Preface

Abstract

This issue of the Journal is dominated by a set of papers presenting theoretical studies and computer simulations devoted to optimization of several types of multiuser wireless systems.
This part begins with two papers written by M. Addad and A. Djebbari. The first one, titled “Suitable Spreading Sequences for Asynchronous MC-CDMA Systems”, presents new codes for broadband Visible Light Communications (VLV) – a method relying on modulated light emitted by light emitting diodes (LEDs) for short-range data transmission in various environments. Optical Code Division Multiple Access (OCDMA) is a strong candidate for VLC applications. Multiple access interference is the predominant source of bit errors, as it  causes transmission errors when system users are transmitting asynchronously. In this case, the so-called Zero Cross-Correlation (ZCC) codes (orthogonal sets of sequences where no overlapping of ones occurs and a zero zone exists) ensure the best system performance, also in the presence of synchronization problems and multipath propagation. (...)