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 Using the Short PN Code: Summary The 32,768 chip long Short PN Code is truncated into 512 starting-offsets where adjacent offsets are separated by 64 chips. On the Forward Link, Short PN Offsets are assigned to cells and sectors (One PN Offset per omnicell or per sector) on a dedicated basis. Used as such, they provide isolation between cells or sectors due to their relatively small cross-correlation factor. Because they exhibit randomness properties, Short PN Codes are also used to provide quadrature spreading on the Forward Link. So, two Short PN Sequences are actually used: An in-phase sequence PNi(t - t A) and a Quadrature Sequence PNq(t - t A). These two sequences have the same length, same speed of 1.2288 million chips per second, the same phase (t A) for a given cell or sector, but they have different generating-polynomials (different Shift Register Taps). In the Reverse Link, the zero-offset of the Short PN Code pair PNi(t- 0)) and PNq(t- 0) is used to provide Quadrature PN Spreading at the Mobile. CODE: AN INTRODUCTION By Dr. Ernest Simo © 1999 DR. ERNEST SIMO - SPACE2000