bluuebunny/crossref_metadata_2025_split huggingface dataset:
Medium access control protocols for wireless mobile ad hoc networks: issues and approaches
Authors: Issariyakul Teerawat , Hossain Ekram , In Kim Dong 
Published: December 2003

AbstractIn this article, a comprehensive survey of the medium access control (MAC) approaches for wireless mobile ad hoc networks is presented. The complexity in MAC design for wireless ad hoc networks arises due to node mobility, radio link vulnerability and the lack of central coordination. A series of studies on MAC design has been conducted in the literature to improve medium access performance in different aspects as identified by the different performance metrics. Tradeoffs among the different performance metrics (such as between throughput and fairness) dictate the design of a suitable MAC protocol. We compare the different proposed MAC approaches, identify their problems and discuss the possible remedies. The interactions among the MAC and the higher layer protocols such as routing and transport layer protocols are discussed and some interesting research issues are also identified. Copyright © 2003 John Wiley & Sons, Ltd.
Ultra‐wideband wireless communications
Authors: Zhuang Weihua , Shen Xuemin (Sherman) , Bi Qi 
Published: December 2003

AbstractUltra‐wideband (UWB) communication techniques have attracted a great interest in both academia and industry in the past few years for applications in short‐range wireless mobile systems. This is due to the potential advantages of UWB transmissions such as low power, high rate, immunity to multipath propagation, less complex transceiver hardware, and low interference. However, tremendous R&D efforts are required to face various technical challenges in developing UWB wireless systems, including UWB channel characterization, transceiver design, coexistence and interworking with other narrowband wireless systems, design of the link and network layers to benefit from UWB transmission characteristics. This paper is to provide an overview of UWB communications, summarize the previous research results, and identify further research issues that need to be tackled. The emphasis is placed on the commercial wireless communications. Copyright © 2003 John Wiley & Sons, Ltd.
Isotropic air‐interface technologies for fourth generation wireless communications
Authors: Chen Hsiao‐Hwa , Lin Jin‐Xiao , Chu Shin‐Wei , Wu Chi‐Feng , Chen Guo‐Sheng 
Published: December 2003

AbstractTo implement 4G wireless that should deliver a much higher data‐rate than that possible in the current 3G systems, development of innovative air‐link technologies is the key. This article reviews our on‐going research activities in the design of ‘isotropic air‐interface technologies’ capable of substantially improving air‐link performance of a CDMA wireless system. To enable bidirectional high‐speed data transmission in the future 4G systems, the problem associated with incompatible up‐ and down‐link performance in 2–3G systems has to be addressed. The importance of the issue becomes even more evident due to the fact that the future wireless needs to support ‘mobile server’ applications, where a mobile terminal may act as a data source such that up‐link traffic can possibly exceed that in down‐link. In this article, two alternative methods enabling isotropic air‐interface will be discussed, either using ‘isotropic spreading techniques’ that ensure a homogeneous link‐performance regardless of its operation mode (synchronous or asynchronous), or relying on a precision up‐link synchronization control techniques to pave a way for successful application of orthogonal codes in up‐link channels, which otherwise are asynchronous and destroy the ‘orthogonality’ amongst the codes. The isotropic spreading techniques can minimize multiple access interference (MAI) and multipath‐interference (MI), the prevalent impairing effects in the current 2–3G systems. This article will introduce a promising complete complementary CC/DS‐CDMA scheme based on isotropic spreading techniques, which carries several extremely attractive properties such as MAI‐free, MI‐free, near–far effect resistance and low hardware complexity. The performance of the proposed CC/DS‐CDMA scheme is limited only by noise. To implement up‐link synchronization control, smart antenna and GPS‐based techniques play an important role and a working example based on TD‐SCDMA standard will be illustrated. Finally, we will also discuss the TDD techniques and its significance to implement isotropic air‐interface technologies for the future 4G systems. Copyright © 2003 John Wiley & Sons, Ltd.
The future evolution of wireless mobile communications
Authors: Bi Qi , Seymour James 
Published: December 2003

