Simplifying Wireless Social Caching

Social groups give the opportunity for a new form of caching. In this paper, we investigate how a social group of users can jointly optimize bandwidth usage, by each caching parts of the data demand, and then opportunistically share these parts among themselves upon meeting. We formulate this problem as a Linear Program (LP) with exponential complexity. Based on the optimal solution, we propose a simple heuristic inspired by the bipartite set-cover problem that operates in polynomial time. Furthermore, we prove a worst case gap between the heuristic and the LP solutions. Finally, we assess the performance of our algorithm using real-world mobility traces from the MIT Reality Mining project dataset and two mobility traces that were synthesized using the SWIM model. Our heuristic performs closely to the optimal in most cases, showing a better performance with respect to alternative solutions.Comment: Parts of this work were accepted for publication in ISIT 2016. A complete version is submitted to Transactions on Mobile Computin

Privacy in Index Coding: Improved Bounds and Coding Schemes

It was recently observed in [1], that in index coding, learning the coding matrix used by the server can pose privacy concerns: curious clients can extract information about the requests and side information of other clients. One approach to mitigate such concerns is the use of $k$-limited-access schemes [1], that restrict each client to learn only part of the index coding matrix, and in particular, at most $k$ rows. These schemes transform a linear index coding matrix of rank $T$ to an alternate one, such that each client needs to learn at most $k$ of the coding matrix rows to decode its requested message. This paper analyzes $k$-limited-access schemes. First, a worst-case scenario, where the total number of clients $n$ is $2^T-1$ is studied. For this case, a novel construction of the coding matrix is provided and shown to be order-optimal in the number of transmissions. Then, the case of a general $n$ is considered and two different schemes are designed and analytically and numerically assessed in their performance. It is shown that these schemes perform better than the one designed for the case $n=2^T-1$

Application-Tailored Security: Lessons from Theory to Practice

With the increase of inter-connected devices, it is of paramount importance to ensure the security of the exchanged information. While cryptographic techniques provide tools to provide confidentiality and data integrity, such techniques may not provide the most efficient solutions. In addition, applications today have challenging performance requirements, with the emergence of time-critical applications such as vehicle networks, as well as resource-limited inter-connected devices such as the devices used in the Internet-of-Things. For such applications, novel security solutions that are application-tailored are needed to meet the performance requirements while adhering to the constraints imposed by the available resources. In this thesis, we adopt this methodology for security design: by understanding the nature of the application, the possible adversaries that may target the communication system, as well as the performance requirements, we design suitable and efficient security solutions. We show this methodology in the context of three different scenarios. The first scenario is data broadcasting in the context of the index coding problem. We study the problem of providing privacy guarantees against curious clients who are interested in knowing the requests and side information sets of other clients. We first design index codes with higher privacy levels than conventional index codes. We also provide a mechanism, which we call k-limited-access schemes, which transforms any index coding technique into another code with higher privacy guarantees. The second scenario is in the context of communication systems which relies on millimeter waves. We tackle the problem of secret key establishment. We propose a secret key establishment protocol which allows two communicating parties to establish shared secret keys at very high rates. We showcase the performance of our proposed technique in two different applications: in millimeter wave wireless systems such as 5G networks and IEEE 802.11ay, and vehicle platooning. The last scenario is in the context of Cyber-Physical Systems. We first argue that, in many situations, an adversary is interested in learning the state vector of the control system. In such cases, a more suitable security metric would be a distortion-based one which leads the adversary to make state estimates that are far from the actual value. We then propose security schemes that require a very small number of secret key bits and still perform well according to the proposed metric: we show that our proposed schemes are in fact optimal for many cases

Censoring for Type-Based Multiple Access Scheme in Wireless Sensor Networks

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