Analytical wide-band modeling of high frequency resistance in integrated spiral inductors

For integrated spiral inductor synthesis, designers and design automation tools require efficient modeling techniques during the initial design space exploration process. In this paper, we introduce an analytical frequency-dependent resistance model for integrated spiral inductors. Based on our resistance formulation, we have developed a systematic technique for creating wide-band circuit models for accurate time domain simulation. The analytical resistance model provides a fast alternative to field solver-based approaches with typical errors of less than 2.6 percent while surpassing the accuracy of several other analytical modeling techniques by an order of magnitude. Furthermore, the wide-band circuit generation technique captures the frequency-dependent resistance of the inductor with typical errors of less than 3.2 percent.     

Thermal Annealing and Propagation of Shockley Stacking Faults in 4H-SiC PiN Diodes

Stacking faults within 4H-SiC PiN diodes are known to be detrimental to device operation. Here, we present electroluminescence (EL) images of 4H-SiC PiN diodes providing evidence that electrically and optically stimulated Shockley stacking fault (SSF) propagation is a reversible process at temperatures as low as 210°C. Optical beam induced current (OBIC) images taken following complete optical stressing of a PiN diode and that lead to a small number of completely propagated SSFs provide evidence that such defects propagate across the n–/p+ interface and continue to grow throughout the p+ layer. These observations bring about questions regarding the validity of the currently accepted driving force mechanism for SSF propagation.     

Phase Noise Effects and Mitigation in OFDM Systems over Rayleigh Fading Channels

In this paper, we provide an exact analysis of phase-noise effects on orthogonal frequency division multiplexing (OFDM) performance. We focus on the phase-noise inter-carrier interference (ICI) and derive a closed-form expression for the signal-to-interference-noise ratio (SINR), which helps in understanding how system behavior changes with a certain parameter. An ICI reduction (ICIR) scheme was proposed in [14] and the algorithm performance over AWGN channel was thoroughly studied. In this paper, we further extend this work to Rayleigh fading channel and investigate the effects of multipath fading on the phase-noise mitigation. It is shown by the study that the ICIR algorithm reduces the phase-noise ICI a great deal before channel estimation and improves greatly system performance. Finally, numerical results show the effectiveness of the proposed approaches. Guanghui Liu was born in Sichuan, China, in 1976. He received the B.S. degree from Sichuan Teachers College, Nanchong, Sichuan, China in 1999, received the M.Sc. and Ph.D. degrees in electronic engineering from University of Electronic Science and Technology of China (UESTC), Chengdu, Sichuan, China, in 2002 and 2005 respectively. Dr. Liu serves as a reviewer for the IEEE Transactions on Communications, the IEEE Transactions on Broadcasting and the IEEE Transactions on Wireless Communications. As a research engineer, he is now with Samsung Electronics, Suwon, Republic of Korea. His research interests include synchronization, channel estimation and equalization, phase-noise suppression in OFDM communication systems. Weile zhu was born in Sichuan, China, in 1940. Since 1988 he has been a professor of signal processing with University of Electronic Science and Technology of China, Chengdu, China. He was a visiting scholar researching image processing in University of Illinois from 1980 to 1981, researching pattern recognition in Purdue University from 1982 to 1983, and researching intelligent robot in Stanford University from 1990 to 1991. His research interests include digital video codec and transmission, multicarrier modulation, and HDTV etc.     

A Clock Synchronization Algorithm for Multihop Wireless Ad Hoc Networks

In multihop wireless ad hoc networks, it is important that all mobile hosts are synchronized. Synchronization is necessary for power management and for frequency hopping spread spectrum (FHSS) operations. IEEE 802.11 standards specify a clock synchronization protocol but this protocol suffers from the scalability problem due to its inefficiency contention mechanism. In this paper, we propose an automatic self-time-correcting procedure (ASP) to achieve clock synchronization in a multihop environment. Our ASP has two features. First, a faster host has higher priority to send its timing information out than a slower one. Second, after collecting enough timing information, a slower host can synchronize to the faster one by self-correcting its timer periodically (which makes it becoming a faster host). Simulation results show that our ASP decreases 60% the average maximum clock drift as compared to the IEEE 802.11 and reduces 99% the number of asynchronism in a large-scale multihop wireless ad hoc networks.     

