On the complexity of routing in wireless multihop network

Wireless backbone networks represent an attractive alternative to wired networks in situations where cost, speed of deployment, and flexibility in network design are important. In typical configurations, users connect to wireless routers of the backbone network, which then redirect the traffic to one of the existing network gateways. To improve the network performance, wireless backbone routers redirect their traffic to the network gateways so as to maximize amount of traffic that can be sup- ported by the network. In this paper, we prove that this problem is NP-hard as a result of the wireless interference that is created between geographically close transmission links. We consequently design and investigate the performance of interference-aware algorithms suitable for multi-channel environments against more traditional routing approaches. We evaluate their performance in simulated environments based on data taken from existing networks, and show that interference-based heuristics exhibit advantageous performance in non-uniform deployment

Interference-Aware Routing in Wireless Mesh Networks

User demand for seamless connectivity has encouraged the development of alternatives to traditional communications infrastructure networks. Potential solutions have to be low-cost, easily deployable and adaptive to the environment. One approach that has gained tremendous attention over the past few years is the deployment of a backbone of access points wirelessly interconnected, allowing users to access the wired infrastructure via wireless multi-hop communication. Wireless Mesh Networks (WMN) fall into this category and constitute a technology that could revolutionize the way wireless network access is provided. However, limited transfer capacity and interference resulting from the shared nature of the transmission medium will prevent widespread deployment if the network performance does not meet users' expectations. It is therefore imperative to provide efficient mechanisms for such networks. Resource management encompasses a number of different issues, including routing. Although a profusion of routing mechanisms have been proposed for other wireless technologies, the unique characteristics of WMNs (i.e. fixed wireless backbone, with the possibility to embed multiple interfaces) prevent their straight forward adoption in WMNs. Moreover, the severe performance degradations that can result from the interference generated by concurrent data transmissions and environmental noise call for the development of interference-aware routing mechanisms. In this thesis, we investigated the impact of interference on the network performance of wireless mesh networks. We designed algorithms to associate routers to gateways that minimize the interference level in single-channel and multi-channel networks. We then studied the performance of existing routing metrics and their suitability for mesh networks. As a result of this analysis, we designed a novel routing metric and showed its benefits over existing ones. Finally, we provided an analytical evaluation of the probability of finding two non interfering paths given a network topology

Approximate Bayesian Computation, stochastic algorithms and non-local means for complex noise models

International audienceIn this paper, we present a stochastic NL-means-based denoising algorithm for generalized non-parametric noise models. First, we provide a statistical interpretation to current patch-based neighborhood filters and justify the Bayesian inference that needs to explicitly accounts for discrepancies between the model and the data. Furthermore, we investigate the Approximate Bayesian Computation (ABC) rejection method combined with density learning techniques for handling situations where the posterior is intractable or too prohibitive to calculate. We demonstrate our stochastic Gamma NL-means (SGNL) on real images corrupted by non-Gaussian noise

An extended model of vesicle fusion at the plasma membrane to estimate protein lateral diffusion from TIRF microscopy images.

BACKGROUND: Characterizing membrane dynamics is a key issue to understand cell exchanges with the extra-cellular medium. Total internal reflection fluorescence microscopy (TIRFM) is well suited to focus on the late steps of exocytosis at the plasma membrane. However, it is still a challenging task to quantify (lateral) diffusion and estimate local dynamics of proteins. RESULTS: A new model was introduced to represent the behavior of cargo transmembrane proteins during the vesicle fusion to the plasma membrane at the end of the exocytosis process. Two biophysical parameters, the diffusion coefficient and the release rate parameter, are automatically estimated from TIRFM image sequences, to account for both the lateral diffusion of molecules at the membrane and the continuous release of the proteins from the vesicle to the plasma membrane. Quantitative evaluation on 300 realistic computer-generated image sequences demonstrated the efficiency and accuracy of the method. The application of our method on 16 real TIRFM image sequences additionally revealed differences in the dynamic behavior of Transferrin Receptor (TfR) and Langerin proteins. CONCLUSION: An automated method has been designed to simultaneously estimate the diffusion coefficient and the release rate for each individual vesicle fusion event at the plasma membrane in TIRFM image sequences. It can be exploited for further deciphering cell membrane dynamics

Lifetime estimation of moving vesicles in frequency-domain fluorescence lifetime imaging microscopy

International audienceWe propose a framework for correcting the effect of vesicles motion in frequency domain FLIM imaging. Estimation of movement and lifetime are decoupled and alternatively performed. Robust M-estimation is involved to improve the accuracy of our estimate. Our method has been evaluated with both simulated and real samples

On the probability of finding non-interfering paths in wireless multihop networks

Abstract. Multipath routing can improve system performance of capacity-limited wireless networks through load balancing. However, even with a single source and destination, intra-flow and inter-flow interference can void any performance improvement. In this paper, we show that establishing non-interfering paths can, in theory, leverage this issue. In practice however, finding non-interfering paths can be quite complex. In fact, we demonstrate that the problem of finding two non-interfering paths for a single source-destination pair is NP-complete. Therefore, an interesting problem is to determine if, given a network topology, non-interfering multipath routing is appropriate. To address this issue, we provide an analytic approximation of the probability of finding two non-interfering paths. The correctness of the analysis is verified by simulations

Local heuristic for the refinement of multi-path routing in wireless mesh networks

We consider wireless mesh networks and the problem of routing end-to-end traffic over multiple paths for the same origin-destination pair with minimal interference. We introduce a heuristic for path determination with two distinguishing characteristics. First, it works by refining an extant set of paths, determined previously by a single- or multi-path routing algorithm. Second, it is totally local, in the sense that it can be run by each of the origins on information that is available no farther than the node's immediate neighborhood. We have conducted extensive computational experiments with the new heuristic, using AODV and OLSR, as well as their multi-path variants, as underlying routing methods. For two different CSMA settings (as implemented by 802.11) and one TDMA setting running a path-oriented link scheduling algorithm, we have demonstrated that the new heuristic is capable of improving the average throughput network-wide. When working from the paths generated by the multi-path routing algorithms, the heuristic is also capable to provide a more evenly distributed traffic pattern

Lifetime MAP reconstruction in frequency-domain fluorescence lifetime imaging microscopy

International audienceWe propose a robust statistical framework for reconstructing lifetime map corrupted by vesicle motion in frequency domain FLIM imaging. Instrumental noise is taken into account to improve lifetime estimation. Robust M-estimators and MLestimators allow to jointly estimate motion and lifetime. Performances are demonstrated on simulated and real samples

Lifetime estimation on moving sub-cellular objects in frequency domain FLIM imaging

International audienceFluorescence lifetime is usually defined as the average nanosecond-scale delay between excitation and emission of fluorescence. It has been established that lifetime measurement yields numerous indications on cellular processes such as inter-protein and intra-protein mechanisms through fluorescent tagging and Förster resonance energy transfer (FRET). In this area, frequency domain fluorescence lifetime imaging microscopy (FD FLIM) is particularly well appropriate to probe a sample non-invasively and quantify these interactions in living cells. The aim is then to measure fluorescence lifetime in the sample at each location in space from fluorescence variations observed in a temporal sequence of images obtained by phase modulation of the detection signal. This leads to a sensitivity of lifetime determination to other sources of fluorescence variations such as intracellular motion. In this paper, we propose a robust statistical method for lifetime estimation on both background and small moving structures with a focus on intracellular vesicle trafficking