Information-theoretic secrecy for wireless networks

The aim of information-theoretic secrecy is to ensure that an eavesdropper who listens to the wireless transmission of a message can only collect an arbitrarily small number of information bits about this message. In contrast to cryptography, there are no assumptions on the computational power of the eavesdropper. Information-theoretically secret communication has been studied for many particular wireless network topologies. In the main part of this thesis, we consider such communication for arbitrary acyclic wireless network topologies. We provide lower and upper bounds on the strong perfect secrecy capacity for the case when the channels of the network are either Gaussian or deterministic. These results are based on the recent understanding of the capacity of wireless networks (without secrecy constraints) by Avestimehr, Diggavi and Tse. As a side result, we give inner and outer bounds on the capacity region for the multisource problem in arbitrary wireless networks with Gaussian or deterministic signal interaction. For linear deterministic signal interaction, we find the exact capacity region. For Gaussian signal interaction, we are able to bound the gap between the two bounds on the capacity region. This gap depends only on the network topology, but not on the signal-to-noise ratio (SNR), which leads to an approximation of the capacity region for the high SNR regime. We further consider a particular network topology, called the fan-network, in which we assume that an eavesdropper has physical access to every node in a subset of the relay nodes. We give a general upper bound on the perfect secrecy capacity, and we characterize the perfect secrecy capacity for two special cases. In the second part of the thesis, we consider interactive secrecy, i.e., secrecy in the presence of a public feedback link from the destination to the source. We focus on the problem of secret key generation rather than secret communication. The benefit of public discussion for secret key generation in a broadcast channel was first shown by Maurer. We extend his ideas to a relay network called the line network, leading to a lower bound on the strongly secret key capacity for this network topology. Finally, we introduce a new channel coding setup called the interference-multiple access (IMA) channel. This channel is a variant of the interference channel where one of the receivers is required to decode the messages from both transmitters. We derive an inner bound on the capacity region of the IMA channel, as well as an outer bound for the so-called structured IMA channel. In a semi-deterministic version of the structured IMA channel, the bounds match, providing a characterization of the capacity region. In the Gaussian case, we obtain a 1 bit-approximation of the capacity region. We also show an inner bound on the equivocation-capacity region for the IMA channel, where we require that part of the private message for one receiver is kept information-theoretically secret from the other receiver

Lossy Source Coding with Gaussian or Erased Side-Information

In this paper we find properties that are shared between two seemingly unrelated lossy source coding setups with side information. The first setup is when the source and side information are jointly Gaussian and the distortion measure is quadratic. The second setup is when the side information is an erased version of the source. We begin with the observation that in both these cases the Wyner-Ziv and conditional rate-distortion functions are equal. We further find that there is a continuum of optimal strategies for the conditional rate distortion problem in both these setups. Next, we consider the case when there are two decoders with access to different side-information sources. For the case when the encoder has access to the side information we establish bounds on the rate-distortion function and a sufficient condition for tightness. Under this condition, we find a characterization of the rate-distortion function for physically degraded side information. This characterization holds for both the Gaussian and erasure setups

Assessing Wind Impact on Semi-Autonomous Drone Landings for In-Contact Power Line Inspection

In recent years, the use of inspection drones has become increasingly popular for high-voltage electric cable inspections due to their efficiency, cost-effectiveness, and ability to access hard-to-reach areas. However, safely landing drones on power lines, especially under windy conditions, remains a significant challenge. This study introduces a semi-autonomous control scheme for landing on an electrical line with the NADILE drone (an experimental drone based on original LineDrone key features for inspection of power lines) and assesses the operating envelope under various wind conditions. A Monte Carlo method is employed to analyze the success probability of landing given initial drone states. The performance of the system is evaluated for two landing strategies, variously controllers parameters and four level of wind intensities. The results show that a two-stage landing strategies offers higher probabilities of landing success and give insight regarding the best controller parameters and the maximum wind level for which the system is robust. Lastly, an experimental demonstration of the system landing autonomously on a power line is presented

Cooperative source coding with encoder breakdown

This paper provides an inner bound to the rate-distortion region of a source coding setup in which two encoders are allowed some collaboration to describe a pair of discrete memoryless sources. We further require some robustness in case one of the encoders breaks down. This is modeled by having a second decoder, observing the messages from only one of the encoders. We prove the tightness of this inner bound for two special cases. In the first, one of the sources is required to be recovered losslessly if there is no encoder breakdown. In the second, the robustness requirement is dropped and only one of the sources is to be represented. For the second case, we explicitly compute the rate-distortion region for the quadratic Gaussian and binary Hamming problems

Cooperative source coding with encoder breakdown

Cooperative source coding with encoder breakdown Abstract — This paper provides an inner bound to the ratedistortion region of a source coding setup in which two encoders are allowed some collaboration to describe a pair of discrete memoryless sources. We further require some robustness in case one of the encoders breaks down. This is modeled by having a second decoder, observing the messages from only one of the encoders. We prove the tightness of this inner bound for two special cases. In the first, one of the sources is required to be recovered losslessly if there is no encoder breakdown. In the second, the robustness requirement is dropped and only one of the sources is to be represented. For the second case, we explicitly compute the rate-distortion region for the quadratic Gaussian and binary Hamming problems. I

The Wyner-Ziv Problem with Noisy Side-Information at the Encoder

In the problem of lossy source coding with side-information, it is well known (Wyner and Ziv 1976) that knowledge of the side-information at the encoder improves the rate-distortion trade-off for binary sources and the Hamming distortion measure. We consider a scenario where the encoder has access to a noisy version of the binary side-information. We evaluate the rate-distortion function for this scenario and characterize it as an optimization problem over four parameters. When the sources are Gaussian and the distortion measure is the squared error, it is known that encoder side-information does not improve the rate-distortion trade-off. However, knowing the side-information at the encoder greatly reduces the coding complexity. We investigate the question whether the knowledge of noisy side-information can improve the coding complexity for such sources. However, our results suggest that this is not the case

On cooperative secrecy for discrete memoryless relay networks

In this paper we consider information-theoretically secure communication between two special nodes ("source" and "destination") in a memoryless network with authenticated relays, where the secrecy is with respect to a class of eavesdroppers. We develop achievable secrecy rates when authenticated relays also help increase secrecy rate by inserting noise into the network

Using Three States for Binary Consensus on Complete Graphs

We consider the binary consensus problem where each node in the network initially observes one of two states and the goal for each node is to eventually decide which one of the two states was initially held by the majority of the nodes. Each node contacts other nodes and updates its current state based on the state communicated by the last contacted node. We assume that both signaling (the information exchanged at node contacts) and memory (computation state at each node) are limited and restrict our attention to systems where each node can contact any other node (i.e., complete graphs). It is well known that for systems with binary signaling and memory, the probability of reaching incorrect consensus is equal to the fraction of nodes that initially held the minority state. We show that extending both the signaling and memory by just one state dramatically improves the reliability and speed of reaching the correct consensus. Specifically, we show that the probability of error decays exponentially with the number of nodes N and the convergence time is logarithmic in N for large N. We also examine the case when the state is ternary and signaling is binary. The convergence of this system to consensus is again shown to be logarithmic in N for large N, and is therefore faster than purely binary systems. The type of distributed consensus problems that we study arises in the context of decentralized peer-to-peer networks, e.g. sensor networks and opinion formation in social networks - our results suggest that robust and efficient protocols can be built with rather limited signaling and memory