Code Correlation
In this context, correlation has a specific mathematical meaning. In general the
correlation function has these properties:
• It equals 1 if the two codes are identical
• It equals 0 of the two codes have nothing in common
Intermediate values indicate how much the codes have in common. The more they have
in common, the harder it is for the receiver to extract the appropriate signal.
There are two correlation functions:
Cross-Correlation: The correlation of two different codes. As we’ve said, this should
be as small as possible.
Auto-Correlation: The correlation of a code with a time-delayed version of itself. In
order to reject multi-path interference, this function should equal 0 for any time delay
other than zero.
The receiver uses cross-correlation to separate the appropriate signal from signals meant
for other receivers, and auto-correlation to reject multi-path interference.