Impact of Scheduling in the Return-Link of Multi-Beam Satellite MIMO Systems

The utilization of universal frequency reuse in multi-beam satellite systems introduces a non-negligible level of co-channel interference (CCI), which in turn penalizes the quality of service experienced by users. Taking this as starting point, the paper focuses on resource management performed by the gateway (hub) on the return-link, with particular emphasis on a scheduling algorithm based on bipartite graph approach. The study gives important insights into the achievable per-user rate and the role played by the number of users and spot beams considered for scheduling. More interestingly, it is shown that a free-slot assignment strategy helps to exploit the available satellite resources, thus guaranteeing a max-min rate requirement to users. Remarks about the trade-off between efficiency-loss and performance increase are finally drawn at the end of the paper.Comment: Submitted and accepted to IEEE GLOBECOM 2012 Conference, 6 pages, 10 figure

Comparing TFP Catching-up and Capital Deepening in US and European Growths: A Directional Distance Function Approach

In Solow’s model the income convergence between countries arises from two main sources: a capital deepening effect resulting from the diminishing returns of the production technology and a technological transfer/diffusion effect related to Total Factor Productivity (TFP) differences. A large literature has been devoted to analyze these effects but most of the studies suffer from three weaknesses by defining the US as the a priori technological leader, by using a parametric functional form and by assuming constant returns to scale for the technology. Our paper offers an alternative approach based on a non-parametric programming framework and the estimation of directional distance functions. We explicitly separate country TFP differences into two components: a technology effect and a scale effect to study the catching-up process on each of them. We also analyze the role of the capital deepening effect by introducing a relevant measure of the structural efficiency which reveals inefficiencies due to changes in input-ratio differences. Our empirical work focuses on 15 European countries (EU) and the US over the period 1980-2004. We use time series procedures to test for convergence for individual countries or sub-sets of countries.TFP Catching-up, Capital Deepening, Convergence, Directional Distance Function. Running title: Comparing TFP Catching-up and Capital Deepening

A Simple Model to Generate Hard Satisfiable Instances

In this paper, we try to further demonstrate that the models of random CSP instances proposed by [Xu and Li, 2000; 2003] are of theoretical and practical interest. Indeed, these models, called RB and RD, present several nice features. First, it is quite easy to generate random instances of any arity since no particular structure has to be integrated, or property enforced, in such instances. Then, the existence of an asymptotic phase transition can be guaranteed while applying a limited restriction on domain size and on constraint tightness. In that case, a threshold point can be precisely located and all instances have the guarantee to be hard at the threshold, i.e., to have an exponential tree-resolution complexity. Next, a formal analysis shows that it is possible to generate forced satisfiable instances whose hardness is similar to unforced satisfiable ones. This analysis is supported by some representative results taken from an intensive experimentation that we have carried out, using complete and incomplete search methods.Comment: Proc. of 19th IJCAI, pp.337-342, Edinburgh, Scotland, 2005. For more information, please click http://www.nlsde.buaa.edu.cn/~kexu/papers/ijcai05-abstract.ht

Linear programming solutions and distance functions under a constant returns to scale technology

This note generalizes analytical relationships among activity variables of DEA models previously derived by Boussemart, Briec and Leleu (2007). We relax the asumption of constant returns to scale by showing that the key results hold under a weaker asumption of homogeneity. We use the notion of alpha-returns to scale to extend the analysis to strictly increasing and decreasing returns, covering now the whole range of returns to scale for multi-output homogenous technologies.Data envelopment analysis, Methodology, Production

More evidence on technological catching-up in the manufacturing sector

Production frontiers for the manufacturing sector are estimated to determine a “country specific” catching-up process of Total Factor Productivity (TFP).TFP gains are gauged at the manufacturing industry level for 14 OECD countries over the 1970-2001 period. Our TFP measure does not assume technical or allocative efficiency which are inherent drawbacks of usual TFP indices. We show that catching-up processes can be very different between sub-periods and across countries. A significant catching-up process was at work in the manufacturing sector between 1970 and 1986 then it overturned over the period 1987-2001. During the first sub-period, the speed of technological catching-up of the euro-zone countries is definitely higher than those of the other European or OECD nations whereas the divergence noted in second sub-period has the same order of magnitude among the three groups.Catching-up; TFP change index; Technology adoption; Production Frontier

Could Society’s willingness to reduce pesticide use be aligned with Farmers’ economic self-interest?

agricultural intensification (AI), agricultural extensification (AE), pesticide reduction, environmental performance, non parametric cost-functions

Technology Adoption in French Agriculture and the Role of Financial Constraints

Successive CAP reforms have increased the exposure of European agriculture to market forces. As a result, farmers have become preoccupied with their competitiveness and have progressively adopted best practices. However, these long-run technological adjustments could be slowed down by eventual shortrun financial constraints. This contribution measures the role of these financial constraints on the catching-up component of total factor productivity for a panel of French farmers in Nord-Pas-de-Calais region during 1994-2001. For TFP estimates based on non-parametric distance functions, the second stage econometric results indicate that the technological adaptation is significantly conditioned by financial constraints.TFP catching-up, distance function, financial constraints, Agricultural Finance, Farm Management, Research and Development/Tech Change/Emerging Technologies,

Short- and Long-Run Credit Constraints in French Agriculture: A Directional Distance Function Framework Using Expenditure-Constrained Profit Functions

This empirical application investigates the eventual presence of credit constraints using a panel of French farmers. This is the first European application using a direct modelling approach based upon axiomatic production theory. The credit constrained profit maximisation model proposed by Färe, Grosskopf and Lee is extended in three ways. First, we rephrase the model in terms of directional distance functions to allow for duality with the profit function. Second, we model the presence of credit constraints in the short-run and investment constraints in the long-run using short- respectively long-run profit functions. Third, we lag the expenditure constraint one year to account for the separation between planning and production. We find empirical evidence of both credit and investment constraints, though their relative impact on the degree of financial inefficiency is rather low in the short-run. Financially unconstrained farmers are larger, perform better, and seem to benefit from a virtuous circle where access to financial markets allows better productive choices. In the long-run, almost all farms seem to suffer from credit constraints for financing their investments.proportional distance function, profit function, credit constraint

How can allocative inefficiency reveal risk preference? An empirical investigation on French wheat farms

We focus on a simple framework on wheat producer behaviour in a context of price output uncertainty. More precisely, we establish a relationship between ex post output price level and allocative inefficiency that allows to characterize farmers’ risk preferences. Given this analysis, the connection between risk aversion and other socioeconomic variables (such as degree of output specialisation, total asset, debts, farmer’s age…) can furthermore empirically be explored. This relationship is empirically tested on an unbalanced panel including about 650 wheat producers located in the French Department of Meuse over 1992- 2003.Producer behaviour, allocative inefficiency, risk aversion, Crop Production/Industries, Risk and Uncertainty,