Composite CDMA—a statistical mechanics analysis

Jack Raymond, David Saad

Research output: Contribution to journalArticlepeer-review


Code division multiple access (CDMA) in which the spreading code assignment to users contains a random element has recently become a cornerstone of CDMA research. The random element in the construction is particularly attractive as it provides robustness and flexibility in utilizing multiaccess channels, whilst not making significant sacrifices in terms of transmission power. Random codes are generated from some ensemble; here we consider the possibility of combining two standard paradigms, sparsely and densely spread codes, in a single composite code ensemble. The composite code analysis includes a replica symmetric calculation of performance in the large system limit, and investigation of finite systems through a composite belief propagation algorithm. A variety of codes are examined with a focus on the high multi-access interference regime. We demonstrate scenarios both in the large size limit and for finite systems in which the composite code has typical performance exceeding those of sparse and dense codes at equivalent signal to noise ratio.
Original languageEnglish
Article numberP05015
JournalJournal of Statistical Mechanics
Issue number5
Publication statusPublished - 21 May 2009

Bibliographical note

© 2009 IOP Publishing Ltd and SISSA


  • random graphs
  • networks
  • disordered systems
  • source and channel coding


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