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Access Systems (access + system)
Selected Abstracts2-Dimensional code design for an optical CDMA system with a parallel interference cancellation receiverEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 7 2007Mikaël Morelle The objective of this paper is to design a two-Dimensional Optical Code Division Multiple Access system (2D-OCDMA) for application in access networks, with coding and decoding functions performed by electronic devices. We present a new construction method of Multi-Wavelength Optical Orthogonal Codes (MWOOC), which permits a high flexibility in the code parameters choice. This work evaluates in the noiseless case, the MWOOC potentialities for two receiver structures: a Conventional Correlation Receiver (CCR) and a Parallel Interference Cancellation receiver (PIC). We show that with a PIC receiver, it is possible to design two-Dimensional codes that respect the access specifications. Copyright © 2007 John Wiley & Sons, Ltd. [source] Development of mobile broadband interactive satellite access system for Ku/Ka bandINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2006Yun-Jeong Song Abstract It is difficult to implement the broadband satellite Internet and broadcasting service for mobile environment. The paper presents the design and implementation of a mobile broadband satellite access system. In case of the system design, mobile terminal service is considered a critical factor than fixed terminal services, such as resource management, antenna tracking, weak signal recovery. In the paper, mobile broadband interactive satellite access technology system (MoBISAT) is presented. The system network, which is composed of a star network, consists of time division multiplexing-based forward link and multi-frequency time division multiple access-based return link. The MoBISAT provides both Ku-band satellite TV and Ka-band high-speed Internet base on DVB-S/DVB-RCS standards to the passengers and crews for land, maritime and air vehicles. The key factors of hub and mobile terminal are addressed for the design and implementation of the MoBISAT. Especially, the design and implementation of the return link demodulation method, resource management scheme and mobile terminal structure including mobile antenna are described. Copyright © 2006 John Wiley & Sons, Ltd. [source] Reducing the information gap: Digital library development in BrazilPROCEEDINGS OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE & TECHNOLOGY (ELECTRONIC), Issue 1 2002Cavan McCarthy Principal Brazilian digital library initiatives were identified and characterized. Significant projects in the area of science and research include gateway sites for research (Prossiga), set up and maintained cooperatively, also a multinational access system for regional electronic journals (SciELO). Systems which offer access to texts of the Brazilian classics predominate in the field of literature and hmanities. Digital libraries have had a significant impact on Brazil. Government financing was critical for implanting these new services. Institutions which already have a strong background in advanced technology have significantly better chances of success in the digital library field. Cooperative projects have also had significant impact. [source] How do individual transferable quotas affect marine ecosystems?FISH AND FISHERIES, Issue 1 2009Trevor A Branch Abstract Published papers were reviewed to assess ecosystem impacts of individual transferable quotas (ITQs) and other dedicated access systems. Under ITQs, quota shares increase with higher abundance levels, thus fishers may request lower total allowable catches (TACs) and pay for monitoring and research that improves fishery sustainability. Mortality on target species generally declines because catches are closer to TACs and because ghost fishing through lost and abandoned gear decreases. High-grading and discarding often decline, but may increase if landings (and not catches) count against ITQs and when there is little at-sea enforcement. Overall, ITQs positively impact target species, although collapses can occur if TACs are set too high or if catches are routinely allowed to exceed TACs. Fishing pressure may increase on non-ITQ species because of spillover from ITQ fisheries, and in cases where fishers anticipate that future ITQ allocations will be based on catch history and therefore increase their current catches. Ecosystem and habitat impacts of ITQs were only sparsely covered in the literature and were difficult to assess: ITQs often lead to changes in total fishing effort (both positive and negative), spatial shifts in effort, and fishing gear modifications. Stock assessments may be complicated by changes in the relationship between catch per unit effort, and abundance, but ITQ participants will often assist in improving data collection and stock assessments. Overall, ITQs have largely positive effects on target species, but mixed or unknown effects on non-target fisheries and the overall ecosystem. Favourable outcomes were linked to sustainable TACs and effective enforcement. [source] Performance evaluation for asynchronous MC-CDMA systems with a symbol timing offsetINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2009Myonghee Park Abstract This paper models a symbol timing offset (STO) with respect to the guard period and the maximum access delay time for asynchronous multicarrier-code division multiple access systems over frequency-selective multipath fading channels. Analytical derivation shows that STO causes desired signal power degradation and generates self-interferences. This effect of the STO on the average bit error rate (BER) and the effective signal-to-noise ratio (SNR) is evaluated using the semi-analytical method, and the approximated BER and the SNR loss caused by STO are then obtained as closed-form expressions. The tightness between the semi-analytical result and the approximated one is verified for the different STOs and SNRs. Furthermore, the derived analytical results are verified via Monte Carlo simulations. Copyright © 2008 John Wiley & Sons, Ltd. [source] Comparison of coded orthogonal frequency division multiplexing and multicarrier code division multiple access systems for power line communicationsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2004P. L. Katsis Abstract Orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC-CDMA) systems