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 Let us examine the simplified processes at each receiver (each Mobile). The received or input to Mobile A is: Input = di(t)• PN(t - t A) + dj(t)• PN(t - t B) Mobile A is assumed to have synchronized with cell A. So, it is tuned to cell A with its local Short PN Code set to PN(t - t A). Mobile A will then "multiply" its local Code PN(t - t A), with the received or incoming input signal . The resulting output signal is: Output = di(t) • PN(t - t A) • PN(t - t A) + dj(t) • PN(t - t B) • PN(t - t A) As noted earlier, the normalized auto-correlation PN(t - t A) • PN(t - t A) is 1. And the normalized cross-correlation PN(t - t B) • PN(t - t A) is -1/L. For large values of L therefore, the second term can be ignored. This simply reduces the output to di(t). (Note that the signal from cell B is nicely ignored!) CODE: AN INTRODUCTION By Dr. Ernest Simo © 1999 DR. ERNEST SIMO - SPACE2000