Efficient rate-power allocation for OFDM in a realistic fading environment

The implementation of practical adaptive resource allocation scheme remains a key criterion to be satisfied for realising spectrally efficient multitone wireless communications. The ever-increasing demand for spectrally efficient broadband wireless transmission technologies has spurred intensive research leading towards the implementation of adaptive OFDM and adaptive MIMO systems. Efforts in this direction have been frustrated however by the lack of a clear and accurate description of the fading behaviour typically encountered in the broadband wireless transmission environment. This has been partially been overcome by the use of mathematical modelling which captures certain large-scale characteristics of the channel and facilitates theoretical research. The “average” channel parameters gleaned from these processes is typically then used to inform the design and configuration of wireless networking equipment after the broad application of generous safety margins. The resulting solu�tion is therefore quite robust to certain transient channel quality degradation yet the generous safety tolerances render it unable to exploit other transient transmission quality improvements We seek to overcome the problems associated with this ap�proach by applying a theoretically sound novel adaptive resource allocation framework to actual broadband wireless channel development data. The allocation framework is derived from the optimal OFDM allocation scheme for a known channel [1]: the channel development data is obtained from actual measurement of a broadband wireless mobile environment [2]. Prediction tech�niques are employed to overcome the time lag between channel assessment and symbol transmission. We present the details of the predictive resource allocation scheme used and include a broad characterisation of the transmission environment in terms of the time-varying fading processes observed. We provide some results of the application of this scheme as typical performance levels that may be achieved in an actual transmission environment

Catalytic Ni/Cr-Mediated Macrocyclization without Use of High-Dilution Techniques

The feasibility of catalytic Ni/Cr-mediated macrocyclization was demonstrated for the two substrates chosen from the halichondrin area. With 5 mol % of Ni and Cr catalysts, the macrocyclization was realized without use of high-dilution techniques. The reported method has a number of appealing features, including user-friendliness, easy workup, apparent scalability, and cost-effectiveness. In addition, all the required reagents are commercially available or obtainable in one or two steps from commercially available chemicals

Operationally Simple and Efficient Workup Procedure for TBAF-Mediated Desilylation: Application to Halichondrin Synthesis

An operationally simple and efficient workup method for tetrabutylammonium fluoride (TBAF)-mediated t-butyldimethylsilyl (TBS) deprotection has been developed. The procedure includes addition of a sulfonic acid resin and calcium carbonate, followed by filtration and evaporation. This method eliminates the tedious aqueous-phase extraction process to remove excess TBAF and materials derived from TBAF, thereby making the protocol highly amenable to multiple TBS deprotections. Its efficiency and usefulness were demonstrated by using the transformation of 1a to 3a in the halichondrin synthesis

Concise and Highly Stereoselective Synthesis of the C20–C26 Building Block of Halichondrins and Eribulin

A concise, stereoselective, and scalable synthesis of the C20–C26 building block of halichondrins and Eribulin is reported. The synthesis relies on three key transformations: regiospecific Ru-catalyzed intramolecular hydrosilylation, highly stereoselective S_N2′ substitution, and selective conversion of a C–Si to C–I bond. It is carried out in a 5-pot/4-workup operation without chromatographic purification, except for filtration through a silica-gel plug, to give the C20–C26 building block (<i>dr</i> > 200:1; <i>ee</i> > 99%) in ca. 60% overall yield from epoxide <b>1</b>

Synthesis and Structure of Tolyporphin A <i>O,O</i>-Diacetate

The revised structure of tolyporphin A O,O-diacetate (2b) was synthesized by assembling fragments 4, 5, and 12. The synthetic substance was found to be identical to the O,O-diacetate derived from natural tolyporphin A in every respect, thus establishing the relative and absolute configurations of this natural product

A Novel Example for Optical Resolution of Racemic Ketones Originating from Batrachotoxin Synthesis

A Novel Example for Optical Resolution of Racemic Ketones Originating from Batrachotoxin Synthesi

Air-Stable Heterobimetallic Catalysts to Effect Ni/Cr-Mediated Couplings with a ca. 1:1 Molar Ratio of Coupling Partners at Low Catalyst Loadings

Two air-stable Ni,Cr-heterobimetallic catalysts have been prepared from ligands 7 and 11, obtained from scyllo-inositol in four and three steps, respectively. Both catalysts smoothly promote Ni/Cr-mediated coupling reactions with a ca. 1:1 molar ratio of coupling partners. The catalyst derived from 11 exhibits a better catalytic profile, thereby allowing Ni/Cr-mediated coupling reactions to be achieved with a wide range of substrates at a low catalyst loading in an operationally simple manner

New Catalytic Cycle for Couplings of Aldehydes with Organochromium Reagents

A new catalytic cycle has been developed to effect all three subgroups of Cr-mediated couplings, i.e., (1) Ni/Cr-mediated alkenylation, alkynylation, and arylation, (2) Co/Cr-mediated 2-haloallylation, alkylation, and propargylation, and (3) Cr-mediated allylation. In the presence of chiral sulfonamide ligands, good asymmetric inductions can be achieved for some of the Ni/Cr-mediated alkenylation, Co/Cr-mediated 2-haloallylation and propargylation, and Cr-mediated allylation

A Novel Example for Optical Resolution of Racemic Ketones Originating from Batrachotoxin Synthesis

A Novel Example for Optical Resolution of Racemic Ketones Originating from Batrachotoxin Synthesi

Experimental Support for the Primary Stereoelectronic Effect Governing Baeyer−Villiger Oxidation and Criegee Rearrangement

Experimental Support for the Primary Stereoelectronic Effect Governing Baeyer−Villiger Oxidation and Criegee Rearrangemen