are comparatively evaluated for power line communications (PLC) in a frequency-selective fading environment with additive coloured Gaussian noise which is used to model the actual in-home power line channel. OFDM serves as a benchmark in order to measure the performance of various MC-CDMA systems, since multicarrier modulation systems are considered the best candidate for this kind of channel. Both single-user and multi-user cases are taken into account, making use of the appropriate combiner schemes to take full advantage of each case. System efficiency is enhanced by the application of different coding techniques, a fact which shows that powerful coding can make the difference under such a hostile medium. The impact of block interleaving is investigated, while the simulation examines how different modulation schemes fair under the imposed channel conditions as well. The performance of the system is assessed by the commonly used bit error rate vs signal-to-noise ratio diagrams and there is also a comparison regarding throughput efficiency among all the tested systems. As stated in Section 4, a promising PLC application is attained. Copyright © 2004 John Wiley & Sons, Ltd. [source] Applying aggregation operators for information access systems: An application in digital librariesINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 12 2008Enrique Herrera-Viedma Nowadays, the information access on the Web is a main problem in the computer science community. Any major advance in the field of information access on the Web requires the collaboration of different methodologies and research areas. In this paper, the concept of aggregation operator playing a role for information access on the Web is analyzed. We present some Web methodologies, as search engines, recommender systems, and Web quality evaluation models and analyze the way aggregation operators help toward the success of their activities. We also show an application of the aggregation operators in digital libraries. In particular, we introduce a Web information system to analyze the quality of digital libraries that implements an important panel of aggregation operators to obtain the quality assessments. © 2008 Wiley Periodicals, Inc. [source] Modeling and simulation of mixed traffic on a prioritized shared mediumINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 1 2003Jeffrey J. Evans Network access systems (NAS) such as digital loop carriers (DLC) are increasingly utilizing a shared medium, such as Hybrid Fiber Coax (HFC) to provide point-to-multi-point access from the public switched telephone network (PSTN) to the end user (consumer). New services, such as direct access to the packet switched network (PSN, WWW) have been added to DLC equipment in such a way as to provide for a prioritized set of services over a shared medium in an effort to take advantage of otherwise unused bandwidth. The introduction of such services requires the modeling and analysis of these network access systems. This becomes complex when considering the variability in different service type traffic characteristics. This work identifies a traffic engineering problem of prioritized circuit switched and packet switched (PSTN/PSN) traffic over the same shared medium as it may relate to "perceived" quality of service (QoS). Copyright © 2002 John Wiley & Sons, Ltd. [source] Enhancement of throughput and fairness in 4G wireless access systems by non-orthogonal signalingBELL LABS TECHNICAL JOURNAL, Issue 4 2009Joerg Schaepperle Besides having significantly enhanced throughput, fourth generation (4G) cellular wireless access systems are expected to be cost efficient and provide sufficient performance even at the cell edge. This paper proposes a new method, called radial space-division multiple access (RDMA) for improving the system's spectral efficiency significantly and providing fairness among users without increasing the number of antennas and without requiring fast backbone communication and synchronization between base stations. The basic idea is to approach the capacity of the multi-user channel under fairness constraints by exploiting not only the angular dimension of space, as in space-division multiple access (SDMA), but also the radial dimension. Non-orthogonal signaling for simultaneous transmission of multiple signals over the same radio resource and joint detection in the receiver are used. Significant throughput gains are achieved with low complexity methods requiring only long term channel statistics and no instantaneous channel state information at the transmitter. Detailed link and first simple systemlevel simulation results in the context of the evolution of IEEE 802.16/Worldwide Interoperability for Microwave Access (WiMAX) systems towards 802.16m show that system throughput can be doubled without requiring more advanced analog hardware or increasing bandwidth or transmit power. © 2009 Alcatel-Lucent. [source] IP-driven access-independent resource management in converged access networksBELL LABS TECHNICAL JOURNAL, Issue 2 2007Markus Bauer A key requirement on future networks is to provide the user with seamless broadband access for triple-play services via any available access technology with high end-to-end quality of service. In this paper we propose a novel resource management concept on the network layer that utilizes service- and user-specific cross-layer metrics to control the resources in an all-Internet Protocol (IP) access network optimally via IP mechanisms such as routing and traffic engineering. We interpret any link, wireless or wireline, as an IP-hop in an all-IP network where major lower layer information is included in such metrics. This approach turns out to be access technology,independent, leading to a unified resource management concept in a "converged" wireline/wireless environment. With this proposal, we leverage flat IP-based cellular architectures like the Alcatel-Lucent Base Station Router (BSR) technologies and show how wireless and wireline access nodes can be integrated into future converged all-IP networks. The paper is based on results from ScaleNet, a European research initiative that is dedicated to advancing a vision of a scalable and flexible next-generation access network that provides an IP-optimized integration of heterogeneous access systems for future broadband multimedia services. © 2007 Alcatel-Lucent. [source] | |||||||||||||