High Mobility Conditions Research Articles

A Comparative Study of Coverage Estimation and Quality of Service for DVB-H Urban Networks Using a Specialized RF Planning Software

The Digital Video Broadcasting - Handheld (DVB-H) standard is the ETSI standard for delivering broadcasting services of high data rates to handheld devices, under high mobility conditions. This paper will compare the different modulation techniques used by the DVB-H standard from the coverage point of view. The coverage estimation simulations have been made with a specialized RF planning tool using real Geographic Data for the metropolitan region of Athens. Thus, we will present a comparative study, of various planning factors like coverage percentage and location probability and compare them for the different modulation schemes used.

Performance analysis of multi-radio AODV in hybrid wireless mesh networks

Wireless Mesh Networks (WMNs), based on commodity hardware, present a promising technology for a wide range of applications due to their self-configuring and self-healing capabilities, as well as their low equipment and deployment costs. One of the key challenges that WMN technology faces is the limited capacity and scalability due to co-channel interference, which is typical for multi-hop wireless networks. A simple and relatively low-cost approach to address this problem is the use of multiple wireless network interfaces (radios) per node. Operating the radios on distinct orthogonal channels permits effective use of the frequency spectrum, thereby, reducing interference and contention. In this paper, we evaluate the performance of the multi-radio Ad-hoc On-demand Distance Vector (AODV) routing protocol with a specific focus on hybrid WMNs. Our simulation results show that under high mobility and traffic load conditions, multi-radio AODV offers superior performance as compared to its single-radio counterpart. We believe that multi-radio AODV is a promising candidate for WMNs, which need to service a large number of mobile clients with low latency and high bandwidth requirements.

A Novel Approach to Supporting Multipoint-to-Point Video Transmission over Wireless Ad Hoc Networks

It is predicted that there will be a high demand for video applications in future wireless networks including wireless ad hoc networks. However, supporting video applications over mobile ad hoc networks is more complicated than with other networks due to the lack of support from a preinstalled infrastructure. In this paper, we tackle this problem by adopting the concept of multipoint-to-point video transmission used in wire-line networks. A novel framework designed with features to accommodate the characteristics of ad hoc networks is presented. There are two key features in our proposal. First, Multiple Description Coding (MDC) scheme is used for video coding to reduce the redundancy by avoiding the transmission of duplicate video frames. Second, the routing protocol is expanded to include finding disjoint routes from video sources to the receiver so that a single link breakage or a single intermediate node failure affects transmission from only the minimum number of nodes. Furthermore, the use of disjoint routes also enables the workload to be distributed more evenly within the network. A simulation study was carried out using NS-2 to demonstrate the performance of the proposed mechanism. We show that the proposed mechanism outperforms conventional point-to-point transmission, especially under conditions of high mobility.

Leaving group effects on the selectivity of the gas‐phase fragmentation reactions of side chain fixed‐charge‐containing peptide ions

The effect of trialkylsulfonium versus quaternaryalkylammonium ions on the multistage gas-phase fragmentation reactions of side chain, fixed-charge, cysteine-containing peptides has been examined in a quadrupole linear ion trap. These tandem mass spectrometry experiments reveal that selective loss of dialkylsulfide from fixed-charge sulfonium ion derivatives is the dominant fragmentation pathway regardless of the degree of proton mobility, indicating that it is the most energetically favored fragmentation pathway. In contrast, the loss of trimethylamine from the side chain of fixed-charge ammonium-ion-containing cysteine derivatives appears to be less energetically favored, and as a result extensive charge-remote fragmentation is observed under low proton mobility conditions, while under conditions of high proton mobility, amide bond fragmentation reactions dominate. These findings are supported by molecular orbital calculations at the B3LYP/6-31 + G(d, p) level of theory, which showed that the neutral loss of dimethylsulfide is both thermodynamically and kinetically preferred over the loss of trimethylamine.

Impact of frequency offsets and IQ imbalance on MC-CDMA reception based on channel tracking

New air interfaces are currently being developed to meet the high spectral efficiency requirements of the emerging wireless communication systems. Multicarrier code-division multiple access (MC-CDMA) is seen as a promising candidate for the fourth-generation (4G) cellular communication systems because it can interestingly deal with the multipath propagation at a low processing complexity. Besides spectral efficiency and power consumption, the production cost of the transceiver should also be optimized. Direct conversion radio frequency (RF) receivers are appealing because they avoid costly intermediate frequency (IF) filters. However, they imply RF IQ separation, introducing a phase and amplitude mismatch between the I and Q branches. A communication system based on MC-CDMA is sensitive to synchronization errors and front-end non-idealities because it uses a long symbol duration. The goal of this paper is to evaluate the impact of the carrier frequency offset, the sampling clock offset, and the IQ imbalance on the MC-CDMA downlink system performance, considering a receiver based on channel tracking designed to cope with high mobility conditions. It is demonstrated that part of the effects is compensated by the channel estimation and an expression of the variance of the remaining symbol estimation error is provided. For the cellular system and the target performance considered in this paper, specifications are defined on the non-idealities. The results are validated with bit-error rate simulations

