CDMA Code Division Multiple Access

1

• CDMA (Code Division Multiple Access)
• unique code assigned to each user i.e., code
  set partitioning
• used mostly in wireless broadcast channels
  (cellular, satellite, etc)
• all users share same frequency, but each user has
  own chipping sequence (i.e., code) to encode
  data
• encoded signal (original data) X (chipping
  sequence)
• decoding inner-product of encoded signal and
  chipping sequence
• allows multiple users to coexist and transmit
  simultaneously with minimal interference

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CDMA Encode/Decode
Fig. 1
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CDMA two-sender interference
Fig. 2
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Homework

• Consider the single-sender CDMA example in Fig.
  1. What would be the senders output (for the two
  data bits shown) if the senders CDMA code was
  (1, -1, 1, -1, 1, -1, 1, -1)?
• Consider sender 2 in Fig. 2. What is the senders
  output to the channel (before it is added to the
  signal from sender 1) Z 2i,m ?
• Suppose that the receiver in Fig. 2 wanted to
  receive the data being sent by sender 2. Show
  (by calculation) that the receiver is indeed able
  to recover sender 2s data from the aggregate
  channel signal by using sender 2s code.