41,688 research outputs found
MAC Centered Cooperation - Synergistic Design of Network Coding, Multi-Packet Reception, and Improved Fairness to Increase Network Throughput
We design a cross-layer approach to aid in develop- ing a cooperative
solution using multi-packet reception (MPR), network coding (NC), and medium
access (MAC). We construct a model for the behavior of the IEEE 802.11 MAC
protocol and apply it to key small canonical topology components and their
larger counterparts. The results obtained from this model match the available
experimental results with fidelity. Using this model, we show that fairness
allocation by the IEEE 802.11 MAC can significantly impede performance; hence,
we devise a new MAC that not only substantially improves throughput, but
provides fairness to flows of information rather than to nodes. We show that
cooperation between NC, MPR, and our new MAC achieves super-additive gains of
up to 6.3 times that of routing with the standard IEEE 802.11 MAC. Furthermore,
we extend the model to analyze our MAC's asymptotic and throughput behaviors as
the number of nodes increases or the MPR capability is limited to only a single
node. Finally, we show that although network performance is reduced under
substantial asymmetry or limited implementation of MPR to a central node, there
are some important practical cases, even under these conditions, where MPR, NC,
and their combination provide significant gains
A Case for Partial Funding of Pensions with an Application to the EU Candidate Countries
The paper examines the effects of ageing and makes a case for partial pre-funding of pensions. The argument is based on inter-generational fairness in a situation where pension expenditure as compared to wages increases due to low fertility and increasing longevity. We illustrate the approach by using data representing a typical EU Candidate Country of Central and Eastern Europe with a relatively high pension replacement rate. Pre-funding can take place within the public sector or in a privatised second pillar. We emphasise the need for a consistent framework to cover the many different institutional options available for pension financing.Pension system reform, partial pre-funding, ageing
Population ageing and public finance targets
The paper incorporates intergenerational fairness into a framework to analyse long-term sustainability of public finances under population ageing. It establishes a link between ageing-related public expenditure projections and public finance targets, thereby clarifying the connection between pension reforms and general government budget balance and debt targets.population ageing, public finances, sustainability of public finances, budget balance targets, pension reforms, pensions, Oksanen
PLTL Partitioned Model Checking for Reactive Systems under Fairness Assumptions
We are interested in verifying dynamic properties of finite state reactive
systems under fairness assumptions by model checking. The systems we want to
verify are specified through a top-down refinement process. In order to deal
with the state explosion problem, we have proposed in previous works to
partition the reachability graph, and to perform the verification on each part
separately. Moreover, we have defined a class, called Bmod, of dynamic
properties that are verifiable by parts, whatever the partition. We decide if a
property P belongs to Bmod by looking at the form of the Buchi automaton that
accepts the negation of P. However, when a property P belongs to Bmod, the
property f => P, where f is a fairness assumption, does not necessarily belong
to Bmod. In this paper, we propose to use the refinement process in order to
build the parts on which the verification has to be performed. We then show
that with such a partition, if a property P is verifiable by parts and if f is
the expression of the fairness assumptions on a system, then the property f =>
P is still verifiable by parts. This approach is illustrated by its application
to the chip card protocol T=1 using the B engineering design language
Spectrum Sharing in mmWave Cellular Networks via Cell Association, Coordination, and Beamforming
This paper investigates the extent to which spectrum sharing in mmWave
networks with multiple cellular operators is a viable alternative to
traditional dedicated spectrum allocation. Specifically, we develop a general
mathematical framework by which to characterize the performance gain that can
be obtained when spectrum sharing is used, as a function of the underlying
beamforming, operator coordination, bandwidth, and infrastructure sharing
scenarios. The framework is based on joint beamforming and cell association
optimization, with the objective of maximizing the long-term throughput of the
users. Our asymptotic and non-asymptotic performance analyses reveal five key
points: (1) spectrum sharing with light on-demand intra- and inter-operator
coordination is feasible, especially at higher mmWave frequencies (for example,
73 GHz), (2) directional communications at the user equipment substantially