AbstractAt the start of the 21st century, wireless mobile communications has witnessed an unprecedented growth fueled by information explosion and technology revolution. After much fierce technology competitions and uncertainties, two third‐generation (3G) wideband standards have emerged to dominate the wireless mobile communications for years to come. They are the CDMA2000 [1] and the universal mobile terrestrial system (UMTS) [2] standards, both of which are based on code‐division multiple‐access (CDMA) technology. In this paper, we shall indicate how current 2G digital wireless systems might evolve into these 3G systems. We shall examine the likely innovative techniques to be adopted for further evolution of the two systems and the possible capacity gains obtainable by utilizing these techniques. Copyright © 2003 John Wiley & Sons, Ltd.
Downlink radio resource optimization in wide‐band CDMA systems
Authors: Chen Yue , Cuthbert Laurie 
Published: December 2003

AbstractSoft handover is analysed and optimized in the downlink direction of a WCDMA system in this paper. Downlink is chosen because the asymmetric nature of most new services supported by the next generation of mobile networks requires more capacity in that direction, and so this is likely to be the limiting factor. The study also sets out to resolve the often controversial opinions about the system level performance with soft handover in the downlink direction. Here, the performance of soft handover is investigated on the link level and on the system level separately. Apart from power control, the cell‐selection scheme and power limits (which are ignored by most of the previous work in the literature) are also included. Results show that from the point of view of link quality, soft handover can prevent the downlink traffic channel power going beyond the power limit. From the system level point of view, the downlink capacity can be increased by choosing a proper soft handover overhead. The optimum value of the overhead depends closely on the cell‐selection threshold and the radio environment. The paper proves that soft handover is an effective way for interference‐reduction and radio resource optimization in the downlink direction for WCDMA systems. Copyright © 2003 John Wiley & Sons, Ltd.
Reverse link capacity of SIR‐based power‐controlled CDMA systems with antenna arrays
Authors: Yu Jin , Yao Yu‐Dong 
Published: December 2003

AbstractIn this paper, reverse link capacity, in terms of user capacity, of a code‐division multiple access (CDMA) system with both beamforming and antenna diversity under a multipath environment is analyzed and compared. Signal‐to‐interference ratio (SIR) based power control is assumed in the system. Antenna elements are divided into several groups to achieve antenna diversity gain. Antenna elements in a group are closely spaced to perform beamforming in order to suppress the own‐cell and other‐cell interference, while those groups are widely spaced to achieve the diversity gain. Based on the comparison, a most efficient use of the antenna array according to the distribution of antenna elements among the groups is obtained. Instead of using tedious iterative methods to evaluate user capacity, a simple closed‐form capacity expression with respect to antenna diversity and beamforming gains, a target SIR and the CDMA processing gain is derived. Numerical results indicate significant capacity improvement with the antenna array. Copyright © 2003 John Wiley & Sons, Ltd.
Spectrum demand for systems beyond IMT‐2000 based on data rate estimates
Authors: Mohr Werner 
Published: December 2003

AbstractIn different regions, research activities on systems beyond third generation mobile communication started already around 1999. The major drivers for these systems are the increasing demand for personal mobile communications with respect to performance, applications, traffic demand and easy to use including communications involving machines. From the user perspective, increasing personal mobility enforces mobile communications in business and the private sector. ITU‐R WP8F, ITU‐T SSG and bodies like WWRF are currently working on the vision of systems beyond IMT‐2000 on global basis in cooperation with the research activities and are defining the basic requirements. New elements of these systems for the mobile access (up to 100 Mbps peak cell capacity) and the nomadic/wireless local area access (up to 1 Gbps peak cell capacity) are being discussed. These requirements result in a huge amount of needed spectrum. In this paper, the impact on spectrum demand for a new mobile broadband access element is investigated with respect to estimated data rate requirements from the user perspective. For that purpose, the radio interface is described in generic form based on a modified Shannon channel capacity formula to obtain generalized results independent of a particular radio interface concept. With the relation between cluster size, carrier/interference‐ratio and coverage requirements the spectrum demand and system throughput is calculated in closed form for the case of a radio interface with fixed and adaptive modulation and coding. The nomadic/wireless local area access according to ITU‐R is not considered here. These investigations are based on simplified system concepts without considering advanced antenna, scheduling and network deployment concepts. Copyright © 2003 John Wiley & Sons, Ltd.
Future mobile broadband wireless networks: a radio resource management perspective
Authors: Periyalwar Shalini , Hashem Bassam , Senarath Gamini , Au Kelvin , Matyas Robert 
Published: December 2003