Channel and Data Estimation for Ad Hoc Networks and Cognitive Radio

Estimation of channel and data characteristics by the receiver is important in adaptive wireless transmission protocols and in cognitive radio. This paper formulates the estimation problem with the help of an illustrative example from the IEEE 802.11a OFDM standard. The problem reduces to the estimation of the common component variance and mixing probabilities in a finite Gaussian mixture, with known values for component means. Using the known component means, μ₁, ... , μ _M , a set of non-linear transformations, and of the data (mixture random variable X) are used to develop convergent and computationally efficient estimators for both the noise variance and the vector of symbol probabilities. The estimation equations can be implemented recursively or with a batch processing algorithm. Asymptotic variances of the estimates and the Cramer–Rao minimum variance bounds are derived. The estimates converge to true unknowns even when the sequences of noise and data symbols are dependent sequences. The OFDM example is simulated with parameters corresponding to the highest acceptable error rate. For a time-varying channel model chosen from the literature, it is shown that our estimator receives considerably more than adequate amount of data during an average time interval of unchanging channel characteristics. Analytical results, numerical results and related issues are discussed.     

Location Management in PCS Networks by Caching Two-Level Forwarding-Pointers

One of the challenging tasks in Personal Communication Services (PCS) is to efficiently maintain the location of PCS subscribers who move from one region to another (hereafter called mobile users). When a mobile user receives a call, the network has to quickly determine its current location. The existing location management scheme suffers from high signaling traffic in locating the mobile users. Two-level forwarding pointer scheme has been proposed from per-user forwarding pointer scheme to reduce the cost of signaling traffic. In this paper, we enhance the two-level forwarding pointer scheme. When a mobile user moves from its current Registered Area (RA), which is served by Mobile Switching Center (MSC), to another RA the local switch that acts as a parent of those two MSCs maintains this movement in its memory (hereafter called cache entry). A cache entry is used to locate rapidly the mobile user instead of querying the Home Location Register (HLR) and waiting for its reply. HLR is centralized in the network and far away from the mobile users so that the signaling traffic crossing it is expensive. Sometimes the cache entry may be failed to reach the mobile user then a two-level forwarding pointers will be created from the corresponding Visitor Location Register (VLR), attached to its MSC, through a correct path to locate the mobile user. Thus, there is a saving in cost of querying the underlying HLR. The analytical results indicate that such proposal efficiently reduces the signaling traffic cost for all values of Call to Mobility Ratio (CMR), this is especially considerable when CMR ≥1, without any increase in the call setup delay. Salah M. Ramadan (samohra@yahoo.com) received the BS and MS degrees from Computers Engineering Department, Al-Azhar University, Cairo, Egypt, in 1995 and 2002, respectively. From 2002, he was a Ph.D. student in Computers Engineering Department at Al-Azhar University and is currently pursuing the Ph.D. degree, where he is a research assistant in the Wireless Networks Branch. His research interests include traffic management in ATM networks, routing protocols, mobility management in PCS networks, and mobile computing. He is currently an instructor in Cisco Academy, Egypt. Ahmed M. El-Sherbini (Sherbini@mcit.gov.eg) received the Ph.D. in Electrical and Communication Engineering, Case Western University, U.S.A. March 1983 and M.Sc. in Communication Engineering, Cairo University, Giza, Egypt, June 1980. (M. Sc. Research Studies at the Ecole Nationale Superieure des Telecommunications (ENST), Paris, France). He is the Director, National Telecommunication Institute – Ministry of Communications and Information Technology, Egypt and Professor of Electrical and Communication Engineering Dept. Faculty of Engineering, Cairo University, Egypt. M. I. Marie received his B.Sc., M.Sc. and Ph.D. in electronic and communication engineering from Cairo University on 1972, 1981, 1985, respectively. Now he is a professor of communications at Computer and System Engineering department Al-Azhar University, Cairo, Egypt. His fields of interest includes digital communication, computer networks and protocols development. M. Zaki (azhar@mailer.scu.eun.eg) is the professor of software engineering, Computer and System Engineering Department, Faculty of Engineering, Al-Azhar University at Cairo. He received his B.Sc. and M.Sc. degrees in electrical engineering from Cairo University in 1968 and 1973 respectively. He received his Ph.D. degrees in computer engineering from Warsaw Technical University, Poland in 1977. His fields of interest include artificial intelligence, soft computing, and distributed system.     

