We develop an analytical framework for distribution of popular content in an information centric network (ICN) that is comprised of access ICNs, a transit ICN, and a content provider. Using a generalized Zipf distribution to model content popularity, we devise a game theoretic approach to jointly determine caching and pricing strategies in such an ICN. Under the assumption that the caching cost of the access and transit ICNs is inversely proportional to popularity, we show that the Nash caching strategies in the ICN are 0-1 (all or nothing) strategies. Further, for the case of symmetric access ICNs, we show that the Nash equilibrium is unique and the caching policy (0 or 1) is determined by a threshold on the popularity of the content (reflected by the Zipf probability metric), i.e., all content more popular than the threshold value is cached. We also show that the resulting threshold of the Access and Transit ICNs, as well as all prices can be obtained by a decomposition of the joint caching and pricing problem into two independent caching only and pricing only problems.

We evaluate joint caching and pricing strategies among access networks, transit networks and content providers in an Information Centric Network (ICN). Specifically, we develop game theoretic models to study the interaction between the caching and pricing strategies among the above entities in the ICN. We first study static Nash strategies under various conditions and observe that the ICNs always choose 0-1 (all or nothing) caching strategies depending on the relative caching costs and prices at the transit ICN. We then use the insights gained to design dynamic pricing and caching strategies using a repeated game formulation. Using a model where the cost of caching changes as a function of the state of the cache, we study joint caching and pricing strategies for the access networks, transit networks and content providers, when the caching costs change linearly as well as exponentially.

Content-centric networking (CCN) adopts a receiver-driven, hop-by-hop transport approach that facilitates in-network caching, which in turn leads to multiple sources and multiple paths for transferring content. In such a case, keeping a single round trip time (RTT) estimator for a multi-path flow is insufficient as each path may experience different round trip times. To solve this problem, it has been proposed to use multiple RTT estimators to predict network condition. In this paper, we examine an alternative approach to this problem, CHoPCoP, which utilizes explicit congestion control to cope with the multiple-source, multiple-path situation. Protocol design innovations of CHoPCoP include a random early marking (REM) scheme that explicitly signals network congestion, and a per-hop fair share Interest shaping algorithm (FISP) and a receiver Interest control method (RIC) that regulate the Interest rates at routers and the receiver respectively. We have implemented CHoPCoP on the ORBIT testbed and conducted experiments under various network and traffic settings. The evaluation shows that CHoPCoP is a viable approach that can effectively deal with congestion in the multipath environment.

This paper presents a three phase grid connected DC/AC inverter with active and reactive power (VAR) control for medium size renewable and distributed DC energy sources. The inverter, based on a voltage sourced inverter (VSI) configuration, allows the local residential energy generation to actively supply reactive power to the utility grid, at the same time, this topology allows to work this installation in stand-alone (grid disconnected) mode maintaining nominal and clean voltage at nominal power. A low complexity grid synchronization method was introduced to generate direct and quadrature components of the grid voltage in a simple and computationally efficient manner in order to generate a synchronized current reference for the current loop control. Simulations were performed on Matlab/Simulink platform and a prototype was also developed in the lab to prove the effectiveness of the designed filter, controllers and grid synchronization method. The dSPACE hardware in the loop (HTL) was used, providing a good solution for laboratory implementation.

The advances in radio design and wireless networking, along with the growth of multimedia home entertainment technologies, is creating the concept of a cognitive digital home requiring spectrum coexistence of various devices and networks of networks. A framework for resource allocation in a Cognitive Digital Home (CDH) with a multiplicity of radio access technologies (RAT) such as cognitive radios and legacy radio devices supporting heterogeneous applications is developed. We consider two channel access models in the CDH for addressing spectrum coexistence of legacy devices: (i) Pessimistic Controllability (PC) Model where the Home Genie node (HG) has no influence over legacy devices, and (ii) Switched RAT (SR) Model where the HG has perfect control of legacy devices. Distributed algorithms for maximizing sum rate and maximizing service capacity are designed using partial dual decomposition techniques. A distributed power control scheme is also designed for efficient use of energy. An admission control scheme based on pricing information obtained from the distributed algorithms is used to improve system feasibility.

