Finding sub-optimum signature matrices for overloaded code division multiple access systems

• Published in: IET communications Vol. 7; no. 4; pp. 295 - 306
• Main Authors: Khoozani, Mohsen Heidari, Marvasti, Farokh, Azghani, Masoumeh, Ghassemian, Mona
• Format: Journal Article
• Language: English
• Published: Stevenage The Institution of Engineering and Technology 01.03.2013; John Wiley & Sons, Inc
• Subjects: binary inputs; bit error rate; channel capacity; Code division multiple access; computational complexity; conjugate gradient method; Criteria; Design engineering; distance criteria; Enlargement; error statistics; Expansion; genetic algorithm; gradient methods; Mathematical analysis; matrix algebra; matrix dimensions; objective functions; Optimization; overloaded CDMA system; overloaded code division multiple access systems; particle swarm optimisation; signature matrix optimisation techniques; Signatures; small‐scale signature matrices; suboptimum signature matrices; sum channel capacity; distance criteria; particle swarm optimisation; suboptimum signature matrices; channel capacity; objective functions; code division multiple access; overloaded code division multiple access systems; bit error rate; matrix algebra; small-scale signature matrices; genetic algorithm; binary inputs; sum channel capacity; matrix dimensions; overloaded CDMA system; conjugate gradient method; gradient methods; computational complexity; error statistics; signature matrix optimisation techniques
• ISSN: 1751-8628; 1751-8636; 1751-8636
• DOI: 10.1049/iet-com.2012.0208

The objective of this study is to design sub-optimal signature matrices for binary inputs for an overloaded code division multiple access (CDMA) system as developed by this author group. In this study, the authors propose to use the sum capacity, the bit error rate and distance criteria as objective functions for signature matrix optimisation. Three optimisation techniques, the genetic algorithm, the particle swarm optimisation and the conjugate gradient (CG) are exploited in this work. Since the optimisation computational complexity increases by matrix dimensions, it is practically impossible to directly optimise the large signature matrices. In order to address this problem, a method is proposed to enlarge small-scale signature matrices. It is also proved that the sum channel capacity of the enlarged matrix is scaled by its enlargement factor. The results indicate that this proposed signature matrices provide higher sum capacity than the commonly used signature matrices. The authors also address that this matrices are applicable for highly overloaded CDMA systems.