On-Demand Utility-Based Power Control Routing for Energy-Aware Optimization in Mobile Ad Hoc Networks

In this paper, we propose a novel on-demand energy-aware routing protocol, UBPCR [utility-based power control routing], which reduces the trade-offs that arise in the other energy-aware route selection mechanisms that have recently been proposed for mobile ad hoc networks. Our approach is based on an economic framework that represents the degree of link's satisfaction (utility). With UBPCR, the utility function for any transmitter-receiver pair is defined as a measure of the link's preference regarding the signal-to-interference-and-noise ratio (SINR), the transmit power, and the transmitter's residual battery capacity. During a route-searching process, each intermediate node between the source and the destination is executed via two consecutive phases: the scheduling phase and the transmit power control phase. The scheduling algorithm finds the proper qualified data slot for the receiving channel so that the transmissions of independent transmitters can be coordinated. The transmit power control determines the optimal power, if one exists, that maximizes the corresponding link's utility. Extensive simulations show that the UBPCR protocol can achieve incompatible goals simultaneously and fairly. Chan-Ho Min received the B.S. degree in Industrial Management and the M.S. degree in Industrial Engineering from Korea Advanced Institute of Science and Technology (KAIST) in 2000 and 2002, respectively, where he is currently pursuing the doctoral degree in Industrial Engineering (Telecommunication Engineering Interdisciplinary Program) at KAIST. His research interests include the optimization problems of radio resource management for broadband wireless/cellular/ad hoc/satellite communication networks. In particular, he focuses on mobile ad hoc networking. Sehun Kim received the B.S. degree in Physics from Seoul National University, Seoul, Korea, and the M.S .and Ph.D. degrees in Operations Research from Stanford University. In 1982, he joined the faculty of the Korea Advanced Institute of Science and Technology (KAIST), where he is currently a Professor of Industrial Engineering. His research has been in the areas of combinatorial and nonlinear optimization. Recently, he is working on the application of optimization techniques to the design and analysis of computer and communication systems. He has published a number of papers in Mathematical Programming, Operations Research Letters, Journal of Optimization Theory and Applications, IEEE Trans. on Vehicular Technology, and International Journal of Satellite Communications.     

Passivation of Surface and Interface States in AlGaN/GaN HEMT Structures by Annealing

The Ni/AlGaN interfaces in AlGaN/GaN Schottky diodes were investigated to explore the physical origin of post-annealing effects using electron beam induced current (EBIC), current–voltage (I–V) characteristics, and X-ray photoelectron spectroscopy (XPS). The EBIC images of the annealed diodes showed that the post-annealing process reduces electrically active states at the Schottky metal/AlGaN interfaces, leading to improvement of diode performance, for example a decrease in reverse leakage current and an increase in Schottky barrier heights. Pulsed I–V characteristics indicate the Fermi level is up-shifted after annealing, resulting in a larger sheet carrier density at the AlGaN/GaN interface. Unintentional oxidation of the free AlGaN surface during the post-annealing process, revealed by XPS analysis, may prevent electron trapping near the drain-side of the gate edges. We suggest that the post-annealing process under an optimized conditions can be an effective way of passivating AlGaN/GaN heterojunction field-effect transistors.     

Reverse Converters for a New Moduli Set {2<Superscript>2n</Superscript> − 1, 2<Superscript>n</Superscript>, 2<Superscript>2n</Superscript> + 1}

A new moduli set derived from a recently proposed four moduli set is considered, in this paper. The problem of reverse conversion has been considered, and it is shown that the proposed moduli set needs less reverse conversion time and area requirements than the converter for the four moduli set from which it is derived. The proposed moduli set is also compared with two other well-known three moduli sets and for realizing the same dynamic range regarding the area and conversion times of the residue number system (RNS)-to-binary converters.