Space-time trellis codes over rapid rayleigh fading channels with channel estimation?part ii: performance analysis and code design for non-identical channels

We consider the maximum likelihood (ML) receiver design, performance analysis and code design for space-time trellis codes (STTC) over non-identical, rapid fading channels with imperfect channel state information (CSI). The exact pairwise error probability (PEP) and PEP bounds for the ML receiver are obtained. A new code design criterion exploiting the statistical information of the channel estimates is proposed, which can minimize the performance loss caused by channel estimation error. New codes are obtained via an iterative search algorithm with reduced complexity. Under actual channel estimation conditions, our codes perform better than the existing codes in the literature which are designed on the assumption of identical channels, and perfect CSI at the receiver. More performance gain can be achieved by our codes when the degree of imbalance among the links is higher.     

Simulation and analysis of performance on the Compass™ enhanced by GEO and IGSO

Positioning accuracy of the Global Navigation Satellite System (GNSS) can be analyzed by Positioning Dilution Of Precision (PDOP). In order to enhance the navigating performance of Asia and the Pacific areas, this paper analyzes the next generation Beidou™ navigation satellite system (Compass™) enhanced by Geostationary Earth Orbit (GEO) and Inclining GeoSynchronized Orbit (IGSO). As global navigation satellite system, Compass™ must be robust enough to avoid system layoff, when some nodes are not available. So, the Compass™ enhanced by GEO and IGSO constellation is proposed and analyzed its PDOP proformance, this paper shows some exciting results of performance of Compass™ enhanced by GEO and IGSO. From the simulation results, we can found that: when more than fifteen satellites are invalid, the enhanced system could be operating normally.     

PMOS breakdown effects on digital circuits – Modeling and analysis

The degradations in the pMOS device due to gate oxide breakdown introduced by voltage stress were investigated experimentally. The stress-induced shifts in gate leakage and I–V characteristics were presented. A combined Verilog-A and sub-circuit model was first time introduced and employed to simulate the pMOS breakdown behaviors. The Verilog-A model can accurately simulate the power law characteristics of breakdown gate leakage current with a fractional coefficient. With the developed model, the simulated results and the measurements have good agreements. The traditional logic circuits, such as the inverter and the latch, have been investigated through Cadence simulations with the improved models. The latch suffers from the gate oxide breakdown significantly. The NULL Convention Logic (NCL) circuit has also been examined and analyzed systematically. The results showed substitute degradations due to the pMOS gate oxide breakdown.     

Advanced thermal failure analysis and reliability investigations – Industrial demands and related limitations

The thermal interaction between actively operated integrated circuits and applied characterization tools is one of the most important ones within failure analysis (FA) and reliability/methodology (RM) investigations. Hereby different kind of thermal interaction mechanisms can be utilized, whereas these mechanisms have to be separated for instance into classes with respect to thermal excitation and/or detection, spatial limitations, and underlying physical principle. Although they all have in common the capability to link the thermo-electric device characteristic to a representing output signal, they have to be interpreted in completely different ways. Therefore, within this paper we discuss from a practical engineering point of view established FA/RM characterization techniques by means of infrared-lock in thermography (IR-LIT) and thermal induced voltage alteration (TIVA) case studies as well as the capability of non established ones like scanning thermal microscopy (SThM), thermal reflectance microscopy (TRM), and time domain thermal reflectance (TDTR). Hereby we focus on the complementarities of the methods for localization and characterization as well as on the according industrial demands and related limitations.     

Signal design and system operation of GlobalstarTM versus IS‐95 CDMA – similarities and differences

The Globalstar^TM system provides telephone and data services to and from mobile and fixed users in the area between ±70 degrees latitude. Connection between user terminals and the PSTN is established through fixed terrestrial gateways via a constellation of low earth orbiting (LEO) satellites. Globalstar uses an extension of the IS‐95 CDMA standard that is used in terrestrial digital cellular systems. The LEO satellite link is sufficiently different from the terrestrial cellular link that certain departures from IS‐95 were needed both in signal design as well as in system operation. This paper describes some of the similarities and differences of Globalstar air interface versus IS‐95. This revised version was published online in August 2006 with corrections to the Cover Date.     

Novel flexible and transparent microstrip low-pass filter design with Π-shaped DGS

A new design for a transparent low-pass filter(LPF) using a flexible polyethylene terephthalate(PET) material and metallic copper was proposed in this paper. The transparent microstrip filter employs an asymmetric Π-shaped structure with dimensions of 260.000 mm×13.000 mm×0.148 mm, which owns a narrow transition band and achieves an insertion loss of less than 1.0 dB below 0.26 GHz. Furthermore, the insertion loss of the transparent microstrip filter can exceed 30 dB in the stopband from 1.02 GHz to 6.50 GHz. Square holes are added to the copper layer to improve the transparency of the LPF, and the filter performance can be adjusted by changing the square hole area and resolution. Additionally, multiple identical structures are cascaded to increase the insertion loss in the stopband while maintaining the passband. The transparent microstrip LPF has the characteristics of flexibility, high transparency, and significant insertion loss in the stopband, making it suitable for applications that require electromagnetic protection in a clear field of vision.     

