14,578 research outputs found
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A survey of handover algorithms in DVB-H
Digital Video Broadcasting for Handhelds (DVB-H) is a standard for
broadcasting IP Datacast (IPDC) services to mobile handheld terminals.
Based on the DVB-T standard, DVB-H adds new features such as time
slicing, MPE-FEC, in-depth interleavers, mandatory cell id identifier,
optional 4K-modulation mode and the use of 5 MHz bandwidth in addition
to the usually used 6, 7, or 8 MHz raster. IPDC over DVB-H is proposed
for ETSI to complement the DVB-H standard by combining IPDC and
DVB-H in an end-to-end system. Handover in such unidirectional broadcasting
networks is a novel issue. In the last few years since the birth of
DVB-H technology, great attention has been given to the performance
analysis of DVB-H mobile terminals. Handover is one of the main research
topics for DVB-H in mobile scenarios. Better reception quality and greater
power efficiency are considered to be the main targets of handover
research for DVB-H. New algorithms for different handover stages in
DVB-H have been the subject of recent research and are currently being
studied. Further novel algorithms need to be designed to improve the
mobile reception quality. This article provides a comprehensive survey of
the handover algorithms in DVB-H. A systematic evaluation and categorization
approach is proposed based on the problems the algorithms solve
and the handover stages being focused on. Criteria are proposed and analyzed
to facilitate designing better handover algorithms for DVB-H that
have been identified from the research conducted by the author
Cell Selection in Wireless Two-Tier Networks: A Context-Aware Matching Game
The deployment of small cell networks is seen as a major feature of the next
generation of wireless networks. In this paper, a novel approach for cell
association in small cell networks is proposed. The proposed approach exploits
new types of information extracted from the users' devices and environment to
improve the way in which users are assigned to their serving base stations.
Examples of such context information include the devices' screen size and the
users' trajectory. The problem is formulated as a matching game with
externalities and a new, distributed algorithm is proposed to solve this game.
The proposed algorithm is shown to reach a stable matching whose properties are
studied. Simulation results show that the proposed context-aware matching
approach yields significant performance gains, in terms of the average utility
per user, when compared with a classical max-SINR approach.Comment: 11 pages, 11 figures, Journal article in ICST Wireless Spectrum, 201
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Incorporating Digital Repeaters into the Soft Handover Standard in Digital Video Broadcasting Handheld
Digital Video Broadcasting for Handhelds (DVB-H) is a standard for broadcasting IP data services to portable devices. Handover in unidirectional broadcast networks is a novel issue introduced by this technology. This paper proposes and analyses the Repeater Aided Soft Handover (RA_handover) algorithm for a DVB-H receiver with MIMO antennas and presents the benefits of implementing RA_handover compared with a handover process without repeaters. For network planning and optimisation purposes simulation models are developed to analyse the RA_handover approach. It is shown that RA_handover could greatly improve the quality of service and consume much less front-end battery power than a handover method without repeaters. In addition, the cost introduced by the algorithm is briefly estimated. In conclusion, curves are given that show the relationship between quality of service and consumed battery power, which provide further support for including RA_handover in the DVB-H soft handover standard. The paper provides valuable outcomes for service providers and standard policy makers
Efficient Micro-Mobility using Intra-domain Multicast-based Mechanisms (M&M)
One of the most important metrics in the design of IP mobility protocols is
the handover performance. The current Mobile IP (MIP) standard has been shown
to exhibit poor handover performance. Most other work attempts to modify MIP to
slightly improve its efficiency, while others propose complex techniques to
replace MIP. Rather than taking these approaches, we instead propose a new
architecture for providing efficient and smooth handover, while being able to
co-exist and inter-operate with other technologies. Specifically, we propose an
intra-domain multicast-based mobility architecture, where a visiting mobile is
assigned a multicast address to use while moving within a domain. Efficient
handover is achieved using standard multicast join/prune mechanisms. Two
approaches are proposed and contrasted. The first introduces the concept
proxy-based mobility, while the other uses algorithmic mapping to obtain the
multicast address of visiting mobiles. We show that the algorithmic mapping
approach has several advantages over the proxy approach, and provide mechanisms
to support it. Network simulation (using NS-2) is used to evaluate our scheme
and compare it to other routing-based micro-mobility schemes - CIP and HAWAII.
The proactive handover results show that both M&M and CIP shows low handoff
delay and packet reordering depth as compared to HAWAII. The reason for M&M's
comparable performance with CIP is that both use bi-cast in proactive handover.
The M&M, however, handles multiple border routers in a domain, where CIP fails.
We also provide a handover algorithm leveraging the proactive path setup
capability of M&M, which is expected to outperform CIP in case of reactive
handover.Comment: 12 pages, 11 figure
Context-Aware Handover Policies in HetNets
Next generation cellular systems are expected to entail a wide variety of wireless coverage zones, with cells of different sizes and capacities that can overlap in space and share the transmission resources. In this scenario, which is referred to as Heterogeneous Networks (HetNets), a fundamental challenge is the management of the handover process between macro, femto and pico cells. To limit the number of handovers and the signaling between the cells, it will hence be crucial to manage the user's mobility considering the context parameters, such as cells size, traffic loads, and user velocity. In this paper, we propose a theoretical model to characterize the performance of a mobile user in a HetNet scenario as a function of the user's mobility, the power profile of the neighboring cells, the handover parameters, and the traffic load of the different cells. We propose a Markov-based framework to model the handover process for the mobile user, and derive an optimal context-dependent handover criterion. The mathematical model is validated by means of simulations, comparing the performance of our strategy with conventional handover optimization techniques in different scenarios. Finally, we show the impact of the handover regulation on the users performance and how it is possible to improve the users capacity exploiting context information
Safer clinical systems : interim report, August 2010
Safer Clinical Systems is the Health Foundation’s new five year programme of work to test and demonstrate ways to improve healthcare systems and processes, to develop safer systems that improve patient safety. It builds on learning from the Safer Patients Initiative (SPI) and models of system improvement from both healthcare and other industries.
Learning from the SPI highlighted the need to take a clinical systems approach to improving safety. SPI highlighted that many hospitals struggle to implement improvement in clinical areas due to inherent problems with support mechanisms. Clinical processes and systems, rather than individuals, are often the contributors to breakdown in patient safety. The Safer Clinical Systems programme aimed to measure the reliability of clinical processes, identify defects within those processes, and identify the systems that result in those defects. Methods to improve system reliability were then to be tested and re-developed in order to reduce the risk of harm being caused to patients. Such system-level awareness should lead to improvements in other patient care pathways.
The relationship between system reliability and actual harm is challenging to identify and measure. Specific, well-defined, small-scale processes have been used in other programmes, and system reliability has been shown to have a direct causal relationship with harm (e.g. care bundle compliance in an intensive care unit can reduce the incidence of ventilator-associated pneumonia). However, it has become evident that harm can be caused by a variety of factors over time; when working in broader, more complex and dynamic systems, change in outcome can be difficult to attribute to specific improvements and difficulties are also associated with relating evidence to resulting harm.
The overall aim of Phase 1 of the Safer Clinical Systems programme was to demonstrate proof-of-concept that using a systems-based approach could contribute to improved patient safety. In Phase 1, experienced NHS teams from four locations worked together with expert advisers to co-design the Safer Clinical Systems programme
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