Beamforming and Interference Cancellation for Capacity Gain in Mobile Networks

The growth of wireless communication continues. There is a demand for more user capacity from new subscribers and new services such as wireless internet. In order to meet these expectations new and improved technology must be developed. A way to increase the capacity of an existing mobile radio network is to exploit the spatial domain in an efficient way. An antenna array adds spatial domain selectivity in order to improve the Carrier-to-Interference ratio (C/I) as well as Signal-to-Noise Ratio (SNR). An adaptive antenna array can further improve the Carrier-to-Interference ratio (C/I) by suppressing interfering signals and steer a beam towards the user. The suggested scheme is a combination of a beamformer and an interference canceller.The proposed structure is a circular array consisting of K omni-directional elements and combines fixed beamforming with interference cancelling. The fixed beamformers use a weight matrix to form multiple beams. The interference cancelling stage suppresses undesired signals, leaking into the desired beam.The desired signal is filtered out by the fixed beamforming structure. Due to the side-lobes, interfering signals will also be present in this beam. Two alternative strategies were chosen to cancel these interferers; use the other beamformer outputs as inputs to an adaptive interference canceller; or regenerate the outputs from the other beamformer outputs and generate clean signals which are used as inputs to adaptive interference cancellers.Resulting beamformer patterns as well as interference cancellation simulation results are presented. Two different methods have been used to design the beamformer weights, Least Square (LS) and minimax optimisation. In the minimax optimisation a semi-infinite linear programming approach was used. Although the optimisation plays an essential role in the performance of the beamformer, this paper is focused on the application rather then the optimisation methods.     

Nickel-catalysed diversification of phosphine ligands by formal substitution at phosphorus

We report a diversification strategy that enables the direct substituent exchange of tertiary phosphines. Alkylated phosphonium salts, prepared by standard alkylation of phosphines, are selectively dearylated in a nickel-catalysed process to access alkylphosphine products via a formal substitution at the phosphorus center. The reaction can be used to introduce a wide range of alkyl substituents into both mono- and bisphosphines. We also show that the alkylation and dearylation steps can be conducted in a one-pot sequence, enabling accelerated access to derivatives of the parent ligand. The phosphine products of the reaction are converted in situ to air-stable borane adducts for isolation, and versatile derivatisation reactions of these adducts are demonstrated.

Phosphine substituents can be exchanged by standard alkylation of a phosphine and a subsequent dearylation of the resulting phosphonium salt. A wide variety of alkyl groups can be introduced into both mono- and bidentate ligands using this method.     

Zur Kolloidchemie der Humusstoffe

Ohne Zusammenfassung     

Hierarchically Structured Materials for Bone Regeneration: Biomimetic Morphology,Micro-Mechanics and Properties

The contribution describes the development of a biocompatible nanocomposite material consisting of a resorbable polymeric matrix and osteoinductive nanoparticles that can be used to manufacture compact products, porous scaffolds, hybrid nanofibers, and alternating porous/compact structures. It is shown that the material has a good balance of stiffness, strength and toughness. The material supports osteoblast proliferation. Based on a modular design principle, several prototypes for hierarchical 3D constructs are proposed.     

Trees,tight-spans and point configurations

Tight-spans of metrics were first introduced by Isbell in 1964 and rediscovered and studied by others, most notably by Dress in 1984, who gave them this name. Subsequently, it has been found that tight-spans can be defined for more general maps, such as directed metrics and distances, and more recently for diversities. In this paper, we show that all of these tight-spans, as well as some related constructions, can be defined in terms of point configurations. This provides a useful way in which to study these objects in a unified and systematic way. We also show that by using point configurations we can recover results concerning one-dimensional tight-spans for all of the maps we consider, as well as extending these and other results to more general maps such as symmetric and asymmetric maps.     

Influence of nanoscale particle roughness on the stability of pickering emulsions

The wetting behavior of solid surfaces can be altered dramatically by introducing surface roughness on the nanometer scale. Some of nature's most fascinating wetting phenomena are associated with surface roughness; they have inspired both fundamental research and the adoption of surface roughness as a design parameter for man-made functional coatings. So far the attention has focused primarily on macroscopic surfaces, but one should expect the wetting properties of colloidal particles to be strongly affected by roughness, too. Particle wettability, in turn, is a key parameter for the adsorption of particles at liquid interfaces and for the industrially important use of particles as emulsion stabilizers; yet, the consequence of particle roughness for emulsion stability remains poorly understood. In order to investigate the matter systematically, we have developed a surface treatment, applicable to micrometer-sized particles and macroscopic surfaces alike, that produces surface coatings with finely tunable nanoscale roughness and identical surface chemistry. Coatings with different degrees of roughness were characterized with regard to their morphology, charging, and wetting properties, and the results were correlated with the stability of emulsions prepared with coated particles of different roughness. We find that the maximum capillary pressure, a metric of the emulsions' resistance to droplet coalescence, varies significantly and in a nonmonotonic fashion with particle roughness. Surface topography and contact angle hysteresis suggest that particle roughness benefits the stability of our emulsions as long as wetting occurs homogeneously (Wenzel regime), whereas the transition toward heterogeneous wetting (Cassie-Baxter regime) is associated with a loss of stability.     

A nonmonotone filter method for nonlinear optimization

We propose a new nonmonotone filter method to promote global and fast local convergence for sequential quadratic programming algorithms. Our method uses two filters: a standard, global g-filter for global convergence, and a local nonmonotone l-filter that allows us to establish fast local convergence. We show how to switch between the two filters efficiently, and we prove global and superlinear local convergence. A special feature of the proposed method is that it does not require second-order correction steps. We present preliminary numerical results comparing our implementation with a classical filter SQP method.