Combining ideal beamforming and Alamouti space-time block codes

The simplest Alamouti space-time block code is coupled with a larger number of transmit antennas via ideal beamforming to achieve higher diversity gain. It is shown that the combined system can remain both full diversity and full code rate without orthogonality loss. Simulation results show a significant performance gain over the conventional space-time block codes.     

Groups of algebraic integers used for coding QAM signals

Linear block codes over Gaussian integers and Eisenstein integers were used for coding over two-dimensional signal space. A group of Gaussian integers with 2²ⁿ elements was constructed to code quadrature amplitude modulation (QAM) signals such that a differentially coherent method can be applied to demodulate the QAM signals. This paper shows that one subgroup of the multiplicative group of units in the algebraic integer ring of any quadratic number field with unique factorization, modulo the ideal (Pⁿ), can be used to obtain a QAM signal space of 2p^2n-2 points, where p is any given odd prime number. Furthermore, one subgroup of the multiplicative group of units in the quotient ring Z[ω]/(pⁿ) can be used to obtain a QAM signal space of 6p^2n-2 points; one subgroup of the multiplicative group of units in the quotient ring Z[i](pⁿ) can be used to obtain a QAM signal space of 4p^2n-2 points which is symmetrical over the quadrants of the complex plane and useful for differentially coherent detection of QAM signals; the multiplicative group of units in the quotient ring Z[ω]/(2ⁿ) can be used to obtain a QAM signal space of 3·2^2n-2 points, where i=√-1, ω=(-1+√-3)/2=(-1+i√3)/2, p is any given odd prime number, Z[i] and Z[ω] are, respectively, the Gaussian integer ring and the Eisenstein integer ring. These multiplicative groups can also be used to construct block codes over Gaussian integers or Eisenstein integers which are able to correct some error patterns     

Dynamic Flow Model for Borrowing Channel Ordering Assignment Scheme in Cellular Mobile Systems

A mathematical model that predicts the dynamic flows in cellularmobile networks that allocate channels using the Borrowing ChannelOrdering Assignment (BCO) scheme is described in this paper. Two types ofhandoff procedures – the prioritized and non-prioritized schemes –will be considered in the model. Discrete event simulations wereperformed and the results were found to be comparable to the resultsobtained using the mathematical model. Application to comparative studyof the dynamic behaviours of the BCO, the simple borrowing channel assignment(BCA) and the Fixed Channel Assignment (FCA) schemes is also presented.     

Using an acoustic Doppler current profiler in a small river

Some practical and theoretical concepts related to the use of an acoustic Doppler current profiler (ADCP) in a small river are examined. The importance of understating the limitations of the measurement equipment and a system for locating the exact position of the ADCP are discussed. Details of a new measurement protocol which is suitable for small rivers are presented. Small samples of data measured in the River Blackwater are used to illustrate the concepts outlined in the paper. It is concluded that ADCPs can be successfully used in small rivers provided sufficient care is taken over their deployment and subsequent data analysis. However, in some cases it is acknowledged that additional modifications to the ADCP may need to be undertaken as illustrated in the paper.     

Radiolocation in CDMA Cellular System Based on Joint Angle and Delay Estimation

This paper considers the problem of wireless location in code-divisionmultiple-access (CDMA)cellular system. Through the method of jointly estimating angle of arrival(AOA) and time ofarrival (TOA), a novel scheme is proposed for radiolocation in multipathenvironment, especiallywhen line-of-sight (LOS) path is not available to every base station involvedin location servicefor a mobile subscriber. The Cramer-Rao bound (CRB) is derived for the jointestimator. Based onsimulation results, the accuracy of the proposed wireless location scheme inCDMA system is assessed.     

Characterization and modeling of static and cyclic relaxation in nonconductive adhesives

Adhesive interconnections are considered to be attractive alternatives to lead or lead-free solder interconnects because of their lower processing temperatures and extendability to fine pitch applications. However, reliability issues, such as moisture-induced delamination and viscoelastic relaxation of the adhesive in both steady-state and cyclic loading, continue to pose a challenge to widespread implementation. To date, the static and cyclic relaxation characteristics of nonconductive adhesives (NCAs) are yet to be understood. This paper attempts to provide insights into this static and cyclic relaxation behavior through experimental characterization and modeling. The viscoelastic property of a typical NCA material was characterized, and a simulation program with integrated circuit emphasis (SPICE) modeling program was used to model the cyclic relaxation behavior. The modeling results were successfully validated with a series of experiments. This showed that cyclic relaxation of the adhesive can be successfully modeled using linear-viscoelastic property. The phenomenon of slower relaxation of the adhesive under cyclic loading than that in static loading suggests that accelerated reliability testing used in solder-joint fatigue durability investigations may not be directly applicable to the adhesive interconnections. A rework methodology applicable to adhesive interconnects using cyclic loading has also been proposed.     

Influences of post weld heat treatment on fatigue crack growth behavior of TIG welding of 6013 T4 aluminum alloy joint (Part 1. Fatigue crack growth across the weld metal)

The present study evaluates the influences of PWHT on FCG behavior and tensile properties of TIG butt welded Al 6013-T4 sheets. Crack propagation tests were carried out on compact tension (CT) specimens. The T82 heat treatment was varied in three artificial aging times (soaking) of 6, 18 and 24 hours. The results of T82 heat treatment with artificial aging variations were tested for their fatigue crack growth rates at the main metal zone, the heat-affected zone (HAZ), and the welded metal zone. It has been observed that the various agings in heat treatment T82 are sensitive to the mechanical properties (fatigue crack growth rate test, tensile test). The results show that PWHT-T82 for 18 hours aging is the highest fatigue resistance, while the aging 18 hours provided the highest tensile test result.     

Intracellularly Degradable Hydrogen‐Bonded Polymer Capsules

The assembly of low‐fouling polymer capsules with redox‐responsive behavior and intracellular degradability is reported. Thiol‐containing poly(2‐ethyl‐2‐oxazoline) (PEtOxMA_SH) brushes are synthesized by atom transfer radical polymerization (ATRP) of oligo(2‐ethyl‐2‐oxazoline)methacrylate and glycidyl methacrylate (GMA) and subsequent ring‐opening reaction of the GMA. Sequential deposition of PEtOxMA_SH/poly(methacrylic acid) (PMA) multilayers onto silica (SiO₂) particle templates and crosslinking through disulfide formation yield stable capsules after the removal of the SiO₂ templates by buffered hydrofluoric acid (HF). The redox‐responsive nature of the disulfide crosslinking groups enables the degradation of these capsules under simulated intracellular conditions at pH 5.9 and 5 mm glutathione (GSH). Furthermore, capsule degradation is observed after incubation with dendritic (JAWS II) cells. Even at high capsule‐to‐cell ratios, PEtOxMA_SH capsules show only negligible cytotoxicity. Quartz crystal microgravimetry (QCM) studies, using 100% human serum, reveal that films prepared from PEtOxMA_SH exhibit low‐fouling properties. The degradation and low‐fouling properties are promising for application of PEtOxMA_SH films/capsules for the delivery and triggered release of therapeutics.