Centralized and Cooperative Transmission of Secure Multiple Unicasts using Network Coding

We introduce a method for securely delivering a set of messages to a group of clients over a broadcast erasure channel where each client is interested in a distinct message. Each client is able to obtain its own message but not the others'. In the proposed method the messages are combined together using a special variant of random linear network coding. Each client is provided with a private set of decoding coefficients to decode its own message. Our method provides security for the transmission sessions against computational brute-force attacks and also weakly security in information theoretic sense. As the broadcast channel is assumed to be erroneous, the missing coded packets should be recovered in some way. We consider two different scenarios. In the first scenario the missing packets are retransmitted by the base station (centralized). In the second scenario the clients cooperate with each other by exchanging packets (decentralized). In both scenarios, network coding techniques are exploited to increase the total throughput. For the case of centralized retransmissions we provide an analytical approximation for the throughput performance of instantly decodable network coded (IDNC) retransmissions as well as numerical experiments. For the decentralized scenario, we propose a new IDNC based retransmission method where its performance is evaluated via simulations and analytical approximation. Application of this method is not limited to our special problem and can be generalized to a new class of problems introduced in this paper as the cooperative index coding problem

Network coding for cooperative data exchange

In this thesis we study cooperation between wireless devices with the goal of obtaining more efficiency in bandwidth usage, energy consumption or delay in wireless communication systems. We investigate different networking scenarios. However, all the scenarios have a common framework: we consider a set of messages and a set of clients where each client initially holds a subset of messages (or some side information about the messages) and is willing to cooperate with other clients by exchanging network coded packets to obtain its desired set of messages. The desired set of messages by each client can be any arbitrary subset of messages and possibly the entire set of messages. We refer to this family of problems as the coded cooperative data exchange (CDE) problems. Cooperation between wireless devices can be highly efficient as the short range links between devices are usually faster, cheaper and more reliable than cellular communication links. In the first scenario in this thesis, all clients are interested in the same set of messages and the network is fully connected. We find a polynomial time algorithm to obtain the optimal number of transmissions and maximize the fairness in the number of transmissions by the clients subject to optimality in the total number of transmissions. A more general scenario where clients are interested in arbitrary subsets of messages is also studied. This problem which we refer to as the cooperative index coding (CIC) is an NP-hard problem. We provide a heuristic algorithm to reduce the number of transmissions as well as an analytical approximation on the total number of transmissions required for fully connected networks. We further extend our heuristic to general wireless network topologies. Mobility of the clients is another topic of study in this thesis. Mobility changes the topology of the network over time. We use probabilistic methods to approximate the number of required transmissions in the cooperative data exchange problem by taking the dynamics of the network into account. We propose an energy efficient heuristic algorithm which is based on the idea of encouraging clients with higher connectivity degree to transmit at each time. Finally we propose a system for dissemination of delay tolerant information to a large group of wireless clients spread over a large area, such as a city. The system is highly bandwidth efficient at the service provider side as it broadcasts only a fraction of information to each sub-area (cell) and the clients exchange information while they move arbitrarily over the entire area and across the cells. Several fully distributed algorithms for scheduling transmissions with different objectives are provided and evaluated via extensive numerical experiments. This is also the first study using realistic synthetic human mobility traces in the context of network coded gossiping

Coded cooperative data exchange for multiple unicasts

The advantages of coded cooperative data exchange has been studied in the literature. In this problem, a group of wireless clients are interested in the same set of packets (a multicast scenario). Each client initially holds a subset of packets and will

Energy Efficient Coded Cooperative Data Exchange for Mobile Users

In this paper, we generalize the problem of network coded cooperative data exchange from a fixed broadcast topology to dynamic networks with mobile peers. In this problem a group of wireless clients are interested in obtaining a set of packets through cooperation, where each client initially holds a subset of packets. Unlike recent studies where cooperation is enabled through a fixed error free broadcast channel among fixed or stationary peers, we assume that peers move randomly between transmission rounds, have a limited transmission range and suffer from packet erasures. In this case giving an exact solution to the problem of minimum number of transmissions is difficult, if not impossible. Therefore, we propose two different heuristic transmission strategies to decrease the total number of transmissions compared to uncoded transmissions. We compare the performance of these two strategies in terms of energy consumption (total number of transmissions) by analysis and simulations. In particular, we show that when packet delivery delay is not an issue, the total number of transmissions can be dramatically decreased at the price of a small overhead