Development of microstructure in Cr and Cr/CoCrPt films made by pulsed laser deposition

Cr films and Cr/CoCrPt bilayer films have been grown using ion-beam-assisted pulsed laser deposition (PLD). High mobility conditions such as a substrate temperature above 350 °C, a low deposition rate, and a high laser energy promote the formation of a {100} bcc crystallographic preferred orientation in the Cr layer, while a {110}-oriented film is formed under other conditions. The {100} orientation can be formed at lower temperatures if the film is bombarded by energetic Ar ions during growth. CoCrPt grows with the hcp-{112̄0} orientation on bcc-Cr {100} underlayers, which is the same epitaxial relationship that occurs in sputtered Cr/Co-alloy films used in hard disk recording media. PLD CoCrPt films also have magnetic properties broadly similar to those of sputtered films. The PLD film microstructure development is interpreted in terms of the preferential nucleation of {100}-oriented Cr crystals during the early stages of film growth.

Microstructure and mechanical properties of nanocomposite (Ti,Si,Al)N coatings

In this work (Ti,Si,Al)N films were deposited using only rf or a combination of rf and d.c. reactive magnetron sputtering. Chemical composition, thickness, film structure and mechanical properties of the films were investigated by means of Rutherford backscattering (RBS), electron microprobe analysis (EPMA), ball-cratering, X-ray diffraction (XRD) and ultramicroindentation, respectively. All samples showed high hardness values, exceeding, in some cases, 50 GPa. XRD results revealed the formation of a mixture of two phases whose structure is similar to TiN. One phase is noted as being TiN bulk with a lattice parameter of 0.428 nm and develops only in conditions of high surface mobility. This behaviour can be associated with the segregation of the SiN x phase, though the formation of an amorphous AlN phase cannot be excluded. Another phase, which is noted as TiSiAlN ( a≈0.420 nm), where Si and Al atoms substitute the Ti atoms on the TiN lattice, develops in situations of lower surface mobility. The thermal stability of these coatings was studied by thermal treatments in a vacuum atmosphere, where it was found that a small increase in hardness was obtained after 1 h heat treatment at 800°C.

Crawling Bands or Monitoring Bands: How to Manage Exchange Rates in a World of Capital Mobility

This paper discusses the choice of exchange‐rate regime. It is argued that in general floating is undesirable, because of the extreme weakness of the economic mechanism that holds the exchange rate close to a level consistent with the fundamentals. Of the alternatives, fixed rates can occasionally make sense, where several conditions are all satisfied. But under current conditions of high capital mobility the more prudent choice will in most cases be a system of limited flexibility, in the form of a ‘crawling band’ (a wide band that is adjusted in small steps so as to keep it in line with the fundamentals, but is defended in the traditional ways) or possibly a ‘monitoring band’ (a wide band with similar properties, which is defended only when the rate goes outside the band).

Evolution of short- and long-range order during Si incorporation on GaAs(0 0 1) observed by RAS and RHEED during MBE

Abstract The Si incorporation on GaAs(0 0 1) has been studied in real time by reflection high-energy electron diffraction (RHEED) and reflectance anisotropy spectroscopy (RAS) at conditions of enhanced adatom mobility. In the RAS spectra, besides resonances due to As and Ga dimers on the GaAs surface also features due to Si dimers in single and double layers as well as As dimers adsorbed on them are identified. The incorporation process is very complex due to Si-induced As desorption, combined incorporation of Si and As, and readsorption of As on (Si, Ga). At conditions of high adatom mobility (low As4 pressure) a single Si layer is nearly completed before Si incorporation in a second layer takes place, whereas for reduced adatom mobility (high As4 pressure) islanding with Si incorporation in a double layer is found in early growth stages.

Performance bounds of a multiple-step paging strategy in future universal mobile telecommunication systems

In future mobile telecommunications, due to the huge number of users and the specific functions that support mobility, a significant amount of signaling load will have to be carried by the finite capacity of the radio link. Hence, methods aiming at radio link signaling load reduction are welcome. In this paper we propose and analyze a method that saves paging signaling load by exploiting information related to the terminal location during the most recent interaction between the terminal and the network. The penalty paid is extra processing power and extra paging delays. An analytical model is developed so as to describe the performance versus traffic intensity and mobility conditions. The performance of the proposed paging scheme is investigated, and it is shown that the method operates well even in the worst case, which is the high user mobility conditions. Possible extensions of the method, which exploit information related to the mobility degree of each individual user or information characterizing the mobility conditions in a certain location area, are also proposed.

ACADEMIC APTITUDE AND READING TEST SCORES OF DISADVANTAGED CHILDREN SHOWING VARYING DEGREES OF MOBILITY

In any urban school system, one can identify a large group of pupils, characterized by low motivation and lack of goals, whose school performance is substandard. Predominately, such children are drawn from homes where the adults have had little schooling. In many instances, large family size, poverty, discrimination, high mobility, and slum conditions are complicating factors. Typically, the child from such a home is disadvantaged--he enters school lacking the experiences, skills, and values of his non-disadvantaged peers.