Search results for "TELECOMMUNICATION"

Improving point matching on multimodal images using distance and orientation automatic filtering

2016

International audience; Speed Up Robust Features SURF is one of the most popular and efficient methods used for image registration task. In order to achieve a correct registration, a good matching of feature point is required. However in the case of multimodal images, the high and non-linear intensity changes between different modalities led to many outliers (mismatching of detected points) and consequently a fail in the registration. Therefore, in this paper we introduce an efficient method devoted to the detection and removal of such outlier. It's based on an automatic filtering of outliers on both distance and orientation between features points. We tested our proposed method on a set of…

Part V Introduction

2009

Workshop on Sources of Polarized Leptons and High Brightness Electron Beams

2011

This volume contains the proceedings of the International Workshop on Sources of Polarized Leptons and High Brightness Electron Beams (PESP2010). The workshop was hosted by the University of Bonn from 21–24 September 2010. PESP2010 has been conducted as satellite workshop preceding the International SPIN Physics Symposium (SPIN2010). In view of the expanding and challenging field of the production of high brightness lepton beams, the selection of workshop topics was extended to cover the demands of modern accelerator developments and applications. As novel light sources such as FELs and ERLs place new requirements on the properties of unpolarized beams in terms of brightness and intensity, …

Facing the inevitable? : The public telecom monopoly’s way of coping with deregulation

2016

AbstractThe telecommunications industry has gone through a total restructure since the late 1970s, as state-owned national monopolies have given way to listed enterprises and competitive international markets. Scholars have explained wide-ranging privatisation and deregulation at a general level, but what happened to the former state-owned monopolies and how they adapted to the emerging business-oriented environment, has had with less scrutiny. It has been assumed that external factors caused these institutions to adapt a business approach, but did these organisations themselves have any significant power of decision in these processes? This article explains how one of these former state or…

Online Hyperparameter Search Interleaved with Proximal Parameter Updates

2021

There is a clear need for efficient hyperparameter optimization (HO) algorithms for statistical learning, since commonly applied search methods (such as grid search with N-fold cross-validation) are inefficient and/or approximate. Previously existing gradient-based HO algorithms that rely on the smoothness of the cost function cannot be applied in problems such as Lasso regression. In this contribution, we develop a HO method that relies on the structure of proximal gradient methods and does not require a smooth cost function. Such a method is applied to Leave-one-out (LOO)-validated Lasso and Group Lasso, and an online variant is proposed. Numerical experiments corroborate the convergence …

Performance comparison of HARQ and ARQ mechanisms in IEEE 802.16 networks

2008

The IEEE 802.16 technology defines several link level mechanisms to retransmit erroneous data. In this paper we compare the performance of the ARQ and HARQ mechanisms in the IEEE 802.16 networks. Our simulations results show that in general HARQ provides a better performance. However, ARQ can compete successfully with it due to a smaller signaling overhead. Furthermore, since ARQ does not require a dedicated uplink signaling channel for the acknowledgments messages, it results in better resources utilization in the uplink direction.

Analysis of duplexing modes in the IEEE 802.16 wireless system

2010

The IEEE 802.16 standard defines two main duplexing modes: Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). The FDD can be divided further into Full-FDD (F-FDD) and Half-FDD (H-FDD). F-FDD requires full duplexing support from subscriber stations and works with two frequency bands. TDD operates a single frequency band, but it does not need full-duplexing support. H-FDD is a combination of these: it works with two frequency bands and does not require full-duplexing support. The cost of this is a more complicated scheduling and added overhead. Still, H-FDD might be the only possible duplexing mode in some occasions. In this paper, these duplexing modes are compared and the…

Increasing the VoIP Capacity through MAP Overhead Reduction in the IEEE 802.16 OFDMa Systems

2010

One of the main issues with supporting VoIP service over 802.16 networks is the signalling overhead caused by the downlink MAP messages due to frequent transmissions and small packets. To decrease the MAP overhead, the 802.16 standard proposes some mechanisms, such as the compressed MAP and sub-MAPs. In this paper, we show by means of extensive dynamic simulations that sub-MAPs can reduce dramatically the signalling overhead associated with VoIP traffic and significantly improve overall VoIP capacity. At the same time, since sub-MAPs are more sensitive to packet drops, they tend to increase the number of HARQ retransmissions in downlink and transmission delays in the uplink direction.

Adaptive contention resolution parameters for the IEEE 802.16 networks

2007

In the IEEE 802.16 networks, the base station allocates resources to subscriber stations based on their QoS requirements and bandwidth request sizes. A subscriber station can send a bandwidth request when it has an uplink grant allocated by the base station or by taking part in the contention resolution mechanism. This paper presents analytical calculations for parameters that control the contention resolution process in the IEEE 802.16 networks. In particular, the backoff start/end values and the number of request transmission opportunities are considered. The simulation results confirm the correctness of theoretical calculations. They also reveal that the adaptive parameter tuning results…

Experimental Assessment of the Backoff Behavior of Commercial IEEE 802.11b Network Cards

2007

It has been observed that different IEEE 802.11 commercial cards produced by different vendors experience different performance, either when accessing alone the channel, as well as when competing against each other. These differences persist also when thorough measurement methodologies (such as RF shielding, laptop rotation, etc) are applied, and alignment of the environmental factors (same laptop models, traffic generators, etc) is carried out. This paper provides an extensive experimental characterization of the backoff operation of six commercial NIC cards. It suggests a relevant methodological approach, namely a repeatable, well defined, set of experiments, for such a characterization. …