Shabnam Sodagari

On a Truthful Mechanism for Expiring Spectrum Sharing in Cognitive Radio Networks

We study how truthfulness can be enforced as a dominant strategy when a number of secondary cognitive radios participate in an online expiring spectrum sharing auction, held by the primary to lease its spectrum holes. The types of secondary cognitive radios, announced to the primary, are composed of valuation and arrival-departure periods. We show how, by the suitable choice of channel allocation and pricing schemes, the collusion incentive among secondary cognitive radios can be reduced. The performance of the deployed dynamic auction is compared with that of the Vickrey-Clarke-Groves (VCG) offline auction as a benchmark.

Strategies to Achieve Truthful Spectrum Auctions for Cognitive Radio Networks Based on Mechanism Design

In this paper, we investigate the design of a truthful auction for the case when a primary spectrum owner is willing to lease its idle spectral resources in sequential time periods. The secondary cognitive radios participate in the spectrum sharing auction by declaring to the primary their types, which consist of their arrival and departure time instances and valuations. The adapted methodology aims at reducing the collusion incentive among secondary users through the proper choice of the pricing policy and replacing second-price policy, such as in Vickrey-Clarke-Grove (VCG) auctions, by the critical value auction. Furthermore, the proposed auction is dynamic and is performed on-line, in contrast to static off-line schemes such as VCG. Simulation results confirm the anti-cheating property of the proposed auction scheme.

Denial of Service Attacks in Cognitive Radio Networks through Channel Eviction Triggering

Security issues associated with successful operation of cognitive radio networks (CRNs) recently are gaining a lot of attention. In this paper we focus on a specific class of Denial of Service attack that is executed through Channel Eviction Triggering (CET), whereby the adversary nodes unduly invoke mechanisms inherent in CRN operation to protect the licensed users and thus disrupt secondary access to the otherwise idle licensed bands. Skewing the spectrum sensing decision of a CRN through sensing mis-reports is a manifestation of CET attacks. Whereas most studies in the literature focus on making the cooperative sensing more robust against such sensing misreports, we tackle the problem from an incentive perspective and develop strategies to minimize the utility difference of truthful and cheating cognitive radios so as to alleviate the incentive of mis-reporting. Our numerical results verify the effectiveness of the proposed CET defense scheme.

On cost-sharing mechanisms in cognitive radio networks

We present a framework and pertinent formulations for a coalition of secondary cognitive radios that are willing to lease inactive spectrum band from a primary system through auctioning and to share the received bandwidth and the associated cost among themselves using multiple access techniques. We cast this scenario to submodular class of games and show how a link can be established between the truthful auctioning mechanism and the cost-sharing algorithm. Simulation results verify that the deployed cost-sharing technique leads to encouraging the secondary cognitive radios to truthfully announce their bids. Copyright

Combating channel eviction triggering denial‐of‐service attacks in cognitive radio networks

We focus on a specific class of denial-of-service (DoS) attacks that is executed through Channel Eviction Triggering (CET), whereby adversary nodes unduly invoke mechanisms inherent in a cognitive radio (CR) network (CRN) operation to protect the licensed users and thus disrupt secondary access to the otherwise idle licensed bands. Skewing the spectrum sensing decision of CRN through sensing misreports is a manifestation of CET attacks. Whereas most studies in the literature focus on making the cooperative sensing more robust against such sensing misreports, we tackle the problem from the novel perspective of incentive alleviation. We distinguish two classes of such DoS attacks, which we refer to as CET and CET-jamming attacks. In the former case, the incentive of adversary CRs is to remove the competition of truthful CRs in accessing the licensed spectral ranges. The latter class of DoS attack deals with scenarios in which the adversary nodes are mainly interested in denying the chances of communication of CRN over primary bands and as such their incentive cannot be modelled by the same utility maximisation model as truthful CRs. We propose a solution for each class of attacks, and our numerical results verify the effectiveness of the proposed CET defence scheme in both cases. Copyright

Time-Optimized and Truthful Dynamic Spectrum Rental Mechanism

The process of admitting secondary spectrum users via spectrum auctions provides a convenient framework for the primary license holder to control utilization of its idle resources. While most existing solutions in the literature are static, offline auction mechanisms, the dynamics of arrival and departure of secondary bidders, as well as the uncertainty of availability of a given sub-channel for leasing in future, calls for novel auction strategies. In this paper we propose a dynamic, online auction design that addresses two key issues. First, we determine optimal auction instances so as to maximize the profitability of this auction model. Further, by utilizing critical pricing strategy, the incentive of bidding secondaries to misreport their price, time of arrival, and departure is alleviated and hence a truthful, profitable auction results. Our numerical results verify the profitability of this dynamic auction as compared with static Vickrey-Clarke-Groves auctions with fixed auction time.

Power-optimized cooperative spectrum sensing in cognitive radio networks using bandit processes

Power saving and management is a critical aspect of cooperative spectrum sensing in cognitive radio networks, in which a group of secondary cognitive radio nodes share the task of spectrum sensing in order to detect gaps in the spectral bands temporally or spatially not utilized by primary transceivers, facilitating dynamic allocation of physical layer and networking resources that finds application to emergency networks and the military, among others. We show how the problem of power-optimized cooperative spectrum sensing can be cast to a monotonic class of restless bandit processes and present analysis and computationally efficient solutions. Our numerical results verify the effectiveness of the proposed power-optimized spectrum sensing scheme.

Optimum parameter estimation for non-local means image de-noising using corner information

Non-local means (a.k.a. NL-means) method for image de-noising averages the similar parts of an image to reduce random noise. The de-noising performance of the algorithm, however, highly depends on the values of its parameters. In this paper, we introduce a method for finding the optimum parameters, present a linear estimation for the h parameter, and demonstrate that the most important parameter in this method is almost independent of the image and depends only on the noise. We also show that the de-noising performance can be increased by using corner information of noisy image. Our modifications result in better de-noising performance at less computational cost.

Error concealment in image communication using edge map watermarking and spatial smoothing

We propose a novel error concealment algorithm to be used at the receiver side of a lossy image transmission system. Our algorithm involves hiding the edge map of the original image at the transmitter within itself using a robust watermarking scheme. At the receiver, wherever a lost block is detected, the extracted edge information is used as border constraint for the spatial smoothing employing the intact neighboring blocks in order to conceal errors. Simulation results show the superiority of our technique over existing methods even in case of high packet loss ratios in the communication network.

Reduced reference image quality assessment metric using optimized parameterized wavelet watermarking

We propose a novel reduced reference quality assessment metric for image transmission rooted in an optimization approach toward parameterized wavelet-based data hiding. The approximation coefficients of one level parameterized wavelet transform of the original image at the transmitter are embedded into that of the horizontal and vertical detail coefficients in a robust and invisible manner to be used as a feature of the original image for comparisons at the receiver side. The best wavelet type used for decomposition is obtained by a curve fitting process, resulting in the most optimum parameters in terms of which the wavelet transform is formulated using genetic algorithm. Simulation results demonstrate the efficiency of our proposed image quality metric in that it has strong correlation with already established image quality metrics, e.g., Structural Similarity Index (SSIM).