Chaos multiculturel ou utopie urbaine, la ville plurilingue dans le cinéma de science-fiction de Métropolis à Élysium

International audienc

Merging Belief Propagation and the Mean Field Approximation: A Free Energy Approach

We present a joint message passing approach that combines belief propagation and the mean field approximation. Our analysis is based on the region-based free energy approximation method proposed by Yedidia et al. We show that the message passing fixed-point equations obtained with this combination correspond to stationary points of a constrained region-based free energy approximation. Moreover, we present a convergent implementation of these message passing fixedpoint equations provided that the underlying factor graph fulfills certain technical conditions. In addition, we show how to include hard constraints in the part of the factor graph corresponding to belief propagation. Finally, we demonstrate an application of our method to iterative channel estimation and decoding in an orthogonal frequency division multiplexing (OFDM) system

Message-Passing Algorithms for Channel Estimation and Decoding Using Approximate Inference

We design iterative receiver schemes for a generic wireless communication system by treating channel estimation and information decoding as an inference problem in graphical models. We introduce a recently proposed inference framework that combines belief propagation (BP) and the mean field (MF) approximation and includes these algorithms as special cases. We also show that the expectation propagation and expectation maximization algorithms can be embedded in the BP-MF framework with slight modifications. By applying the considered inference algorithms to our probabilistic model, we derive four different message-passing receiver schemes. Our numerical evaluation demonstrates that the receiver based on the BP-MF framework and its variant based on BP-EM yield the best compromise between performance, computational complexity and numerical stability among all candidate algorithms.Comment: Accepted for publication in the Proceedings of 2012 IEEE International Symposium on Information Theor

Can a populist political party bear the risk of granting complete property rights? Electoral outcomes of Mexico's second land reform

The Mexican land reform, one of the most sweeping in the world, proceeded in two steps: it granted peasants highly incomplete property rights on more than half of the Mexican territory starting in 1914, creating strong economic and political dependence for beneficiaries on the ruling political party; and complete property rights starting in 1992, allowing beneficiaries to relate directly to the market. We analyse the impact on political behaviour of switching from incomplete to complete property rights. We use for this the 13-year nationwide rollout of the certification programme and match land reform communities (ejidos) before and after titling with electoral outcomes in corresponding sections across seven electoral episodes. We find that, in accordance with the investor class theory, granting complete property rights induced a conservative shift toward the challenger pro-market party. This shift was strongest where vested interests created larger benefits from market-oriented policies as opposed to public transfer policies. We also find that beneficiaries of the one-time irreversible transfer of a land title failed to reciprocate through votes for the benefactor party, the long time ruling party. The outcome shows that it is difficult for an authoritarian populist party to engage in a land reform that grants complete property rights, suggesting why so many land reforms are either not implemented due to political risk or remain at the ineffective level of incomplete property rights

Uncoordinated and Decentralized Processing in Extra-Large MIMO Arrays

We propose a decentralized receiver for extra-large multiple-input multiple-output (XL-MIMO) arrays. Our method operates with no central processing unit (CPU) and all the signal detection tasks are done in distributed nodes. We exploit a combined message-passing framework to design an uncoordinated detection scheme that overcomes three major challenges in the XL-MIMO systems: computational complexity, scalability and non-stationarities in user energy distribution. Our numerical evaluations show a significant performance improvement compared to benchmark distributed methods while operating very close to the centralized receivers.Comment: 14 pages, 3 figure