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 How the Short PN Code is Used: Shifted versions of the same PN Sequence exhibit very good (but not excellent) cross-correlation properties, (-1/L). So, we can use the various offsets of the same sequence as different codes: 1 - In principle, all 32,768 offsets of the Short PN Code can be respectively treated as different codes since they are mutually isolated by a cross-correlation factor of -1/L, while maintaining an auto-correlation factor of 1. 2 - However, if two adjacent offsets are used, a Multipath of the leading sequence (delayed by exactly one chip) would look identical to the lagging sequence. 3 - In IS-95, a 64-chip separation is recommended between Short PN Offsets. A one-chip distance is [3•10exp(8)/1.2288•10exp(6)] or 244m. So, a 64-chip separation represents a minimum Multipath separation distance of 15,616m. 4 - A 64-chip offset separation on the Short PN Code yields 512 offsets that will be used to isolate cells and sectors. CODE: AN INTRODUCTION By Dr. Ernest Simo © 1999 DR. ERNEST SIMO - SPACE2000