Jun 172009
1. Binary XOR operation allows the original symbol reconstruction.
Do spread:
symbol sequence X (XOR) some code Y => some signal Z
Do despread:
some signal Z (XOR) some code Y => symbol sequence X
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2. Let’s assume there are 10 users who want to send its data X1, X2, …, X10.
Let’s assume they have their own codes Y1, Y2, …., Y10.
Let’s assume they send data at the same time.
Let Z be all summation of Xi (XOR) Yi .
I’m only interested in X1 signal. But, how can I extract X1 from all summed signal Z ?
If Yi are othogonal (i.e., Yi XOR Yj => all zero if i and j are different), then
Z (XOR) Y1 => X1
This is the fundamental concept of spread spectrum.
