Editorial

Abstract

Welcome to the second issue of Volume 2 of Wireless Communications and Mobile Computing/ (WCMC). We have been receiving a large number of great articles and we would like to assure you that we are grateful for your contributions. Our fast review process and publication turnaround has caught the attention of our authors and readers. We are working hard with the John Wiley staff to make the review process more efficient by introducing a new system soon. Once that is implemented, we will be able to process more manuscripts in a short span of time. In the meantime, we appreciate receiving your quality manuscripts and would like to invite you to sit back and enjoy reading the articles in this issue. As always, we welcome your contributions, whether by submitting manuscripts and/or special issues. We also appreciate any comments/feedback you have regarding WCMC. Send your comments to any of the editors and/or to the Wiley office. Multicast protocols in mobile ad-hoc networks have been an area of active research for the past couple of years. In the first paper, Papavassiliou and An discuss the issues, challenges, and protocols related to multicasting in mobile ad-hoc wireless networks. They survey several existing multicasting protocols in mobile ad-hoc networks and summarize the activities of recent advances in the field. A qualitative comparison of these protocol characteristics according to several distinct features and performance parameters is presented. Finally, they present an overview of research and development efforts in the area of group mobility modeling in mobile ad-hoc networks. Next, Cui and Bassiouni present an analysis of hierarchical cellular networks with mobile base stations, termed as totally mobile wireless networks (TMWNs). Their performance evaluation concentrated on comparing the results of a two-tier system's throughput, handoff blocking rate and new call success rate with those obtained by a one-tier model. Under all load conditions, their results show that the two-tier system outperforms the one-tier system if the number of channels is kept the same. Other conditions have been studied and results have been presented. An analytical model to compute the new call and handoff blocking probabilities in TMWN is given and evaluated. Extensive results are presented. In the third article, a software architecture for GPRS session management (SM) is presented by Haung and Lin. This software architecture is designed to accommodate 3G wireless networks. It is compatible, modular, and flexible. The aim of the architecture is to support a GPRS support node. In a situation where single-band and dual-band PCS handsets co-exist, the channel assignment becomes a concern. In the fourth article, Chang and Li propose load-balancing channel assignment schemes to improve the system performance. To further improve the system capacity, a channel reassignment scheme is also presented. Modeling and simulation results are carried out. The results indicate that both load-balancing and channel re-assignment techniques significantly increase the system capacity as the percentage of dual-band handsets increases. Furthermore, the load-balancing with channel re-assignment scheme that combines both techniques achieves the best system performance, even when the percentage of dual-band handsets is as low as 25%. To reduce the peak-to-average power ratio (PAR) of an orthogonal frequency division multiplexing (OFDM) signal, a set of fixed permutations are used by Jayalath and Tellambura. This set of permutations is applied on K − 1 interleavers are used to produce K − 1 permuted sequences from the same information sequence. To reduce the technique's complexity, an adaptive approach is adapted. Simulation results show that random interleavers and odd-even symmetric interleavers are performing equally well in reducing the PAR. Other results for the out-of-band radiation and the bit error rate performance of interleaved OFDM (IOFDM) and conventional OFDM are also presented and discussed. In the sixth paper, Liu and Li propose a new modulation scheme to improve the performance of DS-CDMA systems in fast time-dispersive fading channels called differential space–time modulation for DS-CDMA (DST-CDMA). They study three different types of receivers using this new scheme. Then, they compare the three types under different design combinations. Finally, Sheikh and Shah present an application of LMS algorithm with optimum step size (µopt-LMS) for fading channel estimation. The expression for optimum step size of the LMS algorithm is modified for use in the fading channel estimation problem. The robustness of the proposed µopt-LMS algorithm is demonstrated via simulation in different channel conditions. Thanks to all the authors and the reviewers. We appreciate your support and hope that you continue your dedication to WCMC.