The last few years have seen an exponential increase in mobile data use, coming primarily as a result of the “iPhone revolution”. Mobile operators are currently facing traffic demands higher than what their networks can support, which has triggered the need of implementing offloading mechanisms at different levels of the architecture. One of the problems is that existing mobility procedures are highly centralized, requiring all data traffic to traverse the mobile operator's network core. This paper presents an evolved 3GPP architecture that supports full distributed mobility management, while allowing incremental deployment and co-existence with existing solutions.

The advances in radio design and wireless networking, along with the growth of multimedia home entertainment technologies, is creating the concept of a cognitive digital home requiring spectrum coexistence of various devices and networks of networks. Recent work in has considered a framework for resource allocation in a cognitive digital home (CDH) with a multiplicity of radio access technologies (RAT) such as cognitive radios and legacy radio devices supporting heterogeneous applications. A spectrum manager, named the home genie node (HG), is used to coordinate spectrum coexistence across different services, with degrees of freedom ranging from transmission parameters such as frequency, bandwidth, and power, to the choice of radio access technology itself. Distributed algorithms for the resource allocation problems in a CDH, namely maximizing sum rate and maximizing service capacity, which have been previously solved using centralized approaches in, are designed and studied using partial Lagrangian decomposition techniques in this paper.

The advances in radio design and wireless networking, along with the growth of multimedia home entertainment technologies, is creating the concept of a cognitive digital home requiring spectrum coexistence of various devices and networks of networks. In this paper, we introduce a framework for resource allocation in a cognitive digital home with a multiplicity of radio access technologies such as cognitive radios and legacy technologies supporting heterogeneous applications. A spectrum manager, named the home genie node, is introduced to coordinate spectrum coexistence across different services, with degrees of freedom ranging from transmission parameters such as frequency, bandwidth, and power, to the choice of radio access technology itself. We study problems of sum rate maximization as well as maxmin rate allocation which are mixed integer nonlinear programs, and propose simple heuristic solutions for the same.

We propose a PHY-authentication protocol to detect spoofing attacks in wireless networks, exploiting the rapid-decorrelation property of radio channels with distance. In this protocol, a PHY-authentication scheme that exploits channel estimations that already exist in most wireless systems, cooperates with any existing-either simple or advanced-higher-layer process, such as IEEE 802.11i. With little additional system overhead, our scheme reduces the workload of the higher-layer process, or provides some degree of spoofing protection for ``naked" wireless systems, such as some sensor networks. We describe the performance of our approach as a function of the spoofing pattern and the snapshot performance that can be easily measured through field tests. We discuss the implementation issues of the authentication protocol on 802.11 testbeds and verify its performance via field tests in a typical office building.

Since the IEEE 802.11 DCF adopted the Binary Exponential Back-off (BEB) algorithm in its contention window adjustment scheme, many alternative back-off algorithms were proposed in order to enhance the performance. Among them is an Exponential Increase Exponential Decrease (EIED) back-off algorithm, whose performance was simulated and analyzed in a special case of doubling or halving the contention window size. This paper provides an analytical analysis for the general EIED algorithm. A closed form saturation throughput and a closed form saturation delay are derived. Our analytical results further establish the performance improvement of the general EIED algorithm over the BEB algorithm and the basic EIED algorithm.

