How PN Codes are used in IS-95 CDMA Systems
By Dr. Ernest Simo
1.0 Using the Short PN Code
Summary of PN Codes Properties:
Some key characteristics of Pseudo-Random Noise Sequences or PN Codes can be summarized as follows:
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1 - An N-Stage Linear Shift Register can be used to generate PN Sequences, yielding codes
with a maximum length L = 2N - 1
- The Short PN Code with a length of 32,768 chips, a speed of 1.2288 million chips per
second and a cyclic period of 26.67 ms.
- The Long PN Code with a length of approximately 4.4 trillion chips, a speed of 1.2288 million chips per second and a period of 41-42 days.
2 - In IS-95 systems, two types of PN Codes are used:
3 - The full length Auto-correlation of a PN Code is equal to the code length (L). Normalized over the length, it is 1.
4 - The full length Correlation of two time-shifted versions of a PN Code is always -1 if their time shift differential is equal or greater than 1 chip. Normalized over the length (L), it is -1/L. Note that for a large value of L, this cross-correlation value is very small. Not zero, however!
5 - PN Codes exhibit Randomness properties and can be suitably used as spreading and scrambling sequences.
PN Sequences - Part 2
By Dr. Ernest Simo
© 1999 DR. ERNEST SIMO - SPACE2000