On the performance of improved quadrature spatial modulation

Quadrature spatial modulation (QSM) utilizes the in‐phase and quadrature spatial dimensions to transmit the real and imaginary parts of a single signal symbol, respectively. The improved QSM (IQSM) transmits two signal symbols per channel use through a combination of two antennas for each of the real and imaginary parts. The main contributions of this study can be summarized as follows. First, we derive an upper bound for the error performance of the IQSM. We then design constellation sets that minimize the error performance of the IQSM for several system configurations. Second, we propose a double QSM (DQSM) that transmits the real and imaginary parts of two signal symbols through any available transmit antennas. Finally, we propose a parallel IQSM (PIQSM) that splits the antenna set into equal subsets and performs IQSM within each subset using the same two signal symbols. Simulation results demonstrate that the proposed constellations significantly outperform conventional constellations. Additionally, DQSM and PIQSM provide a performance similar to that of IQSM while requiring a smaller number of transmit antennas and outperform IQSM with the same number of transmit antennas.     

A Multi-radio 802.11 Mesh Network Architecture

The focus of this paper is to offer a practical multi-radio mesh network architecture that can realize the benefits of multiple radios. Our architecture provides solutions to challenges in three key areas. The first is the construction of a split wireless router that enables modular wireless mesh routers to be constructed from commodity hardware. The second is the design of a centralized channel assignment algorithm that considers the inter-dependence between channel assignment and routing in order to create high-throughput channel-diversified routes. Third is the design and implementation of several communication protocols that are necessary to make our architecture operational. Our system is comprehensively evaluated on a 20-node multi-radio wireless testbed. Results demonstrate that our architecture makes feasible the deployment of large-scale high-capacity multi-radio mesh networks built entirely with commodity hardware. Our implementation is available to the community for research and development purposes.     

Novel Approach for Modeling Wireless Fading Channels Using a Finite State Markov Chain

Empirical modeling of wireless fading channels using common schemes such as autoregression and the finite state Markov chain (FSMC) is investigated. The conceptual background of both channel structures and the establishment of their mutual dependence in a confined manner are presented. The novel contribution lies in the proposal of a new approach for deriving the state transition probabilities borrowed from economic disciplines, which has not been studied so far with respect to the modeling of FSMC wireless fading channels. The proposed approach is based on equal portioning of the received signal‐to‐noise ratio, realized by using an alternative probability construction that was initially highlighted by Tauchen. The associated statistical procedure shows that a first‐order FSMC with a limited number of channel states can satisfactorily approximate fading. The computational overheads of the proposed technique are analyzed and proven to be less demanding compared to the conventional FSMC approach based on the level crossing rate. Simulations confirm the analytical results and promising performance of the new channel model based on the Tauchen approach without extra complexity costs.     

Synthesis,characterization, and crystal structures of organonickel(II) complexes coordinated to novel 1‐bromo‐2,6‐bis{[(λ5‐phosphanylidene)imino]methyl}benzene NCN‐pincer ligands

A novel family of four 1‐bromo‐2,6‐bis{[(λ⁵‐phosphanylidene)imino]methyl}benzene ligands has been synthesized and characterized. The phosphiniminomethyl substituents are decorated with either three phenyl groups, two phenyl and one cyclohexyl group, one phenyl and two cyclohexyl groups, or three cyclohexyl groups. Each ligand was metallated using zero‐valent nickel through an oxidative addition to form a family of organonickel(II) complexes, namely (2,6‐bis{[(triphenyl‐λ⁵‐phosphanylidene)imino]methyl}phenyl‐κ³N,C¹,N′)bromidonickel(II) dichloromethane hemisolvate, [NiBr(C₄₄H₃₇N₂P₂)]·0.5CH₂Cl₂, (2,6‐bis{[(cyclohexyldiphenyl‐λ⁵‐phosphanylidene)imino]methyl}phenyl‐κ³N,C¹,N′)bromidonickel(II) diethyl ether hemisolvate, [NiBr(C₄₄H₄₉N₂P₂)]·0.5C₄H₁₀O, (2,6‐bis{[(dicyclohexylphenyl‐λ⁵‐phosphanylidene)imino]methyl}phenyl‐κ³N,C¹,N′)bromidonickel(II), [NiBr(C₄₄H₆₁N₂P₂)], and (2,6‐bis{[(tricyclohexyl‐λ⁵‐phosphanylidene)imino]methyl}phenyl‐κ³N,C¹,N′)bromidonickel(II), [NiBr(C₄₄H₇₃N₂P₂)]. This family of complexes represents a useful opportunity to investigate the impact of incrementally changing the steric characteristics of a complex on its structure and reactivity.     

