Demand For Spectrum Research Articles

Fields in an FSS screened enclosure

Efficient use of the radio spectrum demands frequency reuse in increasingly localised regions in the built environment. It may be possible to employ frequency selective screens (FSS) to provide electromagnetic separation of adjacent areas. To study the signal isolation capability of these structures, field distributions have been measured inside a small enclosure with one wall clad with FSS which had very broad reflection bands. The FSS arrays were densely packed linear dipoles, on rigid and on flexible film substrates. Measurements were made at 2.45, 5.0 and 8.1 GHz. The spatial isolation was very significant: the signal attenuation averaged over the enclosed volume was 20 to 30 dB, but the field amplitudes and insertion losses were position dependent. The variations were characterised by Rayleigh statistics, except for the highest field levels. There, the observed probability density functions (pdfs) often deviated from the Rayleigh form, possibly owing to signal leakage around the FSS edges, especially with thin film substrates, indicating problems in applying it satisfactorily to existing surfaces. In an existing building, it might therefore be acceptable to replace only part of a wall with frequency selective material, metallically screening the remainder. In new buildings, frequency selectivity would be built in, with electromagnetic performance addressed at the design stage.

Spectrum demand for systems beyond IMT‐2000 based on data rate estimates

AbstractIn different regions, research activities on systems beyond third generation mobile communication started already around 1999. The major drivers for these systems are the increasing demand for personal mobile communications with respect to performance, applications, traffic demand and easy to use including communications involving machines. From the user perspective, increasing personal mobility enforces mobile communications in business and the private sector. ITU‐R WP8F, ITU‐T SSG and bodies like WWRF are currently working on the vision of systems beyond IMT‐2000 on global basis in cooperation with the research activities and are defining the basic requirements. New elements of these systems for the mobile access (up to 100 Mbps peak cell capacity) and the nomadic/wireless local area access (up to 1 Gbps peak cell capacity) are being discussed. These requirements result in a huge amount of needed spectrum. In this paper, the impact on spectrum demand for a new mobile broadband access element is investigated with respect to estimated data rate requirements from the user perspective. For that purpose, the radio interface is described in generic form based on a modified Shannon channel capacity formula to obtain generalized results independent of a particular radio interface concept. With the relation between cluster size, carrier/interference‐ratio and coverage requirements the spectrum demand and system throughput is calculated in closed form for the case of a radio interface with fixed and adaptive modulation and coding. The nomadic/wireless local area access according to ITU‐R is not considered here. These investigations are based on simplified system concepts without considering advanced antenna, scheduling and network deployment concepts. Copyright © 2003 John Wiley & Sons, Ltd.

