Browsing by Author "Kurt, Mehmet Necip"

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Open Access
Jammer placement algorithms for wireless localization systems
(2016-07) Kurt, Mehmet Necip
The optimal jammer placement problem is proposed and analyzed for wireless localization systems. In particular, the optimal location of a jammer node is obtained by maximizing the minimum of the Cram´er-Rao lower bounds (CRLBs) for a number of target nodes under location related constraints for the jammer node. For scenarios with more than two target nodes, theoretical results are derived to specify conditions under which the jammer node is located as close to a certain target node as possible, or the optimal location of the jammer node is determined by two of the target nodes. Also, explicit expressions are provided for the optimal location of the jammer node in the presence of two target nodes. In addition, in the absence of distance constraints for the jammer node, it is proved, for scenarios with more than two target nodes, that the optimal jammer location lies on the convex hull formed by the locations of the target nodes and is determined by two or three of the target nodes, which have equalized CRLBs. Numerical examples are presented to provide illustrations of the theoretical results in different scenarios. Furthermore, an iterative algorithm is proposed for numerically determining the optimal jammer location. At each iteration of the algorithm, the jammer node is moved one step along a straight line with the purpose of increasing the CRLB(s) of the target node(s) with the minimum CRLB in the system. It is shown that the algorithm converges almost surely to the optimal jammer location under certain conditions for an infinitesimally small step size in the absence of location constraints for the jammer node. Simulations illustrate the effectiveness of the proposed algorithm in finding the optimal jammer location and its superiority in terms of the computational complexity compared to the exhaustive search over all feasible locations.
Open Access
Maximization of correct decision probability via channel switching over Rayleigh fading channels
(IEEE, 2016) Keskin, Musa Furkan; Kurt, Mehmet Necip; Tutay, Mehmet Emin; Gezici, Sinan; Arıkan, Orhan
In this study, optimal channel switching (time sharing) strategies are investigated under average power and cost constraints in order to maximize the average number of correctly received symbols between a transmitter and a receiver that are connected via multiple additive Gaussian noise channels. The optimal strategy is shown to perform channel switching either among at most three channels with full channel utilization (i.e., no idle periods), or between at most two channels with partial channel utilization. In addition, it is stated that the optimal solution must operate at the maximum average power and the maximum average cost, which facilitates low-complexity approaches for calculating the optimal strategy. For two-channel strategies, an upper bound in terms of the noise standard deviations of the employed channels is provided for the ratio between the optimal power levels. Furthermore, a simple condition depending solely on the systems parameters is derived, under which partial channel utilization cannot be optimal. Numerical examples are presented to demonstrate the validity of the theoretical results.