Cell planning with capacity expansion in mobile communications: atabu search approach

The cell planning problem with capacity expansion is examined in wireless communications. The problem decides the location and capacity of each new base station to cover expanded and increased traffic demand. The objective is to minimize the cost of new base stations. The coverage by the new and existing base stations is constrained to satisfy a proper portion of traffic demands. The received signal power at the base station also has to meet the receiver sensitivity. The cell planning is formulated as an integer linear programming problem and solved by a tabu search algorithm. In the tabu search intensification by add and drop move is implemented by short-term memory embodied by two tabu lists. Diversification is designed to investigate proper capacities of new base stations and to restart the tabu search from new base station locations. Computational results show that the proposed tabu search is highly effective. A 10% cost reduction is obtained by the diversification strategies. The gap from the optimal solutions is approximately 1~5% in problems that can be handled in appropriate time limits. The proposed tabu search also outperforms the parallel genetic algorithm. The cost reduction by the tabu search approaches 10~20% in problems: with 2500 traffic demand areas (TDAs) in code division multiple access (CDMA)     

Effects of channel thickness variation on bias stress instability of InGaZnO thin-film transistors

Here, we report on the effects of channel (or active) layer thickness on the bias stress instability of InGaZnO (IGZO) thin-film transistors (TFTs). The investigation on variations of TFT characteristics under the electrical bias stress is very crucial for commercial applications. In this work, the initial electrical characteristics of the tested TFTs with different channel layer thicknesses (40, 50, and 60 nm) are performed. Various gate bias (V_GS) stresses (10, 20, and 30 V) are then applied to the tested TFTs. For all V_GS stresses with different channel layer thickness, the experimentally measured threshold voltage shift (ΔV_th) as a function of stress time is precisely modeled with stretched-exponential function. It is indicated that the ΔV_th is generated by carrier trapping but not defect creation. It is also observed that the ΔV_th shows incremental behavior as the channel layer thickness increases. Thus, it is verified that the increase of total trap states (N_T) and free carriers resulted in the increase of ΔV_th as the channel layer thickness increases.     

Simulation and modeling: simulating optical interconnects

The computer-aided design tool can be used in choosing design parameter values that help lower the cost and increase reliability. Good tools are also necessary to minimize the length of the design cycle to bring products to market in a timely manner. Some tools exist that can be used for simulating and designing optical interconnects, but they are intended for electronics and are used for lack of tools more suitable for their unique needs. Currently, no computer-aided design tools encompass all the simulation methodologies required to address the design needs of optical interconnects. After reviewing briefly the various CAD tools that are available, the authors discuss in more detail two tools developed recently: iSMILE (illinois Simulator for the Modeling of Integrated-circuit Level Elements), a CAD tool for the rapid development and simulation of new circuit-level optoelectronics models; and iFROST (illinois FibeR-optic and Optoelectronic Systems Toolkit), a high-level simulator of digital lightwave links     

The effects of sulphur fertilisers on the content of sulpho-amino acids in seeds of cowpea (Vigna unguiculata)

Seed meals of three cowpea (Vigna unguiculata) cultivars, grown in pots containing sulphur-deficient soil supplemented with 0, 0.2, 0.6, 1.8, 5, 15 and 45 parts/10⁶ sulphate-S levels in the soil solution, were examined for total nitrogen, total sulphur and sulpho-amino acid contents. The sulphur content and the ratio of sulphur to nitrogen were found to increase with the increasing level of sulphate-S fertilisation up to ca 5 parts/10⁶. Compared with the control the sulpho-amino acid content in seeds of cowpea TVu 76 increased with S-supplementation up to 5 parts/10⁶ and that of cowpea Sitao Pole increased with S up to 1.8 parts/10⁶. Similar levels (7 and 2 parts/10⁶ respectively) of sulphate-S were required in the soil solution to obtain 95% of the maximum yields of cowpea seeds. The content of sulpho-amino acids in the seeds from 5 parts/10⁶ treatments were similar to those reported for cowpeas grown under field conditions at IITA and elsewhere with adequate levels of soil sulphur for maximum yield.     

