Energy-Efficient Routing for Frequency-Hop Wireless Networks

The use of adaptive-transmission protocols in wireless, store-and-forward, packet communication networks may result in large differences in the energy requirements of the alternative paths that are available to the routing protocol. Routing metrics can provide quantitative measures of the quality and energy efficiency of the paths from the source to the destination. Such measures are required if the routing protocol is to take advantage of the potential energy savings that are made possible by an adaptive-transmission protocol. An energy-efficient protocol suite for routing and adaptive transmission in frequency-hop wireless networks is described and evaluated, several routing metrics are compared, and tradeoffs among energy efficiency, delay, and packet success probability are investigated.     

A review of metabolism of labeled glucoses for use in measuring glucose recycling

The fate of tritium from each carbon of D-glucose and the metabolism of L-glucose and 2-deoxy-D-glucose are known. Differences in metabolism of labeled glucoses can be used to quantify physical and chemical recycling of glucose. Only physical recycling is measured by [1-3H]-L-glucose, whereas [U-14C]-D-glucose measures total recycling. The difference between [1-3H]-L-glucose and [U-14C]-D-glucose, therefore, is chemical recycling. Recycling from extracellular binding sites and hepatic glucose 6-phosphate can be measured by difference between [1,2-3H]-2-deoxy-D-glucose and [1-3H]-L-glucose, and the difference in irreversible loss of the two will measure extrahepatic uptake of D-glucose. Recycling via Cori-alanine cycle plus CO2 is the difference in irreversible loss measured by using [6-3H]-glucose and [U-14C]-D-glucose. Recycling via the hexose monophosphate pathway can be determined by difference in irreversible loss between [1-3H]-D-glucose and [6-3H]-D-glucose. Recycling via CO2 and glycerol must be measured directly with [U-14C]glucose, bicarbonate, and glycerol. Recycling via hepatic glycogen can be estimated by subtracting all other measured chemical recycling from total chemical recycling. This review describes means to quantify glucose recycling in vivo, enabling studies of mechanisms for conservation and utilization of glucose.     

Routing for multimedia traffic in wireless frequency-hopcommunication networks

A new method is described for routing multimedia traffic in a frequency-hop (FH) store-and-forward packet radio network. The method is illustrated for traffic of two types, each type having its own throughput, delay, and error-rate requirements. A typical application is the routing of voice and data packets in a distributed multiple-hop network. In such an application, voice packets cannot tolerate much delay, but they are allowed to contain a small number of frame erasures while data packets must be delivered error-free even if a moderate delay is required to do so. The fully distributed routing protocol presented in the paper takes into account the type of service required for each type of traffic, and it adapts to the interference as seen by the FH radio receivers in the network. Our approach to multimedia routing is based on least-resistance routing with different link and path resistance metrics for different message types. Each of the resistance metrics for a link reflects the ability of the link to provide the service required by the one of the message types. This includes, but is not limited to, a measure of the likelihood of successful reception by the FH radio receiver for that link. The route selection for a particular type of packet depends on the resistances of the links along the routes from that packet's source to its destination. In general, different routes may be selected for different types of packets. The primary conclusion of this paper is that the quality of service increases for each of the two types of multimedia traffic if the routing protocol accounts for the type of message that is being relayed     

Growth of InGaN HBTs by MOCVD

The design and growth of GaN/InGaN heterojunction bipolar transistors (HBTs) by metalorganic chemical vapor deposition (MOCVD) are studied. Atomic-force microscopy (AFM) images of p⁺InGaN base layers (∼100 nm) deposited under various growth conditions indicate that the optimal growth temperature is limited to the range between 810 and 830°C due to a trade-off between surface roughness and indium incorporation. At these temperatures, the growth pressure must be kept above 300 Torr in order to keep surface pit density under control. An InGaN graded-composition emitter is adopted in order to reduce the number of V-shaped defects, which appear at the interface between GaN emitter and InGaN base and render an abrupt emitter-base heterojunction nearly impossible. However, the device performance is severely limited by the high p-type base contact resistance due to surface etching damage, which resulted from the emitter mesa etch.     

