Spreading Codes:
| di(t) | +1 | +1 | +1 | +1 | -1 | -1 | -1 | -1 | +1 | +1 | +1 | +1 |
| ci(t) | -1 | +1 | +1 | -1 | -1 | -1 | +1 | -1 | +1 | +1 | -1 | -1 |
| di(t) · ci(t) | -1 | +1 | +1 | -1 | +1 | +1 | -1 | +1 | +1 | +1 | -1 | -1 |
| di(t) · ci(t) | -1 | +1 | +1 | -1 | +1 | +1 | -1 | +1 | +1 | +1 | -1 | -1 | ci(t) | -1 | +1 | +1 | -1 | -1 | -1 | +1 | -1 | +1 | +1 | -1 | -1 |
| di(t) · ci(t) · ci(t)=di(t) | +1 | +1 | +1 | +1 | -1 | -1 | -1 | -1 | +1 | +1 | +1 | +1 |
Furthermore, in order to provide good isolation between users (Code Division Multiple Access), a set of orthogonal codes must be used.
The codes used in practice are not perfectly orthogonal. However, they exhibit very good isolation characteristics.
Linear Shift Registers are used to generate the kind of spreading codes utilized in CDMA-based IS-95 systems. They are referred to as Pseudo-Random Noise (PN) codes or sequences.
CODES: AN INTRODUCTION
By Dr. Ernest Simo
© 1999 DR. ERNEST SIMO - SPACE2000