Design of UWB monopole antenna with dual notched band characteristics by using π-shaped slot and EBG resonator

In this paper, we propose the design of coplanar waveguide (CPW) ultra-wideband (UWB) dual notched band monopole antenna with a π-shaped slot and EBG is proposed. The designed antenna produces an impedance bandwidth of 2.7–11.7 GHz (VSWR < 2), except with 3.4 GHz (3.3–3.7 GHz) for S-band WiMAX application and 6.9 GHz (6.5–7.2 GHz) for C-band IEEE INSAT applications. Here, the lower and upper notches are realized by proposing a π-shaped slot on the radiating element and an electromagnetic bandgap structure as a resonator integrated on either side of the ground plane. Meanwhile, the impedance over a frequency range and current distribution are also plotted for the proposed design. The antenna prototype is fabricated and characterized experimentally for validation purpose. Fair matching is observed among the simulated and measured results.     

Capacity and error probability performance analysis for MIMO MC DS-CDMA system in η–μ fading environment

In this paper, we investigate the effect of multiple input multiple output (MIMO) systems on the performance of the multicarrier direct sequence code division multiple access (MC DS-CDMA) system operating over independent identically distributed (i.i.d) η–μ flat fading environment in terms of average error probability and average channel capacity. We derive the instantaneous signal to interference noise ratio (SINR) at the output of the receiver. Hence, based on moment generating function (MGF) approach, we obtain the probability density function (PDF) of the instantaneous SINR. Closed form expressions of average error probabilities for the system are developed and expressed in Appell's and Lauriccella's hypergeometric functions. Furthermore, we achieve exact expression of average channel capacity for the system. Finally, we validate our results using Monte Carlo simulation technique and also compare with those already available in the literature.     

Mobility model and performance analysis for zone‐based registration in CDMA mobile communication system

In this paper, we describe a mobility model and analysis for zone-based registration in the CDMA mobile communication system. We first propose a simple and proper mobility function for single zone-based registration. We establish the circumstances of multiple zone-based registration, which is based on the mobility function of single zone-based registration, and perform computer simulations for the circumstances. Using the simulation results, we obtain the optimal number of zones, N, that minimizes signaling traffic on radio channels. Results show that, in most cases, N is 2. We also show that multiple zone-based registration has lower signaling traffic on radio channels than single zone-based registration, and zone‐based registration must be implemented as multiple zone‐based registration. This revised version was published online in August 2006 with corrections to the Cover Date.     

A new approach to the design and analysis of peer‐to‐peer mobile networks

This paper introduces a new model and methodological approach for dealing with the probabilistic nature of mobile networks based on the theory of random graphs. Probabilistic dependence between the random links prevents the direct application of the theory of random graphs to communication networks. The new model, termed Random Network Model, generalizes conventional random graph models to allow for the inclusion of link dependencies in a mobile network. The new Random Network Model is obtained through the superposition of Kolmogorov complexity and random graph theory, making in this way random graph theory applicable to mobile networks. To the best of the authors' knowledge, it is the first application of random graphs to the field of mobile networks and a first general modeling framework for dealing with adhoc network mobility. The application of this methodology makes it possible to derive results with proven properties. The theory is demonstrated by addressing the issue of the establishment of a connected virtual backbone among mobile clusterheads in a peertopeer mobile wireless network. Using the Random Network Model, we show that it is possible to construct a randomized distributed algorithm which provides connectivity with high probability, requiring exponentially fewer connections (peertopeer logical links) per clusterhead than the number of connections needed for an algorithm with a worst case deterministic guarantee.     

Thermal analysis and design of a 75-W hybrid-type DC–DC converter for space applications

Hybrid DC–DC converters for space applications should be designed for operation at full rated power within the military specification for temperature range of −55 to +125 °C. Hence, the thermal design is a crucial step in the design process of converter, ensuring that no component of the converter exceeds its rated maximum operating temperature. One of the objectives of this work is to guarantee that all electronic components operate below their maximum allowable temperature. For this purpose, a three dimensional model of a converter based on the finite element method was developed. Results based on numerical simulation were validated by experimental data from infrared camera. The total amount of dissipated power in every component was determined experimentally based on a prototype converter. In the case of a component with high power consumption, such as the field effect transistor, the increase in temperature was minimized by applying designed heat sink with a high-thermal-conductivity material.     

Development of parallel-connected pump–valve-coordinated control unit with improved performance and efficiency

Recently, there has been a growing demand for electro-hydraulic systems that can offer both high control performance and high energy efficiency. Traditionally, high performance is achieved using expensive high-bandwidth servo valve-controlled units. However, the inevitable throttling losses that occur in such systems severely decrease their energy efficiency. For a higher energy efficiency, pump-controlled systems have become the standard choice in this field. Nevertheless, their dynamic performance is inferior to that of valve-controlled systems. Considering the individual advantages of the valve- and pump-controlled units, our previous work proposed the idea of a parallel-connected pump–valve-coordinated system. In this study, a generic form of the coordinated control unit is discussed, and further improvements are made to the control design. In addition, comprehensive experimental studies are conducted with a variable-displacement pump and a servo motor-driven pump equipped with a direct pump-control component. Favorable results are obtained, demonstrating that the proposed system can achieve better tracking performance than a typical valve-controlled system, while simultaneously improving the energy efficiency.     

