Results 1  10
of
161
QoSbased transmit beamforming in the presence of eavesdroppers: An artificialnoiseaided approach
 IEEE Tans. Signal Process
, 2011
"... Abstract—Secure transmission techniques have been receiving growing attention in recent years, as a viable, powerful alternative to blocking eavesdropping attempts in an open wireless medium. This paper proposes a secret transmit beamforming approach using a qualityofservice (QoS)based perspectiv ..."
Abstract

Cited by 31 (7 self)
 Add to MetaCart
(Show Context)
Abstract—Secure transmission techniques have been receiving growing attention in recent years, as a viable, powerful alternative to blocking eavesdropping attempts in an open wireless medium. This paper proposes a secret transmit beamforming approach using a qualityofservice (QoS)based perspective. Specifically, we establish design formulations that: i) constrain the maximum allowable signaltointerferenceandnoise ratios (SINRs) of the eavesdroppers, and that ii) provide the intended receiver with a satisfactory SINR through either a guaranteed SINR constraint or SINR maximization. The proposed designs incorporate a relatively new idea called artificial noise (AN), where a suitable amount of AN is added in the transmitted signal to confuse the eavesdroppers. Our designs advocate joint optimization of the transmit weights and AN spatial distribution in accordance with the channel state information (CSI) of the intended receiver and eavesdroppers. Our formulated design problems are shown to be NPhard in general. We deal with this difficulty by using semidefinite relaxation (SDR), an approximation technique based on convex optimization. Interestingly, we prove that SDR can exactly solve the design problems for a practically representative class of problem instances; e.g., when the intended receiver’s instantaneous CSI is known. Extensions to the colludingeavesdropper scenario and the multiintendedreceiver scenario are also examined. Extensive simulation results illustrate that the proposed ANaided designs can yield significant power savings or SINR enhancement compared to some other methods. Index Terms—Artificial noise, physicallayer secure communications, semidefinite relaxation, transmit beamforming. I.
Optimal power flow over tree networks
 PROCEEDINGS OF THE FORTHNINTH ANNUAL ALLERTON CONFERENCE
, 2011
"... The optimal power flow (OPF) problem is critical to power system operation but it is generally nonconvex and therefore hard to solve. Recently, a sufficient condition has been found under which OPF has zero duality gap, which means that its solution can be computed efficiently by solving the conve ..."
Abstract

Cited by 28 (12 self)
 Add to MetaCart
(Show Context)
The optimal power flow (OPF) problem is critical to power system operation but it is generally nonconvex and therefore hard to solve. Recently, a sufficient condition has been found under which OPF has zero duality gap, which means that its solution can be computed efficiently by solving the convex dual problem. In this paper we simplify this sufficient condition through a reformulation of the problem and prove that the condition is always satisfied for a tree network provided we allow oversatisfaction of load. The proof, cast as a complex semidefinite program, makes use of the fact that if the underlying graph of an n n Hermitian positive semidefinite matrix is a tree, then the matrix has rank at least n  1.
Quadratically constrained quadratic programs on acyclic graphs with application to power flow
, 2013
"... ..."
EXACT AND STABLE RECOVERY OF ROTATIONS FOR ROBUST SYNCHRONIZATION
, 1211
"... Abstract. The synchronization problem over the special orthogonal group SO(d) consists of estimating a set of unknown rotations R1, R2,..., Rn from noisy measurements of a subset of their pairwise ratios R −1 i Rj. The problem has found applications in computer vision, computer graphics, and sensor ..."
Abstract

Cited by 22 (9 self)
 Add to MetaCart
(Show Context)
Abstract. The synchronization problem over the special orthogonal group SO(d) consists of estimating a set of unknown rotations R1, R2,..., Rn from noisy measurements of a subset of their pairwise ratios R −1 i Rj. The problem has found applications in computer vision, computer graphics, and sensor network localization, among others. Its least squares solution can be approximated by either spectral relaxation or semidefinite programming followed by a rounding procedure, analogous to the approximation algorithms of MaxCut. The contribution of this paper is threefold: First, we introduce a robust penalty function involving the sum of unsquared deviations and derive a relaxation that leads to a convex optimization problem; Second, we apply the alternating direction method to minimize the penalty function; Finally, under a specific model of the measurement noise and the measurement graph, we prove that the rotations are exactly and stably recovered, exhibiting a phase transition behavior in terms of the proportion of noisy measurements. Numerical simulations confirm the phase transition behavior for our method as well as its improved accuracy compared to existing methods. Key words. Synchronization of rotations; least unsquared deviation; semidefinite relaxation; and alternating direction method 1. Introduction. The
Convex Optimizationbased Beamforming  From receive to transmit and network designs
, 2010
"... In this article, an overview of advanced convex optimization approaches to multisensor beamforming is presented, and connections are drawn between different types of optimizationbased beamformers that apply to a broad class of receive, transmit, and network beamformer design problems. It is demons ..."
Abstract