alleviate the potential disadvantages of spectrum sharing (such as higher
multiuser interference), (3) large numbers of antenna elements can reduce the
need for coordination and simplify the implementation of spectrum sharing, (4)
while inter-operator coordination can be neglected in the large-antenna regime,
intra-operator coordination can still bring gains by balancing the network
load, and (5) critical control signals among base stations, operators, and user
equipment should be protected from the adverse effects of spectrum sharing, for
example by means of exclusive resource allocation. The results of this paper,
and their extensions obtained by relaxing some ideal assumptions, can provide
important insights for future standardization and spectrum policy.Comment: 15 pages. To appear in IEEE JSAC Special Issue on Spectrum Sharing
and Aggregation for Future Wireless Network
Program transformation for functional circuit descriptions
We model sequential synchronous circuits on the logical level by signal-processing programs in an extended lambda calculus Lpor with letrec, constructors, case and parallel or (por) employing contextual equivalence. The model describes gates as (parallel) boolean operators, memory using a delay, which in turn is modeled as a shift of the list of signals, and permits also constructive cycles due to the parallel or. It opens the possibility of a large set of program transformations that correctly transform the expressions and thus the represented circuits and provides basic tools for equivalence testing and optimizing circuits. A further application is the correct manipulation by transformations of software components combined with circuits. The main part of our work are proof methods for correct transformations of expressions in the lambda calculus Lpor, and to propose the appropriate program transformations
A case for partial funding of pensions with an application to the EU Candidate Countries.
The paper examines the effects of ageing and makes a case for partial pre-funding of pensions. The argument is based on inter-generational fairness in a situation where pension expenditure as compared to wages increases due to low fertility and increasing longevity. We illustrate the approach by using data representing a typical EU Candidate Country of Central and Eastern Europe with a relatively high pension replacement rate. Pre-funding can take place within the public sector or in a privatised second pillar. We emphasise the need for a consistent framework to cover the many different institutional options available for pension financing.pension systems, demographics, reform
Pension reform: key issues illustrated with an actuarial model
The paper examines pension reforms under ageing. With stylised facts, ageing is traced to low fertility and increasing longevity. Given these persistent factors, pension systems must be reformed to avoid an unfair burden being left for future generations. The main results for reform blueprints are: In a Defined Benefit (DB) system, partial pre-funding is needed to achieve intergenerational fairness unless benefits are sufficiently reduced; partial privatisation is an option for the management of the accumulating funds.Transition from a DB to a Notional Defined Contribution (NDC) system is another reform option; it reduces the replacement rates to levels which match prescribed contribution rates; an NDC public pillar can be accompanied by a second pillar, managed by the private sector.An effective retirement age increase is necessary to moderate the increase in pension expenditure and to preserve adequate pension levels.ĂÂ Pension reforms have important effects on public finance target setting.ĂÂ The presentation is non-technical and does not require prior knowledge of pension reforms.pension reform, Defined Benefit (DB) system, Notional Defined Contribution system, pension expenditure, public finance, Oksanen
Generalized planning: Non-deterministic abstractions and trajectory constraints
We study the characterization and computation of general policies for families of problems that share a structure characterized by a common reduction into a single abstract problem. Policies mu that solve the abstract problem P have been shown to solve all problems Q that reduce to P provided that mu terminates in Q. In this work, we shed light on why this termination condition is needed and how it can be removed. The key observation is that the abstract problem P captures the common structure among the concrete problems Q that is local (Markovian) but misses common structure that is global. We show how such global structure can be captured by means of trajectory constraints that in many cases can be expressed as LTL formulas, thus reducing generalized planning to LTL synthesis. Moreover, for a broad class of problems that involve integer variables that can be increased or decreased, trajectory constraints can be compiled away, reducing generalized planning to fully observable nondeterministic planning
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