Coordination of wavelength and time-window assignment in WDM-based TDM hybrid-PONs

In passive optical networks (PONs), the low effectiveness in terms of service utilization and network evolution have been important design issues. In this article, we introduce a hybrid access network architecture, so called scalable WDM-based Ethernet hybrid-PON (SWE-PON), which features a wavelength-division-multiplexed (WDM) feeder network using a combination of tunable laser device (TLD) and cyclic arrayed waveguide grating (AWG) and time-division-multiplexed (TDM) distribution network based on a reflective transmission mode. Necessary conditions needed to guarantee flawless packet transmission through normal WDM/TDM hierarchical PONs including the SWE-PON, are analyzed. We also propose a hierarchical fair time-window allocation mechanism which coordinates wavelength assignment and time-window bandwidth allocation so that high link utilization and fair bandwidth allocation are guaranteed in every multiplexing level.

A CORDIC-based digital protective relay and its architecture

This paper presents new approach for a hardware architecture for a digital protective relay. All functions for the measurements and relay co-ordination can be calculated with a generalized COordinate Rotation DIgital Computer (CORDIC) algorithm instead of by approximation and extrapolation. The resulting protective relay has higher processing capability making it more able to handle parallel multi-channel sources than existing digital/numerical relays are. Co-ordination accuracy can be also improved by the use of the CORDIC algorithm. This architecture was successfully implemented in a 0.35 μm CMOS technology and then verified.     

Surface graft copolymerization enhanced adhesion of an epoxy-basedprinted circuit board substrate (FR-4) to copper

The lamination of surface modified printed circuit board (PCB) substrate, FR-4(R), from argon plasma pretreatment and UV-induced graft copolymerization with glycidyl methacrylate (GMA), to copper foil was carried out at elevated temperature and in the presence of an epoxy adhesive. The structure and chemical composition of the graft copolymerized surfaces and interfaces of the glass fiber-reinforced and epoxy-based FR-4 substrates were studied by X-ray photoelectron spectroscopy (XPS). The effects of the plasma pretreatment time, the UV illumination time, as well as the curing temperature, on the adhesion strength between the FR-4 substrate and copper were investigated. The assemblies involving GMA graft copolymerized FR-4, or the FR-4-GMA/epoxy resin/Cu assemblies, exhibited a significantly higher interfacial adhesion strength and reliability, in comparison to those assemblies in which only epoxy adhesive alone was used. The enhanced adhesion in the assemblies involving GMA graft copolymerized substrate arises from the fact that the covalently tethered GMA graft chains on the FR-4 surface can become covalently incorporated into the epoxy resin, resulting in the toughening of the epoxy matrix and increased interaction with copper     

A movable safety zone scheme in urban fiber-optic microcellularsystems

We consider an urban fiber-optic microcellular system in which a cigar-shaped cell consists of several microzones with their own antenna sites connected to a central station through optical fibers. To increase the efficiency of radio resources and reduce unnecessary handoffs between microzones, we propose a movable safety zone scheme. A safety zone is a virtually guarded area that does not permit cochannel interference. Outside the safety zone, cochannels can be reused. The safety zone can move under the condition that its user does not meet cochannel interference as he moves to an adjacent microzone. Considering user mobility characteristics in the cigar-shaped cell, we analyze and evaluate the proposed system in terms of intracell and intercell handoff rates, blocking probability, intracell call-dropping probability, and channel reuse parameter. The proposed system can handle a traffic capacity of about 12 Erlangs for seven traffic channels under a call blocking probability of 1% and generates a negligible number of intracell handoffs compared with those of intercell handoffs     

Satellite UMTS/IMT2000 W-CDMA air interfaces

The third-generation IMT-2000 initiative of the International Telecommunication Union is aiming at the provision of a limited family of global standards providing worldwide multimedia wireless services in a host of environments encompassing indoor picocells to satellite megacells. The ITU IMT-2000 initiative has been supported by several regional standardization bodies such as the European Telecommunication Standard Institute with its Universal Mobile Telecommunication System. In this article a few air interface proposals for the satellite component of UMTS/IMT-2000 based on adaptation of the emerging terrestrial wideband CDMA standards are reviewed. In particular, S-UMTS requirements are examined together with W-CDMA applicability to the satellite environment. It is shown that with minor adaptations, the terrestrial W-CDMA air interface provides an efficient solution for the satellite UMTS component. This commonality will certainly help in the realization of low-cost low-size dual-mode user terminals encompassing both terrestrial and satellite components