C. Emre Koksal

On secrecy capacity scaling in wireless networks

This paper studies the achievable secure rate per source-destination pair in wireless networks. First, a path loss model is considered, where the legitimate and eavesdropper nodes are assumed to be placed according to Poisson point processes with intensities λ and λe, respectively. It is shown that, as long as λe/λ = o((logn)-2), almost all of the nodes achieve a perfectly secure rate of Ω(1/√n) for the extended and dense network models. Therefore, under these assumptions, securing the network does not entail a loss in the per-node throughput. The achievability argument is based on a novel multihop forwarding scheme where randomization is added in every hop to ensure maximal ambiguity at the eavesdropper(s). Second, an ergodic fading model with n source-destination pairs and ne eavesdroppers is considered. Employing the ergodic interference alignment scheme with an appropriate secrecy precoding, each user is shown to achieve a constant positive secret rate for sufficiently large n. Remarkably, the scheme does not require eavesdropper CSI (only the statistical knowledge is assumed) and the secure throughput per node increases as we add more legitimate users to the network in this setting. Finally, the effect of eavesdropper collusion on the performance of the proposed schemes is characterized.

A nanoradio architecture for interacting nanonetworking tasks

Abstract Nanotechnology has the potential to have a significant impact on a number of application areas. The possibility of building components at the nanoscale revolutionized the way we think about systems by enabling myriad possibilities, that were simply impossible otherwise. At the same time, countless challenges were raised in system design. One such challenge is to build components that act together to handle complex tasks that require physically separate components to work in unison. To achieve coordination, these components have to be capable of communicating reliably, either with a central controller or amongst themselves. In this research, we propose to build analytical foundations to analyze and design nanonetworks, consisting of individual stations communicating over a wireless medium using nanotransceivers with nanotube antennas. We give a simple nanoreceiver design and analyze its basic limitations. Based on the insights drawn, we propose a communication-theoretic framework to design reliable and robust nanoreceivers. With the basic limitations of the nanocommunications via nanoantennas in mind, it is possible to develop mathematical tools to help construct nanonetworks that execute basic sequential tasks in a reliable manner with minimal amount of communication and computation required. In this paper, we present a communication-theoretic analysis of networks of nanoscale nodes equipped with carbon nanotube-based receivers and transmitters. Our objective is to analyze the performance characteristics of nanoscale nodes and expose their fundamental capabilities and limitations. The presented analysis is intended to serve as the basis of nanonetwork design enabling various applications.

Securing massive MIMO at the physical layer

We consider a single-cell downlink massive MIMO system in the presence of an adversary capable of jamming and eavesdropping. We show that, classical attacks of eavesdropping and data jamming can be simultaneously rendered useless. Specifically, we show that, the secure degrees of freedom (DoF) attained in the presence of classical attacks is as same as the maximum DoF attained under no attack. We propose a novel beamforming strategy that establishes information theoretic security without need to Wyner encoding. We next introduce a new attack strategy that involves jamming pilot signals and eavesdropping in succession. We show that under such an attack, the maximum secure DoF is equal to zero. Furthermore, the maximum achievable rates of users vanish even in the asymptotic regime in number of base station (BS) antennas. We develop counter strategies for this new attack in which we use secret key to encrypt the pilot sequence. We show that hiding the training signal assignments from the adversary enables the users to achieve a secure DoF, identical to the one achieved under no attack.

Provably delay efficient data retrieving in storage clouds

One key requirement for storage clouds is to be able to retrieve data quickly. Recent system measurements have shown that the data retrieving delay in storage clouds is highly variable, which may result in a long latency tail. One crucial idea to improve the delay performance is to retrieve multiple data copies by using parallel downloading threads. However, how to optimally schedule these downloading threads to minimize the data retrieving delay remains to be an important open problem. In this paper, we develop low-complexity thread scheduling policies for several important classes of data downloading time distributions, and prove that these policies are either delay-optimal or within a constant gap from the optimum delay performance. These theoretical results hold for an arbitrary arrival process of read requests that may contain finite or infinite read requests, and for heterogeneous MDS storage codes that can support diverse storage redundancy and reliability requirements for different data files. Our numerical results show that the delay performance of the proposed policies is significantly better than that of First-Come-First-Served (FCFS) policies considered in prior work.

Design and analysis of systems based on RF receivers with multiple carbon nanotube antennas

Abstract In this paper, possible uses of systems composed of multiple CNT-based EM receivers are introduced and their communication-theoretical analysis developed. Four possible example applications that involve multiple CNTs are discussed and their system-level design is emphasized. Then, a communication-theoretical analysis of the performance of a generic system that involves multiple CNT-based RF receivers is introduced. The generic receiver system in question is the underlying component of the example applications and their system-level design. Furthermore, the analysis provides some insights into fundamental questions such as communication rate and encoding of information in nanoscale devices.

