CDMA (from Tanenbaum, Computer Networks p. 137) Assume the following CDMA chip sequences for +1 (0 has the complementary chip sequence): A: (-1 –1 –1 +1 +1 -1 +1 +1) B: (-1 –1 +1 –1 +1 +1 +1 –1) C: (-1 +1 –1 +1 +1 +1 –1 –1) D: (-1 +1 -1 -1 -1 -1 +1 –1)

Complementary codes (for 0) B: (+1 +1 -1 +1 -1 -1 -1 +1) C: (+1 -1 +1 -1 -1 -1 +1 +1) D: (+1 -1 +1 +1 +1 +1 -1 +1) To show that these chipsets are orthogonal we assume that A, B, C, D send bits at some time and receiver can recover individual signals

Example A sends 0, B sends 1, C sends 0, D does not send Signals sent 1 1 1 -1 -1 1 -1 -1 -1 -1 1 -1 1 1 1 -1 1 -1 1 -1 -1 -1 1 1 1 -1 3 -3 -1 +1 1 -1 received

Example from CDMA 1 -1 3 -3 -1 +1 1 -1 1 -1 3 -3 -1 +1 1 -1 Multiple this termwise with each of the chipsets At A ((1)(-1) + (-1)(-1) +(3)(-1)+(-3)(1)+ (-1)(1) +(+1)(-1)+ (1)(1) + (-1)(1))/8 = (-1+1-3-3-1-1+1-1)/8 = -8/8 = -1 (for 0) At D (1)(-1) + (-1)(1)+(3)(-1)+ (-3)(-1) + (-1)(-1) +(1)(-1) +(1) 1+ (-1)(-1) = 0 (did not send)