Radio Resource Management for Wireless Internet

It is anticipated that there will be a strong market for a rich variety of wireless internet-based multimedia devices in the not-too-distant future. It is quite difficult to predict the nature of these devices as well as the corresponding applications; but it is certain that those devices and applications will have very different QoS, rate, delay and power constraints. Arguably, effective management of radio resources (through techniques such as interference management and cancellation, dynamic resource allocation and control, packet scheduling and call admission control) is not only essential in future networks, but is also the key factor in the efficient and affordable deployment and operation of these networks. Proportional to its importance, radio resource management appears to be an immensely complex task as well in future wireless networks. However, it is not yet clear whether this task is inherently difficult or whether it only appears so due to our lack of sufficient understanding of this multidimensional problem. As deeper insight into this field is developed by researchers, it is foreseeable that very efficient and straightforward (although suboptimal) algorithms can be developed. Research activities towards 4th generation mobile communication networks have already started; in the meanwhile, the standards for the 3rd generation networks are continuously being revised for higher performance. Not surprisingly, one main area of focus in all these activities is the better management of radio resources. This Special Issue is composed of nine papers (the first three of which are invited papers from the industry) discussing various aspects of radio resource management within the framework of wireless internet. The first invited paper, authored by Shalini Periyalwar et al. (Nortel Networks, Canada), is a visionary one in which radio resource management related issues are discussed for the envisioned future mobile broadband wireless networks. In the second invited paper, Werner Mohr (Siemens, Germany) presents an analytical model for estimating the spectrum demand for beyond-3G mobile networks, based on projected data rate requirements. In the third and final invited paper, Ralph Gholmieh (Ericsson, USA) and Farideh Khaleghi discuss one important feature in the recently revised version of the IS-2000 standard, the control-hold mode, which aims to maximize the throughput in the forward link. In the paper entitled ‘Linear successive interference cancellation in DS-CDMA systems’, Fredrik Berggren and S. Ben Slimane analyze the capacity performance of a receiver with interference cancellation capability which is supported by a novel interference cancellation-aware power control algorithm. The following two papers discuss different aspects of scheduling in CDMA networks. The first paper, authored by Sonia Aissa, Amine Maaref and Paul Mermelstein, proposes a novel flow control algorithm for multi-rate networks with interference cancellation, while the second paper authored by Tao Shu and Zhisheng Niu, demonstrates the optimum method of choosing (with respect to throughput maximization) concurrently transmitting data users. The paper authored by Walid Ibrahim, John W. Chinneck and Shalini Periyalwar, proposes a novel QoS-based charging and resource allocation framework which may potentially allow the network operators to pursue a wide variety of policy options. In the paper entitled ‘Radio resource management techniques for UE-MAC in 3GPP W-CDMA systems’, Sheng-Tzong Cheng and Jian-Liang Lin investigate the adverse effects of rapid transmission rate changes on the BER and they

Hedge Fund Collateralized Fund Obligations

Credit structuring technology has been very successfully employed to create the market for collateralized debt obligations (CDO). CDOs redistribute credit risk to meet investor demands for a wide spectrum of rated securities with scheduled interest and principal payments, securitized by diversified pools of debt instruments. The equity components of CDOs are leveraged investments that offer unique risk and return benefits and have created a market for alternative investments linked to the credit markets. Among the more recent innovations in structuring technology is the advent of collateralized fund obligations (CFO). In these structures, investors gain exposure to a diverse collection of funds through a fund of funds manager. The capital structure of a collateralized fund obligation is similar to traditional CDOs, meaning that investors are offered a spectrum of rated debt securities and equity interest. Although any managed fund can be the source of collateral, the target collateral in these structures tends to be hedge funds, along with funds that finance the needs of growing companies, such as private equity and mezzanine funds. Investors benefit from a risk-tranching approach to investing in a diversified pool of funds that are often difficult to access separately. Collateralized fund obligations tend to be structured as arbitrage market value CDOs, meaning that the fund of funds manager focuses efforts on actively managing the fund to maximize total return while restraining price volatility within the guidelines of the structure. In this report, we focus our research efforts on understanding the structure and rating methodology of hedge fund CFOs. We also discuss the motivation for investing in a diversified pool of hedge funds, the collateral type we view as being among the most popular for the burgeoning market of CFOs. Where applicable, we compare hedge fund and private equity CFO structures as well.

The “Softer” End of the Bipolar Spectrum

The prevalence and diversity of bipolar disorder may be under appreciated. Recent data suggest that when clinicians look beyond strict DSM-IV criteria for bipolar disorder, we find that as many as 5%-7% of the general public may suffer from some form of "bipolar spectrum disorder." At the same time, the comorbidity between bipolar disorder and other psychiatric conditions may create understandable confusion in diagnosis and treatment. Recognition of bipolar depression and the "soft end" of the bipolar spectrum demands not only the identification of the hallmarks of bipolarity, but a heightened awareness of the problems of missed diagnosis and inappropriate treatment. By attending to some key historical and clinical clues, the psychiatrist is more likely to detect bipolar spectrum disorder and provide appropriate treatment for it.