AbstractFuture wireless evolution envisages high rates, low hierarchy in the network architecture, antenna array processing, multiple access modes and multihop operation as part of the system concept. To exploit the increased capabilities of the systems in conception, efficient resource management strategies need to be developed. The goal of this paper is to examine the key aspects of the evolution which impact radio resource management for the mobile broadband wireless network, and to emphasize the areas that need to be addressed for servicing mobile users with varying quality of service requirements. Copyright © 2003 John Wiley & Sons, Ltd.
Benefits of the control‐hold mode for the support of the forward packet data channel in IS‐2000
Authors: Gholmieh Ralph , Khaleghi Farideh 
Published: December 2003

AbstractThe most recent revisions of the IS‐2000 standards are being designed with the view of maximizing the achievable throughput while maintaining an acceptable Quality‐of‐Service (QoS) for the supported voice and data sessions. Revision C of the IS‐2000 standard is specifically geared towards maximizing the throughput on the forward link. However, this increase in forward link capacity requires adding new reverse link overhead channels thereby decreasing reverse link capacity. This paper describes the Control‐Hold mode designed to reduce the resource usage of reverse link overhead channels. In particular, the focus is on the DV‐control‐hold (DVCH) mode jointly proposed by Ericsson and Nortel for the 1xEVDV standard and adopted as an optional feature in the IS‐2000 standard as part of its Revision C 5. The DV‐control‐hold mode is an intermediary state between the active and dormant modes of a mobile. In this state, a mobile station uses less resources than when active and can also be quickly reactivated (typically in 20 ms). The QoS achieved for mobile stations (MSs) that use the Active‐DVCH‐Dormant state machine is compared to the performance of MSs with regular Active‐Dormant state machines. Simulation results show that the introduction of the DVCH mode increases both, the achievable forward link throughput and the number of admissible mobiles per sector. When the DVCH mode is introduced and for the typical ‘Active‐to‐Dormant’ timer values of 3 and 6 s, the number of admissible sessions per sector increases by 35% and 66% respectively, while the corresponding throughput increases by 14% and 50%. Copyright © 2003 John Wiley & Sons, Ltd.
Linear successive interference cancellation in DS‐CDMA systems
Authors: Berggren Fredrik , Slimane S. Ben 
Published: December 2003

AbstractSuccessive interference cancellation techniques have the potential to reduce the interference and therefore increase the capacity of cellular radio systems. In this work, we analyze a linear DS‐CDMA receiver utilizing soft feedback interference cancellation. To be able to meet diverse QoS requirements, we introduce a power control scheme that takes into account heterogeneous service levels as well as the impact of imperfect interference cancellation. We address the capacity resulting from this receiver and give its user capacity region on closed‐form. We show that our results are general and provide a framework for capacity comparison for many proposed linear successive cancellation receiver models. Several receiver modifications are included, partial interference cancellation; when only part of the signal is canceled, and limited cancellation; when not every signal is canceled. We derive the minimum power solution of a single‐cell, from which convergent multicellular distributed power control algorithms that iteratively update the powers are suggested. The numerical results show that there are large gains in user capacity from interference cancellation when theEb/I0requirements are high. However, regardless of the required targets the maximum capacity is always achieved through partial successive interference cancellation. It is also found that the power levels are sensitive to the cancellation efficiency and worse performance than single‐user detection can occur. Copyright © 2003 John Wiley & Sons, Ltd.
Identifying the Effect of Tidal Height on Offshore Wind Speed Profiles
Authors: Khan Demian , Watson Simon J. , Infield David G. 
Published: December 2003

