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access icon free Generalisation of code division multiple access systems and derivation of new bounds for the sum capacity

  • Author(s): Shayan Dashmiz 1 ; Mohammad Reza Takapoui 2 ; Sajjad Moazeni 3 ; Mehrdad Moharrami 4 ; Melika Abolhasani 5 ; Farokh Marvasti 4
    • View affiliations
    • Affiliations: 1: Department of Finance, London School of Economics and Political Sciences, London WC2A 2AE, UK;
      2: Electrical Engineering Department, Stanford University, Stanford, CA 94305, USA;
      3: Electrical Engineering and Computer Science Department, University of California at Berkeley, Berkeley, CA 94720-1770, USA;
      4: Advanced Communication Research Institute (ACRI), Department of EE, Sharif University of Technology, Tehran 1455618181, Iran;
      5: Department of Computer Science, University of Maryland, College Park, MA 20742, USA
  • Source: Volume 8, Issue 2, 23 January 2014, p. 153 – 162
    DOI:  10.1049/iet-com.2013.0344 , Print ISSN 1751-8628, Online ISSN 1751-8636
© The Institution of Engineering and Technology
Received 15/07/2012, Accepted 20/08/2013, Revised 16/08/2013, Published 07/01/2014

In this study, the authors explore a generalised scheme for the synchronous code division multiple access (CDMA). In this scheme, unlike the standard CDMA systems, each user has different codewords for communicating different messages. Two main problems are investigated. The first problem concerns whether uniquely detectable overloaded matrices (an injective matrix, i.e. the inputs and outputs are in one-to-one correspondence depending on the input alphabets) exist in the absence of additive noise, and if so, whether there are any practical optimum detectors for such input codewords. The second problem is about finding tight bounds for the sum channel capacity. In response to the first problem, the authors have constructed uniquely detectable matrices for the generalised scheme and the authors have developed practical maximum likelihood detection algorithms for such codes. In response to the second problem, lower bounds and conjectured upper bounds are derived. The results of this study are superior to other standard overloaded CDMA codes since the generalisation can support more users than the previous schemes.

Inspec keywords: channel capacity; matrix algebra; codes; code division multiple access; maximum likelihood detection

Other keywords: detectable overloaded matrices; synchronous code division multiple access; codewords; generalised scheme; injective matrix; sum channel capacity; one-to-one correspondence; maximum likelihood detection algorithms; standard CDMA systems; overloaded CDMA codes; conjectured upper bounds

Subjects: Algebra; Radio links and equipment; Multiple access communication; Codes; Other topics in statistics

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