Online packet scheduling with hard deadlines in multihop communication networks

The problem of online job or packet scheduling with hard deadlines has been studied extensively in the single hop setting, whereas it is notoriously difficult in the multihop setting. This difficulty stems from the fact that packet scheduling decisions at each hop influences and are influenced by decisions on other hops and only a few provably efficient online scheduling algorithms exist in the multihop setting. We consider a general multihop network topology in which packets with various deadlines and weights arrive at and are destined to different nodes through given routes. We study the problem of joint admission control and packet scheduling in order to maximize the cumulative weights of the packets that reach their destinations within their deadlines. We first focus on uplink transmissions in the tree topology and show that the well known earliest deadline first algorithm achieves the same performance as the optimal off-line algorithm for any feasible arrival pattern. We then address the general topology with multiple source-destination pairs, develop a simple online algorithm and show that it is O(PM log PM)-competitive where PM is the maximum route length among all packets. Our algorithm only requires information along the route of each packet and our result is valid for general arrival samples. Via numerical results, we show that our algorithm achieves performance that is comparable to the non-causal optimal off-line algorithm. To the best of our knowledge, this is the first algorithm with a provable (based on a sample-path construction) competitive ratio, subject to hard deadline constraints for general network topologies.

Control of wireless networks with secrecy

We consider the problem of cross-layer resource allocation in time-varying cellular wireless networks, and incorporate information theoretic secrecy as a Quality of Service constraint. Specifically, each node in the network injects two types of traffic, private and open, at rates chosen in order to maximize a global utility function, subject to network stability and secrecy constraints. The secrecy constraint enforces an arbitrarily low mutual information leakage from the source to every node in the network, except for the sink node. We first obtain the achievable rate region for the problem for single and multi-user systems assuming that the nodes have full CSI of their neighbors. Then, we provide a joint flow control, scheduling and private encoding scheme, which does not rely on the knowledge of the prior distribution of the gain of any channel. We prove that our scheme achieves a utility, arbitrarily close to the maximum achievable utility.

Update or Wait: How to Keep Your Data Fresh

In this work we study how to manage the freshness of status updates sent from a source to a remote monitor via a network server. A proper metric of data freshness at the monitor is the age-of-information, which is defined as how old the freshest update is since the moment this update was generated at the source. A logical policy is the zero-wait policy, i.e., the source submits a fresh update once the server is free, which achieves the maximum throughput and the minimum average delay. Surprisingly, this zero-wait policy does not always minimize the average age. This motivates us to study how to optimally control the status updates to keep data fresh and to understand when the zero-wait policy is optimal. We introduce a penalty function to characterize the level of “dissatisfaction” on data staleness, and formulate the average age penalty minimization problem as a constrained semi-Markov decision process (SMDP) with an uncountable state space. Despite of the difficulty of this problem, we develop efficient algorithms to find the optimal status update policy. We show that, in many scenarios, the optimal policy is to wait for a certain amount of time before submitting a new update. In particular, the zero-wait policy can be far from the optimum if (i) the penalty function grows quickly with respect to the age, and (ii) the update service times are highly random and positive correlated. To the best of our knowledge, this is the first optimal control policy which is proven to minimize the age-of-information in status update systems.

On the effect of colluding eavesdroppers on secrecy capacity scaling

In a powerful secrecy attack, eavesdroppers can collude, i.e., they can share their observations. Securing information in such a scenario will be an even more challenging task compared to non-colluding case. We here analyze the effect of eavesdropper collusion on the achievable performance in both the path loss and ergodic multi-path fading models. We provide two results: 1) For the Poisson point process model in a random extended network, if the legitimate nodes have unit intensity (λ = 1) and the colluding eavesdroppers have an intensity of λ<inf>e</inf> = O((log n)^−(2+p)) for any p > 0, almost all of the nodes can achieve a secure rate of Ω(1/√n); I and 2) In the K-user Gaussian interference channel with E external colluding eavesdroppers, a secure degrees of freedom of η =[1/2−E/K]⁺ per frequency-time slot is achievable for each user in the ergodic setting (in the absence of the eavesdropper channel state information).

How Vulnerable Is Vehicular Communication to Physical Layer Jamming Attacks

There has been numerous studies on the security of vehicular networks, focusing mainly at higher layers of the network stack. Vulnerabilities of vehicular communications at the physical layer have not been explored thoroughly. To that end, we study internal and external vehicular communication under a variety of attack strategies involving jamming at the physical layer. We consider a couple of attack strategies, differing in how the attacker jams the resource blocks within a targeted spectrum. In particular, we focus on flat and random jamming, which are oblivious to the existing assignments and smart jamming, which senses the assignments and allocates power in frequency accordingly. For intra- vehicular setting, we consider an attacker attached to various locations within the vehicle. We used software-defined radios in an actual vehicle to emulate potential realistic attack setups and tested the effectiveness of various attack strategies. We show that, the smart jamming attack can lead to significant degradations in communication performance, to the extent of a complete blockage even with a low jamming power, in most setups. For external communication setting, we consider a busy intersection and study uplink communication in a multicellular LTE network. Using a system-level LTE simulator we developed, we show that a flat jamming attack by a static attacker can degrade the global performance significantly, while the smart jamming attack by a stalking attacker can almost block the communication initiated from a targeted vehicle. In short, we demonstrate via real-world experiments and system-level simulations that, with an appropriate strategy, the impact of a physical layer jamming attacker can be highly detrimental to both internal and external vehicular communication, seriously threatening the security of vehicular networks.