Organophotoredox-Mediated Amide Synthesis by Coupling Alcohol and Amine through Aerobic Oxidation of Alcohol

The combination of an organic photocatalyst [4CzIPN (1,2,3,5-tetrakis(carbazol-9-yl)-4,6 dicyanobenzene) or 5MeOCzBN (2,3,4,5,6-pentakis(3,6-dimethoxy-9 H-carbazol-9-yl)benzonitrile)], quinuclidine, and tetra-n-butylammonium phosphate (hydrogen-bonding catalyst) was employed for amide bond formations. The hydrogen-bonded OH group activated the adjacent C−H bond of alcohols towards hydrogen atom transfer (HAT) by a radical species. The quinuclidinium radical cation, generated through single-electron oxidation of quinuclidine by the photocatalyst, employed to abstract a hydrogen atom from the α-C−H bond of alcohols selectively due to a polarity effect-produced α-hydroxyalkyl radical, which subsequently converted to the corresponding aldehyde under aerobic conditions. Then the coupling of the aldehyde and an amine formed a hemiaminal intermediate that upon photocatalytic oxidation produced the amide.     

Evaluation of the European market for satellite-UMTS terminals

This paper is concerned with dimensioning the potential market for Satellite-Universal Mobile Telecommunications System (S-UMTS) terminals in Europe. In order to size the market, the satellite component is assumed to play a complementary role to its terrestrial counterpart. According to this role, the market segments for S-UMTS and potential users for each terminal type have been identified. Different terminal types have also been categorised according to their supported level of mobility and their usage type: whether for individual usage or for group usage. A mapping is made between the terminal types and the potential user groups. The market size for each terminal type is predicted using the Logistic model, taking into account the tariff and the wealth of each individual country in Europe. Analysis is performed for EU15 and non-EC European countries for each terminal type under consideration. Copyright © 1999 John Wiley & Sons, Ltd.     

Mobility management incorporating fuzzy logic for heterogeneous aIP environment

The next generation in mobility management will enable different mobile networks to interoperate with each other to ensure terminal and personal mobility and global portability of network services. However, in order to ensure global mobility, the deployment and integration of both satellite and terrestrial components are necessary. This article is focused on issues related to mobility management in a future mobile communications system, in a scenario where a multisegment access network is integrated into an IP core network by exploiting the principles of Mobile IP. In particular, attention is given to the requirements for location, address, and handover management. In a heterogeneous environment, the need to perform handover between access networks imposes particular constraints on the type of information available to the terminal and network. In this case, consideration will need to be given to parameters other than radio characteristics, such as achievable quality of service and user preference. This article proposes a new approach to handover management by applying the fuzzy logic concept to a heterogeneous environment. The article concludes with a presentation of mobility management signaling protocols     

Studies Towards the Synthesis of ATP Analogs as Potential Glutamine Synthetase Inhibitors

In research directed at the development of adenine triphosphate (ATP) analogs as potential glutamine synthetase (GS) inhibitors, adenine and allopurinol derivatives have been synthesized either as novel ATP analogs or as scaffolds for the construction of such analogs.

Satellite-UMTS traffic dimensioning and resource managementtechnique analysis

The universal mobile telecommunications system (UMTS) will consist of space UMTS (S-UMTS) and terrestrial UMTS (T-UMTS) components. An algorithm for predicting the traffic capacity in terms of the number of subscribers for the satellite component of UMTS is presented. The algorithm takes into account the takeup characteristics of new products, the growth of gross domestic product (GDP), the projection of population, the tariff of the service, and price fall over the forecast period. The predicted traffic is used to generate a traffic grid in terms of Erlang of dimension 36×72 in steps of 5° in both the latitude and longitude directions. The traffic grid is used to evaluate the performance of a dynamic channel allocation (DCA) technique as, well as a fixed channel allocation (FCA) technique. Both channel allocation techniques have been considered with the queuing of handover (QH) requests. In order to compare the respective techniques' performance, a low-earth orbit mobile satellite system (LEO-MSS) mobility model is developed to take into account the effect of satellites' motion during interbeam handovers. A theoretical model for obtaining the values of blocking probabilities for low-traffic loads is presented. Finally, the performance of the DCA-QH technique is compared with the FCA-QH technique under suitably defined traffic and mobility conditions     

Conserved core substructures in the overlay of protein-ligand complexes

The method of conserved core substructure matching (CSM) for the overlay of protein-ligand complexes is described. The method relies upon distance geometry to align structurally similar substructures without regard to sequence similarity onto substructures from a reference protein empirically selected to include key determinants of binding site location and geometry. The error in ligand position is reduced in reoriented ensembles generated with CSM when compared to other overlay methods. Since CSM can only succeed when the selected core substructure is geometrically conserved, misalignments only rarely occur. The method may be applied to reliably overlay large numbers of protein-ligand complexes in a way that optimizes ligand position at a specific binding site or subsite or to align structures from large and diverse protein families where the conserved binding site is localized to only a small portion of either protein. Core substructures may be complex and must be chosen with care. We have created a database of empirically selected core substructures to demonstrate the utility of CSM alignment of ligand binding sites in important drug targets. A Web-based interface can be used to apply CSM to align large collections of protein-ligand complexes for use in drug design using these substructures or to evaluate the use of alternative core substructures that may then be shared with the larger user community. Examples show the benefit of CSM in the practice of structure-based drug design.