AbstractThe rise and fall of the sea surface due to the tide effectively moves an offshore wind turbine hub through the wind shear profile. Offshore wind farms are being built around the coasts of Europe, including in the Baltic and the North Sea. Tidal ranges in the North Sea are greater than those in the Baltic, and the potential effect on the wind shear profile of the change in sea surface height is likely to be more significant. This article seeks to identify the effect of tidal height on the shear profile at a mast off the east coast of the UK where the maximum tidal range is 7 m. Definite evidence for the effect of tidal height on wind shear is presented, though the effect is small and there is considerable scatter in the data. Copyright © 2003 John Wiley & Sons, Ltd.
Synthese und Kristallstruktur von bis‐1, 3‐Dimethoxyethan‐trichloro‐samarium(III) und tris‐N, N‐Diisopropylcarbamato‐samarium(III)
Authors: Baisch Ulrich , Schnick Wolfgang 
Published: December 2003

AbstractDas Diisopropylcarbamat von Samarium konnte durch Umsetzung von SmCl3(DME)2 (DME = 1, 2‐Dimethoxyethan) mit Diisopropylamin und gasförmigem CO2 in Toluol in Form hellgelber Einkristalle erhalten werden, die mittels Einkristall‐Röntgenstrukturanalyse untersucht wurden (Sm4(O2CNiPr2)12, C2/c, Z = 4, a = 2914, 2(2); b = 1974, 2(1), c = 2328, 7(2) pm, T = 200 K, R1 = 0, 0345, 15050 unabhängige Reflexe, 590 verfeinerte Parameter). Sm4(O2CNiPr2)12 ist im Festkörper tetramer, dabei ist Samarium auf drei verschiedene Arten von Carbamat‐Liganden koordiniert bzw. von diesen verbrückt. SmCl3(DME)2 wurde aus Sm2O3 und SOCl2 in überschüssigem DME erhalten und kristallisiert in Form farbloser Kristalle (SmCl3(DME)2, P21/c, Z = 4, a = 1160, 8(2); b = 898, 9(2), c = 1572, 9(2) pm, R1 = 0, 0349, 4639 unabhängige Reflexe, 146 verfeinerte Parameter). SmCl3(DME)2 liegt monomer vor, dabei ist Samarium verzerrt pentagonal‐pyramidal von drei Cl sowie zwei DME umgeben.
Mononucleare Oxalamidinkomplexe von Kupfer(I), Palladium(II) und Ruthenium(II) durch gekoppelte Kation‐/Anionkoordination
Authors: Böttcher Lars , Scholz Alexander , Walther Dirk , Weisbach Nancy , Görls Helmar 
Published: December 2003

AbstractOxalamidine R1N=C(NHR2)‐C(=NHR2)=NR1 (H2A: R1 = R2 = p‐tolyl; H2B: R1 = R2 = mesityl) reagieren mit [Cu(CH3CN)4] (BF4)/PPh3 unter Bildung der Einkernkomplexe {[(Ph3P)2Cu]AH2(F4B)} (1) und {[(Ph3P)Cu]BH2(F4B)} (2). Die Kristallstrukturanalysen von Einkristallen zeigen, dass CuI an die 1, 4‐Diazadieneinheit koordiniert ist, während Tetrafluoroborat über Wasserstoffbrücken an die 1, 2‐Diamineinheit gebunden ist („gekoppelte Kation‐/Anionkoordination”︁). [(allyl)PdCl]2 reagiert mit H2A zum Allylkomplex [(allyl)PdAH2···Cl2(allyl)Pd] (3). Mit H2B wird die analoge Verbindung 4 gebildet. In diesen Komplexen ist das (allyl)Pd+‐Fragment an den 1, 4‐Diazadienteil des neutralen Oxalamidinliganden koordiniert und das Anion [allylPdCl2]‐ über Wasserstoffbrücken an der gegenüberliegenden 1, 2‐Diaminseite gebunden. Durch analoge gekoppelte Kation‐/Anionkoordination lassen sich auch RuII‐Komplexe, z. B.[(p‐Cymo l)Ru(Cl)CH2···Cl] (6) und [(4, 4′, 4″‐tri‐t‐butyl‐terpyridin)(Cl)RuAH2···Cl] (9) herstellen.
Cyclopentadienyl Complexes of Samarium with Bis(phosphanyl)amides
Authors: Gamer Michael T. , Canseco‐Melchor Graciela , Roesky Peter W. 
Published: December 2003

