Jun 212009
Pseudorandom codes are used at the scrambling phase in UMTS.
It identifies the specific UE to the Node B and it identifies specific Node B using a unique scrambling code.
Good auto-correlation (strong correlation) and good cross-correlation (low correlation) are good characteristics for PN codes.
Auto-correlation measures the correlation between the signal and a time-delayed version of itself. It is used in initial synchronization.
Cross-correlation measures the correlation between a signal and some other code. If this value is low, the interference level is low.
It is difficult to find a high auto-correlation and low cross-correlation at the same time. There should be some tradeoff.