How to shuffle and scatter pieces of a puzzle over a metropolitan area

We propose a new architecture for broadcasting an enormous amount of information over a large population of users in a typical urban area via multiple base stations for delay tolerant applications. The core idea is that each base station partially broadcasts the information instead of transmitting the whole information. In particular, the large target file is broken into M smaller chunks and is provided to N base stations. Each base station i independently generates M i < M linear combinations of the chunks using random linear network coding (RLNC) techniques and broadcasts it to the users in its coverage area. Users then code and exchange packets in their possession via their short range communication links (e.g. bluetooth). Thanks to the random nature of human mobility patterns, it is expected that after a while, the placement of the users would be mixed enough so that users can obtain sufficient number of chunks to decode the entire file. The proposed architecture provides a fundamentally bandwidth efficient scheme for delay tolerant broadcast applications and has the potential to be implemented in practice. In particular, the proposed approach is completely opportunistic i.e. it does not require any routing algorithm. We evaluate the performance of the proposed architecture via extensive simulations using a well known human mobility patterns simulator

Instantly decodable network codes for cooperative index coding problem over general topologies

We consider a group of n wireless clients and a set of k messages. Each client initially holds a subset of messages and is interested in an arbitrary subset of messages. Each client cooperates with other clients to obtain the set of messages it wants by exchanging instantly decodable network coded (IDNC) packets. This problem setting is known as the cooperative index coding problem. Clients are assumed to be connected through an arbitrary topology. In the absence of any known algorithm to complete the exchange of packets for general network topologies, we propose a greedy algorithm to satisfy the demands of all the clients with the aim of reducing the mean completion time. Our algorithm, in a completely distributed fashion, decides which subset of clients should transmit at each round of transmission and which messages should be coded together by each transmitting client to generate an IDNC packet. The algorithm encourages transmissions which are decodable for a larger number of clients and attempts to avoid collisions. We evaluate the performance of our algorithm via numerical experiments

A Generalized Model for Cost and Fairness Analysis in Coded Cooperative Data Exchange

We consider the issues of cost and fairness in the problem of cooperative data exchange among a group of wireless clients. In this problem, each client initially holds a subset of packets and needs to obtain the full set of packets through cooperation with other clients via a shared broadcast channel. To find minimum cost transmission schemes, we propose a general model for the problem which is based on network information flow with side information available to the sinks. As a special case of minimum cost solutions, the minimum number of required transmissions is studied in detail. We show that packet splitting is a natural consequence of solving the linear programming associated with the mentioned network flow problem. Our main observation is that splitting the packets not only minimizes the number of transmissions, but also it results in considerably more fairness compared to the case where splitting is not allowed. Hence, incentive-based long-term cooperation among users can be sustained

Instantly decodable network coding for delay reduction in cooperative data exchange systems

This paper investigates the use of instantly decodable network coding (IDNC) for minimizing the mean decoding delay in multicast cooperative data exchange systems, where the clients cooperate with each other to obtain their missing packets. Here, IDNC i

Secure Routing for Multi-Hop Ad Hoc Networks with Inhomogeneous Eavesdropper Clusters

This paper studies finding the secure path according to the secrecy connectivity probability (SCP) in the multi-hop ad hoc networks in the presence of inhomogeneous eavesdropper clusters. We consider both random and fixed eavesdropper clusters, where the former case assumes that there is no knowledge of the locations of the clusters and the latter case assumes that the locations of the clusters can be estimated accurately. Firstly, we derive the end-to-end SCP to characterize the secrecy performance of a given path in a general multi-hop wireless network with half-duplex (HD) randomize-and-forward relaying. Then we consider a full-duplex (FD) scheme at the legitimate receiver, which receives the useful information while broadcasting a jamming signal to the potential eavesdroppers to further enhance the secrecy connectivity. Then, a novel secure routing algorithm which can provide the maximum SCP for any legitimate transmitter/receiver pair in a distributed manner is proposed. The theoretical analysis is verified by Monte Carlo simulation results. The results show that our secure routing algorithm provides similar results compared to an exhaustive search. For the random eavesdropper cluster case, the optimal route is independent of the knowledge of the cluster, which is the same as the homogeneous eavesdropper case. However, for the case where eavesdropper clusters are fixed and their locations are known a priori, the optimal path selection depends on the radii and locations of the eavesdropper clusters and the average number of eavesdroppers in each cluster