AbstractThe first heteroleptic bisphosphanylamide complex of the lanthanides, [(η5‐C5Me5)2Sm{η2‐N(PPh2)2}] is reported. [(η5‐C5Me5)2Sm{η2‐N(PPh2)2}] can be obtained by the reaction of the potassium bisphosphanylamide complex, [K(THF)n][N(PPh2)2] (n = 1.25 ‐ 1.5) with [(η5‐C5Me5)2Sm(μ‐Cl)2K(THF)]∞ or in a one‐pot reaction starting from SmCl3 and [K(THF)n][N(PPh2)2] followed by an addition of KC5Me5. Both, [(η5‐C5Me5)2Sm{η2‐N(PPh2)2}] and [(η5‐C5Me5)2Sm(μ‐Cl)2K(THF)]∞ have been characterized by standard analytical/spectroscopic techniques, and their solid‐state structures were established by single crystal X‐ray diffraction.
Erste Dipyridylamide der Selten‐Erd‐Elemente: Neuartige Selten‐Erd‐Stickstoff‐Koordinationen in [Ln(N(C5H4N)2)3]2, Ln = La, Gd, Yb
Authors: Müller‐Buschbaum Klaus 
Published: December 2003

AbstractDie solvensfreien Reaktionen der Selten‐Erd‐Elemente Lanthan, Gadolinium und Ytterbium mit einer Schmelze von 2‐2′‐Dipyridylamin ergaben farblose bis gelbe, transparente Kristalle der Verbindungen [Ln(N(C5H4N)2)3]2, Ln = La, Gd, Yb. Es handelt sich um die ersten Dipyridylamide der Selten‐Erd‐Elemente. Alle drei Verbindungen sind homoleptisch und zeigen ausschließlich N‐Atome als Koordinationspartner der Selten‐Erd‐Elemente. Neben endständigen, einfach chelatisierenden Dipyridylamid‐Gruppen, verbrücken weitere Amid‐Liganden unter Heranziehen aller drei N‐Atome doppelt chelatisierend. Es bilden sich Dimere ohne Metall‐Metall‐Bindungen. Die stark unterschiedlichen Ionenradien von LaIII, GdIII und YbIII bewirken deutlich unterschiedliche Umgebungen der Selten‐Erd‐Atome, obwohl Bindungstypen und Stöchiometrie gleich sind. Yb und Gd zeigen eine C.N. von acht, La hingegen von zehn N‐Atomen. Deutlich unterschiedliche Kristallstrukturen und IR‐Spektren sind die Folge.
Synthesen und Kristallstrukturen der homöotypen Selenitbromide Bi8(SeO3)9Br6 und CsSm21(SeO3)24Br16
Authors: Ruck Michael , Schmidt Peer 
Published: December 2003

AbstractBi8(SeO3)9Br6 wurde auf der Basis thermodynamischer Berechnungen aus BiOBr und SeO2 über eine Autotransportreaktion im Temperaturgradienten von 670 nach 660 K synthetisiert. Kristalle von CsSm21(SeO3)24Br16 entstanden aus der Umsetzung äquimolarer Gemenge von SmOBr und SeO2 im CsBr‐Flux bei 1070 K. Beide Selenitbromide kristallisieren in der orthorhombischen Raumgruppe B2/b 2/a 2/b(Nr. 68) mit pseudo‐tetragonaler Gittermetrik (Bi8(SeO3)9Br6: a = b = 1588, 4(5), c = 1830, 5(5) pm, Z = 533, 3; CsSm21(SeO3)24Br16: a = b = 1579, 7(2), c = 1796, 3(2) pm, Z = 2). In den Kristallstrukturen sind die Schweratome in quadratischen Netzen organisiert. Die O‐Atome der pyramidalen Selenit‐Gruppen verknüpfen sie zu Schichtpaketen [BiIII21, 33(SeIVO3)24Br16] bzw. [CsSmIII21(SeIVO3)24Br16], die nach [001] gestapelt sind. In CsSm21(SeO3)24Br16 gewährleistet der Ersatz eines SmIII‐Kations pro Formeleinheit durch ein CsIKation die Elektroneutralität; im Fall von Bi8(SeO3)9Br6 = BiIII21, 33(SeIVO3)24Br16 wird die Ladungsbilanz durch Unterbesetzung von Bi‐Atomlagen ausgeglichen. Die Eigensymmetrie der konstituierenden Schichtpakete, welche der quadratischen Schichtgruppe P (4/n) 2/b 2/m entspricht, führt zur Ausbildung pseudo‐meroedrischer Zwillinge nach [110].
The Electronic Structure of Tantalum Oxynitride and the Falsification of α‐TaON
Authors: Lumey Marck‐Willem , Dronskowski Richard 
Published: December 2003