Heterogeneous Networks to Support User Needs with Major Challengesfor New Wideband Access Systems

Third generation mobile radio systems are currently being deployed in different regions of the world. Future systems beyond the third generation are already under discussion in international bodies and forums such as ITU, WWRF and R&D programs of the European Union and in other regions. These systems will determine the research and standardization activities in mobile and wireless communication in the next years. Based on the experience from the third generation future systems will be developed mainly from the user perspective with respect to potential services and applications including traffic demands. This is directly related to the paradigm shifts from the first generation to systems beyond third generation. International bodies are already discussing basic system requirements. The basic system architecture of heterogeneous networks with different complementing access systems is from the today's perspective the most economic approach for systems beyond 3G to satisfy user and operator needs for reasonable cost. Such system architectures enable the deployment of system capacity according to the traffic requirements with the user experience ``Optimally Connected, Anywhere and Anytime'' with seamless service provision between different access systems. New radio interface components with high data rate as additional components of systems beyond 3G are being proposed in international bodies. Key issues of such systems are coverage due to reduced range and the huge spectrum demand. In this paper the international context, the user perspective, revenue and traffic expectations are presented. This results in the basic system requirements and the potential system architecture of heterogeneous networks. Major challenges for the new wideband radio interfaces are the impact on range and spectrum demand. Basic investigations are presented on these issues to critically review requirements on future systems.

Dual band folded monopole/loop antenna for terrestrial communication system

With the introduction of DCS1800 to meet the demands for a wider frequency spectrum for mobile communication systems, novel antenna structures capable of generating dual resonance are in demand. An antenna structure based on the geometry of a bent folded monopole antenna capable of dual resonance frequencies operation is discussed. This antenna is able to cover the GSM/DCS 1800 communication system bands.

Compatibility analysis between proposed feederlinks of non-geostationary mobile-satellite services and existing services near 1·4 GHz

Current frequency allocations for non-geostationary mobile-satellites (NGSO-MSS) are all below 1 GHz, a very crowded portion of the radio frequency spectrum. To the extent that feeder links to satellites in that service can use frequencies in bands above 1 GHz, the demand for additional spectrum below that point will be lessened. Feeder links can use higher bands that would be less desirable, or even unusable, for service links to the large number of small, low-power, user terminals with low-gain antennas envisaged for this service. Two possible bands above 1 GHz, 1390–1393 MHz and 1429–1432 MHz, are close to the 1400–1427 MHz band that is important to two passive (non-radiating) science services. To the extent that out-of-band emissions from NGSO MSS systems can be reduced to levels acceptable to the science services, the efficiency of use of orbit and spectrum resources can be increased. Copyright © 1999 John Wiley & Sons, Ltd.

Compatibility analysis between proposed feederlinks of non‐geostationary mobile‐satellite services and existing services near 1·4 GHz

Current frequency allocations for non-geostationary mobile-satellites (NGSO-MSS) are all below 1 GHz, a very crowded portion of the radio frequency spectrum. To the extent that feeder links to satellites in that service can use frequencies in bands above 1 GHz, the demand for additional spectrum below that point will be lessened. Feeder links can use higher bands that would be less desirable, or even unusable, for service links to the large number of small, low-power, user terminals with low-gain antennas envisaged for this service. Two possible bands above 1 GHz, 1390–1393 MHz and 1429–1432 MHz, are close to the 1400–1427 MHz band that is important to two passive (non-radiating) science services. To the extent that out-of-band emissions from NGSO MSS systems can be reduced to levels acceptable to the science services, the efficiency of use of orbit and spectrum resources can be increased. Copyright © 1999 John Wiley & Sons, Ltd.

A dynamic channel allocation technique based on Hopfield neural networks

The interest in global spectrum allocation techniques is growing with the always increasing spectrum demand for (cellular) mobile communications. However, the best algorithms suffer from high computational times that reduce the possibility of a practical implementation. This paper deals with a dynamic channel allocation (DCA) technique based on an energy function whose minimization gives the optimal allocation. Due to the particular formulation of such an energy function, the minimization can be performed by a Hopfield neural network for which a fast hardware implementation has been recently proposed in the literature. The performance of the proposed DCA technique is derived by computer simulations. Comparisons with a classical fixed allocation technique (FCA) and a different DCA technique are shown to highlight the better performance of the proposed DCA technique.

