Spreading Technology in WCDMA
Spreading consists of 2 steps:
- Channelization operation, which transforms data symbols into chips
- Scrambling operation is applied to the spreading signal
- Spreading means increasing the bandwidth of the signal beyond the bandwidth normally required to accommodate the information. The spreading process in UTRAN consists of two separate operations: channelization and scrambling.
- The first operation is the channelization operation, which transforms every data symbol into a number of chips, thus increasing the bandwidth of the signal. The number of chips per data symbol is called the Spreading Factor (SF). Channelization codes are orthogonal codes, meaning that in ideal environment they do not interfere each other.
- The second operation is the scrambling operation. Scrambling is used on top of spreading, so it does not change the signal bandwidth but only makes the signals from different sources separable from each other. As the chip rate is already achieved in channelization by the channelization codes, the chip rate is not affected by the scrambling.