AbstractWe have performed electronic structure calculations from first principles (LDA & GGA, plane waves & muffin‐tin orbitals, pseudopotentials & all‐electron techniques) on the two reported polymorphs of TaON. For the experimentally well‐characterized β‐TaON adopting the baddeleyite structure type, there is excellent agreement between all accessible observables despite the supposedly correlated character of an oxynitride phase. Concerning hexagonal α‐TaON proposed first in 1966, one finds tremendous contradictions between theory and experimentally reported data (molar volume, total energy differences, electronic transport etc.) In combination with the communicated X‐ray diffraction diagram, α‐TaON is considered an erroneous entry in the solid‐state chemical literature that needs to be removed from the crystallographic databases.
GaP5 und InP5: Ungewöhnliche Moleküle eröffnen neue Wege zur Reindarstellung von III/V‐Halbleitermaterialien
Authors: Köppe R. , Steiner J. , Schnöckel H. 
Published: December 2003

AbstractIn Analogie zu η5‐gebundenem Ga(CH)5 werden für isolobale GaP5‐ und InP5‐ Moleküle quantenchemische Rechnungen zur thermodynamischen Stabilität durchgeführt. Auf dieser Basis lassen sich die Zersetzungsgleichgewichte (z. B. GaP5 (g) = GaP(f) + P4 (g)) berechnen. Durch Transportversuche bei hohen Phosphordrücken können diese theoretischen Ergebnisse bestätigt werden, d. h. GaP3 und GaP5 bzw. InP3 und InP5 sind die für GaP und InP transportrelevanten Gasphasenspezies. Diese Ergebnisse aus der Grundlagenforschung ermöglichen es erstmals, die zahlreichen in jüngster Zeit erschienenen Arbeiten über nanoskalige GaP/InP‐Systeme zu verstehen und weitere Anwendungen im Bereich der Abscheidung von reinsten III/V‐Halbleitern zu erschließen.
[{(C2H5)2NH2}2In2Ge2S8] · [(C2H5)2NH]0.25: A Three‐Dimensional Thiogermanate‐Indate Framework Based on the Interconnection of [In2Ge2S6S4/2]2‐ Adamantane‐Like Building Units
Authors: Pitzschke Dragan , Bensch Wolfgang 
Published: December 2003

AbstractThe new compound [{(C2H5)2NH2}2In2Ge2S8] · [(C2H5)2NH]0.25 was synthesized under solvothermal conditions using elemental In, Ge, and S in diethylamine. The title compound crystallizes in the orthorhombic space group Pna21 with a = 12.804(3)Å , b = 17.615(4)Å, c = 13.067(3)Å, V = 2947.2Å3, and Z = 4. The structure consists of (In/Ge)S4 tetrahedra as primary building units and four such tetrahadra are joined via common corners to form [In2Ge2S6S4/2]2‐ adamantane‐like building units. These building units are interconnected yielding a three‐dimensional anionic tetrahedral framework resembling that of cristobalite if the adamantane‐like cages are seen as supertetrahedra. Three types of channels with diameters ranging from 8.2 · 10.3Å to 8.5 · 13.1Å intersect the structure. Charge compensation is achieved by [(C2H5)2NH2]+ cations which are located within the voids of the anionic network. The compound decomposes in two steps yielding In2S3 and Ge as solid residue.