Cited by 21 (0 self)
 Add to MetaCart
In this article, an overview of advanced convex optimization approaches to multisensor beamforming is presented, and connections are drawn between different types of optimizationbased beamformers that apply to a broad class of receive, transmit, and network beamformer design problems. It is demonstrated that convex optimization provides an indispensable set of tools for beamforming, enabling rigorous formulation and effective solution of both longstanding and emerging design problems.
Phase Retrieval from Coded Diffraction Patterns
, 2013
"... This paper considers the question of recovering the phase of an object from intensityonly measurements, a problem which naturally appears in Xray crystallography and related disciplines. We study a physically realistic setup where one can modulate the signal of interest and then collect the inten ..."
Abstract

Cited by 21 (5 self)
 Add to MetaCart
This paper considers the question of recovering the phase of an object from intensityonly measurements, a problem which naturally appears in Xray crystallography and related disciplines. We study a physically realistic setup where one can modulate the signal of interest and then collect the intensity of its diffraction pattern, each modulation thereby producing a sort of coded diffraction pattern. We show that PhaseLift, a recent convex programming technique, recovers the phase information exactly from a number of random modulations, which is polylogarithmic in the number of unknowns. Numerical experiments with noiseless and noisy data complement our theoretical analysis and illustrate our approach.
Linear precoding designs for amplifyandforward multiuser twoway relay systems
 in Proc. IEEE GLOBECOM
, 2011
"... AbstractWe investigate the linear precoding designs for multiuser twoway relay system (MUTWRS) where a multiantenna basestation (BS) communicates with multiple singleantenna mobile stations (MSs) via a multiantenna relay station (RS). The amplifyandforward (AF) relay protocol is employed. Th ..."
Abstract

Cited by 20 (6 self)
 Add to MetaCart
(Show Context)
AbstractWe investigate the linear precoding designs for multiuser twoway relay system (MUTWRS) where a multiantenna basestation (BS) communicates with multiple singleantenna mobile stations (MSs) via a multiantenna relay station (RS). The amplifyandforward (AF) relay protocol is employed. The design goal is to optimize the precodings at BS, RS or both so as to minimize the total meansquare error (MSE) of the uplink messages while maintaining the individual signaltointerferenceplusnoise ratio (SINR) requirement for each downlink signal. We show that the BS precoding design problem can be converted to a standard second order cone programming (SOCP), while the RS precoding is nonconvex for which a local optimal solution is obtained using an iterative algorithm. A joint BSRS precoding is also obtained by alternating optimization of BS precoding and RS precoding with guaranteed convergence. Numerical results show that RSprecoding is superior to BSprecoding. Furthermore, the joint BSRS precoding can significantly outperform the two individual precoding schemes. The implementation issues including complexity and feedback overhead are also discussed.
Monitoring and Optimization for Power Grids: A Signal Processing Perspective
 IEEE SIGNAL PROCESSING MAGAZINE
, 2012
"... ..."
Linear precoding for multipair twoway MIMO relay systems with maxmin fairness
 IEEE Trans. Signal Process
, 2012
"... Abstract—Twoway relaying has demonstrated significant gain in spectral efficiency by applying network coding when a pair of source nodes exchange information via a relay node. This paper is concerned with the scenario where multiple pairs of users exchange information through a common relay node e ..."
Abstract

Cited by 16 (5 self)
 Add to MetaCart
(Show Context)
Abstract—Twoway relaying has demonstrated significant gain in spectral efficiency by applying network coding when a pair of source nodes exchange information via a relay node. This paper is concerned with the scenario where multiple pairs of users exchange information through a common relay node equipped with multiple antennas. We aim to design linear precoding at the relay based on amplifyandforward strategy. The goal is to maximize the minimum achievable rate among all the users subject to a peak relay power constraint so as to achieve the maxmin fairness. We first convert this nonconvex problem into a series of semidefinite programming problems using bisection search and certain transformation techniques. A quasioptimal solution is then obtained by using semidefinite relaxation (SDR). To reduce the design complexity, we further introduce a pairwise zeroforcing (ZF) structure that eliminates the interference among different user pairs. By applying this structure, the precoding design problem is simplified to a power allocation problem which can be optimally solved. A simplified power allocation algorithm is also proposed. Simulation results show that the proposed SDRbased precoding not only achieves high minimum user rate but also maintains good sumrate performance when compared with existing schemes. It is also shown that the proposed pairwise ZF precoding with simplified power allocation strikes a good balance between performance and complexity. Index Terms—Multipleinput multipleoutput (MIMO), multiuser, nonregenerative relay, precoding, twoway relaying. I.
private communication
, 2006
"... Pathways to eliciting aid: The effects of visual representations of human suffering on empathy and help for people in need ..."
Abstract

Cited by 14 (0 self)
 Add to MetaCart
(Show Context)
Pathways to eliciting aid: The effects of visual representations of human suffering on empathy and help for people in need