CDMA (from Tanenbaum, Computer Networks p. 137)
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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)
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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
Transcript of CDMA (from Tanenbaum, Computer Networks p. 137)
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)
• 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
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 • 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)
