Wireless Pers Commun (2007) 42:537–542 DOI 10.1007/s11277-006-9209-4 Iterative near–far resistant channel estimation by using a linear minimum mean squared error detector Ahmet Rizaner · Hasan Amca · Kadri Hacıo˘ glu · Ali Hakan Ulusoy · Ansgar Scherb Received: 18 November 2004 / Accepted: 10 September 2006 / Published online: 28 June 2007 © Springer Science+Business Media B.V. 2007 Abstract Channel estimation techniques for CDMA system need to combat multiple access interference (MAI) to improve the estimation performance. The linear MMSE detector has certain advantages with res- pect to the near–far problem and can be used to develop a channel estimation algorithm. In this paper, an effi- cient iterative method for near–far resistant single-user mobile radio channel estimation in slow fading multi- path direct sequence code division multiple access (DS-CDMA) channels is presented. Computer simula- tion results demonstrate that a significant performance improvement can be achieved with the proposed method especially under extreme near–far conditions. Keywords CDMA · Multi-path channel · Channel estimation A. Rizaner (B ) · H. Amca · A. H. Ulusoy Department of Information Technology, School of Computing and Technology, Eastern Mediterranean University, Magosa-KIBRIS, Mersin 10, Turkey e-mail: ahmet.rizaner@emu.edu.tr K. Hacıo˘ glu University of Colorado at Boulder Center for Spoken Language Research Boulder, Boulder, CO 80309, USA A. Scherb Department of Communications Engineering, University of Bremen - FB1, D-28334, Bremen, Germany 1 Introduction Reliable coherent communication over mobile wireless channels requires accurate estimation of time-varying multipath channel parameters. Multiple access inter- ference (MAI) and near–far resistance are the main factors affecting the performance of channel estima- tion techniques for direct sequence code division mul- tiple access (DS-CDMA) systems. Although, several multi-user channel estimation algorithms have been proposed to mitigate MAI, these algorithms require high-computational complexities [2, 5]. In addition, the knowledge of the spreading sequences and timings of all the users are required. A multi-user near–far resis- tant channel estimation problem is addressed in [5] by using a linear decorrelating detector to remove the MAI prior to channel estimation. The techniques developed for single-user communications, are mostly devoted to combat Gaussian white noise. However, even a small amount of near–far effect can drastically degrade the performance of single-user estimators and strict power control is necessary for reliable estimation. The effects of the near–far problem on the performance of the single-user channel estimation systems have not yet been fully investigated, and practical solutions to the near–far resistant estimation problem is still to be found. A single-user near–far resistant channel esti- mation problem is considered in [1] where interfering users are modeled as colored non-Gaussian noise. In this approach, a maximum-likelihood estimation technique is used that requires the knowledge of the 123