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CDMA (from Tanenbaum, Computer Networks)

CDMA (from Tanenbaum, Computer Networks). 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).

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CDMA (from Tanenbaum, Computer Networks)

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  1. CDMA (from Tanenbaum, Computer Networks) 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)

  2. Complementary codes (for 0) • 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) • 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

  3. Example • A sends 0, B sends 1, C sends 1, 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

  4. Example from CDMA 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)

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