The multipath-rich wireless environment associated with typical wireless usage scenarios is characterized by a fading channel response that is time-varying, location-sensitive, and uniquely shared by a given transmitter-receiver pair. The complexity associated with a richly scattering environment implies that the short-term fading process is inherently hard to predict and best modeled stochastically, with rapid decorrelation properties in space, time, and frequency. In this paper, we demonstrate how the channel state between a wireless transmitter and receiver can be used as the basis for building practical secret key generation protocols between two entities. We begin by presenting a scheme based on level crossings of the fading process, which is well-suited for the Rayleigh and Rician fading models associated with a richly scattering environment. Our level crossing algorithm is simple, and incorporates a self-authenticating mechanism to prevent adversarial manipulation of message exchanges during the protocol. Since the level crossing algorithm is best suited for fading processes that exhibit symmetry in their underlying distribution, we present a second and more powerful approach that is suited for more general channel state distributions. This second approach is motivated by observations from quantizing jointly Gaussian processes, but exploits empirical measurements to set quantization boundaries and a heuristic log likelihood ratio estimate to achieve an improved secret key generation rate. We validate both proposed protocols through experimentations using a customized 802.11a platform, and show for the typical WiFi channel that reliable secret key establishment can be accomplished at rates on the order of 10 b/s.

We consider secret key generation for a “pairwise independent network” model in which every pair of terminals observes correlated sources that are independent of sources observed by all other pairs of terminals. The terminals are then allowed to communicate publicly with all such communication being observed by all the terminals. The objective is to generate a secret key shared by a given subset of terminals at the largest rate possible, with the cooperation of any remaining terminals. Secrecy is required from an eavesdropper that has access to the public interterminal communication. A (single-letter) formula for secret key capacity brings out a natural connection between the problem of secret key generation and a combinatorial problem of maximal packing of Steiner trees in an associated multigraph. An explicit algorithm is proposed for secret key generation based on a maximal packing of Steiner trees in a multigraph; the corresponding maximum rate of Steiner tree packing is thus a lower bound for the secret key capacity. When only two of the terminals or when all the terminals seek to share a secret key, the mentioned algorithm achieves secret key capacity in which case the bound is tight.

We investigate perfect secret key generation for a ¿pairwise independent network¿ model in which every pair of terminals observes correlated sources that are independent of sources observed by all other pairs of terminals. The terminals are then allowed to communicate interactively in multiple rounds over a public noiseless channel of unlimited capacity. This communication is observed by all the terminals as well as by an eavesdropper. The objective is to generate a perfect secret key shared by a given set of terminals at the largest rate possible. All the terminals cooperate in generating the secret key, with perfect secrecy being required from the eavesdropper. For this model, we introduce the concept of communication for perfect omniscience using which we first obtain a single-letter characterization of the perfect secret key capacity. Moreover, this perfect secret key capacity is shown to be achieved by linear noninteractive communication, and coincides with the (standard) secret key capacity. Our second contribution, exploiting the notion of communication for perfect omniscience, is a new nonasymptotic and computable upper bound for the combinatorial problem of maximal Steiner tree packing in a multigraph. Thus, our work establishes certain connections among perfect secrecy generation and communication for perfect omniscience for the pairwise independent network model, and Steiner tree packing.

Two cooperative relaying protocols are presented and analyzed. The first emphasizes PHY cooperation via synchronized transmissions and distributed space-time coding from the Base Station (BS) and Relay Station (RS) to the User Equipment (UE) during the protocol's cooperative phase. The second protocol emphasizes MAC cooperation using different MAC flows from the BS and RS to the UE during the cooperative phase and utilizing successive interference cancellation (SIC) at the UE. This paper discusses and compares the two protocols' flexibility and performance aspects via analytical and simulation results.

We consider the problem of counting mobile stations based on feedback they provide. For this problem we propose an anonymous contentious feedback mechanism which permits efficient counting and relate the resulting estimation problem to a well know combinatorial problem of "coupon collection." Using this relationship, we analyze the estimation problem in an idealized setting. We find the ML estimator and demonstrate that it is inappropriate in this setting. We then propose an estimator which is shown to achieve good performance over a large range of parameters.