NeXOS – The design,development and evaluation of a rehabilitation system for the lower limbs

Recent years have seen the development of a number of automated and semi-automated systems to support physiotherapy and rehabilitation. These deploy a range of technologies from highly complex purpose built systems to approaches based around the use of industrial robots operating either individually or in combination for applications ranging from stroke rehabilitation to mobility enhancement. The NeXOS project set out to investigate an approach to the rehabilitation of the lower limbs in a way which brought together expertise in engineering design and mechatronics with specialists in rehabilitation and physiotherapy.The result is prototype of a system which is potentially capable in operating in a number of modes from fully independent to providing direct support to a physiotherapist during manipulation of the limb. Designed around a low cost approach for an implementation ultimately capable of use in a patients home using web-based strategies for communication with their support team, the prototype NeXOS system has validated the adoption of an integrated approach to its development. The paper considers this design and development process and provides the results from the initial tests with physiotherapists to establish the operational basis for clinical implementation.     

Mid-wavelength InAs/GaSb type-Ⅱ superlattice barrier detector with nBn design and M barrier

This study reports the performance of an InAs/GaSb type-Ⅱ superlattices(T2SLs) detector with nBn structure for mid-wavelength infrared(MWIR) detection. An electronic band structure of M barrier is calculated using 8-band k·p method, and the nBn structure is designed with the M barrier. The detector is prepared by wet etching, which is simple in manufacturing process. X-ray diffraction(XRD) and atomic force microscope(AFM) characteristics indicate that the detector material has good crystal quali...     

Formaldehyde emissions in large rotating electrical machines – root cause analysis, background and prevention

Odours have been generated during commissioning and first time operation of large rotating electrical machines. These emissions were observed in machines from several manufacturers. Subsequent investigations indicated that formaldehyde was present. The main source of the emissions was located in the insulation varnish of the sheets of the stator core. In core sheet varnishes, formaldehyde containing precursors are often used as crosslinking agents. Energy input during the curing process, determines the extent of reversibly bonded formaldehyde after the cure. Weakly bonded formaldehyde is released when the coated sheets are heated during the early operation of the generator. The influence of the curing conditions on the formaldehyde emissions of stator core sheets was investigated in laboratory experiments. Experiments showed a decrease in formaldehyde emissions by increasing the energy input during the curing process. Even if the energy input was high enough to achieve the required mechanical (e.g. cross cut test), chemical (e.g. rubbing alcohol test) and electrical properties (e.g. surface resistivity), the formaldehyde release could still be reduced by further increase of the energy input. Appropriate material properties do not correlate with the amount of releasable formaldehyde in the varnish. This gives an opportunity to modify the curing to reduce or eliminate the emissions without negatively impacting the insulating properties. The influence of the chemistry of the varnishes on the formaldehyde release was also studied. Varnishes based on phenolic and melamine resins give the highest emissions, while the polyester-based varnishes showed no emissions. The temperature dependence and the kinetics of the formaldehyde release of stator core sheets are investigated in model tests. The laboratory experiments on the kinetics of the emissions showed, that at a certain temperature the majority of formaldehyde is emitted over a short time. Later emissions approach zero with continued thermal exposure. Temperature tests on stator core sheets in the range of 30–100°C showed, that at 30°C small amounts of formaldehyde are released. Interestingly, the formaldehyde emission does not increase linearly with increasing temperature, it shows a first maximum at about 60°C and a second maximum at about 100°C. This implies chemical reactions associated with definite activation energies that are required for splitting off the formaldehyde. Measures can be taken, during lamination processing, to avoid improper formaldehyde emission in large rotating electrical machines (safety measures and venting in existing machines, optimization of the curing process, development of formaldehyde free coatings for stator core laminations).     

A task‐oriented priority queue for telephone switch design: with modified FCFS and forking

When developing a telephone switch, it is useful to know how long it will take to process the various tasks associated with call processing. The model developed in this paper gives expected sojourn times for those tasks. It is a priority queueing model with a modified firstcome firstserved (FCFS) service discipline, which mimics the treatment of tasks in actual system software. The model is an M/G/1 queueing model with preemption (preemptive resume). It consists of multiple queues, one for each distinct priority, where each task has been preassigned a constant priority. Within each priority queue, the tasks are further grouped by type. An arriving task will join the back of the group of tasks of its type, regardless of where this group is positioned in the queue. Upon completion of a task, several tasks of different types can enter the priority queues. This is referred to as forking. Call processing involves many ordered sets of tasks (jobs or classes), some of which will contain forks. The model produces results that compare favorably with those obtained by simulation.