323,255 research outputs found
A new NS2 tool to investigate QoS management over mobile WiMAX
No full textWiMAX is one of the most interesting solutions for broadband wireless access, supporting multimedia traffics and applications through an appropriate QoS flow management both for fixed and mobile devices. To study its performance and to test new functionalities, simulation tools play a central role. In this paper we propose a new simulation module compliant to IEEE 802.16. Our key contribution is to offer the research community a useful tool for the investigation of QoS management on mobility in the WiMAX scenario. The developed tool includes the implementation of five QoS classes and of handover procedures. This module is validated and tested through exhaustive simulations, showing its conformance with the defined specifications. Copyright © 2011 ICST.WiMAX is one of the most interesting solutions for broadband wireless access, supporting multimedia traffics and applications through an appropriate QoS flow management both for fixed and mobile devices. To study its performance and to test new functionalities, simulation tools play a central role. In this paper we propose a new simulation module compliant to IEEE 802.16.
Our key contribution is to offer the research community a useful tool for the investigation of QoS management on mobility in the WiMAX scenario. The developed tool includes the implementation of five QoS classes and of handover procedures.
This module is validated and tested through exhaustive simulations, showing its conformance with the defined specifications
Design and implementation of a new scheduler for enhancing multi-rate fairness in IEEE 802.16
No full textWithout the definition of a mandatory scheduling algorithm for channel resource assignment, WiMAX is open to Quality of Service (QoS) enhancements by research groups and developers, at the aim of managing heterogeneous flows with different QoS requirements. Furthermore, besides performance enhancement, another key issue arises for QoS delivery: it is known as multi-rate fairness and it deals with efficient resource allocation for providing sufficient bandwidth to high rate flows, without penalizing low rate ones. In this paper, uplink scheduling algorithms are studied and an innovative solution is proposed to achieve performance enhancement, multi-rate fairness and improved QoS management. After an overview of the state of the art, two scheduling algorithms based on Deficit Round Robin are studied, implemented and tested in NS2 simulator. The schedulers are validated and compared through exhaustive simulations, showing the benefits coming from the adoption of the proposed scheduling mechanism
An innovative uplink scheduler for enhancing multi-rate fairness in WiMAX
No full textWiMAX is one of the most interesting solutions for broadband wireless access, offering QoS features for multimedia traffics and applications. However, without the definition of a mandatory scheduling algorithm for the assignment of channel resources, WiMAX standard is open to enhancements by QoS research groups and developers. In this paper, BS uplink scheduling algorithms are considered and an innovative solution is proposed in order to improve multi-rate fairness and QoS management. The proposed scheduler, named E-DRR, has been compared with the existing solutions through exhaustive simulations, showing its enhancements in terms of QoS performance and multi-rate fairness in resource allocation. © 2011 IEEE
A cross-layer jitter-based TCP for wireless networks
No full textThe Transmission Control Protocol (TCP) is one of the main communication protocols in the Internet, and it has been designed to provide an efficient reaction to packet loss events which are due to network congestion. Congestion is the main cause of losses in wired networks, but in today heterogeneous networks, loss events can also be introduced due to higher error rates on wireless channels, host mobility, and frequent handovers. Unfortunately, all packet losses are interpreted by TCP as a sign of congestion, triggering an inappropriate reaction which reduces its transmission rate and leads to performance degradation. In order to avoid this problem, it is important for TCP to correctly understand whether the reason of a packet loss is due to congestion or to a problem in the wireless link. This paper presents an innovative jitter-based cross-layer TCP algorithm, named XJTCP. It adopts the jitter ratio as loss predictor, joined with a layer two notification, in order to correctly infer the nature of a loss event. Performance evaluation and comparison with other common TCP implementations shows how XJTCP can be an interesting solution in the presence of wireless environments
Intraframe compression of radar image sequences for ship traffic control applications
No full textIn this paper, an intraframe scheme for high compression of X-band radar images for ship traffic control is proposed. We used a proprietary radar simulator which generates maritime scenarios as seen by one or more radar sites. We propose a modified adaptive discrete cosine transform (MADCT) scheme which allows us to classify each 8 by 8 image block by means of a threshold criterion based on ac and dc activity. The strategy of transmission of the DCT coefficients, the recovering process of blocks incorrectly discarded, and the bit-allocation phase have been properly designed to fit with the particular application. Accurate experimental results, in terms of PSNR and compression ratio, prove the superiority of the novel scheme with respect to standard coding techniques. ©2005 Copyright SPIE - The International Society for Optical Engineering
Performance comparison of JTCP over QoS-aware WiMAX networks
No full textTCP is the main transport-layer communication protocol in traditional wired networks. This is also due to its efficient behavior in presence of congestion events. However, networks with wireless links and mobile hosts provide significant non-congestive losses due to bit error rate, host motion and handover mechanisms. TCP incorrectly interprets these events as a sign of network congestion, throttling its transmission rate and causing degradation of end-to-end performance. In order to enhance TCP performance on wireless networks, several algorithms have been introduced to correctly deduce whether a loss occurs for a real congestion event. This paper carries out a performance evaluation of an innovative algorithm, called Jitter-based TCP (JTCP), over WiMAX networks. Realistic IEEE 802.16e MAC and PHY layers are adopted for performing simulations, showing that JTCP outperforms other TCP versions over WiMAX networks
Géographie humaine de la Grèce : B. Kayser, Géographie humaine de la Grèce. Eléments pour l'étude de l'urbanisation. Préface du Professeur S. G. Andreadis
No full textTaillefer François. Géographie humaine de la Grèce : B. Kayser, Géographie humaine de la Grèce. Eléments pour l'étude de l'urbanisation. Préface du Professeur S. G. Andreadis. In: Revue géographique des Pyrénées et du Sud-Ouest, tome 36, fascicule 1, 1965. pp. 53-54
A DCT-based adaptive compression algorithm customized for radar imagery
No full textIn this paper an adaptive DCT-based image compression algorithm for radar images is proposed, tested and compared to JPEG and to classical coding algorithms for remote sensing imagery. The Modified Adaptive Discrete Cosine Transform (MADCT) scheme is proposed, which allows to classify each image block by means of a threshold criterion based on AC and DC activity. The strategy of transmission of the DCT coefficients, the recovering process of blocks incorrectly discarded, and the bit-allocation phase have been properly designed to provide high compression of two classes of images: X-band real-aperture radar images for ship traffic control, and SAR images for browsing applications. The experimental results, in terms of PSNR and compression ratio, prove the superiority of the novel scheme with respect to standard coding techniques
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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