Terrestrial digital video broadcasting for mobile reception using OFDM

Performance of a system design for digital video broadcasting is examined with emphasis on mobile reception. Orthogonal frequency division multiplexing (OFDM) is used to achieve good bandwidth efficiency and to mitigate the intersymbol interference resulting from the channel delay spread. The resulting equivalent channel including OFDM can be modeled as a flat Rayleigh fading channel plus an interchannel interference (ICI) term due to the channel Doppler spread. This ICI term is analyzed and shown to result in an error floor. Performance improvements due to antenna diversity and trellis-coded modulation (TCM) are given. Finally, multiresolution modulation is discussed as a means of achieving graceful degradation and giving degrees of freedom for further performance improvement.This research was supported by the Multimedia Systems R & D Laboratory, Hitachi, Ltd.     

Block Copolymer Surface Reconstuction: A Reversible Route to Nanoporous Films

Thin films of block copolymers have been used as templates and scaffolds for the fabrication of arrays of nanostructured materials. In general, a chemical modification of the film or the removal of one of the components by photodegradative methods is required to produce a nanoporous film that serves as a template or scaffold. Here, however, the preferential interaction of one of the components with a solvent is shown to produce a reconstruction of the block copolymer film that, upon drying, leads to the generation of a nanoporous template. The area density of the pores is identical to that of the original copolymer thin film. Since no chemical reactions occurr, the process is fully reversible. Upon heating the copolymer film above its glass‐transition temperature, mobility is imparted to the copolymer and the original copolymer film with oriented domains is recovered. The film reconstruction significantly simplifies the generation of nanoporous templates.     

Silicon‐Modified Rare‐Earth Transitions—A New Route to Near‐ and Mid‐IR Photonics

Silicon underpins microelectronics but lacks the photonic capability needed for next‐generation systems and currently relies on a highly undesirable hybridization of separate discrete devices using direct band gap semiconductors. Rare‐earth (RE) implantation is a promising approach to bestow photonic capability to silicon but is limited to internal RE transition wavelengths. Reported here is the first observation of direct optical transitions from the silicon band edge to internal f‐levels of implanted REs (Ce, Eu, and Yb); this overturns previously held assumptions about the alignment of RE levels to the silicon band gap. The photoluminescence lines are massively redshifted to several technologically useful wavelengths and modeling of their splitting indicates that they must originate from the REs. Eu‐implanted silicon devices display a greatly enhanced electroluminescence efficiency of 8%. Also observed is the first crystal field splitting in Ce luminescence. Mid‐IR silicon photodetectors with specific detectivities comparable to existing state‐of‐the‐art mid‐IR detectors are demonstrated.     

Propagation considerations for emerging satellite communicationsapplications

The effects of rain and other propagation concerns for new applications areas, currently in operation or planned for implementation by the end of this decade, are described. The areas include: VSAT systems employing low operating margins and/or low elevation angles; traditional communications applications operating with inclined geosynchronous orbits; and mobile and personal communications applications employing networks of low earth orbit (LEO) satellites. Prediction modeling and analysis techniques applicable to these areas are described. Analytical results for a range of operational parameters involving low-margin, low elevation angle, inclined geosynchronous, and LEO systems are presented     

Testing analogue functions using m-sequences

A prototype systems level approach to testing embedded analogue functions in VLSI circuits is described. The technique is self-contained and can be used for wafer, package and field testing. The technique can be easily integrated into a digital test environment. The fault detection capabilities of the method are demonstrated by simulation results.<>     

Fade rates at 13 GHz on Earth-space paths

Fade rate distributions for 13 GHz signals on Earth-space paths have been compiled from the equivalent of 15 station-years of radiometer data that were recorded in Canada. Fade rates of up to 0.42 dB per second were found with the high fade rates tending to occur when the attenuation was also high. As with attenuation statistics, fade rate statistics for Earth-space paths are determined mainly by the climate that is local to the ground station.