over a radio link requires a definite bandwidth to be successfully transmitted and received.

Eb / No = Ec / No ×PG