A high frequency search for highly dispersed pulsars

The majority of known pulsars have been discovered by pulsar searches at low radio frequencies (v< 1 GHz). However, such searches are subject to various deleterious effects, viz the Galactic background radiation (∝v−2.8), dispersion smearing (∝v−3) and also scatter broadening (∝v−4.4). Dispersion smearing and, in particular, scatter broadening prohibit the detection of pulsars with high dispersion measures at low frequencies (cf. Fig. 1a). This is highlighted by the fact that all 11 known pulsars with DM>600 cm−3pc have been discovered during the only two surveys performed to date above 1 GHz, i.e. at 1.4 GHz by Clifton et al. (1992) and at 1.5 GHz by Johnston et al. (1992). However, scattering is still a limiting factor at even 1.4/1.5 GHz. For example B1750—24 is observed with a double component profile at 4.85 GHz (Kijak et al. 1996), whereas at 1.4 GHz the components are completely smeared out due to scatter broadening (cf. Clifton et al. 1992). Therefore, the galactic population of highly dispersed pulsars is still not known. In order to reveal this hidden sample, we have recently started a search in Effelsberg at 4.85 GHz where limitations due to scattering are essentially not existent (see Fig. 1a). The use of this extraordinary high frequency for pulsar searches enables us to observe with a large bandwidth but a small number of filterbank channels, so that the necessary computer power is radically reduced. However, the general steepness of pulsar spectra demands a highly sensitive observing system, otherwise, only the most luminous sources can be detected. A serious disadvantage of a high frequency search is the small telescope beam requiring a lot of observing time to search even a small area of the sky. A restriction of the search area is therefore highly recommended.

ATR-IR Spectroscopy for the Investigation of Solution Reaction Kinetics: Hydrolysis of Trimethyl Phosphate

ATR-IR spectroscopy is proposed as a versatile technique for the investigation of reaction kinetics in solution, particularly in aqueous solution. Subtraction of the solvent spectrum and thus quantitative absorption measurements are possible. In contrast to thin-film transmission spectroscopy, thermostatting is feasible. The high information content of IR spectra demands high-resolution spectra measured at many wave-numbers, and, for kinetic investigations, series of spectra are measured. A multivariate nonlinear least-squares fit is proposed that effectively overcomes the difficulties related to large numbers of data and parameters. As a test for the method, the base-catalyzed hydrolysis of trimethyl phosphate in aqueous solution was investigated. The rate constant is 1.6 × 10−1 s−1 at 40°C and pH 13.

Do algal-dwelling amphipods react to the ‘critical zones’ of a coastal slope?

The so-called ‘critical zones’ where water movement changes drastically from surf pounding to oscillation, and from oscillation to drift with increasing depth, pose different problems to phytal amphipods on rocky coasts. The faunal spectrum and ecological demands of 66 species (in a collection of 12 000 individuals) inhabiting three coastal slopes off eastern Sicily are examined. Amphipods inhabiting the uppermost algal belts of the splash- and surf-region experiencing highest hydrodynamism are excellent swimmers and specialized to eat sporeling algae or graze the living epistratum (herbivores). Within the adjacent oscillation-zone, where speed of water movement is less, but orbiting motion still prevails over directional flow, caprellids and stenothoids are dominant. Their presence seems connected with the occurrence of hydroids or bryozoans. They may be commensals catching their prey out of the hydranths or polyps or even biting tentacles of their host (omnivores). Their capacity to cling is excellent a...

Statutory protection for the water requirements of natural ecosystems

A project was recently registered with the National Parks Board to investigate the need for legal protection of the water requirements of natural ecosystems and the existing legislation which provides such protection. There is a distinct lack of legal protection, which is identified and discussed in this paper. It is submitted that the current South African water law is outdated and in need of reform so as to accommodate the demands of a wider spectrum of user sectors. Since the amendment of the existing water allocation system (in a country where water is a scarce resource) could be politically a disconcerting step, it should be made only after due consideration of the various needs for water, the historical foundation of the existing system, and a study made of effective systems in countries with similar water problems. An in-depth study of the historical development of South African water law has already revealed interesting yet abrogated concepts, which can possibly serve as a means of protecting the natural water requirements.

