Open AccessGeneralisation of code division multiple access systems and derivation of new bounds for the sum capacity
Author(s) -
Dashmiz Shayan,
Takapoui Mohammad Reza,
Moazeni Sajjad,
Moharrami Mehrdad,
Abolhasani Melika,
Marvasti Farokh
Publication year - 2014
Publication title -
iet communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.355
H-Index - 62
eISSN - 1751-8636
pISSN - 1751-8628
DOI - 10.1049/iet-com.2013.0344
Subject(s) - code division multiple access , injective function , code (set theory) , upper and lower bounds , division (mathematics) , mathematics , computer science , channel (broadcasting) , matrix (chemical analysis) , scheme (mathematics) , channel capacity , algorithm , theoretical computer science , discrete mathematics , arithmetic , telecommunications , set (abstract data type) , mathematical analysis , materials science , composite material , programming language
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.