We investigate secret key generation for a ldquopair-wise independent networkrdquo model in which every pair of terminals observes correlated sources which are independent of sources observed by all other pairs of terminals. The terminals are then allowed to communicate interactively in multiple rounds over a public noiseless channel of unlimited capacity, with all such communication being observed by all the terminals. The objective is to generate a secret key shared by a given subset of terminals at the largest rate possible. All the terminals cooperate in generating the secret key, with secrecy being required from an eavesdropper which has access to the public interterminal communication. We provide a (single-letter) formula for the secrecy capacity for this model, and show a natural connection between the problem of secret key generation and the combinatorial problem of maximal packing of Steiner trees in an associated multigraph. In particular, we show that the maximum number of Steiner tree packings in the multigraph is always a lower bound for the secrecy capacity. The bound is tight for the case when all the terminals seek to share a secret key; the mentioned connection yields an explicit capacity-achieving algorithm. This algorithm, which can be executed in polynomial time, extracts a group-wide secret key of the optimum rate from the collection of optimum and mutually independent secret keys for pairs of terminals.

Securing communications requires the establishment of cryptographic keys, which is challenging in mobile scenarios where a key management infrastructure is not always present. In this paper, we present a protocol that allows two users to establish a common cryptographic key by exploiting special properties of the wireless channel: the underlying channel response between any two parties is unique and decorrelates rapidly in space. The established key can then be used to support security services (such as encryption) between two users. Our algorithm uses level-crossings and quantization to extract bits from correlated stochastic processes. The resulting protocol resists cryptanalysis by an eavesdropping adversary and a spoofing attack by an active adversary without requiring an authenticated channel, as is typically assumed in prior information-theoretic key establishment schemes. We evaluate our algorithm through theoretical and numerical studies, and provide validation through two complementary experimental studies. First, we use an 802.11 development platform with customized logic that extracts raw channel impulse response data from the preamble of a format-compliant 802.11a packet. We show that it is possible to practically achieve key establishment rates of ~ 1 bit/sec in a real, indoor wireless environment. To illustrate the generality of our method, we show that our approach is equally applicable to per-packet coarse signal strength measurements using off-the-shelf 802.11 hardware.

We consider a pair-wise independent network in which every pair of terminals observes a common pair-wise source that is independent of all the sources accessible to the other pairs. We propose a method for secret key agreement in such a network that is based on well-established point-to- point techniques and repeated application of the one-time pad over a graphical representation of the network. Three specific problems are investigated. (1) Each terminal's observations are correlated only with the observations of a central terminal. All these terminals wish to generate a common secret key. (2) Two designated terminals wish to generate a secret key with the help of other terminals. (3) All terminals wish to generate a common secret key. In each of these cases, we show that our two-step approach can yield an optimal protocol, in terms of the resulting secret key rates. Furthermore, such a protocol is provided for the first two problems, while an efficient protocol is given for the third problem.

We consider the secrecy inherent in the reciprocal nature of multipath fading channels and present a technique to generate a shared perfectly secret key by two terminals observing a multipath fading channel. Using this technique we quantify the secrecy that can be generated from ITU cellular channels for the 2 GHz frequency range.

We present a method for secrecy extraction from jointly Gaussian random sources. The approach is motivated by and has applications in enhancing security for wireless communications. The problem is also found to be closely related to some well known lossy source coding problems

We consider the broadcast-relay channel: a broadcast channel where receivers are permitted to assist in the distribution of data to other receivers by relaying. We extend the previous results and demonstrate that effective transmission strategies can be derived by combining well-known techniques for broadcast and relay channels. Additionally, we derive new outer bounds to capacity regions

In this paper, we analyze the effect of scaling laws in random heterogeneous networks. This paper describes a square grid with shortcuts and a scaling law with wired shortcuts

We determine the capacity region of a degraded Gaussian relay channel with multiple relay stages. This is done by building an inductive argument based on the single-relay capacity theorem of Cover and El Gamal. For an arbitrary distribution of noise powers, we derive the optimal power distribution strategy among the transmitter and the relays and the best possible improvement in signal-to-noise ratio (SNR) that can be achieved from using a given number of relays. The time-division multiplexing operation of the relay channel in the wideband regime is analyzed and it is shown that time division does not achieve minimum energy per bit.