The analysis of diffusion processes in real-world propagation scenarios often involves estimating variables that are not directly observed. These hidden variables include parental relationships, the strengths of connections between nodes, and the moments of time that infection occurs. In this paper, we propose a framework in which all three sets of parameters are assumed to be hidden and we develop a Bayesian approach to infer them. After justifying the model assumptions, we evaluate the performance efficiency of our proposed approach through numerical simulations on synthetic datasets and realworld diffusion processes.
Data transfer in opportunistic Delay Tolerant Networks (DTNs) must rely on unscheduled sporadic meetings between nodes. The main challenge in these networks is to develop a mechanism based on which nodes can learn to make nearly optimal forwarding decision rules despite having no a-priori knowledge of the network topology. The forwarding mechanism should ideally result in a high delivery probability, low average latency and efficient usage of the network resources. In this paper, we propose both centralized and decentralized single-copy message forwarding algorithms that, under relatively strong assumptions about the networks behaviour, minimize the expected latencies from any node in the network to a particular destination. After proving the optimality of our proposed algorithms, we develop a decentralized algorithm that involves a recursive maximum likelihood procedure to estimate the meeting rates. We confirm the improvement that our proposed algorithms make in the system performance through numerical simulations on datasets from synthetic and real-world opportunistic networks.
Abstract-Understanding the process by which a contagion disseminates throughout a network is of great importance in many real world applications. The required sophistication of the inference approach depends on the type of information we want to extract as well as the number of observations that are available to us. We analyze scenarios in which not only the underlying network structure (parental relationships and link strengths) needs to be detected, but also the infection times must be estimated. We assume that our only observation of the diffusion process is a set of time series, one for each node of the network, which exhibit changepoints when an infection occurs. After formulating a model to describe the contagion, and selecting appropriate prior distributions, we seek to find the set of model parameters that best explains our observations. Modeling the problem in a Bayesian framework, we exploit Monte Carlo Markov Chain, Sequential Monte Carlo, and time series analysis techniques to develop batch and online inference algorithms. We evaluate the performance of our proposed algorithms via numerical simulations of synthetic network contagions and analysis of real-world datasets.
Even in the absence of a physical network infrastructure, it is important that mobile devices can take advantage of the opportunities presented to them to maintain communication. Opportunistic networks are a class of mobile networks that must rely on unscheduled sporadic meetings between nodes to achieve communication. The main challenge in these networks is to route messages towards a destination with high delivery probability, low average latency and efficient usage of network resources. Despite the numerous proposals for opportunistic routing protocols, there are relatively few analytical characterizations of their behaviour. In this paper, we propose both centralized and decentralized message forwarding algorithms that, under relatively strong assumptions about the network's behaviour, minimize the expected latency to a destination. After presenting proofs of the optimality of our proposed algorithms, we confirm their improvement in system performance through numerical simulation.
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