PN Sequences - Part 2 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: 1 - An N-Stage Linear Shift Register can be used to generate PN Sequences, yielding codes with a maximum length L = 2N - 1 2 - 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. 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. CODE: AN INTRODUCTION By Dr. Ernest Simo © 1999 DR. ERNEST SIMO - SPACE2000