Optimal policies for integrating heterogeneous services on isdn channels

A technique for the classification and evaluation of hierarchical access integration policies of ISDN channels is proposed. The essence of the basic control decisions based on several parameters of the servers and channel is captured in a single priority-based-layered model of multiple queues. We solve for the resulting delay of different policies and investigate the performance in one tractable limit of this model. Using our understanding of the problem parameters and their interaction, we propose a number of heuristic policies for the general model. The results of the general problem complexity investigations suggest the use of simulation models. Problem parameters considered are channel acceptable access delay value, number of servers needed, and flow duration time of a request. Preemptive and non-pre-emptive policies on queued traffic are considered. Performance considers average delay, delay variation and channel utilization. Simulation data on these policies suggest that policies that favour shorter services given better overall delay over a wide range of system parameters. Policies that favour longer and broadband services, on the other hand, show better quality and smaller delay variation.     

Performance analysis of the forward link cdma2000 1xEV‐DO evolution for multirate services in cellular wireless system

In this paper, we propose a combined analytical and simulation framework for performance evaluation of the forward link in the cdma2000 evolution for data only (1xEV‐DO) cellular systems with throughput and spectral efficiency being used as performance metrics. A closed form expression for the aggregate average throughput is derived in terms of system‐dependent parameters and a discrete random process that reflects the stochastic behavior of the transmission channel. The random process is expressed in terms of the cumulative distribution function (CDF) of the users signal‐to‐interference‐plus‐noise ratio (SINR). Quantitative results for throughput and spectral efficiency are presented for a variety of users distribution models, base station antenna types and frequency reuse factors for the cases of sectorized and non‐sectorized cells. Furthermore, we study the impact of the cell radius on the system performance. Copyright © 2006 John Wiley & Sons, Ltd.     

A Bluetooth Based Sensor Network for Civil Infrastructure Health Monitoring

Communicating with sensors has long been limited either to wired connections or to proprietary wireless communication protocols. Using a ubiquitous and inexpensive wireless communication technology to create Sensor Area Networks (SANs) will accelerate the extensive deployment of sensor technology. Bluetooth, an emerging, worldwide standard for inexpensive, local wireless communication is a viable choice for SANs because of its inherent support for some of the important requirements – low power, small form factor, low cost and sufficient communication range. In this paper we outline an approach, centered on the Bluetooth technology, to support a sensor network composed of fixed wireless sensors for health monitoring of highways, bridges and other civil infrastructures. We present a topology formation scheme that not only takes into account the traffic generated by different sensors but also the associated link strengths, buffer capacities and energy availability. The algorithm makes no particular assumptions as to the placement of nodes, and not all nodes need to be in radio proximity of each other. The output is a tree shaped scatternet rooted at the sensor hub (data logger) that is balanced in terms of traffic carried on each of the links. We also analyze the scheduling, routing and healing aspects of the resulting sensor-net topology.     

TiN Nanoparticles for Enhanced THz Generation in TDS Systems

By virtue of the surface plasmon resonance effect, plasmonic nanoparticles (NPs) can localize the light field and significantly enhance the performance of some optoelectronic devices. In this work, NPs are employed for an enhanced generation of terahertz radiation from LT-GaAs-based antennas. Therefore, we have prepared plasmonic TiN NPs by direct ultrasonication (ULS) and pulsed laser ablation (PLA) techniques. The zeta potential, particle size, and absorbance were used to characterize the NPs in their colloidal forms in a comparison to commercial Au NPs. A layer of polydispersed titanium nitride (TiN) NPs prepared by PLA and deposited on the surface of an LT-GaAs device shows a significant improvement of terahertz signal generation from these devices with an enhancement of the peak to peak amplitude of 100%.     

Transmit antenna selection of correlated MIMO multiuser cognitive radio networks in Nakagami‐m fading channels

In this paper, we examine the impact of antenna correlation on transmit antenna selection with receive maximal ratio combining (TAS/MRC) in multiple‐input multiple‐output multiuser underlay cognitive radio network (MIMO‐MCN) over a Nakagami‐m fading environment. The secondary network under consideration consists of a single source and M destinations equipped with multiple correlated antennas at each node. The primary network composed of L primary users, each of which is equipped with multiple correlated antennas. For the considered underlay spectrum sharing paradigm, the transmission power of the proposed secondary system is limited by the peak interference limit on the primary network and the maximum transmission power at the secondary network. In particular, we derive exact closed‐form expressions for the outage probability and average symbol error rate of the proposed secondary system. To gain further insights, simple asymptotic closed‐form expressions for the outage probability and symbol error rate are provided to obtain the achievable diversity order and coding gain of the system. In addition, the impact of antenna correlation on the secondary user ergodic capacity has been investigated by deriving closed‐form expressions for the secondary user capacity. The derived analytical formulas herein are supported by numerical and simulation results to clarify the main contributions. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance evaluation of OFDM and single‐carrier systems using frequency domain equalization and phase modulation

