Smart antennas in wireless communications: base-station diversity and handset beamforming

We review diversity and smart antenna research applied to both base-stations and terminals. To illustrate the performance gains possible, the paper describes research being conducted by the Smart Antenna Group at Virginia Tech, in both smart base-stations and smart handheld terminals.     

Coordinating the technology transfer and transition of informationtechnology: a phenomenological perspective

Legislation mandates that America's national laboratories share their expertise in developing and commercializing technological innovations. Similarities and differences between the new-product development process (NPDP), as practiced by corporations, versus processes involved in technology movement, as practiced by the national labs, are discussed. The major stages within each and the activities key to the success of each stage are identified. The emphasis is on the need to coordinate the transition and transfer processes within the laboratory organizations affiliated with the Department of Defense (DoD). Data were collected from one of the “best of the best” DoD labs. Personal interviews and mail questionnaires were used to gather the perceptions of employees involved with developing and refining 22 innovative information technologies. The phenomenological approach to data collection and analysis was used. The findings suggest that technology movement embodies seven stages that parallel NPDP. When viewed over all seven, technology transfer is perceived to be more reflective of “technology push,” while transition is more like “market pull.” The NPDP embraces elements of both transfer and transition. The implications of coordinating both are discussed, as well as ways to enhance communication among all parties involved     

Strain measurement in thin pseudomorphic SiGe layers of submicron wires using Raman spectroscopy

The internal strain in thin heteroepitaxial Si_1−xGe_x layers was investigated before and after etching the material between the remaining narrow stripes. The strong inner stress in pseudomorphic heterostructures, caused by the difference in the lattice constants of Si and Si_1−xGe_x, relaxes in small regions after removing the surrounding layer material which mediates the stress. Strain and relaxation were determined from micro-Raman measurements. These measurements were compared with calculations using a two-dimensional finite element program to predict the strain distributions in Si_1−xGe_x layers. Assuming a pure elastic relaxation of the pseudomorphic strain we have found a reasonably good agreement between the measured and calculated Raman shifts.     

Mixed analog/digital matrix-vector multiplier for neural network synapses

In this work we present a hardware efficient matrix-vector multiplier architecture for artificial neural networks with digitally stored synapse strengths. We present a novel technique for manipulating bipolar inputs based on an analog two's complements method and an accurate current rectifier/sign detector. Measurements on a CMOS test chip are presented and validates the techniques. Further, we propose to use an analog extension, based on a simple capacitive storage, for enhancing weight resolution during learning. It is shown that the implementation of Hebbian learning and back-propagation learning in this system is possible using very little additional hardware compared to the recall mode system.     

A novel random wireless packet multiple access method using CDMA

Random packet CDMA, a novel packet-based multiple access scheme for connectionless, uncoordinated random channel access is proposed. Random packet CDMA, or RP-CDMA, utilizes a novel packet format which consists of a short header and a data portion. Each header is spread with a unique spreading code which is identical for all users and packets, while the data portion of each packet is spread by a randomly chosen spreading sequence. The receiver operates in two stages: header detection and data detection. For header detection a conventional spread spectrum receiver is sufficient. Headers are spread with a large enough processing gain to allow detection even in severe interference. The data portion is decoded with a sophisticated receiver, such as a multiuser detector, which allows for successful decoding of overlapping active packets. It is shown that the RP-CDMA system is detector capability limited and that it can significantly outperform spread ALOHA systems whose performance is limited by the channel collision mechanism. RP-CDMA also experiences a much smaller packet retransmission rate than conventional or spread ALOHA, and provides better spectral efficiencies.     

Unipolar SiC power devices and elevated temperature

The paper discusses the limitations and perspectives of unipolar SiC devices for the use in high temperature applications. After clarifying the requirements for the next generation high temperature semiconductor components, these data are reflected to the performance of devices available or in development today. For Schottky barrier diodes, the limits of today’s standard technology are shown and the strategy for developing an improved device is sketched. For switching devices, the two competing concepts - normally on JFETs and normally off MOSFETs - are compared. Advantages for JFET structure are worked out, mainly based on the fact that no oxide interface is involved. The theoretical considerations are checked by experiments.     

Heim- und Gebäudeautomatisierung zur Effizienzsteigerung in Gebäuden

Automation systems are used in homes and buildings for many reasons. One important issue concerning this context is efficiency, particularly in large buildings. By using home and building automation, resources and devices can be controlled, monitored and maintained from one central office. The main feature is, however, to connect heating, ventilation, light systems and other devices used in homes and buildings together in one single network. That way, new possibilities concerning energy management and efficiency in general are opened.     

Analysis of the linear methods for determining copolymerization reactivity ratios,VIII. A critical reexamination of radical copolymerization of methylmethacrylate or styrene

The reactivity ratios of selected methylmethacrylate or styrene copolymerisation systems have been reviewed in terms of the extended Kelen-Tüd?s method. r-values, together with their 95% confidence limits have been calculated. Quantities δ and Q, suitable for classification of the systems, have been applied. Of the 71 reevaluated methylmethacrylate systems 40 (56.3%) were found to belong to class I and 20 (28.2%) to class I(!), i. e. 60 (84.5%) systems for which the conventional copolymerisation equation was found to be adequate. For 3 (4.2%) systems belonging to class II the two-parameter model does not hold and 8 (11.3%) systems were related to class III, i. e. systems for which the experimental data are inconsistent and the published r-values meaningless. 32 styrene copolymerisation systems were reevaluated with the following classification: 19 (59.4%) systems in class I, 5 (15.6%) systems in class I(!), 2 systems in class II and 6 (18.8%) in class III.     

Correction scheme for close-range lidar returns

Because of the effect of defocusing and incomplete overlap between the laser beam and the receiver field of view, elastic lidar systems are unable to fully capture the close-range backscatter signal. Here we propose a method to empirically estimate and correct such effects, allowing to retrieve the lidar signal in the region of incomplete overlap. The technique is straightforward to implement. It produces an optimized numerical correction by the use of a simple geometrical model of the optical apparatus and the analysis of two lidar acquisitions taken at different elevation angles. Examples of synthetic and experimental data are shown to demonstrate the validity of the technique.