By Dr. Ernest Simo
17.0 Summary of PN Codes Properties
Some key characteristics of Pseudo-random Noise sequences or PN codes can be summarized as follows:
- An N-stage Linear Shift Register can be used to generate PN sequences, yielding codes with a maximum length L = 2 N - 1
- In IS-95 systems, two types of PN codes are used:
- 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.
- 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 full length Auto-correlation of a PN code is equal to the code length (L). Normalized over the length, it is 1.
- 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!
- PN codes exhibit randomness properties and can be suitably used as spreading and scrambling sequences.
© 2001 DR. ERNEST SIMO - SPACE2000