Water‐Soluble Porphyrin Diglycosides with Photosensitizing Properties

In the presence of oxygen, tumors and viruses can be destroyed by photosensitizing porphyrins. Indispensable for clinical applications is, inter alia, a good solubility in water. It has now been possible to prepare two porphyrin diglycosides which are water‐soluble and stable as well as equally strongly photosensitizing as Rose Bengal. With these properties they ideally fulfill the demands of a wide spectrum of photomedicinal applications.

The Development, Testing And Application of an Efficient Steady State Gas Field Performance Evaluation Model

Abstract Network theoretic concepts have been applied to the analysis and design of distribution network systems for some time. Notable applications include the analysis of water distribution networks, electrical network systems and, more recently, systems in the gas distribution industry. However, application ·of the technique to the simulation of natural gas field collection systems has been limited to the analysis of surface gathering configurations. This paper is an extension of this concept to allow for the inclusion of gas reservoirs and production strings. The paper presents the matrix formulation of the problem to Include all components of a natural gas gathering system. The application of the N-dimensional Newton-Raphson technique to the solution of the resulting system of nonlinear algebraic equations is discussed, and it includes an outline of a procedure that ensures convergence without the need for acceleration parameters. The application of the resulting model to an evaluation of the performance of a gas reservoir is given. The treatment includes, in addition to conventional analyses, the comprehensive evaluation of:the effect of liquid production on gathering and transmission line pressure drops; andthe effect of water influx on the performance and ultimate recovery from water-drive gas reservoirs. INTRODUCTION The increasing importance of natural gas in the energy supply spectrum demands comprehensive techniques for forecasting the future performance and deliverability of natural gas fields. The deliverability of natural gas fields is a function of pressure drops that occur in the reservoir, the production string and the surface facilities. Although it is possible to isolate each of these pressure drop segments for independent evaluation, the over-all performance of the total system and consequent optimum production plan for a natural gas field can best be determined through an evaluation that simultaneously considers the effect of all three pressure drops. Network theory provides a comprehensive and efficient means of achieving this objective. Literature Review A number of papers have appeared in the literature dealing with the forecasting of gas field deliverability and associated reservoir and gathering system performance. Dempsey et al.(1) proposed an iterative solution of the problem which consisted of two so-called subglobal iteration loops involving independent solution of the equations for the surface system, the production string and the reservoir. A compatibility test was necessary to match pressures and flow rates between iteration steps. The application of network theoretic concepts to the flow of fluid in networks has been reported in civil engineering literature(2,3) for water distribution systems and in electrical engineering literature for electrical networks(4,5,6). The formulation of problems using the concept of networks leads to a system of simultaneous algebraic equations. Iterative techniques must be used to obtain solutions to the unknowns when the system of equations is nonlinear. Application of network theoretic concepts to the simulation of natural gas gathering systems was first reported by Stoner(7) and more recently by Berard and Eliason(8). Stoner reported covergence problems in the iterative procedure and proposed the use of a heuris

Controlled markets for spectrum management

The electromagnetic spectrum is apportioned among various radio services and users by centralized authority. A combination of judicial procedures and system engineering methods are used, even to the level of assigning [1] channels to users within a given service. However, as demand for spectrum is increasing, some inefficiencies of this process are becoming evident. The user has little incentive to use spectrum efficiently because using less spectrum often requires greater investment without compensating reductions in operating costs. The goal of economic efficiency, in contrast, requires a balanced use of resources, rather than minimal use of spectrum. In this paper, several techniques are presented which rely on marketplace forces to move toward economic efficiency, and could be implemented within the current spectrum management framework. Incentives would be created for improved efficiency and equity.