In this paper, we study the performance of the continuous phase modulation (CPM)‐based orthogonal frequency division multiplexing (CPM‐OFDM) system. Also, we propose a CPM‐based single‐carrier frequency domain equalization (CPM‐SC‐FDE) structure for broadband wireless communication systems. The proposed structure combines the advantages of the low complexity of SC‐FDE, in addition to exploiting the channel frequency diversity and the power efficiency of CPM. Both the CPM‐OFDM system and the proposed system are implemented with FDE to avoid the complexity of the equalization. Two types of frequency domain equalizers are considered and compared for performance evaluation of both systems; the zero forcing (ZF) equalizer and the minimum mean square error (MMSE) equalizer. Simulation experiments are performed for a variety of multipath fading channels. Simulation results show that the performance of the CPM‐based systems with multipath fading is better than their performance with single path fading. The performance over a multipath channel is at least 5 and 12 dB better than the performance over a single path channel, for the CPM‐OFDM system and the proposed CPM‐SC‐FDE system, respectively. The results also show that, when CPM is utilized in SC‐FDE systems, they can outperform CPM‐OFDM systems by about 5 dB. Copyright © 2010 John Wiley & Sons, Ltd.     

High IIP3 and Low-Noise CMOS Mixer Using Non-linear Feedback Technique

A third-order intermodulation cancelation technique using a non-linear feedback is proposed to design a low-power low-distortion mixer in a 65 nm standard CMOS technology. The IM3 cancelation is achieved by estimating distorting error at a non-linear feedback element and subtracting it from the input. The linearization technique is utilized in the input trans-conductance of the mixer. The circuit functionality is analyzed using Volterra series. The covering frequency range of the mixer is 800 MHz to 5 GHz. The technique increases the input-referred third-order intercept point (IIP3) and input 1 dB compression point to +16.4 dBm and −1.87 dBm, respectively. It obtains a gain of 9 dB and an input-referred noise of 1.84 nV/?{}/\sqrt{}Hz while consumes 8.75 mA from 1.2 V supply. The layout of the mixer occupies 0.315 mm × 0.296 mm of silicon area.     

1.2 nm capacitance equivalent thickness gate stacks on Si-passivated GaAs

Experiments to increase the specific capacitance of MOS capacitors consisting of HfO₂ on a passivating interfacial layer (IL) of amorphous Si (a-Si) on GaAs are described. XPS analysis of the layers and electrical measurements on the capacitors are combined to study the evolution of the gate stack during deposition and subsequent heat treatments. It is shown that oxidation of the a-Si IL is a major factor in preventing the attainment of a scaled capacitance equivalent thickness (CET). By controlling the deposition of the layers, the gate metal and the heat treatments, a highly scaled gate stack with a CET of 1.2 nm and a leakage reduction of more than 4 orders of magnitude with respect to SiO₂/Si was realized.     

Inverse modeling and its application in the design of high electronmobility transistors

An inverse modeling technique is introduced to determine the structural and physical parameters of HEMT from the desired data for maximum transconductance. The technique is based on the availability of analytical expressions describing the electron carrier concentration, the current, the transconductance, the capacitances and the unity current gain frequency of a HEMT. Empirical formulae are obtained that relate the maximum transconductance to the doped AlGaAs thickness, spacer layer thickness, dopant density and aluminum mole fraction. The technique is applied to the design of a HEMT and shows good agreement with the experimental data     

Prediction of subharmonic oscillation in switching regulators: from a slope to a ripple standpoint

New exact critical conditions for predicting subharmonic instability in switching regulators are approximated by simple design-oriented expressions valid under practical conditions. These simplified expressions contain the ripple and slope information of the feedback control signal. Depending on the converter topology, the controller used and values of parasitic parameters, either the slope or the ripple can be dominant in predicting instability. A discussion on the validity of this interpretation is illustrated through six different examples of switching regulators using the concept of the spectral radius and the relative degree of the system loop. Using this approach, the boundary between the desired stable region and the subharmonic instability can be easily obtained. The theoretical results are validated by means of numerical simulations.