ARTICLE IN PRESS Int. J. Electron. Commun. (AEÜ) ( ) – www.elsevier.de/aeue Local search multiuser detection Leonardo D. Oliveira a , Fernando Ciriaco a , Taufik Abrão b, ∗ , Paul Jean E. Jeszensky a a Telecommunications and Control Engineering Department (EPUSP-PTC), Escola Politécnica of University of São Paulo São Paulo, SP 05508-900, Brazil b Electrical Engineering Department (UEL-DEEL), State University of Londrina, Londrina, PR 86051-990, Brazil Received 13 September 2007; accepted 19 January 2008 Abstract In this work, a wide analysis of local search multiuser detection (LS-MUD) for direct sequence/code division multiple access (DS/CDMA) systems under multipath channels is carried out considering the performance-complexity trade-off. It is verified the robustness of the LS-MUD to variations in loading, E b /N 0 , near–far effect, number of fingers of the Rake receiver and errors in the channel coefficients estimates. A compared analysis of the bit error rate (BER) and complexity trade-off is accomplished among LS, genetic algorithm (GA) and particle swarm optimization (PSO). Based on the deterministic behavior of the LS algorithm, it is also proposed simplifications over the cost function calculation, obtaining more efficient algorithms (simplified and combined LS-MUD versions) and creating new perspectives for the MUD implementation. The computational complexity is expressed in terms of the number of operations in order to converge. Our conclusion pointed out that the simplified LS (s-LS) method is always more efficient, independent of the system conditions, achieving a better performance with a lower complexity than the others heuristics detectors. Associated to this, the deterministic strategy and absence of input parameters made the s-LS algorithm the most appropriate for the MUD problem.  2008 Elsevier GmbH. All rights reserved. Keywords: Multiuser detection; Particle swarm optimization; Local search; Genetic algorithm; Computational complexity 1. Introduction A direct sequence/code division multiple access (DS/ CDMA) system is characterized by the spreading spectrum (SS) through the direct sequence, what results in sharing of the transmission band among all of the active users. The re- ceived signal, composed by the sum of all of the transmitted signals, is usually detected through a Rake receiver. In spite of performing in the sense of to maximize the signal–noise ratio (SNR) and to explore the path diversity, the Rake receiver is unable to eliminate the multiple access interfer- ence (MAI) and the self-interference (SI), resulting in the channel capacity loss. Thus, an increasing number of users ∗ Corresponding author. E-mail address: taufik@uel.br (T. Abrão). 1434-8411/$ - see front matter  2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2008.01.009 sharing the system and power disparities imply in a loss of its performance. An alternative to overcome this is to adopt multiuser detection (MUD) techniques, and the best strategy, in terms of performance, is based on the maximum likelihood function. The optimum multiuser detector (OMUD) 1 proposed by Verdú in 1984 [1] shows that information of the interfer- ing can be used to eliminate MAI from the user of interest. Evolutions of that work [2,3] indicated that the OMUD pos- sesses high-computational complexity and its implementa- tion is not viable in real time, especially when the number of active users in the system becomes expressive. 1 Herein, the acronym MUD is used interchangeably to mean “mul- tiuser detector” (device) or “multiuser detection” (technique). Please cite this article as: Oliveira LD, et al. Local search multiuser detection, Int J Electron Commun (AEU) (2008), doi: 10.1016/j.aeue.2008.01.009